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he

oo tffects

uclear

g eapons
The

Effects

of

Nuclear

Weapons

Compiled and edited by

Samuel Glasstone and Philip J. Dolan

Third Edition

Prepared and published by the

UNITED STATES DEPARTMENT OF DEFENSE

ard the

UNITED STATES DEPARTMENT OF ENERGY

197i•
PREFACE

When "The Effects of Atomic Weapons" was published in 1950, the explosive

energy yields of the fission bombs available at that .ime were equivalent to som;.

thousands of tons (i.e., kilotons) of TNT. With the development of thelmonucleai

(fusion) weapons, having energy yields in the range of millions of tors (i.e.,

megatons) of TNT. a new presentation, entitled "Thc Effect3 of N'iclkar Weapons," was issued in 1957. A completely revised edition was nublisheJ in 1962 and

this was reprinted with a few changes early in 1964.

Since the last version of "The Effects of Nuclear Weapons" was prepared, much

new information has become available concerning nuciear weapons effects. This

has come in part from the series of atmospheric tests, including several at very high

altitudes, conducted in the Pacific Ocean area in 1962. In addition, laboratory

studies, theoretical calculations, and computer simulations have provided a better

understanding of the various effects. Within the limits imposed by security requirements, the new information has been incorporated in the present ed',tion. in

particular, attention may be called to a new chapter on the electromagnetic pulse.

We should emphasize, as has been done in the earlier editions, that numerical

values given in this book are not--nd cannot be--exact. They must inevitably

include a substantial margin of error. Apart from the difficulties in making

measurements of weapons effects, the results are often dependent upon circumstancti which could not be predicted in the event of a nuclear attack. Furthermore,

two weapons of different design may have the same explosive energy yield, but the

effects could be markedly different. Where such possibilities exist, attention is

called in the text to thie limitations of the data presented; these limitations should not

be overlooked.

The material is arranged in a manner that should permit th~e general reader to

obtain a good understanding of the various topics without having to cope with the

more technical details. Most chapters are thus in two parts: the first part is written at

a fairly low technical level whereas the second treats some of the more technical and

ma-dhematical aspects. The presiltat'on allows the reader to omit any or all of the

latter sections without loss of continuity.

T!,•- choice of units for expressing numerical data presented us with a dilemma.

The exclusive use of international (SI) or metric units would have placed a burden

on many readers not familiar with these units, whereas the inclusion of both SI and

common units would have complicated many figures, especially thos;e with

logarithmic scales. As a compromise, we have rei.,ined the older units and added an

explanvtion of the SI systern and a table of appropriate conversion factors.
Preface

Many organizations and individuals contributed in one way or another to lhi:

r'ývision ol "The Effects of Nuclear Weapons," and their couperation is gratefully

acknowledged. In particular, we wish io express our -Appreciation of tne help given

us by L. J. Deal and W. W. S',hroebel of the Energy Research and De-elopment

Administra!ion and by Cmdr. H. L. Hofpe of the Department Cf Defense.

Samuel Glasstone

Philip J. Dolan

,!
ACKNO WLEDGEMENTS

Preparation of this revision of "The Effects of NuC:hai Weapons" was made

possible by the assistance and cooperation of members of the organizat;.ons listed

below.

Department of Defense

Headquarters, Defense Nuclear Agency

Defense Civil Preparedness Agency

Armed Forces Radiobiology Research Institute

U.S. Army Aberdeen Research and Development Center. Ballistic Research Lab- ,.

oratories

U.S. Army Engineer Waterways Experimert Station

Naval Surface Weapons Center

Department of Defense Contractors

Stanford Research Institute

General Electric. TEMPO

Mission Research Corporation

Department of Corn,,- e,1ce

National Oceanic and Atmospheric Adminiý.,ation

Atomic Ene 1,y Commission/

Energy Research anrVOevelopment Administvation

Headquarters Divisions and the '!,ooratories:

Brookhaven National Labor-.tory

Health and Safety Labor-,ory

Lawrence Livermore L;.oeratory

Los Alamos Scientif,. Laboratory

Lovelace Biomedi,.-Al and Environmental P: .--x.-rch Laborateries

Oak Ridge Nati4 ial Laboratory

Sandia Labori'ýjries

A.
CONTENTS

Page

CHAPTER I-General Principles of Nuclear Explosions ........... I

Characteristics of Nuclear Explosions ..... ..................... I

ScienTiti Basis of Nuclear Explosions .......................... 12

CHAPTER I1.--..Descript ions of NuJear E'x!,)ioE... .................. 26

Introduction ........................................... 26

Description of Air end Surface Bursts .......................... 27

Description of Hign-Altitude Bursts ............................ 45

Description of Underwater Bursts ........................... ..48

Description of Underground Bursts ............................ 58

Scientific Aspect:; of Nuclear Explosion Phe,,rcmena ................ 63

CHAPTER Ill-Air Blast Phenomena iii Air and Surface Bursts ...... ... 80

Characteristics of the Blast Wave in Air ....... ................ .. 80

Reflection of Blast Wave at a Surface .......................... 86

Modification of Air Blast Phenomena .......................... 92

Technical Aspezts of Blast Wave Phenomena ..................... 96

CHAPTEP IV-Air Blast Loading .............................. 127

Interaction of Blast Wave with Structures ....................... 127

Interaction of Objects with Air Blast ..... ..................... !32

CHAP rER V--Structural Damage from Air Blast ................... 154

Introduction ........................................... 154

Factors Affecting Response ................................ 156

Commercial and Administrative Structures ...................... 58

Industrial Structures ..... ................................. 61')

Residential Structures ..... ............................... - 5

'Transportation ......................................... 189

Utilities .............................................. 195

Miscellaneous Targets ................................. 206

Analysis of Damage from Air Blast ....................... 212

CHAPTIUR VI-Shock Effects of Surface and Subsurface Bursts . . . 231

Characteristics of Surface and Shallow Underground Bursts .......... 231

Deep Underground Bursts ....... ......................... 238

Damage to Structures .................................... 241

Characteristics of Underwater Bursts .......................... 244
Technical Aspects of Surface and Underground Bursts .............. 253

Tecnnical Aspects of Deep Underground Bursts ................... 260

Loading on Buried Structures ............................... 263

Damage from Ground Shock ................................ 265

Technical Aspects of Underwater Bursts ....................... 268

CHAPTER VII-Thermal Radiation and Its Effects ................... 27o

Radiation from the Fireball ................................. 276

Thermal Radiation Effects .................................. 282

incendiary Effects ....................................... 296

Incendiary Effects in Japan ................................. 300

Technical Aspects of Thermal Radiation ........................ 305

Radiant Exposure-Distance Re!ationsnipý .................... ... 316

CHAPTER VIII-Initial Nuclear Radiation ...... .................. 324

Nature of Nuclear Radiations ............................... 324

Gamma Rays .......................................... 326

Neuwrons ............................................. 340

Transient-Radiation Effects on Electronics (TREE) ................. 344

Technical Aspects of Ini;ial Nuclear Radiation ................... 353

CHAPTER IX-Residual Nuclear Radiation and Fallout ............... 387

Sources of Residual Radi'ition ............................. .,°,

Radioactive Contarninat'on from Nuclear Explosions .............. 40)

Fallout Distribution in Land Surface Bursts .... ................. 414

Fallout Predictions for Land Surface Bursts .... ................. 422

Attenuation of Residual Nuclear Radiation ..................... 4r39

Delayed Falloi,t ......................................... 442

Technical Aspects of Residual Nuclear Radiation .............. ... 450

CHAPTER X-Radio and Radar Effects .......................... 461

Introduction ............................................ 461

Atmospheric Ionization Phenomena ........................... 462

Ionization Produced by Nuclear Explosions .... ................. 466

Effects on Radio and Radar Signals ........................... 479

Technical Aspects of Rad-n -nd Radar Effects ................... 489

CHAPTER XI-The Electromagnetic Puise and its Effects .......... ... 514

Origin and Nature of the EMP ..... ......................... 514

EMP Damage and Protection ................................ 523

Theory of the EMP ...................................... 532

CHAPTER XII-Biological Effects ...... ....................... 541

Introduction ........................................... 54i

Blast Injuries ........................................... 548

Burn Injuries ........................................... 560

Nucleat Radiation Injury ................................... 575
Characteristics of Acu:• Whole-Body Radiation Injury .............. 583

Ccmbir.d injuries ....................................... 588

Late Effects of Ionizing Radiation ..... ....................... 589

Effects of Early Fallout .................................... 594

Long-Term Hazard from Delayed Fallout ....................... 604

Genetic Effects of Nuclear Radiation .......................... 609

Pathology of Acute Radiation Injury .......................... 614

Blast-Related Effects ..................................... 618

Effects on Farm Anima!s and Plants ........................... 618

Glossary ................................................ 629

Guide to SI Units ......................................... 642

Index .................................................. 644
C-IAP!'ER I

GENER AL PRINCIPLES OF

NUCLEAR EXPLOSIONS

CHARACTERISTICS OF NUCLEAR EXPL OSIONS

INTRODUCTION\ the ground, however, the term "shcck"

1.01 An explosion, in general, re- is used, because the effect ;-, itke that of

sults from the very rapid release of a a sudden impact.

large amourpt of energy within a limited 1.02 Nuclear weapons are similar to

space. This is true for a conventional those of more conventional '.ypes insofar

"high explosive," such as TNT, as well as their destructive action is due mainly

as foe a nuclear (or atomic) explosion,' to blast or shock. On th', other hand,

although the energy is produced in quite there arc several basic differences be

different ways (§ 1.11). The sudden tween nuclear and 'igh-explosive

liberation of energy causes a consider- weapons. In the first lIace, nuclear exable increase of temperature and pres- plosions can be maly thousands (or

sure, so that all the materials present are millions) of times nrore powerful than

converted into hot, compressed gases. the largest conven~ional detonations.

Since these gases are at very high tern- Second, tor the release of a given

peratures and pressures, they expand amount of energy, .he mass of a nucleat

rapidly and thus initiate a pressure explosive would tIe much less than that

wave, called a "shock wave," in the or a conventiona', high explosivse. Consurrounding medium-air, water, or sequently, in the former case, there is a

earth. The characteristic of a shock much smaller ariount of material availwave is that there is (ideally) a sudden able in the weatpon itself that is conincrease of pressure at the front, with a vert,,•d into the hot, compressed gases

gradual decrease! behind it, as shown in mentioned above. This results in someFig. 1.01. A shock wave in air is gen- what different mechanisms for the inierally referred to as a "blast wave" tiation of the blast wave. Third, the

because it resembles and is accompan- temperatures teached in a nuclear exied by a very strong wind. In water or in plosioai are very much higher than in a

IThe terms "nuclear" and atomic" may be used interchangeably sc far as weaponF, explosions, and

energy are concerned, but "nuclear" is preferred for the reason givenu in § I.1i.

I
2 ,GFNERAI. PRIN(IPI.ES OF NIC! EAR LXH OSIONS

u. I

10.

0-

C-)

0

AMBIENT ORESSURE

DISTANCE

Figure I.01. Variation ef pressure (in excess of ambient) with distance ir, an ioeal shock

wave.

conventional explosion, rnd a fairly understanding uf the mechenicai and thae

large pioportion of the energy in a nu- various radiation rhenomena associated

clear explosion is emitted in the form of w'ith a nuclear explosion are of vital

light and heat, generally referred to as importartce.

"thei'mal radiation." This is capable of 1.04 The purpose of this book is to

causing skin burns and of startling fires at describe the cifferent forms in which thIe

considerable distances. Fourth, the nu- energy of a .uclzar explosion are reclear explosicn is accompanied by leased, to cxplain how tihey are propahighly-penetratlng and harmful invisible gated, and to show how they may affect

rays, called the "initial i-.uclear radia- people (end other living organisms) and

tion." Finally the substances remain.ng materials. Where numerical values are

after a nuclear explosion are radioac- given for specific observed effects, it

tive, emitting similar rad!ations wver an should be kept in mind that there are

extended period of time. This is known inevitable uncertainties Lssociated with

as the "residual nuclear radiation" or the data, for at least two reasons. in the

"residual radioactivity" (Fig. 1.02). first place, there are inherent difficulties

1.03 It is because o: these funda- in making exact mcasuremenis of

mental differences between a nuclear weapons effects, The results are often

and a conventional explosion, including dependent on circumstznces which are

the tremendously g;,eater power of the difficult, it not impossible, to control,

former, (hat the effects of nuclear even in a test anJ certainly cannot be

weapons require special consideration. predicted in the event of au attack. FurIn this connection, a knowledge and thermore, two weapons producing the

ip
(HARACIERISTICS OF NUCI EAR EXPLOSIONS 3

BLAST AND SHOCK "-.. THERMAL RADIAM ION

NUCLEAR EXPLOSION

/

INITIAL RESIDUAL

NUCLEAR RADIATION NUCLEAR RADIATION

Figure 1.02. Effects of a nuclear -xplosio,.

same amount of explosive energy may various m:!tals, such as iron, copper.

have different quantitative effects be- and zinc. A less iamiliar element, which

cause of differences in composition and his attained prominence in recent years

design. because of i6s use as a source of nuclear

1.05 It is hoped, nevertheless, that energy, is uranium, normally a solid

the information contained in this vol- metal.

ume, which is the best available, racy be 1.07 The smallest part of any eleof assistance to :hose responsible for ment that can exist, whi'e stifl retaining

defense planning and in making nrepa- the characteristics of the element, is

rations to deal with the emergencies (hat called an "atom" of that element. Thus,

may arise from nuclear warfare. In ad- there are atoms of hydrogen, of iron, of

dition, architects iznd engineers may be urznium, and so on, for all the elements.

able to utilize the data in the design of The hydrogen atom is the lightest of all

structures having increased resistance to atems, whereas the atoms of uranium

damage by blast, shock, and fire, and are the heaviest of those found on earth.

wihich provide shielding against nuclean Heavier atoms, such as those of plutoradiations. nium, also important for the release of

nuclear energy, have been made artiiiATOMIC STRUCTURE AND ISOTOPES cially (§ 1.14). Frequently, two or more

atoms of the s.ime or of different ele1.06 All substances are made up ments join together to form a "molefrom one or more of about 90 different cule."

kinds of simple materials known as 1.08 Every atom consists of a rela-

"elements." Among the common ele- tively heavy central region or "num-nts are the gases hydrogen, oxygen, cleus, " surrounded by a number of very

and nitrogen; the solid nonmetal& car- light particles known as "electrons."

bon, sulfur, and phosphorus; ani Fuither, the atomic nucleus is itself
4 G-NERAI PRIN( IPIL-S OF1 N't(I F1AR FXPI 0OsIONS

,nade up of a definite number of fun- sequently referreu to as uranium-235

damental particles, referred to as "pro- and uranium-238, rcpectively. The nutons" arld "neutrons." These two par- clei of both isotopes contain 92 protitles have almost the same mass, but tons-as do the nuclei of all uraolium

they differ in the ,espect that the proton isotopes-but the former have in addicarries a unit charge of positive elec- tion 143 neutrons and the latter 146

tricity whereas the neutron, as its name neutrons. The general term "nuclidc" is

implies, is uncharged electrically, i.e., used to describe any atomic species disit is neutral. Because of the protons tinguished by tlhe composition of its nupresent in the nucleus, the la,.ter has a cleus, i.e., by the number of protons

positive electrical charge, but in the and the number of neutrons. Isotopes of

normal atom this is exactly balanced by a given elementt are nuciides having the

the negative charge carried by the elec- same number of protons but different

trons surrounding the nucleus, numbers of neutrons la their nuclei.

1.09 The essential difference be- 1.11 In a conventional explosion,

tween atoms of different elements lies in the energy released arises from chemical

the number of protons (or positive reactions; these involvc a rearrangement

charges) in the nucleus; this is called the among the atomn;, e.g., of hydrogen, "atomic number" of the element. Hy- carbon, oxygen, and nitrogen, present

drogen atoms, for example, contain in the chemical high. explosive material.

only one proton, helium atoms have two In a nuclear explos,)n, on the other

protons. uranium atoms have 92 pro- hand, the energy is produced as a resuit

tons, and plutonium atoms 94 protons. of the formation of diffceent atomic nuAlthough all the nuclei of a given ele- clei by the redistribution of the protons

ment contain the same number of pro- and aeutrons within the interacting nutons, they may have different numbers clei. What is sometimes referred to as

of neutrons. The resulting atomic spe- atomic energy is thus actually nuclear

cies, which have identical atomic energy, since it results from particular

numbers but which differ in theie nuclear interactions. It is for the same

masses, are called "isotopes" of the reason, too, that atomic weapons are

particular element. All but about 20 of preferably called "nuclear weapons."

the elements occur in nature in two or The forces between the protons and

more isotopic forms, and many other neutrons within atomic nuclei are treisotopes, which axe unstable, i.e., ra- mendously greater than those between

dioactive, have been obtained in various the atoms; consequently, nuclear energy

ways. is of a much higher order of magnitude

1.10 Each isotope of a given ele- than conventional (or chemical) energy

ment is identified by its "mass when equal tasses are considered.

number," which is the sum of the 1.12 Many nuclear processes are

numbers of protons and neutrons in the known, but not all are accompanied by

nucleus. For example, the element ura- the release of energy. There is a definite

nium, as found in nature, consists equivalence between mass and energy,

mainly of two isotopes with mass and when a decrease of mass occurs in a

numbers of 235 and 238; they are con- nuclear reaction there is an accompany-
(HARACTERISTICS OF NUCI.EAR foXPLOSIONS -

ing release of a certain amount of energy are found in nature, the fissionable isorelated to the decrease in mass. These tope used in nuclear weapons, plutomass changes awe really a reflection of nium-239, is made artificially from urathe difference in the internal forces in nium-238.

the various nuclei. It is a basic law of 1.15 When a free (or unattached)

nature that the conversion of any system neutron enters 'he nucleus of a fissionin which the constituents are held to- able atom, it can cause the nucleus to

gether by weaker forces into one in sp!it into two smaller parts. This is the

which the forces are stronger must be fission process, which is accompanied

accompanied by the release of energy, by the release of a large amount of

and a corresponding decrease in mass. energy. The smaller (or lighter) nuclei

1.13 In addition to the necessity for which result are called the "fission

the nuclear process to be one in which products." The complete fission of I

there is a net decrease in mass, the pound of uranium or plutonium releases

release of nuclear energy in amounts as much explosive energy as does the

sufficient t, cause an explosion requires explosion of about 8,000 (short) tons of

that the reaction should be able to re- TNT.

produce itself once it has been started. 1.16 In nuclear fusion, a pair of

Two kinds of nuclear interactions can light nuclei unite (or fuse) together to

satisfy the conditions for the production form a nucleus of a heavier atom. An

of large amounts of energy in a short example is the fusion of the hydrogen

time. They are known as "fission" isotope known as deuterium or "heavy

(splitting) aiai "fusion" (joining to- hydrogen." Under suitable conditions,

gether). The former process takes place two deuterium nuclei may combine to

with some of the heaviest (high atomic form the nucleus of a heavier element,

number) nu'clei; whcreas the latter, at helium, with the release of energy.

the other extreme, involves some of the Other fusion reactions are described in

lightest (low atomic number) nuclei. § 1.69.

1.1,4 The materials used to produce 1.17 Nuclear fusion reactions can

nuclear explosions by fission are certain be brought about by means -of very high

isotopes of the elements uranium and temperatures, and they are thus referred

plutonium. As noted above, uranium in to as "thermonuclear processes." The

nature consists mainly of two isotopes, actual quantity of energy liberated, for

namely, uranium-235 (about 0.7 per- a given mass of material, depends on

cent), and uranium-238 (about 99.3 the particular isotope (or isotopes) inpercent). The less abundant of these volved in the nuclear fusion reaction. As

isotopes, i.e., uranium-235, is the read- an example, the fusion of all the nuclei

ily fissionable specie; that is commonly present in i pound of the hydrogen isoused in nuclear weapons. Another iso- tope deuterium would release roughly

tope, uranium-233, does not occur nat- the same amount of energy as the ex-

-rally, but' it is also readily fissionable plosion of 26,000 tons of TNT.

and it can be made artificially starting 1.18 In certain fusion processes,

with thorium-232. Since only insignifi- between nuclei of the hydrogen isocant amounts of the element plutonium topes., neutrons of high energy are lib-.
___ - - --------

6 GCsNFN,,RA. PRINCIPI.ULS OF NUCLEA.-R EXPLOSIONS

erated (see § 1,72). These can cause have the energy equivalent of I million

fission in the most abundant isotope tons (or 1,00M kilotons) of TNT. The

(uranium.? (8) in ordinary uranium as earliest nuclear bombs, such as were

well as ... uranium.-235 and p~utoniumn- dropped over Japan in 1945 and used in

239. Consequently, association of the the tests at Bikini in 1946, released very

appropriate fusion reactions with natural ro:ighly the same quantity of energy as

uranium can result in an extensive utili- 20,000 tons (or 20 kilotons) of TNT

zation of the latter for the release of (see, however. § 2.24). Since that time,

energy. A device in which fission and much more powerful weapons, with enfusion (thermonuclear) reactions are ergy yields in the megaton range, have

combined can therefore produce an ex- been developed.

plosion of great power. Such weapons 1.21 From the statemetit in § 1.15

might typically release about equal that the fission of I pound of uranium or

amounts of explosive energy from fis- plutonium will release the same amount

sion and from fusion. of explosive energy as about 8,(XX) tons

1.19 A distinction has sometimes of TNT, it is evident that in a 20-kiloton

be(.n made between atomic weapons, in nuclear weapon 2.5 pounds of material

which the energy arises from fission, on undergo fission. However, the actual

the one hand, and hydrogen (or thermo- weight of uranium or plutonium in such

nuclear) weapon::, involving fusion, on a weapon is greater than this amount. In

the other hand. In each case, however, other words, in a fission weapon, only

the explosive eoergy results from nu- part of the nuclear material suffers fisclear reactions, so that they are both sion. The efficiency is thus said to be

correctly describe:! as nuclear weapons. less than 10() percent. The material that

In this book, therefore, the general has not undergone fission remaias in the

terms "nuclear bomb" and "nuclear weapon residues after the explosion.

weapon" will be used, irrespective of

the typeo of nuclear reaction producing DISTRIBI.'TION OF ENERGY IN

the energy of the explosion. NUCLEAR EXPLOSIONS

1.22 It has been mentioned that one EXPLOSION important difference between nuclear

and conventional (or chemical) explo1.20 The "yield" of a nuclear sions is the appearance of an appreciable

weapon is a measure of the amount of proportion of the energy as thermal raexplosive energy it can produce. It is the diation in the former case. The M- ic

usual practice to state the yield in terms reason for this difference is that, weight

of the quantity of TNT that would gen- for weight, the energy produced by a

erate the same amount of energy when it nuclear explosive is millions of times as

explodes. Thus, a I-kiloton nuclear great as that produced by a Chemical

weapon is one which produces the same ceplosive Consequently, the temperaamount of energy in an explosion %as tures reached in the former case are very

does I kiloton (or 1,000 tons) of TNT. much higher than in the latter, namely,

Similariy, a I-megaton wv.apon would tens of millions of degrees in a nuclear
CHARACTERISTICS OF NUr:LEAR EXPLOSIONS /

explosion compared with a few thou- somewhat higher altitudes, where there

sands in h conventional explosion. As a is less air with which the energy of the

result of this great difference in temper- exploding nuclear weapon ran interact,

ature, the distribution of the explosion the proportion of energy cot,-Verted into

energy is quite differeut in the two shock is decreased whereas that emitted

cases. as thermal radiation is correspondingly

1.23 Broadly speaking, the energy increased (§ 1,36).

may be divided into three categories: 1.25 The exact distribution of enkinetic (or external) Lrnergy, i.e., energy ergy between air shock and thermal raof motion of electrons, atoms, and mol- diation is related in a complex manner to

ecules as a whole; internal energy of the explosive energy yield, the burst

these particles; and thermal radiation altitude, and, to some extent, to the

energy. The proportion of thermal radi- weapon design, as will be seen in this

ation energy increases rapidly with in- and later chapters. However, an apcreasing temperature. At the moderate proximate rule of thumb for a fission

temperatures attained in a chemical cx- weapon explodod in the air at an altitude

plosion, the amount of thermal radiation of less than about 40,000 feet is that 35

is comparatively small, and so essen- percent of the explosion energy is in the

tially all the energy released at the time form of thermal radiation and 50 percent

of the explosion appears as kinetic and produces air sh( ck. Thus, for a burst at

internal energy. This is almost entirely moderately low altitudes, the air shock

converted into blast and shock, in the energy from a fission weapon will be

manner described in § !.01. Because of about half of that from a conventional

the very much higher temperatures in a high explosive with the same total ennuclear explosion, however, a consid- ergy release; in the latter, essentially all

erable proportion of the energy is re- of the explosive energy is in the form of

leased as thermal radiation. The manner air blast. This means that if a 20-kiloton

in which this takes place is described fis,-ion weapon, for example, is cxlater (§ 1.77 et seq.). ploded in the air below 40,000 feet or

1.24 The fraction of the explosion so, the energy used in the prodt4ction of

energy received at a distance from the blast would be roughly equivalent to

burst point in each of the forms depicted that from 10 kilotons of TNT.

in Fig. 1.02 depends on the nature and 1,26 Regardless of the height of

yield of the weapon and particularly on burst, approximately 85 percent of the

the environment of the explosion. For a explosive energy of a nuclear fission

nuclear detonation in the atmosphere weapon produces air blast (and shock),

below an altitude of about 100,000 feet, thermal radiation, and heat. The refrom 35 to 45 percent of the explosion maining 15 percent of the energy is

energy is received as thermal energy in released as various nuclear radiations.

the visible and infrared portions of the Of this, 5 percent constitutes the iiiiiial

spectrum (see Fig. 1.74). In addition, nuclear radiation, defined as that probelow an altitude of about 40,000 feet, duced within a minute or so ot the

about M0 percent of the explosive energy explosion (§ 2.42). The final 10 percent

is used in the production of air shock. At of the total fission energy represents that
8 GENERAl PRINCIe'l.FS OF NUCLEAR FXPLOSIONS

of the residual (or delayed) nuclear ra- travel great distances through air and

diation which is emitted over a period of can penetrate considerable thicknesses

time. This is largely due to the radioac- of material. Although they can neither

tivity of the fission products present in be seen nor felt by human being:;, exthe weapon residues (or debris) after the cept at very high intensities which cause

explosion. In a thermonuclear device, in a tingling sensation, gamma rays and

which only about half of the total energy neutrons can produce harmful effects

arises from fission (§ 1. 18), the residual even at a distance from their source.

nuclear radiation cariies only 5 percent Consequently, the initial nuclear radiaof the energy released in the explosion. tion is an important aspect of nuclear

It should be noted that the-e are no explosions.

nuclear radiations from a conventional

explosion since the nuclei are unaffected 1.29 The delayed nuclear radiation

in the chemical reactions which take arises mainly from the fission products

place. which, in the course of their radioactive

decay, emit gamma rays and another

1.27 Because about 10 percent of type of nuclear radiation called "beta

the total fission energy is released in the particles." The latter are electrons, i.e.,

[(? iil i ,c:d,,,; nuclear radiation some particles carrying a negative electric

time after the detonation, this ik not charge, moving with high speed; they

included when the energy yield of a are formed by a change (neutron --

nuclear explosion is stated, e.g., in proton + electron) within the nuclei of

terms of the TNT equivalent as in the radioactive atoms. Beta particle%,

§ 1.20. Hence, in a pure fission weapon which are also invisible, are much less

the explosion energy is about 90 percent penetrating than gamma rays, but like

of the total fission energy, and in a the latter they represent a potential hazthermonuclear device it is, on the aver- ard.

age, about 95 percent of the total energy

(if the fission and fusion reactions, This 1.30 The spontaneous em;,s;ion of

common conventiorn will be adhered to beta particles and gamma rays from rain subsequent chapters. For example, dioactive substances, i.e., a radioactive

when the yield of a nuclear weapon is Puclide (or radionuclide), 'uch as the

quoted or used in equations, figures, fission products, is a gradual process. It

etc., it will represent that portion of thc takes place over a period of time, at a

energy delivered within a minute or so, rate depending upon the nature of the

and will exclude the contribution of the material and upon the amount present.

residual nuclear radiation. Because of the continuous decay, the

quantity of the radionuclide and the rate

1.28 The initial nuclear radiation of emission of radiatiun decrease steadconsists mainly of "gamma rays," ily. This means that the residual nuclear

which are electromagnetic radiations of radiation, due mainly to the fission

high energy (see § 1.73) originating in products, is most intense soon after the

atomic nuclei, and ne-utrons. These ra- explosion but dimini hes in the course

diations, especially gamma rays, can of time.
CHARACTERISTICS OF NUCLEAR EXPLOSIONS

TYPES OF NUCLEAR EXPLOSIONS leaves the fireball appears as air blast.

although some is generally also trans1.31 The immediate phenomena mitted into the ground. The thermal raassociated with a nuclear explosion, as diation will travel long distances

well as the effects of shock and blast and through the air and may be of sufficient

of thermal and nuclear radiations, vary intensity to cause moderately severe

with the location of the point of burst in burns of exposed skin as far away as 12

relatioih to the surface of the earth. For miles from a I-megaton explosion, on a

descriptive purposes five types of burst fairly clear day. For air bursts of higher

are distinguished, although many varia- energy yields, the corresponding distions and intermediate situations can tances will, of course, be greater. The

arise in practice. The main types, which thermal radiation is largely stopped by

will be defined below, are (I) air burst, ordinary opaque mate;ials; hence,

(2) high-altitude burst, (3) underwater buildirigs and clcthing can provide proburst, (4) underground burst, and (5) tection.

surface burst. 1.34 The initial nuclear radiation

1.32 Provided the nuclear explosion from an air burst will also penetrate a

takes place at an altitude where there is long way in ,ir, although the intensity

still an appreciable atmosphere, e.g., falls off fairly rapidly at increasing disbelow about 100,000 feet, the weapon tances from the explosion. The interacresidues almost immediately incorporate tions with matter that result in the abmaterial from the surrounding medium sorp'tion of energy from gamma rays and

and for,-.r an intensely hot and luminous from neutrons are quite different, as will

mass, roughly spherical in shape, called be seen in Chapter VIII. Different mathe "fireball." An "air burst" is de- terials are thus requied for the most

fined as one in which the weapon is efficient removal of these radiations; but

exploded in the air at an altitude below concrete, especially if it incorporates a

100,000 feet, but at such a height that heavy element, such as iron or barium,

the firebal! (at roughly maximum bril- represents a reasonable practical comliance in its later stages) does not touch promise for reducing the intensities of

the surface of the earth. For example, in both gamma rays and neut'ons. A

the explosion of a i-megaton weapon thickness of about 4 feet of ordinary

the fireball may grow uttil it is nearly concrete would probably provide ade5,700 feet (1.1 mile) acrcss at maxi- quate protection from the effects of thf.

mum brilliance. This means that, in this initial nuclear radiation for people at 0.

particular case, the explosion must distance of abo-it I mile from an air

occur at least 2,850 feet above the burst of a 1-megaton nuclear weapon.

earth's surface if it is to be called an air However, at this distance the blast effect

burst. would be ;o great that only specially

1.33 The quantitative aspects of an designed blast-resistant structures would

air burst will be dependent upon its survive.

energy yield, but the general phenom- 1.35 'in the event ot a moderately

ena are much the same in all cases. high (or high) air burst, the fission

Nearly all of the shock energy that products remaining after the nuclear exA'-' ', . * , . . .
10 (G-ENERAI PRINCIPLES OF NUCLEAR EXPLOSIONS

plosior will be dispersed in the atmos- proportion of the explosion energy is

phere. The residual nuclkar radiation released in the form of thermal radiation

arising from these products will "x of than at lower altitudes, For explosions

minor immediate consequencc on (ie above about 140,000 feet, the second

ground. On the other hand, if the b.rst factor becomes the more important, and

occurs neare" the earth's surface, the the fraction of the energy that appears a,-

fission products may fuse with particles thermal radiation at the time of the exof earth, part of which will soon fall to plosion becomes smaller.

the ground at points close to the explo- 1.37 The fraction of the explosion

sion. This dirt and other debris will be energy emitted from a weapon as nucontaminated with radioactive material clear radiations is independent of the

and will, consequently, represent a pos- height of burst. However, the partition

sible danger to living things. of that energy between gamma rays and

1.36 A "high-altitude bu;-st" is de- neutrons received at a distance will vary

fined as one in which the explosion takes since a significant fraction of the gamma

place at an altitude in excess of 100,000 rays result fiom interactiorls of neutrons

feet. Above this level, the air density is with nitrogen atoms in the air at low

so low that the interaction of tho weapon altitudes. Furthermore, the attenuation

energy with the surroundings is mark- of the initial nuclear radi•itior. with inedly different from that at lower alti- creasing distance from tno explosion is

tudes and, moreover, varies with the determined by the total amount of air

altituue. The absence of relativety dense through which the radiation travels.

air causes the fireball characte,'isl'ics in a This means that, for a given explosion

high-altitude explosion to differ from energy yield, more initial nuclear radiathose of an air burst. For example, the tion will be received at the same slant

fraction of the energy converted into range on the earth's surface from a

blast and shock is less and decreases high-altitude detonation than from a

with increasing altitude. Two factors moderately high air burst. In both cases

affect the thermal energy radiato.d at the residual radiation fron: the fission

high altitude. First, since a shock wave products and other weapon residues will

does not form so readily in the less not be significant on the ground

dense air, the fireball is able to radiate (§ 1.35).

thermal energy that would, at lower al- 1.38 Both tP, initial and the residtitudes, have been used in the proacuc- ul nuclear ru'.ations from high-altitude

tion of air blast. Second, the less dense barsts will interact with the constituents

air allows energy from the exploding of the atmosphere to expel electrons

weapoin to travel much farther than at from the atoms arid molecules. Since the

lower altitudes. Some of this energy ehectron carries a negative electrical

simply warms the air at a disance from charge, the residual part of the atom (or

the fireball and it does not contribute to molecule) is positively charged, i.e., it

the energy that can be radiated within zý is a positive ion. This process is referred

short time (§ 1.79). In general, the first to ais "ionizatiot,,', and the separated,

of these factors is effective between electrons and positive ions are Callkd

100,000 and 140,000 feet, aoid a larger "ior pairs." The existeace of large
CHARACTF-RI"TICS OF NtJ I.EAR EXP.OSIONS 11

numbers of electrons and ions ait high erally be less ,ai1 fo, an air burst.

altitudes ma' have seriously degrading However, the residual nuclear radiatien,

effects on the propagation of rvdio and i.e.. the radiation emitted after the first

redar signals (see Chapter XV. The free rrninutc, now becomes of considerable

electrons resulting from gamma-ray significance, since large quantities of

ionization of the air ir. a high-altitude earth or water in the vicinity of the

explosion may also interact with the explosion will be contaminated with raearth's magnetic field to generate strong dioactive fission products.

electromagnetic fields capable of caus- 1.40 A "surface bur"" is regarded

ing damage to unprotected electrical or as one which occurs either at or slightly

electronic equipment located in an ex- above the actual suriace of the land or

tensive area below the burst. The phe- water. Provided the distance above thc

nomenon known as the "eledtromagne- surface is not great, the phenomena are

tic pulse" (or EMP) is described in essentially the same as .'or a burst ocChapter XI. The EMP can also be pro- curring on the surface. As the height of

duced in surface and low air bursts, but burst increases up to a point where the

a much smaller area around the detona- fireball (at maximum brilliance in its

tion point is affected. later stages) no ;onger touches the land

1.39 If a nuclear explosion occurs or water, the-e is a transition zone in

under such conditions that its center is which the behavior is intermediate bebeneath the ground or under the surface tween that of a true surface burst and of

of water, the situation is described as an an air burst. In surface bursts, the air

"underground burst" or an "under- blast and ground (or water) shock are

water burst," respectively. Since some produced in varying proportions deof the effects of these two types of pending on the energy of the explosion

explosions are similar, they will be and the height of burst.

considered iere together as subsurface 1.41 Although the five types of

bursts. In a subsurface burst, most of the burst have been considered as being

shock energy of the explosioil appears fairly distinct, there is actually no clear

as underground or unt;,'rwater shock, line of demarcation betweei ,hem. It

but a certain proportion, ,hich is less will be apparent that, as the height of the

the greater the depth of ,he burst, exp!osion is decreased, a high-altitude

escapes and produces air blast. M'uch of burst will become an air burst, and an

the thermal radiation and of thu initial air burst will become a surface burst.

nuclear radiation will be abý, .rbed Similarly, a sulface burst merges into a

within a short distance of the exploion. subsurface explosion at a shallow depth,

The energy of the absorbed radiations when part of 'he fireball actually breaks

will merely contribute to the heating of through the surface of the land or water.

the ground cr body of water. Depending It is nevertheless a matter of convenupon the depth ot the explosioit, some ience, as will be seen in later chapters,

of the thermal and nuclear radiations to divide nuclear e,,plosions into the five

will escape, but the intensiti,.s will gen- general types defined above.
12 GENERAL. PRINCIPILES OF NUCLEAR EXPLOSIONS

SCIENTIFIC BASIS OF NUCLEAR EXPLOSIONS 2

FISSION ENERGY equivalent to 1.6 x IC G' erg or i.6 x

10 '' joule. The manner in which this

1.42 The significant point about the energy is distributed among the fission

fission of a uranium (or plutonium) nu- fragments and the various radiations ascleus by means of a neutron, in addition sociated with fission is shown in Table

to the release of a large quantity of i.43.

energy, is that the process is accompanied by the instaitaneous emission of two Table 1.43

or more neutrons, thus, DISTRIBUTION OF FISSION ENERGY

MeV furanium-235 e

Neutron 4- (or uranium-233) Kinetic energy of fission fragn,-,.. 165 ± '

(or plutonium-239) Instantaneous gamma-ray energy 7 _ I

Kinetic energy of fission neutrons 5 ± 0.5

Beta parlicles from fission products 7 ± I

fission fragments + Gamma rays from fission products 6 ± I

2 or I neutrons + energy. Neutrinos from iission products 10

Total energy per fission 200 ± 6

The neutrons liberated in this manner

are able to induce fission of additi-inal 1.44 The results in the table may be

uranium (or plutonium) nuclei, each taken as being approximately applicable

such process resulting in the emission of to either uranium-233, uraniura-235, or

more reutrons which can produce fur- plutornium-239. These are the only three

ther fission, and so on. Thus, in prin- known substances, which are reasonciple, a single neutron could start off a ably stable so that they can be stored

chain of nuclear fissions, the number of with'out appreciable decay, that are capnuclei suffering fission, and the energy able of undergoing fission by neutrons

liberated, increasing at a tremendous of all energies. Hence, they are the only

rate, as wil! be seen shortly. materials that can by used to sustain a

1.43 There are many different ways fission chain. Uraniurr-238, the most

in which the nuclei of a given fission- abundant isotope in mAtural uranium

able species can split up into two fission (§ 1. 14), and thorium-232 will suffer

fragments (initial fission products), but fission by neutrons of high energy only,

the total amount of energy liberated per but not by those of lower energy. For

fission does not vary greatly. A satis- this reason these substances cannot susfactory average value of this energy is tain a chain reaction. However, when

200 million electron volts. The million fission does occur in these elements, the

electron volt (or 1 MeV) unit has been energy distribution is quite similar to

found convenient for expressing the en- that shown in the table.

ergy released in nuclear reactions, it is 1.45 Only part of the fission energy

2The remaining (more technical) sections of this chapter may be omitted without loss of continuity.
SCIENTIFIC BASIS OF NUCLEAR FXPI.OSIONS 13

is immediately available in a nuclear CRITICAL MASS FOR A FISSION

explosion; this inciudes the kinetic en- CHAIN

ergy of the fission fragments, most of

the energy of the instantaneous gamma 1.46 Although two to three neurays, which is converted into other trons are produced in the fission reaction

forms of energy within the exploding for every nucleus that undergoes fission,

weapor,, and also most of the neutron not all of these neutrons are available for

kinetic energy, but only a small fraction causing further fis3ions. Some of the

of the decay energy of the fission prod- fission neutrons are lost by escape,

ucts. There is some compensation trom whereas others are lost in various nonenergy reieased in reactions in which fission reactions. In order to sustain a

neutrons are captured by the weapon fission chain reaction, with continuous

debris, and so it is usually accepted that release of energy, at least one fission

about 180 M'eV of energy are immedi- neutron must be available to cause furately available per fission. There are ther fission for each neutron previously

6.02 X 102, nuclei in 231 grams of absorbed in fission. If the conditions are

uranium-235 (or 239 grams of pluto- such that the neutrons are lost at a faster

niuni-239), and by making use of fa- rate than they are formed by fission, the

miliar conversion :'actors (cf. g 1.43) chain reaction would not be self-susthe results quoted in Table 1.45 may be taining. Some energy would be proobtained for the energy (and other) duced, but the amount would not be

equivalents of I kiloton of TNT. The large ,-nough, and the rate of liberation

calculations are based on an accepted, would not be sufficiently fast, to cause

although somewhat arbitrary, figure of an e,;ective explosion. It is necessary,

10 12 calories as the energy released in therefore, in order to achieve a nuclear

the explosion of this amount of TNT.3 exploion, to establish conditions under

which the loss of Iveutrons is minimized.

In this connection, it is especially imTable 1.45 portant to consider the neutrons which

EQUIVALENTS OF I KILOTON OF TNT escape from the substance undergoing

fission.

Complete fission of 0.057 kg (57 grams or 1.47 The escape of neutrons occurs

2 ounces) fissionable material at the exterior of the uranium (or plutoFission of 1.45 x 102' nuclei niun) miterial The -ate of loss by

1012 calories

2.6 x ifi', million electron voits escape will thus be determined by the

4.18 x 101'1 ergs (4.18 x 1011 jouls•) surface area. On the other hand, the

1.16 x 10t kilowatt-hours fission process, which results in the for3.97 x 10 British thermal units mation of more neutrons, takes place

'The majority of the experimental and theoretical values of tne explosive energy ieleased by TNT

range from 900 to I1.190 calories per gram. At one time, there was some uncertainty as to whether the

term "kilo.on" of TN4T referred to a short kiloton (2 x 106 pounds), a metric kiloton (2.205 x 10f

pounds;, or a long kiloton (2.24 x 106 pounds). In order to avoid ambiguity, it was agreed that the term

"kiloton" woule refer to the release of 1012 calories of ePxplosive e ergy. This is equivalent to I short

kiloton of TNT if the energy release s 1,102 calories per gram or to I long kiloton if the energy' is 984

calories pe: gram of TNT.
14 GENERAL PRINCIPLES OF NUCLEAR EXPLOSIONS

throughout the whole of the material and neutron from the system is indicated by

its rate is, therefore, dependent upon the the head of an arrow. Thus, an arrowmass. By increasing the mass of thý: head within the sphere means that fisfissionable material, at constant density, sion has occurred and extra neutrons are

the ratio of the surface area to the mass produced, whereas an arrowhead outis decreased; consequently, the loss of side the sphere implies the loss of a

neutrons by escape relative to their for- neutron. It i: evident from Fig. 1 .48 that

mation by fission is decreased. The a much greater fraction of the neutrons

same result can also be achieved by is lost from the smaller than from the

having a constant mass but compressing larger mass.

Iit to a smaller volume (higher density), 1.49 If the quantity of a fissionable

so that the surface area is decreased. isotope of uranium (or plutonium) is

1.48 The situation may be under- such that the ratio of the surface area to

stood by reference to Fig. 1 .48 showing the mass is large, the proportion of

two spherical masses, one larger than neutrons lost by escape will be so great

the other, of fissionable material of the that the propagation of a nuclear fission

same density. Fission is iniitiated by a chain, and hence the production of an

neutron represented by a dot within a explosion, will not be possible. Such a

small circle. It is supposed that in each quantity of material is said to be "subao.. uf ilssiua three neutrons are emitted; critical." But as the mass of the piece of

in other words, one neutron is captured uranium (or plutonium) is increased (or

and three are expelled. The removal of a the volume is decreased by compresFigure 1 .48. Effect of increased mass of fissionable material in reducing the proportion of

neutrons lost by escape.
SCIENTIFIC BASIS OF NUCLEAR EXPL.OSIONS 15

sion) and the relative loss of neutrons is ATTAINMENT OF CRITICAL MASS IN

thereby decreased, a point is reached at A WEAPON

which the chain reaction can become

self-sustaining. This is referred to as the 1.51 Because of the piesence of

"critical mass" of the fissionable mate- stray neutrons in the atmosphere or the

rial under the existing conditions. possiLtility of their being generated in

1.50 For a nuclear explosion to take various ways, a quantity of a suitable

place, the weapon must thus contain a isotope of uranium (or plutonium) exsufficient amount of a fissionable ura- ceeding the critical mass would be likely

niurn (or plutonium) isotope for the to melt or possibly explode. It is necescritical mass to be exceeded. Actually, sary, therefore, that before detonation, a

the critical nass depends, among other nuclear weapon should contain no piece

things, on ti.Lt shape of the material, its of fissionable material that is as large as

composition and density (or compres- the critical mass for the given condision), and the presence of impurities tions. In order to produce an explosion.

,Ahich can remove neutrons in nonfis- the material must then be made "supersion reactions. By surrounding the fis- critical," i.e., larger than the critical

sionable material with a suitable neutron mass, in a time so short as to preclude a

"reflector," the loss of neutrons by subexpiosive change in the configuraescape can be reduced, and the critical tion, such as by melting.

mass can thus be decreased Moreover, 1.52 Two general methods have

elements of high density, which make been described for bringing obout a nugood reflectors for neutrons of high en- clear explosion, that is to say, for

ergy, provide inertia, thereby delaying quickly converting a subcritical system

expansion of the exploding material, into a supercritical one. In the first

The action of the reflector is then like method, two or more pieces of fissionthe familiar tamping in blasting opera- able material, each less than a critical

tions. As a consequence of its neutron mass, are brought together very rapidly

reflecting and inertial properties, the in order to form one piece that exceeds

"tamper" permits the fis,,;ionable mate- the critical mass (Fig. 1.52). This may

rial in a nuclear weapon to be used more be achieved in some kind of gun-barrel

efficiently. device, in which an explosive propellant

SURCRITICAL SUBCRITICAL SUPERCRITICAL

MASS MASS MASS

EXPLOSIVE PROPELLANT

(IMMEDIATELY AFTER FIRING)

(BEFORE FIRING) THEN EXPLODES

Figure 1.52. Principle ot a gun-assembly nuclear device.
16 GENERAL PRINCIPLES OF NUCLEAR EXPLOSIONS

is used to blow one subcriticL.: piece of source can then initiate a chain reaction

fissionable material from the breech end leading to an explosion.

of the gun into another subcritical piece

firmly held in the muzzle end. TIME SCALE OF A FISSION

1.53 The second method makes use EXPLOSION

of the fact that when a subcritical quantity of an appropriate isotope of uranium 1.54 An interesting insight into the

(or plutonium) is strongly compressed, rate at which the energy is released in a

it can become critical or supercrit'.cal as fission explosion can be obtained by

indicated above. The compression may treating the fission chain as a series of

be achieved by mans of a spherical "generations." Suppose that a certain

arrangement of specially fabricated number of neutrons are present initially

shapes (lenses) of ordinary high explo- and that these are captured by fissionsive. In a hole in the center of this able nuclei; then, in the fission process

system is placed a subcritical sphere of other neUtrons are released. These neufissionale material. When the high- trons, are, in turn, captured by fissionexplosive lens system is set off, by able nuclei and produce more neutrons,

means of a detort.tor on the outside of and so on. Each stage of the fission

each lens, an inwardly-directed spheri- chain is regarded as a generation, and

cal "implosion" wave is produced. A the "generation time" is the average

similar wave can b- realized without time interval betweer successive generlenses by detonating a large number of ations. The time required for the actual

points distributed over a spherical sur- fission of a nucleus is extremely short

face. When the implosion wave reaches and most of the neutrons are emitted

the sphere of uranium (or plutonium), it promptly. Consequently, the generation

causes the laWter to be compressed and time is essentially equal to the average

become supercritical (Fig. 1.53). The time elapsing between the release of a

introduction of neutrons from a suitable neutron and its subsequent capture by a

SUBCRI rlCAL COMPRESSED

SUOERCFITICAL

MASS

'•' "' ' EXPLO IVE PLOS..ION

S> . ....... .. . , , . ..;. ",

(IMMEDIATELY AFTER FIRING)

(BEFORE FIRING) THEN EXPLODES

Figure 1 .53. Principle of an implosion-type nuclear device.
SCIENTIFIC BASIS OF NUCLEAR EXPLOS;ONS 17

fissionable rucleus. This time depends, elapsed during the time r. and if this is

among other things, on the energy (or represented by n, it follows that

speed) of the neutron, and if most of the N = re'-. (1.55.1)

neuttons are of fairly high energy,

usually referred to as "fast neutrons," 1.56 If the value of ., is known,

the generation time is about a one-hun- equation (1.55.1) can be used to caldred-millionth part (10-8) of a second, culate either the neutron population after

i.e., 0.01 microsecond.4 any prescribed number of generations in

1.55 It was mentioned earlier that the fission chain, or, alternatively, the

not all the fission neutrons are available generations required to attain a particufor maintaining the fission chain because lar number of neutrons. For uraniumsome are lost by escape and by removal 235, f is about 2.5, 1 may be taken to be

in nonfission reactions. Suppose that roughly 0.5, so that x, which is equal to

when a nucleus captures a neutron and f - I - 1, is close to unity; hence,

suffers fission fneutrons are released; let equation (1.55. 1) may be writ:en as

I be the average number of neutrons N - Noen or N - N0 10,•12' (1.56.1)

lost, in one way or another, for each

fission. There will thus be f- I neutrons 1.57 According to the data In Table

available to carry on the fission chain. If 1.45, it would need 1.4; x 102:: fisthere are N neutrons present at any in- sions, and hence the same numbr r of

stant, then as a result of their capture by neutrons, to produce 0. 1 kiloton euivfissionable nuclei N(f -- 1) neutrons will alent bf energy. If the fission chain is

be produced at the end of one genera- initiated by one neutron, so that N, is I1

tion; hence, the increase in the number it follows front equation (1.56. 1 ) thlar it

of neutrons per generation is N(f - I) - would take approximately 51 generaNor N(J- I - 1). For convenience, the tions to prrduce the necessary number

quantity f- I- I, that is, the increase in of neutrons. Similarly, to release 100

neutrons per fission, will be represented kilotons of energy would require 1.45 x

by x. If g is the generation time, then the 0) 2

5 neutror, and this number would be

rate at which the number of neutron,: atrained in aoout 58 generations. It is

increases is given by seen, therefore, that 99.9 percent of the

Rate of neutron increase energy of a 100-kiloton fission explodN/dt = Nx/,. sion is released during the last 7 generations, that is, in a period of roughly

The solution of this equation is 0.07 microsecond. Clearly, most of the

N = N e"'x fission energy is released in an extremely short time period. The same

where N, is the number of neutrons c3nclusion is reached for any value of

present initially ard Nis the number at a the fission explosion energy.

time t later. The fraction t/g is the 1.58 In 50 generations or so, i.e.,

number of generations which have r.:ughly half microsecond, after the ini4A microsecond is a one-millionth part of a second, i.e., 10 -second; a hundredth of a microsecond,

i.e., 10 8 second, is often called a "shake." The gcneration time in fission by fast neutrons is thus

roughly I shake.
18 (YENERAL. PRINCIPi-ES OF NU('i.EAR EXPLOSIONS

liation of the fission chain, so much fragments are produced. The nature and

energy will have been released--about proportions of the fission fragment nu10ol calories-that extremely high tern- clei vary to some extent, depending on

peratures will be attained. Conse- the particular substance undergoing fisquently, in spite of the restraining effect sion and on the energy of the neutrons

of the tamper (§ i.50) and the weapon causing fission. For example when

casing, the mass of fissionable material uranium-238 undergoes fissior as a rewill begin to expand rapidly. The time sult of the capture of ieutrons of very

at which 1ýhis expansion commences is high energy released in certain fusion

called the "explosion time." Since the reactions (§ 1.72), the prodtict,; :ire

expansion permits neutrons to escape :somewhat different, especially in their

more readily, the mass becomes subcri- relative amounts, from those formed

tical and the self-sustaining chain reac- from uranium-235 by ordinary fission

tion soon ends. An appreciable propor- neutrons.

tiorn of the fissionable material remains

unchanged and some fissions will con- 1.61 Regardless of their origin,

tinue as a result of neutron capture, but most, if not all, of the approximately 80

the amount of energy released at this fission fragments are the nuclei of rastage is relatively small. dioactive forms (radioisotopes) of well1.59 To summarize the foregoing known, lighter elements. The radioacdiscussion, it may be stated that because tivity is usually manifested by the

the fission process is accompanied by emission of negatively charged beta

the instantaneous liberation of neutrons, particles (§ 1.29). This is frequently,

it is possible, in principle to produce a although not always, accompanied by

self-sustaining chain reaction accorn- gamma radiation, which serves to carry

panied by the rapid release of large off excess energy. In a few speciai

amounts of energy. As a result, a few cases, gamma radiation only is emitted.

pounds of fissionable material can be

made to liberate, within a very small 1.62 As a result of the expulsion of

fraction of a second, as much energy as a beta particle, the nucleus of a radiothe explosion of many thousands of tons active substance is changed into that of

of TNT. This is the basi, principle of another element, sometimes called the

nuclear fission weapons. "decay product." In the case of the

fission fragments, the decay products

are generally also radioactive, and these

FISSION PRODUCTS in turn may decay with the emission of

beta particles and gamma rays. On the

1.60 Many different, initial fission average there are about four stages of

product nuclei, i.e., fission fragments, radioactivity for each fission fragment

are formed when uranium or plutonium before a stable (nonradioact;ve) nucleus

nuclei capture neutrons and suffer fis- is formed. Because of the large number

sion. There are 40 or so different ways of different ways in which fission c!...,

in which the nuclei can split up when occur and the several stages of decay

fission occurs; hence about 80 different involved, the fission product mixture
SCIENTIFIC BASIS OF NUCLEAR EXPLOSIONS 19

becomes very complex. 5 More than 300 about one-kenih (10 percent) of its

different isotopes of 36 light elements, amount at , hour, Within approximately

from zinc to terbium, have been iden- 2 days, the activity will have decreased

tified among the fission products. to I percent o

0 the I-hour value.

1.63 The rate of radioactive 1.65 In addition to the beta-particle

change, i.e., the rate of emission of beta and gamma-ray activity due to the fisparticles and gamma radiation, is sion products, there is another kind of

usually expressed by means of the residual radioactivity that should be

"half-life" of the radic,.uclide (§ 1.30) mentioned. This is the activity of the

involved. This is defined as the time fissionable material, part of which, as

required for the radioactivity of a given noted in § 1.58, remains after the exquantity of a particular nuclide to de- plosion. The fissionable uranium and

crease (or decay) to half of its original plutonium isotopes are radioactive, and

value. Each individual radionuclide has their activity consists in the emission of

a definite half-life which is independent what are called "alpha particles."

of its state or its amount. The half-lives These are a form of nuclear radiation,

of the fission products have been found since they are expelled from atomic nuto range from a small fraction of a clei, but they differ from the beta parsecond to something like a million ticles arising from the fission products in

years. being much heavier and carrying a pos1.64 Although every radionuclide itive electrical charge. Alpha particles

present among the fission products is are, in fa t, identical with the nuclei of

known to have a definite half-life, the helium atoms.

mixture formed after a nuclear explosion is so complex that it is not possible 1.66 Because of their greater mass

to represent the decay as a whole in and charge, alpha particles are much

terms of a half-life. Nevertheless, it has less penetrating than beta particles or

been found that the decrease in the total gamma rays of the same energy. Thus,

radiation intensity from the fission very few alpha paricles from radioacproducts can be calculated approxi- tive sources can travel more than I to 3

mately by meqns of a fairly simple for- inches in air before being stopped. It is

mula. This will be given and discussed doubtful that these particles can get

in Chapter IX, but the general nature of through the unbroken skin, and they

the decay rate of fission products, based certainly cannot penetrate clothing.

on this formula, will be apparent from Consequently, the uranium (or plutoFig. 1.64. The residual radioactivity nium) present in the weapon residues

from the fission products at 1 hour after does not constitute a hazard if the latter

a nuclear detonation is taken as 100 and are outside the body. However, if pluthe subsequent decrease with time is tonium enters the body by ingestion,

indicated by the curve. It is seen that at through skin abrasions, or particularly

7 hours after the explosion, the fission through inhalation, the effects may be

product activity will have decreased to serious.

3The general term "fission products" is used to describe this :omplex mixture.
20 GENERAL PRINCIIPL ES OF NUCLEAR IXPILOSIONS

100

I--

0 80

a..

z

0

60

U. 12) _ _

LJ 20

ILl

0

I-- 20

-J

0 2 4 6 8 10 12

TIME AFT.H EXPLOSION (HOURS)

Figure 1,64, Rate of Decay of fission products after a nuclear explosion lactivity is ta.,en as

I(X) at I hour after the detonation),

FUSION (THERMONUCLEAR) tritium (3H or T). All the nuclei carry a

REACTIONS single positive charge, i.e., they all

cootain one proton, but they differ in the

1.67 Energy production in the sun number of neutrons. The lightest ('H)

and stars is undoubtedly due to fusion nuclei (or protons) contain no neutrons;

reactions involving the nuclei of various deuterium (D) nuclei contain one ,ieulight (low atomic weight) atoms. From tron, and tritium (T) nuclei contain two

experiments made in laborawories with neutrons.

charged-particle accelerators, it was 1.68 Several different fusion reacconcluded that the fusion of isotopes of tions have been observed between the

hydrogen was possible. This element is nuclei of the three hydrogen isotopes,

known to exist in three isotopic forms, involving either two similar or two difin which the nuclei have mass numbers ferent nuclei. In order to make these

(§ 1. 10) of 1, 2, and 3, respectively. reactions occur to an appreciable extent,

These are generally referred to as hy- the nuclei must have high energies. One

drogen (1H), deuterium (2H or D', and way in ,hicia this energy can be sup-
SCII-NTI[It BASIS (OF NUt I [EAR [FAN OSI NS 21

plied is to raise the temperature to very "11i + -, 'He + "1' -f 4.8 MeV,

higl-, levels. In these circumstances the

fusion processes are referred to as where "l.i represents the lithium-6 iso-

"thermonuclear reactions,"i as men. tope, which rnakes up about 7.4 percent

tioned in § 1.17. of natural lithium. Other reactions can

1.69 Four thermonuclear fusion re- occur with lithium-l6 or the more abunactions appear to he of ink rest for the dant isotope lithium-7 and variou:, parproduction of energy because they are titles produced in the weapon. Hewexpected tco occur sufficiently rapidly at ever. the reaction shown above is of

realizable temperatures' these are: most interest for two reasons: ( I ) it has a

high probability of .)ccurr,,nce and (2) if

[) f ) 'He I. n 4- 3.2 MeV the lithium is placed in the weapon i1

I1 + 1) ' 4- 11-I + 4.0 MeV the form of the compound lithium dCIiT 1) = "He n t + 17.6 MeV teride (LID). the tritium formed in the

T 4 T - 'fit +- 2n + 11.3 MeV, reaction has a high probability of interacting with the deuterium, l.arge

where Hie is the symbol for helium and n amounts of energy are thus released by

(mass = I ) represents a neutron. The the third reaction in § 1.69, and addienergy liberated in each case is given in tiOnal neutrons are produced to react

million electron volt (MeV) unit,,. The with lithium-6.

firsi two of these reactions occur with 1.71 In order to make the nuclear

almost equal probability at the tempera- fusion reactions take place at the relures associated with nuclear explosions quired rate, temperatures of the order of

(several tens of million degrees Kelvin), several tens (if million degrees are necwhereas the third reaction has a much essary. The only practical way in which

higher probability and the fourth a much such temperatures can be obtained on

lower probability. Thus, a valid com- earth is by means of a fission explosion.

parison of the energy released in fusion Consequently, by combining a quantity

reactions with that produced in fission of deuterium or lithium deuteride (or a

can be made by noting that, as a result mixture of deuterium and tritium) with a

of the first three reactions given above, fission device, it s;hould bc possible to

live deuterium nuclei, with a total mass initiate one or more of the thermonuof 10 units, will liberate 24.8 McV upon clear fusion reactions given above. If

fusion. On the other hand, in the fission these reactions, accompanied by energy

process, e.g., of uranium-235, a mass evolution, can be propagated rapidly

of 235 units will produce a total of about through a volume of the hydrogen iso200 MeV of energy (§ 1.43). Weight tope (or isotopes) a thermonuclear exfor weight, therefore, the fusion of deu- plosion may be realized.

terium nuclei would produce nearly 1.72 It will be observed that in three

three times as much energy as the fis- of the fusion reactions given in § I.69,

sion of uranium or plutonium, neutrons are produced. Because of their

1.70 Another reaction of thermonu- small mass, these neutrons carry Oft

clear weapons interest, with tritium as a most of the reaction energy; conseproduct, is quently, t•v: have sufficient energy to
22 GENFRAIL PRIN('IPLES OF NUCLEAR EXPIOSIONS

cause fission of uranium-238 nuclei. As the velocity of light, 186.000 miles per

stated earlier, this process requires neu- second. E'xctromagnetic radiations

trons of high energy. It is possible, range from the very short wavelength

therefore, to make use of the thermonu- (or very high frequency) gamma rays

clear neutrons by surrounding the fusion (§ i.28) and X rays, through the invisiweapon with , blanket of ordinary ura- ble ultraviolet to the visible region, and

niun'. The higt-energy neutrons are then to the infrared and radar and radio

then captured by uranium-238 nuclei- waves of relatively long wavelength

the latter undergo fission, thereby con- (and low frequency).

tributing to the overall energy yield of 1.74 The approximate wavelength

the explosion, and also to the residual and frequency regions occupied by the

nuclear radiation arising from the fission different kinds of elec:romagnetic radiproducts. On the aveage, the energy ations are indicated in Fig. 1.74. The

released in the explosion of a thermo- wavelength X in centimeters and the

nuclear weapon originates in roughly frequency v in hertz, i.e., in waves (or

equal amounts from fission and fusion cycles) per second. are related by Xv =

processes, although there may be varia- c, where c ;s the velocity of light, 3.00

tions in individual cases, In "boosted" x 10"1 cn, per second. According to

fission weapons, thermonuclear neu- Planck's theory, the energy of the cortrons serve to enhance the fission proc- responding "quantum" (or unit) of eness; energy released in the thermonu- ergy, carried by the "photon," i.e., the

clear reaction is then a ,;mall fraction of postulated particle (or atom) of' radiathe total energy yield. tion, is given by

THERMAL RADIATION E (ergs) = hv '-

1.73 The observed phenomena as- 1 (19 !

sociated with a nuclear explosion and --- (.74.1)

the effects on people and materials are

largely determined by the thermal radi- where h is a univeis!- constant equal to

ation and its interaction with the sur- 6.62 '< 10 ,27 erg- ,.',nd. The energy

roundings. It is desirable, therefore, to quantum values fo; t!,, various electroconsider the nature of these radiations magne ic radiations ,re included in Fig.

somewhat further. Thermal radiation: 1 .74; tile results arc i,:xpressed either in

belong in the broad category of what are MeV, i.e., million electron volt, in

known as "electromagnetic radia- keV, i.e, kilo (or thousand) electron

tions." These are a kind of wave motion volt, or in eV, i.e., electron volt, units.

resulting from oscillating el,,ctric These are obtained from equation

charges and their associated magnetic (1 .74. 1) by writing it in the form

fields. Ordinary visible light is the most

familiar kind of electromagnetic radia- E (MeV) 1.24 x 10

tion, and all such radiations travel X(cm)

through the air (or, more exactly, a It is seen that the energy of the radiavacuum) at the same velocity, namely, tions decreases from let( to right in the
SCIENTIFIC BASIS OF NUCLEAR EXPLOSIONS 23

x - )

- U,,

00

z, > E ,>

<0

0 x

00

o > 5

L. x a - L.< <

> <

, I..

o × < : x L.b ,<

<

L <,

- Lb

> V1 ' 

< >

00

>-
24 GFNERAL PRINCIPLES OF NUCL EAR EXPIOSIONS

figure, i.e., as the wavelength increases in the spectral region with wavelengths

and :he frequency decreases. shorter than the ultraviolet.

1.75 The (thermal) radiation energy 1.77 When a nuclear weapon exdensity for matter in temperature equi- plode,, tempe-rature equilibrium is raplibrium is given by idly established in the residual material.

Ex 10 'T4 ergs/cm3 Within about one microsecond after the

E (radiation)= 7.6 ×explosion, some 70 to 80 percent of the

where T is the temperature in degrees explosion energy, as defined in § 1.27,

Kclvin. At the temperature of a con- is emitted as prirmary thermal radiation,

ventional chemical explosion, e.g., mos. of which %`onsio- )f soft X rays.6'

5,000*K, the radiation energy density is Almost all of the res nergy is in

then less than I erg/cml, compared with the form of kinetic energy ot the weapon

roughly 108 ergs/crzl' for the material debris at this time. The interaction of the

energy, i.e., kinetic energy and internal primary thermal radiation and the debris

(electronic, vibirational, and rotational) particles with the surroundings will vary

energy. Hernce, as indicated in § 1.23, with the altitude of burst and will deterthe radiation energy is a very small mine the ultimate partition of energy

pioportion df the total energy. In a nu- between the thcrmal radiation received

clear explosion, on the other hand, at, a distance and shock.

where temperatures of several tens of 1.78 When a nuclear detonation

miliion degrees are reached, the radia- occurs in the air, :,vhere the atmos•pheric

tion energy density will be of the order/ pressure (and density) is near to seaof 1016 ergsicm.3 , whereas the materia,/ level conditions, the soft X rays in the

energy is in the range of 1014 to 10-15 primary thermal radiation are comergs/cm-. It has been estimated that/in a pletely absorbed within a distance of a

nuclear explosion some 80 percent of few feet. Some of the radiations are

the total energy may be present ýnitially degraded to lower energies, e.g., into

as thermal radiation energy. / the ultraviolet region, but most of the

1.76 Not on!y does the/radiation energy of the primary thermal radiation

energy density increase wi /t tempera- serves to heat the air immediately surture but the rate of its emitsion as ther- rounding the nuclear burst. It is in this

mal radiation increasek correspond- manner that the fireball is foirmed. Part

ingly. For materials at temperatures of a of the energy is then reradiated at a

few thousand degrees Kelvin, the en- lower temperature from the fireball and

ergy is radiated slowly, with the greatest the remainder is converted into shock

part in the ultraviolet, visible, and in- (or blast) energy (see Chapter II). This

frared regions of the electromagnetic explains why only about 35 to 45 perspectrum (Fig. 1.74). At the tempera- cent of the fission energy from an air

tures of a nucluar explosion, however, burst is received as thermal radiation

not only is the radiation energy emitted energy at a distance, although the privery rapidly, but most of this energy is mary thermal radiation may constitute

hX rays are frequently distinguished as "hard" or "soft." The latter have longer wavelengths and

lower energies, and they are more easily absorbed than hard X rays. They are, nevertheless, radiations of

high energy compared with ultraviolet or visible light.
SCIENTIFIC BASIS %D. NUCLEAR EXPLOSIONS 25

as much as 70 to 80 percent of the total. Although the total energy emitted as

Furthermore, because the secondary thermal radiation in a high-altitude enthermal radiation is emitted at a leer plosioai is greater than for an air Lurst

temperature, it lies mainly in the region closer to sea level, about half is reraof the spectrum with longer wavelengths diated so slowly by the heated air that it

(lower photon energies), i.e., ultravio- has no great significance as a cause of

let, visible, and infrared 7 (see Chapter damage. The remainder, however, is

VII). radiated very much more rapidly, i.e..

1.79 In the event of a burst at high in a shorter time interval, than is the

altitudes, where the air density is low, case at lowet altitudes. A shock wave is

the soft X r'ys travel long distances generated from a high-altitude burst, but

before they are degraded and absorbed. at distances of normal practical interest

At this stage, the available energy is it produces a smaller pressure increase

spread throughout such a large volume than from an air burst of the same yield.

land mass) that most of the atoms and These matters are treated more fully in

molecules in the air cannot get very hot. Chapter II.

BIBLIOGRAPHY

BRorwt, H. I.., "Review of Nuclear Weapons HOISINGTON, D. B., "Nucleonics FundamenEffects," Annual Review of Nuclear Science, tais," NMcGtaw-Hill Book Co., Inc., 1959,

18, 153 (1968). Chapter 14,

CRO(KI'.R, G. R., "Fission Product Decay LAURENCEF, W. L., "Men and AMoms," Simon

Chains: Schematics with BrancHng Fractions, and Schuster, Inc., 1959.

Half-Lives, and Literature References," U.S. SE.DON, R. W., "An Introduction to Fission

Naval Radiological Defense Laboratory. June Explosions," University of California.

1967, USNRDL-TR-67-111 Lawrence Radiation Laboratory, ILivermo.,

Dot AN, P. J., "Calculated Abundances and Ac- July 1969, UCID-15554.

tivities of the Products of High Energy Neutron SM'TrH, H. DeW_, "Atomic Energy for Military

Fission of IJranium-238," Defense Atomic Purposes," Princeton University Press, 1945.

Support Agency, May 1959, DASA 525. W.AVLR, L. E.. P. 0. ST'ROM, and P, A, KHi.-

GI AS, TONi., S., "Sourcebook on Atomic En- t.EF..N, "Estimated Total Chain and Indepen- eigy," D. Van Nostrand Co., Inc., Third Edi- dent Fission Yields for Several Neutron-Intion, 1967. duced Fission Processes " U.S, Naval

Radiological Defensc Laboratory, March 1963,

USNRDl.-TR--633.

,It is sometimes referred to as the "prompt thermal radiation" because only that which is received

within a few seconds of the explosion i, iignificant as a hazard.
CHAPTER 1I

DESCRIPTIONS OF NUCLEAR EXPLOSIONS

INTRODUCTiON

2.01 A number of characteristic 2.02 Thac descriptions of explosions

phenomena, sor-e of which are visible at very high altitudes as well as those in

whereas others are neo directly apparent, the air nearer to khe ground refer mainly

are associated with nuclear uxplosions. to nucleir devices with ený.rgie,, in the

Certain aspects of these phenomena will vicinity of i-megaton I'NT equivalent

depend on the type of burst, i.e., air, For underwater bursts, the information

high-altitude, sutlface, or subsurface, as is based on the detonations of a few

indicated in Chapter 1. This depeadence weapons with roughly 20 to 30 kilotons

arises from direct ard secondary in- of TNT energy in shallow and moderateractions of the output of the exploding tely, deep, and deep water. Indications

weapon with its enviroment, and leads will be given of the results to be exto variations in the distribution of the pected fhr explosions of other yields. As

energy released, particularly among a general rule, however, the basic phe-.

biast, shock, and thermal radiation. In nomena for a burst iVi d particular enviaddition, the design of the weapon can ronment are not greatly dependent upon

also affect the energy distribution. Fi- the energy of the explosion. In the folnally, meteorological conditions, such lowing discussion it will le supposed,

as temperatip:e, humidity, wind, precip- first, that a typical air burst takes place

itation, and Ltmospheric pressure, and at such a height that the fireball, even at

even the nature of the terrain over which its maximum, is well above the surface

the explosion occurs, may infuence of the earth. The modifications, as well

some of the observed effects. Neverthe- as the special effects, resulthg from a

less, the gross phenomena associated surface burst and for one at very high

with a particular type of nuclear explo- altitude will be included. In addition,

sion, namely, high-altitude, air, sur- some of the characteristic phenomena

face, underwater, or underground, re- associated with ugdLrwater and undermain unchangcd. It is such phenomena ground nuclear explosions will be dethat are described in this chapter. scribed.

26

I
DESCRIPTION OF AIR AND SURFACE BURSTS 27

DESCRIPTION OF AIR AND SURFACE BURSTS

THE FIREBALL fireball referred to in § 1.32; a typical

fireball accompanying an air burst is

2.03 As already seen, the fission of shown in Fig. 2.04. The surfac: brighturanium (or plutonium) or the fusion of ness decreases with time, but after aoout

the isotopes of hycirogen in a nuclear a millisecond,' the fireball from a Iweapon leads to the liberatioi, of a large megaton nuclear weapon would appear

amount of energy in a very small period to an obserer 50 miles away to be many

of time within a limited quantity of times more brilliant than the sun at

matter. As a result, the fission products, noon. In several of the nuclear tests

bomb casing, and other weapon parts made in the atmosphere at low altitudes

are raised to extremely high tempera- at the Nevada Test Site, in all of which

tures, similar to those in the center of the energy yields were less than 100

the sun. The maximum temperature at- kilotons, the glare in the sky, in the

tained by the fission weapon residues is early hours of the dawn, was visible 400

several tens of million degrees, which (or more) miles away. This was not the

may be compared with a maximurn of result of direct (line-of-sight) transmis5,000°C (or 9,000°F) in a conventional sion, but rather of scattering and difhigh-explosive weapon. Because of the fraction, i.e., bending, of the lietit rays

great heat produced by the nuclear ex- by particles of dust and possibly by

plosion, all the materials are converted moisture in the atmosphere. However,

into the gaseous form. Since the gases, high-altitude bursts in the megaton

at the instant of explosion, are restricted range have been seen directly as far as

to the region occupied by the original 700 miles away.

constituents in the weapon, tremendous

pressures will be produced. These pres- 2.05 The surface temperatures of

sures are probably over a million times the fireball, upon which the brightness

the atmospheric pressure, i.e., of the (or luminance) depends, do not vary

order of many millions of pounds per greatly with the total energy yield of the

square inch. weapon. Consequently, the observed

2.04 Within less than a millionth of brightness of the fireball in an air burst is

a second of the detonation of the roughly the same, regardless of the

weapon, the extremely hot weapon res- amount of energy released in the exploidues radiate large amounts of energy, sion. Immediately after its formation.,

mainly as invisible X rays, which are the fireball begins to grow in size, enabsorbed within a few feet in the sur- gulfing the surrounding air. This growth

rounding (sea-level) atmosphere (Q is accompanied by a decrease in tem1.78). This leads to the formation of an perature because of the accompanying

extremely hot and highly luminous (in- increase in mass. At the same time, the

candescent) spherical mass of air and fireball rises, like a hot-air baloon.

gaseous weapon residues which is the Within seven-tenths of a millisecond

A millistcond is a one-thousandth part of F second.
28 0ES('RIPTIONS OF NUCIEAR EXPLOSIONS

Figure 2.04. Fireball from an air burs;t in the megaton energy range, photographed from an

allntude of 12.000 feet at a distance of about 50 miles. The fireball is partially

surrounded by the condensation cloud (see § 2.48).

from the detonation, the fireball from a increases in size and cools, the vapors

1-megaton weapon is about 440 feet condense to form a cloud containing

across, and this increases to a maximum solid particles of the weapon debris, as

value oi about 5,700 feet in 10 seconds. well as many small drops of water

It is then rising at a rate of 250 to 350 derived from the air sucked into the

feet per second. Aftcr a minute, the rising fireball.

fireball has cooled to such arn extent that 2.07 Quite early in the ascent of the

it no longer emits visible radiation. It fireball, cooling of the outside by radiahas then risen roughly 4.5 miles from tion and the drag of the air through

the point of burst. which it rises frequently bring about a

change in shape. The roughly spherical

THE RADIOACTIVE CLOUD form becomes a toroid (or doughnut),

although this shape and its associated

2.06 While the fireball is still lumi- motion are often soon hidden by the

nous, the temperature, in the interior at radioactive cloud and debris. As it

least, is so high that all the weapon ascends, the toroid undergoes a violent,

materials are ii the form of vapor. This internal circu!atory motion as shown in

includes the radioactive fission prod- Fig. 2.07a The formation of the toroid

ucts, uranium (or plutonium) that has is usually observed in the lower part of

escaped fission, and the weapon casing the visible cloud, as may be seen in the

(and other) materials. As the fireball lighter, i.e., more luminous, portion of
DESCRIPTION OF AIR AND SURFACE BURS-.S 29

Fig. 2.07b. The circulation entrains radizktions. As the fireall cools and

more air through the bottom of the condensation occurs, the color of the

toroid, thereby cooling the cloud and cloud changes to white, mainly due to

dissipating the energy contained in the the water droplets as in an ordinary

fireball. As a result, the toroidal motion cloud.

slows and may stop completely as the 2.09 Depending on the height of

cloud rises toward its maximum height. burst of the nuclear weapon and the

2.08 The color of the radioactive nature of the terrain below, a strong

cloud is initially red or reddish brown, updraft with inflowing winds, called

due to the presence of various colored "afterwinds," is produced in the imcompounds (nitrous acid and oxides of mediate vicinity. These afterwinds can

nitrogen) at the surface of the fireball. cause varying amounts of dirt and debris

These result from chemical interaction to be sucked up from the earth's surface

of nitrogen, oxygen, and water vapor in into the radioactive cloud (Fig. 2.07b).

the air at the existing high temperatures 2.10 In an air burst with a moderate

and under the influence of the nuclear (or small) amount of dirt and debris

UPDRAFT THROUGH

'CENTER OF TOROID

W. St 

TOROIDAL CIRCULAT ION

OF HOT GASES

S ~ ~EM A .COOL AIR BEING DRAWN

VTr UP INTO HOT CLOUD

Figure 2.07a. Cutaway showing artist's conception of toroidal circulation within the

radioactive cloud from a nuc!ear explosion.
30 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

i44

4%

Figure 2.07b. Low air burst showing toroidJal firehafI and dirt cloud.
DESCRIPTION OF AIR AND SUPFACE BURSTS 31

drawn up into the cloud, only a rela- Table 2.12

tively small proportion of the dirt par- RATE OF RISE OF RADIOACTIVE CLOUD

ticles Secome contaminated with ra- FROM A I-MEGATON AIR BURST

dioact!, "y. This is because the particles Height Time Rate of Rise

do not mix intimately with the veapoa (mile." (minutes) (miles per hour)

residues in the cloud at the tim , %hen ---

the fission products are still vaporiz.-d 2 0.3 330

and about to condense. For P burst near 0.7 270 6 I .I 2 2 ". )

the land surface, however, large quanti- 0 2.5 140

ties of dirt and other debris are drawn 12 3.9 27

into the cloud at early times. Good

mixing then occurs during the initial ute. The average rate of rise during the

phases of cloud formation and growth. first minute or so is nearly 300 miles per

Consequently, when the vaporized fis- hour (440 feet per second). These values

sion products condense they do so on should be regarded as rough averages

the foreign matter, thus forming highly only, and large deviations may be ex-

,dioactive particles (§ 2.23). pected in different circumstances (see

2.11 At first the rising mass of also Figs. 10.158a, b, c).

weapon residues carries the particles 2.13 The eventual height reached

upward, but after a time they begin to by the radioactive cloud depends upon

fall slowly under the influence of grav- the heat energy of the weapon, and upon

ity, at rates dependent upon their size. the atmospheric conditions, e.g., moisConsequently, a lengthening (and wi- ture content and stability. The greater

dening) column of cloud (or smoke) is the amount of heat generated the greater

produced. This cloud consists chiefly of will be the upward thrust due to buoyvery snvall particles of radioactive fis- ancy and so the greater will be the

sion products and weapon residues, distance the cloud ascends. The maxwater droplets, and larger particles of imum height attained by the radioactive

dirt and debris carried up by the after- cloud is strongly influenced by the ttowinds. popause, i.e., the boundary between the

2.12 The speed with which the top troposphere below and the stratosphere

of the radioactive cloud continues to above, assuming that the clotutd attains

ascend depends on the meteorological the height of the troposphere. 2

conditions as well as on the energy yield 2.14 When the cloud reaches the

of the weapon. An approximate indica. tropopause, there is a tendency for it to

tion of the rate of rise of the cloud from spread out Laterally, i.e., sideways. But

a i-megaton explosion is given by the if sufficient energy remains in the radioresults in Table 2.12 and the curve in active cloud at this height, a portion of it

Fig. 2. 12. Thu., in general, the cloud will penetrate the tropopause and ascend

will have attained a height of 3 mile. in into the more stable ,ir C.z the strato30 seconds and 5 miles in about a nrtin- sphere.

!The tropopause is the boundary between the troposphere and the relatively stable air of the

stratosphere. it varies with season and latitude, ranging from 25,000 feet near the poles to about 55,000

feet in equatorial regions (§ 9.129).

.A!
32 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

s0

<7 50 --- -0

K°- I

cn C', I

o 60.. .... .

40

00

0

240 4-*

U- X LL I 0

o

S20 --- * 04'

o w

:w ....! . . . .. I0. 

0 1 2 3 4 5 6

TIME AFTER EXPLOSION (MINUTES)

Figure 2.12. Heiglht of cloud top above burst height at various times after a I-mcgaton

explosion for a moderately low air burst.

2.15 The cloud attains its maximum the height curve in the range of about

height after about 10 minutes and is then 20- to 100-kilotons TNT equivalent is

said to be "stabilized." It continues to duc to the effert of the tropopause in

grow laterally, however, to produce the slowing down the cloud rise. For yields

characteristic mnushuom shape (Fig. below about 15 kilotons the heights in2.15). The cloud may continue to be dicated are distances above the burst

visible for about an hour or more before point but foi higher yields the values aie

being dispersed by the winds into the above sea levl. Fok land surface bursts,

surrounding atmosphere where it the maximum ch',,:'d height is Eormewhat

merges with natural clouds in the sky. less tl' given by Fig. 2.16 because of

2.16 The dimensions of the stabi- thz: mass of dirt and debris carried aloft

lized .loud formed in a nuclear explo- by the explosion.

sion depend on the meteorological con- 2.17 For yields below about 20 kiditions, whirh vary with tine and place. lotons, the radius of the stem of the

Approximate average values .:)f cloud mushroom cloud is about half the cloud

height and radius (at about 10 minutes radius. With increasing yield, however,

after the explosion), attained in land the ratio of these dimensions decreases,

surface or low air bursts, for conditions and for yields in the megaton range the

most likely to be encountered in the stem may be only one-fifth to one-tentl'

continental United States, are given in as wide as the cloud. For clouds wh*h

Fig. 2.16 as a function of the energy do not penetrate the tropopause the baFyield of the explosion. The flattening of of the mushroom head is, very roughl),
DESCRIPTION OF AIR AND SURFACE 13URSTS 33

I2WO

Figure 2.!5. The mushroom cloud formed in i nuclear explosion in the megaton energy

range, photographed from an altitude of I 2,000 feet a distance of about 50

miles.

at about one-half the altitude of the top. C-iARACTERISTICS OF A SURFACE

For higher yields, the broad base will BURST

probably be in the vicinity of the tropopause. There is a change in cloud shape 2.18 Since many of the phenomena

in going from the kiloton to the megaton and effects of a nuclear explosion ocrange. A typical cloud from a l0..kiloton curring on or near the earth's surface are

air burst would reach a height of .9,000 similar to those associated with an air

feet with the base at about 10,000 feet; burst, it is convenient before proceeding

the horizontal extent would also be further to refer to some of the special

roughly IC,000 feet. For an explosion in characteristics of a surface burst. In

the megaton range, however, the hori- such a burst, the fireball in its rapid

zontal dinjensioris are greater than the initial growth, abuts (or touches) the

total height (cf. Fip. 2.16). surface of the earth (Fig. 2.18a). Be-
34 I)FSCRIPTI(ONS OF NU('I FAR EkXPIOSIONS

20300 1 1 11t 1 l 1•• I r ~ i T- 1 1 11111I 1 1 1 1111115 l t 

280

- 260 -C 

U

4C

?" 200 ' RDII ,, I0 0 - €COU -402 a

c 1200RDV

o 

?

IS

160 30V

U) P

1 40

120 - _ .

M I

100

0 --- I .]_.i- : , i ,l l l i I I Ill~ _ . . . .L I l W 130 I0 21 5i ; " i 0 0 60

00~I

YIELD (KILOTONS)

Figure 2, 16. Approximate values of slabili;ed cloud height and radius as a function of

explosion yield for land surface or low air bursts•.

Figure 2.18a. Fireball formed by a nuclear explosion in the megaton energy range near the

earth's surface. The maximum diameter of the fireball was 31⁄4 miles.

?I
I)iDS('RIIPTION O1 AIR AND) SURFA('I- HURSIS 35

Figure 12, I 8h. Format ion of dirt cloud in ,tirlace bursit

cause of th' intense heat, some of the sists of particles ranging in size from the

rock, soil, and other material in the area very small (.,es produced by condensais vaporized and taken into the fireball. tion as the fireball cools to the much

Additional material is melted, either larger debris particles which have been

completely or on its surface, and the raised by the afterwinds. The exact

strong afterwinds cause large amounts composition of the cloud will, of

of dirt, dust, and other particles to be course, depend on thl nature of the

sucked up as the firebaHl rises (Fig. surface materials and the extent of their

2.18b). contact with the fireball.

2.19 An important difference be- 2.20 For a surface burst associated

tween a surface burst and an air burst is, with p moderate amount of debris, such

consequently, that in the surface burst as has neen the case in several test

the radioactive cloud is much more explosion, in which the weapons were

heavily loaded with debris. This con- detonated near the ground, the rate of
36 I)IS(CRIIPt iONS OU NLT(I FAR I. l l OSION S

rise of the cloud is much the same as solid particles formed upon further

given earlier for an air burst (Table cooling are contaminated fairly uni2.12). The radioactive cloud reaches a formly throughout with the radioactive

height of several miles before spreading fission products and other weapon resiout abruptly into a mushroom shape. dues,' but as a general rule the contain2.21 When the fireball touches the ination is found mainly in a thin shell

earth's surface, a crater is formed as a near the surface of the particles (§ 9.50).

result of the vaporization of dirt and In water droplets, the small fission

other material and the removal of soil, product particles occur at discrete points

etc(., by the Mdast wave and winds ac- within the drops. As the violent disturcompanying the explosion. The size of bance due to the explosion subsides, the

the crater will vary with the height contaminated particles and droplets

above the surface at which the weapon gradually descend to earth. This pheis exploded and with the character of the nomenon is referred to as "fallout,"

soil, as well as with the energy of the and the same name is applied to the

explosion. It is believed that for a I- particles themselves when they reach

megaton weapon there would be ne ap- the ground. It is the fallout, with its

preciable crater formation unless deto- associated radioactivity which decays

nation occurs at an altitude of 450 feet over a long peritd of time, that is the

or less. main source of Mte residual nuclear rL,-

2.22 If a nuclear weapon is ex- diation referred to in the preceding

ploded near ti water surface, large chanter.

amounts of water are vaporized and 2.24 The extent and nature of the

carried up into the radioactive cloud, fallout can range between wide exWhen the cloud reaches high altitudes tremes. The actual situation is deterthe vapor conderses to form water mined by a combination of circumdroplets, similar to those in an ordinary stances associated with the energy yield

atmospheric clouid, and design of the weapon, the height of

the explosion, the nature of the surface

TIHF FALLOUT beneath the point of burst, and the meteorological conditions. In an air burst,

A.23 In a surface burst, large quan- for example, occurring at an appreciable

lities of earth or water enter the fireball distance above the earth's surface, so

at an early stage and are fused or va- that no large amounts of surface materiporized. When sufficient cooling ha-, als are sucked into the cloud, the conoccurred, the fission produicts and other taminated particles become widely disradioactive residues tecorre incor- persed. The magnitude of the hazard

porated with the earth pirticles as a from fallout will then be far less than if

result of the condensatioii of vaporizr ed the explosion were a surface burst. Thus

fission products into fused particles of at Hiroshima (height of burst 1670 feet,

earth, etc. A small proportion of the yield about 12.5 kilotons) Und Nagasaki

'These residues inc:lude radioactive species fornmd at the time of the expiosion by neutron capture in

various materials (§ 9.31).
DF)•ERIPTION OF AIR AND SURFA('CE BURSTS 37

(height of burst 1640 feet, yield about 10 hours elapsed before the contami22 kilotons) injuries due to fallout were nated p•,rticles beganl to fall at the excompletely absent. tremities of the 7,000 square mile area.

2.25 On the other hand, a nuclear By that time, the radioactive cloud had

explosion occurring at or ncar the thinned out to such an extent that it was

earth's surface can result in severe con- no longer visible. This brings up the

!amination by the radioactive fallout. important fact that taiioui can occur

From the 15-megaton thermonuclear even when the cloud cannot be seen.

device tested at Bikini Atoll on March Nevertheless, the area of contamination

i, 1954-- the BRAVO shot of Opera- which presents the most serious hazard

tion CASTLE-the fallout caused sub- generally results from the fallout of visstantial contamination over an area of ible particles. The sizes of these parmore than 7,(X)0 square miles. The ticles range from that of fine sand, ie.,

contaminated region was roughly cigar- approximately 100 micrometers 4 in dishaped and extended irore than 20 stat- ameter, or smaller, in the more di:;,ant

ute miles upwind and over 350 miles portions of the fidlout crea, to picces

downwind. The width in the crosswind about the size of a marble, c"., roughly

direction was variable, tie maximum I cm (0.4 inch) in diameter, mn4, even

being over 60 milI,, (§ 9, 104). larger close to the burst point.

2.26 The meteorological conditions 2.28 Particles in this size rang.• arwhich determitne the shape, extent, and rive on the ground within one day after

location of the fallout pattern from a the explcsion, and will not have traveled

nuclear explosion are the height of the too tar, e.g., up to a few hundred miles,

tropopaose, atmospheric wind!, and the from the region of the shot, depending

occurrence of precipitation. For a given on the wind. Thus, the fallout patt.rn

explosion energy yield, type of bursv, from particles of visible size is Cetaband tropopause height, the fallout pat- lished within about 24 hours after the

tern is affected mainly by the directions burst. 'This is referred to as "early"

and speeds of the winds over the fallout fallout, also sometimes called "local"

area, from the earth's surface to the top or "close-in" fallout. In addition, there

of the stabilized cloud, which may be as is the depositicrn of very small particles

high as 100,0(X) feet Furthermore, which descend very slowly over large

variations in the winds, from the time of areas of the earth's surface. This is the

burst until the particles reach the "delayed" (or "worldwide") fallout, to

ground, perhaps several hours later, af- which residues from nuclear explosions

feet the ,allout pattern following a nu- of various types---air, high-altitude,

clear explosion (see Chapter IX). surface, and shallow subsurface-may

2.27 It should be understood that contribute (see Chapter IX).

fallout is a gradual phenomenon ex- 2.29 Although the test o; March I,

tending over a period of time. In the 1954 produced the most extensive early

BRAVO explosion, for example, about fallout yet recorded, it should te pointed

4A micrometer (also called a micron) is a onc-millionkh part of a meter, i.e., 10 " meter, or ab iut

0.00004 (or 4 x I0 ') inch,
38 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

out that the phenomenon was not nec- THE BLAST WAVE

essaril) characteristic of (nor restricted

to) thermonuclear explosions. It is very 2.32 At a fraction of a second after

probable that if the same device had a nuclear explosion, a high-pressure

been detonated at an appreciable dis- wave develops and moves outward from

tance above the coral island, so that the the fireball (Fig. 2.32). This is the shock

large fireball did not touch the surface of wave or blast wave, mentioned in § 1.01

the ground, the early fallout would have and to be considered subsequently in

been of insignificant proportions. more detail, which is the cause of much

2.30 The general term "scaveng- destruction accompanying an air burst.

ing" is used to describe various proc- The front of the blast wave, i.e., the

esses resulting in the removal of ra- shock front, travels rapidly away from

dioactivity from the cloud and its the fireball, behaving like a moving wall

deposition on the earth. One of these (if highly compressed air. After the

processes arises from the entrainment in lapse of 10 scconds, when the fireball of

the cloud of quantities of dirt and debris a I-megaton nuclear weapon has atsucked up in a surface (or near-surface) tained its rnixim•in size (5,700 feet

nuclear burst. The (.ondcnsation of the across), the shock front is some 3 miles

fis!;ion-product and othcr radioactive farther ahead. At 50 seconds after the

vapors on the particles and their sub- explosion, when the fireball is no longer

sequent relatively rapid fall to earth visible, the blast wave has traveled

lea0ds to a certain degree of scavenging, about 12 miles. It is then moving at

2.31 Another scavenging process, about 1,150 feet per second, which is

which can occur at any time in the slightly faster than the speed of sound at

history of the radioactive cloud, is that sea level.

due to rain falling through the weapon 2.33 When the blast wave strikes

dehris, and carrying contaminated par- the surface of the earth, it is reflected

ticles down with it. This is one mecha- back, similar to a sound % ave producing

nism for the production of "hot spots," an echo. This reflected olast wave, like

i.e. areas on the ground of much higher the original (or diret) wave, is also

ac.tivity than the surroundings, in both capable of causing rmaterial damage. At

carly and delayed fallout patterns. Since a certain region on the surface, the porains (other than thundershowers) gen- sition of which depends chiefly on the

erally originate trom atmospheric clouds height of the burst and the eneýrgy of the

whose tops Lire between about 10,000 explosion, the direct and reflected wave

and 30,(00 feet altitude, it is only below fronts merge. This merging phenomethis region that scavenging by rain is non is called the "Mach effect." The

likely to take place. Another effect that "overpressure," i.e., the pressure in

rain may have if it occurs either during excess of the normal atmospheric value,

or after the deposition of the fallout is to at the front of the Mach wave is generwash radioactive debris over the surface ally about twice as great as that at the

of the ground. This may result in direct blast wave front.

cleansing some areas and red6cing their 2.34 For an air burst of a I -mcgaton

activity while causing hot spots in other nuclear weapon at an altitude of 6,500

(lower) areas. feet, the Mach effect will begin approxi I
DESCRIPTION OF AIR AND SURFACE BURSTS 39

Figure 2.32. The faintly luminous shock front seen just ahead of the fireball soon alter

breakaway (O;ee § 2.121!0.

imately 4.5 seconds after the explosion, weapon is 10 miles from ground zero,

in a rough circle at a radius of 1.3 mile!; the ovcrpressure will have decreased to

from ground zero.s The overpressure on roughly I pound per square inch.

the ground at the blast wave front at this 2,36 The distance from ground zero

time is about 20 pounds per square inch, at which the Mach effect commences

so that the total air pressure is more than varies with the height of burst. Thus, as

double the normal atmospheric pres- seen in Fig. 2.32, in the low-altitude

sure.', (100 feet) detonation at the TRINITY

2.35 At first the height of the Mach (Alamogoido) test, the Mach front was

front is small, but as the: blast wave front apparent whc.n the direct shock front had

continues to move outward, the height advanced a short distance from the fireincreases steadily At the same time, ball. At the other extreme, in a very

however, the overpressure, like that irn high air burst there might be no detectthe original (or direct) wave, decreases able Mach effect. (The TRINITY test,

correspondingly because of the continu- conducted on July 16, 1945 near Alaous loss of energy amid the cver-increas- mogordo, New Mexico, was the first

ing area of the advancing front. After test of a nuclear (implosion) weapon;

the lapse of about 40 seconds, when the the yield was t.stimated to be about 19

Mach front from a 1-megaton nuclear kilotons.)

'The term "ground zero" refers to the point on the earth's surface immediately below (or above) the

point of detonation. For a burst over (or linder) water, the corresponding point is generally called

"surfac:e zero." The term "s-irfacc zero" or "surface ground zero" is also commonly used for ground

surface and underground explosions. In some pubi.cations, ground (r surface) zero is called the

"hypocenter ' of the explosion.

"-The norawl a.•ospheric pressure at sea level is 14.7 pounds per square inch.

AJ
40 DESCRIPMIONS OF NLCLEAR EXPLOSIONS

2.37 Strong transient winds are as- the first is of very short duration,

sociated with the passage of the shock whereas the second lasts for a much

(and Mach) front. These blast -winds (§ longer time. The behavior is quite gen3.07) are very much stronger than the eral for aih (and surface) bu.sts, alground wind (or afterwind) due to the though the duration times of the pulses

updraft caused by the rising fireball (§ increase with the energy yield of the

2.09) which occurs at a later time. The explosion.

bias! winds may have peak velocities of 2.N9 Corresponding to the two surseveral hundred miles an hour fairly face-temperature pulses, there are two

near to ground zero; even at more than 6 pulses of emission of thermal radiation

miles from the explosion of a I..megaton from the fireball (Fig. 2.39). In the first

nuclear weapon, the peak velocity will pulse, which lasts about a tenth of a

be greater than 70 miles per hour. It is second for a I-megaton explosion, the

evident that such strong winds can con- surface temperatures are mostly very

tribute greatly to the blast damage re- high. As a result, much of the radiation

suiting from the explosion of a nuclear emitted by the fireball during this pulse

weapon. is in the ultraviolet region. Although

ultraviolet radiation can cause skin

THERMAL RADIATION FROM AN AIR burns, in most circumstances following

BURST an ordinary air burst the first pulse of

thermal radiation is not a significant

2.38 Immediately after the explo- hazard in this respect, for several reasion, the weapon residues emit the pri- sons. In the first place, only about I

mary thermal radiation (§ 1.77). Be- percent of the thermal radiation appears

cause of the very high temperature, in the initial pulse because of its short

much of this is in the form of X rays duration. Second, the ultraviolet rays

which are absorbed within a layer of a are readily attenuated by the intervening

few feet of air; the energy is then re- air, so that the dose delivered at a disemitted from the fireball as (secondary) tance from the explosion may be cornthermal radiation of longer wavelength, paratively small. Furthermore, it apconsisting of ultraviolet, visible, and pears that the ultraviolet radiation from

infrared rays. Because of certain phe- the first pulse could cause significant

romena occurring in the fireball (see § effects on the human skin only within

2. 106 et seq.), the surface temperature ranges at which other thermal radiation

undergoes a curious change. The tem- effects are much more serious. It should

perature of the interior falrs steadily, blit be mentioned, however, that although

the apparent surface temperature of the the first radiation pulse may be disrefireball decreases more rapidly for a garded as a source of skin burns, it is

small fraction of a second. Then, the capable of producing permanent or

apparen! surface temperature increases temporary effects on the eyes, especially

again for a somewhat longer time, after of individuals who happen to be looking

which it falls continuously (see Fig. in the direction of the explosion.

2.123). In other words, there are effec- 2.40 In contrast to the first pulse,

tively two surface-temperature pulses; the second radiation pulse may last for
DESCRIPTION OF AIR AND SURFACE BURSTS 41

II , ' ,I

I0

j -.

fu.J 9

L) 8

2 46

V).

i

WJZ 4

0i 3

< 2

- I I I i i ii I i i

I 2 3 4 5 6 7 8 9 10 11 12

TIME AFTER EXPLOSION

(RELATIVE SCALE)

Figure 2.39. Emission of thermal radiai ion in two pulses in an air burst.

several seconds, e.g., about 10 seconds INITIAL NUCLEAR RADIATION FROM

for a 1-megaton explosion; it carries AN AIR BURST

about 99 percent of the total thermal

radiation energy. Since the temperature!, 2.41 As stated in Chapter 1, the exare lower than in the first pulse, most of plosion of a nuclear weapon is assothe rays reaching the earth consist of ciated with the emission of various nuvisible and infrared (invisible) light. It is clear radiations, consisting of neutrons,

this radiation which is the main cause of gamma rays, and alpha and beta parskin burns of various degrees suffered ticles. Essentially all the nzutrons and

by exposed individuals up to 12 miles or part of the gamma rays are emitted in

more, and of eye effects at even greater the actual fission process. These are redistances, from the explosion of a I- ferred to as the "prompt nuclear radiamegaton weapon. For weapons of tions" because they are produced sihigher energy, the effective damage multaneously with the nuclear

range is greater, as will be explaine-d in explosion. Some of the neutrons liberChapter VII. The radiation from the ated in fission are immediately captured

second pulse can also cause fires to start and others undergo "scattering colliunder suitable conditions. sions" with various nuclei present in the

.1'
42 I)[S(RIFTIONS OF NUCL'I EAR EXPI OSIONS

weapon. These processes are frequently cerned. Thus, when the radioactive

accompanied by the instantaneous cloud has reached a height of 2 miles,

emission of gamma rays. In addition, the effects of the initial nuclear radiamany of the escaping neutrons undergo tions are no longer significant. Since it

similar interactions with atomic nuclei takes roughly a minute for the cloud to

of the air, thus forming an extended rise this distance, the initial nuclear rasource of gamma rays around the burst diation was defined as that einitted in the

point. The remainder of the gamma rays first minute after the explosion.

and the beta particles are liberated over 2.44 The foregoing arguments are

a period of time as the fission prooucts based on the characteristics of a 20-

undergo radioactive decay. The alpha kiloton nuclear weapon. For a detonaparticles are expelled, in an analogous tion of higher energy, the maximum

manner, as a result of the decay of the distance over which the gamma rays are

uranium (or plutonium) which has effective will be larger than given

escaped fission in the weapon. above. However, at the same time, therc

2.42 The initial nuclear radiation is is an increase in the rate at which the

generally defined as that enitted from cloud rises. Similarly for a weapon of

both the fireball and the radioactive lower energy, the effective distance is

c.oud within the first minute after the less, but so also is the rate of ascent of

explosion. It includes neutrons and the cloud. The period over which the

gamma rays given off almost instantan- initial nuclear radiation extends may

eously, as well as the gamma rays consequently be taken to be approxiemitted by the fission projucts and other mately the same, namely, I minute,

radioactive species in the rising cloud. It ir-2spective of the energy release of the

should be noted that the alpha and beta explosion.

particles present in the initial radiation 2.45 Neutrons are the only signifihave not been considered. This is be- cant nuclear radiations produced dicause they are so easily absorbed that icctiy in the thermonuclear reactions

they will not reach more than a few mentioned in § 1.69. Alpha particles

yards, at most, from the radioactive (helium nuclei) are also formed. but

cloud, they do not travel very far from the

2.43 The somewhat arbitrary time explosion. Some of the neutrons will

period of I minute for the duration of escape but others will be captured by the

the initial nuclear radiations was origi- vanious nuclei present in the exploding

nally based upon the following consid- weapon. Those neutrons absorbed by

erations. As a consequence of attenua- fissionable species may lead to the libtion by the air, the effective range of the eration of more neutrons as well as to

fission gamma rays and of those from the emission of gamma rays. In addithe fission products from a 20-kiloton tion, the capture of neutrons in nonfisexplosion is very roughly 2 miles. In sion reactions is usually accompanied

other words, gamma rays originating by gamma rays. It is seen, therefore,

from such a source at an altitude of over that the initial radiations from an explo2 miles can be ignored, as far as their sion in which both fission and fusion

effect at the earth's surface is con- (thermonuclear) processes occur consist

I___ _ _(
DESCRIPTION OF AIR AND SURFACE B URSTS 43

essentially of neutrons and gamma rays. fireball. This glow may persist for an

The relative proportions of these two appreciable length of time, being disradiations maty bc somewhat different tinctly visible near the head of the rath~an for a weapon ir, which all the en- dioactive cloud. It is believed to be the

ergy release is clue to fission, but for ultimate result of a complex scries of

present purposes, the difference may be prccesses initiated by the action of the

disregarded. various radiations on the nitrogen and

oxygen of the air.

THE ELECTROMAGNETIC PULSE 2.48 Another early phenomenon

following a nuclear explosion in certain

2.46 ff a detonation occurs at or circumstances is the formation of a

near the earth's surface, the EMP phe- "condensation cloud." This is somenomenon referred to in § 1 .38 produces times called the Wilson cloud (or

intense electric and magnetic fields cloud-chamber effect) because it is the

which may extend to distances up to result of conditions anaiogous to those

several miles, depending on the weapon utilized by scientists in the Wilson cloud

yield. The close-in region near the burst chamber. It will be seen in Chapter III

point is highly ionized and large electric that the pa-sage of a high-pressure

currents flow in the air and the ground, sho.zk front in air is followed by a rareproducing a pulse of electromagnetic faction (or suction) wave. During the

radiation. Beyond tthis close-in region compression (or blast) phase, the temthe electromagnetic field strength, as perature of the air rises and during the

measured on (or n,-ar) the ground, drops decompression (or suction) phase it

sharply and then more slowly with in- falls. For moderately low blast prescreasing distance from the explosion. sures, the temperature can drop below

The intense fielcds may damage unpro- its original, preshock value, so that if

tected electrical and electronic equip- the air contains a fair amount of water

ment at distances exceeding those at vapor, condensation accompanied by

which significant air blast damage may cloud formation will occur.

occur, especially for weapons of low 2.49 The condensation cloud which

yield (see Chapter XI). was observed in the ABLE Test at Bikini in 1946 is shown in Fig. 2.49.

OTHER NUCLEAR EXPLOSION Since the device was detonated just

PHENOMENA above the surface of the lagoon, the air

was nearly saturated with water vapor

2.47 Tlhere are a number of inter- and the conditions were suitable for the

esting phenomena associated with a nu- production of a Wilson cloud. It can be

clear air burst that are worth mentioning seen from the photograph that the :oud

although they have no connection with formed some way ahead of the fireball.

the destructive or other harmful effects The reason is that the shock front must

of the explosion. Soon after the detona- travel i considerable distance before the

tion., a violet-colored glow may be ob- blast pressure has fallen sufficiently for a

served, particularly at night or in dim low temperature to be attained in the

daylight, at some distance from the subsequent decompression phase. At the
44 DI-SCRIPTIONS OF NUCLEAR EXPLOSIONS

p-"

Figure 2.49. Condensation cloud formed in an air burst over water.

Figure 2.50. Late stage of the condensation cloud in an air burst over water.
D)FS(RIPTION (iF HIGH-AIITFUDF BURSTS 45

time the temperature has dropped to that as the air warmed up and th,. water

required for condensation to occur, the dropl ts evaporated. The original

blast wave front has moved still farther dome-like cloud first changed to a ring

away, as is apparent in Fig. 2.49, where shape, as seen in Fig. 2.50, and then

the disk-like formation on the surface of disappeared.

the water indicates the passage of the 2.51 Since the Wilson condensation

shock wave. cloud forms after the fireball has emitted

2.50 The relatively high humidity most ot its thermal radiation, it has little

of the air makes the conditions for the influence on this radiation. It is true that

formation of the condensation cloud fairly thick clouds, especially smoke

most favorable in nuclear explosions clouds, can attenuate the thermal radiaoccurring over (or under) water, as in tion reaching the earth from the fireball.

the Bikini tests in 1946. The cloud However, apart from being formed at

commenced to form I to 2 seconds after too late a stage, the condensation cloud

the detonation, and it had dispersed is too tenuous to have any appreciable

completely within another second or so, effect in this conn,'c;ion.

DESCRIPTION OF HIGH-ALTITUDE BURSTS

INTRODUCTION the vicinity of Johnston Island. The

2.52 Nuclear devices were ex- STARFISH PRIME devi'e, with a yield

ploded at high altitudes during the sum- of 1.4 megatons, was exploded at an

mer of 1958 as part of the HARDTACK altitude of about 248 miles on July 9.

test series in the Pacific Ocean and the 1962 (GCT). The three submegaton d,?-

ARGUS operation in the South Atlantic vices, CHECKMATE, BLUEGILL

Ocean. Additional high-altitude nuclear TRIPLE PRIME, and KINGFISH, weie

tests were conducted during the FISH- detonated at altitudes of tens of miles on

BOWL test series iii 1962. in the October 20, 1962, October 26, 1962,

HARDTACK serie.-' two high-altitude and November 1, 1962 (GCT), respecbursts, with energy yields in the mega- tively.

ton range, were set off in the vicinity of 2.53 The ARGUS operation was

Johnston Island, 700 miles southwest of not intended as a test of nuclear weapHawaii. The first device, named TEAK, ons or their destructive effects. It was an

was detonated on August 1, 1958 experiment designed to provide infor-

(Greenwich Civil Time) at an altitude of mation on the trapping of electrically

252,000 feet, i.e., nearly 48 miles. The charged particles in the earth's magnetic

second, called ORANGE, was exploded field (§ 2 145). The operation consisted

at an altitude of 141,000 feet, i.e., of three high-altitude nuclear detonanearly 27 miles, on August 12, 1958 tions, each having a yield from I to 2

(GCT). During the FISHBOWL series, kilotons TNT equivalent. The burst ala megaton and three submegaton de- titudes were from about 125 to 300

vices were detonated at high altitudes in miles.

Ii
46 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

HIGH-ALTITUDE BURST PHENOMENA red luminous spherical wave, arising

apparently from electronically excited

2.54 If a burst occurs in the altitude oxygen atoms produced by a shock

regime of roughly 10 to 50 miles, the wave pas-ing through the low-density

explosion energy radiated as X rays will air (Fig. 2.56).

be deposited in the burst region, al- 2.57 At about a minute or so after

though over a much larger volume of air the detonation, the TEAK fireball had

than at lower altitudes. In this manner, risen to a height of over 90 miles, and it

the ORANGE shot created a large fire- was then directly (line-of-sight) visible

ball almost spherical in shape. In gen- from Hawaii. The rate of rise of the

eral, the fireball behavior was in agree- fireball was estimated to be some 3,300

ment with the expected interactions ' f feet per second and it was expanding

the various radiations and kitetic energy horizontally at a rate of about 1,000 feet

of the expanding weapon dehris ,,vith the per second. The large red luminous

ambient air (§ 2.130 et seq.). sphere was observed for a few minutes:

2.55 The mechanism cf fireball for- at roughly 6 minutes after the explosion

iation changes appreciably at still it was nearly 600 miles in diameter.

higher burst altitude, since the X rays 2.58 The formation and growth of

are able to penetrate to greater distances the fireball changes even more drastiin the low-density air. Starting at an cally as the explosion altitude increases

explosion altitude of about 50 miles, the above 65 miles. Because X rays can

interaction of the weap,,.n debris energy penetrate the low-density atmosphere to

with the atmosphere becomes the domi- great distances before being absorbed,

nant mechanism for producing a fire- there is no local fireball. Below about

ball. Because the debris is highly ion- 190 miles (depending on weapon yield),

ized (§ 1.38), the earth's magnetic field, the energy initially appearing as the

i.e., the geomagnetic field, will influ- rapid outward motion of debris particles

ence the location and distribution of the will still be deposited relatively locally,

late-time fireball from bursts above resulting in a highly heated and ionized

about 50 miles altitude. region. The geomagnetic field plays an

2.56 The IlEAK explosion was ac- increasingly important role in controlcompanied by a sharp and bright flash of ling debris motion as the detonation allight which was visible above the hori- titude increases. Above about 200

zon from Hawaii, over 700 miles away. miles, where the air density is very low,

Because of the long range of the X rays the geomagnetic field is the dom~rnant

in the low-density atmosphere in the factor in slowing the expansion of the

immediate vicinity oi the burst, the ionized debris across the field lines.

fireball grew very rapidly in size. In 0.3 Upward and downward motion along

second, its diameter was already I1 the field lines, however, is not greatly

miles and it increased to 18 miles in 3.5 affected (§ 10.64). When the debris is

seconds. The fireball also ascended with stopped by the atmosphere, at about 75

great rapidity, the initial rate of rise miles altitude, it may heat and ionize the 4k

being about a mile per second. Sur- air sufficiently to cause a visible region

rounding the fireball was a very large which will sabsequently rise and ex1*i'+

I . • -,; d..

,
DESCRIPTION OF HIGH-AtTITUDEt BURSTS 47

Figure 2,56. Fireball and red luminous spherical wave formed after the TEAK high-allitude

shot. (The photograph was taken from Hawaii. 780 miles from the exploson. )

pand. Such a phenomenon was observed graded over a region of several thousand

following the STARFISH PRIME miles in diameter for a period lasting

event, from shortly after midnight until

2.59 A special feature of explosions sunrise. Some very-high-frequlency

at altitudes between about 20 and 50 (VHF) communications circuits in the

miles is the extreme brightness of the Pacific area were unable to function for

fireball. It is visible at distances c sev- about 30 seconds after the STARFISH

eral hundred miles and is capable of PRIME event.

producing injury to the eyes over large 2ý61 Detonations above about 19

areas (§ 12.79 et seq.). miles can produce EMP effects (§ 2.46)

2.60 Additional important effects on the ground over large areas, increasthat result from high-altitude bursts are ing wifh the yield of the explosion and

the widespread ionization and other dis- the height ef burst. For fairly large

turbances of the portion of the upper yields and burst heights, the EMP fields

atmosphere known as the ionosphere. may be significant at nearly all points

These dis:Lrbances affect the propaga- within the line of sight, i.e., to the

tion of radio and radar waves, some- horizon, from the burst point. Although

times over extended areas (see Chapter these fields are weaker than those in the

X). Following the TEAK event, propa- close-in region surrounding a surface

gation of high-frequency (HF) radio burst, they are of sufficient magnitude to

communications (Table 10.91) was de- damage some unprotected electrical and
48 DESCRIPTIONS OF NUCLEAR EXPLOSION'S

electronic equipment. The mechanism is attributed to the motion along the

of formation and the effects of the EMP lines of the earth's magnetic field of beta

are treated in Chapter XI. particles (electrons), emitted by the ra2.62 An interesting visible effect of dioactive fission fragments. Because of

high-altitude nuclear explosions is the the natural cloud cover over Johnston

creation of an "artificial aurora." Island at the time of burst, direct obserWithin a second or two after burst time v,.kA of the ORANGE fireball was not

of the TEAK shot a brilliant aurora possible from the ground. However,

appeared from the bottom of the fireball such observations were made from airand purple streamers were seen to craft flying above the low clouds. The

spread toward the north. Less than a auroras were less marked than from the

second later, an aurora was observed at TEAK shot, but an aurora lasting 17

Apia, in the Samoan Islands, more than minutes 'was again seen from Apia.

2,000 miles from the point of burst, Similar auroral effects were observed

although at no time was the fireball in after the other high-altitude explosion,:

direct view. The formation of the aurora mentioned in § 2.52.

DESCRITI'iON OF UNDERWATER BURSTS

SHALLOW UNDERWATER the explosion was illuminated by the

EXPLOSION PHENOMENA fireball. The distortion caused by the

water waves on the surface of the lagoon

2.63 Certain characteristic phe- prevented a clear view of the fireball,

nomena are associated with an under- and the general effect was similar to that

water nuclear explosion, but the details of light seen through a ground-glass

vaqy with the energy yield of the screen. r'he luminosity persisted for a

weapon, the distance below the surface few thousandths of a second, but it disat which the detonation occurs, and the appeared as soon as the bubble of hot,

depth and area of the body of water. The high-pressure gases (or vapors) and

description given here is based mainly steam constituting the fireball reached

on the observations made at the BAKER the water surface. At this time, the gases

test at Bikini in July 1945. In this test, a were expeiled and cooled, so that the

nuclear weapon of approximately 20- fireball was no longer visible.

kilotons yield was detonated well below 2.65 In the course of its rapid exthe surface of the lagcon which was pansion, the hot gas bubble, while still

about 200 feet deep. These conditions underwater, initiates a shock wave. Inmay be regarded as corresponding to a tersection of the shock wave with the

shallow underwater explosion, surface produces an effect which,

2.64 In an underwater nuclear det- viewed from above, appears to be a

onation, a fireball is formed, but it is rapidly expanding ring of darkened

smaller than for an air burst. At the water. This is often called the "slick"

BAKER test the water in the vicinity of because of its resemblance to an oil

h
I)-S('RIPTION OF UNDERWATF.R •URSIS 49

slick. Following closely behind the dark is proportional to the pressure of the

region is a white circular patch called direct sho,.k wave, and so it is greatest

the "crack," probably caused by re- directly above. the detonation point.

flection of the water shock wave at the Consequently, tl,e water' in the center

surface. rises more rapidly (and for a longer

time) than water farther away. As a

2.66 Immediately after the appear- result, the sides of the spray dome beance of the crack, and prior to the for- come steeper as the water uises. The

mation of the Wilsop cloud (§ 2.48), a upward motion is terminated by the

mound or column ol broken water and downward pul! (if gravity and the resisspray, called the "spray dome," is tance of the air. The total time of rise

thrcwn up over the point of burst (Fig. and the maximum height depend upon

2.66). This dome is caused by the ye- thc energy of the explosion, and upon its

locity imparted to the water near the depth below the water surface, Addisurface by the reflection oi the shock tional slick, crack, and spray-dome

wave and to the subsequent breakup of phenomena may result if the shock wave

the surface layer into drops of spray, reflected from the water bottom and

The initial upward velocity of the water compression waves produced by the gas

Figure 2.66. The "spray dome" formed over the point of burst in a shallow' underwalcr

explomson.

_ _,___ __
50 DIFS('RPIIIONS O1 NIJ(t F. AR X P1 ()SIONS

b'thble (§ 2.86 el seq.) reach the surface tive contents of the bubble are vented

with suflicicn! intensity, through this hollow column and may

2.67 If the depth of burst is not too form a cauliflower-shaped cloud at the

great, the bubble remains essentlaIly in- top (Fig, 2.67b.)

tact until it rises to the surface of the 2.68 In the shallow underwater

water. At this point the steam, fission (BAKER) burst at Bikini, the spray

gases, and debris are expelled into the dome began to form at about 4 milliatmosphere. Part of the shock wave seconds after the explosion. Its initial

passes through the surface into the air, rate of rise was roughly 2,5(M feet per

and because of the high humidity the second, but this was rapidly diminished

conditions are suitable for the formation by air resistance and gravity. A few

of a condensation cloud (Fig. 2.67a), As milliseconds later, the hot gas bubble

the pressure of the bubble is released, reached the surface of the lagoon and

water rushes into the cavity, and the the column began to form, quickly

resultant complex phenomena cause the overtaking the spray dome. The maxwater to be thrown up as a hollow cyl- imuigi height attained by the hollow

inder or chimney of spray called the column, through which the gases ",column" or "plume." The radioac- vented, could not be estimated exactly

1~

AlF

Figure 2.67a. The condensation cloud formed after a shallow underwater e.ploion. (The "crack" due to the shock wave can be seen on the water surface.)

_ _ _ _ _ _ _ _
DESCRIPIfON M- U N I)IWAIV1 IMHLRSI'S .51

Figutre 2.,67h, Formiimui o f til hc l1'thiv voIIutII in it shiltlivw undefrvw ittr vy\ iiojI)f Owt~ lop

i.s strrIurlded by it lat (itfil t condenlsait j )) l ud.

Figutre 2.68. TIhe radoat(i( Ive cloud atnd first stages (of the base surge following a shallow

underwater burst. Watter is 1w~ginning it) fall back fromt the columni into the

lutgoon,
52 IFIS( RIPIIINS ()l. N11( I AR I:XI( OSIONS

because the upper part was surrounded and ultimately rosc to a height of nearly

by the rii(Iioactive cloud (Fig 268). 1O,O(XM feet b-fore being dispersed. Th i

The c•olumn was probably some 6,000 is considerably less than the height atfeet high and the maximum diameter tained by the radioactive cloud in an air

was about 2(J(X) feet. The walls were burst.

probably 300 fcet thick, and approxi- 2.70 The disturbance created by the

mately a million tons of water were underwater burst caused a series of

raised in the column. waves to move outward from the center

2.69 The cauliflower-shaped cloud, of the explosion across the surface of

which concealed part of the upper por- Bikini lagoon At I I seconds after the

tion of the column, contained some of detonation, the first wave had a maxthe fission products and other weapon imum height of 94 feet and was about

residues, as well as a large quantity of I ,(XX) feet front surface zero. This

water in small droplet form. In addition, moved outward at high speed and was

there is evidence that material sucked up followed by a series of other waves, At

fromn the bottom of the lagoon was also 22,0(X) feet from surface zero, the ninth

present, for a calcareous (or chalky) wave in the series was the highest with a

sediment, which must have dropped height of 6 feet.

from this cloud, was found on the decks 2.71 It has been observed that cerof ships some distance from the burst. tain underwater and water surface bursts

The clotu. was roughly 6,00) feet across have caused unexpectedly serious

' '

€' .

dod

Figure 2.73. The development of the base surge following a shallow underwater explosion.

a ,
DESCRIPTION OF UNDERWATER BURS'IS 53

flooding of ne.arby beach area.u, the base surge had the ippearance of a mass

depth of inundation being sometimes of stratocumulus ciouds which eventutwice as high as the approaching waýer ally reached a thickness of several

wave. The extent of inundation is re- thousand feet (Fig. 2.74). A moderate lo

lated in d complex manner to a number hezvy rainfall, moving with the wind

of factors which include the energy and lasting for nearly an hour, develyield of the explosion, *he depth of oped from the cloud mdss. In its early

burst, the depth of the water, the cAm- stages the rain was augmented by the

position and contour of the bottom, and small water droplets still descending

the angle the approaching wave makes from the radioactive cloud.

with the shoreline. 2.75 In the few instances in which

base surge formation has been observed

THE VISIBLE BASE SURGE over water, the visible configuration has

been quite irregular. Nevertheless, to a

2.72 As the column (or rilume) of good approximation, the base surge can

water and spray fell back into the lagoon be representt ' as a hollow cylinder with

in the BAKER test, there developed a the inner diameter about two-thirds of

gigantic wave (,nr cloud) of mist corn- the outer diameter. The heights of the

pletely surrounding the column at its visible base surge clouds have generally

base (Fig. 2.68). This doughnut-shaped ranged between 1,000 and 2,000 feet.

cloud, moving rapidly outward from the 2.76 The necessary conditions for

column, is called the "base surge " It is the formation of a base surge have not

essentially a dense z!oud of small water been definitely established, al.hough it

droplets, much like the spray at the base is reason!bly certain that no base surge

of Niagara FL,!; (or other high water- would accompany bursts at great

falls), but having the property of flow- depths. The underwater test shots upon

ing almost as if it were a homogeneous which the present analysis is based have

fluid. all created both a visible aid an invisible

2.73 The base surge at Bikini com- (§ 2.77) base surge. The only marked

menced to form at 10 or 12 second..; after difference between the phenomena at

the detonation. The surge cloud, bil- the various tests is that at Bikini

lowing upward, rapidly attained a height BAKER there was an airborne cloud,

of 900 feet, and moved outward at an evidently composed of fission debris and

initial rate of more than a mile a minute. steam. The other shots, which were at

Within 4 mirutes the outer radius of the somewhat greater depths, produced no

cloud, growing rapidly at first and then such cloud. The whole of the plume fell

inore slowly, was nearly 31⁄2/ miles back into the surface of the water where

across and its height had t.[n increased the low-lying base surge rloud was

to 1,800 feet. At this stage, the base formed.

surge gradually rose from the surface of

the water and began to merge with the THE RADIOACTIVE BASE SURGE

radioactive cloud and other clouds in the

sky (Fig. 2.73). 2.77 From the weapons effects

2.74 After about 5 minutes, the standpoint, the importance of the base
54 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

Figure 2.74. Final stage in the development of the base surge.

surge lies in the fact that it is likely to be fallout or rainout on to the surface of the

highly radioactive because of the fission water (or ship or shore station) from the

(and other) residues present either at ""ts radioa,.tive base surge, but in many

inceotion, or dropped into it from the cases it is expected to pass over without

radioactive cloud. Because of its ra- depositing any debris. Thus, according

dioactivi!y, it may represent a hazard for to circumstances, there may or may not

a distance of several miles, especially in be radioactive contamination on the

the downwind direction. The fission surfaces of objects in the vicinity of a

debris is suspended in the form of very shallow underwater nuclear burst.

small particles that occupy the same 2.78 The radioactive base surge

volume as the visible base surge at early continues to expand in the same manner

times, that is, within the first 3 or 4 as would have been expected had it

minutes. However, when the small ren ned visible. It drifts downwind eiwater droplets which make the base ther as an invisible, doughnut-shaped

surge visible evaporate and disappear, cloud or ay several such possibly conthe radioactive particles aid gases re- centric clouds that appremate a lowmain in the air and contirue to move lying disc with no hole in the center.

outwards as an invisible radioactive The latter shape is more probable for

base surge. There may well be some deeper bursts. The length of time this
DESCRIPTION. OF UNDERWATER tSURSTS 55

base surge remains radioactive will de- people and as a source of fire are conpend on the energy yield of the explo- cerned.

sion, the burst depth, and the nearness 2.81 It is probable, too, that most of

of the sea bottom to the point of burst. the neutrons and gamma rays liberated

In addition, weather conditions widl within a short time of the initiation of

control depletion of debris due to rain- the explosion will also be absorbed by

out and diffusion by atmospheric winds, the water. But, when the fireball reaches

As a general rule, it is expected that the surface and vents, the gamma rays

there will be a rconsiderable hazard from (and beta particles) from the fission

the radioactive base surge within the products will represent a form of initial

first 5 to 10 minutes after an underwater nuclear radiation. In addition, the radiexplosion and a decreasing hazard for ation from the radioactive residues

half an hour or more. present in the column, cloud, and base

2.79 The proportion of the residual surge, all three of which are formed

nuclear radiation that remains in the within a few seconds of the burst, will

water or that is trapped by the falling contribute to the ini~al effects.

p!ume and returns immediately to the 2.82 Homever, th, water fallout (or

surface is determined by the location of rainout) from the clouc and the base

the burst and the depth of the watei, and surge are also responsible for the residperhapý; als,) by the nature of the bottom ual nuclear radiation, as described

material. Althrugh as much as 90 per- above. For an underwater birst, it is

cent of the fission prodLct and other thus less meaningful to make a sharp

radioactivity cou'd be left behind in the distinction between initial and residual

water, the base surge, both visible and radiations, such as is done in the case of

invisible, could still be extremely ra- an air burst. The initial nuclear radiadioactive in its early stages. tions merge conwinuously into those

which are produced over a period of

time following the nuclear explosion. TH-ERMAL AND NUCLEAR

RADIATIONS IN UNDERWATER

BURST DEEP UNDiERWATER EXPLOSION

PHENOMENA

2.80 Essentially all the thermal radiation emitted by the fireball while it is 2.83 Because the effects of a deep

still submerged is absorbed by the sur- underwater nuclear cxplosion are

!ounding water. When the hot steam and largely of military interest, the phe

gases reich the surface and expand, the nomena will be des,:rihed in general

cooling is so rapid that the temperature terms and in less detail than for a shal.

drops almost immediately to a point low underwater burst. The following

where there is no further appreciable discussion is based largely on observaemission of thermal radiation. It fol- tions made at the WAHOO shot in

lows, therefore, that in an underwater 1958, when a ni,,le~r weapon was denuclear explosion the thermal radiation tonated at a depth of 500 feet in deep

can be ignored, as far as ;Is effccts on water. The geaeration of large-scale

4&1,'-
56 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

water waves in deer underv,,rt :r bursts imum size is reached. If it is not too near

will be considered in Charier VI. the surface or the bottom at this time,

2.84 Th( spray dome formed by the the bubble remains nearly spherical. As

WAHOO explosion ro:,_ to a height of a result of the outward momentum of tie

90C feet above the surface of the water water surrounding the bubble, the la:ter

(Fig. 2.84a). Shortly aftcr the maximum actually overexpands; that is to say,

height was attained, the hot gas and when it attains its maximum size it:

steam bubble burst through the dome, contents are at a pressure well bel•w the

throwing out a plume with jets in all ambient water pressure. The higher

directions; the highest jets reached an pressure outside the bubble then causes

elevation of 1,700 feet (Fig. 2.84b). it to contract, resulting in an increase of

There was no airborne radioactive the pressure within the bubble and concloud, such as was observed in the densation of some of the rteam. Since

shallow underwater BAKER shot. The the hydrostatic (water) pressure is larger

collapse of the plume created a visible at the bottom of the bubble than at the

base surge extending out to a distance of top, the bubble does not remain spheriover 21⁄2/2 miles downwind and reaching a cal during the contraction phase. The

maximum height of about 1,000 feet bottom moves upward faster than the

(Fig. 2.84c). This base surge traveled top (which may even remain stationary)

outward at an initial speed of nearly 75 and reaches the top to form a toroidal

miles per hour, but decreased within 10 bubble as viewed from above. This

seconds to less than 20 miles per hour. causes turbulence and mixing of the

2.85 There was little evidence of bubble contents with the surrounding

the fireball in the WAHOO shot, be- water.

2.87 The momentum of the water

cause of the depth of the burst, and only set in mot b ntum of the buba small amount of thermal radiation sti oinb otato ftebb

aesmalld. amoinitil otearm radiation ble causes it to overcontract, and its

escaped. The initial nuclear radiation inenlpsurocemebcms internal pressure once more becomes

was similar to that from a shallow un- higher than the ambient water pressure.

derwater burst, but there was no linger- A second compression (shock) wave in

ing airborne radioactive cloud from the water commences after the bubble

which fallout could occur. The radioac- reaches its minimum volume. This

tivity was associated with the base surge compression wave has a lower peak

while it was visible and also after the ompresso we has a lo wer peak wate ha drples evported.Thein-overpressure but a longer duration than

water droplets had evaporated. The in- the initial shock vave in the water. A

visibl,, radioactive base surge contin- second cycle of bubble expansion and

ued to expand while moving in the

downwind direction. However, very lit- 2.88cif the detin o r

tleradoaciviy ws fundon he ur- 2.88 If the detonation occurs far

tie radioactivity was found on the sur- enough below the surface, as in the

WIGWAM test in 1955 at a depth of

2.86 The hot gas bubble formed by about 2,000 feet, the bubble continues

a deep underwater nuclear explosion to pulsate and rise, although after three

rises through the water and continues to complete cycles enough steam will have

expand at a decreasing rate until a max- condensed to make additional pulsations
DE1SC RIPTION OF UNDERWATER BURSTS 57

Figure 2.84a. Spray dome observed 5.3 seconds after CX 7 IkoSion in deep water.

F~igure 2,84h. Piume obsirvod 11,7 seconds after explosion in deep water.

Fiegure 2.54c. Formation of base surge at 45 seconds after explosion in deep water.
58 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

unlikely. During the pulsation and up- umn which may break up into jets that

ward motion of the bubble, the water disintegrate into spray as they travel

surrounding the bubble acquires consid- through the air.

erable upward momentum and eventually breaks through the surface with a 2.89 The activity levels of the rahigh velocity, e.g., 200 miles per hour dioactive base surge will be affected by

in the WIGWAM event, thereby creat- the phase of the bubble when it breaks

ing a large plume. If water surface through the water surface. Hence, these

breakthrough occurs while the bubble levels may be expected to vary widely,

pressure is below ambient, a pheaiome- and although the initial radiation intennon called "blowin" occurs. The plume sities may be very high, their duration is

is then likely to resemble a vertical col- expected to be short.

DESCRIPTION OF UNDERGROUND BURSTS

SHALLOW UNDERGROUND The rapid expansion of the gas bubble

EXPLOSION PHENOMENA initiates a ground shock wave which

2.90 For the present purpose, a travels in all directions away from the

shallow underground explosion may be burst point. When the upwardly directed

regarded as one which produces a sub- shock (compression) wave reaches the

stantial crater resulting from the earth's surface, it is reflected back as a

throwout of earth and rock. There is an rarefaction (or tension) wave. If the

optimum depth of burst, dependent on tension exceeds the tensile strength of

the energy yield cf the detonation and the surface material, the upper layers of

the nature of the lock medium, which the ground will spall, i.e., split off into

gives a crater of maxinium size. The more-or-less horizontal layers. Therl. as

mechanism of the formation of such a result of the momentum imparted by

throwout (or excavation) craters will be the incident shock wave, these layers

considered here. For shallower depths move upward at a speed which may be

of burst, the behavior approaches that of about 150 (or more) feet per second.

a surface burst (§§ 2.18, 6.03 et seq.), 2.92 When it is reflected back from

whereas for explosions at greater depths the surface, the rarefaction wave travels

the phenomena tend toward those of a into the ground toward the expanding

deep underground detonation (§ 2. 101 gas sphere (or cavity) produced by the

et seq.). explosion. If the detonation is not at too

2.91 When a nuclear weapon is ex- great a depth, this wave may reach tile

ploded under the ground, a sphere of top of the cavity while it is still growing.

extremely hot, high-pressure gases, in- The resistance of the ground to the up- '

cluding vaporized weapon residues and ward growth of the cavity i. thus derock, is formed. This is the equivalent creased and the cavity expands rapidly

of the fireball in an air or surface burst. in the upward direction. The expanding
DESCRIPTION OF UNDERGROUND BURSTS 59

gases and vapors can thus supply addi- crater depends on the energy yield of the

tional energy to the spalled layers, so detonation and on the nature of the exthat their upward motion is sustained for cavated medium, In general, for equiva time or even increased. This effect is alent conditions, the volume ot the

referred to as "gas acceleration." crater is roughly proportional to the

2.93 The ground surface m-nving yield of the explosion.

upward first assumes the shape of a 2.94 The relative extents to which

dome. As the dome continues to in- spalling and gas acceleration contribute

crease in height, cracks form through to the formation of a thk'owout crater

which the cavity gases vent to the at- depend to large extent on the moisture

mosphere. The mound then disinte- content of the rock medium. In rock

grates completely and the rock frag- containing a moderately large proporments are thrown upward and outward tion of water, the cavity pressure is

(Fig. 2.93). Subsequently, much of the gready increased by the presence of

ejected material collapses and falls water vapor. Gas acceleration then plays

back, partly into the newly formed an important role in crater formation. In

crater and partly onto the surrounding dry rock, however, the coptribution of

"lip." The material that falls back im- gas acceleration to the upward motion of

mediately into the crater is called the the ground is generally small arid may

"fallback," whereas that descending be unobservable.

on the lip is called the "ejecta." The 2.95 As in an underwater burst, part

size of the remaining (or "apparent") of tile energy released by the weapon in

*Figure 2.93. Shallow underground burst.

j ,.
60 DESCRIPTIONS O0: NUCLEAR EXPLOSIONS

a shallow underground explosion ap- tamination over a large area, the extent

pears as an a~r blast wave. The fraction of which depends upor; the depth of

of the energy imparted to the air in the burst, the nature of the soil, and the

form ')f blast ,depends primarily on the atmospheric conditions, as well as upon

depth of burst for the given total energy the energy yield of the explosion. A dry

yield. The greater the deptn of burst, the sandy terrain would be particularly consmaller, in general, will be the propor- ducive to base surge formation in an

tion of shoc: energy that escapes into underground burst.

the air. For a sufficiently deep explo- 2.97 Throwout crater formation is

sion, there is, of course, no blast wave. apparently always accompanied by a

base surge. If gas acceleration occurs.

BiSE SURGE AND MAIN CLOUD however, a cloud consisting of particles

of various sizes and the hot gases

2.96 When the fallback from a escaping from the explosion cavity genshallow underground detonation de- erally also forms and rises to a height of

scends to the ground, it entrainsi air and thousands of feet. This is usually refne dust particles which are carried ferred to as the "main cloud," to disdownward. The dust-laden air upon tinguish it from the base surge cloud.

reaching the ground moves outward as a The latter surrounds the base of the main

result of its momentum and densi:y, cloud and spreads out initially to a

thereby producing a base surge, similar greater distance. The main cloud and

to that observ'ed in shallow underwater base surge formed in the SEDAN test

explosions 1"ie base surge of dirt par- (100 kilotons yield, depth of burial 635

ticlks move, .itward from the center of feet in alluvium containing 7 percent of

the explosion and is subsequently car- water) are shown in the photograph in

ried downwind. Eventually the particles Fig. 2.97, taken six minutes after the

settle out and produce radioactive con- explosion.

Figure 2.97. Main cloud and base surge 6 minutes after the SEDAN underground burst.
DESCRIPTION OF UNDERGROUND BURSTS 61

2.98 Both the base surge and the DEEP UNDERGROUND EXPLOSION

main cloud are contaminated with ra- PHENOMENA

dioactivity, and the particles present 2.101 A deep underground explocontribute to the fallout. The larger sion is one occurring at such a depth that

pieces are the first to reach the earth and the effects are essentially fully conso they are deposited near the location tained. The surface above the detonation

of the burst. But the smaller particles point may be disturbed, e.g., by the

r ýmain suspended in the air some time formation of a shallow subsidence crater

and may be carried great distances by or a mound, and ground tremors may be

the wind before they eventually settle detected at a distance. There is no sigout. nificant venting of the weapon residues

to the atmosphere, although some of the

THERMAL AND NUCLEAR noncondensable gases present may seep

RADIATIONS IN! UNDERGROUND oui gradually through the surface. The

BURSTS United States has conducted many deep

underground tests, especially since

2.99 The situations as regards ther- September 1961. Almost all of the exma', and nuclear radiations from an un- plosion energy has been contained in the

derground burst are quite similar to ground, and, except in the few cases of

those described above in connection accidental venting or seepage of a small

with an underwater explosion. As a fraction of the residues, the radioactivity

general rule, the thermal radiation is from these explosions has also been

almost completely absorbed by the confined. The phenomena of deep unground material, so that it does not rep- derground detonations car, be described

resent a significant hazard. Most of the best in terms of four phases having

neutrons and ea:ly gamma rays are also markedly different time scales.

removed, although the capture of the 2.102 First, the explosion energy is

neutrons may cause a considerable released in less than one-millionth part

amount of induced radioactivity in of a second, i.e., less than one microvarious materials present in the soil (§ second (§ 1.54 footnote). As a result,

9.35). This will constitute a smail part the pressure in the hot gas bubble

of the residual nuclear radiation, of im- formed will rise to severa! million atportance only in the close vicinity of the mospheres and the temperature wili

point of burst. The remainder of the reach about a million degrees within a

residual radiation will be due to the few microseconds. In ihe second (hycontaminated base surge and fallout. drodyaamic) stage, which generally is

2.100 For the reasons given in § of a few tenths of a second duration, the

2.82 for an underwater burst, the initial high pressure of the hot gases initiates a

and residual radiations from an under- strong shock wave which breaks away

ground burst tend to merge into one and expands in all directions with a

another. The distinclion which is made velocity equal to or greatcr than the

in the case of air and surface bursts is speed of -,ound in the rock medium.

consequently less significant in a sub- During the hydrodynamic phase, the hot

surface explosion, gases continue to expand, although
62 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

mote slowly than initially, and form a tion. RAINIER was a 1.7-kiloton nu.

cavity of substantial size. At the end of clear device detonated in a chamber 6 x

this phase the cavity will have attained 6 x 7 feet ira size, at a depth of 790 feet

its maximum diameter and its walls will below the surface in a compacted volbe lined with molten rock. The shock canic-ash medium referred to geologicwave will have reached a distance of ally as "tuff." During the hydrodynasome hundreds of feet ahead of the cav- mic stage the chamber expanded to form

ity and it will have crushed or fractured a spherical cavity 62 feet in radius,

much of the rock in the region it has which was lined with molten rock about

traversed. The shock wave will continue 4 inches thick. The shock from the exto expand and decrease in strength plosion crushed the surrounding meeventually becoming the "head" (or dium to a radius of 130 feet and fracleading) wave of a train of seismic tured it to 180 feet. Seismic signals were

waves (§ 6.19). During the third stage, detected out to distances of several

the cavity will cool and the molten rock hundred miles and a weak signal was

material will collect and solidify at the recorded in Alaska. The chimney exbottom of the cavity. :ended upward for about 400 feet from

2.103 Finally, the gas pressure in the burst point. Further information on

the cavity decreases to the point when it cavity and chimney dimensions is given

can no longer support the overburden, in Chapter VI.

Then, in a matter of seconds to hours, 2.105 Deep underground nuclear

the roof falls in and this is followed by detonations, especially those of high

progressive collapse of the overlyipg yield, are followed by a number of

rocks. A tall cylinder, commonly re- minor seismic tremors called "afterferred to as a "Thimney," filled with shocks," the term that is used to debroken rock or rubble is thus formed scribe the secondary tremors that gener-

(Fig. 2.103). If the top of the chimney SPACE

does not reach the ground surface, an

empty space, roughly equivalent to the ..

cavity volume, will remain at the top of FRAC KURED-oc . ... ... ,. :... 

the chimney. However, if the collapse ., APPROXIMATE ....... • ': •':".• BOUNDARY

of the chimney material should reach the OF CHIMNEY

surface, the ground will sink into to the ( CHIMNE" RUBBLE ) • ,:i;::!;. ::.i

empty space thereby forming a subsi- (RBLE ..

dence crater (see Fig. 6.06f). The collapse of the roof and the formation of .

the chimney represen•ed the fourth (and - l."

last) phase of the underground explo- , EXPLOSION •"""• 

sion. SOL.IOIFII:D - POINT

2.104 The effects of the RAINIER MOLTEN ROCK

event of Operation Plumbbob in 1957 evet o OpraionPlu~bob n 157 Figure 2.1'03. The rubble c'himney formed

will provide an example of the extent to a.Terubble ohe farmey

whic th surouning edirr m beafter collaps.t of the cavity

which the surrounding medium may be in a deep uiderground nuaffected by a deep underground detona- clear detonation.

it
SCIENTIFIC ASPECTS OF NUCLEAR EXPLOSION PH-NOMI:NA 63

ally occur after the main shock of a large test sites. No co,:rreaion has been found

earthquake. In tests made in Nevada and between underground nucicar dotonaon Amchitka Island in the Aleutians, the tions and the occurrenuV of natural

aftershocks have not constituted a earthquakes in the vicinity (§ 6 24 et

danger to reople or to structures off the seq.).

SCIENTIFIC ASPECTS OF NUCLEAR EXPLOSION

PHENOMENA 7

INTRODUCTION internal and radiation energy. Some of

the electrons are removed entirely from

2.106 The events which follow the the atoms, thus causing ionization,

very large and extremely rapid energy whereas others are raised to hig, h-1r enrelease in a nuclear exFlosion are mainly ergy (or excited) states while still rethe consequences of the interaction of mainiag attached to the nuclei. Within

the kinetic energy of tIe fissimn frag- an extremely short time, perhaps a hul•-

ments and the thermal r,kdiations with dredth of a microsecond or so, the

the medium :surrounding ti,e explosion, weapon residues consist essentially of

The exact nature of these interactions, completely and partially stripped (ionand hence the directly obse-vable arid ized) atoms, many of the latter being in

indirect effects they produce, that is to excited states, together with the corresay, the nuclear explosion phenomena, sponding free electrons. The sy'item

are dependent on such propertie, of the then imm.dvat,,-1 emits electromagnetic

medium as its temperature, prssure, (thermal) ra,.iation, the nature of which

density, and composition. It is thf vari- is deterrnined by the temperature. Since

ations in these factors in the erviron- this is Af the order of' several times 10l

ment of the nuclear detonation that ac- degrees, most of the energy emitted

count for the different types of response within a microsecond or so is in the soft

associated with air, high-altiti;de, sur- X-ray region (§ 1.77, see also § 7.75).

face, and subsurface bursts, as d-- 2.108 The primary thermal ra~iiascribed e. lier in this chapter. tiori leaving the exploding weapon is

2.107 Immediately after the explo- absorbed by the atoms and molecules of

sion time, the temperature of the the surrounding medium. The medium

weapon material is several tens of mil- is thus heated and the resulting fireball

lion degrees and the pres'iures are es- re-radiates part of its energy as the sectimated to be many million atmos- ondary thermal radiation of longer wave

pheres. As a result of numerous inelastic lengths (§ 2.38). The remainder of the

collisions, part of the kinetic energy of trnergy contributes to the shock wave

the fission fragments i!. converted into formed in the surrounding medium. U!-

7The remaining (more techni -al) sections ol ihis chapter may be omitted without loss of continu;ty.

411

I *, - I It•" I i -
64 I)ESCRIPTIONS OF= NU(CI FAR FX1I OSIONS

timately, essentially all the thermal ra- from a nuclear explosion is in the soft

diation (and shock wave energy) is ab- X-ray region of the spectrum. If the

soibed an1 apr..ars as heat, although it burst occurs in the lower part of the

may be spt,..Ad over a large volume. In a atmosphere where the air density i,' apdense medium such as earth or water, preciable, the X rays are absorbed in thL

the degradation and absorption occur immediate vicinity of the burs[, and they

within a short distance from the explo- heat the air to high temperatures. This

sion, but in air both the shock wave and sphere of hot air is sometimes referred

the thermal radiation may travel consid- to as the "X-ray fireball." The volume

erable distances. The actual behavior of air involved, resultant air temperadepends on the air density, as will be tures, and ensuing behavior of this fireseen later. ball are all deteriniiied by tne burst con2.109 It is apparent that the kinetic ditions. At moderate and low altitudes

energy of the fission fragments, consti- (below about 100,000 feet), the X rays

tuting some 85 percent of the total en- arc aborbed within some yards of the

ergy released, will distribute itself be- burst point, and the relatively small

tween thermal radiation, on the one volume of air involved is heated to a

hand, and shock and blast, on the other very high temperature.

hand, in proportions determined largely 2.111 The energies (or waveby the nature of the ambient medium. lengths) of the X rays, as determined by

The higher the density of the latter, the the temperature of the weapon debris,

greater the extent of the coupling be- cover a wide range (§ 7.73 etseq.), and

tween it and the energy from the ex- a small proportion of the photons

ploding nuclear weapon. Consequently, (§ 1.74) have energies considerably in

when a burst takes place in a medium of excess of the average. These high-enhigh density, e.g., water or earth, a ergy photons are not easily absorbed and

larger percentage of the kinetic energy so they move ahead of the fireball front.

of the fission fragments is converted into As a result of interaction with the atshock and blast energy than is the case mospheric molecules, the X rays so alter

in a less dense medium, e.g., air. At the chemistry and radiation absorption

very high altitudes., on the other hand, properties of the air that, in the air burst

where the air pressure is extremely low, at low and moderate altitudes, a veil of

there is no true fireball and the kinetic opaque air is generated that obscures the

ener'gy of the fission fiagments is dissi- early growth of the fireball. Several mipated over a very large volume. In any croseconds elapse before the fireball

event, the form and amount in which the front emerges from the opaque X-ray

thermal radiation is received at a dis- veil.

tance from the explosion will depend on 2.112 The X-ray fireball grows in

the nature of the intervening medium, size as a result of the transfer of radiation from the very hot interior where the

DEVELOPMENT OF THE FIREBALL IN explosion has occurred to the cooler

AN AIR BURST exterior. Durirg this "radiative

2.110 As seen above, most of the growth" phase, most of the energy

initial (or primary) thermal radiation transfer in the hot gas takes place in the
S('IiNTIFICI ASPECTS O" NLI(I FAR FXII) OSION P11IINOMUIN,\ 65

following manner. First, an atom, too- very high temperatures the photons are

lecule, ior, or electron absorbs a photon not readily absorbed. As a result, *he

of radiation and is thereby converted energy distribution and telmpra:ure are

into an excited state. The atom or other fairly uniform throughout the volume of

particle remains in this state for a short hot gas, The fireball at this stage is

time and then emits a photon, usually of consequently referred to as the "isolower enegy. The residual energy is thermal sphere." The name is someretained by the particle either as kinetic thing of a misnomer, since temperature

energy or as internal energy. The emit- gradients do exist, particularly near the

ted photon moves off in a random di- advancing radiation front.

rection with the velocity of light, and it 2.115 As the fireball cools, the

may then be absorbed once again to transfer of' energy by radiation and raform another excited parti:lc. The !atter diative gi'owth become less rapid bewill then re-emit a photon, and so on. cause of the decreasing mean fee path

The radiation energy is thus transmitted of the phtoons. When the average ternfrom one point to anothcr within the perature of the isothermal sphere has

gas, at the same time, the iverage pho- dropped to about 3(X),O(X))C, the cxton energy (and radiation frequency) pansion veleJty will have decreased to

decreases. The energy lost by the pho- a value c'jmnparable to the local acoustic

tons serves largely to heat the gas (sound) velocity. At this point, i shock

through which the photons travel, wave develops at the fireball front and

2.113 If the mean free path of the the su'bsequent growth of the fireball is

radiation, i.e., the average distance a dominated by the shock and associated

photon travels between interactions, is hydrodynamic expansion, The phenomlarge in comparison with the dimensions enon of shock formation is sometimes

of the gaseous volume, the transfer of called "hydrodynamic separation." For

energy from the hot. interior to the cooler a 2(J-kiloton burst it occurs at about a

exterior of the firebali will occur more tenth of a millisecond after the explorapidly than if the mnean free rath is sion when the fireball radius is roughly

short. This is because, tn their outward 40 feet.

motion through the gas, the photons 2.116 At very early times, beginwith short mean free paths will be ab- ning in less than a microsecond, an,

sorbed and re-emitted several times. At "inner" shock wave forms driven by

each re-emission the photon moves thc expanding bomb debris. This shock

away in a random direction, v-id so the e:(pands outward within the isothermal

effective rate of transfer of energy in the si'here at a velocity exceeding the local

outward direction will be less than for a acoustic velocity. The inner shock

photor of long mean free path which overtakes and merges with the outer

undergoes little or no absorption and ;hock at the fireball front shortly after

re-emission in the hot gas. hydrodynamic separation. The relative

2.114 In the radiative growth importance of the debris shock wave

phase, the photon mean ficee paths in the depends on the ratio of the yield to the

hot fireball are ,of the order of (or longer mass of the exploding device and on the

than) the fireball diameter because at the altitude of the explosion (§ 2.136). The

1I
66 DEtS(CRIPTIONS O01 N!(I [-AR [\XII OSIONS

debris shock front is a strong source of perature regions form. The outer region

ultraviolet radiation, and for weapons of absorbs the radiation from the isothersmall yield-to-mass ratio it niy replace mal sphere in the center and so the latter

the X-ray fireball as the dominant en- cannot be seen. The photographs,

ergy source for the radiative growth. therefore, show only the exterior surface

2.117 As the (combined) shock of the fireball.

front from a normal air burst moves 2.119 From the shapes of the curves

ahead of the isothermal sphere it causes at the right of Fig. 2.118 the nature of

a tremendous compression of the am- the pressure changes in the fireball can

bient air and the temperature is thereby be understood. In the isothermal stage

increased to an extent sufficient to the pressure is uniform throughout and

render the air incandescent. The lumi- drops sharply at the outside, but after a

nous shell thus formed constitutes the short time, when the shock front has

advancing visible fireball during this separated from the isothermal sphere,

"hydrodynamic phase" of fireball the pres:sure near the surface is greater

growth. The fireball now consists of two than in the interior of the fireball. Within

concentric regions. The inner (hotter) less than I millisecond the steep-fronted

region is the isothermal sphere of uni- shock wave has traveled some distanc.:e

form temperature, and it is surrounded ahead of the isothermal region. The rise

by a layer of luminous, shock-heated air of the pressure in ihc fireball to a pe!Ak,

at a somewhat lower, but still high, which is characteristic of a shock wave,

temperature. Because hot (over followed by a sharp drop at the external

8,0 00°C) air is effectively opaque to surface, implies that the latter is identivisible radiation, the isothermal ,phere cal with the shock front. It will be

is not visible through the outer shocked noted, incidentally, from the photoair. graphs, that the surface of the fireball,

2.118 Some of the phenomena de- which has hithierto been somewhat unscribed above are represented schemat- even, has now become sharply do-fined.

ically in Fig. 2.118; qualitative temper- 2.120 For some time the fireball

ature profiles ate shown at the left and continues to grow in size at a rate depressure profiles at the right of a series termined by the propagation o" the

of photographs of the fireball at various shock front in the surrounding air. Durintervals after the detonation of a 20 ing this period the temperatuie of the

kiloton weapon. In the first picture, at shocked air decreases steadily so that it

0. 1 millisecond, the temperature is becomes less opaque. Eventually, it is

shown to be uniform within the fireball transparent enough to permit the much

and to drop abruptly at the exterior, so hotter and still incandescent interior of

that the condition is that of the isother- the fireball, i.e., the isotherrmal sphere,

mal sphere. Subsequently, as the shock to be seen through the faiitly visible

fron, begitis to move ahead of the isoth- shock front (see Fig. 2 '2). "The onset of

ermal sphere, the temperature is no this condition at about 15 nilliseconds

longer unitorm, as indicated by the (0.015 second) after the de'onation of a

more gradual fall near the outside of the 20-kiloton weapon, for ex imple, is refireball. Eventually, two separate tem- ferred to as the "breakaw.ty."

p
SCIENTIFIC ASPECTS OF NUCLEAR EXPLOSION PHENOMENA 67

TEMPERATURE PRESSURE

Figure 2.1 18. Variation of terriperature and pressure in the fireball. (Times and dimensions

apply to a 20-kiloton air burst.)

2.121 Following the breakaway, in which the radius increases with time,

the visible fireball continues to increase in the period from roughly 0. 1 nijllisecin size at a slower rate than before, the ond to I second after the detonation of a

maximum dimensions being attained 20-kiloton nuclear weapon, is shown in

after about a -;fcond or so. The manner Figure 2.12 1. Attention should be called

'w
68 DIIS(RIPIIONS Of- NU(I F\R EXIPI OSIONS

700 -T

.J APPROXIMATE BREAKAWAY -

_j i

1 - - . .. .. .. -- . ..

a:: 20C0

(n,

70 _0

0- 410 0 10

TIME AF"'ER EXI.-OSION (SECONDS)

Figure 2. 121. \ ariation of radius of luminous fireball with time in a 20-kiloton air burst.

to the fact that both scales are logarith- as the temperature falls below a few

mic, so that the lower portion of the thousand degrees, the ability to absorb

curve (at the left) does not represent a and radiate decreases.

constant rate of growth, but rather one 2.123 From about the time the firethat falls off with time. Nevertheless, ball temI, erature has fallen to

the marked decrease in the rate at which 300,000TC, when the shock front begins

the fireball grows after breakaway is to move ahead of the isothermal sphere,

apparent from the subsequent flattening until close to the time of the first tern.

of the curve. perature minimum (§ 2.38), the expansion of tie fireball is governed by the

TEMPERATURE OF THE FIREBALL laws of hydrodynamics, It is then possible to calculate the temperature of the

2.122 &t indicated earlier, the inte- shocked air from the measured shock

rior temperature of the fireball decreases velocity, i.e., the rate of growth of the

steadily, but the apparent surface tern- fi;eball. The variationl of the temperature

perature, whi..n irfluences the emission of the shock fron,: with time, obtained in

of thermal radiation, decreases to a this manner, is s;hown by the full line

minimum and then increases to a max- from 10-4 to 10 2 second in Fig. 2.123,

imum before the final steady decline, for a 20-kiloton explosion. But photoThis behavior is related to the fact that at graphic and spectroscopic observations

high temperatures air both absorbs and of the surface brightness of the advancemits thermal radiatipn very readil,, but ing shock front, made from a distance,
WCIENTIFIC ASPECTS OF NUCLEAR EXPLOSION PHENOMENA 69

2i

10 S~ CALCULATED

FROM SHOCK VELOCITY

0 2

w

:l 2 . ....-- . ...

w

w IO 4 "

I- /, /

";OBSERVED ' "_

2 --.-------------- 1

-.. .1....-i....~ -

2 4 7 2 47 T 2 4 7 2 4 7 2 4 7 I-4 0"I0 0-I II

10- 1 O3 10'2 10-111

TIME AFTER EXPLOSION (SECONDS)

Fitgure 2.123. Variation of apparent fireball surface temperature with time in a 20-kilotn

air burst.

indicate the much lower temperatures correspoiids to a temperature considerrepresented by the broken curve in the abiy lower than that of the shock front.

figure. The reason for this discrepancy is 2.124 Provided the temperature of

that both the nuclear and thermal radia- the air at the shock front is sufficiently

tions emitted in the earliest stages of the high, the isothermal sphere is invisible

detonation interact in depth with the (§ 2.117). The rate at which the shock

gases of the atmosphere ahead of the front emits (and absorbs, radiation is

shock front to produce ozone, nitrogen determined by its temperature and radioxide, nitrous acid, etc. These sub- dius. The temperature at this time is

stances are strong absorbers of radiation considerably lower than that of the

coming from the fireball, so that the isothermal sphere but the radius is

brightness observed some disiance away larger. However, as the temperature of i
70 DESCRIPTIONS OF NUCLEAR EXPL OSIONS

the shocked air approaches 3,000'C explosions of other energy yields. The

(5,400'F) it absorbs (and radiates) less minimum temperature of the radiating

readily. Thus the shock front becomes surface and the subsequent temperatur~e

increasingly transparent to the radiation maximum are essentially independent of

from the isothermal sphere and. there is a the yield of the explosion. But the times

gradual unmasking of the still hot iso- at which these temperatures occur for an

thermal sphere, representing breakaway air burst increase approximately as the

(§ 2.120). 0.4 power of the yield (Chapter VII).

2.125 As a result of this unmasking The time of breakaway is generally very

of the isothermal sphere, the apparent soon after the thermal minimum is atsurface temperature (or brightness) ot tained.

the fireball increases (Fig. 2.123), after

passing through the temperature mini- SIZE OF THE FIREBALL

mum of about 3,000'C attributed to the

shock front. This minimum, represent- 2.127 The size of the fireball ining the end of the first thermal pulse, creases with the energy yield of the

occurs at about I I milliseconds (0.011 explosion. Because of the complex ;nsecond) after the explosion time for a teraction of hydrodynamnic and radiation

20-kiloton weapon. Subsequently, as factors, the radius of the fireball at the

the brightness continues to increase thermal minimum is nGt very different

from the minimum, radiation from the for air and surface bursts of the same

fireball is emitted directly from the hot yield. The relationship between the

interior (or isothermal sphere), largely average radius and the yield is then

unimpeded by the cooled air iii the given approximately by

shock wave ahead of it; energy is then R(athrlmimu)=90 O4

radiated more rapidly than before. The R(athrlmimu) 9

apparent surface temperature increases where R is the fireball radius in feet Atnd

to a maximum of about 7,700'C W is the explosion yield in kilotons

(14,000F), and this is followed by a TNT equivalent. The breakaway phesteady decrease over a period of seconds nomenon, on the other hand, iý deteras the fireball cools by the emission of mined almost entirely by hydrodynamic

radiation and mixing with air. It is (lur- considerations, so that a distinction

ing the second pulse that the major part should be made between air and surface

of the thermal radiation is emitted in an bursts. For an air burst the radius of the

air burst (§ 2.38 et seq.). In such a fireball is given by

burst. th, irate of emission of radiation is R (at breakaway) for

greatest when the surface temperature is air burst ==110 WO4 (2.127.1)

at the m~ximuni.

2.126 The curves in Figs. 2.121 For a corntact surface burst, i.e., in

and 2. 123 apply to a 20-kiloton ruclear which the exploding weapon is actually

burst, but similar results are obtained for on the surface, 8 blast wave energy is

KFor most purposes, a contact surfL.cc burst may he defined as one for which the burst point is not more

than 5 W, feet above or below the surface.
SCIENTIFIC ASPECTS OF NUCLEAR EXPLOSION PHENOMENA 71

reflected back from the surface into the be expected. however, to be small

fireball (§ 3.34) and W in equation enough to he tolerable under emergency

(2.127. 1) should probably be replaced conditions.

by 2 W, where W is the actual yield. 2.129 Other aspects of fireball .ize

Hence, for a contact surface burst, are determined by the conditions under

R (a brekawy) fr cotac surace which the fireball rises, li the fireball is

R(tburea aw y for contact surface2 small compared with an atmospheric

burs ~ 14 (.12.2) scale height, which is about 4.3 miles at

For surface bursts in the transition range altitudes of interest (§ 10. 123), the late

between air bursts and contact bursts, fireball rise is caused by buoyant forces

the radius of the fireball at breakaway is similar to those acting on a bubble rising

somewhere between the values given by in shallow water. This is called

equations (2.127. 1) and (2.127.2). The "buoyant" rise. The fireball is then essize of the fireball is not well defined in sential!y in pressure equilibrium with

its later stages, but as a rough approx- the surrounding air a.s it rises. If the

imation the maximum radius may be initial fireball radius is comparable to or

taken to be about twice that at the time greater than a scale height, the atmosof breakaway (cf. Fig. 2,121). pheric pressure on the bottom of thle

2.128 Related to the fireball size is fireball is much larger than the pressure

the question of the height of burst at on the top. This causes a very rapid

which early (or local) fallout ceases to acceleration of the fireball, referred to as

be a serious problem. As a guide, it may "ballistic' rise. The rise velocity bebe stated that this is very roughly related comes so great compared to the expanto the weapon yield by sion rate that the fireball ascends almost

H (maimumfor ocallike a solid projectile. "Overshoot"

Hf(aximum) for local: 2.281 then occurs, in which a parcel of dense

fallut) 80 O:, 2.12.1) air is carried to high altitudes where the

where H feet is the maximum value of ambient air has a lower density. The

the height of burst for which there will dense "bubble" will subsequ.ently exbe appreciable local fallout. This ex- pand, thereby decreasing its density.

pression is plotted in Fig. 2.128. For an and will fall back until it is in a region of

explosion of 1,000 kilotons, i.e., I me- comparable density.

gaton yield, it can be found from Fig.

2.128 or equation (2.128. 1) that signif- HIGHI-ALTITUDE BURSTS

icant local fallout is probable for heights

of burst less than about 2,900 feet. It 2.130 For nuclear detonations a'%

should be emphasized that the heights of heights up to about 100,000 feet (19

burst estimated in this manner are ap- miles), the distribution of explosion tvproximations only, with probable errors ergy between thermal radiation and blast

of ±30 percent. Furthermore, it must varies only to a small extent with yield

not be assumed that if the burst heigh1t and detonation altitude (§ 1 .24). But at

exceeds the value given by equation burst altitudes above 100,000 feet, the

(2.128. 1) there will definitely be no distribution begins to change more nolocal fallout. The amount, if any, may ticeably with increasing height of burst
72 DESCRIPTIONS OF NUCLEAR EXPLOSIONS

2 X 10" - r- r--m i- ~ 'rT

7

4

2

10

(n 4

10/•- - /--- ---

z

00o 0

I -

M 2-

-j 10 _ _

z

0

U) 4

0~

-J I 1- __ __ _ ______ ______

wLJ 2

10 - - - - _ _

2 --

0.1 0.2 0.4 0.7 1 2 4 7 10

HEIGHT OF BURST (THOUSANDS OF FEET)

Figure 2.128. Approximate maximum heighi of burst for appreciable local fallout.

i

i
SCIENTIFiC ASPECTS OF NUCLEAR EXPLOSION PHENOMENA 73

(see Chapter VII). It is for this reason the X-ray veil to form than in an air

that the level of 100,000 feet has been burst (§ 2. 111I).

chosen for distinguishing between air 2.132 Because the primary thermal

bursts and high-altitude bursts. There is, radiation energy in a high-altitude burst

of cou~rse, no sharp change in behavior is deposited in a much larger volume of

at this ekcvation, and so the definition of air. the energy per unit volume available

a high-altituide burst as being at a height for the development of the shock front is

above 100,G%) feet is somewhat arbi- less than in an air burst. The outer shock

trary. There is a progressive decline in wave (§ 2.116) is Aow to form and

the blast energy wi'h increasing height radiative expansion predominates in the

of burst above 100,000 feet, but the growth of the fireball. The air at the

proportion of the explosion energy re- shock front 'does not become hot enough

ceived as effective thermal radiation on to be opaque at times sufficiently early

the ground at first increases only shli.,tly to mask the radiation front and the firewith altitude. Subsequently, as the burst ball radiates most of its energy very

altitude increases, the effective thermal rapidly. There is no apparent temperaradiation received on -. e ground de- ture minimum as is the case for an air

creases and becomes less than at in burst. Thus, with increasing height. a

equal distairce from an air burst of t ie series of changes take place in the thersamne trital yield (§ 7.,102). mal. pulse pheuiomena: the surface temn2.131 Fo, nuclear, explosions at a! perature minimum becomes less protitudes be:ween 100,O0 and about nounced and eventually disappears, so

270,000 feet (51 miles) the fireball phe- that the thermal radiation is emitted in a

nomena. are affected by the low density single pulse of fairly short duration. In

of the air. The probability of interaction the absence of the obscuring opaque

of the primary thermal radiation, i.e.. shock front, the firebatll surface is visible

the thermal X rays, with atoms and throughout the period of radiative

molecules in the air is markedly de- growth and the temperature is higher

creased, so that the photons have long than for a low-altitude fireball. Both of

mean free paths and travel greater dis- these effects contribute th the increase in

tances, on the average, before they are the thermal radiation emission.

absorbed or degraded into heat and. into- *- 2.133 A qualitative comparison of

radiations of longer wavelength (smaller the rate of arrival of thermal radiation

photon energy). The volume of the at- energy at a distance from the burst point

mosphere in which the energy of the as a function of time for a megatonradiation is deposited, over a period of a range explosion at high altitude and in a

millisecond or so, may exteiid for sev- sea-level atmosphere is shown in Fig.

eral miles, the dimensions inc-easing 2.133. In a low (or moderately low) air

with the burst altitude. The interaction burst, the thermal radiation is emitted in

of the air molecule-, with the prompt two pulses, but in a high-altitude burst

gamm-,a rays, neutrons, and high-energy there is only a single pulse in which

component of the X rays produces a most of the radiation is emitted in a

strcong flash of fluorescence radiation relatively short time. Furthermore, the

(j' 2. 140), but there is less tendency for thermal pulse from a high-altitude ex-
74 DtSCRIPrioNS 01: NL T(i I-,-R t:XPI.OSIONS

very large volume and mass of air in the

X-ray pancake, the temperatures

reached in the layer are much lower than H,-,H A ...... ,j those in the fireballs from bursts in the

normal atmosphere. Various excited

atoms and ions are formed and the radiS1" FVFt V ATM•OSpHIFIRI s ations of lower energy (longer waveC- length) re-emitted by these species represent the thermal radiation observed at

a distance.

2.133 For heights of burst up to

TIME about 270,000 feet, the early fireball is

Figure 2.133. Qualitative coniparison of approimately spherical, although at the

rate,, of arrival of thermal higher altitudes it begins to elongate

radiation at a given distance vertically. The weapon debris and the

from high-altitude and sea- incandescent air heated by the X rays

level burts. roughly co-•-ide. Above 270.000 feet,

plosioni is richer in ultraviolet radiation however, the debris tends to be separate

than is the main (second) pulse froti an from the X-ray pancake. The debris can

air burst. The reason is that formation of rise to great altitudes, depending on the

ozone, oxides of nitrogen, and nitrous explosion yield and the burst %eight: its

acid (§ 2.123), which absorb strongly in behavior and iouization effects are dethis spectral region, is decreased. scribed in detail in Chapter X. The in2.134 For burst altitudes above candescent (X-ray pancake) region, on

about 270.000 feet, there is virtually no the other hand, remains at an essentially

absorption of the X rays emitted in Lj)- constant aiitude regardless of the height

ward directions. The downward directed of burst. 'From this region the thermal

X rays are mostly absorbed in a layer of radiation i.i emitted as a single pulse

air, called the "X-ray pancake," which containing a substantially smaller probecomes incandescent as a result of en- portion of the total explosion energy but

ergy depositien. The so-called pancake of somewhat longer duration than for

i'z more like the frustum of a cone. de,;onations below roughly 270,000 feet

pointing upward, with a thickness of (see § 7.89 el seq.).

roughl) 30,000 feet (or more, and a 2.136 Although the energy deTiity

mean altitude of around 270,000 feet; in the atmosphere as the result of a

the radius at this altitude is approxi- high-aliitude burst is small compared

mately equal to the height of burst with that from an air burst of the same

minus 270,000 fect. The height and di- yield, a shock wave is ultimately pr'.

inensions of the pancake are deter mined duced by the weapon debris (", 2.116),

largely by the emission temperature for at least for bursts up to about 400,000

the primary X rays, which depends on feet (75 miles) altitude. For example,

the weapon yield and design, but the disturbance of the ionosphere in the vivalues given here are regarded as being cinity of Hawaii after the TEAK shot (at

reasonable averages. Because of the 252,000 feet altitude) indicated that a
SCIENTIFIC ASPECTS OF NUCIEAR EXPLOSION P'HENOMEN\ 75

shock wave was being propagated at feet, the first brief fluorescence that can

that time at an average speed of about be detected, within a microsecond or so

4,200 feet per second. The formation of of the explosion time, is called the

the iarge red, luminous sphere, several "Teller light." The excited particles are

hundred miles in diameter, surrounding produced initially by the prompt (or inthe fireball, has been attributed to the stantaneous) gamma rays that accomelectronic ex(.Itation of oxygen atoms by pany the fission process and in the later

the energy of the shock wave. Soon stages by the interaction of fast neutrons

after excitation, the excess energy was with nuclei in the air (§ 8.53).

emitted as visible radiation toward the 2.140 For bursts above 100,000

red end of the spectrum (6,300 and feet. the gamma rays and neutrons tend

6,364 A). to be absorbed, with an emission of

2.137 For bursts above about fluorescence, in a region at an altitude of

400,000 feet, the earth's magnetic field about 15 miles (80,000 feet), since at

plays an increasingly important role in higher altitudes the mean free paths ini

controlling weapon debris motion, and the low-density air are too long for apit becomes the Jominant factor for ex- prcciable local absorption (§ 10.29).

plosions above 200 miles or so (Chapter The fluorescence is emitted over a relaX). At these altitudes, the shock waves tively long period of time because of

are probably magnetohydrodynamic time-of-flight delays resulting from the

(rather than purely hydrodynamic) in distances traveled by the photons and

character. The amount of primary ther- neutrons before they are absorbed. An

mal radiation produced by these shock appreciable fraction of the high-energy

waves is quite small. X rays escaping from the explosion region are deposited outside the fireball

and also produce fluorescence. The relative importance of the X-ray fluores2.138 Various transient fluorescent cence increases with the altitude of the

effects, that is, the emission of visible burst point.

and ultraviolet radiations for very short 2.141 High-energy beta particles

periods of time, accompany nuclear ex- associated with bursts at sufficiently

plosions ;r the atmosphere and at high high altitudes can also cause air fluoaltitudes. ,''hese fiTcts arise from elec- rescence. For explosions above about 40

tronic excitaiion (and ionization) of miles, the beta particles emitted by the

atoms an,. molecules in the air resulting weapon residues in the downward difrom interactions with high-energy X rection are absorbed in the air roughly at

rays from the fireball, or with gamma this altitude, their outward spread ering

rays, neutrons, beta particles, or other restricted by the geomagnetic field lines

charged particles of suffi:ient energy. (§ 10.63 el seq.). A region of air fluoThe excess energy of the excited atoms, rescence, called a "beta patch," may

mrolecules, and ions is then rapidly then be formed. If the burst is at a

emitted as fluorescence radiation. sufficiertly high altitude, the weapon

2.139 In a conventional air burst, debris ions can themselves produce flui.e., at an altitude below about 100,000 orescence. A fraction of these ions can
76 DES('RIPTI,)NS OF NU(I EAR E-XPILOSIONS

be channeled by the geomagnetic field to sever]d minutes compared with fractions

an altitude of about 70 miles where they of a second for air fluorescence. Furare stopped by the atmosphere (§ 10.29) therriore. the radiations have somewhat

and cause the air to fluoresce. Under diffcrent wavelength characteristics

suitable conditions, as will be explained since they are emitted, as a general rule,

below, fluorescence due to beta particles by a different distribution of excited

and debris ions can also appear in the spccies.

atmosphere in the opposite hemisphere 2.143 The geomagnetic field exerts

of earth to the one in which the nuclear forces on charged particles, i.e., beta

explosion occurred. particles (electrons) and debris ions, so

that these particles are constrained to

AURORAL PHENOMENA travel in helical (spiral) paths along the

field lines. Since the earth behaves like a

2.142 The auroral phenomena as- magnetic dipole, and has north and

sociated with high-altitude explosions south poles, the field lines reach the

(§ 2.62) are caused by the beta particles earth at two points, called "conjugate

emitted by the radioactive weapon resi- points," one north of the magnetic

dues and, to a varying extent, by the equator and the other south of it. Hence,

debris ions. Interaction of these charged the charged particles spiraling about the

particles with the atmosphere produces geomagnetic field lines will enter the

excited molecules, atoms, and ions atmosphere in corresponding conjugate

which emit their excess energy in the regions. It is in these regions that the

form of visible radiations characteristic auroras may be expe ted to form (Fig.

of natural auroras. In this respect, there 2.143).

is a resemblance to the production of the 2.144 For the high-altitude tests

air fluorescence described above. How- conducted in 1958 and 1962 in the viever, auroras are produced by charged cinity of Johnston Island (§ 2.52), the

particles of lower energy and they per- charged particles entered the atmossist for a much longer time, namely, phere in the northern hemisphere be500 MILES BETA PARTICI ES

SPIRALING

•j..• •d¢•400•4 .•. ALONG MAGNETIC

,.LINES OF FORCE

"DEBRIS ATER

IBURS AE MINUTES

A MAGNETIC

EQUATOR GAMMA RAY

13ETA IONIZATION IONIZATION BETA ,

AND AURORA IONIZATION

CONJUGATE AREA AND

AURORA

Figure 2. 143. Phenomena associated with high-altitude explosions.
SCIF.NTIFIC ASPVCTS OF NU'CI EAR EXPTC.'ION PHENOMENA\ 77

tween Johnston Island and the main f )rth. from one conjugate region to the

Hawaiian Islandis. whereas the conju- .$ther. a number of times before they are

gate region in the southern hemisphere eventually captured in tlhe atmosrhere.

region was ir the vicinity of the Sa- (More will be said in Chipter X about

moan, Fiji, ard Tonga Islands. It is in the interactions of the geoviagnetic field

these areas ,hat auroras were actuall', with the charged particles amd radiations

observed, Li addition to those in true produced by a nuclear expl( siol.)

areas of the; nuclear explosiois. 2.147 In addition to the motion of

2.145; Because the beta parti les the charged particles along the field

have high velocities, the beta auror i,ý in lines, there is a tendency for them to

the remote (southern) heniispher.- ap- move across the lines wherever the

peared within a fraction ol a secý,nd of magnetic field strength is not uniform.

those in the hemisphere where th,, bursts This results in an eastward (Ilngituhad occurred. The debris ions, 1'awcver, dinal) drift around the earth superimtravel more slowly and so tfe debris posed on the back-and-forth spiral moaurora in the remote heniisph, re, if it is tion between regions near the conjugate

formed, appears at a somc what later points. Within a few houcs after a hightime. The beta aurorms art. generally altitude nuclear detonation, the beta

most intense at an altiLude of 30 to 60 particles form a shell completely around

miles, whereais the inte isity of the the earth. In -ihe ARGUS experiment

debris auroras is greates in the 60 to (§ 2.53), in which the bursts occurred at

125 miles tange. Remote conjugate beta altitudes of 125 to 300 miles, wellauroras can occur if t0 e detonation is, defined shells of about 60 miles thickabove 25 miles, where is debris auroras ness, with measurable electron densiappea' only if the det ,nation altitude is ties, were establishei and remained for

in excess of some 20.) miles. several days. This has become known as

the "ARGUS effect." Similar phenomThIE ARGUS E' FECF ena were observed after the STARFISH

PRIME (§ 2.52) wid other high-altitude

2.146 For bursts at sufficiently high nuclear explosions;.

altitudes, the dcbris ions, moving along

the earth's magnetic field lines, are EFFECT ON THE OZONE LAYER

mostly brought to rest at altitudes of

about 70 miles near the conjugate 2.148 Ozone (O0) is formed in the

points. There they continue to decay and upper atmosphere, mainly in the stratoso act as a stationary source of beta sphere (see Fig. 9.126) in the altitude

particles which spiral about the geo- range of approximately 50,000 to

magnetic hiJues of force. When the par- 100,000 feet (ioughly 10 to 20 miles),

ticles enter a region where the strength by the action of solar radiation on moof the earth's magnetic field increases iecular oxygen (02). The accumulation

significantly, as it does in the vicinity of of ozone is limited by its decomposithe conjugate points, some of the beta tion, partly by the absorption of solar

particles are turned back (or reflected). ultraviolet radiation in the wavelength

Consequently, they may travel back and range from about 2. iO0 to 3,000 A and

1$
78 DESCRIPTIONS OF NUCl EAR EXPLOSIONS

partly by chemical reaction with traces adverse effects oti plant and animal life.

of nitrogen oxides (and other chemical 2.150 As seen in §§ 2.08 and

species) present in the atmosphere. The 2.123, nuclear explosions are accouchemical decomposition occurs by way parted by the formation of oxides of

of a complex series of chain reactions nitrogen. An air burst, for example, is

whereby small quantities of nitrogen estimated to produce about 1012 moleoxides can cause considerable break- cules of nitrogen oxides per megaton

down of the ozone. The equilibrium (or TNT equivalent. For nuclear explosions

steady-state) concentration of ozone at of intermediate and moderately high

any time represents a balance between yield in the air or near the surface, the

the rates of formation arid decomposi- cloud reaches into the altitude range of

tion; hence, it is significantly dependent 50,000 to !00,000 feet (Fig. 2.16);

on the amount of nitrogen oxides pres- hence, the nitrogen oxides from such

ent. Solar radiation is, of course, an- explosions would be expected to enother determining factor- the normal hance mechanisms which tend to deconcentration of ozone varies, conse- crease the ozone concentration. Routine

quently, with the latitude, season of the monitoring of the atmosphere during

year, time of day, the stage in the solar and following periods of major nuclear

(sunspot) cycle, and perhaps with other testing have shown no significant

factors not yet defined. change in the ozone concentration in the

2.149 Although the equilibrium sense of marked, long-lasting perturbaamount in the atmosphere is small, lions. However, the large natural variararely exceeding 10 parts by weight per tions in the ozone layer and uncertainmillion parts of air, ozone has an im- ties in the measurements do not allow an

portant bearing on life on earth. If it unambiguous conclusion to be reached.

were not for the absorption of much of Theoretical calculations indicate that

the solar ultraviolet radiation by the extensive use oil nuclear weapons in

ozone, life as currently known could riot warfare could cause a substantial deexist except possibly in 'he ocean. A crease in the atmospheric ozone consignificant reducion in the ozone con- centration, accompanied by an increase

centration, e.g., as a result of an in- in adverse biological effects due to ulcrease in the amount of nitrogen oxides, traviolet radiation. The ozone layer

would be expected to cause an increased should eventually recover, but this

incidence of skin cancer and to have might take up to 25 years.

BIBLIOGRAPHY

BtAU1 K, F. and F, R. (;it Mom) , "The ElicIt of HoQuist, W. P.. and J W, SNYWIt, 'ConjuAtmospheric Nuclear Explosions on Total gate Auroral Measurements froin the 1902 .! S,

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uary 1975, Paper P 1076, IDA Log. No, HQ and Airglow,'' I. M. McCormac, Id., Rein

74 -16720. hold Publishing Corp.. 1967.

*Hi imt, H-. A., e l, , "Blast Wave," Univer lBRI KWI:1)1)1, !. 1 . . "Temperature in Atomic

sity of California, Los Alamos Scientific l.abo- Esplosions," in "'rempemature, Its Meaiureratory, March. 1958, IA 2(X0 ). mneri and (onlroi iii Scit;nce and Ihdustry,'
SCIENTIFIC ASPECTS OF NUCIEAR EXPLOSION PHENOMENA 79

Reinhold Publishing Cv-p.. 195.5, Vol. [I. Nti SON, 1). B., 'EMP Impact on U.S De'-

1p. 395. fense.'' Survive. 2. No. 6. 2 (1969).

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(1968). April 1966, Uniiscrsity of California, Lawrence

ChRist OI i i os. N. C , "'The' Argus Experi- Radiation L~aboratory. Livermore. TID-69)5

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Foi t'y. N. M., and M. A, RimPI;R54SN, ''Stra- with Nuclear Explosives.L Ias Vegas. Nevada,

tosoheric Nitric Oxide Production from Past Januar\ 1970, American Nuclear SocietN and

Nuclear Explosions and Its Relevance to Pro- UlS. Atomic Energy Commission. CONFjected SST Pollution,' Institute for Defense 7(8)101. Vols. I and 2.

Analyses. August 19'72. Paper P-894, IDA "Proceedings for the Symposium on Public

L~og. No. HQ 72 -144.52, Health Aspectý of Peaceful Uses oif Nuclear

(Il M1ORF. F. R., ''The Production o( Nitrogen Explosives.'' Las Vegas. Ni_:sada, April 1969,

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Institute for Defense Analyses., July, 1974. SWRHL-82.

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GI ASSIONt , S_, "Public Satety and Under- Excavation,' Nuclear Application.% and Techground Nuclear Detonations.,' U.S. Atomic untolgy, 7, 188 et seq ( 1969).

Energy Commission, June 197 1, TID- 25708 SNAY, H. G.. and R. C. TiprtON, "Charts for the

Ht~ss, W. N , Ed.. ''Collected Papers on the Parameters of Migrating Explosion Bubbles.'

Artificial Radiation Belt from the July 9. 1962 U.S. Naval Ordnance L~aboratory, I1962,

Niucl(-ar Detonation.'' J. Geophys.. Res.. 68. NOLTR 62- 184.

605 ct seq. ( 1963). Stiui~itR. W. R., and S. MAISJSHIItA. ''Photo-

*HoF.Ri iN, H.. ''United States High-Altitude graphs of the High Altitude Nuclear E 'xplosion

Test Experiences.'' University of California, TEAK.'' J, Geoph'v~s. Res., 65. 545 (1960)),

L~os Alamos Scientific Labo~ratory. October StI4AN( i.. J. N., and I.. Mii I th.R ''Blast Phi'-

1970, '_A 6405. nomena from Explo:;ions and an Air-Water In-

*JOWNSON,) G. W., and C.E. Vtoitrit ''Plie- terface,'' U.S. Army Engineer Waterways Exnoiuenology of Contained Nuclear Explo. periment Station. 1966, Report 1, Misc. Paper

sions." University of California, I~awrence 1 814.

Radiation L~aboratory. Livermori'. December TrAI tiFt. E., e( al.. ''The Constructive' Uses of

195h. UCRL 5124 Rev. 1. Nuclear F~plosives," McGraw-Hill Book

*JI0NSON, G. W., el al.. ''Underground Nu- Company. 1968,

clear IDetonations.'' University of California. VAN DORtN. W. G., B. IA: NVI' AU if., andI

lawrencc Radiation I.ahoratory, L~ivermore. L.. HwANG, ''Handbook of Explosion-Geniajly 1959, UCRI. 5626. crated Water Waves, Vol. I--- State of the Art."

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Altitude Explosions.'' J, Geophy,. Res., 64.

1149 (1959).

*The se do~cu ment s ma he purchased fro nt thle N ational 'Tec hnicalI In fo rmat ion ( 'enuter, .,S,

I epaitmenti of 'onmmterce, Springfieldl, Virginia, 22161.I
CHA PTER III

AIR BLAST PHENOMENA IN AIR AND SURFACE

BURSTS

CHARACTERISTICS OF THE BLAST WAVE IN AIR

DEVELOPM4ENT OF THE BLAST tion in the overpressure with time and

WAVE distance will be described in succeeding

sections. The maximum value, i.e., at

3.01 Most of the material damage the blast wave (or shock) front, is called

caused by a nuclear explosion at the the "peak overpressure." Other

surface or at a low or mouierate altitude characteristics of the bias! wave, such as

in the air is due-directly or indi- dynamic pressure, duration, and time of

rectly-to the shock (or blast) wave arrival will also be discussed.

which accompanies th- explosion. 3.03 As stated in Chapter II, the

Many structures will suffer some dam- expansion of the intensely hot gases at

age from air blast when the overpressure extremely high pressures in the fireball

in the blist wave, i.e., the excess over causes a shock wave to form, moving

the atmospheric pressure (14.7 pounds outward at high velocity. The nmain

per square inch at standard sea level characteristic of this wave is that the

conditions), is about one-half pound per pressure rises very sharply at the movsquare inch ot more. The distance to ing front anm fall' .IT toward the interior

which this overpressure level w1l ex- region of the explosion. In the very

tend depends primarily on the energy early stages, tor example, the variation

yield (§ 1.20) of th! explosion, and on of the pressure with distance from the

the height of the burst. It is conse- center of the fireball, at a given instant,

quently dteirable to consider in some is somewhat as illustrated in Fig. 3.03

detail the phenomena associated with for an ideal instantaneously ,ising)

the passage of a blast wave through the shock fEmit. It is seen that, prior to

air, breakaway (§ 2.120). presaures at the

3.02 A difference in the air piessure shock front are two or three times as

aztlng on separate surfaces 3f a structure large as the already very high pressures

produces a force on the structure. In in the interior of the firebalL.

conridering the destructive effect of a 3.04 A,ý the blkst wave travels in the

blast wave, one of its important charac- air away from its source, the overprc!.;

teristics is the overpressure. Th-. v4ria- sure at the front steadily (Jecreases, and

80)
CHARACTERISTICS OF THE BI-AiT W'AVE IN AIR 81

the pressure behind the front falls off in a so-callea "negative phase" of the

a regular manner. After a short time, biast wave forms. This development is

when the shock front ha,; traveled a seen in Fig. 3.04, which shows thte

certain distance from the fireball, the overpressuires at six successive times,

pressure behind the front drops below indicated 1y the numbers 1, Z. 3, 4 5,

that of the surrounding atraosphere and .,nd 6. !n the curves marked t, through 1,

PEAP. OVERPRESSURE

.J-J

fn

IbJ

I-

-r

z

hl

wLI,

n -(I S H O C K F R O N T - - - "

DISTANCE FROM EXPLOSION CFNTER

Figure 3.03. Variation of overpressure with distance in the fireba.i.

w

Ct

(r

UISTANCE FROM EXPLOSION

Fig'ire 3 04. 'Variation of overpressurc in air with distance at successive times.
82 AIR BI.AST PHENOMENA IN AIR A%.D SURFAC- HURSTS

the pressure in the blast wave has not and they approach equality when the

faic.n below atmospheric, but in the peak pressures have decayed to a very

curve marked t., it is seen that at some low ievel.

distance behind the shock front the

overpressure has a negative value. In THE DYNAMIC PRESSURE

this region th. air pressure is below that 3.06 The destructive effects of the

ot the original (or ambient) atmosphere, blast wave are frequentl) related to valso that an "underpressure" rather than ues of the peak overpressure, but there

an overpressuie exists. is another import.4nt quantity c-lled the

3.05 During the negative (rarcfac- "dynamic pressure." Fot a great - ariety

tiorp or suction) phase, a partial vacuum of building types, the degree of blast

is produced and the air is sucked in, damage depends largely on the drag

instead of being pushed away from the force associated with the strong winds

explosioin as it i:; when the overpressure accompanying the passage of the blast

is positive. At the end of the i-egative wave. TIhe drag force is influenced by

phase, which is somewhat longer than certain characteris:ics-primarily the

the positive phase, the pressure has es- shape and ,ize--f the structure, bvt

sertially returned to ambient. The peak this force alsc, depends on the peak

(or maximum) values of the underpres- value of the dynamic pressure and its

sure are usually small compared with duration 'At a given location.

the peak rsitive overpressures; the 3.07 The dynamic pressure is proformer are gcnerally not more than portional te the square of the wind veabout 4 pounds per square inch below locity and to the density of the air beth- ambient pressure whereas the posi- hind the shock front. Both of these

tive overpressure may be much larger. quantities maty bc related to the overWith increasing distance from the ex- pressure under ideal conditions at the

plosion, both peak values decrease, the wave front by certain equations, which

positive more rapidly than the negative, will be giver, later (see § 3.55;. For very

Table 3.07

PEIA, OVERFRESSURE AND DYNAMIC PRESSURE AND MAXIMUM WIND VELOCITY

IN AIR AT SEA LEVEL CALCULATED FOR AN IDEAL SHOCK FRONT

Peak overnres- Peak dynamic Maximum wind

sure (pounds per pressure (pounds velocity (miles

square inch) per square inch) per hour)

2W() 330 2,078

150 222 1,777

1(X) 123 1,415

72 74 1,168

i0 41 934

30 17 669

20 8.1 5(02

I0 2.2 294

5 0.6 163

2 0. 1 70
(CHARACiERISIRI(S O(F TH- BLAST rWAVF IN' AIR 83

strong shocks the peak dynamic pres- range, For example, at a distance of I

sure is largL.r than the peak overpres- mile from a 20-kiloton explosion ill the

sure, but below 70 pounds per square air the arrival time would be about 3

inch ovt.rpres.,are at sea level the dy- seconds, whereas at 2 miles it would be

namic pressure is the smaller. Like the about 7.5 seconds. The corresponding

peak shock overpressure, the peak dy- times for a I-megaton burst would he

namic pressure generally decreases with roughly 1.4 and 4,5 seconds. respecincreasing distance from the explosion tively.

center, although at a different rate. 3.10 It is evident that the blast wave

Some peak dynamic pressures and from an explosion of higher yield will

maximum blast wind velocities corre- arrive at a given point sooner than one

sponding to various peak overpressures. for a lower yield. The highet the overas calculated for an ideal shock front in pressure at the shock front, the grcater is

air at sea level (§ 3.53 et seq.) are given the velocity of the shock wave (see

in Table 3.07. The results are based on Figure. 3.55). Initially, this velocity

1,1 16 feet per second (761 miles per may be quite high, several times the

hour) as the velocity of sound in air (see speed of sound in air (abojit I. 100 leet

Table 3.66). pei second at sea 'evel). As :he blast

3.08 The winds referred to above, wave progresses outward, the pressure

which determine the dyn-amic pressure at the front decreases and the velocity

in the shock wave, art a direct conse- falls off accordingly. At long ranges.

quence of the air blast. More will be when the overpressure has decreased to

said about these winds shortly. There less than abou! I pound per :quare inch.

are also other winds associated with the velocity of the blast wave apnuclear explosions. These include the proaches the ambient speed of sound.

afterwinds mentioned in § 2.09, and the 3.11 When the (ideal) shock front

firestorrms which will be diescribed in arrives at the observation point, the

Chapter VII. overpressure will increase shdrply from

zero to its ra.axlmlnm (ot peak) value.

CHANGES IN THE BLAST WAVE Subsequently the overpressure JeWITH TIME creascs. as indicated by the upper curve

in Fig 3. I . The overpr-sssure drops to

3.09 From the pr,.ticai standl,•int, zero ir. a short line, znd this marks the

it is of intercst t,) examine the changes enJ of the positive (or compressien,

of overpressure and dynasnic pressure phase of die O:verpressure at the given

with time at a fixed location (or obser- location. rhe duration of the overpresvation point). For a short interval after sure positive phase increases with the

the detonation, ther: will be no change energy yield ard the distance from the

ii the ambient pressure because ic takes explosion. For a 20-kiloton air burst, for

some time for the blast wave to travel exampie, this phase lasts roughly I secfrom the point of the explosion to the ond to 1 .4 seconds at 'lant -anges of I to

given location. This time interval (or 2 miles, for a I megaton explosion, the

arrival time) depends upon the energy respecti we durations would bLe approxiyield of the expf,)sion and the siant mately 1.4 to 2.3 seconds.
84 AIR HI ASTI PHI-NOMI.N.1 IN \IR \ND) StR RU('F BtRSTS

TIME

TE~ i

"•ATIMOSiPMLRIC (COMPRE SSON

•o - ,I 

r• POSgT'vE PHASE -- "NEGATIVE PI4ASE

r WNEAK EW WI ND F COLE 

AWA^ PRoM I TOWARD AWAV rROV

I EYPLOSiON EXPLOSION I XPLOSýON

(DECREASING TO ZZRC] I

- I E .......- '---..--I

•.• ! NAI !rPRESS JRlE

PO~lI~l•PHAI[ ••IP!•'-NEGATIVE PHASE "

[t:lur,,. 3. I ! \"ariatio)n of {)crlpre,,,urc and dynamic' prE,,,,Ur • ih Iirnc at a fixed lo.'ation.

3. i2 Provided the observation point than the positive phase and it may last

is at a suflicient distance from the ex- for several seconds. When this phase is

plosion, the overpressure will continue ended, the blast wave will have passed

to decrease after it falls to zero so) that it ',he given observation point.

becomes negative. During thir; negative 3.1.3 Changcs in the wind and in the

(or suction) phase, the pressure in the associated dynamic pressure accompi.ny

shock wave is less than the ambient the changes with time of the overprcsatmospheric pressure. However, as seen sure. With the arrival of the shock front

in § 3.05, the underpressure is never at a given location, a 1•trong wind cornvery large. After decreasing gradually to mences, blowing away fromt tie exploa minimum value, ti'e pressure starts to sioni point. This blast wind is often reincrease until it becomes equal to the ferred ,) as a 'transient wind" because

normal atmospheric pressure, and the its velocity decreases rapidly with time.

overpressure is zero again. The negative The maximum velocity of the transi-nt

phase of the blast wave is usually longer wind can be quite high, as indicated by

ort
( H\R\( INRIVII(RS (1 H. HI *8S1 .\k\\W, 1I1 \IR 85

the values corresponding to various time. This matter will be discuss-,,d more

peak overpressures given in Table 3.07. fuy " lter in this chapter 57 et

The wind velocity decreases as the seq.).

overpressure decreases, but it continues 3.16 By the time the \%ind cescs

to blow for a time after the end of !he blowing away from the explosion, the

positive overpressure phase isee Fig. overpres-urc is definitely negative (sec

3.11 ). The reason is that the momentum Fig. 3. I i): that is to say. the pressure in

of the air in motion behind the shock the blast wave is less than the ambiert

front keeps the wind blowing in the atmospheric pressure. Hence. air is

same direction even after the overpres- drawn in from outside and. as a result.

sure has dropped to zero and has started the wind starts to blow in the opposite

to become negative. dircction, i.e.. toward the explosion.

3.14 Since the dynamic pressure is but with a relatively small velocity. A

related to the square of the wind veloc- short time after the overpressure minity. the changes in the dynamic pressure imum is passed, the wind again reverses

with time will correspond to the changes direction and blows,. once more, away

in the wind just described. The dynamic from the explosion point. The feeble

pressure increases suddenly when the wind apparently results from expansion

(ideal) shock front arriveýs at the obser- of the air due to an increase of temperavation point. Then it decreases, but tur" that occur at this stage

drops to zero some time later than the 3.17 The changes in the dynamic

overpressure, as shown by the lower pressure corresponding to the foregoing

curve in Fig. 3. II. The dynamic pres- wind changes after the end of the dysure positive phase is thus longer than namic pressure positive phase are indithe o'erpressure positive phase. The cated in Fig. 3. 11. The dynamic presratio of the dynamic pressure and over- sure finally decreases to zero when the

pressure positive phase durations de- ambient atmospheric pressure is respends on the pressure levels involved. tored and the blast wave has passed the

When the peak pressures are high, the observation point.

positive phase of the dynamic pressure 3.18 It should be noted that the dymay be more than twice as long as for namic pressure remains positive (or

the overpressure. At low peak pres- zero) even when the overpressure is

sures, on the other hand, the difference negative. Since the overpressui: is the

is only a few percent. difference between the actual blast wave

3.15 As a general rule. the peak pressure ,.nd the ambient atmospheric

overpressure and the peak dynamic pressure, a negative overpressure

pressure behind the shock front are quite merely implies that the actual pressure is

different (sec Table 3.07). Furthermore, less than the atmospheric pressure. The

the dynamic pressure takes somewhat dynamic pressure, on the other hand, is

longer than the overpressure to drop to an actual pressure without reference to

zero during the positive phase. Conse- any other pressure. It is a measure of the

quently, it is evident that the overpres- kinetic energy, i.e., energy of motion,

sure and dynamic pressure at a given of a certain volume of air behind the

location change at different rates with shock front (§ 3.55). The dynamic
86 MAF• BI .\ST PH-NOMF-N.\ IN NIR AN)D St RF \( - HIRSIS

pressure is consequently positive it the fects. e.g.. due to tire (see Chapter VII

air is movin,, or zero if it is not. the ma, continue long after the blast wae

dlrection in which the pressure acts de- has passed

pends on the direction of motion, i.e..

the wind direction (see Fig. 3.11 ). 3.20 There may :,•e some direct

3.19 Nearl) all the direct damage damage to structures during the negative

caused b) both overpressure and dy- phase of the oerpressure: for example.

namic pressure occurs during the posi. large windov s which are poorl, held

tive overpressure phase of the blast against oulwavi motion. brick veneer.

xa\,c. Although the dynamic pressure and plaster wals may be dislodged b-,

persists for a longer time. its magnitude tripped air at normal pressure. But the

during this additional time is usually so maximum undcrpressure (and correlow that the destructive effects are not sponding dynamic pressure) is generall.

very significant. The damage referred to quite small in comparison with the peak

here is that caused directly by the blast pressures at the shock front. hence,

%kave. This will be largely terminated by there is usually much less direct damage

the end of the ov-erpressure positive in the negative than in the positive

phlise. but the indirect destructive ef- overpressure phase of the blast wave.

REFLECTION OF BLAST WAVE AT A SURFACE

INCIDENT AND RIFLECTED \VAV-S surface will experience a single pressure

increase, since the reflected wave is

3.21 When the incident blast wave formed instantaneously. Consequently.

from an e--piosion in air strikes a more the overpressurc at the surface is generdense medium such as the earth's sur- alls considered to be entirely i reflected

Vice, e.g.. either land or water, it is pressure. For a smeoth (or ideal) surreflected. The formation of the reflected face, the total reflected overpressure in

wave in these circumstances is repre- the region near ground zero will be more

',ented in Fig. '.21 This figure shows than 'wice the value of the peak overfour stages in the outward motion of the pressure of the incident blast wave. The

spheriLal blast wave originating from an exact value of the peak reflected pres.

air burst. In the first stage the wave front sure will depend on the strength of the

has not reached the ground, the second incident wave (§ 3.56) and the angle at

stage is somewhat later in time, and in which it strikes the surface (§ 3.78).

the third stage, which is still later, a The nature of the surface also has an

reflected wave. indicated by the dashed important effect (§ 3.47), but for the

line, has been produced. present the surface is assumed to be

smooth so that it acts as an ideal reflec3.27 When such reflection occurs. tor. The variation in overpressure with

an individual or object precisely at the time, as observed at a point actually on

4
REFLECTION OF BLAST WAVE AT A S.jURF-aVt 87

the surface not too far from ground within the region of -regular- refieczero,' such as A in Fig. 3.21. is depicted tion. i.e.. where the incident and rein Fig. 3.22 for an ideal shock front flected wsaves do not merge except on

The point A may be considered as lying the surface.

A

GROUND ZERO

Figure 3.21 Reflection of biast wave at the carth'% %urfacc in an air hurt. t lo t, reprewent

.u.C ,,i ',C litilc .

p INCIDENT OVERPRESSURE

WLl p, TOTAL OVERPRESSURE

AFTER REFLECTION

U,

U)

0-0 P

tj TIME

Figure 3.22. Variation of overpressure with time at a pxoint on the surface in the rc•gion of

regular reflection.

SFor an explanation of the term "ground zcro," sec § 2.34.

ii _

. ..... . .. . ... ________________________-" 
88 A!R 01 AST PHFNOMIN\ IN .AIR `kND StRFA(F ItRSI-S

3.23 At any location somewhat a point above the surface, such as B in

above thc surface in this region, two Fig. 3.21, is based on the tacit assumpseparate shocks will be felt, the first ;ion that the two waves travel with apbeing due to the incident blast wave and proxiniately equal velocities. This asthe second to the reflected wave, "hnich sumption is reasonably justified in the

arrives a short time later (Fig. 3.23). early stages. when the wave front is not

This situation can be illustrateJ by con- far from ground zero. However, it will

sidering the point B in Fig. 3.21, also in be evident that the reflected wave

the regular reflection region. When the always travels through air that has been

incident wave front reaches this point, at heated and compres-ed by the passage

time ti, the reflected wave is still some of the incident wave. As a result, the

distance away. There will, conse- reflected wave front move,, faster than

quently, be a short interval before the the incident wave and, under certain

reflected wave reaches the point above conditions, eventually overtakes it so

the surface at time ti. Between t, and .t1, that the two wave fronts merge to prothe reflected wave has spread out to duce a single front. This process of

some extent, so that its peak overpres- wavy, interaction is called "Mach- or

sure will be less than the value obtained "irregular" reflection. The region in

at surface ievel. In determining the ef- which the two waves have merged is

fects of air blast on structures in the therefore called the Mach (or irxegular)

regular reflection region, it may be nec,- region in contrast to the regular region

essary to consider the magnitude and where they have not merged.

also the directions of motion of both the 3.25 The merging of the incident

incident and reflected waves. After pas- and reflected waves is indicated schesage of the reflected wave, the transient matically in Fig. 3.25, which show,, a

wind direction near the surface becomes portion of the profile of the blast wave

ess;entiaily horizontal close to the surface. The situation at a

3.24 The following discussion con- poim fairly close to ground zero, such as

cerning the delay between 1he arrival of A in Fig. 3.21, is represented in Fig,

the incident and reflected wave fronts at 3.25a. At a later stage, farther from

P INCIDENT OVERPFRESSURE

U po TOTAL. OVERPRESSURE

cr_ AFTER REFLECTION

V)

LU

0-1 C_ Pr

•t rTIME

Figure 3.23. '.:ariatium, of overpressure with time at a point above the surface in the region

of reular reflection. !I

J' 1
REFLECTION OF B!AST WAVE AT A SURFACE 89

ground zero, as in Fig. 3.25b, the the three shock fronts ha,: been called

steeper front of the reflected wave shows the "Mach Y."

that it is traveling faster than, and is 3.26 As the reflected wave conovertaking, the incident wave. At tne tinues to overtake the incident wave, the

stage represented by Fig. 3.25c, the triple point rises aud the height of the

reflected wave near the ground has Mach sten. increases (Fig. 3.26). Any

overtaken and merged with the incident object located either at or above the

wave to form a single front called the ground, within the Mach region and

"Mach stem." The point at which the below the triple point path, will experiincident wave, reflected wave, and ence a single shock. The behavior of

Mach fronts meet is referred to as the this merged (or Mach) waie is the same

"triple point."2 The configuration of as that previously described for blast

INCIDENT

INCIDENT WAVE

WAVE

INCIDENTREFLECTED

WAVE WAVE

REFLECTED REFLECTED XTRIPLE POINT

WAVE WAVE

MACH STEM

a b C

Figure 3.25. Merging of incident and reflected waves and formatioui of Mach Y configuration of shock fronts.

R- REFLECTED WAVE

0.-INCIDENT WAVE

R 

I

R STEM

REGION OF REGULAR REGION OF MACH

REFLECTION REFLECTION

Figure 3.26. Outward motion of the blast wave near the surface in the Mach region.

I

2 At any instant the so-caile& "triple point" is not really a point, but a horizontal circle with its center

on the vertical line through the burst point; it appears as a point on a sectional (or profile) drawing, such

as Fig. 3.25c.
90 AIR HI ASr PHFNOMF.NA IN AIR AND SI'RF.,\('IBURSTS

waves in general. The overpressure at a ground zero as the height of burst inpaiticular location will fall off with time creýases for a given yield, and also as the

and the positive (compression) phase yield decreases at a specified height of

will be followed by a negative (suction) burst. For moderate heights of burst,

phase in the usual manner. Mach merging of direct and reflected

3.27 At points in the air above the waves occurs at a distance from ground

triple point path, such as at an aircraft or zero approximately equal to the burs:

at the top of a high buii'ding, two pres- height. As the height of burst is insure increases will be felt. The first will creased, the distance from ground zero

be due to the incident blast wave ard the at which the Mach effect commences

second, a short time latet, to the re- exceeds the burst height by larger and

fPected wave. When a weapon is deton- larger amounts.

ated at the surface. i.e., in a contact

surface burst (§ 2. 127 footnote), only a HEIGHT OF BURST AND BLAST

singi, merged wave develops. Conse- DAMAGE

quently, rnly one pressure increase will

be observed either on or above the 3.30 The height ui burst and energy

ground. yield of the nuclear explosion are im3.28 As far as the destructive action portarnt factors in determining the extent

of the air blast is concerned, there are at of damage at the surface. These two

least two important aspects of the re- quantities generally define the variation

flection process to which attention of pressure with distance from ground

should be drawn. First, only a single zero and owher associated blast wa,,e

pressure incrcase is experienced in the characteristics, such as the distance

Mach region below the triple point as from ground zero at which the Mach

compared to the separate incident and stem begins to form. As the height of

reflected waves in the region of regular burst for an explosion of given energy

reflection. Second, since the Mach stem yield is decreased, or as the eneigy yield

is nearly vertical, the accompanying for a given height of burst increases, the

blast wave is traveling in a horizontal consequences are as follows: (I) Mach

direction at the surface, and the transient reflection commences nearer to ground

winds are approximately parallel to the zero, and (2) the overpressure at the

ground (Fig. 3.25). Thus, in the Mach surface near ground zero becomes

region. the Alast forces on abovegrcund larger. An actual contact surface burst

structures and other objects are directed leads to the highest possible overpresnearly horizontally, so that vertical sur- sures near ground zero. In addition

faces are loaded more intensely than cratering and ground shock phenomena

horizontal surfaces. are observed, as will be described in

3.29 The distance from ground zero Chapter VI.

at which the Mach stem begins to form 3.31 Because of the relation bedepends p-.imarily upon the yield of the tween height of burst and energy of the

detonation and the height of the burst explosion, the air blast phenomena to be

above the ground. Provided the height expected on the ground from a weapon

af burst is not too great, the Mach stem of large yield detonated at a height of a

forms at increasing distances fiom few thousand feet will approach those of
RIUHI FA"IION 01 III1 W\AV% A I A StURF:..(I.

a near surface burst On the other hand, bdrst'" curves. Such curves have been

explosions of weapons of smaller en- prepared for various blast wave properergy yields at these same or even lower ties. e.g , peak overpressure. peak dylevels will have the characteristics of air namic pressure, time of arrival, and

bursts. A typical example of the latter positive phase duration, and will be

situation is found in the nuclear explo- presented and discussed later (§ 3.69 et

sion which occurred oser Nagasaki. seq.). \a'% s of these (and other) propJapan, in World War i1 when a weapon erties ,an be detcmined from the

having a yield of approximately 22 ki- curves, by application of appropriate

lotons of TNT equivalent was detonated scaling fadtors, for any explosion yield

at a height of about 1,640 feet. By and height of burn.,t.

means of certain rules, called "scaling

laws." which are described in the tech- CONTACT SURFACE BURST

nical section of this chapter (§ 3.60 et

seq.), it is found that to .,roduce similar 3.34 The general air blast phenomblast phenomena at ground distances ena resulting from a contact surface

proportional to the heights of burst, for a burst arc somewhat different from those

I-kiloiun weapon the height of burst for an air burst as described above. In a

would have to be roughly 585 feet and surface explosion the incident and refor a I-megaton explosion about 5,850 flected shock waves merge instantly, as

feet. In these three cases, the Mach stem seen in § 3.27, and there is no region of

,aornation would occur at distances from regular reflection. All objects and strucground zero that are not very different tures on the surface, even close to

from the respective heights of burst. ground zero, are thus subjected to air

3.32 It shouid be no-ed that there is blast similar to that in the Mach region

no single optimum height of burst, with below the triple point for an air burst.

regard to blast effects, for any specified For an ideal (absolutely rigid) reflecting

explosion yield Ix cause the chosen burst surface the shock wave characteristics,

height will be determined by the nature i.e , overpressure, dynamic pressure,

o. the target. As a ,ule, strong (op ;,P'Id) etc., at the shock front would corretargets will require the equivalent of a spond to that for 9 "free air" burst, i.e.,

low air burst or a surface burst. For in the absence of a surface, with twice

weaker targets, which are destroyed or the energy yield. Behind the front, the

damaged at relatively low overpressures various pressures would decay in the

or dynamic pressures, the height of same manner as for an air burst. Beburst may be raised to increase the cause of the immediate merging of the

damage areas, since the required pres- incident and reflected air blast waves,

sures will extend to a larger range than: there is a single shock front which is

for a iow air or surface burst. hemisphericil in form, as shown at suc3.33 The variation of blast charac- cessive times, t, through t4, in Figure

teristics with distance from ground zero 3.34. Near the surface, the wave front is

for air bursts occurring at different essentially vertical and the transient

heights are most conveniently repre- winds behind the front will blow in a

sented by what are called "height of horizontal direction
92 AIR BLAST PHENOMENA IN AIR AND SURFACE BURSTS

t

SURFACE GROUNU ZERO

Figure 3.34. Blast wave from a contact surface burst, incident and reflected waves

coincide.

MODIFICATION OF AIR BLAST PHENOMENA

TERRAIN EFFECTS variation in peak ovcrpressure at any

point on a hill from that expected if the

3.35 Large hilly Iund masses tend to hill were not present depends on the

increase air blast effects in some areas dimensions of the hill with respect to the

and to decrease them in others The energy yield and location of the explochange in peak overpressure appears to sion. Since the time interval in which

depend on the slope angle and on the the pressure increase or decrease occurs

actual value of the pressure. The in- is short compared to the length of the

crease (or "spike") in r-ak overpres- positive phase, the effects of terrain on

sure which occurs at thr, base of a hill is the blast wave are not expected to be

attributable to the re$,ection of the blast significant for a large vai etv of strucwave by the frormt slope. This spike tural types.

tends to broaden or lengthen with time 3.36 It is important to emphasize,

as the wave travels up the hill. How- in particular, that shielding from blast

ever, a reduction in peak overpressure effects behind the brow of a large hill is

occurs as the blast wave moves over the not dependent upon line-of-sight concrest and down the back slope. The siderations. In other words, the fact that

pressure at the wave hont does not rise the point of the explosion cannot be seen

instantaneously, as in an ideal shock from behind the hill by no means imwave (see Fig. 3.11), but somewhat plies that the blast effects will not be

more gradually, although the behavior felt. It will be shown in Chapter IV that

soon becomes normal as .he blast wave blast waves can easily bend (or diffract)

proceeds down the hil!. In general, the around apparent obstructions.
MODIFICATION OF AIR BI.AST PH-NOMEN.,% 93

3.37 Although prominent terrain enced hundreds of miles from the burst

features may shield a particular target point. Such phenomena, which have

from thermal radiation, and perhaps also been observed with large TNT detonato some extent from the initial nuclear tions as well as with nuclear explosions,

radiation, little reduction in blast darn- are caused by the bending back to the

age to structures may be expected. ex- eairth of the blast wave by the atmroscept in very special circ~imstances. phere.

Nevertheless, considerable protection 3.40 Four general conditions which

from debris and other missiles (§ 3.50) can lead to this effect are known. The

and drag forces may be vehieved for first is a temperature "inversion" near

5'1.ch movable objects as heavy con- the earth's surface. Normally, the air

struction equipment by placing them temperature in the lower atmosphere

below the surface of ihe ground in open (troposphere) decreases with increasing

.:;,.avations or deep trenches or behind altitude in the daytime. In some cases,

steep carth mounds. however, the temperature near the sur3.38 The departure from idealized face increases instead of decreasing with

or flat terrain presented by a city com- altitude; this is called a temperature inple," may be considered as an aspect of version. It can arise either from nighttopography. It is to be expected that the time cooling of the ground surface by

presence of many buildings close to- the radiation of heat or from a mass of

gether wil! cause local changes in the warm air moving over a relatively cold

blast wave, especially in the dynamic surface. The result of an inversion is

pessur,-. Some shiLiding may result that the overpressure on the ground at a

from intervening objects and structures; distance from the explosion may be

however, in other areas multiple reflec- higher thai' would otherwise be extions between buildings and tile chan- pected. Conversely, when unstable

neling caused by streets may incease conditions pre',ail, and the temperature

the overpressure and dynamic pressure. near the earth's surface decreases rapidly with altitude, as in the afternoon or

METEOROLOGICAl CONDITIONS in ir.. qical climates, the blast wave is

bent away from the ground. The over3.39 The presence of large amounts pressure then decays with distance faster

of moisture in the atmosphere may af- than expected.

fect the properties of a blast wave in the 3.41 The second situation exists

low overpressure region. But the proba- when there are high-speed winds aloft.

bility of encountering significant con- !f the normal decrease in the temperacentrations of atmospheric liquid water ture of the air with increasing altitude is

that would influence damage is consid- combined with an upper wind whose

ered to be small. Meteorological condi- 3peed exceeds 3 miles per hour for each

tions, however, can sometimes either 1,000 feet of altitude, the blast wave

enlarge or contract the area over which w0l be refracted (or bent) back to the

light -:ructural damage would normally ground. This usually occurs with jetbe (,xpected. For example, window stream winds, where maximum velocibreakage and noise have been exeri- ties are found between 25,000- and
94 AIR BLAST :H4ENOMEN\ IN AIR AND SF.TRFACE BURSTS

50,0nJ-feet altitudes. Thesie conditions that they reach thL grovnd at distances

may cause several "rays" to converge beyond 100 miles from the burst, geninto a sharp iocus at one location on the era'ly it, the oppomite direction trom the

ground, and the concentration of blast principal mesospheric signals, i.e., in

energy there will greatly exceed the the upwit.d direction. Most of the blast

value that would otherwise occur at that wave energy is absorbed in the lowdistance. The first (or direct striking) den~.ity air at high altitudes, and no

focus from a jet stream duct may be at structural damage has been reported

20 to 50 miles from the explosion. Since from thermospheric ducting. However,

the blast energy is reflected from the sharp pops and crackies have been heard

ground and is again bent back by the when the waves from large explosions

atmosphere, the focus may be repeated reach the ground.

at regularly spaced distances. In an explosion of a 20-kiloton weapon in the air EFFECT OF ALTITUDE

at the Nevada Test Site, this effect

caused windows to break "/5 to 100 3.44 The relations between overmiles away. pressure, distance, and time that de3.42 Bending of blast waves in the scribe the propagation of a blast wave in

downwind direction can also be pro- air depend upon the ambient atmosduced by a layer oi relatively warm air pheric conditions, and these vary with

at a height of 20 to 30 miles ir the lower the altitude. In reviewing the effects of

mesosphere (see Fig. 9.126). in these elevation on blast phenomena, two

levels winds blow from the west in cases will be considered; one in which

winter and from east in summer, en- the point of burst and the target are

hancing blast pressures and noise at essentially at the same altitude, but not

downwind distances from 70 to 150 necessarily at sea level, and the second.

miles (first direct strike). Reflections when the burst and target are at different

trom the ground, and subsequent re- altitudes.

fractions by the lower mesosphere, 3.45 For -)n air burst, the peak

cause the usual repeat focus pattern. overpressure at a given distance from

Focusing of this type has resulted in the the explosion will depend on the ambreakage of windows on the second bient atmospheric pressure and this will

ground strike at 285 miles downwind vary with the burst altitude. There are a

from a 17-kiloton nuclear air burst. number of simple correction factors,

Large explosions have been distinctly which will be given later (§ 3.65 et

heard at even greater distances.' seq.), that can be used to allow for

3.43 The fourth condition is differences in the ambient conditions,

brought about by the very high temper- but for the present it will be sufficient to

atures in the thermosphere, the region of state the general conclusions. With inthe atmosphere above an altitude of creasing altitude of both target and burst

about 60 miles (Fig. 9.126). Blast point, the overpressure at a given diswaves ar, ducted in the thermosphere so tance from an explosion of specified

'The situations described here and in § 3.43 could also be considered as temperature inversions.
MODIFICATIO)N OF AIR BLAST PHENOMENA 95

yield wiil generally decrease. Corre- which the blast wave passes. In considspondingly, an ircrease may usually be ering the effects of the surface, a disexpected in both the arrival time of the tinction is made ,',eiween ideal (or nearly

shock front and in the duratioe, of the ideal) and n..nideal surface conditions.

positive phase of the blast wave. For An "ideal" surface is define:d as a perelevaticas of less than 5,000 feet or so tectly flat surface that reflects all (and

above sea level, the changes are smadl, ab.;oros none) of the eiiergy, both thcrand since most surface targets are it mal (heat) and blast, that strikes it. No

lower altitudes. it is rarely necessary to area of the earth's surface is ideal in this

make the corrections. sense, but some surfaces behave almost

3146 The effect when the burst and IPke idea! surfaces and they are classitarget are at different eievations, ý'uch as fled as "nearly ideal." Fqr an ideal (or

for a high air burst, is somewhat more nearly i'Jeal) surface the properties of

complex. Since th2 blast wave is in- the blast wave are essentially free of

fluenced by changes in air temperaturc mechanical and thermal effects. If the

anJ pressure in the atmosphere through surface is such that these effects are

which it travel-,, some variations in the significant, it is said to be "nonideal."

pressure-distarnc- relationship at the ?.48 The terrain phenomena desurface might be expected. Within the scribed in § 3.35 et seq. are examples of

range of significant damaging o'erpres- mecharical factors that can change the

sures, these differences are small for characteristics of the blast wave. In

weapons of low energy y~eld. For gzneral, the nature of the reflecting surweapons of high yield, where the blast face can affect the peak ove.pressure

vw.ae travels over appreciably longer and the formation auid growth of the

distances, local variations, such as. tem- Mach stem. Absorption of some of the

perature inversions and refraction, may blast tnergy in the ground, which will

be expected. Consequertly, a detailed be considered in § 3.51, is to be reknowledge of ,ne atmosphere on a par- garded as another type of mechanical

ticular day would be necessary in order effect on the blast wave due to a nonto make precise calculations. For plan- ideal surface.

ning purposes, however, when the tar- 3.49 Many surfaces, especially

get is at an appreciable elevation above when the explosion can raise a cloud of

sea level the ambient conditions at the dust, are nonideal because they absorb

target altitude are used to eva!uate the substantial amounts of heat energy. In

correction factors referred to above, these .ircumstances, the properties of

the blast wave may be modified by the

SURFACE EFFECTS foi'mntion of an auxiliary wave, called a

"precursor," that precedes the main in3.47 For a given height of burst and cident wave. The characteristics of the

explosion energy yield, some variation blast wave will then be quite different

in blast wave characteristics may be from those that would be observed on an

expected over differtnt surfaces. These ideal (oi nearly ideal) surface. Precursor

variations are determined primarily by phenomena, which are complex, are

the type and extent of the surface over discussed more fully it, § 3.79 et seq.

A __

- . . . . . . . -1 4
96 AIR BLAST PHENOMENA IN AIR AND SURFACE BURSTS

3.50 Somewhat related to the con- blast wave immediately above it. For

dition of the surface are the effects of large overpressures with long positiveobjects and material picked up by the phase duration, the sliock will penetr, t!,

blast wave. Damage may be caused by some distance into the ground, but blast

missles such as rocks, boulders, and waves which are weaker and of shorter

pebbles, as well as by smaller particles duration are attenuated more rapidly.

such as sand and dust. This particulate The major principal stress in the soil

matter carried along by the blast wave will be nearly vertical and albout equal in

does not necessarily affect the overpres- magnitude to the air blast overprCssure,

sures at the shock front. In dusty areas, fhese matters will be treated in more

however', the blast wave may pick up detail in Chapter VI.

e-,,ugh dust to increase the dynamic

pressure over the values corresponding 3.52 For a high air burst, the blast

to the overpressure in an ideal blast overpressures are expected to be rellwave. There may also be an increase in tively small at ground leel; the effects

the velocity of air particles in the wave of ground shock ;nduced by air blast

due to precursor action. Consequently, will then be negligible. But if the overthe effect on structures which are dam- pressure at the surface is large, there

aged mainly by dynamic pressure will may be damage to buried structures.

be correspondingly increased, espe- However, even if the structure is strong

cially in regions where the precursor is enough to withstand the effect of the

strong. ground shock, the sharp jolt resulting

from the impact of the shock wave can

GROUND SHOCK FROM AIR BLAST cause injury to occupants and damage to

loose equipment. In areas whcre the air

3.51 Another aspect of the blast blast pressure is high, certain public

wave problem is the possible effect of an utiilties, such as sewer pipes and drains

air burst on underground structures as a made of relatively rigid materials and

result of the transfer of some of the bNast located at shallow depths, may be damwave energy into toe groLnd. A minor aged by earth movement, but relatively

oscillation of the surtace is experienced flexible meta! pipe will not normally be

ard a ground shock is produced. The affected. For a surface burst in which

strength of this shozk at any point is cratering occurs, the :iituation is quite

determined by the overpressure in the different, as will be seen in Chapter VI.

TECHNICAL ASPEC IS OF BLAST WAVE PHENOMENA4

PROPERTIES OF THE IDEAL BLAST chapter, and the remaining sections will

WAVE be devoted mainly to a consideration of

some of the quanti.ative aspects o, blast

3.53 The characte.is ics of the blRst wave phenomena in air The oasi- relawave hav2 been discussed in a qualita- tionships among the properties of a blast

tive manner in the earlier parts of this wave having a sharp front at which there

4The remaining :;ections of this chapter may be omitted without loss of continuity.

*1
TECFNICAL ASPECTS OF BLAST WAVE PHENOMENA 97

is a sudden pressure discontifuity, i.e., The particle velocity (or ?eak wind vea true (or ideal) shock front, are derived locity behind the sho(k front), u, is

from the Rankine-Hugoniot conditions given by

based on the conservation of mass, energy, and momentum at the shock front. 1 + 3'+ i 12

These conditions, together with the U = +P 2-y 

equation of state for air, permit the

derivation of the requi~ed relations involving the shock velocity, the particle 5p- 5p

(or wind) velocity, the overpressure, the 7Po ( + 6 p/7 P0)

112

dynamic pressure, and the density of the The density, p, of the air behind the

air behind the ideal shock front. shock front is related to the ambient 3.54 The blast wave properties in density, pa' by

the region of regular reflection are

somewhat complex and depend on the

angle of incidence ot the wave with the p = 2yP1, + (y + ')p

grournd and the overpressure. For a N1 2-yP0 + (-y- I)p

contact surface burst, when there is but

a single hemispherical (merged) wave, 7

as stated in § 3.34, and in the Mach 7

region below the triple point path for an The dynamic pressure, q, is defined by

air burst, the various blast wave characteristics at the shock front are uniquely q = '/2 PU2,

related by the Rankine-Hugoniot equa- so that it is actually the kinetic energy

tions. It is for these conditions, in which per unit volume of air immediately bethere is a single shock front, that the hind the shock front; this quantity has

fiilowing results are applicable, the same dimensions as pressure. Intro3.55 The shock velocity, U, is ex- duction of the Rankine-Hugoniot equapressed by tions for p and u given above leads to

-y+ I p)12 the relation U = c( + 2-y ' P, __) ' p2

where co is the ambient speed cf sound q 2yP0 + (-y - I)p

(ahead of the shock front), p is the peak _ 5 p 2

overpressure (behind the shock front), T 7 ± + (3.55.1 )

P) is the ambient pressure (ahead of the

shock), and -y is the ratio of the specific between the peak dynamic pressure in

heats of the medium, i.e., air. If y' is air and the peak overpressure and aintaken as 1.4, which is the value at bient pressure. The variations of shock

moderate temperatures, the equation for velocity, particle (or peak wind) velocthe shock velocity becomes ity, and peak dynamic pressure with the

peak overpressure at sea level, as

U6 ,/2 derived from the foregoing equations,

U c 0 P= / are shown graphically in Fig. 3.55.

*1_ _-
98 AIR BLDAST PHENOMENA IN AIR AND SLRFA(CE BURSTS

4 .4 40

2 ?0 2 20

z

z 10

S7 . .. 0_ 7 U - - 7 L7 - X

0 V

z 4V nr"4 4 . ... U-,_ -4 u0 nr_

UjU

0D

U) 2 -J 0.2

3nJ >wa f

Q_ -

0 I<

W-

< -- W 74 -..0.4

2,: 2a -- 0.4

z..._ -IJ 1I 0-0. I

1 2 4 7 10 20 40 70 100

PEAK OVERPRESSUPE (PSI) .

Figure 3.55. Relation of ideal blast wave characteristics at the shock front to peak ,

S~overpressure. ,
TE.CH1-ICA I. ASPECTS O-F HI AS] W1 VE PHLN()NM11 N\ 99

3.56 When the blast wave strikes a rival of the shock fro,:n and p is the p-eak

flat surface, such as that of a s;ructure. overpr4,2sure. is g.ven as a function of

at normal incidence, i.e., head on, the the "norivalized" time. . where

instantaneous (peak) value of the re- is the duralion (o the overpressure posiflected overpressire. p,. is given by tire phase. The parameter indicated on

each curve is ihe peak overprý ssure to

p, = 2p +- (-y + I )q. (3.56.!) which that curvc refers It :s seen.

1 air, therefore, that the variation of the norUpon using equation (3.55.1 for malized (and actual' oerpressure v.with

time depends on the peak overpre,ýsure.

Values of r for various burst conditions 7 + 4'P p (3.56.2) e given in Fig. 3.76.

3.58 Similarly, the variatin of the

It can be seen from equation (3.56.2) normalized dynam;c pressure, (A'1(. that the value of p, i-proaches 8p for with the normalized time. t/It , where rvery large values of the incident over- is the duration of the dynamic pressure

pressure and dynamic pressure (strong positive phase, depends on the peak

shocks), and tends toward 2p for small value of the dynamic pressure. This is

overpressurcs and small dynamic pres- shown by the curves in Fig. 3.58 for

sures (weak shocks). It is evident from several indicated values of the peak dyequation (3.56. 1) that the inctease in the namic pressure- values of r required for

reflected overpressure above the ex- use with this figure will be found in Fig.

pected value of twice the incident value, 3.76. !t should be noted ýhat, since the

i.e., 2p, is due to the dynamic (or wind) duration of the dynamic pressure posipressure. The reflected overpressure tive phase is somewhat longer than that

arises from the change of momentum for the overpressure. i.e., t - is longer

when the moving ait changes direction than r , Figs. 3.57 and 3.58 do not have

as a result of striking the surface. P. a common time base.

curve showing the variation of the in- 3.59 Arlotf:er important blast d.imstantaneous (peak) reflected pressure, age parameter is the "impuise," which

with the peak incident overp:'essure, for takes into z.'ount the duration of the

normal incidence on a flat surface, is positive phase and the variation of the

included in Fig. 3.55. overpiessure during that time. Impulsc

3.57 The equations in § 3.55 give (per unit area) may be denned as 1ý' ý

the peak values of the various blast total aie,. under the curve for the variaparameters at the shock front. The vari- tion of overpressure with time. The

ation of the overpressure at a given point positive phase overpressure impulse

with time after its arrival at that point (per unit area), P•, may then be reprehas been obta;ned by numerical integra- sented mathematically by

tion of the equations of motion and the t+

results are represented in Fig. 3.57. In f= = ' p(t)dt,

these curves the "normalized" overpressure, defined by p(t)/p, where p(t) is where p(t) is ubtaincd Afrom Fig. 3.57 for

the overpressure at time t after the ar- any overpressure between 3 and 3,000

It:( HNI( Al ASP(TS O)F I1 ASI WAVE PH|'NON4 ),*NA 101

> 0.4

',II I

0.65

0 0.8

(,,

psi

z

15

75

LU

0• 0.2 0. 0.6 . . 0. . 1- 0. LIJ

of th nryyed ulscl et aeZ

3 0.0.4' 0. 0. .

shown this relationship between 0(3.61.0 distance and encý-gy yield to hold for yieldsI

up to (and including) the megaton As stated above, the reference exolosion

range. Thus, cube root scaling may be is conveniently chosen :.s having an enapplied with confidence over a wide ergy yield of I kilotont ý,o that W, = 1.

range of explosion energies. According It follows, therefore, from equation

to this taw, if D1) is the distance (or slant (3.6 1. 1) thal

rangz) from a ieference explosion of W, D =D, x 1-, (.12

kilotoaý at which a certain overpressure ~ 3.12

or dynamic pressure is attained, then for where D, refers to the slant range from a

any (xplosion of W kilotons energy I -kiloton explosion. Consequently, if

these same pressures will occur at a the distance D is specifiedl, then the

distance D) given by va~lue of the explosion energy, W, reI , 
102 AIR BL1AST PHENOMENA IN AIR AND SURrACE BURSTS

quired to produce a certain effect, e.e.. bursts wilh !he same scaled height) may

a given peak ovprpressute, can be cal- be expressed in the form

culated. Alternatively, if the e,'ergy, W.

is -pecified, the appropri' ,ange, D, r d W

can be evalukiied from equation 1 = dl W1

(3-61.2). and

3.62 When comparing air bursts

having different energy yields, it is 1 d _ W'"I

convenient to intruduce a scal-d height -d W!, of bi.rst, defined as where t, represents arrival time or posiScaled height of burst tive phase duration and 1, is the lositivc

Actual height of burst phase impulre for a retf' once explosion

of energy W,, and t ,rt,! I refer to any

explosion of energy v ., as before, d,

For explosions of different energies and d ae distances from ground zero. If

having the same scaled height of burst, W, is taken as I kiloton, then the

the cube root scaling law may be applied ;,.•rious quantities are related as follows:

to distances from ground zero, as well

as to distances from the explosion.

Thus, if di is the distance from ground and

zero at which a particular overpressure I* x W1,3 at a distance d---d x IV•'.

or dynamic pressure occurs for a Ikiloton explosion, then for an explosion Examples of the use of the equatri•,ns

of Wkiiotons energy the same pressures developed above will be given later.

will be observed at a disianc,' d determined by the relationship

ALTITUDE CORRECTIONS d= dI × W '.• (3.62.1)

This expression can be used for calcu- 3.64 The data presented (§ 3.55 et

lations of the type referred to in the seq.) for the characteristic properties of

preceding paragraph, except that the a blast wave are strictly applicable to a

distances involved are from ground zero homogeneous (or uniform) atmosphere

instead of from the explosion (slant at sea level. At altitudes below about

ranges). 5,000 feet, the temperatures and pres3.63 Cube root scaling can also be sures in , atmosphere do not change

applied to airival time of the shock very much from the sea-level values.

front, positive phase duration, and pos- Consequently, up to this altitude, it is a

itive phase impulse, with the under- reasonably good approximation to treat

standing that the distances concerned the atmosphere as bking homogeneous

are themselves scaled according to the with sea-level properties. The equations

cube root law. The relationships (for given above may thus be used without

'The symbol dis used for thce ditance from ground zero, whereas DLrefers to the slant range, i.e., the

distance from the actual burst.
TECHNICAL ASPECTS OF BLAST WAVE PHENOMENA 103

correction if the burst and target are both feet, the temperature and pressure at a

at altitudes up to 5,000 fect. If it is mean altitude rmay be used. But if the

iequired to determine the air blast pa- altitude difference is ,.onsiderable, a

rarneters at altitudes wnere the ambient good approximation is to apply the corconditions are appreciably different rection at the target altitude (§ 3.46).

from those at. sea level, appropriate cor- For bursts above about 40,000 feet, an

rection factors must be applied, allowance must be made for changes in

3.65 The general relationships the explosion energy partition (§ 3.67.)

which take into account the fact that the 3.66 In order to facilitate calculaabsolute temperature T and ambient tions based on the equalions in the prepnessure P arc not the same as TO and P0 ceding paragraph, the following factors

respectively, in the reference (I-kiloton) have beer, defined and tabulated (Table

explosion in a sea-level atmosphere, are 3.66):

as follows. For the overpressure p P

P- (,.65.1) s 0

where p is the overpressure at altitude =d

and p, is that at sea level. The corrected

value of the distance from ground zero P 3 T 1/2

for the new overpressure level is then S,

given by

so that d = dlW"' 1 (3.65.2) p pS (3.66.1)

D = Di WIS,. and

A sinilar expression is applicable to the d did, Wsa . (3.66.2)

slan, iange, D. The arrival time of positive phase duration at this new distance IW (3.66.3)

is 1/ 3 (- '2 I I WIW SS" (3.66.4)

t = t I W1 3IR U) i (12

"P TThe reference values P0 and To are for a

(3.65.3) standard sea-level atmosphere. The at- The factor (T//T7W'- appears in this ex- mospheric pressure P0 is 14.7 pounds

pression because the speed of sound is per square inch and the temperature is

proportional to the square roct of the 59'F or 15'C, so that To is 5190 Rankine

absolute temperature. For impulse at al- or 2880 Kelvin. In a strictly hormogentitude, the appropriate relatio,'i;hip is eour, atmosphere the altitude scaling

2/3 1/2 factors SP, Sd' and S, woutd all be unity

I = I( W1/3p) / and equations (3.66.1), etc., would re-

(3,65..1 duce to those in § 3.65. qelow an alti-

(3.65.4) tutde of about 5,000 feet the scaling

The foregoing equations are applicable factors do not differ greatly from unity

when the target and burst point are at and the approximation of a homogenroughly the same a'iitude. If the alti.ude eous (sea-level) atmosphere is not

difference is less than a few thousand seriously in error, as mentioned above.

.L.... . ,----..
104 AIR BILAST PHENOMENA IN AIR AND SURFACE BURSTS

Table 3.66

AVERAGE ATMOSPHV;k!C DATA FOR MID-LATITUDES

Altitude Scaling

Factors Speed

Altitude Temperature Prcssure of Sound

(feet) (degrees Kelvin) (psi) S, S, 5, (ft/sec)

0 288 14 70 1.() .0L 1.00 1,116

1,W(X) 286 1,. 17 0.96 1.01 '1.02 1,113

2,(XX) 284 13.66 0.93 1.03 1.03 1,109

3.0(X) 282 13.17 0.90 1.04 1.05 ,105

40,(X) 280 12.69 0.86 1.03 I .07 1. 10 1

5,(XX) 278 12.23 ,.' 83 1.06 1.08 1,097

10,(Xx) 268 I 0. II (1.6 .) 13 I. 17 I077

15.0(9) 258 8.30 (i.56 1.21 1.28 1,057

20.(XX) 249 6.76 0.46 1. y) I.39 1.037

25,0(X) 239 5.4t 0.37 1.39 i.53 I,0 i6

30,0X) 221) 4.37 0.30 1.50 1.68 995

35.(XX) 219 3.47 C.24 1.62 1.86 973

40.0(X) 217 2.73 0.19 1.75 2.02 968

45,0(X) 217 2.15 0.15 1.90 2,19 968

50,000 217 1.69 0.12 2.06 2.37 968

55,0(X) 217 1.33 0.091 2.23 2.57 968

60,0(X) 217 !.05 0.071 2.41 2.78 968

65,(XX) 217 0.83 0,056 2.61 3.01 968

70,0(X) 218 0.65 0.044 2.83 3.25 971

75,(XX) 219 0.51 0.635 3.06 3.50 974

80.(X) 221 0.41 0.028 3.31 3.78 978

85.0(X) 222 0.32 0.022 3.57 4.07 981

90,0V0 224 0.25 0.017 3.86 4.38 984

95,(XX) 225 0.20 0.01.W 4.17 4.71 988

100,W() 227 0.16 0.011 4.50 5.07 991

I I O,(XX) 232 (. 10 0.(X)70 5.23 5.82 1I00)3

120,000 241 0.067 0.0045 6.04 6.1 1,021

130W(X) 249 0.044 0.0030 6,95 7.47 1,038

140,000 258 0.029 0.0020 7.95 8.41 1,056

150,(X0 266 0.020 0. (X) 13 9.06 9.43 1,073

3.67 The correction factors in the partitioning of the energy compo-

§ 3.66 are applicable for burst altitudes nents when the burst occurs above

up to about 40,000 feet (about 7.6 40,000 feet. At such altitudes, part of

miles). Nearly all of the energy from the energy that would have contributed

nuclear explosions below this altitude is to the blast wave at lower altitude:; is

absorbed hy air molecules near the emitted as thermal radiation.

burst. Deviations from the scaling laws 3.68 To allow for the smaller fracdescribed in the precedin- paragraphs tion of the yield that appears as blast

are caused principally by differences in energy at higher altitudes, the actual
TECHNICAL ASPECTS OF BLAST WAVE PHENOMENA 105

yield is multiplied by a "blast efficiency the general discussion already prefactor" to obtain an effective blast sented. These curves show the variation

yield. There is no simple way to for- of peak overpressure, peak dynamic

mulate th. bast efficiency factor as a pressure, arrival time, and positive

function of altitude since, at high alti- phase duration woh distance from

tudes, overpressure varies with distance ground zero for various heights of burst

in such a manner that the effective blast over a nearly ideal surface. Similar

yield is different at different distances. It curves may also be constructed for other

is possible, however, to specify upper blast wave parameters, but thu- ones

and lower limits on the bWast efficiency presented here are 'generally considered

factor, as shown in Table 3.68 for sev- to be the mosi useful. They apply to

eral altitudes. By using this factor, to- urban targets as well as to a wide variety

gether with the ambient pressure P and of other approximately ideal situations.

the absolute temperature Tat the obser- 3.70 From the curves giv,ýn below

vation point (or target) in the equations the values of the blast wave properties

in § 3.65 (or § 3.66), an Tstimate can &c can be determined for a free air burst or

made of the upper and lower limits of as observed at the surface for an air

the blast parameters. An example of burst at a particular height or for a

such an estimate will be given later. contact surface burst (zero height). The

peak overpressures, dynamic pressures,

Table 3.68 and positive phase duration times obBLAST EFFIC'ENCY FACTORS FOR tained in this manner are the basic cdta

HIGH-ALTITUDE PURSTS to be used in determining the blabt

Burst Altitude Blast Efficiency Factor loading and response of a target to a

(feet) Upper Limit Lower Limit nuclear explosion under specified con-

-- ditions. The procedures for evaluating

40,000 1.0 0. the blast damage to be expected -re

60,000 1.0 0.8 discussed in Chapters IV and V.

90,000 0.9 0.6

120,000 0.7 0 4 3.71 The standard curves give the

150,000 0.4 0.2 blast Aave properties for a 1-kiloton

"TNT equivalent explosion in a sea-level

STANDARD CURVES AND atmosphere. By 'means of these curves

CALCULATIONS OF BLAST WAVE and the scaling laws already presented,

PROPERTIES the corresFlnding properties can be calculated for an explosion of W-kilotons

3.69 In order to estimate th,.. dm- energy yield. Examples of the use of the

age which might be expected to occur a curves are given on the pages racing the

a particular range fror, a given explo- figures. It should be borne in mind that

sion, it is necessary to define the the data have been computed for nearly

characteristics of the blast wave as they ideal conditions and that sigrifizant devary with time and distance. Conse- viati6ns may occur in practice.

quently, standard "height of burst" 3.72 The variation of peak overcurves of the various air blast wave pressure with distance from a 1 -kiloton

properties are given here to supplement TNT equivalent free air burst, i.e., a

-•: "'_
106 AIR BLAST PHENOMENA IN AIR AND S';RPFAC( BURSUS

burst in a homogeneous atinosphcre Figs. 3.73a. h, and c. A horizontal line

where no boundaries or sur ;-es are iF drawn i., the desired height of burst

present, for a standard sea-level atmos- and theit the ground distances for spephere is shown in Fig. 3.72. This , i.rve. cific values of the peak overpressure can

together with the scaling laws and alti- be read off. These curves differ from the

tude corrections described above, may one in Fig. 3.72 for a fren air burst

be used to predict incident overpressures oecause they include the effect of refrom air burvts for those cases in which flection of the blast wave at the earth's

the blast wave arrives at the target surface. 4. curve for peak overpressure

without having been reflected from any versus distance from ground zero for a

surface. Other blast wave characteristics contact surface burst can be obtained by

may be obtained from the Rankine- taking the height of burst in Figs. 3.73a,

Hugoniot equations (§ 3.55 et seq.). b, and c to be zero.

3.73 The curves in Fig. 3.73a 3.75 The curves in Fig. 3.75 indi-

(high-pressure range), Fig. 3.73b (in- cate the variation of the peak dynamic

termediate-pressure range), and Fig. pressure along the surface with distance

3.73c (low,-pressure range) show the from ground zero and height of burst for

variation withl distance from ground a I -kiloton air burst in a standard seazero of the peak overpressure at points level atmosphere for nearly ideal surface

near the ground surface for a i-kiloton conditions. Since height-of-buit charts

air burst as a function of the he;ght of indicate conditions after the blast wave

bilrst. The corresponding data for other has been reflected from the surface, the

explosion energy yields may be ob- curves do not represent the dynamic

tained by use of the scaling laws. The pressure of the incident wave. At

curves are applicable to a standard sea- ground zero the wind in the incident

level atmosphere and to nearly ideal blast wave is stopped by the ground

surface conditions. Deviations from surface, and all of the incident dynamic

these conditions will affect the results, pressure is transformed to static overas explained in previous sections (cf. pressure. Thus, the height-of-burst

§ 3.35 et seq., also § 3.79 et seq.). It is curves show that the dynamic pressure

seen from the figures, especially for is zero at ground zero. At other locaoverpressures of 30 pounds per square tions, reflection of the incident blast

inch or less, that the curves show a wave produces winds that at the surface

pronounced "knee." Consequently, for must blow parallel to the surface. The

any specified overpressure, there is a dynamic pressures associated with these

burst height that will result in a max- winds produce horizontal forces. It is

imum surface distance from ground zero this horizontal component of the dyto which that overpressure extends. This namic pressure that is given in Fig.

is called the "optimum" height of burst 3.75.

for the given overpressure. 3.76 The dependence of the posi3.74 The variation of peak over- tive ph,'3e duration of the overpressure

pressure with distance from ground zero and of the dynamic pressure on the disfor an air burst at any given height can tance from ground zero and on the N

be readily derived from the curves in height of burst is shown by the curves in
TECHNICAI ASPECTS OF BI.AST WAVE PHENOMENA 107

Fig. 3.76, the values for the dynamic sures (§ 4.06 footnote) to be used ill

pressure duration are in parentheses. As determining target loadipg and rein the other cases, the results apply to a sponse. However, further reflection is

1-kiloton explosion in a standard sea- possible at the front face of a structure

level atmosphere for a nearly ideal sur- when it is struck by the blast wave. The

face. It will be noted, as mentioned magnitude of the reflected pressure pr(U)

earlier, that for a given detonation and depends on the side-on pressure p and

location, the Juration of the positive the angle, a, between blast wave front

phase of the dynamic pressure is longer and the struck surface (Fig. 3.78a). The

than that cf the overpressure. values of the ratio p,(ox)/p as a function

3.77 The curves in Figs. 3.77a and of angle of incidence for various indib give the time of arrival of the shock cated side-on pressures Lire given in Fig.

front on the ground at various distances 3.78b. It is seen that for normal incifrom ground zero as a function of the dence., i.e., when a = 00, the ratio

height of burst foi a I-kiloton explosion p,(a)/p is approximately 2 at :ow overunder the usual conditions of a sea-level pressures and inc.eases with the overatmosphere and nearly ideal surface. pressure (§ 3.56). The curves in Fig.

3.78b are particularly applicable in the

3.78 The peak overpressures in Mach region where an essentially vertiFigs. 3.74a, b, and c, which allow for cal shock front moving radially strikes a

reflection at the ground surface, are reflecting surface such as th! front vall

considered to be the side-on overpres- of a structure (see Fig. 4.07).

,Text continued on page 124.)

A..
108 AIR RLA..i PA-ENOMEMA IN AIR AND SURFACE BURSTS

The curve in Fig. 3.72 shows the From Table 3.68, this upper limit for a

variation of peak overpressure with uis- burst at an altitude of 100,000 feet is

tance for a I KT free air burst in a somewhat less than 0 9 Henice, the efstandard sea-level atmosphere. fective yield is approximately

Scaling. For taigets below 5,000 0.9W 0.9 x 2

feet and for burst altitudes below 40,000 1.8 MT 1,800 KT.

feet, the range to which a given peak

overpressure extenids for yields other The shortest distance from burst point

than I KT scales as the cube root of the to target, i.e., where the overpressure

yield, i.e., would be largest, is

D = DI X W,/3, D = 100,000 - 60,000 = 40,000 feet.

where, for a given peak overpressure, From equation (3.66.2), the corre

D, is the distance (slant range) from the sponding dis.ance from a 1 KT burst for

explo.iion for 1 KT, and D is the dis- sea-level conditions is

tance from the explosion for W KT.

(For higher target or burst altitudes, see D D

§ 3.64 et seq.) W13' Sd

From Table 3.66, S, at the target

altitude of 60,00 feet is 2.41; hence;

Example D 40,000 1

(1,800)1/3"' 2.41

Given: A 2 MT bu~rst at an altitude

of 100,000 feet. = 1,360 fe,!.

Find: The highest value of peak From Fig. 3.72, the peek ,verpresoverpressure that reasonably may be sure at a ci.Aiance of 1,360 feet from a I

expected to be incident on a target (an KT ,,ee air burst at sea-levi corditions

aircraft or missile) at an altitude o! is 4.2 psi. The corresponding eV',Lr60,000 feet. pressure at an altitude &r 60,000 feet is

Solution: The blist ficiency factor obtained from equation (3.66. 1) aad

is based on the burst altitude, but the Table 3.66; thus

altitude S,--aling faciors are based on target altitude (§ 3.64). The highest value p = p1 S = 4.2 x 0.071

of peak overpresswe will occur with the = 0.30 psi.

upper limit of the blast efficiency factor. Answer

SI

I

I
IT(HNICAI. ASPECTS OF BLAST WAVE PHENOMEN,, 109

2000 - 7 FTTT

1000 t500 ....... ......... ...............

200 ............... .

, ! (n

a- 5

,-I-. -1 05) ----- -

0.

x1 50 . . . \i --

05 .. . 2.. .. .. L 4 2 ...3 

10 2 . . . . . 2 .. 10 3. 42 . 3 . X.

DISTANCE FROM BURST ( ET)

Figure 3.72 Peak ove-rpressure from a I-kiloton free air 'iurst for sea-level ambient

conditions.

1 _ _ _ _
110 AIR BLAST PHENOMENA IN AIR AND SURFACE BURSTS

The curves in Fig. 3.73a show peak Example

overpressures on the ground in the

high-pressure range as a function of Given: An 80 KT detonation at a

distance from ground zero and height of height of 860 feet.

burst for a I KT burst in a standard Find: The distance from ground

sea-level atmosphere. The broken line zero to which 1 000 psi overpressure

separates the regular reflection region extends

from., the Mach region and indicates Solution: The corresponding height

where the triple point is formed (§ 3.24 of burst for I KT, i.e., the scaled

et seq.). The data are considered appro. heigtlt, is

priate to nearly ideal surface conditions.

(For terrain surface, and meteorologi- h h_ 860 206 feet.

cal effects, see §§ 3.35-3.43, §§ 3.47- h V 11 (80),/.4

3.49, and § 3.79 et seq.) d = di WII'

Scaling. The height of burst and 110 x (80)' 475 fzet

distance from ground zero to which a Answer.

given overpressure extends scale as the

cube root of the yield, i.e., From Fig. 3.73a, an overpressure of

1,000 psi extends 110 feet from ground

d _ h - W zetc for a 200-foot burst heighi for a I

di hi KT weapon. The corresponding distance for 80 KT is

where, for a given peak oveipressure, da

and h, are distance from ground zero d = di W13' =

ano height of burst for I KT, and dand 110 × (80) - 475 feet.

h are the corresponding distaoce and Answer.

height of burst for W KT. For a heipht

of burst of 5,000 feet or less, a homo- The procedure described above is appligeneous sea-level atmosphere may be cable to similar problems for the curves

assumed. in Figs, 3.73b and c.

4

A

)

-. -I- -- . ---.-----.- "
TLCIINICAL A;PIECTS 677- BLAST WAVE PHENOMENA11

500 100 p s,

400- __ -

REGULAR /

%.20 0 REFLECTION

REGION_

-300

500 MACH

~REFLECTION

Lt/ REGION

0

i-200

10000_

0

010200 300 400

DI8%'TANCE FROM GROUND ZERO (FEET)

Figure 3.73ai. Peak overpi essures on the ground for a I -kiloton burst :high-pressure range).
112 AIR BLAST PHENOMENA IN AIR AND SURFACE BURSTS

The curves in Fig. 3.73b show peak Example

overpressures on the ground in the i-ntermediate-pressure range as a functioc, Given: A 100 KT detonation at a

of distance from ground zero and height height of 2o320 feet.

of buist for a I KT burst in a standard Find: The peak overpressure at

sea-level atmosphere. The broken ,ine 1,860 feet from ground zero.

separates the regulai reflection region Solution: The corrc•,,ponding height

from the Mach region and indicates of burst for 1 KT is

where the triple point is formed (§ 3.24

et seq.). The data are -oursidered appro- h h _2.320 = 500 feet.

priate for nearly ideal surface condi- W1,3 (100) 11

tions. (For terrain, surface, and meteor- and the ground distance is

ological etfects, see (§ 3.35-3.43, § 3.47-3.49, and § 3.79 et seq.). ,.- d _1,860 = 400 feet.

Scaling. The height of burst and the W- (100)1, 4

distance from ground zero to which a

given peak overpressure externds scale

as the cube rcot of the yield, i.e., From Fig. 3.73h, at a ground distance of

d h 400 feet and a burst height of 500 feet,

di hi = W-/3w the peak overpressure is 50 psi. Answerr d, h

where, for a given peak overpressure, d, The procedure described above is appliand h, are distance f",Vm grounj zero cable to similar problems for the curves

and height o1 burst for 1 KT, and d and in Figs. 3.73a and c.

h are the correspondirg distance and

height of burst for W t. '. For a height

of burst of 5,000 feet or less, a homogeneous sea-level atn"gphere may be

assumed.

A1

S!I
TECHNICAL ASPECTS OF BLAST WAVE PHENOMENA 113

2 0

CI

0

4)

__ ____Z

__ U3 _oh

00

ILL 4

w -i

I_ z __

0 cm

(131 isn O 1HO13H - -0
114 AIR BLAST PHI-NMENA IN AIR AND SURFA(- BURSTS

The curves in Fig. 3.73c show peak Example

overpressures on the ground in the lowpressure range as a function of distance Given: A 125 K" detonation.

from ground zero and height of burst for Find: The maximum distance from

a I KT burs! in a standard sea-level ground zero to which 4, p:si extends, and

atmosphere. The broken line separaw-s the height of burst at which 4 psi exthe regular reflection region from the tends to this distance.

Mach region -Pd indicates where the Solution: From Fig. 3.73c, the

triple point is formed (§ 3.24 et seq.). maximum ground distance to which 4

The data are considered appropriate for psi extends for a I KT weapon is 2,600

nearly ideal surface condit;ons. (For feet. This occurs for a ourst height of

terrain, surface, and meteorological ef- appioximately 1.100 feet. Hence, for a

fects, see N§ 3.35-3.43, §§ 3,47-3.49, 125 KT detonation, the required burst

and § 3.79 et seq.) height is

Scaling. The height of burst and the

distance from ground zero to which a 1,100 fe 12)

given peak overpressure extends scale = 5,500 feet.

as the cube root of the yield, i.e.,

This is sufficientiy close to 5,000 feet

d h W for a homogeneous atmosphere to be

di hi assumed. The distance from ground

zero is then

where, for a given peak overpressure, d,

and h, are the distance from ground zero d d I W113 = 2,600 x (I25)13

and height of burst for 1 KT, and d ard 13,000 feet. Answer. h are the corresponding distance and

height of burst for W KT For a height

of burst of 5,000 feet or less, a homo- The procedure described above is appligeneous sea-level atmosphere may be cable to similar problems for the curves

assunied. in Figs. 3.73a and b.

It

h|
TECHNICAl. ASPECTS OF BLAST WAVE PHENOMENA 15

~~0

0

I - 0

0

Ur

0

0 C.

21-

0 \LI rrr o

I r 0 

-J >

-- IZ - j~--- I - ~0 Z) J -

o (D LJo L- LL --- t ---- M.-t

o0 0 0 00

0 O0 0 0

(J.3?3.) Sifl8n JO iH!DI3H

ri
116 AIR BLAST PHENOMENA IN AIR AND SURFACE BURSTS

Examle

The curves in Fig. 3.75 show the

horizontal componenm of peak dynamic Given: A 160 KT burst at a ,eight

pressure on the ground as a function of of 3.000 feet.

distance from grounci zero and heighi of Find: The horizontal compfnent of

burst for a I KT burst in a standard peak dynamic pressure on the surface at

sea-level atmosphere. The data are con- 6,000 feet from ground zero.

sidered appropriate for nearly ideal sur- Solution: The corresponding height

face conditions. (For terrain, surface, of bu;rst for I KT is

and meteorological effects, see §§ h h 3,000 = 550 feet.

3.35-3.43, §§ 3.47-3.49, and § 3.79 et h W1/ (160)113

scq.)

Scaling. The height of burst and The corresponding distance t3r I KT

distance from ground zero tio which a is

given peak dynamic pressure value ex- d 6,000

tends scale as the cube root of the yield, - W1' (160), 1 I, 110 feet.

i.e.,

d = From Fig. 3.75, at a distance of 1.110

- = - wo, feet from ground 7.ero and a burst he -ht

d hI of 550 feet, ihe horizontal component of

where, for a given peak dynamic pres- the peak dynamic pressure is approxisure, h, and d, are the height of burst mately 3 psi. Answer.

and distance from ground zero for I KT, Calculations similar to those deand h and dare the corresponding height scribed in connection with Figs. 3.74a

of burst and distance for W KT. For a and c may be made for the horizontal

height of burst of 5,000 feet or less, a component of the peak dynamic preshomogeneous sea-level atmosphere may sure (instead of the peak overpressure)

be assumed. by using Fig. 3.75.

I
TEC'HNICAL ASPEC"IS Of- Fi A\ST WAVE PHENOME:NA i 17

0

-0

0~

0

OD 0

0

Io

0 M.

Lui

o UL o Z

LO)

_ 0

0 -

-04

0 00

-l MO0 0 0 0 0 o 0 0

0 0 0 0 0 0 0 0 0 0

.A- (1 - -]- 3A is~ne l* 
118 AIR BLAST PHENOMENA IN AIR NND SURFACE BURSTS

The curves in Fig. 3.76 show the Examplt

duration on the ground of the positive

phase of the overpressure and of the Given: A 160 KT explosion at a

dynamic pressure (in parentheses) as a heigrt of 3,000 feet.

function of distance from ground zero Find. The positive phase duration

and heigh! of burst for a 1 KT burst in a on the ground of (a) the overpressure,

standard sea-level atmosphere. The (b) the dynamic pressure at 4,000 feet

curves are considered appropriate for from ground zero.

nearly ideal surface conditions. Soltion: The corresponding height

Scaling. The required relationships of burst for I KT is

are

ah h 3,000 = 550 feet, d =h =t =W/'W1 (6)'

di hi ti and the corresponding dista,,ce from

where d1, h,, and t, are the distance from ground zero is

ground zero, the height of burst, and

duration, respectively, for I KT; and d, d= - __ = 4,_", = 740 feet.

h, and t are the corresponding distance, W113 0 00)IP3

height of burst, and duration for WKT. (a) From Fig. 3.76, the positive phase

For a height of burst ot 5.000 feet or duration of the ovepressure for a I KT

less, a homogeneous sea-level atmos- at 740 feet frcm ground zero and a burst

phere may be assumed. heigh: of 550 feet !s 0.18 second. The

corresponding duration of the overpressure positive phase for 160 KT is,

therefore,

t = tiW1.3 = 0.18 x (160);'3

= 1.0 second. Answer.

(b) From Fig. 3.76, tl'- nositive phase

duration of the dynamic ý.:ressure for I

KT at 740 feet from grot: z -o and a

burst height of 550 feet is ( 14 second.

The cortesponding duration of the dynamic pressure positive plase for 160

KT is, therefore,

I = ti 4,= 0.34 x (160) 13

= 1.8 second. Answer.

I __I
TECHNICAL ASPECTS OF BLAST WAVE PHENOMENA I 19

0

0 - O. 1 ro

0

0

0 ci

0

0• 0

o o 2

o I~.0 LL

.8 Ll

> ' / ~z ~

=O .- ,-

/0

•____ _ _ _ _ o 0 O

-r-- r .•

-0 -

I '

i __ __ _ _ _ _--~ cr .~-

0

0 D

___~C .. -- -- _ _

___ 0

!0

. I0 0

___ 0

L1 _

•0 0 0 0 0 0 0 0 0

"0 0 0 0 0 0 0

(1333) ISdfl6 An i 11513H

-A _,
120 AiR BLAST PHENOMENA IN AIR AND SURFACE BURST3

The curves in Figs. 3.77a and b give Example

the time of arrival in seconds of the blast

wave on the ground as a function of Given: A I MT explosion at a

distance from ground zero and height of height of 5,000 feet.

burst for a 1 KT burst in a standard Find: The time of arrival of the

sea-level atmosphere. The curves are ý,last wave at a distance of 10 miles

considered appropriate for nearly ideal ground zero.

surface conditions. Solution: Tne correspo:iding burst

Sca!ing. The required relationships heL.,,t for I KT is

are

h 5,000 500 feet.

d h t W r" (I,000)I/

dI hI tI The corresponding distance from

where d, hI, and t, are the distance from ground zero for I KT is

ground zero, height of burst, and time of D 5,280x 10

arrival, respectively, for I KT, and d, h, d1 =- _,•_ - , 5,280 feet.

and t are the corresponding distance,

height of burst, and time for W KT. For From Fig. 3.77b, at a height of burst of

a height of burst of 5,000 feet or less, a 500 feet and a distance of 5,280 feet

homogeneous sea-level atmosphere may from ground zero, the arriva! time is 4.0

I.e a:sumed, seconds for 1 KT. The corresponding

arrival time for I MT is

I = ti WI = 4.0 x (I,000)111

= 40 seconds. Answer.

_ _ _ _ _ _ _, _'
TECHNICAL ASP~ECTS OF BLAST WAVE PHENOMENA 121

ý0.60 E

6L,00 E

(j)

0.5

0.0

0.2

0 200 400 600 800 1,000 1,200

DISTANCE FROV GROU:JD ZE140 (FEET)

Figure 3.77a. Airiv'al times on the around of blast wvave for 1-kiloton burst (early times;).

4,000

3,000

IL

0

2,000 - - M 1 RELCO4

L______0N____
122 AIR BLAST PHENOMENA IN AIR AND SURFACE BURSTS

The reflected overpressure ratio p,,, I p Example

is plotted in Fig. 3.78b as a function of

the angle of incidence of the blast wave Gi ve Atho re: k a sirfic

front for various values of the peak at t uP. pe angle oe of .35.. t5a c

(side-on) overpressure. The curves

apply to a wave front s;triking a reflect- Finrpr es res

ing surface, such as a wall of a struc- overpressure. tu re.Solution. From Fig. 3.78b. the reture. flected overpressure ratio, p,,,/p, for 50

!, = reflected blast wave overpres- psi and an angle of incidence of 350 is

sure for any given angle of in- 3.6, hence,

cidence (p:si).

p = initial peak incident overpres- Pr051 = 3.6p 3.6 x 50

sure (psi). = Ig0 -. i. Answer.

ot = angle between the blast wave

front and the reflecting surface

(degrees).

. " BLAST WAVE FRONT

a

nEFLECTING SURFACE

Figure 3.78a. Angle of incidence (o) of

blast wave front with refiecting surface.

I
TECHNICAL ASPECTS OF BL-AST WAVE PHENOMENA 1 23

___ 0

_ 0

UJ

C)

0

L41

--- --- ------- K z *

0 0

CLC

a:0

00

zU

00 to it 0

dl'd'OiI8 3nsS3d83O OiTIA
124 AIR BLAST PHENOMENA IN AIR AND SURFACE BURSTS

(Text continued from pape 107.) tends to the ground; if it does, the lower

portion is so weakened and distorted

THE PRECURSOR that it is not easily recognized. Between

the grcund and the bottom edge of the

3.79 The foregoing results have re- main shock wave is a gap, probably not

ferred to biast wave conditions near the sharply defined, through which the ensurfaces that are i'2eal or nearly ideal ergy that feeds the precursor may flow.

(§ 3.47), so that the Rankine-Hugoniot Ahead of the main shc.ck front, the blast

equations are applicable. When the sur- energy in the precursor is free not only

face is nonideal, there may be mechani- te follow the rapidly moving shock front

cal or thermal effects (or both) on the in the thermal layer, but also to propablast wave. Some of the phenomena gate upward into the undisturbed air

associated with mechanical effects were ahead of the main shock front. This

mentioned in § 3.48. As a consequence divergirg flow pattern within the preof thermal nonideal behavior, the over- cursor tends to weaken it, while the

pressure and dynamic pressure patterns energy which is continually fed into the

can be distorted. Severe thermal effect, precursor from th.- main blast wave

are associated with the formation of a tends to strengthen the precursor shock

precuisor (§ 3.49) which produces sig.. front. The foregoing description of what

nificant changes in the parameters of the happens within a precursor explains

blast wave. some of the characteristics shown in

3.80 When a nuclear weapon is de- Fig. 3.81. Only that portion of the pretonated over a thermally nonideal (heat- cursor shock front that i% itt the preshock

absorbing) surface, radiation from the thermal layer travels faster than the

fireball produces a hot layer of air, re- main shock front; tl . energy diverging

ferred to as a "thermal layer," near the upward, out of this layer, causes the

surface. This layer, which often in- upper portion to lose some of its forward

cludes smoke, dust, and other particu- speed. The interaction of the precursor

late matter, 'orms before the arrival of and the main shock front indic",tes that

the blast wave from an air burst. It is the main shock is continually overiaking

thus referred Ito as the preshock thermal this upward-traveling energy. Dust,

layer. Intetaction of the blast wave with which may billow to heights of more

the hot air layer may affect the reflection than 100 feet, shows the upward flow of

process to a considerable extent. For air in the precursor

appropriate combinations of explosion 3.82 Considerable modification of

energ) yield, burst height, and heat-ab- the usual blast wave characteristics may

sorbing surfaces, an auxiliary (or sec- occur within the precursor region. The

ondary) blast wave, the precursor, will overpressure wave form shows a

form and will move ahead of the main rounded leading edge and a slhw rise to

incident wave for some distance. It is its peak amplitude. In highly disturbed

called precursor because it precedes the waveforms, the pressure jump at the

main blast wave leading edge may be completely absent.

3.81 After the precursor forms, the (Anr example of & measured overpresmain shock front usually no longer ex- sure waveform in the precursor region 's
TE('HNI(AI ASPECTS Of-' BASI WAVE PHENOMENA 125

REFLEC iED\ INCIDEN'

BLAST BLAST

WAVE WAVE

MACH STEM

REFLECTED IN;IDENT

BLAST ,LAST

WAVE WAVE

RPREC U RSOR

DUST/' PRESHOCK TNER,.1L LAYER DUST PRESHOCK THERMAL LAYER

EARLY DEVELOPMENT LATE DEVELOPMENT

Figure 3.81. Precursor characteristics.

given in Fig. 4.67a.) Dynamic pressure surface. Thermal effects on the blast

waveforms often have high-frequency wave are also expected to be small for

oscillations that i dicate severe turbu- contact surface bursts, consequently, it

lence. Peak amplitudes of the precursor is believed that in many situations,

waveforms show that the overpressure especially in urban areas, nearly ideal

has a lower peak value and the dynamic bast wave conditions would prevail.

pressure a higher pcak value than over a 3.84 For this reason, the curves for

surface that did not permit a precursor to various air blast parameters presented

form. The higher peak value of the dy- earlier, which apply to nearly ideal surnamic pressure is primarily attributable face conditions, are considered to be

to the increased density of the moving T~hle 3.83

mediumi as a result of the dust loading in

thu air. Furthermore, the normal Ran- EXAMPLES OF

kine-Hugoniot relations at the shock THERMALLY NEARLY IDEAL AND

front no longer apply. THERM kLLY NONIDEAL SURFACES

3.83 Examples of surfaces which Therma, ly Thermally Nonideal

are considered thermally nearly ideal Nearly 'deal (precursor may occur for

(unlikely to produce significant precur- (precursor unlikely) low air bursts)

sor effects) and thermally nonideal (ex- - -- I

pected to produce a precursor for suit- Water Desert sand

Ground covered by Coral able combinations of burst height aild white smoke Asphalt

ground distance) are given in Table Heat-reflecting Sdrface with thick !ow

3.83. Under many conditions, e.g., for concrete vegetatior.

scaled heights of burst in excess of 800 Ice Surface covered by dark

feet or at large ground distances (where Packed snow smoke

Moist soil with Most agricultural areas the peak overpressure is less than about spare vegetate.. Dry soil with spars:

6 psi), precursors are not expected to Commerc;-4 and indus- vegetation

occur regardless of yield and type of ,-.,i areas

I,
126 AIR BL.AST PHENOMENA IN AIR AND SURFA.CE BURSTS

most representative for general use. It the much higher theoretical factor for an

shou!d be noted, however, that blast ideal shock front as given by equation

phenomena and damage observed in the (3.56.2).

precursor region for low air bursts at the 3.85 Similarly. the dynamic presNevada Test Site may have resulted sure waveform will probably be irregu-.

fron1 nonideal behavior of the surface. lar (§ 3.82), but the peak value may be

Under such conditions, the overpressure several times that compjted from the

waveform may be irregular and maý, peak overpressure by the Rankineshow a slow rise to a peak value some- Hugoniot relations. Damage to and diswhat less than that expected for nearly placement of targets which are affected

ideal conditions (§ 3.82). Conse- by dynamic pressure may thus be conquently, the peak value of reflected siderably greater ii tne nonideal precurpressure on the front face of an object sor region for a given value of peak

struck by the blast wave may not exceed overpressure than under neariy ideal

the peak value of .he incident pressure conditions.

by more than a factor of two instead of

BIBLIOGRAPHY

*BANISTER, J. R.. and L. .1. VORT MAN, "Ef- Goifl sriNE. H. H., and J. Vo,,i NEUMANN,

fects of a Precursor Shock Wave on Blast "Blast Wave CalculAtions," Comm. on Pure

Loading of a Structure," Sandia Corporation, and Appl. Math. 8. 327 (1955.

Albuquerque, New Mexico. October 1960, LErHo, D. L. and R. A. LARSON, "Long Range

WT--1472. Propagatio;n of Spherical Shockwaves from Ex-

*Br•IHt:_ H. A., et al., "Biast W".vz," Univer- plostons in Air," U.S. Naval Ordnance Labosity of California, Los Alamos Scientific Labo- ratory, July 1969, NOLTR 69- 88.

ratory, March 1958, LA-2000. LIt-:PMANN, H. W.. and A. E. PucKPir,

BRINKI.FY, S. R , JR., and J. G. KIRKWOOD, "Aerodynamics of a Compressible Fluid,"

"Theory of the Propagation of Shock Wives." John Wiley and Sons, Inc , 1947.

Phys. Rev,.. 71, 606 (1947); 72, 1109 (1')47). PENNEv, W. G., D). E. J. SAMUELS, and G. C.

BRODE. H. L., "Numerical Solution of Spheri.'al ScoRi;Itu, "The Nuclear Explosive Yields at

Blast Waves," J. Appl. Phys. 26, 766 (1955) Hiroshima and Nagasaki," Phil. Tras. Roy.

BRODE, H. L., "Review of Nuclear Weapons Soc., A 266. 357 (1970,.

Effects," Ants. Rev. Nuclear Science. 18, I.0 RI-t), J. W., "Airblast from Plowshare Proj-

(1968). ects," in Proceedings for the Symposium on

BRODF, H. L., "Height o" Burst Fffects at High Public Health Aspects of Peaceful Uses of NuOverpressures,'' Rand Corporation, S-,.ita clear Explosives, Southwestern Radiological

Monica, California, July 197G, P'M-6301- Health Laboratory, April 1969, SWRHL-82, p.

DASA, DASA 2506. 309.

COURANi, R., and K. 0. FRIIEDRI(.HS, "Super. TAYILOR, G. I., "The For'nalion of a Blast Wave

sonic Flow and Shock Waves," lnterscicnce by a Very Intense Explosi-n," Proc. Roy.

Publishers, Inc.. )48. Soc.. A 201, 159, 175 (1950).

*U.S. Standard Atmosphere, U.S. Government

Printing Office, W-ishington, D.C., 1962, Supplements, 1966.

*These documents may be pturchased from the National Fechnical Information Service, U.S.

Department oi Commerce, Arlington, Virginia 22161,
CHAPTER i V

AIR BL.,AST LOADING

INTERACTION OF BLAST WAVE WITH STRUCTURES

INTRODUCTION This tend-, to cause crushing toward the

4.01 The phenomena associated ground, e.g., dished-in roofs, in addiwith the blast wave in air froti, a nuclear tion to distortion due io translationai

explosion have been treated in the pre- motion.

ceding chapter. The behavior of an ob- 4.03 The discussion of air blast

ject or structure exposed to such a wae loading for aboveground structures in

may be considered under two main the Mach region in the secdons that

headings. The first, called the "load- follow emphasizes the sitvation where

ing," i.e., the forces which result from 'he reflecting surface is nearly ideal

the action of the blast pressure, is the (§ 3.47) and the blast wave behaves,

subject of this chaptfr. The second, the normally, ;n accordance with theoretical

"response" or distortion of the structure considerations. A brief description of

due to the particular loading, 's irmated blast wave loading in the precursor rein the next chapter. gior (§ 3.79 et seq.) is also given. For

4.02 For an air burst, the direction convenience, the treatment will be

of propagation of the incident blast somewhat arbitrarily divided 'nto two

wave will be toward the ground at part;: one deals with "diffraction loadground zero. In the regular reflection ing," which is determined mainly by

region, where tLe direction of propa-a- the peak overpressure in the blast wave,

tion of the blast wave is not parallel to and the other with "draig loading," in

the horizontal axis of the structure, the which the dynamic pressure is the sigforces exerted upon structvres will also nificant property. It is important to mehave a considerable downward compo- member, however, that all structures are

nent (prior to passage w" the reflected subjected simultaneously to both types

wave) due to the reflected pressure of loading, siice the overpressire and

buildup on the horizontal surfaces. dynamic pressure cannot be separated,

Conseqv.,"nidy, in addition to the hori- although for certain structures one may

zontal loading, as in the Mach region be more important than the other.

(§ 3.24 et seq.), there will also be ini- 4.04 Details of tho Interaction of a

tially an appreciable downward force. blast wave with any structure are quite

127 !; i
128 AIR BLAST LOADING

comp'icated, particularly if ihe gecine- same pressure is exerted on the sides

try of the structure is comple'K . How- and the roof. The front face, however, is

ever-, it is frequently possible to consider still subjected to wind pressure, alequivalent simplified geometries, and though the back face is shielded from it.

blast loadings of several such geome- 4.07 The developments described

tries are discussed later in this chapter. above are illustrated in a simplified form

in Figs. 4.07a, b, c, d, e; 2 this shows, in

DIFFRACTION LOADING plan, successive stages of a structure

without openings which is being struck

4.05 When the front of an air blast by an air blast wave moving in a horiwave strikes the face of a structure, zontal direction. In Fig. 4.07a the wave

reflection occurs. As a result the over- front is seen approaching the structure

pressure builds up rapidly to at least wi`'1 the direction of motion perpendictwice (and generally several times) that ular to the face of the structure exposed

in the incident wave fitA. The actual to the blast. In Fig. 4.07b the wave has

pressure attained is determined by just reached the fror, face, producing a

various factors, such a, the peak over- high reflected overpressure. In Fig.

pressure of iw'e incident blast wave and 4.07c the blast wave has proceeded

the angle between the direction of mo- about halfway along the structure and in

tion of the wave and the face of the Fig. 4.07d the wave front has just

s•'ructure (§ 3.78). The pressure in- passed the rear of the structure. The

crease is due to the conversion of the pressure on the front face has dropped to

kinetic energy of the air behind the some extent while the pressure is buildshock front into internal energy as t1e ing up on the back face as the blast wave

rapidly moving air behind the shock diffracts around the structure. Finally,

front is decelerated at the face ot the when the wave front has passed cornstructure. Th, reflected shock fro-t pletely, as in Fig. 4.07e, approximately

propagates back into the air in all dir%.c- equal air pressures are exerted on the

tions. The high pressure region expands sides and top of the structure. A presoutward towards the surrounding re- sure difference between front and back

gio-:s of lower pressure. faces, due to the wind forces, v.'ill per4.06 As the wave front moves foi- sist, however, during th vhole positive

ward, the uellected overpressure on the phase of the blast wave. If the structure

fa. '-Re structure drops rapidly to tha' is oriented at an angle to the blast wave,

produced by the blast wave without re- the pressure would immediately bc exfledtion, I plus an added drag force due erted on two faces, instead of one, but

to the wind (dynamic) prcssure. At the the general characteristics of the blast

same time, the air pressure wave bends loading would be similar to that just

oc "diffracts" around the structure, so described (Figs. 4.07f, g, h, and i).

that the structure is eventually engulfed 4.08 The pressure differential beby the blast, and approximately the tween the front and back faces will have

'This is often referrc~t to as the "side-on overpres~ure." since it is the same as that experienced by the

side of the structure, where there is no appreciable reflection.

2A more detailed treatment is given later in this chapter.
INTERACTION OF BLAST WAVE WITH STRUCTURES 129

I- iP ---

a b c d e

-{ /K

Figure 4.07. Stages in the diffraction of a blast wavc by a structuce %ithout openings (plan

view).

its maximum value when the blast wave gulfed the structure (M-g. 4.07e or

has not yet completely surreunded the 4.07i), the pressure differential is small,

strueture, as in Figs. 4.071b, c, andn d o; and the loading is due almost ooti,'ely to

g and h. Such a pressure diffcrenia, will the drag pressure3 exerted on the front

produce a lateral (or translational) force fac'ý. The actua! pressures on all faces of

tending to cause the structure to deflect the structute are in excess of the ambient

and thus move bodily, usually in the atmospheric pressure and will remain

same direction as the blast wave. This so, although decreasing steadily, until

force is known as the "diffraction load- the positive phase of the blast wave has

ing" because it operates while the blast ended. Hence, the diffraction loading on

wa',, is being diffracted around the a structure without openings is eventustructure. The extent and nature of the ally replaced by an inwardly directed

response will depend uporn the size, pressure, i.e., a compression or squeezshape, and weight of the structure and in,,, action, combined with the dynamic

how firmly it is attached to the ground. pre,•sure of the blast wave. In a structure

Other chara.teristics of the structure are with no openings, the loading will cease

also important in determining the re- only when the overpressure drops to

sponse, as will be seen later. zero.

4.09 When the blast wave has en- 4.10 The damage caused during the

'The drag pressure is the product of :he dynow'ic pressure and the drag coefficient (§ 4.29).

* 1 . . ,
130 AIR BLAST I.OADING

diffraction stage will be determined by DRAG (DYNAMIC PRESSURE)

the magnitude of the loading and by its LOADING

duration. The loading is related to the 4.12 During the whole of the overpeak overpressure in the blast wave and pressure positive phase (and for a short

this is consequently an important factor. time thereafter) a structure will be subIf the structure under consideration has jected to the dynamic pressure (or drag)

no openings, as has been assumed so loading caused by the transient winds

far, the duration of the diffraction load- behind the blast wave front. Under

ing will be very roughly the :ime re- nonideal (precursor) conditions, a dyquired for the wave front to move from namic pressure loading of varying

the front to the back of the building, strength may exist prior to the maximum

although wind loading will continue for overpressure (diffraction) loading. Like

a longer period. The size of the structure the diffraction loading, the drag loading,

will thus affect the diffraction loading, especially in the Mach region, is equivFor a structure 75 feet long, the diffrac- alent to a lateral (or translational) ftrce

tion loading will operate for a period of acting upon the structure ',r obiect exabout one-tenth of a second, but the posed to the blast.

squeezing and the wind loading will 4.13 Except at high blast overprespersist for a longer time (§ 4.13). For sur.-s, the dynamic pressures at the face

thin structures, e.g., telegraph or utility of a structure are much less than the

poles and smokestacks, the diffraction rveak overpressures due to the blast wavc

period is so short that the corresponding and its reflection (Table 3.07).. Howloading is negligihie. ever, the drag loading on a structure

4.11 If the building exposed to the persists for a longer period of time,

blast wave has openings, or if it has compared to the diffraction loading. For

windows, panels, light siding, or doors example, the duration of the positive

which fail in a very short space of time, phase of the dynamic pressure on the

tiere will be a rapid equalization of ground at a slant range of I mile from a

pressure between the inside and outside I-megaton nuclear explosion in the air is

of the structure. This will tend to reduce almost 3 seconds. On the other hand,

the pressure differential while diffrac- the diffraction loading is effective only

tion is occurring. The diffraction load- for a small fraction of a second, even for

ing on the structure as a whole will thus a large structure, as seen above.

be Jecreased, although the loadiag on 4.14 It is the effect of the duration

interior walls and partitiors will be of the drag loading on structures which

greater than for an essentially closed constitutes an important difference bestructur',, i.e., one with few operings. tween nuclear ind high-explosive detoFurthermore, if the bui!ding has many nations. For the same peak overpressure

openings, the squeezing (crushing) ac- in the blast wave, a nuclear weapon will

tion, due to the pressure being higher prove to be more destructive than a

outside than inside after the diffraction conventional one, especially for buildstage, will not occur. ings which respond to drag loading.
INTERACTION OF BLAST WAVE WITH STRUCTURES 131

This is because the blast wave is of front and rear exists during the whole of

much shorter duration for a high-explo- tt'is period. Examples of structures

sive weapon, e.g., a few hundredths of which respond mainly to diffraction

a second. As a consequence of the loading 9re multistory, reinforced-conlonger duration of the positive pha'se of crete buildings with small window area,

the blast wave from weapons of high large wall-bearing structures such aS

energy yield, such devices cause more apartment houses, and wood-frame

damage to drag-sensitive structures buildings such as dwelling houses.

(§ 4.18) than might be expected from 4.17 Because, even with large

the peak overpressures alone, structures, the diffraction loading will

generally be operative for a fraction of a

STRUCTURAL. CHARACTERISTICS second only, the duration of the blast

AND AIR BLAST LOADING wave positive phase, which is usually

much longer, will not be significant. In

4.15 In analyzing the response to other words, the length of the blast wave

blast loading, as will be done more full,. positive phase will not materially affect

in Chapter V, it is convenient to con- the net translational loading (or the resider structures in two categories, i.e., suiting damage) during the diffraction

diffraction-type structures and drag-type stage. A diffraction-type structure is,

structures. As these n--nes imply, in a therefore, primarily se!,sitive to the peak

nuclear explosion the former wouid be overpressure in the blas! wave to which

affected mainly by diffraction loading it is exposed. Actually it is the assoand the latter by drag loading. It should ciated reflected overpressure on the

be emphasized, however, that the dis- structure that largely determines the

tinction is made in order to simplify the diffraction loading, and this may be

treatment of real situations which are, in several times the incident blast overfact, very complex. Although it is true pressure (! 3.78).

that some sti'.ictures will respond mainly 4.18 Wh,' :he pressures on difto diffract; in forces and others mainly to ferent areas of a structure (or structural

drag fomces, actually all buildings will element' are quickly equalized, either

respond to both types of loading, The because: of its sma!l size, the characrelativt. impoitance of each type of teristics of the structure (or element), or

loading in causing damage will depend the rapid formation of numerous openupon the type of structure as well as on ings by action of the blast, the diffracthe characteristics of the blast wave. tion forces operate fiwr a very short time.

These facts should be borne in mind in The response of the structure is then

connection with the ensuing disct;usion. mainly due to the dynamic pressure (or

4.16 Large buildings having a drag force) of the blast wind. Typical

moderate!y small window and door area drag-type structures are smokestacks,

and fairly strong exterior walls respond ielephone poles, radio and television

mainly to diffraction loading. This is transmitter towers, electric transmission

because it takes an appreciable time for towers, and truss bri.ges. In all these

the blast wave to engulf the building, cases the diffractiou of the blast wave

and the pressure differential between afound the structure or its component

6_
132 AIR BLAST LOADING

elements requires such a very short time very soon after the blast wave strikes the

that the diffraction processes are neglig- structue, so that the frame is subject to

ible, but the drag loadirng may be con- a relatively small diffraction loading.

siderable. The distortion, or other damage, sub4.19 The drag loading on a struc- sequently experienced by the frame, as

ture is determined not only by the dy- well as by narrow elements of the

namic pressure, but also by the si.apc of structure, e.g., coiumns, beams, and

the structure (or structural element). The trusses, is then caused by the drag

shape factor (or drag coefficient) is less forces.

for rounded or streamlined objects than 4.21 For structures which are funfor irregular or sharp-edged structures or damentally of the drag type, or which

elements. For example, for a unit of rapidly become so because of loss of

piojected area, the loading on a tele- siding, the response of the structure or

phone pole or a smokestack will be less of its components is determined by both

than on an I-beam. Furthermore, the the drag loading and its duration. Thus,

drag coefficient can be either positive or the damage is dependent on the duration

negative, according to circumstances of the positive phase of the blast wave as

(§ 4.29). well as on the peak dynamic pressure.

4.20 Steel (or reinforced-concrete) Consequently, for a given peak dynamic

frame buildings with light walls made of pressure, an explosion of high energy

asbestos ccment, aluminum, or corru- yield will cause more damage to a

gated steel, quickly become drag-sensi- drag..type structure than will one of

tive because of the failure of the walls at lower yield because of the longer duralow overpressures. This failure, accom- tion of the rositive phase in the former

panied by pressure equalization, occurs case (see § 5.48 et seq.).

INTERACTION OF OB.IJCTS WITH AIR BLAST 4

DEVELOPMENT OF BLAS r LOADING the following sections, The second stage

is treated in Chapter V.

4.22 The usvial procedure for pre- 4.23 The blast loading on an object

dicting blast damage is by an analysis, is a function of both the incident blast

supported by such laboratory and full- wave characteristics, i.e. - the peak

scale observations as may be available. overpressure, dynamic pressure, decay,

The analysis is done in two stages: first and duration, as described in Chapter

the air blast loadiig on the particular III, and the size, shape, orientation, and

structure is determined; and second, an response of the object. The interaction

evaluation is made of the response of the of the incident blast wave with an object

structure to this loding. The first stage is a complicated process, for which a

of the analysis for a number of idealized theory, supported primarily by c-,peritargets of simple shape is discussed in mental data from shock tubes and wind

'The remaining (more technical) sections of this chapter may be omitted without loss of continuity.

I ___ ________ ,_
INIITRA("ION (1W )13.1Fj("S W'I-I AIR IrI AS1 1 33

tunnels, has been developed. To reduce may be from two to eight times as great

the complex problem of blast loading to as the incident overpressure (§ 3 56).

reasonable terms, it will be assumed, for The blast wave then bends (or diffracts)

tiL present purpose, that (I) the over- around the cube exerting pressures on

pressures of interest are less than 50 the side.; and top of the object, and

pounds per square inch (dynamic pres- finally on i~s back face. The object is

sures less than about 40 pounds per thus engulfed in the high pressure of the

square inch), and (2) the object being blast wave and this decays with time,

loaded is in the region of Mach reflec- eventually returning to ambient condition. tions. Because the reflecied pressure on

4.24 To obtain a general id-a of the the front face is greater than the pressure

blast loading process, a simple object, in the blast wave above and to the sides,

namely, a cube with one side facing the reflected pressure carnnot be maintoward the explosion, will be selected as tained and it soon decays to a "stagnaan e,.mple. It will be postulated, fur- tion pressure," which is the sum of the

ther, that the cube is rigidly attached to incident overpressure and the dynamic

the ground surface arid remains motion- (drag) pressure. The decay time is

],hss when subjected to the loading. The roughly that required for a rarelaction

blast wave (or shock) front is taken to be wave to sweej from the edges of the

of such size compared to the cube that it front face to the center of this face and

can be considered to be a plane wave back to the edges.

striking the cube. The pressures referred 4.26 The pressures on the sides and

to below are the average pressures on a top of the cube build up to the incident

particular face. Since the object is in the overpressure when the blast front arrives

region of Mach reflection, the blast front at the points in question. This is folis perpendicular to the surface of the lowed by a short period of low pressure

ground. The front of the cube, i.e., the caused by a vortex formed at the front

side facing toward the explosion, is edge during the diffraction process and

normal to the direction of prepagation of which travels along or near the surface

the blast wave (Fig. 4.24). behind the wave front (Fig. 4.26). After

4.25 When the blast wave strikes the vortex has passed, the pressure rethe front of the cube, reflection occurs turns essentially to that in the incident

producing reflected pressures which blast wave which decays with time. The

air flow causes some reduction in the

loading to the sides and top, because, as

'" BLAST WAVE FRONT will be seen in § 4.43, the drag pressure

here has a negative value.

4.27 When the blast wave reaches

the rear of the cube, it diffracts around

the edges, and travels down the back

surface (Fig. 4.27). The pressure takes a

certain time ("rise time") to reach a

Figure 4.24. Blast wave approaching cube more-or-less steady state value equal to

7 rigidly attached to ground. the algebraic sum of the overpressure

I
134 AIR BLAST LOADING

BLAST WAVE FRONT and the drag pressure. The latter is related to the dynamic pressure, q(t), by

VORTEX-) the expression

- Drag pressure = C,#t),

where Cd is the drag coefficient. The

value of Cddepends on the orientation of

the particular face to the blast wave

front and may be positive or negative.

Figure 4.26. Blast wave moving over The drag pressures (or loading) may

sides and top of cube. thus be correspondingly positive or

negative. The quantities p(t) and q(t)

BLAST WAVE FRONT represent the overpressure and dynamic

pressure, respcctively, at any time, t,

VORTEX - after the arrival of the wave front

(§ 3.57 et seq.).

4.30 The foregoing disciissio,- has

referred to the loading on the various

surfaces in a general manner. Foi a

Figure 4 27. Blast wave moving down particular point on a surface, the loading

redr of cube. depends also on the distance from the

point to the edges and a more detailed

treatment is necessary. It should be

and the drag pressure, the latter having a noted that only the gross characteristics

negati,,e value in this case also (§ 4.44). of the development of the loading have

The finite rise time results from a weak- been described here. There are, in actual

tening of the blast wave front as it dif- fact, several cycles of reflected and

fracts around the back edges, accom- rarefaction waves traveling across the

panied by a ternp-rary vortex action, surfaces before damping out, but these

and the time of ti'ansil of the blast wave fluctuations are considered to be of

froni the edges to the center of the back minor significance as far as damage to

face. the structure is concerned.

4.28 When the overpressure at the

rear of the cube attains the value of the EFFECT OF SIZE ON LOADING

overpressuire in the blast wave, the dif- DEVELOPMENT

fraction process may be considered to

have terminated. Subsequently, essen- 4.31 The loading on each surface

tially steady state conditions may be may not be as important as the net

assumed to exist until the pressures have horizontal loading on the entire object.

returned to the ambient value prevailing Hence, it is necessary to study the ret

prior to the arrival of the blast wave. loading, i.e.. the loading on the front

4.29 The total loading on any given face minus that on the back face oi the

face of the cube is equal to the algebraic cube. The net horizontal loading during

sum of the respective cverpressure, p(t), the diffraction process is high because
INTERACTION OF OBJECTS WITH AIR BLAST 135

the pressure on the front face is initially pressure and dynamic pressure loadings,

the reflected pressure and no loading has rather than by any one component of the

reached the rear face. blast loading.

4.32 When the diffraction piocess is

completed, the overpressure loadings on EFFECT OF SHAPE ON LOADING

the front and back faces are essentially DEVELOPMENT

equal. The net horizontal loading is then

relatively small. At this time the net 4.35 The description given above

loading consists primarily of the dif- for the interaction of a blast wave with a

ference between front and back !oadings cube may be generalized to apply to the

resulting from the dynamic pressure loading on a structuie of any other

loading. Because the time required for shape. The reflection coefficient, i.e.,

the completion of the diffraction process the ratio of the (instantaneous) reflected

depends on the size of the object, rather oveipressure to the incident overpresthan on the positive phase dJuration of sure at the blast front, depends on the

the ithcident blast wave, the ditfraction angle at which the blast wave strikes the

loading impulse per unit area (§ 3.59) is structure. For a curved structure, e.g., a

greater for long objects than for short sphere or a cylinder (or part of a sphere

ones. or cylinder), th' reflection varies from

4.33 The magnitude of the dynamic point to point on the front surface. The

pressure (or drag) loading, on the other tin.e of de-cay from reflected to stagnahand, is affected by the shape of the tior, p:essure then depends on th,. size of

obiect and the duration of the dynamic the struc'ture and the location of the

pressure. It is the latter, and not the size point in q,'tstion on the front surface.

of the object, which determines the ap- 4.36 The drag coefficient, i.e., the

plication time (and impulse per unit ratio of the drag pressure to the dynamic

area) of the drag loading, pressure (§ 4.29), varies with the shape

4.34 It may be concluded, there- of the structure. In many cases an

fore, that, for large objects struck by overall (or average) drag coefficient is

blast waves of short duration, the net given, so that the net force on the surhorizorntal loading during the diffracticin face can be determined. In other inprocess is more important than the dy- stances, local coefficients are necessary

namic pressure loading. As the object to evaluate the pressures at various

becomes smaller, or as the dynamic points on the surfaces. The time of

pressure duration becomes longer, e.g., buildup (or rise time) of the average

with weapons of larger yield, the drag pressure on the back surface depends on

loading becomes increasingly impor- the size and also, to some extent, on the

tant. For classification purposes, objects shape of the structure.

are often dsci-ibed as "diffraction tar- 4.37 Some structures have frangible

gets" or "diag targets," as mentioned portions that are easily blown out by the

earlier, to indicate the loading mainly initial impact of the blast wave, thus

responsin~le For dama,.e. Actually, all altering the shape of the object and the

objects are damaged by the total load- subsequent loading. When windows are

ing, which is a combination of over- blown out of an ordinary building, the

A _ _ - _ .,
136 AIR BLAST LOADING

blast wave enters and tends to equalize dures described may provide nc more

the interior and exterior pressures. In than a rough estimate of the blast loadfact, a structure may be designed to ing to be expected.

have certain parts frangible to lessen 4.39 As a general rule, the loading

damage to all s ~h.",,,"-..v of the analysis )f a diffraction-type structure is

structuwe. Thus, the response of certL-in extended only until the positive phase

elements in such cases influences the overpressure falls to zero at the surfa,.e

blast loading on the structure as a under consideration Although the dywhole. In general, the movement of a namic pressure persits after this time,

structural element is not considered to the value is so small thj' the drag force

influence the blast loading on that ele- can be neglected. However, for dragment itself. However, an exception to type structures, the analysis is continued

this rule arises in the case of an aircraft until the dynamic pressure is zero. Durin flight when struck by a blast wave. ing the negative oc~rpressure phase,

both overpressure and dynamic pressure

BLAST LOADING-TIME CURVES are too smnall to have any significant

effect onf structures (§ 3.11 et seq.).

4.38 The procedures whereby 4.40 The blast wave characteristics

curves showing the air blast loading as a which need to be known for the loading

function of time may be derived are analysis and their symbols are sumgiven below. The methods presented are marized in Table 4,40. The locations in

for the following five relatively simple Chapter III where (he data may be obshapes: (I) closed box-like structurc; (2) tained, at a specified distance from

partially open box-like structure, (3) ground zero for an explosion of given

openl frame struture; (4) cylindrical energy yield and height of b'irst. are

structure; aiid (5) semicircular arched ?,so indicated,

structure. These methods can be altered 4.41 A closed box-like structure

somewhat for objects having similar may be represented simply by a parallecharacteristics. For very irregularly lepiped, as in Fig. 4.41, having a length

shaped structures, however, the proce- L, height H, and breadth B. Structures

Tattle 4.40

BLAST WAVE CHARACTERISTICS FOR DETERMINATION OF LOADING

Propert Symbhol Source

Peak overpressure p Figs. 3,73a, h, and c

Time variation of overpressure pM) Fig, 3.57

Peak dynamic pressure q Fig, 3.75

Time variation of dynamic pressure q(t) Fig. 3.5$

Reflected overpressure p Fig. 3.79h

Duration of positive phase of

overpressure t IL Fig. 3.76

Duration of positive phase of

dynamic pressure Fig. 3.76

Blast front ishock) velocity U Fig 3,55
INTERAý'TION OF OBJECTS WITH AIR BLAST 137

L

H

- 5.

Figure 4.41. Representation of closed box-like strkicturc.

with a flat roof and walls of approxi- Front Face. -- The firm;t step is to determately the same blast resistance as the mine the reflected pressure, p,- thi:s

frame will fall into this category. The gives the pressure at the time t = 0,

walls have either no openings (doers when thc blast wave fr-nt strikes the

and windows), or a small number of front face (Fig. 4.42). Next, the tme, t,

such openIings up to about 5 percent of is calculated at which the stagnation

the total area. The pressures on the in- pressuie, p,, is first atained. It has been

tcrior of the structure then remain near found from hIboratory studies that, for

the ambient value existing before the peak ove:'pre'sures being considzred (50

arrival of the blast wave. while the out- pounds per square inch or less), t, cal. be

side ik subjected to blast leading. To represented, to a good approximation,

simplify the treatment, it will te sup- by

posed that one side of the structure faces 3S

toward the explosion and is perpendicu- t -

lar to the direction of propagation of the

Hias: wave. This side is called the front where S is equal to Hor B/2, whichever

face. The loading diagrams are corn- is less, and U is the blas;t frint (shock)

puted below for (a) the front face!, (b) velocity. rhe drag coefficient for the

the side and top, and (c) the back face. front face is unity, so that the drag

By combining the data for (a) and (c), pressure is here eqjual to the dynamic

the net horizontal loading is obtained in pressure. The stagnation pressure is thus

(A').

4.42 (a) Average Loading on p,= [(t,) + q(t),

*1
138 AIR BLAST LOADING

where p() and q(I,) are the overpes- ing at the distance L12 from the front of

.;ure and dynamic pressure at the time t. the structure, so that

The average pressure subsequently

decays with time, so that, Al = P L + Cjq

Pressure at time ! t p(t) + q(t),

where t is any time between t, and t,ý The drag coefficient on the sides and top

The pressure-time curve for the front of the structure is approximately -0.4

face can thus be determined, as in Fig. for the blast pressure range under con4.42. sideration (§ 4.23). The loading in4.43 0() A verage Loading on Sides creases from zero at t = 0 to the value p,,

and Top.--blthough loading comn- at the time LJU, as shown in Fig. 4,43.

mences immediately after the blast wave Subsequently, the average pressure at

strikes the front face, i.e., at t = 0, the any time t is given by

sides and top are not fully loaded until P aU-p

the wave has traveled the distance L, Pressure at timet = -

i.e., at times i = LJU. The average

pressure, p,,, at this time is considered to + CA

be the overpressure plus the drag load- + Ciq -

Pr

Lu

,o,

G.s

I .//-- p'00)+-W')

0

TIME

Figure 4.42. Avcrage front face loading of closed box-fike structure.

'I__
INTERACTION OF OBJECTS WITH AlP, II AST ;39

p,,- - --

w

U,,

C', W p t +;qt

0:1 ý )+ 2j,(-jU

CL

0 D 2 J

TIM•E

Figure 4.43. Average sidt: and top loading of closed box-like structure.

where t lies between LVU and r, + for the postulated blast pressure range. P

i.J2U, as seen in Fig. 4.43. The over- The average pressure at any time tafter

pressute and dynamic pressure, rspec- ti,. attainment of p, is represented by

tively, are the values at the time t -

U2I.1. Hence, the overpressure on the Pressure at time t =

sides and top becomes zero at time r ± ( L ) . dq- U / Lry.U. p t- -0-

4.44 (c) Average Loading n•, Jack

Fa.o.-The shock front arrives at the where t lies between (L + 4S)/U and

back face at time L/U, bui it requires an tU + L/U, as seen in Fig. 4.44.

additional time, 4S/U, for the average

pressure to build ul to the value P, (Fig. 4.45 (d) Net Horizontal Load4.44), where Ph ij given approximatcly ing.-The net loading iL; equal io the

by front loading minus the toack loading.

This subtraction is best performed

r.L=+4 S + Cq (_+4S graphically, as shown in Fig. 4.45. The

\ U U left-hand dia-ram gives the individual

front and back loading curves, as

SlHere, as before, S is equal to H or B/2 derived from Figs. 4.42 and 4.44, rtwhichever is the sinaller. The drag co- spect*ve~y. The difference indicated by

C. efficient on the back face is about -0.3 the shaded region is then transferred to

,;t
140 AIR BLAST LOADING

Pb

+ Cdq(-'

UU

U, Ip

CL&

U TIME

Figure 4.44. Average back face Ioa.,ing of closed box-like structure.

w ccFRONT C

uJ I

TIME TM

Figure 4.45. Net horizontal loading of dlosed box-like stru pure.

w

wJ wI

tZ

SA
INTlFRA(!ION 01: OlJll•S Wi4t1 AIR HI \S1T 1'1I

the right-hand diagram to give the act 4.47 (a) A i'erage L.,ading on Front

pressure. The net loading is necessary Face.-The outside loading is comfor determining the frame response, puted in the same manner as that used

whereas the wall actions are governed for a closed structure, except that S is

primarily by the loadings on the indi- replaced by S'. The quantity S' is the

vidual faces. average distance (for the entire front

.ace) from the certer of a wall section to

PARTIALLY OPEN BOX-LIKE an open edge of the wall. It reptesents

STRUCTURES the average distance which rarefaction

4.46 A partially open box-like waves must tiavel on the front face to

structure is one in which the front and reduce the reflected pressures to the

back wals have about 30 percent of stagnation pressure.

opening., or window area and no interior 4.48 The pressure on the inside of

partitions to influence the passage of the the front face starts rising at zero time,

blast wave. As in the previous case. the because the blast wave immediately

loading is derived for (a) the front face, enters through the openings, but it takes

(b) the sides ard roof, (c) the back face, a time 2L/U to reach the blast wave

and (d) the net horizontal loading. Be- overpressure value. Subsequently, the

cause the blast wave can now enter the inside pressure at any time t is given by

inside of the structure, the loading-time p(t). The dynamic pressures are ascurves must be considered for both the sumed to be negligible on the interior of

exterior and interior of the structure. the structure. The variations of the inPr

w

:3 -- U,

0. OUTSIDE p(/)+q(t)

0 3_s 2L 4+

U V TIME

Pigure 4.48. A verage front face loading of partially open box-like structure.

'7
142 AIR BLAST LOADING

OUTSIDE p(1--•L) + C,/ t

Io I NS IDE p (t - )

I II

0 2 2L * L

I +

U u TIME 2U

Figure 4.49 Average side and top loading of partia!ly open box-like structure.

side and the outside pressures with time dynamic pressure is regarded as being

are as represented in Fig. 4.48. negligible (Fig. 4.50).

4.49 (b) Average Loading on Sides 4.51 (d) Net Horizontal Loadand Top.- The outside pressures are ing.-The net horizontal loading is

obtained as for a closed structure (§ equal to the net front loading, i.e., out4.43), but the inside pressures, as for side minus inside, minus the net back

the front face, require a time 2L/U to face loading.

attain the overpressure in the blast

wave. Here also, the dynamic pressures OPEN FRAME STRUCTURE

or, ihe interior are neglected, and side

wall openings are ignored because their 4.52 A structure in which small

effect on the loading is uncertain. The separate elements are exposed to a blast

loading curves are depicted in Fig. 4.49. wave, e.g., a truss bridge, may be re4.50 (c) Average Loading on Back garded as an open frame structure.

Face.-The outside pressures are the Steel-frame office buildings with a masame as for a closed structure, with the jority of the wall area of glass, and

exception that S is replaced by S', as industrial buildings with asbestos, light

described above. The inside pressure, steel, or aluminum panels quickly bereflected from the inside of the back come open frame structures after the

face, reaches the same value as the blast initial impact of the blast wave.

overpressure at a time LIU and then 4.53 It is difficuit to determine the

decays as p(t - L/U); as before, the magnitude of the loading that the frangI[
INiERACTION OF CHRJCTS WITH AIR BLAST 143

p

fINSIDE ~~ .

S~/

W

0- OUTSIDE p~f-k)+ Cdq(/t73L)

U uU

TIME

Figure 4.50. Average back face loauktig of partially open box-like structure.

ible wal' material transmits to the frame shielding of one member by adjacent

before fai!ing. For -114SS, the load trans- members, the problem must be simplimitted is assumed to be negligible if the flied. A recommended simplification -s to

loading is sufficient to fracture the glass. treat the loading a. an impulse, the

For asbestos, transite, corrugated steel, value of which is obtained in the folor aluminum paneling, an approximate lowing manner. The overpressure loadvalue of the load transmnitted to the ing impulse is determined for an average

frame is an impulse of O.C4 pound-sec- member treated as a closed structure anr

ond per square inch. Depending on the this is multiplied by the number of

span lengths and panel strength, the members. The resu!ting impulse is conpanels are not likely to fail when the sidered as being delivered at the time the

peak overpressure is less than about 2 shock front first strikes the structure, or

pounds per square inch. In this event, it can be separated into two impulses for

the full blast load is transmitted to the front and back faces where the majority

frame. of the elements are located, as shown

4.54 Another difficulty in the treat- below in Fig. 4.56.

ment of open frame structures arises in 4.55 The major portion of the hoadthe computations of the overpressure ing on an open frame struct're con•'its

loading on each individual member of thz drag loading. For an individual

during the diffraction piocess. B3ecause member in the open, the drag coefficient

this process occurs at different times for for I-beams, channels, angles, and for

various members and is affected by members with rectangular cross section
144 AIR BLAST LOADING

REAR WALL IMPULSE

0.04,Ab, + b,,,

Ixl

0

-_.__,.-FRONT WALL IMPULSE S• O.044f,, + /Inm

I--

IL I

2_0U

0 t+L

TIME

Figure 4.56. Net horizontal loading of an open frame structure.

is approximately 1.5. However, because The result may thus be written in the

in a frame the various members shleld form

one another to some extent from the full

blast loading, the average drag coefficient when the whole frame is consid- where A• = IA

ered is reduced to 1.0. The force F, i.e., 4.56 The o~e.Jing (force) versus

pressure multiplied by area, on in ind- time for a frame ot length L, having

vidual neember is thus given by major areas in the plazes of thc front and

rear faces, is shown in Fig. 4.56. The

F (member) = CAq(t)At, symbols A,, and Abw, represent the areas

where Cd is 1.5 and A, is ihe m..nber of the front and back faces, respecarea projected pernendicular to the di- tively, which transmit loads before failrection of blast propagation. For the ure, and lif. and I.. are the overpressure

loading on the frame, lhowevcr, the loading impulses on front and back

members, respectively. Although drag

loading commences immediately after

F(frame) = Cdq(t)Y.A•, t')e blast wave strikes the front faLe.

i.e., at t = 0, the back face is not fully

where Cd is 1.0 and YA, is the sum of loaded until the wave has traveled the

the projected areas : of all the members. distance L, i.e., at time I LIT. The 1
INTERACTION OF OBJECTS WITH AIR BLAST 145

average drag loading, q., on the entire ters are small compared to the lengths.

structure at this time is considered to be The discussion presented here provides

that which would occur at the distance methods for determining ave-age presL/2 from the front of the structure, so sures on projected areas of cylindrical

tlat structures with the direction of propagation of the blast perpendicular to the

q _k _ , axis of the cylinder. SCd A m ore detailed

\2U method for determining the pressuretime curves for points on cylinders is

and the average for,,ce on lhe frame, PI, provided in the discussion of the loading

(frame), is on arched structures in § 4.62 et seq.

The general situation for a blast wave

Fa(frame) = q _.A, approaching a cylindrical structure is

2U/ represented in section in Fig. 4.57.

4.58 (a) A verage Loadiag on Front

where C, is 1 .0, as above. After this Surface.-When an ideal blast wave

time, the average drag force on the impinges on a flat surface of a structure,

frame at any time t is given by the pressure rises instantaneously to the

L reflected value and then it soon diops to

F (frame) at time t =q t - LfA, the stagnation pressure (§ 4.25). On the 211 / curved surface of a cylinder the interaction of the blast wave with the front face

where t lies between L/U and t* + iq is much more complex in detail, However, in terms of the average pressure,

the load appears as a force that increases

CYLINDRICAL STRUCTURE with time from zero when the blast front

4.57 'rhe following treatment is ap- arrives to a maximum when the blast

plicable to structures with a circular wave has propagated one radius. This

cross section, such as telephone poles occurs at a time D/2U, where D is the

and smokestacks, for which the diame- diameter of the cylinder. For the blast

BLAST

WAVE D

FRONT

Figure 4.57. Representation of a cylindrical structure
146 AIR BLAST LOADINGi

U. 2P

V)

W

P N)+ Cdq(W

D 2D

TIME

Figure 4.58. Average pressure variation on the front face of a cylinder.

pressure range being considered, the Complex vortex formation then causes

maximum average pressure reaches; a the average pressure to drop to a minvalue of about 2p as depicted in Fig. 'MUM, P,2, at the time t = 3D/2U,- the

4.58. The load on the froi.t surface then value of PQ. is about half the maximum

decays in an approximately linear man- overpressure at this time, i.e.,

ner to ýhe value it would have at abtout

time t =2D/L'. Subsequently, the aver- I (3D

age pressure decreases as shown. The P 2 p P 2UJ

drag coefficient for the front surface of

the cylinder is 0.8. The average pressure on the side then

4.59 (b) Average Loading on the rises until time 9D/2 U and subsequently

Sides.-Loading of the sides com- decays as shown in Fig. 4.59. The drag

mences immediately after the blast wave coefficient for the side face is 0.9.

strikes the front surface but, as with the 4.60 (c) Average Loading on Back

closed box discussed in § 4.4! et seq., Surface.-The blast wave begins to afthe sides are not fully loaded until the fect the back surface of the 7ylinder at

wave has traveled the distance D, i.e., time D/2U and the average pressure

at time t =DIU. The average pressure gradually builds up to pb, (Fig. 4.60) at

on the sides at this time is indic~ated by a time of about 4D/UJ. The value of p,,, is

p,,, given approxi-nately by given by

P 2 
INTERACTION OF 0H14-.('TS WITH AIR III AST 147

'JJ

cr~) d(

2(. (1

PS 2 --

(10 3D 9D

TIME

Figure 4.59. Average pressure variation on the side face of a cylinder.

The average pressure continues to rise Consequently, the net horizontal loaduntil it reaches a maximum, P62, at a ing cannot be deterr Ited accurately Ir

time of about 20D/U, where the simple procesvi of subtracting thec ) back loading from 1he front loading. A

P6 = ( 20D \ + C ( 20D) rougi approximation of the net load

U U may be obtained by proccdures similar

to those described for a closed box-like

The average pressure at any time t after structure (§ 4.45), but a better approxthe maximum is represented by imation is given by the method referred

to in § 4.65 et seq.

Pres-are at time t =_ D)

2 U ARCHED STRUCTURES

D 4.62 The following treatment is ap-

+ Cqt- 2 U ) plicable to arched structures, such as

ground huts, and, as a rough approximation, to dome shaped or spherical

where t lies between 20D/UJ and r- + structures. The discussion presented

DIQ U. The drag coefficient for the back here is for a semnicylindrical structure

surface is -0.2. with the direction of propagation of the

4.61 The preceding discussion has bhast perpendicular to the axis of the

been concerned with aveIr'3e values of cylinder. The results can be applied to a

the loads on the various surfaces of a cylindrical structure, such as discussed

cylinder, whereas the actual pressures above, since it consists of two such

vary continuously from point to point. semicylinders with identical loadings on
148 AIR BLAST LOADING

D 40 200 +* +-

2U U LT 2U

TIME

Figure 4.60. Average pressure variation on the back face of a cylinder.

each half. Whereas the preceding treat- zontal distance, in the direction of

ment referred to the average loads on the propagation of the blast wave, between

various faces of the cylinder (§ 4.57 et the bottom of the arch and the arbitrary

seq.), the presert discussion describes point z.

the loads at each point. The general 4.63 When an ideal blast wave imsituation is depicted in Hig. 4.62; H is pinges on a curved surface, vortex forthe height of the arch (or tht radius of mation occurs just after reflection, so

the cylinder) and z represents any point that there may be a temporary sharp

on the surface. The angle between the prcssure drop before the stagnation

horizontal (or springing line) and thl pressure is reached. A generalized reI'Une ,oining z to the center of curvature presentation of the variation of the

of the semicircle is indicated by o; and pressure with time at any point, z, is

X, equal to H(I - cos a), is the hori- shown in Fig. 4.63. The blast wave

BLAST

WAVE --

FRONT z

Figure 4.62. Representation of a typical semicircular arched structure. i"

i I

*1
INIF'RAC'TION 01: O)JIJ ("-IS WI1iI A\IR lI A'SI 149

P,

Cr.

0.

ct

0 K

' IME

Figure 4.63. Typical ,e.,sure varia',ion at a point on an arched struiire subjected to a blast

wave.

front strikes the base of the arch at time t larger angles it is less. The rise time t

0 and the time of at rival at the point z, and the time intervals 1, and t,. coneregardless of whether it is on the front or sponding to vortex formation and atback half, is X/U. The overpressure tainment of the stagnation pressure, rethen rises sharply, in the time interval ti, spectively, after th'ý blast ,,wave reaches

io the reflected value, p,, so that t, is the the base of the arch, are also given in

rise time. Vortex formation causes the Fig. 4.64, in terms of the time unit H/U.

pressure to drop to p 2, and this is fol- The rise time is seen to be zero for the

lowed by an increase to pý, the stagna- front half of the arch, i.e., for ot betion pressure; subsequently, the pres- tween 0' and 900, but it is finite and

sure, which is equal to p(t) + Cdq(t), increases with ox on the back half, i.e.,

where Cd is the appropriate drag coeffi- for a o between 90' and 1800. The times

cient, decays in the normal manner. t2 and t, are independent of the angle c.

4,64 The dependence of the pres- 4.65 Since the procedures described

sures p, and p, and the drag coefficient above give the loads normal to the surCd on the angle ot is represented in Fig. face at any arbitrary point z, the net

4.64; the pressure values are expressed horizontal loading is not determined by

as the ratios to p , where p. is the ideal the simple process of subtracting the

reflected pressure for a fiat stLrface. back loading from that on the front. To

When ax is zero, i.e., at the base of the obtain the net horizontal loading, it is

arch, p, is identical with Pr, but for necessary to sum th, horizontai compoILL . • ..
150 AIR BLAST LOADING

1.0 '' -- -•"

./P ', 0.8 _ __ __ _ _ 10___ 

0.6 --- -pr-- p2

04 -- - -L-L_ 7 5 

S22 0

L 0.2

. - 0 2 -- --- . . -.

I0 20 40 60 80 IC0 120 140 160 ISO

ANGLE a• (DEGREES)

Figure 4.64. Variation of pressure ratios, drag coefficient, and time intervals for an arched

structure.

.i-Pr A

r• IMPLUSE pr A -- /T

U.

Z

0

0

X 0.4 q(0)4

I-wZ

TIME

Figurc 4.66. Approximate equivalent net horizontal force loading on semicylindrical

structure.

oI
INTERACTION OF OBJECTS WITH AIR BLAST 151

nents of the loads over the two areas and sure range of interest (§ 4.23). Hence,

then subtract them. In practice, an ap- in addition to the initial impulse, the

proximation may be used to obtain th,. remainder of the net horizontal loading

required result in such cases where the may be represented by the force 0.4

net horizontal loading is considered to q(t)A, as s-en in Fig. 4.66, which apbe important. It may be pointed out that, plies to a single structure. When a frame

in certain instances, especially for large is made up of a number of circular

structures, it is the local loading, rather elements, the methods used are similar

than the net loading, which is the sig- to ihose for an open frame structure (§

nificant criterion of damage. 4.5)) with C'd equal to 0.2

4.66 In the approximate procedure

for determining the net loading, the NONIDEAL BLAST WAVE LOADING

overpressure loading during the diffraction stage is considered to bc. equivalent 4.67 The preceding discussions

to an initial impulse equal to 1,,A(2H/U), have dealt with loading cat~sed by blast

where A is the projected area normal to waves reflected from nearly ideal

the direction of the blast propagation. It ground surfaces (§ 3.47). ;n nractice,

will be noted that 2H/Uis the time taken however, the wave form will not always

for the blast front to traverse the struc- be ideal. In particular, if a precursor

ture. The net drag coefficient for a single wave is formed (§ 3.79 et seq.), the

cylinder is about 0.4 in the blast pres- loadings may depart radically fron

100 __T

80 -

w 60

uJ

Cr

I*J

n. 40

20

o ilf I Ill

0 100 200 300 400 500 600 700

TIME (MSEC)

Figure 4.67a. Nonideal incident air blast (shock) wave.
152 AIR BLAST LOADING

400 2-- I I I]

300

w

n 200

U')

iox

100

0

0 200 400 600

TIME (MSEC)

b.

100 I I I ' I80 -

60 -

00040 w

0.

20

0 200 400~ 600

TIME 'MSEC

C.

40

m 30o

0.

20 0 40 60

U)

U)

0 200 400 600

TIME (MSEC)

d.

Figure 4.67b, c, d. Loading pattern on the front, top, and back, respectively, on a

rectangular block from nonideal bhlst wave.

!
INTERACTION OF OBJECTS WITH AIR III AST 153

those described above. Although it is Comparison of Figs. 4.67b. c, and d

beyond the scope of thu present treat- with the corresponding Figs. 4.42,

ment to provide a detailed discussion of 4.43, and 4.44 indicates the departures

ncnideal loading, one qualitative exam- from ideal loadings tha! may be enpie is given here. Figure 4.67a shows a countered in certain circumstances. The

nonideal incident air blast (shock) wave net loading on this structure was sigand Figs. 4.67b, c, and d give the load- nificantly less than it would have been

mg patterns on the front, top, and back, under ideal conditions, but this would

re•:pecfively, of a rectangular block as not necessarily always be the case.

observed at a nuclear weapon test.

BIBLIOGRAPHY

*AMERICAN SOCIETY Ji' CIvit. ENGINIEERS, Corporation, Burlingame, California, 1965,

"Design of Structures to Resist Nuclear Weap- URS 633-3 (DASA 1460-I), Part I!.

•,•s Effects,"' ASCE Manual of Engineering *Mtic ' iit , J. H., "Nuclear Explosion Effects

Practice No. 42, 1961. on Structui'es and Protective Construction-A

*ARMOUR RESEARCH FOUNDATION, "A Sim- Selected Bibliography," U.S. Atomic Energy

p1e Method of Evaluating Blast Effects on Commission, April 1961, TID-3092.

Buildihigs," Armour Research Foundation, PI(KERINU, E. E., and J. L. BocKF'otr01,

Chicago, lIli-tois, 1954. "Probabilistic Air Blast Failure Criteria for

*BANISTER, J, R., and L, J. VORTMAN, "Efle,:t U San Structures,'" Stanford Research Institute,

of a Precursor Shock Wave on Blast Loading of Menlo Park, Cplifornia, November 1971.

a Structure," 3andia Corporation, Albuquer- Wit I ouGntY, A. B., et al., "A Study of Loadque, New Mcxico, October 1960, WT-1472. ing, Structural Response, and Debris CharacJACOtiStEN, L. S. and R. S. AYRE, 'Engineering teristics of Wall Panels," UFZS Research Co..

Vibrations," McGraw-Hill Book Co., Inc., Burlingairr, California, July 1969.

New York, 1958. Wit roN, C, et al., "Final Report Summary,

KAPI AN, K. and C. WmEIIn u., "Air Blast Load- Structural Response and Loading of Wail

ing in the High Shock Strength Region," URS Panels," URS Research Co., Burlingame, California, July 1971.

*These documents may be purchased from the National Technical Information Service. U.S.

Department of Commerce, Springfield, Virginia 22161.

t - -. . . .
CtAPTER V

STRUCTURAL DAMAGE FROM AIR BLAST

INTRODUCTION

GENERAL OBSERVATIONS bomb. In the former case, the combina5.01 The two preceding chapters tion of high peak cverpressure, high

have dealt with general principles of air wind (or dynamic) pressure, and longer

blast and the loads on structures pro- duration of t!h, positive (compression)

duced by the action of the air blast phase of the olast wave results in "mass

wave. In the present chapter, the actual distoriion" of buildings, similar to that

damage to buildings of various types, produced by earthquakes and hurribridges, utilities, and vehicles caiised by canes. An u.dii,'ry explosion will

nuclear explosions will be considered, usually dan age only part of a large

In addition, criteria of damage to structure, but the blast from a nuclear

various targets will be discussed and weapon can surceund and destroy whole

quantitative relationships will be given buildings in addition to causing locabetween the damage and the distances lized structural damage.

over which such damage may be ex- 5.04 An examination of the areas in

pected from nuclear weapons of dif- lapan affected by nuclear explosions (§

ferent yields. 2.24) shows that small masonry build5.02 Direct damage to structures ings were engulfed by the oncoming

attributable to air blast can take various pressure wave and collapsed corlnforms. For example, the blast may de- pletely. Light structures and residences

flect structural steel frames, collapse were totally demolished by blast and

roofs, dish-in walls, shatter panels, and subsequently destroyed by fire. Indusbreak windows. In general, the damage trial buildings of steel construction were

results from some type of displacement denuded of roofing and siding, and only

(or distortion) and the manner in which twisted frames remained. Nearly everysuch displacement can arise as the result thing at close range, except structures

of a nuclear explosion will be examined, and smokestacks of strong reinfo~ced

5.03 Attention may be called to an concrete, was destroyed. Some buildimportant difference between the blast ings leaned away from ground zero as

effects of a nuclear weapon and those though struck by a wind of stupendous

due to a conventional high-explosive proportions. Telephone poles were

154
;NTRODU CTION 155

snapped off at ground level, as in a enormous numbers of flying missiles

hurricane, carrying the wires down with consisting of bricks (and other mathem. Large gas holders were ruptured sonry), glass, pieces of wood and metal,

and collapsed by the crushing action of etc. These ,;aused considerable amounts

the blast wave. of secondary damage to structures and

5.05 Many buildings, which at a utilities, and numerous casualties even

distance appeared to be sound, were in the lightly damaged areas. In addifound on close inspection to be damaged tion, the large quantities of debris reand gutted by fie. This was f.equently suited in the blockage of stretts, thus

an indirect result of blast action. In making rescue and fire-fighting operasome instances the thermal radiation tion- extremely difficult (Fig. 5.06).

may have been responsible for the ini- 5.07 Many structures in Japan were

tiation of fires, but in many other cases designed to be earthquake resistant,

fires were started by ovei urned stoves which probably made them stronger

and furnaccs and by the rupture of gas than most of their counterparts in the

lines. The loss of water pressure by the United States. On :lhe other hand, some

breaking of pipes, mainly due to the con.;truction was undoubtedly lighter

collapse of buildings, and other circum than in this country. However, contrary

stances arising from the explosions, to popular belief concerning the flimsy

contributed great!y to the additional de- charactei of Japanese residences, it was

struction by fire (Chapter VII). the considered cpinion of a group of

5.06 A highly important conse- architects and engineers, who surveyed

quence of the tremendous power of the the nuclear bonmb damage, that the renuclear exph'sions was the formation of sistance to bast of American residences

rr

Figure 5.06. Debris after the nuclear explosion at Hiroshima.

•- -
156 STRUCTURAL DAMAGE FROM AIR BLAST

in general would not be markedly dif- borne out by the obse:vations on experferent from that of the houses in Hiro- imental structures exposed to air blast at

shima and Nagasaki. This has been nucieac weapons tests in Nevada.

FACTORS AFFECTING RESPONSE

STRENGTH AND MASS ing light frames and long beam spans.

5.08 There are numerous factors Some kinds of lightly built and open

associated with the characteristics of a frame construction also fall into the latstructure which influence the response to !,r category, but well-constructed frame

the blast wave accompanying a nuclear houses have greater strength than these

explosion. Those considered below in- sheds.

clude various aspects of the strength and 5.11 The resistance to blast of

mass of the strui..ture, general structural structures having load-bearing, masonry

design, and ductility (§ 5. !4) of the walls (brick or concrete block), w-thout

component materials and members. reinforcement, is not very good. This is

5.09 The basic criterion for deter- due to the lack of resilience and to the

mining the response of a structure to moderate strength of the connections

blast is its strength. As used in this which are put under stress when the

connection, "strength" is a general blast load is applied laterally to the

term, for ii is a property influenced by building. The use of steel reiiforcemcrnt

many factors some of which -e robvious with structures of this type greatly inand others are jt-c. The mo, -)bvious creases their strength.

indication of strength is, cf course,

massiveness of construction, but this is STRUCTURAL DESIGN

modified greatly by other factors not

immediately visible to the eye. exg., 5.!2 Except for those regions in

resilience and ductility of tLe frame, the which iairly strong earthquake shocks

strength of the beam and column ccn- may be expected, most structures in the

nections, the redur.dancy of supports, UJnited States are designed to withstand

and the amount of diagonal bracing in only the lateral (sideways) loadings

the structure. Some of these factors will produced by moderately strong winds.

be examined subsequently. If the btild- For design purposes, such loading is

ing does not have the same strength* assumed to be static (or stationary) in

along both axes, then orientation with character because natural winds build up

:espect to the burst should also be con- relatively slowly and remain fairly

sidet ed. steady. The blast from a nuclear explo5.10 The strongest strictures are sion, however, causes a lateral dynamic

heavily framed stcei and reinforced- (rather than static) loading; the load is

concrete buildings, particularly those applied extremely rapidly and it lasts for

designed to be earthquake resistant, a second or more with continuously dewhereas the wakest are probably cer- crcasing strength. The inertia, as meatain shed-type industrial structures hav- sured by the mass of the structuie or
FACTORS AFFECTING RESPONSE 157

member, is an important factor in de- have as much ductility as possible. Untermining response to a dynamic lateral fortunately, structural materials are

load, although it is not significant for generally not able to absorb much enstatic loading,. ergy in the elastic range, although many

5.13 Of existing structures, those common materials can take up large

intended to be earthquake resistant and amounts ef energy in the plastic range

capable of withstanding a lateral load befort: they fail. One of the problems in

equal to about 10 percent of the weight, blast-resistant design, therefore, is to

will probably be damaged least by blast. decide how much permanent (plastic)

Such structures, often stiffened by dia- deformation can be accepted before a

phragm walls and having continuity of particular structure is rendered useless.

joints to provide additional rigidity, may This will, of course, vary with the nabe expected to withstand appreciable ture and purpose of thc structure. Allateral forces without serious da~mage. though deformation to the point of collapse is definitely undesirable, some

DUCTILITY lesser deformation may not seriously

5.14 Thz e ductility refers to the interfere with the continued use of the

ability of a ,naterial or structure to ab- structure.

sorb energy inelastically without failure; 5.17 It is evident that ductility is a

in other words, the greater the ductility, desirable property of structural materials

the greater the resistance to failure. required to resist blast. Structural steel

Materials which are brittle have poor and steel reinforcement have this propductility and fail suddenly after passing erty to a considerable extent. They are

their elastic (yield) ioadiag. able to absorb lrge amounts of energy,

5.15 There are two main aspects of e.g., from a blast wave, without failure

ductility to be considered. When a force and thus ieduce the chances of collapse

(or load) is applied to a material so as to of the structure in which they are used.

deform it, as is the case in a nuclear Structural steel has the further advanexplosion, ior example, the initial de- tage of a higher yield point (or elastic

formation is said to be "elastic." Pro- limit) under dynamic than tinder static

vided it is still in the elastic range, the loading; the increase is quite large for

material will recover its original form some steels.

when the loading is removed. However, 5.18 Although concrete alone is not

if the "stress" (or internal force) pro- ductile, when steel and concrete are

duced by the load is sufficiently great, used togcther properly, as in reinthe material passes into the "plastic" forced-concrete structures, the ductile

range. In this state the material does not behavior of the steel will usually prerecover completely after removal of the dominate. The structure will then have

load; that is to say, some deformation is considerable ductility and, consepermanent, but there is no failure. Only quently, the ability to absorb energy.

when the stress reaches the "ultimate Without reinforcement, masonry walls

strength" does failure occuf'. arm. completely lacking in ductility and

5.16 Ideally, a structure which is to readily suffer brittle failure, as stated

suffer little damage from blast should above.
158 STRUCTURAL DAMAGE FROM AIR BLAST

COMMERCIAL AND ADMINISTRATIVE STRUCTURES

INTRODUCTION the interior and contents due to the entry

5.19 In this and several subsequent of blast through doors and window

sections, the actual damage to various openings and to subsequent fires. An

types of structures caused by the air exceptionally strong structure of earthblast from nuclear explosions will be quake-resistant (aseismic) design, todescribed. First, commercial, adminis- cated some 640 feet from ground zero in

trative, and similar buildings will be Hiroshima, is seen in Fig. 5.20a. Alconsidered. Thes2 buildings are of sub- though the exterior walls were hardly

stantial construction and include banks, damaged, the roof was depressed and

offices, hospitals, hotels, and large the interior was de,,troyed. More typical

apartment houses. Essentially all the of reinforced-concrete frame construcempirical information concerning the tion in the United States was the buildeffects of air blast on such multistory ing shown in Fig. 5.20b at about the

structures has been obtained from ob- same distance from ground zero. This

servations made at Hiroshima and Na- suffered more severely than the one of

gasaki. The descriptions given below aseismic design.

are for three general types, namely. 5.21 A factor contributing io the

reinforced-concrete frame buildings, blast resistance of many reinforce.dsteel-frame buildings, and buildings concrete buildings in Japan was the

with load-bearing walls. As is to be construction code established after the

expected from the preceding discussion, severe earthquake of 1923. The height

buildings of the first two types are more of new buildings was limited to 100 feet

blast resistant than those of the third and they were desigred to withstand a

type; however, even light to moderate lateral force equal to 10 percent of the

damage (see Table 5.139a) to frame- vertical load. In addition, the recogsupported buildings can result in ca.- nized principles of stiffening by diasualties to people in these buildings. phragms and improved framing to provide contihinity were specified. The

MULTISTORY, more important buildings were well deREINFORCED-CONCRETE FRAME signed and constructed according to the

BUILDINGS code. However, some were built without regard to the earthquake-resistant

5.20 There were many multistory, requirements and these were less able to

reinforced-concrete frame buildings of withstand the blast wave from the nuseveral types in Hiroshima and a smaller clear explosion.

number in Nagasaki. They varied in 5.22 Close to ground zero the verresistance to blast according to design tical componernt of the blast was more

and construction, but they generally significant and so greater damage to the

suffered remarkedly little damage exter- roof resulted from the downward force

nally. Close to ground zero, however, (Fig. 5.22a) than appeared farther away.

there was considerable destruction of Depending upon its strength, the roof

S. ... • - - IPi tm4
COMMERCIAL AND ADMINISTRATIVE STrRUCTURES 159

Figure 5.20a. Upper photo: Reinfurc-d-concrete, aseimic structure; window fire shutte~rs

were blown hi by blast ana the interior gutted by fire (0 12 -n~ie frium groun~J

zero at Hiroshima.). Lowe; phwo: Burned out interior of similar stri-c~ure.
160 STRUCTURAL DAMAGE FROM AiR BLAST

x

Figure 5.20b. Three-story, reinforced-concrete frame building: walls were 13-inch thick

brick panel with large window openings (0. 13 mile from ground zero at

Hiroshima).

was pushed down and left sagging or it ken out to a aistance of 3Y4 miles and in

failed completely. The remainder of the a few instances out to 8 miles.

structure was less damaged than similar 5.24 The various effects just debuildings farther from the explosion be- scribed have referred especially to reincause of the smaller horizontal (lateral) forced-concrete structures. This is beforces. At greatef distances, from cause the buildings as a whole did not

ground zero, especia!ly in the region of collapse, so that other consequences of

Mach reflection, the consequences of the blast loading could be observed. It

horizontal loading were apparent (Fig. should be pointed out, however, that

5.22b). damage of a similar nature also occurred

5.23 In addition to the failure of in structures of the other types described

roof siabs and the lateral displacement below.

of walls, numerous other blast effects

were observed. These included bending MULTISTORY, STEEL-FRAME

and fracture of beams, failure of col- BU!LDINGS

umns, crushing of exterior wall paneis, 5.25 There was apparently only one

and failure of floor slabs (Fig. 5.23). steel.frame structure having more than

Heavy damage to false ceilings, plaster, two stories in the Japanese cities exand partitions occurred as far out as posed to nuclear explosions. This was a

9,000 feet (i .7 miles) from ground zero, fivw-story structure in Nagasaki at a disand glass windows were generally bro- tance of 4,500 feet (0.85 mile) from
COMMERCIAL AND ADMINISTRATIVE STRUCTURES 161

4k

.~: I

Figure 5.22a. Depressed roof of reinforced-concrete building (0. 10 mile from ground zero

at H-lroshima).

Figure 5.22b. Effects of horizontal loading on wall facing explosion (0.4 mile from ground

zero at Nagasaki).
162 STRUCTURAL DAMAGE FROM AIR BLASt

Figure 5.23. Re inf orced -concrete building showing collapsed roof and floor slabs (0. 10

mile from ground zero at Nagasaki).

ground zero (Fig. 5.25). The only part shown in Fig. 5.26. The heavy walls of

of the building that was not regarded as the structure iransmitted their loads to

being of heavy construction was the the steel frame, the columns of which

roof, which was of 4-inch thick rein- collapsed. Weakening of unprotected

forced concrete supported by unusually steel by fire could hazve contrnbutcd siglight steel trusses. The downward fail- nificantly to the damage to steel-frame

ure of the roof, which was dished 3 feet, structures (§ 5.31).

was the only important structural damage suffered. BUILDING WITH LOAD-BEARING

5.26 Reinforced-concrete f rame WALLS

buildings at the same distance from the

explosion werr also undamaged, and so 5.27 Small structures with light

there is insu~ficient cvidence to permit load-bearing walls offered little resisany conclusions to be drawn as to the tance to the nuclear blast and. in genrelative resistance of the two types of eral, collapsed completely. Large

*;:onstruction. An example of damage to building,. of the same type, but with

a two-story, steel-frame structure is cross wkalls and of somewhat heavier

-----------------------------
COMMERCIAL- AND ADMINISTRATIVE STRUCTURES 163

110

Figure 5.25. At left and back of center is a inulfistory, steei-frame' building (0.35 mile from

gound zero at Nagasaki).
164 STRUCTURAL DAMAGE FROM AIR BLAST

44

"'I.'

Figure 5.26. Two-story, steel-frame building with 7-inch reinforced-concrete wall panels

(0.40 mile from ground zero at Hitoshima). The ,irst story columns buckled

avway from ground zero dropping the secrnd story to the ground.

construction, were more resistant but mained standing. it is apparent that

failed at distances up to 6,300 feet ( 1.2 structures with load-bearing walls posmiles) from ground zero. Cracks were sess few of the characteristics that

observed at thc junctions of cross walls would make them resistant to collapse

and sidewalls when the building re- when subjected to large lateral loads.
INDUSTRIAl. STRUCTURES 165

INDUSTRiAL. STRUCTURES

JAPANESE EXPERIENCE force causing flexurt, combined with a

5.28 in Nagasaki there were many simultaneous small increase in the

buildings of the familiar type used for downward load coming from the impact

industrial purposes, consisting of a steel of the biast on th'ý roof. This caused

frame with roof and siding of corrugated buckling and, in some instances, comsheet metal or of asbestos cement. In plete collapse. Roof trusses were bucksome cases, there were rails for gantry led by compression resulting from latcranes, but the crants were usually of eral blast loading on the side of the

low capacity. In general, construction of building facing the explosion.

industrial-type buildings was compara- 5.30 A difference was noted in the

ble to that in the United States. effect on the frame depending upon

5.29 s)everc damage of these struc- whether a frangible material, like astures eic-iired up to a distance of about bestos cement, or a material of high

6,000 feet (!.14 miles) from ground tensile strength, such as corrugated

zero. Moderately close to ground zero, sheet-iron, was used for roof anJl siding,

the buildings were pushed over bodily, Asbestos cement broke up more readily

and at greater distances they were gen- permitting more rapid equalizatior of

erally left leaning away from the source pressure and, consequently, less strucof the blast (Fig. 5.29). The columns tural damage to the frame.

being long and slender offered little re- 5.31 Fire caused heavy damage to

sistance to the lateral loading. Some- unprotected steel members, so that it

times columns failed due to a lateral was impossible to tell exactly what the

Figure 5.29. Single-story, light steel-frame building (0.80 mile from ground zero at

Hiroshima), partially damaged by blast and further collapsed by subsequent

fire.

(!
166 STRUCTURAL DAMAGE FROM AIR BLAST

blas, effect had been. In general, steel somewhat better than did those made of

frames were badly distorted and would steel.

have been of lit:le use, even if siding

and roofing material had been availab1e NEVADA TESTS

for repairs. 5.35 A considerable amount of in5.32 In some industrial buildings formation on the blast response of

wood trusses were used to support the structures of s-veral different kinds was

roof. These were more vulnerable to obtained in the studies made at the NebNast because of poor framing and con- vada Test Site in 1953 and in 1955. The

nections, and were readily burned out nuclear device employed in the tedt of

by fire. Concrete columns were em- March 17, 1953, was detonated at the

ployed in some cases with steel roof top of a 300-foot tower; the energy yield

trusses; such columns appeared to be was about 16 kilotons. In mne test of

more resistant to buckling than steel, May 5, 1955, the explosion took place

possibly because the strength of con- oi a 500-foot tower and the yield was

crete is decreased to a lesser extent by close to 29 kilotons. In each case, air

fire than is that of steel. pressure measarements made possible a

5.33 Damage correlation, where it was justified, be- to machine toois was twnthblsdagendtepk

caused by debris, resulting from the tverptessuan.

collapse of roof and siding, by fire in 5.36 Three types of metal buildings

wood-frame structures, and by disloca- of standard construction, such as are

tion and oerturning as a result of dam- used for various commercial and i rdusage to the building. In many instances trial purposes, were exposed at peak

the machine tools were belt-driven, so vri ressur es of .3po und s per

fti th ditorionof he uilingpuled overpressures of 3. 1 and 1. 3 pounds per

that the distortion of the building pulled square inch. The main objectives of the

the machine tool off its base, damaging tests, made in 1955, were to determine

or overturning it. the blast oressures at which such struc5.34 Smokestacks, especially these tures would survive, in the sense that

of reinforced concrete, proved to have they could still be used alter moderate

considerable blast resistance (,Fig. repairs, and to provide information upon

5.34a). Because of their shape, they are which cauld be based inlprovements in

subjected essentially to drag loading de'-ign to resist blast.

only and, if sufficiently strong, their

long period of vibration maker" them less STEEL FR AME WITH ALUMINUM

sensitive to blast than many other struc- PANELS

tures. An example of extreme damage to 5.37 The first industrial type builda reinforced-concrete stack is shown in ing had a conventional rigid steel frame,

Fig. 5.34b. Steel smokestacks per- which is familiar to structural engineers,

formed reasonably well, but being with aiuminum-shect panels for roofing

lighter in weight and subject to crushing and siding (Fig. 5.37a). At a blast

were not comparable to reinforced con- overpressure of 3.1 pounds per square

crete. On the whole, well-constructed inch this building was severely dammasonry stacks withstood the blast aged. The welded and bolted steel frame
INDUSTRIAL STRUCTURES 167

K 4

0 ,

Figure 5.34a. Destroyed indw;trial area showing smokestacks still standing (0.5 1 mile from

ground zero at Nagasaki).

remained standing, but was badly dis- building. The aluminum panels on the

torted and pulled away ftom the con- side walls were dished inward slightly,

crete footings. On the side facing the but on the rear wall and rear slope of the

explosion the deflection was about I roof, the sheeting was almost undisfoot at the eaves (Fig. 5.37b). turbed.

5.38 At a peak overpressure of 1.3 5.39 As presently designed, strucpounds per square inch the main steel tures of this type may bc regarded as

frame suffered only slight distortion, being repairable, provided they are not

The aluminum roofing and siding were exposed to blast pressures exceeding I

not blown off, although the panels were pound per square inch. Increased blast

disengaged from the boll fasteners on resistance would probably result from

the front face of the steel columns and improvement in the design of girts and

girls (horizontal connecting members). purlins (horizontal members supporting

Wall anui roof panels facing the explo- rafters), in particular. Better fastenIng

sion were dished irward. rhe center between sill and wall footing and ingirts were torn loose from theii attach- creased resistance to transverse loading

ments to the columns in the front of tl,e would also, be beneficial.

.. _ _ _
168 STRUCTURAL DAMgAGE FROM AIR BLAST

42

I Iý I

Figure 5.34h. A circular, 60 feet high, reinforced-concrete~ s~ack (0.34 mile from ground

zero at Hiroshima). The failure caused by the blast wave occurred 15 feet

above the base
INDUSTRIAL STRUCTURES 169

Figure 5.37a. Rigid steel-frorme building before a nuclear explosion. Nevada Test Site.

Figure 5.37b. Rigid steel-frame building after a nuclear explosion (3.1 psi peak

overpressure).

SELF-FRAMING WITH STEEL PANELS 0.2 pound per square inch) was com5.40 A frameless structure with plete!y demolished (Fig. 5.40b) One or

self .;upporiing walls and roof of light, two segments of wall were blown as far

channel-shaped, interlocking, steel as 50 feet away, but, in general, the bent

panels (16 inches wide) represented the and twisted segments of th, buiiding

second standard type of industrial remained approximately in their original

building (Fig. 5.40a). The one subjected locations. Most of the wall sections

to 3.1 pounds per :q,;are inch peak were still a:tached to their foundation

ov'ýrpressure (and . dynamic pressure of bolts on the -,ide and rear walls of the

iE
170 STRUCTURAL DAMAGE FROM AIR BLAST

Figure 5.40a. Exterior of self-fr.-rr~ing steel pane: building before a nuclear explosion.

- evaaja Test Site.

Oa I

Figure 5.40b. Self-framing steel panel building after a nuclear explosion (3.1 psi peak

overpressure).
INDUSTRIAL STRUCTURES 171

building. The roof had collapsed corn- blast. Blast-resistant improvements

pletely and was resting on the ma- would seem to be difficult to incorporate

chinery in the interior, while maintaining the essential simplic5.41 A!irv.!gh damag,- at 1 .3 ity of design.

pounds per square inch peak overpressure was much less, it was still consid- SELF-FRAMING WITH CORRUGATED

erable in parts of the structure. The front STEEL PANELS

wall panels were buckled inward from I

to 2 feet at the center, but the rear wall 5.43 The third type of industrial

ar.d rear slope of the roof were undam- building was a completely frameless

aged. In general, the roof structure re- structure made of strong, deeply-corrumained intact, except for some deflec- gated 43-inch wide panels of 16-gauge

tion near the center. steel sheet. The panels were held to5.42 It appears that the steel panel g!!her with large bolt fasteners at the

type of structure is repairable if exposed sides and at the eaves and ,oof ridge.

to overpressures of not more than about The wall panels were bolted to the con-

-Y3⁄4 to I l.,-und per square inch. The crete foundation. The entire ,;iructure

buildings are simple to construct but was self-supporting, without frames.

they do not .old together well under girts, or purlins (Fig. 5.43).

•,

Nevada Test Site.

'4,
172 STRUCTURAL DAMAGE FROM AIR BLAST

Figure 5.44. Self-framing corrugated steel panel building after a nuclear explosion (3.1 psi

peak overpressure).

544 At a peak overpressure of 3. 1 dows were broken, cracked, or chipped.

and a dynamic pressure of 0.2 pound per Replacement of the glass where necessquare inch a structure of this type was sary and some minor repairs would have

badly damaged, but all the pieces re- rendered the building completely sernaianed bolted together, so that the viceable.

structure still provided good protection 5.47 The corrugated steel, framLfrom the elements for its contents. The less structure proved to be the most

front slope of the roof was crushed blast-resistant of those tested. It is bedownward, from I to 2 feet, at midsec- lieved thai. provided the overpressure

tion, and the ridge !ine suffered moder- did not exceed about 3 pounds per

ate deflection. The rear slope of the roof square inch, relatively minor repairs

appeared to be essent'illy undamaged would make possible continued use of

(Fig. 5.44). the building. Improvement in the design

5.45 The front and side walls were of doors and windows, so as to rLdu, !

buckled inward several inches, and the the missile hazard f'un broken glass,

door in the front was broken off. All the would be advantageous.

windows were damaged to some extent,

although a few panes in the rear re- POSITIVE PHASE DURATION TESTS

mained in place.

546 Another building of this type, 5.48 Tests were carried out at Neexposed to 1.3 pounds per square inch vada in 1955 and a,. Eniwetok Atoll in

peak overpressure, experienced little the Pacific in 19ý16 to investigate the

structural damage. The roof along the effect of the dura:'on of the positive

ridge line showed indications of down- overpressure phase of a blast wave on

ward deflections of only I or 2 inches, damage. Typical d&ag-type structures

and there was no apparent buckling of were exposed, at approximately the

roof or wall panels. Most of the win- samne overpressure, to nuclear detonai
INDUSTRIAL. STRUCTURZES 173

Figure 5.43a. Steel-frame building with siding and roof of frangible material.

Figure 5.48b. Steel-frame building with concrete siding and window openings of 30

percent of the wall area.
174 STRUCTURAL DAMAGE FROM AIR BLAST

tions in the kiloton and megaton ranges. bolts failed, and yielding was found

Two representative types of small in- between the lower chord (horizontal

dustrial buildings were chosen for these member of the roof truss) and column

tests. One had a steel frame covered connections. The girts on the windward

with siding aird roofing of a frangible side were severely damaged and all of

material and was considered to be d the siding was completely blown off

drag-type structure (Fig. 5.48a). The (Fig. 5.49).

other had the same steel frame and 5.50 The second building, with the

roofing, but it i.ad concrete siding with a stronger siding, was exp9sed in Nevada

window opening of about 30 percent of to a peak overpressure loading of about

the wall area; this was regarded as a 3.5 and a dynamic pressure of 0.3

semidrag structure (Fig. 5.48b). pounds per square inch, with a positive

5.49 In the Nevada tests, with kilo- phase duration of I second. Damage to

ton yield weapons, the first structure this structure was small (F;. 5.50).

was subjected to a peak overpressure of Although almost the whole of the franabout 6.5 and a dynamic pressure of 1. I gible roof was blown off, the only other

pounds pet square inch; the positive damage observed was a small yielding

phase duration of the blast wave was 0.9 at some connections and column bases.

second. A permanent horizontal deflec- 5.51 Structures of the same type

tion of about i5 inches occurred at the were subjected to simildr pressures in

top of the columns. The column anchor the blast wave from a megaton range

Figure 5.49. Structure in Figure 5.48a after exposure to 6.5 psi peak overpressure and I. I

psi dynamic pressure- positive phase duration 0.9 second.

I1
RESIDENTIAL STRUCTURES 175

Figure 5.50. Structure in Figure 5.48b after exposure to 3.5 psi peak overpressure and 0.3

psi dynamic pressu;e; positive phase duration I second.

explosion at Eniwetok; namely, a peak suffered complete collapse (Figs. 5.51a

overpressure of 6.1 and a dynamic and b). Distortion and breakup occurred

pressure of 0.6 pounds per square inch throughout, particularly of columns and

for the drag-type building, and 5 and 0.5 conncctions. It -,,s concluded, therepounds per square inch, respectively, fore, that damage to drag-sensitive

for the semidrag structure. However, structures can be enhanced, for a given

the positive phase now lasted several peak overpressure value, if the duration

seconds as compared with about I sec- of the positive phase of the blast wave is

ond in the Nevada tests. Both structure., increased (cf. § 4.13).

RESIDENTIAL STRUCTURES

JAPANESE EXPERIENCE appeared that, although !he quaii,.y of

5.52 There were many wood.. the workmanship in framing was usually

framed residential structures with adobe high, little attention was paid o good

walls in the Japanese cities which were engineering principles. On the whole,

subjected to nuclear attack, but such a therefore, the construction w•s not well

large proportion were destroyed by fire adapted to resist wracking action (disthat very little detailed information con- tortion). For eximple, mortise and

cerning blast darmaige was obtained. It tenon joints were weak points in the
176 STRUCTURAL DAMAGE FROM AIR BLAST

Figure 5.5 Ia. Structure similar to Figure 5.48a after exposure to 6.1 psi peak overpressure

and 0.6 psi dynamic pressure-, positive phase duration weveral second7,.

%0

ILI

Figure 5 5l1b. Siructute similar to Figure 5.4hb after cxp:ýisdre to 5 psi peak overpressure

anJ 0.5 psi dynamic pressure-, positive phasc duratpcpn ie-eral secondis.
RESIDENTIAL STRUCTURES 177

Figure 5.52. Upper p~1oto; Wood-frarte building, 1 0 mile from ground zero at Hiroshima.

Lower photo: Fram~e of residCeIcc under construction, showing small tenonsFtructure and connections were in gen- (cut into) mnore than was necessary or

eral poor. Timbers wcre often dapped slices psut in improper locations, result-

'-S ~ ~ ~ ~ ~ ~ ~- ~ ~ . ~ . . ~ .. . ~ . ,, ~ .:P. ~ ~ ~ t- ý . ' *W I' .. t .a
1"78 STRUCTURAL DAMAGE FROM AIR BLAST

ing in an overall weakening (Fig. 5.52). different locations. They were of typical

5.53 In Nagasaki, dwellings col- wood-frame construction, with two

lipsed at distances up to 7,500 feet (I .4 stories, basement, and brick chimney

miles) from ground zero, where the (Fig. 5.55). The interiors were plastered

peak overpressure was estimated to he but not paiuted. Sirnce the tests were

about 3 pounds per square inch, and intended for studying the effects of

there was severe structural damage up to blast, precautions were taken to prevent

8,500 feet (1.6 miles). Roofs, wall the houses from burning. The exteriors

panels, and partitions were damaged out were consequently painted white (exto 9,000 feet (1.7 miles), where the cept for the shutters), to reflect the theroverpressure was approximately 2 mal radiation. For the same pu"pose, the

pounds per square inch, but the build- windows facing ihe explosion were

ings would probably have been habit- equipped with metal venetian blinds

able with moderate repairs. having an aluminum finish. In addition,

the houses were roofed with light-gray

NEVADA TESTS shingles; these were of asbestos cement

5.54 The main objectives of the for the house nearer to the explosion

tests made in Nevada in 195-1 and 1955 where the chances of fire were greater.

(§ 5.35) on residential structures were as whereas asphalt shigle:s were used for

follows: (i) to determine the elements the other house. Thete were no utilities

most susceptible to blast damage and of any kind.

consequently to devise methods for 5.56 One of the two houses was

strengthening stroctures of various located in the region of Mach reflection

types; (2) to provide information con- where the peak incident overpressure

cerning the amount of damage to resi- was close to 5 pounds per square inch. It

dences that might be expected as a result was expected, from the effects in Japan,

of a nuclear explosion and to what ex- that this house would be almost corntent these structures would be subse- pletely destroyed-as indeed it was--

quently rendered habitable without but the chief purpose was to see what

major repairs; and (3) to determine how protection might be obtained by persons

persons remaining in their houses during in the basement.

a nuclear attack might be prctected from 5.57 Some indication of the blast

the eflects of blast and radiations. Only damage suffered by this dwelling can be

the first two of these aspects of the tests obtained from Fig. 5.57. it is apparent

will be considered here, since the pres- that the house was ruined beyond repair.

ent chapter deals primarily with blast The first stofy was completely demoleffects. ished and the second story, which was

very badly damaged, dropped down on

TWO-STORY, WOOD.FRAME HOUSE: the first floor debris. The roof was blown 195. TEST off in several sections which !anded at

both front and back of the house. The

5.55 In the 1953 test, two essen- gable end walls were blown apart and

tiall identical houses, of ,. type com- outward, and the brick chimney was

mon in the United States, were placed at broken into several pieces.
RESIDENTIAL STRUCTURES 179

IIIn

Figure 5.55. Wood-frame house before a nuclear explosion,. Nevada Test Site.

Figure 5.57. Wood-frame house after ; nucleaxr explosion (5 -0 peak overpressure).
180 STRUCTI'RAI. I)AMAGF FROM AIR Bi ASI"

Figure 5.59. Woc)d-frame house after a nuclear explosion (I .7 psi peak overpressure).

5.58 The basement walls suffered People in the main and upper Poors

some damage above grade, mostly in would have suffered injuries ranging

the rear. i.e.. away from the explosion, from minor cuts from glass fragments to

The front basement wall was pushed in possible fatal injuries from flying debris

slightly, but was not cracked except at or as a result of translational displacethe ends. The joists supporting the first ment of the body as a whole. Some

floor were forced downward probably damage would also result to the furbecause of the air pressure differential nishings and other contents; of the

between the first floor and- the largely house. Although complte restoration

enclosed basement, and the supporting would have been very costly, it is bepipe columrs were inclined to the rear. lieved that, with the window and door

However, only in Lmited areas did a openings covered, and shoring in the

complete breakthrough from first floor to basement, the house would have been

basement occur. The rest of the base- habitable under emergency conditions.

ment was comparatively clear and the 5.60 The most .ibvious damage was

shelters located there were unaffected. suffered by doors and windows, includS.59 The second house, exposed to ing sash and frames. The front door was

an incident peak overpressure of 1.7 broken into pieces and the kitchen and

pounds per square inch, was badly basement entrance doors were torn off

damaged both internally and externally, their hinges. Damage to interior doors

but it remained standing (Fig. 5.59). varied; those which were open before
RESIDENTIA[ STRUCTURES X

Figure 5.64. Strengthened wood(-rame house after a nuclear explosion (4 p1, I'Wak

overpressure)[

the explosion suffered least. Window some 10 percent above that for normal

glass throughout the house was broken construction, were made: (I) improved

into fragments, and the force on the connection between exterior walls and

sash, especially in the front of (he foundations: (2) reinforced-concrete

house, dislodged the frames. shear walls to replace the pipe columns

5.61 Principal damage to the first- in the basement: (3) increase in sie and

floor system consisted of broken joists. strengthening of connections of firstThe second-story system suffered rela- floor joists' (4) substitution of plywood

tively little in structural respects, al- for lath and plaster: (5) increase in size

though windows were broken and plas- of rafters (to 2 x 8 inches) and wall

ter cracked. Damage to the roof studs: and (6) stronger nailing of winconsisted mainly of broken rafters (2 x dow trames in wall opening,.

6 inches with 16-inch spacing). 5.64 Even with these improve5.62 The basement showed no signs ments, it was expected that almost

of damage except to the windows, and complete destruction would occur at 5

the entry door and frame. The shelters in pounds per square inch peak overpresthe basement were intact, sure, and so one of the houses was

located where the overpressure at the

TWO-STORY, WOOD-FRAME HOUSE: Mach fiont would be 4 pounds per

1955 TEST square inch. Partly because of the increased strength and partly because of

5.63 Based upon the results de- the lowei air blast pressure the house did

scribed above, certain improvements in not collapse (Fig. 5.64). But th,ý supx rdesign were incorporated in two similar structure was so badly damaged that it

wood-frame houses used in the 1955 could not have been occupied without

test. The following changes, which in- expensive repair which would tiot have

creased the estimated cost of the houses been economically advisable.
182 STRUCTURAL. DAM/.GF FROM A!FA BlAST

Figure 5.65. Strengthened wood-frame houe after a nuclear explosion f2.6 psi peak

ovcrpressure ).

5.65 The other strengthened two- TWO-.iTORY. BRICK-WAL L-BEARiNG

story frame house was in a lIcation HOUSE 1955 rEST

where the incident peak overpressure 5.66 For comparison with the tests

was about 2.6 pounds per square inch, on the two-story. wood-frame structures

this was appreciabiy greater than the made in Nevada in 19.3. two bricklower overpressure of the 1953 test. wall-bearing houses of conventional

Relatively heav, damage was experi- construction, similar in sue and layout.

enced. but the condition of the house were exposed to 5 and 1.7 pounds per

was such that it could be made available squarc inch peak (overpressure. respecfor emergency s;helter by shoring and tively, in the 1-)55 tests (Fig. 5.66). The

not too expensive repairs (Fig. 5.65). exterior walls were of brick veneer and

Although there were differences in dIe- cinder block and the foundation walls of

tail, 1he overall damage was moach the cinder block: the floors, partitions, and

same degree as that suffered by the cor- roof were wood-'ramed.

responding house witho'it the improved 5.67 At an incidcnt peak c,,erpresleatures at an overpressure of 1.7 sure of 5 poudis per square inch, the

pounds per square inch. btick-wall house was damaged beyond

• , , •, ,•- •• ,,
RFSiDENTIAI RL( II.RIS 183

II '

Figure 5.66. Unreinforced brick house before a nudear explosion. Ne'.ada Test Site

Figure 5.67. Unreinforced brick house after a nuclear explosion (5 psi peak overpressure).

4;' ._ _ _ _ _
184 STRU'CTURAL DAMAGE FROM AIR BLAST

repair (Fig. 5.67). The iide and back considerable extent. Nevertheless, it:s

walls failed outwawd. The fopt wall condition was such that it could be made

failed initially inward, but its subse- available for habitation by shoring and

quent behavior was obscured by dust. some fairly inexpensive repairs (Fig.

The final lo,:ation of the debris from the 5.68).

fiont wall is therefore uncertain, but

very little fell on the floor framing. The

roof was demolished and blown off, the (RAMBO ER TYPE) HOUSE: 1955 TEST

rear part landing 50 feet behind the

house. Th. first floor had partially col- 5.69 A pair of the so-called

lapsed into "he basement as a result of "rambler" type, single-story, woodfracturing of the floor joists at the center frame houses were erected at the Neof the spans and the load of the second vada 'Fes. Site on concrete slabs poured

floor which fell upon it. The chimney in place at grade. They were of convenwas broken into several large sections. tional design except that each contained

5.68 Farther from the explosion, a shelter, above ground, consisting of

where the peak overpressure was ! .7 the bathroom wails, floor, and ceiling of

pounds per square inch, the corre- reinforced concrete with blast door and

siaonding structure was damaged to a shutter (Fg. 5.69).

Figure 5.68. Unreiiidorced brick house afv'r a nuclzar explosion (1.7 psi peak overpressure).
RESIDFNTIAL STRUCTURES 185

I':

Fimnre 5.69. Rambler-type house before a nuclear explosion, Nevada Test Site. (Note blast

door over bathroom window at right.)

5.70 When exposed to an incident tural damage was a broken midspan

peak overpressure cf about 5 pounds per rafter beam and distortion of the frame.

square inch, one of these lhouses was In addition, the porch roof was iifted 6

demoiished oeyond repair. However, inches off its supports.

the bathroom shelter was not damaged

at all. Although the !atch bolt cn the ONE-STORY, PRECAST CONCRETE

blast shutter failed, leaving the shutter HOUSE: 1955 TEST

unfastened, the window was still intact.

The roof was blown off and the rafters 5.72 Another residential type ,f

were split and broken. The side walls at construction tested in Nevada in l95.,

gable ends wero hlown outward, and fell was a single-story house made of preto the ground. A portion of the front cast, lightweight (expanded shale agwail remained standing, although it was gregale) concrete wall and partition

leaning away frorm the direction of the panels, joincd by welded matching steel

explosion (Fig. 5.70). lugs. Similar roof panels were anchored

5.71 The other house of the same to the walls by special countersurnk and

type, subjected to a peak overpressure grouted connections. The walls were

of 1.7 pounds per square inch, did not supported on concrete piers and a 'consuffer too badly' and it could easily have crete floor slab, poured in place on a

beer. made habitable. Windows were tamped fill after the walls were erected.

broken, doors blown off their hinges, The floor v"as anchored •ecurely to the

and plaster-board walls and ceilings walls, by means of perimetei reinfok'cing

were badly damaged. The main struc- rods held by hook bolts screwed iito

_ _ _ _ _ _ _ _ _ _
186 STRUCTUkAL DAMAGE FROM AIR RI ASi

WN

Figure 5.70. Rambler-tyoe house after a nudear explosion (5 psi pek overpressure).

.-..... w o ..

FigIre 5.72. Reinforced precast concrete house be.fore a nuclear explosion, Nevada Test

inserts in the wall panels. The overall 5.74 There was s3me indication

design was such as to comply with the that the roof slabs at the front of the

Califernia code for earthquake-resistant house were lifted slightly from tmclr

construction (Fig. 5.72). supports, but this was not sufficient to

5.73 This house stood up well, even break any connections. Some of the

at a peak overpressure of 5 pounds per walls were cracked slightly and others

square inch. By replacement of den'ol- shcwf..d indications of miror movement.

ished or badly damagod doors and win- In certain areas the concrete around the

dows, it could havu been made available siab connections was spalled, so that the

for occupancy (fig. 5.73). connectors were exposed. The siecl
RFSIDENTIAL STRUCTURES 1 8"

111111

tilti

Ii -- i - ID 

Figure 5.71 Reinforced precast concrete house after a nucled" explosion (5 psi peak

ovcrpresurel. The LP-gas tank, sheltered by the house- is tssentiaily

undamaged.

window-sash was somewhat distoited, levels, and openings were spanned by

but it remained in place. reinforced lintel courses. The roof was

5.75 At a peak overpressure of 1.7 made of precast, lightweight concrete

pounds per square inch, the precast slabs, similar to those used in tCie preconcrete-slab house suffered relatively cast concrete houses described above

minor damage. Glass was broken ex- (Fig. 5.76).

tansiely, and doors were blown off 5.77 At a peak overpressure of

their hinges and demolished, as in other about 5 pounds per square inch, winhouses exposed to the same air pressure. dows were destroyed and doors blown

Eut, apart from this and distortion of the in the demo!ished. The steel windowsti el wLidow-sash, the only important sash was distorted, but nearly all redamage was spalling of the concrete at mained ia place. The house suffered

the lug connections, i.e., where the sash only minor siructural damage and could

po3jccted intcG the concrete. hive been made habitable at relatively

small cost (Fig. 5.77).

ONE-STORY, REIINFORCED-MASONRY 5.78 There was some evidence th'.t

HOUSE: 1955 TEST the roof slabs had b-.en moved, but not

sufficiently to break any connzctions.

5.76 The last ,ype of house sub- The masonry wall under the large winjected to test in 1955 wvas also of earth- dow (see Fig. 5.77) was pushed in about

quake-resistant design. Tlhe flook" was a 4 inches on the concrete floor slab; this

conc:etc slab, pouted in place at grade. appeared to be due to the omissien of

The walls and partitions were built of dowels between the walls and the floor

lightwc.;ght (expanded shale aggregate) beneaih window openings. Some cracks

8-inch masonry blocks, reinforced with developed in the wall above the sarre

vertical steel rods anchored into the wirdow, probably as a result of irfloor slat. The walls ',cre also rein- proper installation of the reinforced linforced with horizontal steel Zods at two tel course and the 3:bstitution of a pipe
Fig•rC 5 76. " e d mo"blok hOu~e before a nuclear explosion, Nevada Test Figre .' Reinjorc-d Masonry-b~ ho.esite.

7 -i

.... re house after a nocl- explosion (5 psi peak

. Reinf~o;ed MAsonry'-'k hverpressure)

column in the center spa, of the win- sash remained in place but was distore•e h and some opallingfo the concrete

column theenter on spame type Wn- around lug conmectrisn was noted. Oil

around lg cone tion Wthe house 'was

5.d 9 Ahoseo the same type ex- tew'I-tedmg o1 l edl

posed to the bl ast at a peak DyerPressure d he l'le the damage

of 1 .7 pounds per square inch suffered of a minor character . ar d t could readily

little more than the usual destructio' of have been repaired.

doors and window. The steel windo-
TRANSPORTATION i 89

TRAILERZ-COACH MOBILE HOMES: the interior, especially in those coaches

1955 TEST having scree-ns fitted on the inside.

5.80 Sixteen trailer-coaches of Where there were no screens or venetian

various makes, inttmnded f&,f use as mo- blinds, and particularly where there

bile homes, were subjected to bNat in were large picture windows, glass was

the 1955 test in Nevada. Nine were found inside.

located where the peak blast overpres- 5.83 The interiors of !he mr,obile

sure was 1.7 pounds pe| square inch, homes were usually in a state of disorder

and the other seven where the peak due to ruptured panels, broken and upset

oveipressure was about I pound per iurniture, and cup'oards, cabinets, and

square inch. They were parked at wardrobes which had been torn loose

variowu, angles with espect to the direc- and damaged. Stoves, refrigerators, and

tion of ,ravel of the blast wave. heaters were not displaced, and the

5.81 At the higher overpressure two floors were apparently unharmed. The

of the mobile homes were tipped over plumbing was, iii general, still operable

by the explosion. One of these was after the explosion. Consequently, by

originally broadside to the blast, rearranging the displaced furniture, rewhereas the second, at an angle of about pairing cabinets, improvising window

45', was of much lighter weight. All thc coverings, and cleaning up the debris.

others at both locations remained stand- all traier-coaches could have been made

ing. On the wholz, the damage sus- habitable for emergency use.

tained was not of a serious character. 5.84 At the I pound per squzre inmh

5.82 From the exterior, many of the overoressure location some windows

mobile homes showed some dents in were broken, but no major damage was

walls or roof, and a certain amount of sustained. The principal repairs r,:quired

distortion. There were, however, rela- to make the mobile home.s ava-lable for

tively few ruptures. Most windows were occupancy would be window replacebroken, but there was little or no glass in merit or improvised window covering.

TRANSPORTATION

LIGHT LAND TRANSPORTATION distance. An American made automoEQUIPMENT bile was badly damaged and burned at

5.8. In Japan, trolley-car equip- 3,000 feet (0.57 mile) from ground

ment was heavily damaged by both blast zero, but a simiiar vehicle at 6,000 feet

and fire. although the poles were fre- (1.14 miles) suffered only minor damquently left standing. Buses and auto- age.

motiles generally were rendered inop- 5.86 Automobiles and buses have

erable by blast and fire as well as by been exposed to several of the nuclear

damage caused by flying debris. How- test explosions in Nevada, w'here the

ev,-.r, the damage decreased rapidly with conditions, especially as regards dam-
190 STRUCYJHAL DAMAGE F-ROM AIR BLAST

Figure 5.87a. Damage to a.taomob~le originally located behind wood-frame house (5 psi

peak overpressure), the front of this car can be seen in Figure 5.37. Although

badly damaged, tbtw. car could still be driven afte.- the explosion.

Figure 5,87b. Typical public bus damaged by a nuclear explosion, Nevada Tes! Site; thh'

bus, like the one in tl'e kcft background, was overturned, coming to rest as

shown after a displacement of 50 feet.
TRANSPORTATION 19!

age by flue and missiles, were somewhat pounds per square inch location was

different from those in Japan. In the completely destroyed, and only one

Jescriptions that follow, distance is re- wheel and part of the axle were found

lated I', peak overpressu-c. In most after the blast. At 5 pounds per square

cases, iiwever, it was not primarily inch peak overpressure a truck, witin an

overpressure, but drag forces, which earth-boring machine bolted to the bed,

produced the damage. In addition, al- was broadside to the blast. This truck

lowence must be made for the effect of was overturned and somewhat damthe blast wav: precursor (§ 3.79 et aged, but still operable (Fig. 5.39). The

seq.). Hence, the damage radii cannot earth-boring machine was knocked

he de~ermirned from overpressure alone, loose and was on its side leakinae gaso5.87 Some illustrations of the ef- line and water. At the same loca,ion,

fects, of a nuclear explosion on mo- shown to the left of ,hX overturned truck

torized veniiis are shown in Figs. in Fig. 5.89. ",:,s a heavy-duty electric

5.? a and b. At a peak overpressure of 5 • t;-.:, Lruck, iacing head-on to the blast.

pounds per square inch motor veb;,",•, It had the windshield shattered, both

were badly battered, with th•;r tcps and doors and cab dished in, the hood partly

sides pushed in, windows b,'oker, and blown off, and one tool-compartment

hoods bWown open. But the engincs were door dished. There was, however, ric

still operable and the vehicles could be damage to tools or equipment and the

driven away after the explosion. Even at truck was d-riven away without any rehigher blast pressures, when the overall pairs being required.

damage wzs greater, the motors ap- 5.90 At the 1.7 pounds per square

peared to be in'act. inch location, a light-duty electric utility

5,89 During thz 1955 tests in Ne- truck and a fire department 7)-foot

vada, stluies were riade to determine aerial ladder truck sustained minor exthe ce tent to which various emergency terior damage, such as broken windows

veh ,cles and their equipment would be and dished-in panels. There was no

a~ailable for use immediately foliowing damage to equipment in either case, and

a nucltear attack The vehicles included a both vehicles would have been available

rescue truck, gas and electric utility for immediate use after an attack. Two

service or repair tiucks, telephone ser- telephone trucks, two gas utility trucks,

vice trucks, and fire pumpers and ladder a fire department pumper. and a Jeep

trucks. One vehicle was exposed to a firetruck, ext .,sed to a peak overprespeak overpressure of about 30 pounds sure of I pound per square inch, were

per square inch, two at 5 pounds per largely unharmed.

square .r ch, two at 1.7 pounds per 5.11 It may be concluded that vehisquare inch, and six at about I pound cles designed fo)r disaster and emerpe, square inch. It should be empha- gency operation are substantially consized, however, that, foy vehicles in structed, so that they can withstand a

general, overpressure is not usua!ly the peak overpressure of about 3 pounds per

sole or even the primary damage mech- square inch and the associated dynamic

anism. pressure and still be capable of opera5.89 The rescue trnuck at the 30 tion. Tools and equipment are protected
192 STRUCTURAL DAMAGE FROM AIR BLAST

Figure 5.89. Truck broadside to the blest wav2 (5 psi peak overpressure) overturned,

electric utility truck in background head-on to blast was damaged but

remained standing.

from the blast by the design of the truck body rf an empty wooden boxcar,

body or when housed in compartments weighing about 20 tons, was lifted off

with strong doors. the trucks, i.e., the wheels, axles, etc.,

carrying the body, and landed about 6

RAILROAD EQUIPMENT feet away. The trucks themselves were

pulled off the rails, apparently by the

5.92 Railroad equipment sufltred brake rods connecting them to the car

blast damage in Japan and also in tests body. A similar boxcar, at the same

in Ne-,ada. Like motor vehicles, these location, loaded with 30 tons of sandtargets are primarily drag sensitive and bags remained upright (Fig. 5.92b). Aldamage cannot be directly related to though the sides were badly damaged

overpressure. At a peak ove:pressure of and the 'oof demolished, the car was

2 pounds per square inch from a kilo- capable of being moved on its own

ton-range weapon, an empty wooden wheels. At 7.5 pounds per square inch

boxcar may be expected to receive rela- peak overpressure, a loaded boxcar of

tively minor damage. At 4 pounds per the same type was overturned, and at 9

square inch overpressure, the damage tc pounds per square inch it was coma i.,aded wooden boxcar would be more pletely demolished.

severe (Fig. 5.92a). At a peak over- 5.93 A Diesel locomotive weighing

pressure of 6 pounds per square inch the 46 tons was exposed to a peak over-
TRANSPORTA NON 193

Fig-ure 5.92a. Loaded wooden boxcar after a nuclear explosion (4 psi peak overp~essure).

'I'

3.

Figure 5.92b. Loaded wooden broxcar after a nuclear explosion (6 psi peak overpressure).

pressure of 6 pounds per square inch and compartment doors and panels.

while the engine was running. It con- There was no damage to the railroad

tinued to operate normally after the track at this point.

blast, in spite of damage to windows
194 STRUCTURAL DAMAGF FROM AIR BLAST

AIRCRAFT through the water. At closer ranges, air

5.94 Aircraft are damaged by blast blast can cause hull rupture resulting in

effects at lc,,els of peak overpressure as flooding and sinking. Such rupture aplow as I to 2 pounds pcr sqoare inch. pears likely to begin near the waterline

Complete destruction or damage beyond on the s!de facing the burst. Since the

economical repair may be expected at main hull generally is stronger than the

peak overpressures of 4 to 10 pot-nds superstructw'e, structures and equipper square inch. Within this range, the menc exposed above the waterline may

peak overpressure anpears to be the be damaged at ranges well beyond that

main criterion of dam-ge. However, at which hull rupture might occur.

icsts indiate that, at a given overpres- Masts, spars, radar antennas, stacks,

sure, damage to an aircraft oriented with electrical equipment, and other light

the nose toward the burst will be less objects are especially sensitive to air

than damage to one with the tail cr a blast. Damage to masts and stacks is

side, directed toward the explosion, apparent in Fig. 5.96; the ship was ap5.95 Damage to an aircraft exposed proximately 0.47 mi!e from surface zei'o

with its left side to the blast at a peak at the ABLE test (about 20-kiloton air

overpressure of 3.6 pounds per square burst) at Bikini in 1946. Air blast may

inch is shown in Fig. 5.95a. The fu- also roll and possibly capsize the ship;

selage of this aircraft failed completely this effect would be mest pronounced

just aft of the wing. The skin of the for the air blast wave from a large

fuselage, stabilizers, and epoine cowl- weapon striking the ship broadside.

ing was sevwrely buckled. Figure 5.95b 5.97 Blast pressures penetrating

shows damage lo an aircraft oriented through openings of ventilation systems

with its tail toward the burst and ex- and stack-uptake systems can cause

posed to 2.4 pounds pcr square inch damage to interior equipment and compeak overpressure. Skin was dished in partments, and also to boilers. Damage

on the vertical stabilizer, horizontal sta- to the latter may result in immobilizabilizers, wing surface above the flaps, tion of the ship. The distortion of

and outboard wing sections. Ve'ican weather bulkheads may render useless

stabilizer bulkheads and the fuse!age interior equipment mounted on or near

frame near the cockpit were buckled. them. Similarly, the suddenly applied

blast loaJing induces rapid motion of

the structures which may cause shock

SHIPPING damage to interior equipment. Equipment in the superstructure is most su5.96 Damage to ships from an air or sceptible to this type of damage, alsurfact. burst is due primarily to the air though shock motions may be felt

blast, since little pressure is transmitted throughout the ship.

tJ
UTI[ [TIES 195

•;.• • ,,A • _ -,J. #.'., ....

Figure 5.95a. Aircraft after side exposed to a nuclear explosion (3.6 psi peak overpressure)

i 4 83730t

Figure 5.95b. Aircraft after tail expesed to a nuclear explosion (2.4 psi peak overpressure).

UTILITIES

ELECTRICAL DISTRIBUTION bution systems suffered severely. Utilily

SYSTEMS poles were destroyed by blast or fire,

5.98 Because of the extensive dam- and overhead lines were heavily damage caused by the nuclear explosions to aged at distances up to 9,000 feet (1.7

the citics in Japan, the e!ectrical distri- miles) from giound zero (Fig. 5.98).

I
19t; SI PIU('LIRAI flAN4AGI FROM1 AIR BI AST

Figure 5.96. The U.SS. Crittenden after ABLE test: damage resulthil was ger v~

serious (0.47 mile from surface ;.ern'/

Underground elect~ica circuits werce, Motors and generators were aam!Aged by

however, little affc.cted. Switchgear and fire.

transformeis v-.ere not damaged so much 5."9 A fairly extensive study of the

directly by blast as by -,ecoridary effects, tt.ects of a nuclear explosion on electric

,!uch as collapse of the structure in utp~iltkes was niade in the Nev3da tests in

which they were lcc'ted oi- by debris. 195 1. Among the purposes of these tests
UTI.ITiES 197

Figure 5.98. Damage to utility pole (0.80 mile from ground zero at i-Hiroshima).

were the following: (1) to determine the suffer little or no damage (2) to study

blast pressure at which 3tandard electri- the extent and character of the damage

cal equipment might be expected to that might be sustained in a nuclear
198 STRUCTURAL DAMAGE FROM AIR Bh AST

attack; and (3) to detcrmine the r,;;ure 5.102 The only damage suffered by

of the repdirs that would be needed to the high-voltage trans'rission line was

restor, e-ectrical service in those areas the coilz.pse of the sbspension tower,

w1 .W homes and factories would sur- bringing down the distibuvi.-n line with

vive sufficiently to permit their use atter it (Fig. 5. 102a). It may be noted that the

some repair. With these objectives in dead-end tower, which was much

mind, two identical power systems were stronger and heavier, and another suserected; one to be subjected to a peak pension lower of somewhat stronger

ovcrpressuie of about 5 and a dynamic design were only slightly affected (Fig.

pressure of 0,6 pounds per square inch 5. 102b). In some parts of the United

and the other to 1.7 and 0.1 pounds per States, the suspension towers are of

square inch, ;espý,ctively. It will be re- similar heavy construction. Structure.,

called that, at the lower ovcrpressure. of this type ate sensitive to drag forces

typlcai Amer;can residences would not which are related to dynamic pressure

be damaged beyond the. pe'•:-ibilizy of and positive nhase duration. so that the

further use. overpressure is not the important crite5.100 Ea.ch power system consisted rion of damage.

of a high-voltage (69-kV) transmission 5.103 Tlie tran::forrner substation

line on steel towers connected to a con- survived the blast with relatisely minor

ventional, outdoor transformer substa damage to the essential components.

lion. From this proceeded typical over- The metal cubicle, which housed the

head distribution lines on 15 wood meters, batterie., and relays, suffered

poles; the latter were each 45 feet long badly, but this substation and its conand were set 6 feet in the ground. Ser- tents were not essential to the emervice Yrops from the overhead .*m..; sup- gency operation -f the power system.

plied elecoiicity to equipment placed in The 4-kV regulators had been shifted on

soine of the houses used in the tests the co.ncrete pad, resulting in separation

described earlier. Thesu installations of the electrical connections to the bus.

were typical of those serving an urban The glass cells of the batteries were

community. In addition, the 69-kV broken and most of the plates were

transmission line. the 69-kV .:witch rack beyoncd repair. But relays, meters, and

with oil circuit--breakers, and power other in.;trumerts were undamaged, extransformer represented equipment of cept for broken glass. The substation as

the kind that might supply electricity to a whole was in sufficiently sound conlarge industrial plants. dition !.o permit operation on a n.ona,;

5.101 At a peak overpres'-ure of 5 tomatic (manual) basis. By replacing the

and a dynamic p,'essuke of 0.6 pouads batteries, automatic operatior. could

per square inch the power system suf- have been restored.

fered to some extent, but it was not 5.104 Of the 15 wood pole' used to

seriously harmed. The type of damage carry the lines from the substation to the

appeared, on the whole, to be similar to houses, our weie blown down cornthat caused by severe wind storms. In pletely and broken, and two others were

addition to the direct effect of blast, extensively damaged. The collapse of

some destruction was due to missiles. the poles was attributed partly to the
UTILITIES 199

/M Inn

7X 4!rm~,r

~ -;0

I-,igu 5A -2. *cr( C lasdsseso s el vrrsue . ý ya i

S ~ S

-4 - -U

Figure~ 5. 102b Colapsend twr suspension tower. n -i-enr (5 psi peal' overpresr yaics

sr,06pidnmcpressure 30-K from e iloton xpi osion), Nevad a T estte

(Fg 5.0) Ote daag wa e.1w i,530) eel~S h

lieedtohecasued 0.6 pisils dyiii prssr cafrom s p~kotn hcxpi'si), Nevda estect

5.105 ;-cveral Jistributor trans- outs rwvciico~o ohaui

ficrmors had filien Wion the poles and ntur anJ1 copper, -,nO t~le aerial cal-es
20(0 STRUCTURAL DAMAGE FROM AIR BLAST

I.

• , - -,- -- '- " • -

Figre -5. 104. Collapse of utility pokt, on line (5 psi peak overpressure, 0.6 psi dynamic

pressure from 30-kiloton explosion), Nevada Test Site.

were unharmed. Although the pole fine resulted from breakage of pipes inside

would have requited some rebuilding, and at enirances to buildings or on

the general damage was such that it structures, rather than from tne disrupcould have been repaired within a day or tion of underground mains (Figs. 5.106a

so with materials normally carried and b). The exceptional case was one in

stock t-' clectric utility companies. which the 12-inch cast iron water piives

w-e., 3 feet below grad,, in a filled-in

OAS, WATER. AND SEWERAGE area. A number of depressions, up to I

SYSTEMS foot ;r. depth, were produced in the fill,

and these caused failure of the under5.106 The public utility system in ground pipes, presumably due to unNagasaki was similar to that of a some- equal displacements.

what smaller town in the United States, 5.107 There was no appreciable

except that opern sewers were used. The damage to reservoirs and water-treatmost significat damage was suffered by ment plants in Japan. As is generally the

the water supply system, so that it be. case, these were located outside the

came almost iinpossible to extinguish cities, and so were at too great a disfires. kxcept for a special case, de- tance from the explosiors to be damscribed below, loss of water pressure aged in any way. I
UTi IITES 201

Figure 5.105. Transfoirner fallen frc,m collapsed utility pole (5 psi peak overpressure),

Nevada Test Site.

5.108 Gas holders fmfiered heavily tests made in Nevada in 1955 was to

from blast up to 6,000 feet (L. I miles) dete~rmine the ttent to which natural

frmn; ground zero arid the escaping gas and manufaoi.t:ed gas utility installawas ignited, but there was no e~xplosion. tions might be ";ýsrupted by a nuclear

Underground gas mains appear to have explosion. The test was intended, in

been little affected by the blast. particular, to provide information conNATUR~AL AND MANUFACTURED :ýerning the effect of blast oni critical

GAS INSTALLATIONS underground units of a typical) gas dis5.109 One of the objectives of the tribution system.
202 ?-Q,'CTIJR,-I[ DAMAGEI FROM AIR BLASI

Figure 5. 106a. Four-inch gate valve in water main broken by debris fro~m brick wall (0.23

mile from ground zero at l-ir')siima).

Figure 5.106b. Broken portion (f 16-inch wawe main carried on bridge (0 23 mile from

ground .ero at Hiroshima).

t-.110 The installationts tested were transmission and distribution main of

of two kinds, each in duplicate. The first 6-inch steel and covs iron pipe, at a

represented a typical underground gas- depth of 3 feet, with it~s associated ser-
UTILITIES 203

vice p~pes and ariachments. Valve pi's peak cverpressuve location a I 1⁄2&-inch

of either brick or concrete blocks con- pipe pressttre-test riser was bent to the

tained 6-inch valves with piping and ground, and the valve handle, stem, ond

protective cashags. A street regulator- bonnet had blown ott. At the same place

vault held a 6-inch. ,ow-pressure, V*|ot- two 4-inch ventilating pipes of the street

loaded regulator, attached to steel pip- regulator-vaults were sheared off just

ing projecting through the waits. One f below ground level. A few minor leaks

`hese underground systems w ,s installed developed in jute and lead caulked cast

where the blast overpressure was about iron bell and spigot joints because of

30 pounds per square inch and the other g:'ound motion, presumably due to

at 5 pound3 per square inch. No domes- grourid shock induced by air blast. Othtic or ordinary industrial structures at the erwise thc blast effects were negligible.

surface would have survived the higher 5.113 At the peak overpressure of

of these pressures. 1.7 pounds per square in:ch, whe,'- the

houses did not suffer severe damage, 5.11 seondtypeoi *re nstala- (§ 5.59), the service piping both inside

tion consisted of typical service lines of an outsid the se s was u n sade

steel, copper, and plastic materials con- as auso wee pr essur sruu haor ed,

nected to 20-foot lengths of 6-inch steel m s In the two-s ory r ick ho us a

main. Each service pipe rose out of the 5 p n pe sqore ic k oue;-

ground at the side of a housc, and was

pressure, which was demolished beyond

joined to a pressure regulator and meter. press .57, th deoihe pin bse.

The henenteed ipe t,^ all f t e p'air (§ 5.57), the piping i;) ihe base- The ,oipe then entered the' wall of the retwsdslcdad~ta e&

house about 2 feet above floor level. The ofnt col lase of te it floor. T

coppr pasti ad sevce terninted of the collalrse of the first floor. The

copper and plastic services terminated mtras e,.n eahdfo h

inside the wall, so that they would be mtras e..n eahdfo h

isidjec the wtrall s tht thosey woud be fittings and fell to the ground, but the

subject to strain if the house moved on meritlfadheegaoreeun

its ounatin. Te seelse~vce ine meter itself and the regulator were un- its foundation. The steel service line dmgda~ tl prbe l te

similarly terminated inside the wall, but s er a nd eqi pmen tw er

it was also attached outside to piping sentially intact.

that ran around the back of the house at

ground level to connect to the house 5.114 Domestic gas appliances,

piping. This latter connection was made sucn as refrigerators, ranges, room

heaters, clothes dr•,crs, and water heatwith flexible seamless bronze tubing, ers s lotere t d a o e a tenthonly

passing through a sleeve in the wall of There a so ded acement onlt.

thebuidig. typca doestc as p-There was some displacement uf the the building. Typical domestic gas ap- appliances anJ conne,'Lv t., which was

pliances, some attached to the interior related to t dmage which b th

piping, were located in several houses. house. H-owever, e',en• in the collapsed Duplicate installations were located at to-story, eri hse 5. the

pea ovrprssues f 5and1.7poudstwo-story, brick house (§ 5.67), the

peak overpressures of 5 ani 1.7 pounds upset refrigerator art range were prebper square inch, respectively, ably still usable, although largely buried

5.112 Neither of the underground in debr,. . The general conclusion is,

installations was greatly affected by the therefore, that domestic gas (and also

blast. At the 30 t.ounds per square inch electric) appliances would be operable

_ j
204 STRUCTURA! DAMAGE FROM AIR BLAST

in all houses that did not suffeý maior 5.11S The dual-cylinder installastructural damage. tion. e~iposed to 25 pounds per square

inch peak overpressure, suffered most.

LIQUID PFTROLEUM (LP) GAS the regulators were torn loose from their

ISALAQDPTIOLEMNS) A mountings and the cylinders displaced.

One cylinder came to rest about 2,001)

5.115 Various 1,P-gas installatioms feet from its original position- it was

have been expoFd to air blast from badly dented, but was still usable. At

nuclear tests in Neviada to determine, the both 25 and 10 pounds per square inch

effects of typical gas containers ac:d peak overpressure the components, alsupply systems such as are found at though often scparated. could generally

suburban and farm homes and at be salvaged a;.d used afain. The cylinsto-age, industrial, and utility plants. 1,1 der installations at 3 pounds per square

addition, it was of interest to see ,,,a, ihch peak overpres'iure were mostly

reliance might be placed upon LP-gas as damaged by missiles and falling debris

an emergency fuel aftel d nuciear attack. from the houses t, wi,'-h they were

5.116 Two kinds of typical home attached. The cor.ponent parts, except

(or small commercial) LP-gas installa- for the ccpper iobing, .;;Cered littie and

tions were tested: (I) a system consist- were usabic. At .7 pounds p-r square

ing of two replaceable ICC-approved inch, there w.s reither darnage to nor

cylinders each of 100-pound capacity, dislocation of LP-gas cylinders. Of

and (2) a 5C0-gallon bulk storage type those tested, only one cylind,. develsystem filled from a tank truck. Some of oped a leak, and this was a small puncthese installations were in tr q open and ture resulting from impact with a sharp

others were attached, in the usual ;nan- object.

ner, by means of either copper tubing or 5.119 The 500-gallon bulk ga:;

.;tee! pipe service line, to ,.me houses tanks also proved very durable and ex-

,.xposed to :eak overpressures of 5 and pertenced little Jamage. The tank clo1.7 pounds per square inch. Others were sest to the explosion was bounced endlocated where the peak ovcrpressures over-end for a distance of some 700

were about 25 and 10 pounds per square feet; neertheless, it suffered only su..

inch. In these cases, piping from the gas perficially and it, stre..gth and s,.-vic1.acontainers passed through a concrete bility were not impaired. The filler valve

wall simulating the wall of a house. was damaged, but the internal check

5.17 In addition to the foregoing, valve prevented escape of the contents.

a compiete bulk storage plant was The tank exposed at 10 pounds per

erected at a point where the peak over- square inch peak overpressure was

pressure was 5 pounds per square inch. moved about 5 feet, but it sustained

This consisted of an 18,000-gallon tank little or no damage. All the other tanks,

(containing 15,400 gal'ons of propane), at 5 or 1.7 pounds per square inch,

pump compressor, cylinder-filling including those at house,: piped for serbuilding, cylinder dock, an- all neces- vice, were unmoved and undamaged 1

saiy valves, fittings, hose, accessories, (Fig. 5.73).

and interconnecting piping. 5.129 The equipment of the

Jg

.+!u •I!11 ,•,' .IVlllll!ililllll' qNI'IF lll~lII•I "ili~~m~llr1% nl
UTILITIES 205

- 0-

Figu-t 5.120. LJproer photo: LP-gas bulk stor:ge and filling plant before a nuclear explosion. Lower photo: The plant aftcr the explosion (5 psi peak overpress'Jre).

18,00O-ga~lon bulk storage and filling was no leakage of gas. The plant could

plarnt received only superficial damage have been readily put back into operafrom the. blast at 5 pounds per square tion if power, from elcctricity or a gasinch peak ovarpressue. The cylinder- olin.z engine, were restored. If not, li'jfilling building was completely demo'- uid propane in the storage tank could

ished; the scale used for weighing the have been made available by taking adcylinders was wrecked, and a fiilng line vantage of gravity flow in coniunction

was broken at the point where it euiered with the inherent pressure of the gas in

the building (Fig. 5.120). The major the tank.

ope:ating services of the plant would, 5.121 The general conc!usion to be

however, not be affected because the drawn from the tests is that standard

transfer facilities were outside and uin- LP-gas equipment is very rugged, exdamaged. All valves and ncarly all pip- cept fo: cop;er tubing t.onnections.

ing in the plant were intact and there Disruption of the service as a r-sult of a

I_
206 STRUCTURAL DAMAGE FROM AIR BLASF

nuclear attack would probabiy be local- mainly for domestic purposes. it appears

ized and perhaps negligible, so that LP- that the gas supply would not be afgas might prove to be a very useful tected under such conditions that the

emergency fuel. Where LP-gas is used house remains hz,,itablt-.

MISCELLANEOUS TARGETS

COMMUNICATIONS EQUIPMENT vacuum or picture tubes were broken.

S.122 The importance of having The only mobile radio station to be

communications equipment in ooerating seriously affected was one in an autocondition after a nuclear attack is cvi- mobile which was completeiy cru3hed

dent and so a variety of such equipment by a falling chimney.

has been tested in Nevada. Among the 5.i24 A guyed 150-foot antenna

items exposed to air blast were mobile tower was unharmed, wu• an unguyed

radio-communication systems and unith, 120-foot towel, o" lighter construction,

a standard broadcasting transmitter, an- close by, broke off at a height of about

tenna towers, home radic and television 40 feet and fell to the ground (Fig.

rece&vers, telephone equipment (includ- 5. 124). This represented the only

ing a small telephone exchange), public serious damage to any of the equipment

address sound system'-, and sihens. tested.

Some of these were located where the 5.125 The base station antennas,

peak overpressuie was 5 pounds per which were on the towers, appeared to

square inch, and in most cases there withstand blast reasonab!y well, alwere duplicates at 1.7 pounds per square though those avtached to the unguyed

inch. The damage at the latter location tcwer, referred to above, suffered when

was of such a minor character that it the tower collapsed. As would nave

need not be considered here. been expected from their lighter con5.123 At the higher overpressure struction, television antennas for home

region, where typical houses were dam- receivers were more easily damaged.

aged beyond repair, the communica- Several were bent both hi the blast and

tions equipment proved to be very re- the col!apse of the houses upon which

sistant to blast. This equipment is drag they were mounted. Since the houses

sensitive and so the peak overpressure were generally damaged beyond repair

does not deicrmine the exteni of dam- at a peak overpresstire of 5 pounds per

age. Standard broadcast and television square inch, the failt, e of the television

receivers, and mobile radio base stations aitennas is not of great significance. 4

were found to be in working condition, 5.126 Some items, such as power

even though they were covered with lines and telephone service equipment,

debris and had, in some cases, been were frequently attached to utility-line

damaged by missiles, or by being poles. When the poles failed, aS they did

thrown or dropped several feet. No in some cases (§ 5.104), tne communi-

-t I
A . - .. .*

MISCELLANEOUS TARGETS 207

I ..

ctog. . os o w - V

Figure 5.124. Unguyed lightwveight 120-foot antenna tower (5 psi peak overpressure, 0.6

psi dynarmic pressure from 30-kiloton explosion), Nevada Test Site.

cations 3ystems suffered accordingly,. Nagasaki. Those of wood ,were burned A

Although 1he equipment operated satis- in most cases, but steel-girder bridges

factorily after repairs were made ,", the suffered relatively littl" destruction

wire line, it appears that the po~wer sup.- (Figs. 5. 127a and b). One bridge, only

ply represents a weak link in the com- 270 feet from ground zero, i.e., about

munications chain. 2,100 feet from the burst point, which

was of a girder type with z reinforcedBRIDGES concrete deck, showed no sign of any

structural damage. It had, apparently,

5.127 There were a number of dif- beei. deflected downward by the blast

ferent kinds of bridges exposed to the force and had rebounded, causing only a

nuclear explosions in Hiroshima and slight net displacement. Other bridges,

A

I
208 STRUCTURAL DAMAGE FROM AIR BLAST

Pr 4I

R-Ah

Figure 5.1 27a. Bridge with deck of reinforced concrete on 'eýýl-plttc girders; outer girder

had concrete facing (270 feet from groind ze. . at Hiroshima). The railing

was olown down but the deck receiv'ed little Jamage so that traffic

continued.

at greatei distances from ground zero, concrete slab in such a manner as to

.uffered rror- latzral shifting. A rein- duplicate good industrial practice. Two

forced-concrete deck was lifted from the engioe lathes (weighing approximately

supporting steel girder of one bridge, 7,000 and 12,000 pounds, respecapparent[, ý,s a result of reflection of the tively), and two horizontal milling mablast wave from the Eurface of the waier chine; (7,000 !and 10,000 pounds, rebelow. spectively) were expo-Ad to a peak

overpressure of 10 nou.ds rer square

HEAVY-DUT Y MACHINE TOOLS inch. A concrete-block wall, F inches

thick and 64 inches high, was con5.128 The vulnerability of heavy- structed immediately in front of the maduty machine tools and their compo- chines, i.e., between the machines arid

nents 'o air blast from a nuclear explo- ground zero (Fig. 5.128). The purpose

sion was studied at the Nevada Test Site of ,his wall was to simulate i!, •-xterior

to supplement the information from Na- wall of the average industrial plant and

gasaki (§ 5.33). A number of machir 2 to piovide debris and missiles.

tools were anchored on a reinforced-
MISCELLANEOUS TARGETS 209

I: :

Figurc 5.127b, A sleel-plate girder, double-track railway bridge (0 16 mile from ground

zero at Nagasaki). The plate girders were moved about 3 feet by !he blast:

the railroad tr'.ick was bent out of shape and trolley cars wert. demolished.

t-u, the poles were left standing.

5.129 Of the four machines, the rucii (if which resulted from the exthree lighter ones were moved from pect-," tompleic demolition of the ccntheir foundations aad dLmaged quite eret-block wall. Delicate iuiechanisms

badly (Fj-. 5 129a). The fourth, weigh- ar.d appendages, which are usually on

ing 12,000 pounds, which was consid- the exterior and unprotected, suffered

ered as the only one to be actually of the es-pecialIV severely. Gears and gear

heavy-duty type, survived (Fig. cases were damaged, hand valves and

5.129b). From the observations it was control levers were broken off, and

conc!uded that a properly anchored ma- drive belts were broken. It appears,

chine tool of the true heavy-duty type however, that most of the missile damwould be able to withstand peak over- age could be easily repaired if replacepressures of 10 pcJnds per square inch ment parts were available, since major

or more without substantial damage. dismanwling would not be required.

5.130 In addition to the direct ef- 5.131 Behind the two-story brick

fects ,J blast, considt,-able iestruction htwse in the peak overpressure region of

was caused by deblis and missiles, 5 pounds per square inch (§ 5.67), a

. .-

I.• I I 1 •I 15NIIH•" '• II111I •I I •1' I • 1H 9 iB ~ i'll'q||' ' I
210 STRUCTUJR\L DAMAGE FROM AIR BLAST

I,.

Figure 5.128. Machine tools behind masonry wall before a nuclear explo-•on, Nevada Test

Site.

200-ton capacity hydraulic press weigh- vessel weighing roughly 4,100 pounds,

ing some 19,000 pounds was erected. and a steei steam oven approximately

The location was chosen as being the 2'/2 feet wide, 5 feet high, and 9 feet

best to simulate actaal factory condi- long Both buildings suffered extions. This unusually tall (19 feet high) tensivk:ly from blast, but the equipment

and slim piece of equipment shewed experienced little or no operational

little evidence of blast damage, even damage. In one case, the collapsing

though the brick house was dcmcrlished. structure fell on and broke Uff an exIt was probable that the house provided posed part of the milling machine.

some shieding from he blast wave. 5.133 The damage sustained by

Moreover, at the existing blast pressure, machine tools in the Nevada tests was

niis!iles did not have high velocities, probably less than that suffered in ' pan

Such iainor damage as was suffered by at the same blast pressures (§ 5.33).

the machine was probably due to debris Certain destructive factors, present in

falling from the houis,. the latter case, were absent in the tests.

5.132 At the 3-pounds per square First, the conditions were such that there

inch peak overpressure location, tfhere was no damage by fire; and, second,

were two light, industrial buildings of there was no exposure to the elements

standard type. in each of these was after the explosion. In addition, the totzl

placed a vertical milling machine amount of debris and missiles produced

weighing about 3,000 pounds, a 50- in the tests was probably less than in the

gal'an capacity, stainless-steel, pressure industrial buildings in Japan. i 4 1A
MISCELL[ANEOUS TARCETS 211

~~jA A

Figue 5.29a.Machne tolsafter 2 nuclear explosion (10 psi peak overpressure).
212 STFUCTURAI. DAMAGE FROM AIR BIASI

ANALYSIS OF DAMAGE FROM AIR BLAST

iNTRODUCTION use of the structure or object for its

5.134 The remainder of this chapier intended purpose unless major reis concernied with descr;ptions of air- pairs are made.

blast damage criteria for various types

of targets and with the development of Light Damage

damage-distance relationships for predicting :he distances at which Jamage A degree of damage to buildings

may be expected from nuclear explo- resulting in broken windows, slight

sions of different energy yields The damage to loofing and siding,

nature of any target complex, such as a blowing down of light interior parcity, is such, however, that exact pre. titions, aaid sligh, cracking of curdictions are noý possible. Nevertheless, tain walls in buildings. Minor re

by application of proper judgment to the pairs are sufficient to permit use of

available information, results of practi- the structure or 0,jecl for its incal value can be obtained. The conclu- tei.ded purpose.

sio,is given here are considered to be 5.136 For a number of types of tar-

-applicable to average situations that gets, the distances out to which eifferent

might be encountered in an actual target degrees of damage may be erpecied

complex. from nuclear explosions of various

5.135 Damage to structures and yields have been represented by diaobjects is generally classified in three grams, such as Figs. 5.140 and 5. !46.

categories: severe, moderate, and light. These are based on observations made

In several of the cases discussed below, in Japan and at various nuclear tests, on

the specific nature of each type of dan;- experiments conducted in shuck tubes in

age is described, but the following laboratories and with high-expiosi,;es in

broad definitions are a useful guide, field tests, and on theoretical anclyses of

the loading and response of stru~ctures

Severe Damage (see Chapter IV). As a result of these

studies, it is possible to make reasonA -iegice of damage that precludes ably accurate predictions of the response

furthcr use of the *structure or ob- of ihiterior as well as exterior wall panels

ject for its intended purpose with- and complete structures to the air-blast

out essentia!ly complete recorn- wave. These predictions, however,

struction. For a structure or must take into account constructional

buildiar,, collapse is generally im- details of each individual structure.

plied. Moieover, observations made during

laboratory tests have indicated a large

scatter in failure loadings as a resulr of

statistical variations among wall and

A degree of damage to principal material properties. The data io Figs.

members that precludes effective 5.140 and 5.146 are intended, however,

"A

.*
,,kNAIYSIS OF DAMAGE FROM AIR BI AS'T 2 13

to provide only gross estimates fou the there is nicreased drag damage with incategories of st~uctures g-,ven in Tables creased duration a! a given pressure, the

5, 139a and b. The response of a partie- same damage will extend to lower dyular structure may thus deviate from that namic pressure levels. Structures which

shown for its class in the figures. are sensitive to drag loading will there5.' 37 For structures that are darn- fE,re be damaged over a range that is

ageo primarily by diffraction loading larger than is given b) the cube root rule

(§ ,1.03), the peak overpressure is the for diffraction-type structures. In other

important factor in determining the re. words, as the result of a thousand-old

sponse to blast. In some instances, increase in the energy of the explosion,

where detailed analyses have not been the range for a specified damage to a

performed, peak overpressures are drag-sensitive .;tructure will be injriven for various Hnds of damage. Ap- creased by a factor of more than ten, and

proximate damage-distaace relation. the area by more than a hundred.

ships c;,n then he derived by using peak

overpressure-dist3nce curves, and scal- ABOVE-GROUND BUILDINGS

ing laws from Chapter III. For equal AND BRIDGES

scaled heights of burst, as defined in 5.139 The detailed nature o t0ee

§ 3.62, the range for a specified damage damage in the severe, moderate, and

!o a diffraction-sensitive structure in- light categories to above-grcund struccreases in proportion to the cube root, tures of varioui, types are given in

and tbe damage area in proportio-i to the Tables 5.1 39a and b. For convenience,

two-thirds power, of the energy of the the information is divided into two

explosion. This means, for example, groups. TaEle 5.139a is concerned with

that a thousand-fold increase in the en- structures of the type that are primarily

ergy wiHl increase the range for a par- affected by the blast wave during the

ticular kind of diffraction-type damage diffraction phase, whereas the structures;

by a factor of roughly ten; the area over in Table 5. 139b are drag sensitive.

which the damage occurs will be in- 5.140 The ranges for severe and

creased Ly a factor of about a hundred, moderate damage to the structures in

for a given scaled burst height Tables 5. 139a and b are presented in

5.138 Where the response depends Fig. 5. 140, based on zctual observations

mainly on drag (or wind) loading, the and theoretical analysis. The numbers (I

peak overpressure is no longer a useitui to 21) in the figure identify the target

criterion of daokage. The response of a types as given in the first column of the

drag-sensitive s.ructure is determined by tables The data refer to air bursts with

the length of the blast wave positi,,e th, height of burst chosen so as to maxphase as well as by the peak dynamic imize the radius of damage for the parpressuie (§ 4.12 et seq.). The greater ticular target being considered and is not

the energy of the weapon, the farther necessarily the same for different tarwill be the distance ft:)m the explosion ge!s. For a surface burst, the respective

at which the peak dynamic prcssure has ranges are to be multiplied by threea specific value and the loaIger will he fourths. An example illustrating the rse

the duration of the positive ,.•--. Since of the diagram is given.

(Text continued on page 220.)

I,
214 STRUCTURAI DAMAGE FRGM4 AIR i3LAST

Tible 5.139a

DAMAGE CRITERIA FOR STRUCTURES PRINIARILY AFFECTED BY DIFFRACTION

LOADING

Description of Dairn-ge

Structural Description of___------- ___--- - -

T ype Structure Severe Moderate Light

Nultistory M reinforced Walls shattered, se- Walls breacht-d oi SOMrn! ~eCid ng (of

concrete bu'ilding vere framne distor- on the poiri -,f concrete walls and

with rcir'orced c'.ý- tion, incipient col- being so, frame frame.

crete walls, H'ast ;e- lapse. dis;, tled, entrancesistant d&Jin for ways damage,],

30 psi Mach regitri doors blown in or

piessure from I MT, Jammed. ext iv'.'e

no windows. spalling of coq

crc I".

2 Netiltisttory reinforced Walls ihattered, se Uxterior walls se- Windows and doors

concrete buiidiing vere framne disior- vkvrely cracked In- blown in. interior

with concrete %;ijlis, tion, incipieit col- tetior partitiors se- partitions cracked

small window area, 11.pse. ';erly crxked or

three ito eight stories. blown down. Structural :*iame 1,e'riaýici~dy distorted.

coensivý.- spalling

of concrele.

3 Multistory wall-bear- Collapse oif bearing E;~ccii,. rwa:ls se- Window:. and doors

ing huilding, brick walls, :esulting in verely cracked, in- hlo'wn iti, interior

apartment house' total .:ollapsc of tenior p~krtifiti;s se - p,,riiý, ns cracked.

[yp". tip to three s~ructure. verely cracked or

stories, blown dowin.

4 rvu!!istory wall -bear- Collapse of bearing Exterior waxlls fac- Windows and doors

ing bud~ding, moriu- walls, resulting in ing blest ýtverely blown in, interior

inctital t;'pe. up to collapse of struc- cracked, inierior partitions cracked.

four sto~ries. tu:c supported by partitions severely

these uvalls. Sonic cracked with dambeafingv walls may age toward far end

be shielded by in- of building possibly

tervening walls so less intense.

that part of the

structure may rec~ive only mioderate damage.

5 Wood frame build- Framec shattered re- Wall framing Windows arid doors

ing. house type, one sulting in almost cracked. Roof se- Hown in, interior

or two siories. cormplete collapse. verely damaged, in- partitions cracked.

tenior partitions

blown down.,
ANALYSIS OF DAMAGE FROM AIR BLAST 215

Table 5.139b

DAMAGE CRITERIA FOR STRUCTURES PRIMARILY AFrECTED BY D)RAG LOADING

Description of Damage

Structural Dcscription of -- ---- -- - _____-

Type Structure Severe Moderate Light

.) Light steel frame in.- Severe distortion or Minor to major dis- W~ridows. and doors

dlutrial building, sin- colbipse of fiaine. tortion of frameý blown in, lip'ht sidgle story, with up to cranes, if any, not ing ripped off.

5-ton crane capacity; operable u-itil relow strength wills pairs made.

which fail quickty.

7 Hfeavy steel-frame in- Sev,-re distortion or Some distortion ito Windows and doors

dustrial building, sin- collapse oi' framc frame; cranes not blown in, light sidgle story. with 25 to operable: unlti re. ing ripped off.

50-ton cranc capac- pa;ils made.

ity; lightweight, low

strength vvý!lls which

fail quickly.

8 Heavy stee.l fr~.me in- Severe dis~irtit.1 or Some distortion or Windows and doors

dustrial budlding_, sin- collapse of frbrne, frame; cranes not blown in. light sidgle story, with Of, to operable until re- ing ripped off.

1(X)-ton crane c'apac- pairs made.

iiy , flIght-night low

strength walls which

fail quickly.

9 Multistory steel- Severe frame dis- Framne distorted Windo%%s and doors

frame office-type tortion, incip'ent moderately, interior blown in, light sidhuilding, 3 to 10 collapse. partitions blown ing ripped off, intestories Lightweight down. nior partitions

low strength walls cracked.

which fail quickly,

eirthquai'c resistant

coi~ssruction.

1I Mu!tistory steel- Severe Iraime dis- [riume distorted Windows and doors

frame office-type tortion, incipient moderatcly, interior blown in, light sidbuilding. 3 to it) co'lapse. partitions blown ing ripped ofl,. ntcstories. Lightweight down. rior partitions

low sirength walls cracked.

which fail quickly,

non-varthquake resi.itantl conw.1ruction.
216 STRUCrTJRAL DAMAGE FROM AIR BLAST

Table 5.139b (continued)

Description of Damage

Structural Description of

Type Structure Severe Moderate Light

I I Multistory reinfor%:ed Severe frame dis- Frame distorted Windows and doors

concrete frame of- tortion, incipient moderately. iriterior blown in, light sidfice-iype building, 3 collapse. partitions blown ing ripped off. inteto 10 stories; light- down, some spall- rior partitions

weigf,' Iov stvength irg of concrete, crack'd.

walls which fail

quickly, earthquake

resistant construction

12 Multistory reinforced Severe frame dis- Framn distorted Windows an, doors

concrete frame office tortion. incipient mod.rately, irt'rior blown in. light sidtype building, 3 to 10 collapse. part',tions blown ing ripped oft. intostories: lightweight down, some spil- rior paltitions

ýow strength walls ing of co.icret,, cracked.

which fail quickly.

non-earthquake resi.tant construction.

13 Highway .russ Total failure of lat- Substantial dislicr- Capacity of bridge

bridges, 4-lane, spans eral bracing or an- Zion of lateral brac- not significantly re2C0 to 400 ft; chorage, collapse ing or slippage on duced, sligh, distorrailroad truss bridges, of bridge, supports, signifi- tion of some bridge

do,- le track ballast can; reduction in components.

floor, spans 200 to capacity of bridge.

400 ft.

14 Highway truss tDitto) (Ditto) (Ditto)

bridgeF., 2-lane, spans

200 to 400 ft;

railroid truss bridges,

single track ballast or

double track open

floors, spans 200 to

400 ft. railroad truss

bridges, single track

open floor. :pan 400

ft.

15 Ralroad truss (Ditlo) (Ditto) (Ditto)

b.idges, single track

open floor, span 200

ft.

16 Highway girder (Oiti,) (Ditto) (Ditto)

bridges. 4-lane

throdgh. span 75 ft.
ANALYSIS OF DAMAGE FROM AIR BLAST 2I7

Table 5.139b (concluded)

Description of Damage

Structural Description of

Type Structure Severe Moderate Light

17 Highway g;rder (Ditto) (Ditto) (Ditto)

bridges, 2-lane deck.

2-lane through, 4-

lane dch ..Van 15 ft;

railroad girder

bridges, double-track

deck, open or ballast

fl•.or, span 75 f,;

railroad giruer

bridges, singL2 or

double track through,

ballast floors, span 75

ft.

I9 Railroad girder (Ditto) (Ditt-)) (Ditto)

bridges, si.agle track

deck, open or ballast

floors, span 75 ft'

railroad girder

bridges, single or

double track through,

open floors, span 75

ft.

19 Highway girder (Ditto) (Diito) (Ditto)

bridges, 2-lane

through, 4-lane deck

or through, span 200

ft: railroad g'rder

b-idges, double track

deck .,t through, ballast C. ¶or, span 200

ft.

20 Highway girder (Ditto) (Ditto) (Ditto)

bridges, 2 lane deck.

span 200 ft; railroad

girder bridges, single

irack deck or

thiough, ballast

floors, span 200 ftý

railroad girder

bridljes, double track

deck or through,

cpen floors, span 200

ft.

21 Re ilroad girder •Diito) (Ditto) (Oit1,o)

bridges, single track

de,:k or through

open floors, spa, 200

ft.
218 STRUCTURAL DAMAGE FROM AIR BLAST

The various above-ground structures Solution: (a) From the point 5 (at

in Fig, 5.140 are identified (Items I the right) draw a straight line t,- I MT

through 21) and the different types of (1000 KT) on the severe damage scale

damage are described in Tables 5.139a and another to I MT (1000 KT) (un the

and b. The "fan"' from each poin indi- moderate damage scale. The interseccates the ran&c of yields for which the tions of these lines with the distance

diagramn raay be used. For a surface scale give the required sulutionw for the

burst multiply the damage distances ob- optim•,,n burst height, thus,

tained from the diagram by three- Distance for severe damag, -

fourths. The res'ilts are estimated to bc 29,000 feet. Answer.

accurate within ±20 percent for the Distance for moderate damage =

av,•rage target conditions specified in 33,000 feet. Answer.

§ 5.141. (b) For a surface burst the respective

distances are three-fourths those obExample tained above, hence,

Distance for severe damage -

Given: Wood-frame building (Type 22,000 feet. Answer.

5). A I MT weapon is burst (a) at Distance fec moderate damage

optimum height, (b) at tit. "urface. 25,0G0 feet. Answer.

Find: The distances from ground (The values hav: been roundea .t to

zero to which severe and modLratc two significant figures, since greater

damage extend. precisiun is not warranted.)

I,

I
ANALYSIS OF DAMAGE FROM AIR BLAST 2!9

0I

OD

iiN3-41 0 0Nni1 A3Z 30NVISIC hOW' 

21

"" 2

(1•,)1 !39V~VJ 31V300VA :al•lA

S• ,' % U,

I | I I II

_ _ _ - Xh
220 STRUCTURAL DAMAGE FROM AIR BLAST

5.141 The data in Fig. 5. 140 are for pound per !;quare inch dynamic pressuire

certain average target conditions. These occurs.

are that (i) the target is at sea level (no 5.144 The foregoing results do not

correction is necessary if the target alti- take into conNideration the possibility of

tide is less than 5,000 feet); (2) the fire. Generally spcaking, the direct efterrain is fairly flat (rugged terrain fects of !hermal radiation on the strucwould provide some local shielding and tures and other targets under consideraprotection in certain .,reps and local en- tion are inconsequential. However,

hancement of damage 'n others); and (3) thermal radiation may initiate fires. and

the structures have average characteris- in structures with severe or moderate

tics (that is, they are of average size and damage fires may start because of

strength and that orientation of the target disrupted gas and electric utilities. In

with respect to :he burst is; no problem, some cases, as in Hiroshima (§ 7.71),

i.e., that the ratio of loading to resis- the individual fires may develop into a

tance is relatively the same i.i all dire'. mass fire which may exist throughout a

tiois from the target). city, even beyond the range of signifi5.142 The "fan ' fromo each point cant blast damage. The spread of such a

in the figure designating a target type fire depends to a great extent on local

delineates the range of yields overconditios and is delineat theore ranglyields l b oaver therefore uifficult to predict. This limiwhich theoretical analyses have been tainmsbek inidwh ig

made. For yields falling within this

range, the diagram is estimated to be 5.140 is used to es~in,.-te the damage o

accurate within ± 20 percent for t a particular city or target area.

average conditions discussed above. STRUCTURAL ELEMENTS

The significance of rsults obtained by 5.145 For certain structural eleapplying the diagram to conditions that ments, w~th short periods of vibration

depart appreciably f:om the average or to yieids outside the limit~s of the fans (up to about 0.05 second) and small

muto be outsido the udgment of the fa plastic deformation at failure, the con- must be left to the judgment of the ditions for failure can be expressed as a

analyst. peak overpressure without considering

5.143 Figure 5. 140 gives the dis- the duration of the blest wave. The failtances from ground zero for sevee and ure conditions for elements of this type

moderatc damage. Light damage to all are given in Table 5. 145. Some of these

targets except blast-resistant structures elemcnts fail in a brittle fashion, and

and bridges can be expected at the range. thus there is only a small difference

at which the overpressure it I pound per between the pressures that ceuse no

square inch. For the blast-resistant damage and those that produce complete

structure (Type 1) described in Table failire. Other elements may fail in a

5.139a, a peak overpressure of 10 moderately ductile manner, but still

pounds per square inch should be used with little differ-"nce between the presto estimate the distance for lght dam- sores for light damage and complete

age. Lighi damage to bridges can be failure. The pressures are side-on blast

expected at the range at which 0.6 overpressures for panels that face
ANAL.YSIS OF DAMAG(F FROM AIR BLAST 221

Table 5.145

CONDITIONS OF eAIILURE 0C- OVERPIESSURE-SENSITIVE ELEMENIE S

Approximate

side on

peak

overpressuwe

S!ructural elerrment Failure (psi)

Giass wLi-,hws, large and Shattering usujllv. ocia- 0.5- 1.0

small, sional frame lailure,

Corrugated aslhesos siding. Shattering 1.0- 2.0

Corrugated steel or Connectioi idailure fol. I0- 2.0

aluminum paneling, lowe,' by buckling.

Brick wall panel, H in. Shearing and flexure 3.0-10.0

or 12 in. thick (not failures.

reinforced).

Wo( d siding panels, stand- Usually failure occurs at 1,0 2.0

ard house construction. the main connecuions

allowing a whole panel

to he blown ini

Concrete or Llndcr-block Shattering of the wall. 1.5- 5.5

wall panels, 8 in. or

12 in. thick (not

reinforced).

ground zero. For panels that are oriented limits of accuracy are similar to those in

so that there are no ieflected pressures § 5. 141 and, § 5.142, resnectively; the

thereon, the side-on pressures must be possibility of fire mentioned in § 5. 144

doubled. The fraction of the a'ea of a must aiso he kept in mind. The targes

panel wall that contains windows will (Items '. to 13) in the figure are enuinfluence the overpressure required !o merated on the page f~cing Fig. 5.146

damage the panel. Such damage is a and the different types of damag:. ir2

function of the net load, which may be described in the followiag ppragrap;.s.

reduced considerably if the windows fail

early. This allows the pressure to be- Transportation Equipment

come equalized on the two sides of the 5.147 The damage criteria for

wa!l before panel failure occurs. various types of land 1,ansportation

equipment, including civilian motorDRAG-SENSITIVE TARGETS driven vehicles and earth-moving

5.146 A diagram of damnage-dis- equipment, and railroad ro!ling stock

tance relationships for various targets are given in Table 5. 147a. The various

which are largely affected by drag fortes types of damage to merchant shipping

is given in Fig. 5.146. The conditions frotn air blast are des,.-ribed in Table

under which it is applicable ard the 5.147b.

(Text continued on page 225.
222 STRUCTURAL DAMAGE FROM AIR BLAST

The drag-sensitive targets in Fig. Example

5.146 are identified as follows:

I. Truck mounted engineering equip- Given: A transportation type vehiment (unprotected). c;"- (Item 3). A 10 KT weapon is burst at

2. Earth moving engineering equip- (a) the optimum height, (b) at the surment (unprotected). face.

3. Transportation veh;cies. Find: The distances from ground

4. Unloaded railroadd cirs. zero to which severe and m~oderate

5. Loaded boxcars, flatcars, full tank damage extend.

cars, and gerdoP' cars (side-on Solution: (a) Draw straight lines

orientation). fror,-: the points 3 and 3,,, at the right, to

6. Locomotives (side-on orientation) 10 KT on the yield scale at the left. The

7. Telephione lines (radial). iiatersec';ons of these lines with the. dis

8. Telephone lines (transverse). tance sca!e give the solutions for severe

9. Unimproved .-oniferous forest and moderate damrae, respectively, for

stard. the optimum burs( height; thus.

10. Average deciduous forest stand. Distance for severe damage =

11. Loaded boxcars, flatcars, full tank 1,400 feet. Answer.

cars, and gondola cars (eni-on orneritation). Distance for •,oderate damage =

12. Locomotives (end-on or'entatiun). 1,600 feet. Answer.

13. Merchant shipping. (b) For a surface tarst the d,;iances in

Subscript "m" refers to moderate this case are týree-fourths those obdamage an,.' subscript "s" refers to se- tained above; thus,

vere damage.

For a surface burst multiply the dis- Distance for severe damage =

tance by three-fourths for Items I 1,000feet. Answer.

through 8 and by one-half for Items 9 Distance for moderate damae =

and 10. For Items II through 13, the 1,200 feet. Answer.

distances are the same for a surface

burst as for the optimum burst height.

E,,.timated accuracy ± 20 percent for

average targets.

!.+ I
ANALYSIS OF DAMAGE FROM AIR BLAST 223

a EE E E E E

C, 4

E

E E .i .iE• . wE - -- -

O+

E E

0

K I...

CYC

x 0 43 3N % S -" 

-I - -

11L33) ON3~Z ONi1ON9 bNON_- ~3NViSIO

U

C'/

k !
224 STRUCIURAL DAMAGE FkOM AIR BLAST

"Tabie S.147a

DAMAGE CRITERIA FOIR '.AND TRANSP9RTATION EQUIPMENT

Description of equipment Damage Nature of damage

Motor equipmcnt (cars and :rucks). Severe Gross distortion of frame. large displacements, outside appurtenances (doors

and hoods) torn off, need rc-budding

before use.

Mo&d(;ate Turned over and dispiace., badly dented.

frames spru Ag. need ;-t:ijor repairs.

Light Glass broken, dents in body, possibly

turned over, immediately usable.

Railroad ro!ling stock 6w;ox, flat. tank, and Severe Car blown from track and badly smashed,

gondola cars). extensive distortion. some parts usable.

Moderatc Doors demolisned, body damaged, frarmae

distorted, could ipssibly roll to repair

sho~p.

Light Some door and b(edy damage. car car continue in use.

Rauroad locomotives (Diesel or steam). Severe Overturned, parts blown off, sprung and

twisted, major overhaul required.

Moderate Probably ovtrturned. can b- lowed to repair shop after being riglited, need major

repairs

Light Glass breakage and miror damage to parts.

immediately usabie.

Constriction eluipment (bulldozer:i and Severr Extensive distortion ol frame and crushing

graders). of sheet metal, extensive damage to caterpillar tracks and wheels.

Mowera.e Some frame distortion, overturming, track

and whe. damage.

Ligh!, Slight 'a?. t cabs and housing, glass

breakage.

Table 5.!47b

DAMAGE CRWTERIA FOR SHIPPING FROM AFR BLAST

Damage type Nature of di,,n.ge

Severe The ship is either sunk, c:psize&, or damaged !o the extent of requirive. rebuilding.

Moderate The ship ;s immnobilized and requires ex:ensive rep,'irs, esnecial!y to .hock-sersitive

components or their foundations, e.g., propulsive mnachiaiery. ,,oilers. and interior

equipment.

Light The ship may still be able to opctate although there wil! be damage to electronic,

electrical, and mechanical equipmen.
ANALYSIS OF DAMAGE FROM AIR BLAST 225

Communication and Power Lines conditions. A general classification of

forest damage, applicable in most cases, 5.148 Damage to telephone, tele- is given in Tab!e 5.149. Trees are pri.

graph, and utility power lines is gener- marily sensitive to the drag forces from

ally either severe or light. Such damage a blast wave and so it is of interest that

depends on whether the poles support- the damage in an explosion is similar to

ing the lines are damaged or not. If the that resulting from a strong, steady

po.cs are blown down, damage to the wind; the velocities of such winds that

itnes will be seete and extensive re- would produce comparable damage are

pairs will be required. Jn the other included in the table.

hand, if the poles remai-i! standing, the 5.150 The damage-distance results

lines will suffer only light damage and derived from Fig. 5.146 apply in parwill nee t ( little repair. In general, lines ticular to unimproved coniferous forests

extending radially froma ground zero are which have developed under unfavorless susceptible to damage than are able growing conditions ard to most

those running at right angles to this deciduous forests in the temperate zone

direction. when foliation ;s present. Improved coForests nifercus forests, with trees of uniform

5.149 The detailed characteristics height and a smaller average tree density

of the damage to forest stands resulting per acre, are more resistant to blast than

fhom a nuclear explosion will depend o are unimproved forests which have

a variety of conditions, e.g., deciduous grown under unfavorable coviditions. A

or coniferous trees, degree of foliation forest of defoliated deciduo,.% trees is

of the trees, natural or planted stands, also somewhat more blast resistant than

and favorable or unfavorable growing is implic,-! by the data in Fig. 5. 146.

Table 5.149

DAMAGE CRITERIA FOR FORESTS

Equiva•eni

steady

wind 10ocily

Damage type Nalure of damage (miles per hour)

Sever,. Up to 90 percent of tr-es blown down- remainder denuded of branches 130-140

and leaves. (Area in.passahle to vehicles and very difficult on

foot. )

Moderate Aboul 30 percen, of trees blown down' remainder have somc 90-1(X)

branches and la,,,v blown off. (Area passable to vehicles only 41ter

exlensiv, ý:le,,ring.)

Light Cnly aplil.:s to deciduous forest stands. Very few trees blown down, W0. 80

some leaves and branches blown )ff. (Area passable to vehicle,,.)

i
226 STRIUCT(I.RAI I),iMA(FI- FROM AIR BI AST

PARKED AIRCRAFT

nose pointed toward (he burst wil! suffer

5.151 Aircraft are relatively vul- less damage than those with the tail or

nerable to air blast eflects associated either side directcd toward the ,ncomwith nuclear detonations. The forces ing blast wave (§ 5.94). Shielding of

developed by peak overpressures of I to one aircraft by another or by structures

2 pounds per square inch are sufficient to or terrain features may reduce damage,

dish in panels and buckle stiffeners and especially that caused by flying debris.

stringers. At higher overpressures, the Standard tiedown of aircraft, as used

drag forces due to wind (dynamic) when high winds are expected, will also

pressure tend to rotate, translate, over- minimize the extent of damage at ranges

turn, or lift a parked aircraft, so that where destruction might otherwise

damage may then result from collision occur.

with other aircraft, structure,;, or the 5.153 The various damage categoground. Aircraft are also very suscept- rics "or parked transport airplanes, light

ible to damage from flying debris carried liaison airplanes, and helicopters are

by the blast wave. outlined in Table 5.'53 together with

5.152 Sever,' factors ingluence the the approximate peak overpressures at

degree of damage that may be expected which the damage may be expected to

for an aircraft of a given typ*e at a occur. The aircraft are considered to be

specified range from a nuclear detona- parked in the open at random orientation

tion. Aircraft ,.hat are parked with the with respect to the point of burst. Th,:

Table 5.153

DAMAGE CRITERIA FOR PARKED AIRCRAFT

Overpressure

D)amage type Nature of damage (psi)

Severe Major (or depot level) mainte- Transro:t airplanes 3

nance required to restore air- Light lia-son craft 2

craft to operational status. Helicopters 3

Modera:e Field maintenance required tc Transport airplanes 2

restore aircraft to opera- Light liaison craft I

tional status. Helicopters 1.5

Light Flight of the aircraft not pre- Transport airplanes 1.0

vented, AIthough performance Light liaison craft 0.75

may be restricted. Helicopters I.

...
ANALYSIS OF DAMAGE FROM AIR BLAST 227

data in the table are based on tests in from the tank as a consequence of

which aircraft were exposed to detona- sloshing. There iF apparently no cleartions with yields in th2 kiio-on range. cut overall structural collapse which inFor megaton yields, the longer duration itially limits the usefulness of ihe tank.

of tLe positive phase of the blast wave Peak overpressures required for severe

may result in some increase in damage damage to POL tanks of diameter D

over that estimated from small-yield may be obtained from Figs. 5.155a and

explosions at the same overpressure b. Figure 5. !55a is applicable to nuclear

level. This increase ii likely to be sig- explosions with energy yields from I to

nificant at pressures producing severe 500 kilotons and Fig. 5.155b to yields

dama~ge, but wil! probably be less im- over 500 kilotons. Foe yields less than I

portant for moderate and light damage kiloton, the peak overpre:sure for seconditions. vere. damage may be taken to be I pound

5.154 Aircraft with exposed ignit- per square i1-ch

able materials may, tinder certain conditions, be damaged by thermal radiation at distances beyond those at which LIGHTWEIGHT, EARTH COVERED

equivalent damage would result from

blast effects. The vulnerability to ther- 5.156 Air blast is the controlling

mal radiation may be decreased by pro- factor for damage to lightwe;ght earth

tecting ignitable materials from expo- covered structures and shallow buried

sure to direct radkoiion or by painting underground s!ructures. The earth cover

them with protective (light colored) provides surface structures with subcoatings which reflect, rather than ab- stantial protection against air blast and

sorb, most of (he thermal radiation (see also some protection against flying

Chapter VWl). debris. The depth of earth cover above

the structure would usually be deterPOL STORAGE TANKS mined by the deghee of protection from

nuclear radiation required at the design

5.155 The chief cause of faiiure of overpressure or dynamic pressure (see

POL (petroleum, oil, lubricant) storage Chapter VIII).

tanks exposed to the blast wave appears 5.157 The usual method of providto be tht lifting of the tank from its ing earth cover for su,,face or "cut-andfoundation. This results in plastic de- cover" semiburied structures is to build

formation and yielding of the joint be- an eirth mound ovr the portion of the

tween the side aid bo:tom so that leak- structure that is above the normal

age can occur. Severe damage is ground level. If the slope of thc earth

regarded as that damage which is aspo- cover is chosen properly, the blast reciatc•d with loss of thc contents of the flection facto- is reduced and the aerotank by leakage. Furthermore, the leak- dynamic shape of the structure is image can lead to secondary effects, such wroved. This results in a considerable

as the development of fires. If failure by reduction in the applied translational

lifting does not occur, it is expected that forces. An additional benefit of the earth

there will be little, if any, loss of liquid cover is the stiffening or resistance to

ti+
228 STRUCTURAL DAMAGE FROM AIR BLASTV

28 1 1 1 I

-~- t-------0.9 FULL~

a- 00

w

V) 16 _ _ _ _ _ _ _ _ _ _ _

w

w 0.5 FULL

0 \0 0.5 AND 0.9

F4

w 0.9 FULL

4~~~~5 _____ oVE0.5 FULL

100,75,50 FEET IEMPTY

0.3 0.4 0.5 0.6 0.7 0.8

HEICHT/ DIAMETER RATIO

Figure 5.1I55a. Peak overpressures foi- severe blast damnage to floating- or conica;-roof tar~ks

of diameter 0 for explosions from I Ic 500 kilotons.

0.9 AND 0.5

FILLED

6 1- 01 FEET

0.9 AND 0.5

_____E_ 0.9 AND 0.5

U)50 FEET FILLED w

Wi 3 -~---- - w

0

y- 2 - -

w

1___ 100, 75, 50 FEET ___

I EMPTY

0

0304050.6 0.7 S

i-EIGHT/DIAMETEFR RATIO

Figure5. 153b. Peak overpressures foi severe blast damag.! to floating- or conical-roof tanks

of diameter D from explosion,, of 500 kilotons or more.
ANALYSIS OF DAMAGE FgOM AIR BLAST 229

deformation that the earth provides to interface between the earth and the top

flexible strt,'tures by the buttress;ing ac- of the structure.

tion of the soil. 5.159 The lateral blast pressures

5.158 For lightweig'it, shallow exert"ed on the vertical faces of a shallow

buried underground structures the top of NUried structure have been found to be

the earth cover i,- at icast flush with the as low as 15 percent of the blast pressure

original grade but the depth of cover is on the roof in dry, well-compacted, silty

not more than 6 percent of the span. soils. Fo0 most soils, hcwever, this lotSuch structures are not sufficienily deep era! blast pressure is likely to be somefor the ratio of the depth of burial to the what higher and may approach 100 perspan to be large enough to obtain the cent of the roof blast pressure in porous

benefits described in § 5.161. The soil saturated soil. The pressures on the botprovides little anenuation of the air blast tom of a buried struciure, in which the

pressure applied to the top surface of a bottom slab is a structural uni inltegral

shallow buried underground structure. with the walls, may range from 75 to

Observations made at full-scale nuclear 100 percent of the pressure exerted on

tests indicate that there is apparertly no the roof.

increase in pressure on the structure as a 5.160 The damage that might be

result of ground shock reflection at the suffered by a shallow buried structure

Tab.e 5.160

DAMAGE CRITERIA FGR SHALILOW BURIED STRUCTURES

Peak over

Danmage pressure

Type of structure type (psi) Nature of damage

Light, corrugated steel Severe 45- 60 Collapse

arch, sdrface structure Moderate 50- 50 1 urge detormations of

(10-gage corrugated Lnd walls and arch,

steel with a span of also major entrarce

20-25 ft), central ang&e door damage.

of 180*; 5 ft of

earth cover at the

crown.* Light 30- 40 Damage te ventilation

and entrance door.

Buried concrete arch SeN.c.c 220-280 Coilapse.

8-in. thick with a M4oderate 100-220 Large deformations

16 ft span and central with considerable

angle of 180'; 4 ft of cracking a'd ,pallihg.

earth cover at the

crown. Light 120-160 Cracking of panels,

possible entrance

door damage.

*For arched structures reinforced with ribs, the collapse pressure is higher depending on the number of

ribbs.
230 STRUCTrURAI. DAMAGE F ROM AIR BI AsU

will depend on a number of variables, with respect to the blast wave.

including the structural characteristics, 5. 161 Underground structures.

the nature of the soil, the depth of buried at such a depth that the ratio of

burial, and the downv~ard pressure, i.e.. the bhurial depth to the span appioaches

the peak overpressure and direction of (or exceeds) a valuc of 3.0. will obtain

th~e I)las! wave. In Table 5.160 are given some benefit from the attenuation with

the !imiting values of the peak over- 6epth of the pressure induced by iv tr

pressure required to cause various de- blast, and 'from the arching of the load

grees of damage to two types of shallow frýým more deformable areas to iess debu-,ied structures. The range of pres- formable ones. Limited experience at

sures is intended to allow for differences nuclear tests suggests that the arching

in structural design, soil conditions, action of the soil effectively reduces the

shape of earth mound, arnd orientation loading on flexible strdctures.

BIBLIOGRAPHY

JAC01tSFN. IL. S. and R. S, AYF "Engineering *SPARKS, I_ N., 'Nuclear Fffects on Machi e

Vibrations,- McGraw-Hill Book Co., Inc., Tools,-' U.S. Atomic Energy Commission,

1958.December 1956, WT I 184ý *JOHNSIOf,, B. (G., "Damage to Commercial *TANI ott, 43. C., 'Blast Effects of Atomic and Industrial Buildings Exposed to Nuclear Weapons Upoin Curtain Walls anod Partitions of Effects," Feder,'i Civil Defense Administra- Masonry and O'ther Materials,'' Fedc.nil Civil tion. Fcbruary 1956, WT- I 18(.1 Defense Administration, August 1956,. WT

*N1t uIill ,I I , J. H.. "'Nuclcar Explosion Effects 7,11 fin Structures and Protective C7onstruction ---A t(KRP.WanG..WESF. Selectee, Bibliography," U.S. Atomic Energy oTJ(f~ P. Wucea a~poind G. R.pca WtIt.t effect Cormaission, April 1961, TID-30)92. Ptof uleuGar Eixp-Gsion oi Tnicall n andueFad NEWMARK~, N. M., "An Engineering Approach Perlu Ga(PG: nsaadnanF-

~o Bast esisantDesin,''Tra.~. .,erSm. cilities,'' Liquefied Petroleuim Gas AssoLation,

o~f Chu'i Fngineersv, 121, 45 (1956). December 1931j, WT-l 175.

Nopwts, (-. H., et al , 'Struclural Design fo~r Tt)N(;. T. P. an-I N. M. NuWMtARK, "A Review

I~ynarnic Loads,"~ McGraw-Hill Book Co., of Numerical lategratioai Method's for Dynamic Inc., 1959. Response ot Structures,'' University of Illioois

PICKI; 'RINUi, E. E., ant! J. L. Bo K"01I I, "Pro. Structural Research Series No 69, 1954

babilistic Air Blast Failure Criteria for Urban *Wtt I IAMSON, R. H., "Effects of a Nuc'lear St-uctures," Stanford Research lnstilute, Explosion on Commercial Conimunicasions Menlo Park, California, November 1971. Equipment," Federal Civil Defense Adm~nis- *RANt)A: I , P. A , "Damage to Conventional tration, May 1955. ITR-l 1193.

and Special Types oif Residences Exposed to W1iOGR.A Noclear Effects,'" OCDM, . ta. ASuyo od FI-'A. and HHFA. WiI(UHV .Bea. ASuyo od

Mvarch 1961, WT 1194. ;ng. Structural Response, and Dcbris CharacRoOFr)wlS, G. L., "Dyniamics of Framezd Stiuc- teristics of Wall Panels," URS Research Co.,

:ures,'' John Wiley and 'nInc., 1959. Burlingame, California, July 1969.

*SHAW, E. It. and F. P. M( N~t.A, ''Exposure of Wii tots. C., el al., "Final Report Summary, Mobile Homnes and Emergency Vehicles to Nu- Structural Response and Loading of Will

clear Explosions," Federal Civil Defense Ad- Panels,'' URS Research Co.. Burlingamne, Calinln~stration, July 1957, WT- I IN1. if()rnia, July 197:.

*Tihese publicatio.ns may be purcbitsed from the National Tec.hnic:al Information Service, U.S

Deparfmnien of CommerCe. Springfield, Virginia, 22161.
CHAPTER VI

SHOCK EFFECTS OF SURFACE AND SUBSURFACE

BURSTS

CHARACTERISTICS OF SURFACE AND SHALLOW UNDERGROUND

BURSTS

INTRODUCTION

6.01 Surface and shallow urder- sion, as functions of the distance from

ground bursts are defined as those ,ri ground (surface) zero (§ 2. ..4 footnote),

which either t[•c fir•ball or the hot, can then be obtained from the curves

high-pressure gases generated by the given at the end of Chapter Ill. The cube

explosion intersect or break through the root scaling law described there can bN..

earth's surface. In explosions of this used to calculate the blast wave propertype, part of the energy released is spent ties from a contact surface hucst o1 any

in producing a surface crater, whereas specified energy yield. When the burst

much of the remainder aFpears a,; air occurs below the surface, the air blast

blast and ground shock. The greater the arises partly front the ground shock

depth of the burst point below the sur- transmitted through the surface into the

face, the smaller is the energy expended air and partly from the release of the

as air blast. The dimensions of the crater high-pressure gases produced in the ex.

increase at iirst with increasing depth. of plosion. At shallow burst depths the

burial oi the weapon, pass through a latter effect predominates but with inmaximum, and then decrease virtually creasing depth of bu-ial it contributes

t; zero at still greater depths. less and less to the air blast. Furthermore, as the depth of burst is increased,

AIR BILAST the higher overpressirtes closer to surface zero fall oif more rapidly than do

6.02 In a contact surface burst the lower overpressures at greater dis-

(§ 2.127 footnote) fht incident at,d re- tances. More information concerning

flected air biast waves coincide imme- the air blast from shallow underground

(I'ately, forming a hemispherical shock explosions and the effect nf yield and

fron: as shown in Fig. 3.34. The burst depth on the spatial dLribution of

characteristics of the blast wave accom- the overpressure is given ;,a § 6.80Q t

pai) ing a referer,nc (I kilotor) explo- seq.

231 in A
232 SHGCK EFFECTS OF SURFACE AND SUBSURFACE BURSTS

CRATER FORMATION sions may lead to a subsidence crater, to

6.03 The mechanism of crater for- a raised mound above the detonation

mation depends on the height or depth poirnt, or to no permanent displacement

of the burst. For an explosion wel! of the surface at all. If the collapse of

above the surfa,ýe but ;n which the hi~e- the chimney containing bi3ken and

ball intersects the ground (§ 6.08), a crushed material should reach the surdepression crater is formed as a result of face, a subsidenc., crater may be formed

the vaporization of considerable quanti- (0 2.103). In strong earth material, s'.,ch

ties of earth material. This material is .s hard rock the chimney top rray not

sucked upward by ascending air currents react. the surface: surface displacement

resulting from the rising fireball and it may the'i be only tompora'y. If bulking

eventually appears as fallout (Chapter of the broken rock _,cchrs, a surface

IX). For bursts at or near (above or mound may be for-,ied above ;.he chimbelow) the surface, air blast plays a part ney (Fig. 6.05).

in crater formation, in addition to va- 6.06 The ',ariations in the character

porization. Surface material is then re- of the crater is a result of the changes in

moved by being pushed, thrown, and the predoainant mechanism of crater

scoured out. Some of this material falls formatirn as tVe depth of burst (DOB)

back into the crater and most of the incr'ases are illustrated in Figs. 6.06a

remainder is deposited around the edges ,nrough f. The 1iepre';sion crater in Fig.

to form the lip of the crater or is scat- 6 06a `:- fcrrend minly by vaporization,

tered as loose ejecta beyond the. crater. with most of the removed material being

6.04 When the burst is at such a carried away. In a contact (or near surdepth that surface vaporizatior and face) burst, reprcsc'it-.,2 in Fig. 6.06b,

scouring by air blast are not significant, scouring, etc., by an air blast also conseveral other processes may contribute tributes to crater formation and some of

to the formation of a "throwout" crater. the material removed falls back into and

One is the crushing and fracture of the around the crater. At greater depths

ground rraterial tLy the expanding com- (Fig. 6.06c), spallation and gas accelerpressional (shock) wave. Another im- ation be,'ome increasingly important

portant mechanism is spalling, i.e., the and the dimensions of the crater inseparation of earth layers at the surface trease. The crater reaches its largest size

(§ 2,91). The spalled layers will fly up- when gas acceleration is the predominward and be deposited aF ejecta beyond ant mechanism of formation, btt even

the crater or on the lip, or, for moder- then a large quartity of material falls

ately deep burials, they will fall back back (Fig. 6.06d). Finally, Figs. 6 06e

into the crater itself. If the hot, high- and f show examples of bulking and

pressure gases formed by the explosion subsidence. respectively, for deeper unare not vented during the crushing and derground explosions.

spalling phases, the expanding gases 6.07 Two more-or- less distinct

may force the confining earth upward; zones in the .airth surrounding the crater

thus gas accelkration can contribute to may be distinguished (see Fig. 6.70).

Linter formation, as described in § 2.92. First is the "rupture zone" in which

6.05 Finally, deeply buried explo- stresses develop innumerable radial

N
CHARACTERISTICS OF SJRFACE AND SHALLOW UNDEP.GROUl".D BURSTS 233

Figure 6.05. SULKY everit; mound created by the bulking of rock m~aterial in a 0.087-

kilAon nuclear detonatiorn at a depih of 90 feet.

cracks of various sizes. Beyond the CRATER DIMENSIONS

rupture zone is the "plastic zone" in 6.08 For an explosion above the

which the stress level has declined to earth's surface, appreciable iermat*on

such an extent that thiere is no visible of a vaporization (depression) crater will

rupture, although the soil is permanently cý,mmence when the height of burst is

deformed ano compressed to a higher less tHn about a tenth of the maximum

denstv. Plastic deformation and distor- fireball radius (§ 2.127). With decreastiot. of soil around the edges of the ing distance from the surface, the dicrater contribute to the production of the mensions of the crater vary in a complex

cratcr lip. The thicknesses of the rupture niainnr, (specially as the ground is apand plastic zones depend on 'he nature proached, because of the change in the

of the soil, as well is upon the energy mechanism of crater formation. In genyield of the explosion and loeation of eral, however, the depth of the depresthe burst point. It the earth below the sion increases rapidly with decreasing

burst consists of rock, then there will be burst height and the ratio of th- depth to

a rupture zone but little or no plastic raius also increases. The dimensions of

zone. the crater increase with the explosion

n • .,
23-4 SHOCK EFFECTS OF 'SURFACE AND SUBSURFACE BURSTS

Au A

0 .. I- A

U) I. 0

wL C*.** AA'I4 (A, , ~ .. * g0 ~w

U 'g

-,-~~k-'

4a coU.0

ell,,
CHARACTERISTICS OF SURFACE AND SHALLOW UNDERGROUND BURSTS 235

Figure 6. 10. SEDAN event; crater formed by a 100-kiloton explosion in alluvial soil at the

optimum depth of burst (635 feet) for cratering. The crater radius is 611 feet,

the depth 323 feet, and the volume 179 million cubic feet.

yield but the actual values depend on the kilotons are related approximately to

soil characteristics. thost: given above for a yield of 1-kilo6.09 For contact surface bursts, ap- ton by the factor WO 3. For example, for

prohimate values of the crater dinen- a 100..kiloton explosion on the surface

sions can be given. For a I-kiloton ni- of dry soil, the radius of the crater may

clear explosion at the surface, -he be expected to be roughly 60 x (100))'

apparent radius of the crater iii dry soil = 240 feet, and the depth about 30 x

o, dry soft rock is estimated to be about (100)03 = 120 1'eet. Further information

60 feet. The radius at the crest of the lip on crater dimensions will be found in

will be 15 feet or so greater. The appar- § 6.72 et seq.

ent depth of the crater is expected to be 6.10 As the dep.h of burial i. inabout 30 fect. In hard rock, consisting creased, the radius and depth of the

of graphite or sandstone, the dimensions crater also increase until maxima are

will be somewhat less. The radius will reached; deeper burial then results in

be appreciably greater in sol saturated progressively smaller craters. These

with water, and so also will be the initial maximum values of radius and depth for

depth, to which structural damage s a given yield are termed "'optimum"

related. The final depth, however, will (Fig. 6.06d) and depths of burial for

be shallower because of "hydraulic optik;xum crater radius and for optimum

fill," i.e., slump;ng back of wet mate- crater depth are roughly equal. A phorial and the seepage of water carrying tograph of a crater formed at the oploose .oil. All crater dimensions result- timum burst depth is showti in Fig.

ing from a surfzce burst of yield W 6.10. For a I-kiloton weapon, the
236 SHOCK EFFECTS OF SURFACE AND SUBSURFACE BURSTS

deepest crater possib'c, namely, 100 blast wave as it runs over the eartn's

feet. is produccd when th1e burst point is surface. A random type disturbance is

120 feet below the surface; the radius of often superimposed on the ground mothe crater it that depth will also be near tion resulting from these shocks

its optimum, namely about 160 feet. (§ 6.82) but only the latter will be conOptimum values, like all ( rater dimen- sidered here. Each kind of ground shock

sions, are approximately p~roportional to (or pressure) is transmitted through the

WO . Curves showing the variation, of earth downwa~d and outward. The

crater radius and depth with depth of direct ground shock contributes to the

burial in various media appear later in formation of the crater arid the fracture

this chapter (§ 6.70 et seq.). and plastic zones immediately around it.

6.11 If tne soil is saturated and the The air blast pressure, called "airslap,"

high water table is maintained after the is the source of most of the stress on

detonation, the crater dimensions will underground structures beyond the

change wits. (ime. Slumping of the crater area when the burst point is not

crater sides will continue until a stable too deep.

condition it• fnr ih mt.r... .. - 6.13 Although shock waves tiansbe expected that the sides of very large mitted through the earth may be greatly

craters ,kill ultimately slump until their complicated and distorted by the presslopes decrease to 10 to 15 degrees. As ence of geological inhomogeneities,

a resuh, the craters will become shal- certain regularities tend to be found.

lower and broader, in weak saturated Airslw', bor example, almost always resoil with a very high water table, suits ir a single movement downward

slumping occurs immediately. If the soil followed by a slower, partial relaxation

is stronger and the water table not too upward: in sonic soils residual permahigh, there is a time ld,. in the slumping nent compression after airslap is meawhich may be a matter of hours in sands surable and significant. The amount of

and months in clay soils. Examination earth motion depends on the air blast

of craters in coral from high-yield bursts overpressure, the positive phao.e duraat the Eniwet,-)h Proving Grounds has tion, and the character of the soil. Close

shown that the inward rush of water to the surface, airslap motion is initially

carri,'; material which would normally abrupt, similar to the rise of pressure in

constitute the crater lip into the bottom the air shock, but it becomes more

of the crater. gradual with increasing depth.

6.14 In those regions where the air

GROUND SHOCK blast wave front is ahead of the direct

ground shock front at the surface, the

6.12 A nuclear explosion on or near situation is described as being "superthe surface produces a ground shock in seismic;" that is to say, the air blast

two priniary ways, each of which sets wave is traveling at a speed greater than

the earth in anotion; they are 0) by the speed of sound (or seismic velocity)

direct coupling (f explosivc energy to in the earth. The ground motion ihear the

the ground in the neighborhood of the surface is vertically downward, biut it

crater. and (2) by pressure of the air becomes increasingly outward, i.e., ra-
CHARACTERISTICS OF SURFACE AND SHALLOW UNDERGROUND BURSTS 237

dial, from the burst point at greater cities in the ground down to considerdepths bel,:w the surface. able depths.

6.15 On the other hand, when the 6.17 The strength of the shock

air blast front lags behind the shock wave in the ground decreases with infront transmitted directly through the creasing distance from the explosion. and at large dista.ces it becomes similar

ground, the grotvid wave is ';aid to "groutnd, " o u tr u n " the t h e c 

airblast. 

a ir b la s t . T Thve h e a 

Isair ir s l ap 

d tn th e n 

to an acoustic (or seismic) wave. In this

causes the ground r e i n t e f e c s o u d r g u d s h k surface a•t locations region the effects of underground shock

p. duced by a nuclear expiosion, are ahead of it to undergo a characteristic somewhat similar to those of an earthoutrunning motion, generally consisting quake of low intensity. However, the

of two or three cycles of a damred, i e., evidence to date indicates that underdecreasing, motion undulation with the fir:t c ng, unpdardo winh the fir ground explosions do not cause earthblast overpressure decreases with it- quakes, except for minor aftershocks

bhts ovrprssue dcreseswit ii within a few milesg of the burst point

creasing distance from surface zero, so w . fe meq.).

also does the outrunning motion. If the 6.18 e ef o u c

air blast wave reaches fhe observatior 6

point while (he outrunning surface mo- pressure on an underground structure is

tion is stili underway, the a1rslap motion somewhat different in character from

that of air blast on a structure above the wilesu- ground. It. the latter case, as explained

in Chapter IV, the structure experiences

6.16 At iccations close to the burst, something like a sudden blow, ft(Ilowed

the air blast usually travels faster than by drag due to the blast wind. This type

the direct ground shock. The superseis- of behavior is not associated with uninic condition then prevails and the irst deiground shock. Because of the simiground motion is determined essentially larity in density of the medium through

by the airslap. At greater distances, the which a ground shock wave travels and

air blast weakens and its velocity de- that of the underground structure, the

creases significantly, but the ground response of the ground and the structure

shock velocity, which is approximately are closeiy related. In other words, the

the same as the sesimic velocity, does movement (acceleration, velocity, and

not decrease very much. Hence, the displacement) of the underground strucground shock front moves ahead anC'. ture by the shock wave is largely dcleroutrunning becomes the dominant factor mined by the motion and containing

in ground motion. At still greater dis- action of the ground itself. This fact has

tances from surface zero, the effect of an important influence on the structural

airslap disappears or it is so weak that it damage associated with both suiface

merges with the direct ground shock and underground ex'plosions. Damage

without causing any outrunning motion, criteria are outlined in § 6.28 et seq. and

The phenomena described above are are discussed mote fully in § 6.90 et

strongly influenced by the seismic velo- seq.
238 SHOCK FFFFCTS OF cTJRFACE AND SUBSURFACE BURSTS

DEEP UNDERGROUiND BURSTSI

GROUND SHOCK sion appear to be directly related to tle

6.19 In a fully-contained deep un- postdetonation phenomena of cavity

derground explosion there wo'ld be lit- collapse and cniinney growth (§ 2. 103).

tie or no air blast. Much of the energy is Some, aftershocks, however, originate a

expended in forming the cavio, around few miles beyond the region involved in

the burst point and in melting the! rock the development of the chimney. These

(§ 2. 102), and the remainder appears in altershocks are generally considered to

the form of a ground shock wave, As result from small movements along prethis shock wave moves outward it first existing fault planes 2 and to represent

produces a zone of cruibed and com- bhe release of natural strain. (deforrriapressed rock, somewhat similar to th- tion) energy. For explosions of high

rupture zone associated with crater for- energy yields aftershocks may comtinue,

mation (Fig. 6.70). Farthei out, where although at a :'educed -ate, for many

the shock wave is weaker, the ground d:,ys after the chimney has formed.

may become permanently distorted in (.21 The 1.1-megaton BENHAM

the plastic (deformation) zone. Final~y, test was conducted at a depth of 4,600

at considerable distances from the burst feet in tuff (§ 2. 104) at the Nevada Test

point, the weak shock wave (carrying Site on December 19, 1968. During the

les.; than 5 pcrcent of the exploiion period of six weeks following the detoenergy) becomes the leading wae f 1i nation, some 10,000 weak aftershocks

series of seismic waves. A seismic wave were detected, nearly al! within 8 miles

produces a temporury (elastic) displace- of the explosion point. Of these, 640

ment or disturbance of the groano; re- aftershocks were chosen for detailed

covery of the original position, foilow- !,tudy and their locations are shown by

ing the displacement, is generally the small crosses in Fig. 6.21. The thin

achieved after a series of vibrations and !nes indicate i"usitions of known faults

undulations, up and down, to and fro, and the thick iines show approximate)y

and side (o side, such as are typical of where fault displacements were obearthquake motion, served at the surface. It is apparent ithat

a large number of the ;!ftershocks occurred aieng a north-south line, which is

AF"TIERSHOCKS AND FAULTV the general direction of tbt known

DISPLACEMENTS faults. Many of these aftersho,,k2, presumably occurred along hidden ftilts or

6.20 Many of the aftershocks ass;o- other geologicl discontinuities parallel

ciated with a deep undergrourd explo- to the faults.

The phenomena i-nl effects of deep (fully contained) underground explosions are of primary interest

tor nuclear weapens tests. For a more detailed nontechnical discussion see "Public Safety and

Underground Nuclear Detonatioins," U.S. Atomic Epergy Commission, June 197., TID-25708.

'A geological "fault" is a fraclure in the ground at which adjacent rock surfaces are displaced with

respect to each oiher. Ti,.! presen :-- of a faut can sometimes be detect -d by a faull line on the surface, but

hidden faults cank,; be observe' in this way.
DEEP UNDERGROUND BURSTS 239

- DISPLACEMENTS $

-KNOWN FAULTS NXt

K /

/ //

3"( 

I0 E 

/"

x /• A .EN 

/ xX

11lb•35' 

116 025 .

Fig,•rc 6.21 .Locations of 640 aftershock, and s faull displacements 

from the BENHAM

I. I- megaton test.

6.21, most of the ground displacemecnts yield of the explosion.

in the vicinity 

of the BENHAM 

explo 

6.23 

A rough 

rule of thumb 

has

ion occurred 1 along or near pre-existing 

been developed from observations at the

fault line•:. The maximum vertical dis- Ne~vada Tesr Site. According to this

placement was 5 feet, 1 at locations 1 .5 rule, di,•;placement along a fault line

arid 2.5 miles north of the burst point. may occur only if the distance (in feet)

Larger displacements 

have occurred in from surface zero is less; than about

some instances, but 'vertical displace1000 times the cube root of the ene'gy

ments of the surface along or near fault expressed in kilotons of TNT equivalines have been mcstly less than a foot. len~t. Thus, for a 1-megaton (1000-kiloThese displacements, although not con- ton) detonation, displacemcnt 

would be

iinous, may ex',end for a distance of cxpected only if the fault 'ines were

several miles. For the same (or similar) within a distance of roughly 

1000 x

co nd~tio n s, tl',e lin ear ex te n t of d is- ( 10 0 0 ) "/3 0 00 1 x I0 = 10 ,000 feet
240 SHOCK EFFECTS O1: SURFACE ANI SUBSURFACE BURSTS

(about 2 miles). In other words, fault dlate of the high-yield BENHAM event,

lines that -re nowhere closer than 2 by which time 235 undergrcounad tests

miles from a I-megaton deeply buried had been conducted, 616 eaithquakes

explosion would not be significantly af- were observed in a 104-hour period.

fected. However, if any part of the fault There thus appears to be no indication

line is within 2 miles of the detonmon that underground tests have resulted in

site, the actual displacement ma be any significant change in the occurrence

observed along that fault line at a greater of earthquakes in the Nevada area.

distance. 6.26 Two high-yield underground

nuclear e,.plosions on Amchitka Island,

UNDERGROUND EXPLOSIONS AND

U in ýhe Aleutian Island chain, are of speEARTHQUAKES cial interest because the isWand is located

in one of the earth's most seismically

6.24 Fear has been expressed that active regions. The MILROW device,

deep underground nuclear explosions of with a yield of about I megaton TNT

high energy might stimulate ratural ecitlivalent, was detonated on October 2,

earthquakes, but there is no evidence 1969 a! a depth: of 4,000 feet. The

that such is the case. The "hypocenter" explosion was followed by a fcw hunor "focus" of an atershock or an earth- dred small, separate aftershocks which

quake is the point below the surface were apparently related to deterioration

where motion, e.g., slippage at a fault, of the explosion cavity. This aftershock

responsible for the obser~ed disturbance activity decreased at first but later inoriginated. The focal depths, i.e., the creased sharply and then terminated

depths of the hypocenters below the within a few minuts•, of a larger, cornearth's surface, of the aftershocks that plex multiple event at 37 hourv after the

follow deep underground tests in Ne- burst. The simultaneous formation of a

vada have ranged from zero to roughly 4 surface subsidence indicated that commiles, with most depths be~ng between plete collapse of the cavity occurred at

0.6 and 3 miles. Natural earthquakes in this time. Subsequently, 12 small afterthe same area, however, have consider- shocks of a different type. ten of which

ably greater focal depths. Hence, it were detected within 41 days of the

seems unlikely that a nuclear explosion explosion, were observed during a

would stimulate a natural earthquake. period of 13 months. Two of these

6.25 A statistical study has been events were close to the explosion remade of the occurrence of earthquakes gion and most of the others originated a,

in a circular region of 535 miles radius oi near the Rifle Raiige Fault, some 2 ot

around the Nevada Test Site to deter- 3 miles away. They were attributed to

mine the possible effects of underground underground structural adjustments fo!-

explosions. During a period of 104 lowing the explosion.

hours preceding September 15, 1961, 6.27 A more stringent test was prowhen an extensive series of under- vided by the CANNIKIN event on Noground tests was initiated at the Nevada vember 6, 1971 when a nuclear weapon

Test Site, 620 earthquakes were re- with a yield described as being "less &

corded. After December 19, 1968, the than 5 megatons" was exploded at a

,I
DAMAGE TO STRUCTURES 241

dcpth of 5,875 fect below the surfacc of were not clearly relate1 to the explosion

Amchitka Island. The number of initi.al, cavity or to known faults. The hypo.

small aftershocks arising from cavity centers, as weli as those of the tremors

deterioration was !arger than after the following MILROW, were all less than

MILROW test, but otherwise the phe- 4.5 miles deepi, compared with ciepths

nomena were similar. Cavity collapse, exceeding 12 miles for essentially al!

immediately preceded by considerable natural earthquakes in the area. Furactivity, occurred 38 hours after the ex- thermore, there was no evidence of any

plosion. During the next 23 days, 21 increase in the frequency of such earthearth tremors were detected and ore quakes in the sensitive Aleutian Islands

more occurred more than 2 months region following the MILROW and

later, but there were no others during the CANNIKIN events.

next year Of these disturbances, five

DAMAGE TO STRUCTURES

SURFACE AND SHAL.OW with shallow underground (9nd contact

UNDERGROUND BURSTS surface) bursts, especially in connection

6.28 For a nuclea," burst at a mod- with buried structures, are difficult to

erate height above the ground the ciater define. A simple and practical approach

or depression formed will rot be very is to consider three regions around surdeep, although it may cover a large face zero. The first region is that of the

area. Shallow buried and semiburied true crater, which is larger than the

structures near ground zero will be apparent (or observable) crater (§ 6.70.

damaged by this dc.pression of the earth. Within this region there is practically

For deep underground structures, complete destruction. The depth at

ground shock may be the primary factor which underground structures directly

causing damage, but its etffects are prin- beneath the crater will remain undacipally important to people and equip- maged cannot be clearly def.c,-'d. This

ment within the strudtures. As far as depth is dependent upon the att.nuation

structures above ground are concerned, of pressure and ground motion in the

the range of damage will depend upon material.

the characteristics of the blast wave in 6.30 The se.,.nd region, which inair, just as for an air burst (see Chapter cludes the ruptt,,'e and plastic deformaV). The area affected b, air blast will lion zones, extends rough!y out as far as

greatly exceed that in which damage is the major displacement of the ground.

caused by both direct and induced shock In some materials the radius of this

waves in the ground. In the even' of a region may be about two and one-half

contact or near-surface burst, the situa- times the radius of the (apparent) crater.

tion is similar to that in a shallow un- Damage to underground struct:,res is

derground bLrst, as described below, caused by a combination of direct

6.29 The damage criteria associated ground shock and shock induced in the
242 SHOCK EFFECTS OF SURFACE AND SUBSURFACE BURSTS

ground by air blast. Dafimage to doors, DEEP UNDERGROUND BURSTS

air intakes, and other exposed elements 6.33 The ground shock wave from a

may be expected from direct air blast. deep (or moderately deep) underground

The actual mechanism of damage from nuclear explosion weakens into a train

these catises depends upon several of seismic waves which can cause apmore-or-less independent factors, such preciable ground motion at considerable

as size, shape, and flexibility of the Jistances from surface zero. The resftructure, its orientation with respect to sponse of aboveground structures of

the explosion, and the soil characieris- various types to this motion can be prctics (§ 6.90 et seq.). dicted with a considerable degree of

6.31 Along with underground certainty. The procedures for making

structures, mention may be made of these predictions will not 1e described

buried utility pipes and tunnels and here (see § 6.90 et seq. ), but some of

subways. Long pipes ire damagcd pri- tile general conclusions are of interest.

marily as a result of differential motion 6.34 It is natural for buildings,

at the joints and at points where the lines bridges, and other structures to vibrate

enter a building. Failure is especially or oscillate to some extent. Apart from

likely to occur if the utility connections earthquakes and undergiound detonaare made of brittle material and are tions, these vibrations can result from

rigidly attached to the structure. Al- high wiiids, from sonic booms, and

though tunnels and subways would even from vehicles on a nearby street or

probably be destroyed within the crater subway. Every stricture and indeed

region and would suffer some damage in every elcaner t (or component) of a

the plastic zone, it appears that these :;tructure has many natural periods of

structures, particulaily when bored vibration. For the majority of common

through solid rock and lined to minimize structures, the most important .f these

spalling, are very resistant to under- periods is usually the longest one. This

ground shock, is generly a second or two for a tall

6.32 In the !hird region. beyond the building (10 to 20 stories) and a fraction

plastic zone, the effects of ground shock of a second for a short one. Unless th,',

are relative!y unimportant and then air structure has picviously suffered signif-,

blast loading becomes the significant icant damage, the natural periods oi

criterion of structural damage. Strong or vibration do not change very much iedeeply buried inderground structures gardless of the source of the disturbance

will not be greatly affected, but damage that starts the vibration.

to moderately light, shallow buried 6.35 The ground motion caused by

structures and sorme utility pipes will be, a distant underground explosion (or an

determined, to a great extent, by the earthquake) contains vibrations of many

downward pressure, on the ground, i.e., different periods (or frequer~cies) and

by the peak overpressure of the air blast widely varying amplitudes. The waves

accompanying t!'e surface or subsurface of shorter periods (higher frequencies)

burst. Structures which Pre partly above tend to be absorbed by the ground more

and partly below ground will, of course, readily than those of longer periods

also be affected by the direct air blast. (lower frequencies). Consequent!y, the
DAMAGE TO STRUCTUrFS 243

greater the distance from the explosion, sponse of a tall building will increase

the larger is the fraction of seismic en- more than that of a shiort building at the

ergy in ground vibrations with longer same distanze from the explosion.

periods. 6.39 The foregoing generalizations,

6.36 As a result of the effect called based on Nevada Test Site experience,

"resonance," a structure tends to re- imply that at greater distances from unspond, e.g., vibrate, most readily to derground explosions of high energy

ground motion when tie period of the yield there should be a tendency for a

latter is equal or close to one of the larger proportion of the seismic energy

natural periods of vibration, especially to appear in ground motion of longer

the principal (longest) period, of the periods. As a consequence, the restructure. Because the ground to'tion sponses of high-rise buildings, e.g.,

from an underground burst (or an earth nine or more stories, with their longer

quake) is so complex, at least one of the vibration periods, are of spccial interest

natural periods of ihe structure will be at greater distances from undergiound

near to a period in the ground motion. nuclear explosions of high yield. At

All structures may thus be expected to shorter distances, where more seismic

respond to some extent to the ground energy is available, both tall and short

motion from a distant underground ex- buildings could exhibit a significant replosion. If the response is more that, the spcnse.

structure is designed to accept, some 6.40 Tall buildings in Las Vegas,.

damage may occur. Nevada, more than 100 miles from the

6.37 With increasitag distance from area where high.yield nuclear tests were

an explosion of specified yield, the conducted, have been known to sway in

seismic energy decreases, but a larger response to the ground motion produced

fraction of the available energy is pres- by underground explosions, just as they

ent in the ground vibrations with longer do during mild earthquakes or strong

periods. Furthermore, as already seen, winds. No damage. which could be

tall buildings have longer vibration definitely attributed to such explosions,

periods than shorter ones. As a result of however, was recorded in these structhese factors., the response of any stiut- tures prior to thc. HANDLEY event,

ture decreases with increasing d&itance with a yield somewhat greater than I

from an underground explosion, but the megaton, on March 26, 1970. There

decrease is relatively less for the longer was no structural damage in Las Vegas

vibration periods, i.e., for tall build- on this occasion, but nonstructuial

ings, thalk for the shorter periods, i.e., damage was reportea as disturbance of

short buildings. ornamental blocks on one building and a

6.38 As might bo expected, the re- cracked window in another, which

spose of any structur: at a given dis- could be readily repaired. There are no

tance from the burst point increases with tall structures closer to the Nevada Test

tle explosion energy yield. Howevt-x, Site than those in Las Vegas, bmt lowthe increas.. is greater for longer than rise buildings nearer to the test area have

shorter vibration periods. Consequently, experienced minor nonstructura! darnwith increasing energy yield, the re- ag-., as was to be expected.
244 SHOCK EFFECTS OF SURFACE AND SUBSURFACE BURSTS

CHARACTERISTICS OF UNDFRWA [ER BURSTS

SHOCK WAVE IN WATER (air) surface, an entihtly different re6.41 Fhe rapid expansion or the hot flection phenomenon occurs. At this

gas bubble formed by a nuclear explo- surface the shock wave meets a much

sion undei wawer (§ 2.86) results in a less rigid medium, namely the air. As a

shock wave reing sent out through the result a reflected wave is sent back into

water ini all ,Jirections. The shock wave the water, but this is a rarefaction or

is similar 'n general form to the blast tension, i.e., negative pressure, wave.

wave in a r, although it differs in detail. At a point below the surface the combiJus, as ',1 air, there is a sharp rise in nation of the negative reflected wave

oveipre.,sure at the shock front. In with the direct positive wave produces a

water, however the peak overpressure decrease in the water shock pressure.

does iot fall off as rapidly with distance This is referred to as the "surface cutas it does in air. Hence, the peak values off."

in water are much higher than at the 6.44 The idealized variation at a

,'aine distance from an equal explosion given location (or target) of the shock

in air. For example, the peak overpres- overpressure with time after the explos'ire at 3,000 feet from a 100-kiloton sion at a point under water, in the abFurst in deep water is about 2,700 sence of bottom reflections (§ 6.49), is

lnitrids per square inch, compared with shown in Fig. 6.44. The representation

a few pounds per square inch for an air applies to what is called the "acoustic

burst. On the othei hand, the duration of approximation- in which the initial

the shock wave i;-, water is shorter than shock wave and the negative reflected

in air. In water it is of the order oi a few wave are assumed to travel at t'-e same

hindredths of a second, compared with speed. After the lapse of a short intersomething like a second or so in air. va;, which is the time required for the

6.42 The velocity of sound in water shock wave to travel from the explosion

under normal conditions is nearly a mile to the given target, the overpressure

per second, almost five times as great as rises suddenly due to the arrival of the

in air. When the peak pressure is high, shock front. Then, for a period of time,

the velocity of the shock wave is greater the pressure decreases steadily, as in air.

than the normal velocity of sound. The Soon thereafter, the arrival of the reshock front velocity becomes less at flected negative wave from the air-water

lower overpressures and ultinately ap- surface causes the pressure to drop

proaches that of sound, just as it does in sharply, possibly below the normal (hyair. drostatc6 pressure of the water. This

6.43 When the shock wave in water negative pressure phase is of short dustrikes a rigid, submerged surface, such ration.

as the l;ul of a ship or a firm sea bottom, 6.45 The time interval between the

positive (compression) reflection occurs arrival of the direct shock wave at a

as in air (§ 3.78). However, wheii the particular target in the water and that of

water shock wave reaches the upper the cutoff, signaling the arrival of the
CHARACTERISTICS OF UNDERWATER BURSIS 245

PEAK I;HOCK OVERPRESSURE

SW- CUTOFF

cr

a.

AMBIENT WATER PRESSURE

TIME

Figure 6.44. Idealized (acoustic ap'proximat?:,n) variation of water pressure with time in an

underwater explosion a( a point near the air surface in the absence of bottom

reflections.

reflected negative wa-e, depends on the sets in mtion the water through which

shock velocity and on the depdh of burst, the following reflection (rarefaction)

the depth of the target, and the distance wave travels. Within a region near the

from the burst point to the target. l'hese air-water surface--the anomalous re1hree distances determine the lengths of gion- the initial shock wave may he

the paths traveh-d by the diret (posi- strongly attenuated by overtaking raretive) and reflected (negative) shock factions, as shown at point A. At deeper

waves in reaching the underwater target. levels (points B, C, D) differences in the

If the latter is close to the surface, e.g., paths traveled by primary ana reflected

a sha.low ship bottom, then the time waves may be too great to allow signifelapsing between the arrival of the two icant overtaking. Nevertheless, passage

shock fronts will be small and the cutoff of the reflected wave through th,, diswill occur soon after the arrival of the turbed water results in a less sharp suishock front. A surface ship may then face cutoff than for the ideal acoustic

suffer less damage titan a deeper sub- approximation.

merged target at ;he same distance from 6.47 In deep water, when bottom

the explosion. (and other positive) reflcetions are not

6.46 The ideati'ed wave shape in significant, the initial shock wave and

Fig. 6.44 for the acoustic approximation the negative surf3ce reflection are the

is modified in practice, as illustrated in most generally important features qf the

Fig. 6.46. When the shock intensity is pressure disturbance arising from Fn

strong, the reflection tends to overtake underwater detonati.-n. There are, howthe shock wave becaise the shock wave ever, several other effects which may be

_ -V,__ ,-•_ . .. . ..
246 SHOCK EFFECTS OF SURFACE AND SUBSURFACE BURSTS

AIR- WATER SURFACE

StA ANOMALOUS

B REGION

EXPLOSIONCI REIN

/

--ACOUSTIC -ACOUSTIC

OBSERVED

TIME

POINT A POINT B

0OBSERVED -- '.OBSERVED

Cr PULSE AOITHCLIT

tnCUSI Z~S(IRFACE REFLECTION

TIME -. .. SURFACE R~EFLECTION.

I1 ACOUSTiC THEORY,

NO CAVITATI)N

POINT C POINT D

rigure 6.46. r'ypi.-al pressure pulses affe,'ted by air -,vtler surface reflection in the absencc

of bottom reflections.

significamit in .;ome circnastances. rive at a target attenuatcd in strength. In

6.48 One group of such effects is other cases e-iergy may be channeled ui

associated with inhomogeneities of even focused into one part of the mede-usity, temperarIkre, and salinity bje- dium to produce a stronger than excause shock wave speed depend., on. perted shock wave at some point remote

these nonuniform properties of the me- from the detonation. Thus, n many

dium, underwater shock waves are :)ftevn ireas the expected reducticr' of shock

refracted, i.e., changed in dciection, as pressure by suarface cutoff mvy be rewell as reflected. Thi" means that in placed by enhancement due to focusing.

some cases shock energy will be :urned 6.49 Certain effects connected with

away from certain regions and will ar- the bottom may be important, particu-
CHARACTERISTICS OF UNDERWATER BURSTS 247

larly in shallow water. One of these is quently from the rising gas bubble.

the bottom rePction of the primary 6.52 Sec,.,ndary underwater presshock wavc. Unlike the reflection from sure pulses may be a consequence of the

the air, the oottom reflection is a coin- action of the reflected (negative) wave at

pression wave aad increases the pres- the air--water surface. This wave movsure in regions it traverses. The pressure ing downward can cause the temporary

on the target now includes a positive upward separation of water masses in a

reflected pressure in Mddi~ion to the ini- manner analogo-,s to spaling in an untial shock pressure and the negative derground burst (§ 2.91). When these

(air--surface) reflected pressure. The water masses are brought together a~ain

characteristics of the overall pressure by tue action of gravity, the impact may

pulse, and hence the effect on an under- sft in motion a train of waves. The

water !arget, will be dependent on the separation of water masses ;n this way is

magnitudes and signs of the various called spalling if the separated water

pressures and the times of arrival at the flies into the air to produce a spray dome

targct of the two reflected pressures. (§ 2.66) or "cavitation" if an underThese quantities are determined by the water void (or cavity) forms.

three distances mentioned in § 6.45 and

the water depth, as weil as by the ex- AP BLAST FROM UNDERWATER

plosion yield and the nature of me bot- EXPLOSIONS

tom material.

6.50 When the bottom is rock or 6.53 Although the particular mechuther hard malerial and the burst point ii anism wi'N depend on yield and depth of

not too far above ,t, the botom may burst, one or more air blast waves will

contribuie two ,.ompression waves; the generally follow an underwater nuclear

first a simple dcfL.tion of the primary detonation. In the first place, some enwater shock, considered above, and the ergy of the primary shock wave in the

second a reradiatior? of energy transmit- water is transmitted across the water-air

ted a distance through the bottom mate- interface. This air shock remains i'trial. The latter w:,ve "nay become tached to the water shock as it spreads

prominent if it calt run ahead of thc out from the brust point. Second, if the

primary rhock and men radiatc energy s."aled depth of burst, i.e., the actua!

back into the water. In this ,ase the first depth of blirst in feet divided by he

motion observed at a remote station will cube roct of the wearon yield TV in

be due to this bottom-induced wave. kilotons, is less than about 35 fectikilo6.51 in deep underwater nuclear tons s11, the bubble ventsfirectly into the

explosions, the associated gas bubble atmosphe.re dLring its first expansion

may undergo two or three cycle-s of phase, ihereby causing an air shock.

expansion and contraction before it col.- Third, although deeper bursts will no,

lapse-; (§ 2.86 ei seq.). Each cycle leads vent, the spall or spray dome pushing

to distinct compression and rarefaction rapidly upward into the ait call cause an

wave-., called bubble pulses, which air .7hock. Beyond a scaled depth of

move outwari through ,he water isu- approximately 150 feet/kilotonsl/1,

tially from the burst point and subse- however, the spray dome rises too
248 SHOCK EFFECTS OF SURFACE AND SUBSURFACE BURSTS

sl(,wly to caiuse an appreciable air vation of the waves in the BAKER test

shock. The second anO third mecha- (approximately 20-kilotons yield) at Binisms produce air blast waves that lag kini (§ 2.70) indicated that the firs! wave

f,,r behind the primaý4ry water shock, but behaved differently from the succeeding

they can be identified underwater by ones; it was apparently a long, solitary

airs!an, compression, similar to the airs- wave, generated directly by the explolap efiect of explosions at or near the sion, receiving its initial energy from

giound surface (§ 6.12). Thus, an un- the high-velocity outward motion of the

derwater target will always receive the water accompanying the expansior of

!cimary water shock before :hc airslap, the gas bubble. The subsequent waves

if any. Regardles's of the generating were probably formed by the venting of

mechanism, however, atte-iuation of air the gas bubble and refilling of the void

blasi pre.sure with depth of burst below created in the wzter. A photograph of

the watur surface is rapid and follows a !he surface train approaching the beach

pattern similar to that shown in Fig. from the Bikini BAKER test ;s repro6.81 for underground explosions. duced ir Fig. 6.55. Later tests have

shown that the initial, solitary wave is

StýRVACE WAVES FROM characteristic of explosions in shallowv

UNDERVWATER EXPLOSIONS water. Detonations in deep water gener-tte a train )f waves in which the

6,54 Underwater expiksions gener- number of crests and trotghs increases

ati relat.vely slcw, outward-moving as the +rain propagates outward from the

surface waves, which have certain rec- center of the explosion.

ognizable characteistics. These waves, 6.56 Near the BAKEP explosion

originating in the oscillations of the gas the first crest was somewhat higher than

bubble as it breaks the surface, eventu- the succeeding ones, both above the

ally form d train spreading in widening undisturbed water level and in total

circles of steadily oiminishinrj intensity height above the following trough. At

around surface zero. The first surface greatei distances from the burst poit't

wave near the turst is generally too the highest wave was usually one of

steep ýo be sustained; consequently, it those in the succeeding train. The maxbreaks inlo turbulent motion, consum- imum height in this train appeared to

ing a large part of the original energy pass backward ito later and later waves

that would otherw'se be available to tite as the distance from the center insurface wave. Subsequently the train creased This recession of the maximum

travels over deep water almost without wave height hat also been observed in

further energy !css. The energy in this explosions in deep water.

wurface motion has been estimated to be 6.57 The maximum heights and arbetween 2 and 5 percent of the weapon rival times (not always of the first

yield. wave), at various distances from surface

6.55 Certain characteristics of sur- zero, of the water waves accompanying

face waves become more pronounced a 20-kilo!on shallow underwater explowhen the deton~ation occurs in shallow sion are given ii, Table 6.57. These

water rather than in deep water. Obser- results are baed on observations made

I,
CHARACTERISTICS OF UNDERWATER BUIRSTS 249

Figure 6.55 Waves from the BAKER underwater explosion i'c,.ching the beach at Bikint,

I I mniles from surface zcrty..

Table 6.57

MAXIMUM HEIGHTS (CREST TO TRO1JGPI) ANt) ARRIVAL. TIME.'; OF WATIý'R

WAVES AT BIKINI HAKER FEST

D~istance (yards) 330) 660 1,330 ?,04XX 2,7(X) 3i,3(X) 13M)

Wave height (feet) 94 47 -)4 16 1 _- II k)

"Time (seccrn's) 23ý- 48 74 101 127 154

at the Bikini BAKER test. A more geri- is possible to wvhips that are mod:xerately

eralized treatment of wave heights, near to surface zeio. There was eviwhich can be adapted to underwater dence for such damnage to the carrier

explosions of any specified energy, is U.SS. Saratoga, anchoredi ini Bikini lagiven In § 6. 119 el scq. goon almost broadside on to the explo6.58 For !he conditions that existed sieti with its stern 400 yards fr~ni sur

in (he BAKER test, water wave damage kace zero. TI-10 "isiaiiW' structure was
250 SHOCK i•IF:ECTS OF SURFACE AND SUBSURF'ACI- BWJRSTS

Figure 6.58. The aircraft carrier U.SS. Saratoga after the BAKER e~plosion.

not affected by the air blasi, but later thte an exient depending o.i th~e beach slcpe

central part of the structure wias ob- and wave height and steepness (§ 2 7 1)

served to be folded down onl the deck of

the carrier (Fig. 6.5ý). Shortiy after ris- UNDIi-R'ATER CRATERING

in& on the first wave crest, when the

stern was over 43 feet above its previous 6.60 For a niuclear explosion in (or

position, the Saratoga fell into the suc- even just above) a body of water, a

ceeding trough. It appears probable that significant crater forms in the bottom

the vessel was then struck by the second material if the gaseous bubble or a caywave crest which caused the darnadgl to ity in tile %,t-er (§ 6.52) formed by the

the island structuie. explosion makes contact with the bot6.59 Water waves generated by an torn. Such an underwater crater is simiunderwater detonation can cau~z dain- lar to a crater on land formed by an

age in harbors or near the shireline, explosion near the ground surface since

bcoth by the force of the waves and by both are characterized by a J~ish-shaped

inundation. The waves will increase in depression, wider than it is deep, and

height as they move nato shallower surrounded by' a lip raised above the

water, and inundation, similar to that undisturbed surface fsee Fig. 6.70). For

ohserved with tidal waves, can occur to most underwater craters, however, the
CHAkACTERISTICS OF UNDERWATER BURSTS 251

observed ratio of crater radius to depth detonations of TNT and other chemici,!

is larger and the lip height is smaller explosives. However, because of the

than for craters fom 'omparab!e bursts smaller yields, the shock damage from

in similar materials on land. These dif- such explosions is localized, whereas

ferences are caused by wvter displaced the shock wave from a high-yield nuby the explosion washing back over the clear explosion can engulf ar, entire ship

crater. This flow increases the crater and cliuse damage over a large area.

radius by as much as 10 percent ?.:-d 6.63 The effects of an underwater

decreases ti.e depth by up to 30 percet. nuclear burst on a ship may be expected

An exception to this general rule occurs to be of two general types. First, there

when the water layer is so shallow that will be the direct effect of the shock on

the lip form~ied by the initial cratering the vessel's hull, and second, the indiextends above the surface of the water. rect effects resulting from components

Such craters, termed 'unwashed within the ship being set in motion by

craters," approach surface c~aters in the shock. An undlerwaler shock acting

appearance, with higher lips and smaller on the hull of a ship tends to cause

radius-to-depth ratios than washed distortion of the hul ibelow the water

craters. line and rupture of the shell plating, thus

6.61 The Bikini BAKER explosion producing leaks as well as severely

resulted in a measurable increase in str;.ssing the ship's framing The underdepth of the bottom of the lagoon over watei shock also leads to a rapid movean area roughly 2,000 :eet across. The ment in both horizontal -.nd vertical 6dgreatest epparent chan.7c in depth was rections. This motion ca&-:•. damage by

32 feet, but this represent,-d the removal shock to components and equipment

of an el-vated region rather than an within the ship.

excavation in a previously flat surface. 6.64 Main feed lines, main steam

Before the test, samples of sediment linLs, shafting, and boiler brickwork

collected from the bottom of the lagoon within the ship are especially sensitive

consisted ot coarse-grained algal debris to shock. Because of the effects of inermixed with less than 10 percent of sand tia, the supporting members or foundaand mud. Samples taken after the ex- tions of heavy components, such as enplosion were, however, quite different. gines and boilcrs, are likely to collapse

instead of algal debris, layers of mud, or become distorted. Lighter or inadeup to I0 feet thick, were found on the quately fastened articles will be thown

bottom near the burst point, about with great violenec,_, causing

damage to thcmselves, to ),plkheads,

UNDERWATER SHOCK DAMAGE: and to other equipment. Electronic, fire

GENERAL CHARACTERISTICS control, and guide,, missile equiptiient is

likely to be rendered inuperli-,e, at

6 li2 The impact of a smiock wee on least temporarily, by shock effects.

a ship :-i structure, such as a breakwater However, equipment whicn has been

or darn, is comparable to a sudden blow. peoperly designed to be ihock resistant

Shocks of this kind have been experi- will --uffer less seriously (cf. § 6.112 et

enced in comection with underwater .eq.). In general, it appears that the

I _1ýk~
252 SHOCK EFFECTS OF SURFACE AND SUBSURFACE BURSTS

damage io shipboard equipmn, is de- boilers and main propulsive machinery

pendent on thL peak velocity imparted to suffer heavy damage due to; motion

the particular article by the shock wave. caused by the water shock at close-in

6.65 The damage to the hull of a locations. As the range is increased.

ship is related to the energy per unit area auxiliary machinery associated with

of the :;hock wave, evaluated up to a propulsion of the ship does not suffer as

time corresnonding to the surface cutoff severely, but light interior e-quipment,

ne at a characteristic depth. Damage especially electronic equipment, is afto the gate structure of canal locks and fected to ranges considerably beyond

drydock caissons is dependent mainly the limit of hull damage. In vessels

oni the peak pressure of the underwater underway, machinery will probably

shock wave. Within the range of very suffer somewhat more damage than

high pressures at the shock front, such those at anchor.

structures may be expected to sustain 6.68 Although the major portion of

appreciable damage. On the other hand, the shock energy from a Shallow underdamage to large, massive subsurface waier explosion is propagated through

structures, such as harbor installations, the water, a considerable amount is

is more nearly dependent upon the transmitted through the surface as a

shock wave impulse. The impulse is shock (or blast) wave in air. Air blast

dependent upon the duration of the undoubtedly caused some damage to the

shock wave as well as its pressure superstructures of the ships at the Bikini

(0 3.59). BAKER test, but this was insignificant

in comparison to the damage done by

ýI'NDEPWATER SHOCK: BIKINI the underwater shock. A;r blast ,-ouid

EXPERIENCE also cause some damage to ships by

capsizing them. The main effect of the

6.6C. in the shallow, underwater air blast wave, however, would probaBAKER test some 70 ships of various bly be to targets on land, if the explotypes were anchored around the point of sion occurred not too far froin shore.

burst. FMom the observations made after The damage critelia are then the same as

the shot, certain general conclusiýions for a surface burst over land, at the

"-ere drawn, and these will be outlined appropriate overpressures and dyrmamic

here. It should be noted, however, that pressures.

the raiure and extent of the damage 6.69 As the depth of bursi insustained by a surface vessel fioni un- creases, the proportion of the explosion

derwater shock will depend upon the energy going into air blast diminishes,

depth of the burst, yield, depth of water, in a manner similar to that in a burs(

range, +he ship type, whether it is beneath the earth's surface. Conseoperating or riding at anchor, and its quently, the range for a gi,'en overpresorientation with respect to the explo- sure decreases, with the close-in higher

sion. pressures decreasing more rapidly than

6.0,7 In a shallow underwater burst, lower pressures a* longer ranges.
TECHNICAL ASPECTS OF SURFACE AND UNDERGROUND BURS T S 253

TECHNICAL ASPECTS OF SURFACE AND UNDERGROUND B.UR,53T •

CRATER DIMENSIONS quantities given above (and others de6.70 In addition to the rupture and fined in § 6.74 et seq.) can be estimated.

plastic zones (§ 6.07), two ,ther fea- 6.72 Crater dimensions depend

tures of a crater may be defined: these iipoi the depth of burst (or burial), the

are the "'apparent crater" and the "true explosion energy yield, and the characcrater." The apparent crater, which has teristics of the soil. The apparent crater

a radius Ra and a depth Da, as shown in radius and depth, as functions of the

Fig. 6.70, is the depression or hole left depth of burst, are given in Figs. 6.72a

in :he ground after the explosion. The and b for a I-kiloton explosion in four

true crater, on the other hand, extends media. For bursts just above the surface,

beyond the apparent crater t,, thie dis- the heights of burst are treated as negatance at which definite shear has oc- tive depths of burst. Because of the

curred. The volume of the (apparent) rapid change in crater dimensions as the

crate-, assumed to be roughly parabo- depth of bursts passes through zero, the

Iid, is given approximately by values for a contact surface burst ar,

shown explicitly on the figures. The best

Volunie of crater I ,- R2 R. empirical fit to crater data indicates

2 that, for ,i given scaled depth of burst,

i.e., actual depth divided by W, 0, both

6.71 Values of other crater parame- the radius and depth vary approximately

ters indicated in Fig. 6.70 can be es- as Wv'', where Wis the weapon yield.

timated with respect to the apparent The procedure for calculating the dicrater radius and the apparent crater mensions of the apparent crater for any

depth by the following relations. The specified depth oif burst and yield by

radius to the crater lip crest, R,,, is means of these scaling rules is illustrated in the example facing Fig. 6.72a.

R,, = 1.25 RU. The mdxima in the curves indicate the

so-called optimum depth:; of burst. It is

The height of the lip crest, Da, I Is evident that , change in the moistur

content of a soil or rock medium Ca

DI, =1.25 D,. have a significant influence on the si;

of a crater; ý. higher moisture content

The height of the apparent lip above the increases the crater size by increasing

original ground surface, HW, is the plasticity of a soil medium, weakening a rock -redium, and providing a

Ha - 0.25 Da. better coupl of the explosive energy

,o beth soil ,, rock media.

Thus, if R. and D are know.,, the (Text c( "tinued on page 255.)

'The remaining sections of this ch3ptcr may be omitted withcut loss of rontinuily.
254 SHOCK EFFECTS OF SURFACE AND SUBSURFACLE BURSTS

Re~

EJECTA PORTION IDISPLACEMENT OF

OF LIP .- Rol AORIGINAL GROUND

Hal SuRFACE

D 8

jR1i~GINAL:" R[Iru rURE GROWt'D / SURF:E *LL -. ZONE

VAPAR ENT QýC P 05~ ~ CRATER BOUNDARY\ *. /1

-- -' ~--~/ '*ýPLA.STIC

TRUE CRATER.-`- Ile ZONE

BOUJNDARIY .\ ,

Figure 6.70) Cross section of a crater from a subsurface nuclear di-ionationr

Thc curves in Figs. 6.72ai and b give Solu~tion: The scaled burst depth is

the approximate apparent crater radius DOB/W I~ = 270/200"

and depth, respectively, as a function of 2024 1 et

depth of burst (DOB) in wet hard rock.

dry hard rock, wet soil or wet soft rock. From Fi-. 6.72a the apparent crater raand dry soil or dry hard rock. Heights: of dius for a I KT explosion at this depth in

burst (up to 20 feet) are treated as negi- dry .harJ rock is 150 feet (curve 4) and

live depths of burst. from Fig. 6.72b the co.-responding

Scaling. To determine the aippai-ent cr;,,. r depth is 87 feet (curve: 4). Hence,

crater radius and depth for a W K T the apparent crater radius and depth for

yield, the actual hui'st depth is first di- a 20 KT burst at a depth of 270 feet in

vided by W1 to obtain the !:caled depth. dry hard rock are given 4tpproximately

The radius and depth M.) a crater for I as follows:

KT at this depth are obtained from Figs. Critter radius (Rd -, I50 x 200 1

6.72a and b, respective~lv, The results 150O X 2.46 =368 feet.

are then multiplied by `.VC' to obtain the Crv'ter depth (Da) 8: 7 x 20"1

requi~tei dimensions. 87 A 2.46 = 214 feet. Answer.

Evr mph' (With R and D, known, othe.r crater

Giv'en: A 20) KT Lxplosion at a depth (and lip)' dimens'igns can be obtained

of 270 feei in dry hard rork. from the approximate relaiions in §§

Find: Appa~rent crater radius ar.dl 6.71, 6.74, and 6.75.)

depth.
TECHNICAL ASPECTS OF SURFAC' AND UNDERGROUND BURSTS 255

240

I. WET SOIL OR WET SOFT ROC,'

2 DRY SOIL OR DRY SOFT RUCK

3. WFT '4ARD ROCK

4. DRY HARD ROCK

200 -__

3

W 160 _--..... -

W 2

D \

"at

1- 82 feet

l 2 -6 61I et 

3 3-58 feetI

- 4-49feet I

40 .. ... 1 ..

e ( I 

/ _P-I

- 20 0 40 80 120 160 200

DEPTH OF BURST (FEET)

Figure 6. 72a. Apparent crat,"r rv'dius as a function of depth of burst foe a I -kilolon

expio,•Ion in (or above) various media.

CRATER EJECTA ejecta field is divided into two zones: (1)

6.73 Crater eje,.:a consist of soil or the crater lip including the continuous

rock debris that, is thrown beyond the ejecta surrounding the apparent crater

boundaries of the apparent crater. To- (Fig. 6.-70), and (2) the discontinuous

gether with the fallback, which lies be- ejecta, comprising the discrete missiles

tween the true and apparent crater that falI beyond the limit of the continboundaries, ejecta comprise all material uous ejecta.

completely disassociated from the 6.74 The amount and extent of the

parer't medium by the explosion. The continuous ejecta in the crater lip are

-.
256 SHOCK, EFFECTS OF S"'RFACE AND SUBSURFACE BURSTS

160

1. WET SOIL OR WET SOFT ROCK

. DRY SOIL OR DRY SOFT ROCK

3, WET HARD ROCK

4. DRY HARD ROCK

I.- , o . . . . . . . .. I-

"80-j --

= ~// /

W 120

W

a. 40 . ow. 

2 - 28 feet

-22 feet

-20 C 40 e0 120 160 8OO

DEPTH OF BOURS'. (FEET)

Figure 6.72b. Apparent crater d&pth as a funct:on of depth of burst for a I-kiloton explosion

in (:)r •:bovc) various media.

determined primarily oy the explosioi" cates that ejecta mass represents apyield and the location of the burst point, proximately 55 percent of :he apparen~t

although the characteristics of the me- crater mass (the remainder being found

dium have some effect. The radial limit in fallback, compaction, and the dust

of the continuous ejecta, which is the Cloud which is blown away). For an

outer edge of t'.e lip, will usually vary ,explosion of given yield, the ejecta mass

from two to three times the apparent incteases sigrificantly with the depth of

.rater radius. In most cases, a satisfac- burst until the optimum dept' is

tory approximation to the radius of the reached. Ejecta thickness can be esticontinuous ejtcta, Re (Fig. 6.70), is mated for soil in terms of the apparent Il'dius and diameter; ths:

R 2.15 R,.'R \

6.75 The depth of the ejecta de- t. • 0.9 DI( , for R>l.8 R,

creases rapidly in an exponential man-(67.)

net as the distance from surface zero where t. is the ejecta thickness and R is

increases. In general, abou't 80 to 90 thae distance from surface zero to the

percent of the entire eiecta volume is point of interest. In equdtion (6.75.1) it

deposited wvithin the area of the contin-- i,' assumed that the ejecta mass density

uuus ejecta, Analysis of ddta for craters is approximateliy equal tc the original

formed by nu'clear bursts in soil indi- irn-situ density of the medium, which

X

lo ,, r : I
TECHNICAL ASUECTS CE SURFACE kND UNDERGROUND BURSTS 257

could be considered valic' for a soil layer has little effect on the crater ramedium. However, the bulking inherent dius, but may decrease the final depth

in disturbed rock media would rcsult in considerably.

ejecta thicknesses about 30 percent 6.79 For relatively low-yield exgreater than predicted by equation plosions at or very near the surface, the

(6.75.1). bedding or jointing planes in rock can

alter significantly the shape of the crater

GEOLOGIC FACTORS and the direction of the ejection. The

crater shape will tend to follow the di6.76 In additiorn to the nature and rection of the predominant joints; the

water content of the soil, certain other crater radius will increase in thie direcgeologic factors may influence crater tion parallel to the joints and decrease

size and shape. Terrain slopes of about normal to the joints.

50 or more will affect the geometry of a

crater formed by either surface or buried AIR BLAST PRESSURE

explosions, with the influence of the

slope being more evident as burst depth 6.80 Sevral different mechanisms

increases. The surface slope will cause may opcrate to transfer part of the enmuch of the debris ejected by the ex- eigý released in an underground exploplosioii tc fall on the downslope side of sion into the air and thereby produce air

the crater, often resulting in rockslides blast. For explosions at moderate

below the crater area. In additior, the depths, such that the fireball does not

upslope rupture zone may crllapse into break through the surface, the predomthe crater, resulting in an asymmetric inant mechanisms may be described as

crater shape. follows. A shock wave propagated

6.77 In rock, the dip of bedding through the ground arrives at the surface

planes will influence energy propaga- and imparts an upward velocity to the

tion, causing the maximum crater depth air (air particles) at the air--ground into be offset in the down-dip direction. terface, thus initiating an air pulse. At

Little overall effect is noted in regard to the sam,. time, there may be spalling

crater radius, but differences in ejucta and upward mo,.ion of the surface

angles cause the maximum lip height layers, as explained in § 2.91. Meanand ejecta radius to occur in the down- while, the tunderground explosion gases

dip direction. expand, pushing the earti upward so

6.78 A subsurface groundwater that the spall merges into a dome at

table in a soil medium will begin to surface zero. The piston-like acti,,n of

influence the size and shape of the crater the spall and the rising dome increase

when the water table is above the deto- the duration of the initial air pulse. The

nation point. Its effect is to flatten and air blast sustained in this manner apwiden the crater. The influenc2 of a peais on pressure-time records as a sinbedrock layer below a soil medium is gle pulse, termed the air-,transmitted,

similar to that of a water table, although ground-shock-induced pulse. Somewha!

somewhat less pronounced. For explo- later, the explosion gases puncture the

sions at oi near the surtace, the bedrock dome and escape, creating a second air

II
258 S,10('K EFI'u .rs OF SURFA('- ANI) SIBISLIRF.A%('F BURSTS

W GROUND-SHOCK-INDUCED PULSE

a: GAS-VENTING-INDUCED PIJLSc

U) a.

wa:

i>o 0~

0

TIME

Figure 6.•(. Air Hiast overpressure from ,nderground explosio.is of moderate depth. With

increas•ing burst depth, the relative contribution of gas venting decreases and

the time between the pulses increases.

pulse called the gas-venting-induced where .r = ground distance in feet, d =

pulse (Fig. 6.80). depth of the explosion in feet, V =

6.81 With increasing depth of explosion yield in kilotons, and p =

burst, the relative corntributiorn of gas spcific gravity of the ground medium.

venting decreases and the time between The curve in Fig. 6.8! may be used with

the two pulses increases. Nlthough the the relations given above for scaled

mechanisms that generate the air pulses depths of burst, Xhj less than 232

change with depth in a complex manner, feet/KT"-3 . Typical values of specific

a procedure has been developed for gravities are 1.6 for alluvium, 1.9 for

predicting peak overpressures in the iJr tuff, and 2.7 for granite.

near the surfacc as a function of distance

from surface zero over a reasonable GROUND MOTION

range of burial depths; the results are

shown in Fig. 6.81. The value of x may 6.8 [art shom otin a or nr

te obtained from the following rela- the surface accompanyiad g a shallow or

tions: moderately " "p underground burst ,nay be regarded as consisting of systemic

x eP d/126. and random effects. The systemic effects are those associated with air blast

X x/iW/3. and X d d/Wv•, and the shock wave transmitted direc~ly

i
TECH(NICAI. ASPECTS OF SURFACE AND UNDERGROUND BURSTS 259

0.~

V) 5

2 --

Vj)

LLj

ct)

w

w 2\

w -I•

Wj

02 2 5 03 2 4 2 5 5

0- 1 0.... 0

ADJUSTED SCALED GROUND LISTANCE, X, (FT/KT1 1 3 )

Figure 6.81. Peak overpressure of air blast from an underground explosion as a function of

adjustei scaled ground distan'e from a buried -kiloton explosion.

& __1
260 SllOCK -FFECTS OF SURI:A' E AND SUBSURI.ACFE BURSTS

through the ground from the detonation duration o0 the po:;itive air overpressufe

(§ 6 12 et scq.). Random effects inclhde pulse. The overali motion iecord v;

- shock waves in tlne characterized by q! considerable degree

ground, surface wave effects, reflec- of oscillation. When precursors (§,,4

tions. refractions, etc. They depend on 3.49, 3.79) are pre!ent, the records may

such factors as the explosion yield, dis- e-,hibit components of higher frequency,

tance from surface zero, depth of the and a more random type of oscillation.

observation point, and, in particular, the 6.84 By using data obtained during

local geologic conditions. The follow- various nuclear tests, exnressions have

ing discussion will be concerned mainly been derived from which peak ground

with the systemic effects. acceleration, velocity, and dispiacement

6.83 In the s.,perseismic situation, (ti-ansient and permanent), both at the

the downward acceleration oi the surface and down to moderate depths, in

ground due to the air blast is large corn- the superseismic condition can be estipared with the subsequent uatward ac- mated from the peak air overpre,-;sure as

celeration caused by the direct ground evaluated in § 6.8, No simple method

shock. Th'e rco'ird of ground accelera- is presently available for calculating the

tion (or veloLity) versus time obtained effects of outrunning ground motion. As

on a gage mounted neat the surface is far as the effects of the direct !,hock

similar in shape to the air overpressure- wave are concerned, the expecte& retime pulse, at least in the early stages. suits are inferred mainly from data obWhen the direct ground shock wave tained at deep underground tests in

outruns the air blast, there is a slower which the air blast is negligible. The

increase in the acceleration and the di- response of structures to seismic (or

rection may be upward rather than elastic) waves generated at a distance

downward. The acceleration-time pulse frr'.,i the burst point by the ground shock

may then last for a longer time than the wave is considered in § 6.90 et seq.

TECHNICAL ASPECTS OF DEEP UNDERGROUND BURSTS

CAVITY AND CHIMNEY DIMENSIONS The )urpose of the following treatment

6.85 The dimensions of the gas is only to give some rough indications of

cavity and the chimney formed in a deep cavity and chimney dimensicis and it

underground explosion depend on the should not be taken as providing definienergy yeld, on the nature of the me- tive inforniation.

dium in which the explosion occurs, or 6.86 As a rough approximaiion, the

that in which the chimney develops, and volumc of the cavity in a given medium

to some e7tent on the depth of burial. and fixed depth of burial may bc taken to

Because of the variability of the condi- be proportiona! to the explosion energy.

tions, it is not possible to state a rela- Hence, if the cavity is assumed to be

tionship among the factors involved, spherical, its radius should be propor-
TECHNICAl. ASFFCTS OF DFEP UNDERGROUND BLIRSIS 261

tionai to W1', wherc W is the energy chimney may be iromr abOut four to six

yield. Measurements indicate that this times :he catvity radius. The higher facrelationshio is very roughly true, so that tor ippcars to apoly to completely

R/ W' , wnere R is the cavity radius, is bulked granite and the ower to doloapproximately constant for a given me- mite, shale, and incompletel) bulked

dium and burst depth. For moderately granite.

decp, contained explosions the effect of 6.89 From the foreg:oing rough

bpirst depth is small and the following data, it appe-rs that for an underground

velues have been found for R1WI' in explosion in which the top .'t the chinitwo types of media: ney does not reach the earth's surtace

Dense silicate rocks the scaled depth of burial, i.e., dWWI',

(e.g., granite) ...... 35 feeK,,T'K must be greate" than iboul 300

Dense carbonate rocks feet/KT'rl",. It the top of the chimney is

(e.g., dolomite, limestone) fa.rly close to the suc'ace, however,

........... . 25 feet/KT1'1 some of the radioactive gases formed in

These expressions are 3pplicable ap- thc.. nuclear detonaiion couid seep

proximately for burst depths below through the ground intv the atmosphere.

about 2,000 feet. ,n conductirng underground tests, the

6.87 At greater burst depths, the escape of these gases inust be prepressure of the overburdea, which must vented. The scaled depth of burial i:s

be overcome in torming the gas cavity, consequently not less than 400

has some effect on the cavity radius. On feet/KT"'/. For explos~ons of low yield,

the basis of adiabatic compression ot the when the actual depth of burial would be

Gverburdeai material, the cavity radius ielatve!y small, and in media with a

would be expected to be inversely pro- substantial water content, the scaled

portional to (ph)" 2., where p is the der- depths of buial are increased evei moic

sity and h is the height of the overbur- in order to acifieve containment of raden. Limited observations, howev'er, dioactive gases.

itidicate that the exponeila may ditfer

significantly from 0.23. It appears, STRUCTURAL RESPONSE TO

therefore, that a number of facto's, GROUND MOTION

which are not well understood, affect

the relationship between the cavity ra- 6.90 'A semiempirical method for

dius and the overburden pressure at studying (and predicting) the response

depths exceeding 2,000 feet. of structures to ground motion caused

65.88 If the roof of the gas cavity by the seismic wave from an undercollapses upon cooling, as it generally ground explosion makes use of the "re-

(but not always) does, the dimensions of sponse spectrum." A linear oscillator

the chimney are highly dtpendent upon with a single mode of vibration, which

the characteristics of the medium in may be thought of as a simple idealized

which it is formed. As a general rule, structure, is considered. It is assumed to

the radius ef the chimney is from 10 to be subjected to the entire history cf the

20 percent greater than that of the cav- ground motion as actually recorded on a

ity. Furthermore, the height of the seismic instrument at a given location,
262 SHOCK EFFECTE OF SIJKFACE AND SUBSURFACE BURSTS

By utilizing the laws of mechanics, the the distance from the burst point. In

peak response of the idealized structure addition, however, the nature of the

to the ground motion can then be cal- medium through which the seismic

culated. For an elastic oscillator, this wave is propagated and of the groundi

r,-sponse depends only on the natural upon which the structure stands have an

vibration period (or frequency) of the important influence. Because of the

oscillator and the damping ratio. A par- large amount of information accumuticular damping ratio is selected, e.g., lated in underground explosions at the

0.05, and the peak structural response is Nevada Test Site, reasonably good precalculated for one specified vibration dictions can be made of the ground

period by means of the procedure just motions and hence of the response

described. The calculation is; repeated spectra in the general area of the site.

for a range of vibration periods, gener- For underground explosions in other

ally from about 0.05 to 10 seconds. The areas, the results from Nevada are used

results are piotted on a special logarith- as the basis for preliminary calculations

mic paper to give the response spectrum ot response spectra. Modifications are

corresponding to the specified damping then made for differences in geology.

ratio and observed ground motion. Be- 6.93 If the characteristics of a

cause the peak accleration, velocity, and structure are known, an engineer expedisplacement are related mathematic- rienced in ;uch matters can predict from

ally, a single curve gives the variation of the response spectrum whether the

these quantities with the vibration structure will be damaged or not by a

period of the idealized structure, specified underground nuclear explosion

6.91 From the response spec.:um att at a given distance. In making these

a given location it is possible 'o deter- predictions, it must be recalled that a

mine the relative amounts of groand response spectrum applies to a range of

motion energy, from an explosion of linear, elastic o.;cillators, each with a

specified yield, that would cause vibra- single vibration period and an assumed

tion of structures with different natural damping ratio. Such and o.,cillator may

vibration periods. The general conclu- be identified approximately with a sirnsions stated in § 6.37 ei seq., concern- ple, idealized structire having the same

ing the response of strut-tures to the respective vibratior period and dvmping

seismic motion accompanying under- ratio. In real-life situations, however,

ground nuclear explosions, were buildings do not behave as ideal strucreached from a study of response spectra tures with a single vibration period and.

derived from many ground motion re- moreover, the damping ratios vary, alcords obtained at various locations in though 0.05 is a reasonaole average

the vicinity of the Nevada Test Site. value. Consequently, in making damage

estimates, allowances must he made for

6.92 The response spectrum is cal- several variables, i'ncluding structural

culated from the actual ground motion, details, different vibration periods, and

which depends primarily on the yield of the type, age. and condition of the

the explosion, the depth of burst, and structure.
LOADING ON BURIED S&i'RUCTURES 263

LOADING ON BURIED STRUCTURES

GENERAL CONSIDERATIONS ARCHING EFFECT

6.94 Of the ground niotions result- 6.96 If the deformability or; a buried

ing from a nuclear bwst at or near the structure is the same as that of the suisurface (§ 6.12 et. seq.) two types (air- rounding displaced soil, the loads proslap and outrunning) ai'e traceable to the duced on the structure by the air blast

pressure of the airblast wave on the from a nuclear detonati.n will be de'erground surface. Only in the immediate mined by the free-field pressures inneighborhood of the crater will directly duced in the soil by the blast wave. If

coupled ground motion be a significant the deformability of the structure is

damage mechanism. For example, a I- greater or less than that of the soil, the

kiloton explosion on the surface leaves ,i pressures on the structure w'l be less or

crater approximately 49 to 82 feet radius greater, respectiely, than those in the

(Fig. 6.72a;. Yet the free-field peak air soil.

blast overpressure, i.e., the overpres- G.9 7 Results of tests have indicated

sure in the absence of ,itructures. at a that there is no significant buildup of

distance of two crater radii from surface pressure due to reflection at the interface

,ero is several thousand p(,unds per between ,he soil anu a buried structure.

square inch (Fig. 3.73a) and remains It may be assumed, therefore. that

above 100 pounds per square inch up to structures are at least as deformable as

a distance of five or six crater radii. soils and that the free-field pressure,

Outrunning ground motion generally regardless of its direction, can be taken

occurs --o far from surface zero that it is as an upper limit o! the pressure 1,cting

relatively sm.,ll. Therefore, unless a on the structure. If the structure is much

structure is extremely deeply buried, more deformable than the surrounding

i.e., its distance from the iurface is soil, the pressure on the buried structure

similar to its distance from surface zero, w.l! be considerably lower than the

the major threat to it is most likely to free-field pressure at the given depth. In

arise from airslap. For shallow-buried this case, as the free-field pressure is

structures, the 3ir ,last overpressure exerted initially, the structure deflects

may consequently be taken as the effec- away from the soil and a situation is

tive load. For deeply-buried structures, created in which the "arching effect"

attenuation of the shock must be con- within the soil serves to transmit part of

sidered. the blast-induced pressure around the

6.95 For !he purposes of making structure rather tnan through it. Archloading estimates for buried structures, ing, properly speaking. belongs to the

the medium may be described as soil or loading process, but it may also be

rock. In soil, the structure must :esi:;t treated as a factor that enhances the

most of the load, whereas in rock, the resistance of thr .;tructure.

medium itself may carry a large part of 6.98 Irn soil, the load carrying abilthe load. it- oi the medium is a form of arching.
264 SHOCK EFFECTS OF SURFACE AND SUBSURFACE BURSTS

The degree of arching is determined by depths, the in:-ial nonuniformity of load

(I) the structural shape and (2, the ratio cannot be neglected. As a blast wave

of the roof span to depth of burial, passes over a buried arch or dome, the

Shells, such as arches and domes, de- side closest to the explosion is loaded

velop significant arching resistance in earlier than the farther side and, consoils: rectangular strur'tures generally do sequently, an unsymmetrical flexural (or

so to a lesser extent. bending) mode of response is excited.

6.99 The weight of the overburden Furthermore, after tile ;tructure is cornon a buried structure reprt•sents a force pletely engulfed by the hlast wave, the

that must be ovcrco,-ne. Hence, the radial (inwardly directed) loading will

structural strength remaining to oppose be very nearly syn,,,.etrical, although

the shock decreases as the depth of nut uniform. The pressure at the crown,

burial ,s increased. This effect of in- corresponding tc the free-fieliO vertical

creasing overburden on a structure is pressure close to the ground suiface, is

.ountered to some extent by the oppo- then the maximum. Beyonc the crown,

site effect of arching, the rawial pressure decreases in intensity

to a minimum at the springing line

LOADING ON BURIED where, if th.-i arch or dome has a 180'

RECTANGULAR STRUCTURES central angle, the pressure wisI corre..

spond to the free-field lateral (sideways)

6.100 The treatment of the air- pressure at the depth oi the footings.

blast-induced loads on shallow-buried This symmetrical nonuniform loading

rectangular (or box-type) structures re- tends to excite a symmetrical flexural

sult'ag from surface or shallow under- mode of response. In addition to' these

groun• 1,,rsts is similar to the treatment two flexural modes, the structures will

of loads on bluried structures from air also respond in a d'rcct compression

bursts. Thus, the procedures described mode.

in § 5.156 et seq. are applicable, except 6.107 For the flexural modcs to be

that the overpressure at the surface significant, deformatioris corresponding

should be obtained by the method de- to these modes must b-- possible. For

scribed in § 6.81. For a column-sup- such deformations to occ;J;, the passive

ported slab, capitals betw,en the col- resistance of the surrounding soil must

.uuns and the slab may greatly increase be overcome and a wedge of the soil

'he structural resistance. muit be displaced by the deforming

structure. Thus, the passive resistance

of the soil will tend to limit these defor- DOMES mations and prevent the flexural modes

from beirg significant. Although the

6.101 On buried arches and domes flexural modes may be impoitant with

the actual loading is considerabiy more shallow buried structures. ihe'y decrcase

complex because of the constantly in importance very rapidly with depth

changing attitude of the surface of the since the passive resistance of the soil

strtcture with respect to a horizontal increases qui4e rapidly at the, same time.

plane and also because, at very shallow 6 103 In the foregoing discussion it

.A. , -
DAMAGE FROM GROUND SHO(.!. 265

is assumed that the footings do not move underlying material, the radial pressures

with respect to the soil adjacent to them. on the arch or dome may be reduced

If the footings do penetrate into the slightly

DAMAGE FROM GROUND SHOCK

UNDERGROUND STRUCTURES tant, box-type. structures, the several

6.104 The damage to an under- degrees of damage to arches and domes

ground structure itself, as distinct from dre also applicable, but the mechanism

the effects of ground :" ock on its con- of deformation may be. different. In a

tents (§ 6.112), can be readily defined in box struciure, primary reivonsc may be

terms of ipclastic deformation or rol- in flexure of the walls, roof. or base

lapse. For fully buried arches and slabs or in direct stress or buckling of

domes, severe damage corresponds to the walls or column, However, severe

collapse either by elastic or, more fre- damage is still characterized by ex,.esquently, inelastic buckling. If very near sive deformaieni or collapse ihrough

tLe ground surface, the deformations any of these mechanisms, moderate

may be primarily ftxural. Ligh(damage oamagc corresponds to deformaiians of

has little or no meaning unless it refers any of the elements Lssociated with

to partial impairmen' of oFerationr5l ca- spalling of conciete and smaol pernapability of personnel and equipment. nent deflections; and ligh,, damage is

M-,, er.te structural damage for concrete virtually meaning!eis except in terms of

structures car be defind as deformation shock effects on personnel and equipaccomrianied by significant spalling. mernt.

Such deformation woild correspond to 6.106 For v.,',y low yield weapons,

stress levels in the concrcte sl•7htly it is difficult to produce significant dam

above the yield point, i.e., a ductility age to a buried structure unless it is

factor of about 1 .3. This presumes that within the rupture zone around the .ra:er

faiiure is by inelastic deformiiation rather (Fig. 6.',0). With the exception of a

thi.n by elastic buckling, as would be the number of special structural types, e.g..

case in a properly designed blast-resis- pipelines anti small highly resistint

tant ".tLucture. If failure is by elastic reinforced-concrete fortifications, soil

buckling, nsoderate damage cannot be pressures produced by air blast presrealized. sures or the ground surface constitute

6.105 For steel arches and domes, the primary source of damage to buried

moderate structural damage can also be structures.

defined iii terms of a reduced ductility 6.107 It is expected that underfactor, although the nature of such ground structures whose span closely

damage for steel structures is not as matches one-half the wave length of the

clearly evident as in the spalling of shock will "roll with the blow." This

concrete. For underground, blast-resis- expectation has been bornc out by acual I
266 stlocK F~UFi< rS OF- SUR[ACU1 AND SLRBS1R1FACF BURS IS

experience. The movenient of the struc- pressure) wave is reflected from the

lure is intirmatcly conne-ned with the rock-air interface.f E.ven in a soil memovement ol' the soil, as the shock wave ditim. tu~-nels aild suhwa"ý: could surpasses. In other wo~rds, if the particle vive-, flexible structures would resist

acceleration in the soil has certain peak damage by taking advantage of the trehoriz.intal and vertical components. mendous passive earth pressure. Howthen the srn-a!i undergyround structure ever, cvnstruction ini soli should be

may K: c~pccted to have almost the above the water table. if possible.

same peak acceleration components. 6.110 U~nder certain circumstances.

6.108 Sho 'ck damage to under failure of the rock- at tlh tunnel wail will

vround structures is most frequently result i') spalling when taCe reflected tencalculatx- -'with computer 'odes. Graphs sile stress exceeds the tensile strength (if

and tables suitable for hand calculations the ro'.'k. The thickness of spallirig is

have been developed. but such calcttla- dependent upon the magnitude. aurations -,;, time consuming. aind the re- tion, and shape of the pressure wave.

sults are approximations at best. Thb.re upon the si/c anxd shape of the tunnel,

is ev'deri-e that the degrees of damage and upon the physical properties of the

from i~hallow (and moderately shallow~ rock.

explosions can be related to thie appar 'nt 6.111t A structure may extend

crater radius. Some e.xamples of this abov-e the gride level but he protected

relationship are given in Table 6. 108 for by earth pliled oe mounded j* .)ufd -it

moderate: deep unierground struc- (Fig. 6.11 1 ). The idealized surface is

tures. definO' as structures for which the the surface of constan; slop- which is

ratio of the dep~h of covet at the crown equivalent to the ,ttual (curved) surto the span is %or. k-what greater !haii face. If the slope of t, te idealized surface

unitY. Crater radii, and hertce !he da ri- is less than 140, the structure may bic

age distances. Wvii vary with soi; type treated as buried, and t ic ioregoing disI§ f. .72). Deeply buried structures. with cussion of buried arche arid domes is

a ratio of depth of cover 1,o span much applicable If the slope is , nore than 14'.

greater than unity, woold .uwfr le.ss or if tht structure is It-catet. well beyond

damrage. the ;lastic ;!one, the ovcrý; damage is

6.109 Although tunanels and 3ub- djea, -rrined by air blast, ar; is in aicwdays would be destroyed within the Cetdance witn the discus.-ion hii

crater region antd v.ottlJ suffer domage Cniapter..I IV and V

outside this area, these structures, especially when bored through solid rock

and lined to minimize spalling, are very VULNERABILITY OF EQUIPMENT

resistant to ground shock. The rock.

bting an elastic niedium, will 'transmit 6.112 Althougii a structure may

the pressure (compression) wave very suffer little or no damage from grounid

well, and when this wave strikes the motion, its contents, e.g., machirery or

wall of the tunnel, a tension (negative other equipment, niay be re. idered ii;*

;The formation of a negative pressure wave otpon reflection of a compression wave at the suriace of a

less dense m'~ium (air) is discu'~sed more fully i'. ,he treatment of shock waves in water (§ 6.43 etseq.).
I)ANMIU(,I I ROM CROUNI) SIIO(I( 26'7

Table 6.108

DAMAG;E CRITERIA FOR NIODERAThIA' DEEP UNDERGROUJND STRUCTURES

Danmage Distiance from

Structural Typie Type Surface Zero Nature oi Damage

Re!ýIr'ivey small, heavy. Severe I 1/i apparent Collapse

well-des'gnied, under- crater radii

ground structure%. Light 21⁄21 apparent Slight cracking.

crater radii sev'erance of

I~rittle external

connection%.

Relatively long. Severe I`. apparent rOcl',.-mation and

flexihle structures, crater radii rupture.

e.g. buried pipelines, tanks. etc Moderate 2 apparent Slight deforniatit'ii

crater radii and rupture

L ight 211. lo .3 Failure oif

apparent connections.

craier rurdii

operative by the shock. Such equipment it y of that cquipment to al: k~rids of

may be made less vulnerable by suitable motion. rhe restilis are comnmo~ily exshock, mounting. Shock mounts (or pressed as the r.atural vibration freshock isosators) are commonly made of quenc) ot which the equipmenm is most

an elastic material like rubber or they vulnerable and the maximumi aý:celeramay consist of :ipribngs. rhe material lion tolerable at that frequten~y for 50

absorbs much of the eitergy delivered percent probability of severe damage.

ver-.- rapidly by the shock and releases it Some examples of tlie values of these

more slowly, thereby protecting th~e parameters for four classes of equipmounted ý:quipnjent. ment, without and with shock nount6.113 By shaking. vibr-ating. or ng are quoted in Table 6. 113. It is seen

droppin,: p c-s ot equipment. engi- that the shock mounting serves to deneers can cren estimate the vulnerabil- crease ihe most sensitive natural fre-

- REAL SURFACE

~. N/'SURFACE

Figure 6.111I. Configuration of irounded arch.
268 SHOCK EFFECTS O'" SURFACE AND SUBSURFACE BURSTS

Table 6.113

FREQUENCY ANt) VUI.NERABIILITY ACCELERATION OF TYPICAi. EQUIPMEN I'

ITEMS

Typical Value of

Natural Vulnerahili'y

Shock frequency accleratio:,

('lass Item Mounted (gL

A Heavy machinery - motors. No 10 20

generators, transformers, Yes 3 41)

etc. ( .4(XX) Ih).

H Medium and light machine- No 20 40

ry pumps, cond,,nser,. Y e , , 80

air conditioning, fans.

,rnmal motors f" IMXX) lb).

C' Communication equipment, No 25 7

re'ays, rotating magnetic 6 60

drum units of electronic

cqui-ment, etc

1) Storag,- batteries, piping No 20) 70

and duct work. Ye, 5 !50

quency. i.e., increase the period, and te tion. If the peak acceleration on the

ir.crease the acceleration for 50 percent response spectrum corresponding to the

probability of severe damage at that equipment frequency is less than the

frequency. vulnerability acceleration, then the

6.114 Whether or not a specified equipment will probably be undamaged

piece of equipment is likely to be dam- by the narticular ground motion. On the

aged by a particular ground motion can other ilaird, if the response spectrum

be estimated from the data in Table indicates that the equipment may be

6.113 in conjunction with the response damaged, shock mounting should he

spectrum (§ 6.90) for that ground mo- added or improved.

TECHNICAL ASPECTS OF UNDERWATER BURSTS

SHOCK WAVE PROPERTIES plosion have been calculated. The peak

6.115 By combining a theoretical pressure of the shock wave in water for

treatment with measureme- made in various energy yields is shown in Fig.

connection with detonatioiA of high- 6.115 as a function of slant range, R, for

explosive charges under water, some pressures less than 3,000 pounds per

characteristic propertihs of the under- squar.- inch and (in the top righ( corner)

water shock wave from a nuiclear ex- is a function of the scaled slant rarige,

All
FF(HNI(AI ASP("ICTS 011 UN F)I :IRVIF R ItW R S 269

RIW' 1, for higher pressures. The data shocks from th' gfound and other surrefer to "isovelocity'" vater, i.e., water faces. Bottom reflections in water are

in which there are no reflections or re- frequently more nearly acoustic than air

fractions. boast reflections. Consequently, under

6.116 The decrease of the water appropriate conditions, !he influence of

pr'-Ssure with time can be obtained from the tLottom can be treated ideally by

Figs. 6.116a and b. The former gives replacing the tbottom surface with an

the time constant, 0, in terms of the image explosion of the same yield as the

slant range for various yields, and the actual explosion located a distance

latter shows the variationi of p(fyip, below the bottom equal to the distance

where It) is the pressure at time t after of the actual explosion above it.

the arrival of the shock front at the 6.118 In practice, the character of

observation point and p is the peal, the bottom, e.g., mud, loose or packed

pressure at that point, with the reduced sand, or hard rock, has a marked etfect

time 0O. The time constant is the time at o-i the magnitude of the reflected preswhich the shock pitessure has decayed to sure. The distances traveled by the priI/e, i.e., about 37 percent, of its peak mary shock and reflected waves to the

value. (The use of a time constant de- target also influence the pressures.

fined in this manner must not be taken to Wnen the explosi-,i and the target are

imply that the pressure decreases ex- both near the botturm, the reflected presponenially; it does not do so except at sure received -'t the target may be

early times.) The longer the time con- greater that?, equal to, or less than the

stant, the more slowly does th.e water primary pressure. When the burst point

shock pressure decay; it is apparent, and the target are both remote from the

therefore, from Fig. 6.1 16a that the du- bottom, the reiected pressure is generration of the shock wave increases with ally inuct. smal!er because of the greater

the energy yield and the distance from travel distance. In each case, of course,

the explosion point. The data in Figs. the negative pressure reflected from the

6.116a and b may be used to construct a air-water interface must not be overcurve showing the decrease with time of looked. The times of arrival of the rethe pressure at a specified slant range flecteu pressures, after the primary

from .-n underwater explosion, of given shock, may be estimated from the reyield. The area under the curve gives the spective travel distanc,.-, by assuming

pressure impulse of the water shock that the pulses travel with the speed of

wave, analogous to the air overpiessure souind in the water.

impulse defined in § 3-59. (Text confinued ori page 272.)

6.117 In shallow water and in certain circumstances in deep water, the

primary underwater shock pulse wili be

modified by surface and bottom efiects

(§ 6.41 et seq.). Water is much less

compressible than air, and positive reflection phenomena (§ 6.49) are less

well understood than reflections of air

4 1
270 SHOCK EFFECTS CF SURFACE AND SUBSURFACf. BURSTS

The curves in Figs. 6. 115 and 6.116a Exatmple

and b give the parameter- for the pri- Given: A 50 KT burst in deep

mary shock wave from an underwater water.

explosion in deep isovelocity water. Finid: (a) The peak shock pressure p

Figure 6.1 !5 shows the peak pressure p and (h) the pressure p(t) at 0.1 second

as a function of slant range R for various after arrival of the shock wave at a

yields, where the peak pressure is lower distance of 4,(000 yard's from #he burst

than 3,000 psi, and as a function of point.

scaled slant range (R/W'3) for peak Sut;oun: (a) From Fig. 6.115, the

p.'essures above 3,000 psi. Values of the peak shock pressure p at a slant range of

time constant 0 as a function of slant 4,000 yards from a 50 KT burst in deep

range for various yields are given in Fig. water is found to be approximately 470

6.116a, and Fig. 6.1 !6b shows the re- psi. Answer.

duced (or normalized) pressure p(t)/p, (b) From Fig. 6.116a. 'he time conwhere p(t) is the shock pressure at time stant 0 is 50 millisec, i.e , 0.050 sec.

t, as a function of the reduced time t/O. Hence ti/O - 0.1/0.050 = 2. From Fig.

Sccing For yields other than those 6.1 16b, the value of p(t)/p for /O = 2 is

shown in the figures, use linear inter.- about 0.15; henre

polation between apprcpriate curves. PU) 476 x 0.15 70 psi. An. wer.

4,
TFCHINI( Al ASPECTS 01INI)lRW\ HUR AI'RS! S 27!

SCALED SLANT RANGE,

R/W 13(FT/KT 2')

2

0 0

10 00

2 1

171

1 2~ 5.05 1 2 25 1

SLN RANG (TOSAD OFYRS

U, SA

0

LI)I

10 IKJL

1 2 5 1 2 5 0 2 3 0

SLANT RANGE (THOUSANDS OF YARDS)

Figure 6.116a. Shock wave piea conssunt in. deep isovelocity water as a function of slant

range.
272 SHOCK EFFECTS OF SURFACE AND SUBSLRFACF BURSTS

'° \ ,,II I

0.5 -

U-' 0.2

CL

0.

0

2 ot

Uj

0.02

0 I 2 3 4 5 6 7

t

REDUCED TIME -

Figure 6 116b. Pressure-time relationship for water :;hock waves from nuclear explosion in

deep isovelocity water; p is the peak prcsu.re and jXt) is the value at 6ime t

after arr'ival of the -.Liock front.

SURFACE WAVES W in kilotons TNT equivalent. This

6.119 When observed at a point re- expression holds provided the dcpth. d.

mote from surface zero, the idealized feet, of the water in which tihe surface

surface displacement associated with the ' 4 es are produced is in the range 850

train of wave- refei.ed to in § 6.54 is W, _>, d > 256 W !5, where the

shown in Fig. 6.119. In deep water, the lowet limit is the maximum diameter of

wave intensity is representec by the the ga.; bubble (§ 2.86). The relaticn is

peak-to-peak height H of the wave en- valid for any 6epth of burst w~thin the

velope. The manner in which this hleight water. Otlhcr parameters characterizing

diminishes with distance (or tadius) R surface wave, are the length L auk

from surface zero can oe ,xj'res!,:ed to an "?eriod T of thc peak wave. Extrapolaaccuracy of about 35 percent ty the tion of deep water chemical explo0iLPns

relationship indicate thes.,' quantities are given approximately by

H 40,500 R.-. L 1, I)O W1288 fee(

(6.119.1) T - 14.1 WO 4

1eco4 ds

with both Hand R in feet, and the yield where. W is in kilotons.

- - - - , -
TIFC1 NI(AI'% AS~PECTS M UNDU)RW.[IAFFIR BUSTS 2-73

WATER LEVELTIME

Figurc 6.119. An explosion-gencrated wave train as observed at a givecn distance frorn

surface zero.

6.120 The length is a critical factor DAMAGE TO HYDRAULIC

in determining the changes taking place STRUCTURES

in a wave train running into shoal water

(§ 6.59). If water depth bCcomes less 6.12 As is: i'ic case with air blast,

than approximately L13, successýive it is to be expccted !hnat the damrage to an

waves in the train bunch up while -wave ipnderwater -structiure resulting i.rnspeed increases. The period T remains water shock will depend upon tic dithe same. Of equal (,r greater impor- mensions of the structure and certaia

tant-e is wo: fact that, after an initial, characteristic timnes. The particular

small decrease, the height Hi increases times which appear to. be significant are,

as the water through vhciO the wave is or' the one hand. t.'e time 4,orkant of the

ru~nning becoa,tes -mior: ,j~.The In- shock wave (§ 6.116) and, on the ollher

crease in hip~ht of a wave relative to its hand. the nat'iral (or c!'i:tic) rcspcne

lenguth (steepening, con'ainues as t timne and 'lie diffraciien time of the

wave shoals until it becomes unstuble struceture. iethe time required for the

and breaks, unless the bottoin sope :,- !:o shock -;.'a'.' to hc propagated distance:,

shallow that bottkrm Triction dissipates of the order ot mnagnitude oui the dimenthe wave before it breaks. sions of the struicture. ;n the event that

6.121 A bu~st in shallow wawef, inc underwfi;2r structufe is near the, sursuch as Bikini BAKER, -.elivers less face, the citoff time (§ 6.43) would be

energy to the water than a burst oif the significant in certai;a c.Ases.

samet, yield in deep watcr; conseqeerily 6.1121 If the time co~nstant of ih-e

the constant of proportional 1!y in equa- pressure wave and the cutoff titoe are

tion (6. 1,9. 1) becomes less as water large compared to the times whicS' are

depth de~reascs An approxima~lc rela. characterim;ic of the structure, that is to

tionship betwee~i wave heigrn q and say, if the water shock wave is one of

distanc.e R from surface zero for at sh4 1-I relatively long duration, the effect of tPic

1,ow burst (d., -; 100 IW02~) is shock is similar to that of a steady (or

H-10dW) 25 stadr) pressure applied suddenly. In

H 150thtse circumstances, the peak pressure

is the approipriate criterion of damage.

with H and R in feet. Such would be ,',,e case for small, rigid
27~ SHIOCK [ FF1-C IS (IF- SIRFA(1 %ND) SL'HStRFU'U. Wi S'S r

undcrwater ,tructures, ~;l't!iey' :an he ,Ir -water surface reaches the target and

eXPeCted to. have short c-haracterisl',c causes ct47soon af~ter the arrival of th,ý

tme-,. primary shock wave.

6.124 For large. rioid uuiuerwater 6. 125 If the kirge tinde.-vater strut-

-ýIructures, where the duratioti oi the tu_ can accept a substantial amount of

shock widV-, Is short in nopairis.tni with permanent (plastic) deformation as a rethe characteristic '.Imes of thc structurie, sult of -impact wilh the shock fiont, it

the impul!-_ of the shock wave will bc appear, that the damage depends essensigoiifici~nt ip de~termining (he damaige. It tially' on the -'nergy of the shock wave.

should be remembered, in this corinec- If the structure is near the surface, the

tion, t0tal the m;n~gnude of the impuse cutoff effect will decrease the amount of

and damage will be vre atly d.creased if shock cenergy available for causing

tttc nl2,!ýtivc reflected wave from the damage.

BIBLIOGRAPH-Y

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L~atora:tory. A;)rtl 1967, NOOL R -67 -4. Mm Nit , C.. I. J* ('. CRw~iI I , andi I. IDs I R,

li Si N, R, H., and W A. F,0`11 'IS. "is Project 'Mcchanisms ini the tiencratior ito Airhlast hy

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Studies," '-l Boeing Comnpany, Seattle. nance Laboratory, September 1 966, Bolt ,

Washington. t~i'gust 1963. PNE 217E. Beranek and Newman Report No. 141~4,

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Radiation Laboratory. November 1964, tive Structures."University ol Illinois, June

11CR! 12172. l92, AFSAC-T['R 62 0.

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Publications. Inc , 1905. (Reprint of 194H edi- Concepts,' Vibration atid Civil Flt.ineering

tior., Princetoit University Press.) Proceedings of Symposium of British National

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MINE UNDER and MINE CARE, Subtask, quake Engineering. p. 71, Htiterworths. LonNI 21. Cýrater .nvcs~igAttions.- U.S. Army En don. 1966

giaeer WVatcrways Experimr.rnt Station, March PHI! I It's. 1). F... and Tf B. FtI-ti ()Ito i Un197'). Te~chnical Report N- 70--8 derwaic,- Explosion Tests oft Tw-o Steam Pro

ENoGDALI.. E. R., -S-ismiL Effects of the ducirg Explosives. 1. Small Charge T.-sts.-

MILROW and C4.NNIKIN Nuclear Explo- U.." Naval Ordnance Labor.torv'. May 1966,

sions,. Bull. Seismol. Soc. A merica, 62. 1411 NOI.TR-66--79.

(1972). *''Proceedings of the: Secon'! Plowsl,-ire SymnpoFiw.ttc .- ri, 1). J. MIDDLE COURSE I Cr~ittr- sium," Part 1. Phenomentlogy of Underground

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tering Group, June 1971. Techrtical Report 'IS. Lawrence Radiation Laboiatory. Livermore.

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*Gt ASSr N:. S.. "Public Safety and Unider- Radiation Laboratory, Livermnore, TID-7695.

ground Nuclear Detonations." U.S. Atomic *"ltroc.edings of twe Sympos~urr on Engineering

Eneigy Comrnis:aon, June 1971, TID-25708. w.itjo Nuclear Exptosives," Las Vegas, Nevad;'.

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E-xplosions a..J Distint Earthquakes: A Search U.S. Atomic Erretgy Commi!,;,ton, CONFfor Correlationf," Science, 169, 176 (1970). 7(X'101, Vol:i, I and 2.
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*Roi \N. 1 1. C " Nuclear Fi~~~o ~%1O IH\A \ N(- 'Handhook Fpoin(i

logy.- AEC Critical Revie\% Series. V S ersited Water Waves 'o. 1,I State of the Aft."

Atomic: Inergy C~tii~o.Septemihei 19~71, Tet .i Tech, Inc: Pasadena. (U~I fornia. OJcit- 4r

T11)25572, 1969. Report No. iC 1 30

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WHEFL. Series, FIAT TOP Event. Crater 'Water Wave% from I0.(XXI I-lb High-Explosi~e

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VAN D)ORN, W. (., B. 1Li Mi'i,.wLt, and 73. 4621 lt469)

*'rhe~e d1 cumni'ts may be purchased from the NationaI Technical Information Service. fDepartnien: of

Commerce. Spritn.jicld, Virgi:vin 22161
CHAPTER VII

THERMAL RADIATION AND ITS FFFECTS

RADIATION FROM THE FIRFBAI.!

GENERAL. CHARACTERISTICS OF energy is intially in the form of kinetic

THERMAL. RADIATION energy of tfe weapon debris. This kinetic energy is also absorbed by 'he -air

7.01 One of the important dif- at ý, slightly later time (§ 2.101;) and

ferences between a nuclear and a con- serves to further heat the air. The heated

ventional high-explosive weapon is the air, which constitutes the fireball, in turn

large proportion (f the energy of a nu- radiates in a spectral region roughly

clear explosion which is rele sed in th~e similar lo that of sunlight near the

form of thermal tor heat) radiation. Be- earth's surfacv. It is the radiation (ultracause of the enormous amount of energy violet, visible, and infrared) from the

liberated per unit mass in a nuclear fireball, traveling with the velocity .)f

weapon. very high temperatures are at- light, which constitutes the thermal ratained. These are estimated to be several diation at distaices from the explosion.

tens of million degrees, compared with The time elapsing, therefore, between

a few !housand degrees in the case of a the emission of this (secondary) thermal

conventional explosion. As a conse radiation from (lie fireball and its arrival

quence of these high temperatures, at a target mile% away. is quite insignifabout 70 to 80 percent of the total en- icant.

ergy (excluding the energy of the resid- 7.02 It is de,,rable to state specificual radiation) is released in the form of ally what is meant by the term "thermal

electromagnetic radiation of short radiation" as it is used in the present

waveleigth. Initially, the (primavy) chapter. Actually. all the energy rethermal radiations are mainly in the soft leased by a nuclear dotonation. includX-ray region ot the spectrum but, for ing the residual radiation from the

nuclear explosions below about 50 weapon debris, is ultimately degraded to

miles, the X rays are absorbed in air in thermal energy, i.e., heat. Uut only part

the general vicinity of the burst, ihereby of it is regarded as constituting the therheating it le high temperatures. Most of mal radiation of interest which can

the remaining 20 to 30 percent of the cause fire damage and personal in;ury at

276
RA)IA ION FROM iHE FIRFBI 1 277

or near the earth's surface. Some of the miles), the pulse length is somewhat

thermal radiations emitted by the fire- longer.

ball in the very early stages. particularly 7.04 In an ordinary air burst. i.e.. at

in 1h, ultraviolet region, are seklctively :0!titudes up !o some 100,M0) feet,

absorbed by various atomic and molec- roughly 35 :o 45 percent of the total

ular species in the heated air, which energy yield of the explosion is emitted

slowly re-emits this energy in a de- as effective thermal radiation The acgraded, i.e.. longer wavelength, form. iLal fraction of the energy that appears

The delay in reaching the target, and the as such radiation depends on the height

slower rate at which they are delivered, of burst and the total yield, as well as on

lowers the daniaging eqectiveness of the weapon characteristics; estimates of

these radiations. Consequently they are this fiaction for various yields and burst

not considered a:i a part of the thermal altitudes will be given late: (Table

radia!ion for present purposes. It is 7.98). For simplicity, however. ;t is

convenient, therefore, to define the ef- often assumed that 35 percent of the

fective (or prompt) thermal radiation as total energy yield of an air burst is

that emitted from the heated air of the emitted as thermal radiatiom energy.

fireball within the first minute (or less) This means that for every I kiloton TNT

following the explosion, equivalent of energy release, about 0.35

7.03 For an air burst at altitudes kiloton, i.e., 3.5 x 10'' calories or

below about 100,0(M feet (roughly 19 about 410,000 kilowatt-hours, is in the

miles), the thermal radiation is emitted form of thermal radiation. The proporfrom the fireball in two pulses, as de- tion of this energy that reaches the surscribed in Chapter 11. The first, which is face depends on the distance from the

quite short, carties roughly I percent of burst point and on the state of the atthe total radiant energy (§ 2.39). the mosphere.

second pulse is the more significant and 7.05 A nuclear air burst can cause

is of longer duration. The total length of considerable blast damage; however,

the effective thermal pulse increases thermal radiation can result in serious

with the energy yield of the explosion. additional damage by igniting combustThus the duration of the effective pulse ible materials, e.g., finely divided or

from a I-kiloton air burst is about 0 4 th;n 'uels such as dried leaves and

second, whereas from a 10-megatcn newspapers. Thus, fires may be started

explosion it is more than 20 seconds. in buildings and forests and may spread

With increasing altitude the character of rapidly to considerable distances. In adthe thermal radiation pulse changes dition, thermal radiation is capable of

(§ 2.130 et seq.). At altitudes above causing skin burns and eye injuries to

about 100,000 feet, there is only a sin- exposed persons at distances at winich

gle ihermal pulse and its effective dura- thin fuels are not ignited. Thermal radition, which depends on the height of ation ca'i, in fact, be an important cause

burst and the energy yield of the explo- of injuries to people from both direct

sion, is of the order of a second or less exposure and as the result of fires, even

for weapons in the megaton range. For at greater distances than other weapons

explosions above about 270,000 feet (51 effects.
278 [HERMAl RADIATION AND ITS F-FIFF(iS

A1TENUATION OF THERMAL namely. absorption and scatuering.

RADIATION Atoms and molecules present in the air

are capable of absorbing. and thus re7.06 The extent of injury or damage m 11vig ,ertain portions the thermal 1f 

caused by thermal radiation or the 11diain. ert bsortions of t erl

chance of igniting combustible material tivC The sorte o n gtN os uldepends to a large extent upon the tlive for the shorter wavelength ion ulamount of thermal radiation energy re- ygen ole cula s , as w el tion,

ygen molecules. as well as o,,onc.

ceived by a unit area of skin, fabric, or nitrogen dioxide, and nitrous acid other exposed material wi.hin a sboMr*

interval of time. "Th• thermal formed from the gases m the atmosphere energy ,§ 2.1 23L. play an important ptart.

faliing upon a given area from a spe- 7.09 Because of absortion, ihe

cified explosion will be less the farther thr a Bad set o f a . bsu rttin ie

from the explosion, for two reasons: (1) trai ra gion. dec reae marke

the spread of the radiation over an ever iioh reaing dice fro edly

increasing area as it travels away from p iore.som g of b the e i

plosion. Some of the absorbed radiation

the fireball, and (2) attenuation of the is sukequently reradiated, but the

radiation in its passage through the air. emission occurs with cqual probability

These factors will be coaisidercd itn turn. in all directions. so that the quan!ity

7.07 If the radiation is distributed proceeding in the direction of a given

evenly in all directions, then at a dis- tirget is substantially reduced. Consetance D from the explosion the same lucntly. Lt those distances where peramount of energy will tall upon each son, exposed to thermal radiation could

unit area of the surface tof a sphere of survive the biast and initial nuclear raradius 1). The total ar,'a of this spherc is diation eflects, the proportion of ultra-

-IrrD7 . and if E is the thermal radiaiuon violet radiation is quite small. P-towever.

energy produced in the explosion, the the ultraviolet is more effective in causenergy received per unit area at a .is- Ing biological injury than visible andtance 1) would he E'4'TrD-. t'ovided infrared ray,,, so that even the small

there were no attenuation b) the atmos- anieunt present could, under some conrlere. Obviously. this quantity varies ditions. be important.

inversely as the square of the distance 7.10 Attenuation 4s a result of scatfrom the explosion. At 2 miles, fromi a terin., i.e.. by the random diversion of

given explosion, for example, the ther- rays from their original paths, occurs

real energy received per unit area would with radiations of all wavelengths.

be one-foorth of that received at half the Scattering can be caused by molecules,

distance, i.e.. at I mile, from the same such a!. oxygen and nitrogen, pre.ient in

explosion. the air This is, however, not as inipor7.0, ;n order to estimate the tant as scattering resulting from the reamount of thermal encirgy actually flcction and diffraction (or bending) of

reaching the unit area. allow rnce must light rays by particles, e.g., of dust, also be made for the attenuation of the smoke, or tog, in the arnosphere. The

radiation by the alinosphere. This atten- diversion of the radiation as a result of

uation is due to two main causes, scattering interactions leads to a someAS
RADIATION FROM THE FIFEBAL1 2179

what diffusz, rath-er than a direct. tran%- itv. Thi- !s defined ws the horliontal

mission of the thermal radiation. distance at whicl. a large dark object on

the horizon has )us( enough .ontrast

EFFECT OF ATMOSPHERIC %kith !he ;.urroooding sky to Iv discernCON-)i rIONS tale in tf ight. The iiiternitinnal code

for corr,-1:w-ng ýhv visibilitý %"ih tL~e

7.11 The dccrezsc in energ') of conidition of the atmosphere i, t!I~eii in

thermal radia~ion due to sc'ttec-ing by T'able 7.12.

particles in the air depend- upon the 7.13 At first thought, it wvul'ý be

atamospheric conditions, such as the expected that the decrease of tOermal

concentration and size (if the particle%, radiation energy with increasing d*'Sand also -ipon the wzvelength of the tance from the explosion would be

radiation. This mneans that radiations oif greater when the visibility is low than

different wi. elengths. namely. iiltravi- when it is high. But, for ih,-~ reason

olet, visible, and infrared, will stiffer given below, it has beeni found that, at

energy attenuation to different extenis. distances less than about half the visiFor most practical purixoscs. however. it bility, the degree of attenuation of the

is more conven~wrnt and measonably sat- thermal radiation is relatively insensiisfactory. although less precise, to pos- live to atmospheric conditions if at least

tulate a mean auttnuation averaged ovcz muderately clear (10 miles or more)

all the wavelengths present in the ther- visibility prevails. At greater distances,

n~al radiation. however, a larger proportion of Coe ra7.12 The extent to which the at- diant energy is indeed lost as the atmosphere attenuetes thermal energy and me-phciic visibility decreases As a

limits visibility depends largely on the rough approximadtion, the amount of

scattering of radiation. Therefore, .he thermal energy received at a giveii dis-

%iao,~ oif the atmosphere its far as %c ;tter- tance from a nuclear exploision may be

ing is :onccrned can beý --:-rese-ited by assumed to be independent of the visiwhat is know.n as the daytghl -visibil- bility. This leads to overestimates at

ity rarnge-' or. in brief. as the -v~ibil- Jistances greater than about half the

Table 7.12

VISIBilI1TV AND ('OWrz110% OF THE Al MOSPHERF.

Corv~Iition Kidnrneters Mile%

ELxceplonally clear 290 171)

Very clear 50 At

Clear 20) 12

Light haze 10 6

Haze 4 2.5

Thin fog 21 2

Light to thick fog I or less 0.6 or less
"280 THERMAL RADIATION AkND ITS EFF.FCTS

visibility range, but from the standpoint from scattering and abso!ption, cannot

of protection from thermal radiation then he compensated by multiple scatsuch estimates would be preferable to terif'g. Hence, less radiant energy is

those which err in being too low. received at a specified distance from the

7.14 The thermal radiation weceived explosion than ior clear visibility conat a given distance from a nuclear ex- ditions.

plosion is made up of both directly

transmitted (unscattered) and scattered FFECT OF SMOKE. FOG. AND

radiations. If the air is clear, and therc CLOUDS

are very few suspended particles, the

extent of scatzering is small, and the 7.16 In the event of an air burst

radiation received is essentially only cccurring above a layer of dense cloud,

that which has been transmitted from the smoke, or fog, an appreciable portion of

exploding weapon withouk scaitering. If the thermal radiation will be scattered

the air contains a mioderately large upward trom the top of the layer. This

number of part-..les, the amount of ra- scattered radiatioT may be regarded as

diation transmiuted directly wi'l be iess lost, as far as a point on the ground is

than in a clear atmosprhere But this concerned. In addition, most of the radecrease is largely compensated by an diation which penetrates the layer will

increase in the scattetuwd radiation be scattered, and very little will reach

reaching the object (or area) under con- the given point by direct transmissioni.

sideration. Multiple scatleritig, i.e., These two effects will result in a subsubsequent scattering of already scat- stantial decrease in the amount of thertered radiation, which i3 very probable real energy reaching a ground target

when the concentration of particles is covered by fog or smoke, from a nuclear

higl,, wiii result in the arrival or radia- expleosion ab,-ye the layer.

tion at the target from many directions. 7.17 It is important to understand

An appreciable amoun: of thermal radi- that the decrease in thermal radiation by

ation wi!i thus reach the given area in- fog and smoke will be realized only if

direct!y, in addition to that transmitted the burst point is above or, to a lesser

directly. It is because cf the partial extent, within the fog (or similar) layer.

comp.:usation• due to multiple scattering If the explosion should occur in modthat the total amount of" energy from a er' tely clear air beneath A layer of cloud

nuclear explosion falling upon unit area or fog, some of the radiation wnich

at a given distance may not be too would normally proceed outward into

greatly dependent upon the visibility space will be scattered back to eatrth. As

iange, within certain limits, a result, there may be some cases in

7.15 Under atmospherc conditions which the thermal energy received will

of rain, fog, or dense industrial hazc actually be, greater than for the same

absorption due to the increase in water atmospheric transmission conditions

vapor arid carb 3n dioxide content of the witliout a cloud or fog cover. (A layer of

air will play a predominant role in the snow on the ground will have much the

attenuation of thermal tadiz,tion. The same effect as a cloud layeý above the

loss in the directly transmitted radiation, bursi (§ § 7.4?, 7. 100)).

t
RADIATION FROM TH- FIRFRAI I 281

EFFECT OF SHIELDING evaporating surface material, but this is

relatively sa!l (about I or 2 p-rcent) 7.18 Unless it is scattered, thermal and has a minor effect on the thermal

radiation from a nuclear explosion, like radiation emitted. As far as the energy

irdinary light, travels in s:traight lines received at a distance from the explofrom the fireball. Any solid, opaque sion is concerned, other factors are more

material, e.g., a wall, a hill, or a tree, significant. First, there will be a certain

between a given object and the fireball arnount of shielding due to terrain irwill act as a shield and provde protec- ,'egularities and, second, some absorption frcr"i thermal radiation. Some in- tion of the radiation will occur in the

stances of such shielding, many of low layer of dust or water vapor prowhich were observed after the nuclear ducea near the burst point in the early

explosions in Japan, will be described stages of the explosion. In addition,

later. Transparent materials, on the most of the thermal radiation reaching a

o,+ther hand, such as glass or plastics, given target on the ground will have

allow +hermal radiation to pass through traveled th.ough the air nea,- the earth\s

only slightly attenuated. surface. In this part of the atmosphere

7.19 A shield which merely intei- there is considerable absorption by

vencs between a given target and the molecules of water vapor and of carbon

fireball but does not sL.round the target, dioxide and the extent of scattering by

may not be entirely effective under hazy various particles is greater than at higher

atmospheric conditions. A large pro- altitudes. Consequently, in a surface

portion of the thermal radiation re- burst, the amount of thermal energy

ceived, especially at considerable dis- reaching a target at a specified distance

tances from the, explosion, has from the explosion may be from half to

undergone multiple scattering and will three-fourths of that from an a~r burst of

arrive from all directions, not merely the same •otal energy yield. However,

that from the point of burst. This situa- when viewed from above, e.g., from an

tion should be borne in mind in cornec- aircraft. stface explosions exhibit the

tion with the problem of thermal radia- same thermal characteristics as air

tion shielding. bursts.

7.21 In subsurface bursts, either in

TYPE OF BURST the earth or under water, nearly all the

7.20 The foregoing discussion has thermal radiation is absorbed, provided

referred in particular to thermal radia- tnere is no appreciable penetration of the

tion from a nuclear air burst. For other surface by the fireball. The thermal entypes of bu, s! ihe generai effect: are the ergy is then used up in heating and

same, although they differ in degree. melting the soil or vaporizing the water,

For a surface burst, in which the fireball as the case may be. Normal thermal

actually touches the eaith or water, the radiation effects, such as accompany an

proportion of the explosibn energy ap- air burst, are thus absent.

pearing at a distance as thermal radia- 7.22 When nuclear explosions

tion will be less than for an air burst. occur at high altitudes, i.e., somewhat

Somo energy is utilized in melting or above 100,000 feet, the primary thermal
282 THFkMAI RAMiATION AND ITS EFFECTS

X rays from the extremely hot weapon altitude (§ 7.81). with the result that,

residues are absorbed in a large volume although aboui hialf of th'! absorbed ,n-

(and mass) of air because of the low ergy is emit:ed as thermal radiation in

density, as explained in § 2.131 el seq. less tlhan a second, the remaindet of the

Consequently, the fireball temperatures thermal energy is radiated so slowly that

are lower than [or ;n air burst at lower it can be igno;ed as a significant effect.

THERMAL RADIATION EFFECTS

AIISORPT!ON OF THERMAL. material. The extent or fraction of the

XA!T iATION incident radiation that is absorbed de7.23 ',he amount of t.ermal energy pend.. up:,n the nature and color of t'he

falling upon a uutt area exposed to a material or object. Highly reflecting and

nuclear explosi'mn depends upon the transparent subst-nces do not absorb

total energy yield, the height of burst, much of the thermal radiation and sc,

the distance from the explosion. and, to they are relatively resistant to its effects.

some extent, the atmospheric condi- A thin material will often trarsmit a

tions. The thermal radiat-on leaving the iarge propor!ion of the radiation falling

fiieball co.,ers a wide range of wave- upon it and ihus escape serious damage.

lengths, f om the short ultraviolet, A black fabric will absorb a much larger

through the visible, to the infrard re- proportion of the incident thermal radigion. Much Af the ultraviolet radiation is ation than will the same fabiic when

aLsorbed or scattered in its passage white in color. The former vili thus be

through the atmosphere with the result more affected than the latter. A lightthat at a target near the earth's surface colored material will then not char as

less ultraviolet radiation is receivcd than readily as a dark piece of the same

might be expected from the temperature material.

of the fireball.' 7.25 Essentially all of the thermal

7.24 When thermal radiation fal's radiation absorbed seives to raise the

upon any material or object, part may be temperature of the absorbing material

reflected, part will be absorbed, and the and it is the high temperature attaineo

remainder, if any, will pass through and which causes injury or damage, oh even

ultimately fall upon other materials. It is ignition of combustible materiais. An

the radiation absorbed by a parnicular important point about the thermal radiamaterial that produces heat and so de- tion from a nuclear explosion is not only

termines the damage suffered by that that the amount of energy is considerIt is known, from theoretical studies and experimental measurements, that the wavelength corresponding to the maximum energy density of radiation from an ideal (or "black body") radiator, to which

the nuclear fireball is a gooi approximation, decreases with increasing temperature of the radialic'n. At

temperatures above 7,5000K (13,000*F), this maximum lies in the ultraviolet and X-ray regions of the

spectrum (§ 7.78).

i ,A
THERNIAL RADIATION FVFTFTS 283

able, bu M1so that it is emitted in a very ately below the b'itst probably attained

short timo~. This means that the inhensity surface temrperatures of 3,000 to

of the rapation, i.e., the rate at which it 4.0000

OC (,()to 7.2000F). 1: is true

is incider~t upon a particular surface, is that the temperatures fell off r-apidly

very high. Because of th~is high initen- with increasing distance fom the ex

sity, the hea% accompanying the absorp- plosion, but there is some evidence that

tiori of the thermal radiation is produced they reac.hed 1 ,800'C (3,270'F) at

with great rapility. 3,200 feet (0.61 mile) away (6 7.47).

7.26 Since -rnly a small propo-rtion 7.27 The most important physical

of the heat is diss*.pated by conduction in effects of the high temperatures resultthe short time duri,-,g which the radiation ing from the absorption of thermal 1radifalls upon the niate.-ial-except perhaps aiion are burning cf the skin, and

in good heat cot~ductors such a% scorchi'ng, charring, and possibly ignimetals-the absorbed energy is largely tioi; O combustible organic substances,

confined ý'o a shallow depth of the mai- e.g.. wood. fabr'Zs, and paper (Fig.

terial. Cor~sequently, veiy high iemper- 7 27). Thin or porous materials, such as

atures are Attaisn:d at the 'urface. It has lightweight fabrics, newspaper, dried

been -Ftima'ed, for examp . , that in the grass and leaves, and dry rotted wood,

nuclear explosions in iapa&o (§ 2.24), mray flame when exposed to thermai

solid ma!eriais on the ground immedi- radiation. Ont the other hand, thick rrFigure 7.27. Thermal radiation from a nuclear explosion ignited the upholstery and caused

fire to spreadd in an automobile. Nevada Test Site.
284 THER~MAL RAOIATION AND ITS H-I-EC*t1'ý

Figure 7.28a. Therma) effects or, wood-f!:ime housie I second after explosion (about 25

cal/cm

rigure 7.?8b. Thermal effect, on wood-frame house about -Y4 second later,
THERMAL RADIATION EFFECTS 285

ganic materials, for example, wood sai.nple will be more readily damag'i

(more than 1/2 inch thick), plastics, and tnan one t,"at i. damp.

heavy fabrics, char but do not burn. 7.30 An important consideration in

Dense smoke, ad even jets u.' flame, connection wfW"- clLrring and ignition of

may be emitted, but the mawerial does varioaus materials and with the prodticnot sustain ignition. If the material 's tion of skin burns by thermal radiation is

light colored and blackens readily by the rate at which the lzermal energy is

.-harriig in the initial stages of exposure delivered. For a given total amount of

to thermal radiation it will absorb the tOermal energy recý,ived by each unit

subsequent ihermal radiation more area of exposed m, aterial. mhe damage

readily. However, smoke formed in the wili be greater if the energy is delivered

early tstages will partially shield the un- rapidly than if if were delivered slowly.

derlyirg material from subsequent radi- This means tnat, in order to produce the

ation. same thermal effect in a given material,

7.28 This behavior is illustrated i. the tot.l amount of thermatl energy (Qer the photographs taken oF on..z of t, unit area) received must be (Trger for a

wood-frame houses exposed in the 1953 nuclear explsior, of high yield than for

Nevada tests. As mentioned in § 5.55, one of the lower yield, becaune a given

the hoises were given a white exterior arriount of energy is delivered over a

finish iii order to reflect the thermal longer penrio of time, i r., more slowly,

radiation and minimize the chances of in the rormer case.

fire. Virtually at the instant of the burst, 7.31 Thure is evidence that ior

the house front became covered with a thermal radi2tion pulse, of ve,'y short

thick black smoke, ai shown in Fig. duration, such as might ;rise fLom air

7.28a. There was, however, no sign of brsts of low-yield weapons or frcm

flame. Very shortly thereafter, but be- explosions of largc yield at high altifore the arrival of the blast wave, i.e , tudes, this trend is reversed. in othcr

within less than 2 seconds from the words, a given amount of energy may

explosion, the smoke ceased, as is ap- be less effec;.ive if delivered in a very

parent from Fig. 7.28b. Ignition of the short pulse, e.g., a fraction of necond,

wood did not occur. timn in one of moderate (urition, e.g

7.29 The ignition of materials by one or two seconds. In some expertthermal radiation depends upon a men!s in which certain materials were

nurmbei of factors, the two most impor- exposed to short pulses of thermal raditant, apart from the nature of the mate- ation, it was observed that the surfaces

rial itself, being the thickness and the were rapidly degraded and vaporized. It

moisture content. A thin piece of a appeared as if the surfacL had been

given material, for example, will ignite "exploded" off Ifle material, leaving

more easily than a thick one, and a dey the remainder with very little sign of
286 THERMAL RADIATION AND ITS EFFECTS

damage. The thermal energy incident e.g., rayon, will scorch, char, and perupon the material was apparently dissi- haps burn, nylon, cn the C'her hand,

pated in the kinetic energy of the "ex- melts when heated ,o a sufficient extent.

plodirig" surface molecules before the The heat energy required to produce a

radiat~on could penetrate into the depth particular change in a fabric depends on

of the material a variety of circumstances. The following generalizations, however, appear to

THERMAL RADIATION EFFECTS ON hold in most instances.

SKIN AND EYES 7 34 Dark-colored fabrics absorb

the radiation, and hence stiffer damage

7.32 One of the serious conse- more readily than do the same fabrics if

quences of the thermal radiation from a light in color. Even in this conneclion

nuclear explosion is the production of there are variations according to the

"flash burns" resulting from the ab- method of dyeing and the prticular

sorption of radiant energy by the skin of fiber involved. Wool is more resistant to

exposed individuals. In addition, be- radiant energy than cotton or rayon, and

cause of the tocusing action of the lens these are less easily affected than nylon

of the eye, thermal radiation cati cause Orion appea -. io be appreciably more

permanent damage to the eyes o,' per- resistant tha:, iylon. F brics of light

sons who happen to be looking directly weight (for a given arý4) need less thurat the burst; however, such direct view- mal energy to cause specific damage

inc. will be fortuitous and rare. What is than do those of heavy weight. The

expected to be a more frequent occur- energy required, for the same exposure

rencc, and therefore much more impor- time, is roughly proportional to the frbtant to defensive action, is the tempo- ric weight per unit area. Fabric with a

rary loss of visual acuity (flash blindness moderate moisture content behaves like

or dazzle) resulting from the extreme dry fabric, but if the amount of moisture

brightness, particularly at night \•hen is fairly high, more thermal energy will

the eyes have been adapted to the dark. be needed to produce damage.

This may be experienced no matte," w"hat 7.35 Although extensive studies

the direction in which the individual is have been made of the effects of thermal

facing. The various effects of therrwsJ radiation on a large numbet of individradiation on human beings will be con- u'ýl fabrics, it is difficult to summarize

sidered more fully in Chapter XII. the results because of the many variables that have a significant influence.

THERMAL RADIATION DAMIAGE TO Some attempt is nevertheless made in

FABRICS, WOOD, AND PLASTiCS Table 7.35 to give an indication of the

magnitude of the exposures required to

7.33 Mention has already beeti ignite (or otherwise damage) various

made of the damage caused to fabrics by fabric materials by the absorption of

the high serface temferaituc, accompa- thermal radiation. The values are exnying the absorption )f thermal radia- pressed in terms of gram-calories of

tion. Natural fibers, e.g., cotton and thermal energy incident upon a I square

wool, and some sytithetic materials, centimeter area of material, i e..
THERMAL RAD'oTION EFFECTS 287

Table 7.35

APPROXIMATE RADIANT EXPOSURES FOR IGNITION OF FABRICS FOR LOW AIR

BURSTS

Radiant Exposure*

(cal/cmn)

Weight Effect 35 1.4 20

Material (oz/yd-) Color on Material kilotons rnegatonK megatons

CLOTHING FARRICS

Cott:,n 8 White Ignites 32 48 9

Khaki Tears on flexing 17 27 34

Khaki Ignites 20 30 30

Olive Tears on flexing 9 14 21

Olive Ignites 14 19 21

Dark blue Tears on fle), ng II 14 17

Dark blue Ignites 14 19 21

Cotton corduroy V Brown Ignites It 16 22

Cetton denim, new 10 Blue Ignites 12 27 44

Cotton shirting 3 Khaki Ignites !4 21 28

Cotton-nylon mixture 5 Olive Tears on flexing 8 15 17

Olive Ignites 12 28 53

Wool 8 White Tears on flexing 14 25 38

Khaki Tears on flexing 14 24 34

Olive Tears on flexing 9 13 19

Dark blue Tears on flexing 8 12 18

20 Dark blue Tears on flexing 14 20 26

Rainwear (double ne,,- 9 Olive Begins io melt 5 9 13

prene-coated nylon

twill) Olive Tears on flexing 8 14 22

DRAPERY FABRICS

Rayon gabardine 6 BWack ignites 9 20 26

Rayon-acetate dripery 5 Wine Ignites 9 22 28

Rayon gabardine 7 Gold Ignites ** 24t 28t

Rayon twill living 3 Black Ignites 7 17 25

Rayon twill lining 3 Beige Ignites 13 20 28

Acetate-shantung 3 Black lgnite,. lot 22t 35t

Cotton heavy draperies 13 Dark

colors Ignites 15 18 34

VENT FABRICS

Canvas (cotttn) 12 White Ignites 13 28 5I

Canvas 12 Olive

drab Ignites 12 18 28

OTHER FABRICS

Cotton chenille bedspread Light blue Ignites ** I It Ist

Cotton venetian blind

tape, dirty White Ignites 10 18 22

Cotton venetian blind tape White Ignites 131 27t 31t

Cotton muslin window

shade 8 Green Ignites 7 13 19

*Radiant exposures for 'he indicated responses (except where marked t) aie estimated to be valid to

±25% under staneArd laboratory conditions. Under typical field conditions the values are estimated to be

valid within ±50% with a greater fikelihond of higher rather !han lower ialhes For materials marked t,'

ignition levels are estimated to be valid within ±50% under lalboratoT7, conditions and within ± 100%

under f.Ad conditions.

**Data not available or apropriate scaliulg not known.

.!
288 THERMAL RAD!ATION AND 11S EFFECTS

cal/cm2 , generally referred to as the like 10 to 15 calories per square cenoi-

"radiant exposure." Results are pre- meter of therma! energy are required to

sented for low air bursts with arbitrary produce visible charring of unpainted

energy yields of 35 k;ictons, 1.4 mega- and unstained pine, douglaR fir, redtons, and 20 megatons. It will be noted wood, and maple. Dark staining inthat, for the reasons given in § 7.30, the creases the teo.'ency of the wood to

radiant exposure required to produce a char, but light-colored paints and hard

particular effect increases %!ith the yield. varnishes provide protection.2

7.36 Since the shape and duration 7.39 Glass is highly resistant to

of the them ',al pulse depend on !he a>- heat, but as it is very brittle it is sometual burst altitude, as well as on the times replaced by transparent or transyield, the radiant exposures given in lucent plastic materials or combined

Table 7.35 for "low air bursts" are with layers of plastic, as in automobile

somewhat approximate. In general, windshieids, to make it shatterproof.

however, the radiant exposures in the These plastics are organic compounds

three co!umns would apply to nuclear and so are subject to decomposition by

explosions below 100,000 feet altitude heat. Nevertheless, many plastic mat?-

for which the times to the second max- rials, such as Bakelite, cellulose acetate,

imum in the fireball temperature are 0.2, Lucite, Plexiglas, polyethylene, and

1.0, and 3.2 seconds, respectively Teflon, have been found to withstund

(§ 7.85). thernal radiation reianarkably well. At

7.37 Wood is charred by exposure least 60 to 70 cal/cm2 of the-rmal energy

to thermal radiation, tl-e depth of the are required to produce surface melting

char being closely proportional io the or darkening.

radiant exposure. For sufficiently large

amounts of energy per unit area, wood RADIANT EXPOSURES FOR IGNITION

in some massive forms may exhibit OF VARIOUS MATERIALS

transient flaming but persistent ignition

is improbable under the conditions of a 7.40 Studies have been made in

nuclear explosion. However, the tralmsi- laboratories and at nuclear tests of the

tory flame may ignite adjacent combus- radiant eyposures required for the ignitibie material which is not directly ex- tion of various common household

posed to the radiation. In a more-9r-less items and other materials of interest.

finely divided form, such as sawdust, The results for low air bursts with three

shavings, or excelsior, or in a decaye-,, -rbitrary yields are presented in Table

sporgy (punk) state, wood can be ig- 7.40; the conditions and limitations

nited fairly readily by the thermal radi- nc'ed it. § 7.36 also hold here. The

ation from a nuclear explosion, as will radiant exposures given would be applibe seen below, cable to explosions at altitudes below

7.38 Roughly speaking, something 100,000 feet.

2The thermal radiation energy incident on the front of the house referred to in § 7.28 was about 25

cal/cm!.
THERMAL RADIATION EFFECTS 289

Table 7.40

APPROXIMATE RADIANT EXPOSURES FOR IGNITION OF VARIOUS MATERIALS

FOR LOW AIR BURSTS

Radiant Exfxsurc*

(cal!cm-')

Weight Effect 35 I .4 20

Material (oz vd2) r,,or on Material kilotons megatons megatons

HOUSEHOLI) TINDER MATERIALS

Newspape,', shredded 2 Ignits 4 6 II

Newspaper, dark picture area 2 Ignites 5 7 12

Newspaper, printed text area 2 Ienites 6 8 15

Crepe paper I (,reei, Ignites 6 9 16

Kraft paper 3 i'an Ignites I0 13 2')

Bristol board, 3 ply 10 Dark Ignites Ih 20 40

Kraft paper carton, used

(flat side) 16 Brown Ignites 16, 20 40

New bond typing paper 2 Whit%: ignies 24t 30÷ 5()-

Cotton rags Black Ignites 10 15 20

Rayon rags Black Igrnites 4 . 21

Cotton string scrubbing mop (used) Gray Ignites I0W 151 21t

Cotton Ftiring scrubbing mop

(weathered) Crea- ignites I1W 19± 26+

Paper book matches, blue head

exposed Ignites I i t 14+ ZOr

Excelsior, ponderosa pine 2 Ihift'Light

yellow Ignites ** 23± 23t

OUTDOOR TINDER

MATERIALS***

Dry rotted wood punk (fir) Ignites 4+ 6± 8f

Deciduous leaves (beech) Ignites 4 6 8

Fine grass (cheat) Ignites 5 8 1(•

Coarse grass (sedge) !gnites 6 9 II

Pine needles, brown (ponderosa) Ignites 1O 16 21

CONSTRUCTION MATERIALS

Roll roofing. minerai surface Ignites -34 116

Roll rcofing, smooth surface Ignites 30 77

Plywood, dougazs fir Flamin,.

during

eiposure 9 16 20

Rubber. pale latex Ignite:; 50 80 IIt)

Rubber. black Ignites 10 20 25

OTHER MATERIALS

Aluminum aircraft skin (0.020 in.

thick) coated with 0.002 in. of

standard white aircraft paint Blisters 15 30 40

Cotton canvas sandbags, dry filled Failure 10 18 32

Coral sand Explodes

(popcorning) 15 27 47

Siliceous sand Explodes

(popcorning) II 19 35

*Radiant exposure:i for the indicated responses (except where marked t) are estimated to be valid to

±25%X• under stanuard laboratory conditions. Under typical field conditions, the values are estimated to

be valid within ±50% with a greater likelihood of higher rather than lower values. For m3terials marked

t, ignition levels are estimated to be valid within ±+50% under laboratory conditions and within ± I OO%,

under field conditions.

**Data not available or appropriate scaling not known.

***Radiant exposures for ignition of these substances are higiily dependent on the moisture content.
290 THFRMAI RADIATION AND ITS EIFFCTS

RAPIANT EXPOSURE AND SLANT which ate essentially surface bursts (ct.

RANGF § 2. 128), radiant exposures should he

calculated by using the procedures in 7.41 In order io utilize the data in

Tables 7.35 and 7.40 to deteimine how § 7.101 e seq.

far from the burst poit, for aen exhow 7.43 The application of Fig. 7.42

far from the burst point, for an explo- may be illustrated by ,stimating the

sion of given partculr energy mteral oul yield, beobsrve. ignition of ~ a range over which ignition may occur in

newspaper as a result of exposure to a

is required to know how the thermal iO00-kiloton (I-megaton) air burst

energy vat ,es with distance. For a spe- under the conditior, specified above.

cific explosion yield, the variation of According to Table /.40, the radiant

radiation exposure with distance from the ofburt oin deend upn aexposure for the ignition of r~ewspaper

thie point of burst depends upon a is about 8 cal/cm 2 in a I-megaton exnumber of tactors, inc'jding the height plosion. Fig. 7.42 is entered at the paint

of burst and the condition (or clarity) of

the atmosphere. As seen earlier, the on y (1e iedoscl c hesp rndi cuproorton f te ttalvied tat ppersmegaton (I10)1 kilotons): the perpendicuproportion of the toil yield that appears lar line is then followed until it interas thermal energy and the character and ;ects the curve marked 8 cal/cm2 of

duration of the thermal puise vary with radiant exposure. The intersection is

the height of burst. Furthermore, t seen to correspond to a ,;an( range of

height of berst and the atmospheric vis- about 7 miles from the explosion This

ibility determine the fraction of the is the range at which the thermal radiathenuioa energy that can penetrate the tion from a !-megaton air burst (below

atmosphere. 15,000 feet altitude) could cause igni7.42 The variation of saai;'nt expo- tion in newspaper when the visibility is

sure on the ground with slant range from IL i2 e Unerhay oniton, uc

the explosion fer a particular set ofIZ ieUnrhaycdtosuh ctexplosions fan parconvenintilarrset oas often exist in large cities, the visibihconditions can be conveniently repre- ity would be less and the ignition range

sented in the form of Fig. 7.42. These it be l e S i tion raye

might be smaller. Similarly, a layer of

curves were calculated for burst heights dense cloud o. smoke between the target

of 200 W"- feet, where W is the explo- and the burst point will decrease the

sion y-eld in kilotons (see § 7.99), but distance over which a specified ignition

they piovide reasonably good predic- may occur. However, if the explosion

tions of radiant exposures from ai; were to take place t)etween a cloud layer

bursts at altitudes up to about 15,000 and the target or if the ground surface is

feet, for a visibility of 12 miles. This highly reflective, as when covered with

visibility represents the conditions for snow, the disiance would be greater

:ypical urban areas on a clear day. For than indicated by Fig. 7.42.

air bursts at altitudes above !5,000 feet,

Fig. 7.42 is 1ot satisfactory and the THERMAL EFFECTS ON MATERIALS

procedures de:scribed in § 7.93 et seq. IN jAPAN1

should be used. For bursts at low alti- 7.44 Apart from the actual ignit.on

tudes, e.g., less than 180 W04 feet, of combustible materials resu'ling in

'The effects of thermal radiations on people in Japan are described in Chapter XII.

j7'
THERMAL RADIATION EFFECTS 291

0 LI _ _ _

(S3711W) 39NVMI INV-IS

-__ _~--~----.t- I

~!
292 1~~~HEiRN1.1I RADIArION A *%D I VS iF 1 i: IS

Figure7.44a. Flash burns on upholstery of chairs exr.wsed to bomb flash at window (I mile

trom gci,.znd i;cro at Hiroshima, 8 to 9 callcrn2).

fires being started, which will be re- posts *Wcre he~avily cha:-d, but the.

ferred to later. a number o1 other phe- charr,-6 arca "'a,- sharply limited by the

nornena observedi in Japan testified to shadow of a wall. The wall was, howthe intense hee't drw( io thvý absorption of ever, completely demolishcd by the

thermal radiatien. Fabrics (Fig. 7 .

4 4a), bla.,. wave which arrived iafter the therutility poles (Fig. 7.44b), irees, and mal radiatiin. This radiation travels

wokxden oýsts. up io a rad")is of I 1 .000 uith the speed of light, whereas the

fcet _ý t ;) from ground zero to bi-st wave advances much more slowly

Nagasaki (ezitirrai-d 3., ca!AN-m2 radiant t~3.09).

exposure) and 9,000 feet (1 .7 miles) at 7.45 From observations cf the

Hiroshima (estimated 3 cal/cm2 ), if not shadows left by intervening objects

destroyed in the general conflagration, where they shieldied otherwise exposed

were charred and blackened, but only on surfaces (Figs. 7.45a and b), thie diri-cthe side facing the point of burst. Wheie lion of the center of the explosion was

there was protecton by buildings. located with considerable ,:'curacy

walls, hills, and other objects there was Furthermore, by examining the s0idow

no evidence of thermial rý;dimtion effects. effects at various places around the exAn interesting case of shadowing of this plosion, a goiod Indication was obtained

kind wz~s re -orded at Nagasaki. The tops of the height of burs-, Occasionally, a

and upper pafts of a row of wooden distinct penumbra was four~l, and froin
THERMA[ RADIATION EFFEcT 293

FigurL 744b. Flash burns on wooden poles (1 17 miles from ground zero at Nagasaki. 5 to

6 cal/cm2). The uncharred portions werc protected from thermal radiation by

a fence.
294 THERMAL RADIA11ON AND ITS EFFECTS

Figure 7.45a. Flash marks produced by thermal radiation or. asphalt of bridge in Hiro-

:,himra. Where the railirgs served as a protection ftum the radiation, there

were no ,nark,,.: the length and direction of the "shadows" indicate the point

of the bomb explosion.

this it was possible to calculate the di- tals of the stone, and it is estimated that

ameter of the fireball at the time the a temperature of at least 6C0°C

thermial radiation intensity was at a (I , ,00F) I was necessary to produce the

maximum. observed effects. From the depth of the

7.4,6 One of the striking effects of roughening and ultimatt flaking of the

the thermal radiation was the roughen- granite surface, the depth to which tnis

ing of the surface of polishd granite temperature ,vaa3 attained could be dewhere there was direct exposuie. This termined. These observations were used

roughening was attribaited to the un- to calculate the maximum ground temequal expan:;ion of the constituent crys- peratures at the time of the explosion.

I
THERMAI RADIATION tEFFECFS 295

Figure 7.45b. Paint on gas holder scorched by the thermal radiation, ý'xcept where

protected by the valve (0.33 miles from ground. zero at Hiro:;hima).

As mcrntioned in § 7.26, they were ex- same kirAc, it was found that ~i1

tremely High, especially near ground blistering could be obtaired by heafing

F ýero. to 1,800-C (3,270-F) for a period of 4

7.47 Another thermal effect, which stco:nds, although the tdlw't extended

proved to be valuable in subsequer~t deeper hino the tile than it diul in Japan.

studies, was the bubbling or blistering From this result, it wa-; con, 'uWed that

of t~ie dark green (almost black) tile v. ith in the nuclear expl~~osio the tile attained

a pcrous surface widely used for roofing a surface temperature of more than

in Japan (Fig 7.47). The phei~ometion 1 ,800'C for a periodi of lessý than 4

was reported as fat zs 3,200 feet (0.61 seconds.

.nile) from ground zero at Hhoshinia, 7.48 Thme filfee'-rice ir behavior of

where the radiant exposure was e.ý-O- light and d.'rk fabric exposed to thermated to have been 45 cal/c~n2. The size mal radiation in Japan Is also of considof the bubbles arid their extent increased erablc in'-rzstk. I ight. colored fabrics Ciwith proximity to ground zero, and also 'ýer reflect oir ransmit rnost of the

with the directness with which the tile 1,e-ma: radialior. and absorb very Kltle

itself faced the explosion. in a labora- Consequently, they will not reach such a

tory test, using undani-iged tile of the L~igh ternperatmte and will suffer less
296 TIHFRMAi. RADIATION AND ITS EFFECTS

damage than dark fabrics which absorb cotored stripes were urndamaged (Fig

a large proportion of the radiatioin. In 7.48). Similarly, a piece of paper which

one case, a shirt with alternate narrow had received approximately 5 ca!/cm2

light and dark gray stripes had zh.- dark had the characters, written in black ink,

stripes burned out by a radiant exposuwe burned out, but the rest of the paper wits

of about 7 cal/cm2 , whereas the light- not greatly affected.

INCENDIARY EFFECTS

ORIGIN OF FIRES

7.49 There are two general ways in cuits, and broken gas lines. No matter

which fires can originate in a nuclear how the fire originates, its subsequent

explosion. First, as a direct result of the spead will be determined by the amoil'#,

absorption of thermal "adiatiot' thin and distribution of combustible materikindling fuels can be ignited. And sec- als in the vicinity.

ond, as an indirect effect of the destruc- 7.50 In urban areas kindling fuels

tion caused oy the blast wave, fires can which can be ignited by direct exposure

be started by upset stoves, water hec,'- to thermal radiation are located both

ers, and furnaces, electrical short cir- indoors and out of doors. h1uerior igniFigure 7.4/. Blisttred surf:ice of roof tile; left portion of the tile was shielded by an

overlappi.ig one (0.37 mile from ground zero at Hiroshima).
INCENDIARY EFFECTS 297

i%-

Figure 7.4,8. The light-colored Fortions of the material awe intact, but some of the e

dark-colored stripes have been destroyed by the heat fiom the therm. al

radiation.

lion points could receive thermal radia- as shades, curtains, and drapes. Of

tion through a window or other u,?)ening, course, if the window coverings are

The thermal exposuire at ary• interior made of combustible materials, they

point would be roughly proportional to will constitute inter-nal ignition points,

the fraction of the fireball that would he as ais.) will upholstered furniture, bedvisible at that point through the opening. ding, carpets, papers, and fabrics. ExIf the thermal radiation should pass terioi ignition points are paper, trash,M throu~gh a gias,; window, the amount awnings, dry grass, leaves, and dry -

entering a room would be about 80 per- shrubs. Interior ignitions a'e more likely

cent of that failing on the extet ior of the to grow into seff-sustaining fires than are

glass. The reduction is mainly due to exterior ignitions. La, gc amounts of

reflection of tho; radiation, and so 'it is kindling are required to maintain an ig.

essentially independent of the thickness nition for a suftlinent time to ignite a

of the glass. A combination of a glass sound wooden structure, and the ntceswindc~w an,! a sciveen wiil reduce the sary fuel arrangem'ents are much more

transmitted radiation energy to routghly common ind~oors than outdoors•

40 to 50 percent of 'the 7:ncident energy. 7.51 In order for ani ignition to deIn addition, the thermal iadiation will be velop withi.n a room, one or two subSattenuated by window coverings.. such ,;tantial combustible furnishings, such asi

',u 1 UIII~IIIIIIIIII~w

I,' I'
298 THFRMAI. RADIATION AND ITS I FFECTS

an overstutfed chair or couch, a bed, or blast loadirg of urban il;riors shoN,.

a wooden table must be ignited and that the blast wave typically does extinburn vigorously. Fires that become large guish arames bu' often leaves the mateenough to spread generally burn be- rial snmldering so that acttve flaming is

tween 10 and 20 minutes before room revived at a later time. It is not certain.

". ashover. " Flashover occurs when hcwever, to what extent this t'ehavior

flames from a localized fire suddenly would apply to actual urban targets

,spread to fill the rvom. Af:er room subjected to a nuclear expklsion. Alflashover, the fire becomes intense though some fires may be exiinguished

eno|i-,t to penetrate interior partiwoas by the blast, many others will undoubtand to spread to other roo:ns. The blaze edly persist.

from a single fire in an average residei,('x ,oi i! te -xpected to reach peak SPREAD OF FIRES

intensity in at:out an hour.

7.52 In a typical urban area the 7.54 'the spread of fires in a city,

density of interior ignition points is including the development of "mass

usually much greater than that o! exte- fires," depends upon various condirior points. Furthermore, as stated tions, e.g., weather, terrain, closeness

abo,,'e, the probability of ignitions and combustibiiity of buildings, and the

spreading to more substantial fuels is amount of combustible material in a

gre.ater f,,," inte;,ior than for exterior ig- given area. The interaction of blast and

nition points. Nevertheless, fires started fire, as described above, and the extent

ou.doors can also r,ýsult irn significant of blast damage awe also important facdiage. Ignitions of dead weeds or tall tors in determining fire spread. Some

dry grass or brush may develop into conclusions concerning the developfires sufficiently intense to ignite houses. ment and growth of fires from a large

The fuel contained in a pile of trash is number of ignition points were drawn

often sufficient to ignite a structure with from the experiences of World War If

loose, weathered siding. Structures with incenditry raids and the iwo nuclear

very badly vweathered ai-d decayed sid- bomb attacks on Japan, but these expeing or shinglcs may ignite directly from riences we:e not completely docuthe incident thermal radiation. raented. More useful data have been

7.53 Since most of the thermal ra- obtaineu from full-scale and model tests

dial on reaches a target before the bilst conducied in recent years.

wave, the subsequent arrival of the latter 7.55 The spread of fire between

may affect the development of fires ini- buidV . -:, ,, suf rom the igaition of

tiated by !be thermal radiation. In par- comýnasutiL. m•teriijs heated by fires in,

ticular, there :s a possibility that such adjacer! buildings, ignition of heated

fires may be extingaished by the blast combustible materials by contact with

wind. -I:udies of the effects in Japan and flames, sparks, embers, or brands, and

at .arious nuclegr and high-explosive , igni,,on of unheated combustible

tests have given contradictory results mai.erials by contact with flames or

ard they leave the matter unresolved, burning brands. Spread by heating, due

Laboratory experiments that simulate either to convection, i.e., to the flow of

Ii
INCENDIARY EFFECTS 299

hot gases, or to absorption of radiation, g,'eater than those at which radiative and

is a short-range effect, whereas spread convective heating can have a signifiby firebrand,- may be either ';hort or long cant effect. Long-range fire sp.,edd by

range. Hence, an important criterion of brands could reatly extend the area of

the probability of fire spread is the dis- destruction by urban fires resulting from

tance between buildings. The lower the nuclear explosions; there is no single

building density, the less will be the method for pcedicting the spread but

probability that fire will spread from one computer rnodeis are being developed

structure to another. In an urban area, for this purpose.

especially one fairly close to the explosion point, where substantial blast dam- MASS FIRES

age has occurred, the situation would be

changed substantially. A deep, almost 7.53 Uider :;ome conditions the

continuous layer of debris would cover many individual fires crealed by a nuthe ground, thereby providing a medium clear .w"',--ion can coalece irto mass

for the ready spread of fires. Cires. !'-.. types oi mass fires of particu7.56 CombLstible building surfaces lar interest, because of their great poexposed to a thermal radiation intensity teuial for destruction, are "fire storms"

of as low as 0.4 cal/cm2 per second for and conflagrations. In a iire storm many

extended periods of time will u!timately fires merge to form a single convective

burst ;nto flame. The radiating portions column ot hot gases rising from the

of a burning building emit about 4 burning area and strong, fire-induced.

cal/cm2 per second. Conszq-iently, radi- radial (inwardly directed) winds are asation fror.m a burning building may cause sociited with the --onvective columr..

ignition of an adjacent building. Such Thus the fire front is essentially stationignition by radiation is probable for ary and the ourde spread of fire *s

most structures if the dimensions of tlee prevented by the in-rushing wind; howburnitig structure are as large as, or ever, virtually everything combustible

larger than, the distance to the uiAburmed within the fire storm area is eventually

structure. The convective plume uf hot destroyed. Apart frcm a description of

gases from a burning buildiag ',ould the observed phenomena, there is as yet

come into contact with anotiker building no generdiiy accepted definition of a fire

which is farther away than the range for storm. Furthermore, ihe conditions,

radiation fire spread only under coiodi- e.g., weather, ignition-point density,

tions of extremely high wind. There- fuel density, etc., untder which a fire

fore, fire spread by convective heat sinrm may be expected are not known.

transfer is not expected te be a signifi- Nevertheless, based on World War ii

cant factor under normal terrain and experience with mass fires resulting

weather conditions. from air raids on Germany and Japan,

7.57 Fires can be spread between the minin uni requirements for a fire

buildings by burning biands whic;, are storm to develop ane considered b,

borne aloft by the hot gases and carried some authorities to be the following: (1)

downwind for considerable distances. at least 8 pounds of combostibles per

The fires can thus spread to distances square foot of fire area, (2) at !.'st half
30W FHF.RMAI RAFiATION AND ITS .FFEFýCTS

of the structures in the area on fire the development of mass fires in a forest

simultaneously,. (3) a ', ind of less than 9 following primary ignition of dried

miles per hour at the time, and (4) a leaves, grass. and rotten wood by the

mirnimuni burning area of about half a thermal radiation. Some of the factors

square mile. High-rise buildings do not which will influence the growth of such

lend themselves to formation of fire fires are the average density and moiss!orms because of the vertical dispersion ture content of the trees, the I(2L) of

of the combustible material and tbc baf- open to tree-covered areas, topography.

fie effects of the structure% season of the year, and meteorological

7.59 Conilagrations. as distinct conditions. Low atmospheric humidity,

from fire storms, have moving fire fronts strong winrds, and steep terrain favor the which can be driven by the ambient development of forest fires. In general, a

whic be ca rivn b theambentdeciduous forest, particularly when in

wind. The fire can spread as long asw

there is sufficient fuel. Conflagrations leaf, may be expected to burn less rapcan wheras de,,,-lop from a single ignition, idly and with less intensity than a forest fire storms have be,, obsergntiod of coniferous trees. Green leaves and

onlywhersre atorms navber of obesaerd the trunks of irees woUld act as shields only where a large number of fires are aanttemlrdain ota h

burning simultaneously over a relatively against thermal radiation, so that the

largearea.number of points at which ignition large area.

occurs in a foi'est may well be less than

7.60 Another aspect of fire spread is would appear at first sight.

INCENDIARY EFFECTS IN JAPAN

THE NUCLEAR BOMB AS AN about 12.5 kilotons energy yield, nuINCENDIARY WEAPON clear weapons are capable of causing

7.61 The incendiary effects of a tremendous destructinn by fire, as well

nuclear explosion do not present any as by blast.

especially characteristic features. In 7.62 Evideace was obtained from

sri.ipL,, the same overall result, as the nuclear explosions over Japan that

regards destruction by fire and. blast, the damage by fire is much more demight be achieved by the use of con- Pendernt upon local terrain and meteoroventional incendiary and high-explosive logical conditions than are blast effects.

bombs. It has been estimated, for ex- At both Hiroshima and Nagasaki !he

ample, that tie fire damage to buildings distances from ground zero at which

and other structures suffered at Hiro- particular types of blast damage were

shima could have been produced by experienced were much the same. But

about 1,000 !ons of incendiary bombs the ranges of incendia-y effe.cts were

distributed over the city. It can be seen, quite different. In Hiroshima, for examhowever, that since this damage was p~e, the total area severely damaged by

caused by a single nuclear toib of or'ly fire, about 4.4 square miles, was

I
INCENDIARY EFFE'FS IN :APAN' 301

roughly four times as great as in Naga but the temperatures were generally not

saki. Ow contributory cause was the higk enough for ignitin to occur

iregular layout of Nagasaki as corn- (§ 7.28). Rotted and checked (crackzd)

pared with Hiroshima; also greater de- wood and eicelsior, however, have

struction could probably have been been obsurved to burn c(,tnpletely, and

achieved by a change in the bdrst point, the flame was not greatly affected by the

Nevertheless, an important factor was bla.st wave.

the difference in terrain, wih its ass,,- 7.6 It is not known to what extent

ciated building density. Hiroshima was thermal radiation contributed to the inirelatively flat and highly built up, tiation of fire:: in the nuclear bombings

whereas Nagasaki had hilly portions in Japan. It is po)ssibie, that, up t,) a mile

near ground zero that were hare of or so from ground zero, .,ome fires may

structures, have originated from secondary causes.

such as upsetting of stoves, electrical

ORIGIN AND SPREAD OF FIRES IN shortcircuits, broken gas lines, and so

JAPAN on, which were a direct effect of the

blast wave. A numb-r of fires in indus7.63 Den.fite evidence was ob- trial plants were initiatcd F-y fm:rnaces

tained from Japanese observers that the and boilers being overtrned, and by the

therma! radiatiun caused thin, dark cot- collapse of buillding• on themn.

tori cloth, such as the blackout curtains 7.66 Once tiie firer, had started,

that were in common use during the there were several factor,.N directly rewar, thin paoer, and dry, rotted wood to lated to the destruction caused by the

catch fire at dista-nces up to 3,5W0 feet nuclear explosion, that influenced their

(0.66 mile) frorki ground zero. It was spreading. By breaking windows and

reported that a cedar bark roof farther bowing in or danwzving fire shutters

out was seen to burst into flame, ap- (Fig. 7.66), by stripp. ,, wall and roof

parently spontaneousi',, but this was no, shevthing, and coll'psing walls and

definitely con!,rred. Abnormal en- roofs, the blast made many buildings

hanced amounts of radiation, due to more vulnerable to fire. Noncombustible

reflection, scattering, and focusing ef- (fire- resistive) structures were often left

fects, might hý,ve caused fires to origi- in a condition favorable to the internal

nate at isolated pointv (Fig. 7.63). spread of fires by damage at stairways,

7.64 From the evidence of charred elevaters, and in firewall openings as

wood found at both Hir,-shima and Na., wedl as by the rupture 3nd collapse of

gasaki, it was originally concluded that floors and partitions (see Fig. 5.23).

such wood had actually been ignited by 7.67 On the other hand, when

thermal radi.,tion and that the flames combustible frame buildings were

were subsequently extinguished by the blown down, they did not burn as rapblast. But it now seems more probable idly as they would have done had they

that, apart from some exceptional in- remaineci standing. Moreover, the nonstances, there was no a-;tual ignition of combustible debris produced by the

the wood. The absorption of the thermal blast frequently covered and prevented

radiation caused charring in sound wood the burning of combustible material.
302 THERMAi. ADIAION AND ITS EFFECTS

/I

4..

A-

~ 1

Figure 7.63. The top of a A:od pole was reported as being ignited by the thermal radiation

1 .25 miles from ground zero at Hiroshit.,a, 5 to 6 cal/cm2). Note the unburned

surroundings. the nicarest btirned building was 3W4) fee( away.
INCENDIARY EFFECTS IN JAPAN 303

Figure 7 66. Fire shuwters in building blown in or damaged by the blast: shL:;er at center

probably blown outward by blast passing through building (0.57 mile frot,,

ground zero at Hiroshima).

There is some doubt, therefore. whether of fires. Nevertheless, there were a few

on the whole the effeci of the blast was instances where firebreaks assisted in

to facilitate or to hinder the development preventing the burnout of some fire reof fires at Hiroshima aad Nagasaki. sistive buildings.

7.68 Although there were fire- 7.69 One of the important -spects

breaks, both natural, e.g., rivers and of the nuclear attacks on Japan was that,

open spaces, and artificial, e.g., roads in the large area that suffered simultaand cleared areas, in the Japanese cities, neous blast damage, the fire departments

they were not very effective in prevent- were cotr.p'..tely overwhelmed. It is true

ing the fires from spreading. The reason that the firL iighting services and equipwas that fires often started simultan- ment were poor by American ::and:lrds,

eously on both sides of the firebreaks, so but it is doubtful f much could have

that they could niot serve their intended been achieved, under t-e circumr.tances,

purpose. In addition. combustible ma- by more efficient fire departments. At

terials were frequently strewn by the Hiroshima, for example, 70 percent of

blast across th'ý fi,ebreaks and open the firefighting equipment was crushcd

spaces, such as yards and street areas, in the collapse of fire houses, and 80

so that they could not prevent the spread percent of the personnel were unable to

~vri.~31 ~. --. -. -.-. . - -
304 THEW,-1.4A RADIATION AND !TS EFFECTS

respond. Ever, if men and machines had light over the cenri of the city and

survived the blast, many fires would heavier abou' 3,500 to 5,006 feet (0.67

have been inaccessible because of !he to 0.95 mile) to the north and west. Raln

streets being blocked with debris. For in these circumstances was apparently

this reason, and also because of the f,;ar due to the condensation of moisture on

of being trapped, a fire company from particles from the fire when they reached

an area which had escaped destruction a cooler area. The strong inward draft at

was unable to approach closer than ground level wa, a decisive factor in

6,600 feet (1.25 miles) from ground limiting the spread of fire beyond the

zero at Nagasaki. initial ignited area. It accounts for the

7.70 Another contributory factor to fact that the radius of the burned-out

the destruction by fire was the failure of area was so uniform in hiushima and

the water suppl, in both Hiroshima and was not much greate- than the range in

Nagasaki. The which fires started soon aftcr the explo- pumping stations were

not largeiy affected, but serious damage sion. However, v.rtually everything

was, sustained by distribution pipes and combustible within this region was demains, with a resulting leakage and drop stroyed.

in available water pressure. Most of the 7.72 No definite Pre storm occurred

lines above ground .vtxe broke, t-y col- at o;hetwn Nagasaki, although loigbte~ the velocity of theh

iapsirg buildings and by heat from the s incresed towingmieswan h he

fires which melted the pipes. Some he crato ha me A 's.

buried water mains were fracturud and g

o'hers were broke!n due to -the collapsc tablished, perhaps about 2 hours after othes bok'n wre du to~he ollpse ti'e explosion. This wind tended to carry

or distortion of bridges upon which they te feuplohiovalley ind adretion cre

w'ere supported (§ 5. 106). Itte fire up the valley in a direction where

tt ere was nothing to burn. Some 7 hours

7.71 About 20 minutes after the iter, the wind had shifted to the east

det(.nation of the nuclear bomb at Hiro- a id its velocity had dropped to 10 to 15

shima, a mass fire developed Fhowing miles per hour. These winds undoubtmany characteristics usually associated edly restricted the spreaid of fire in the

with fire storms. A wind blew toward respective directions from which they

the burning area of the city from all we-e blowing. The small number of

directions, reaching a maximum veloc- dwellings exposed in the long narrow

ity of 30 to 40 miles per hour about 2 to valley running through Nagasaki proba3 hours aftei- the explosion, decreasing bly did not furnish sufficient fuei for the

to light or moderate and variable in development of a fire storm as ccmpared

direction about 6 hours after. The wind to the many buildings or. the flat terrain

was accompanied by intermittent rain, at Hiroshima.

I,

I
TECHNICAL ASPECTS OF THERMAL RADIATION 305

TECHNICAL ASPECTS OF THERMAL. RADIA1 ION 4

DiSTrRIBUTION AND ABSORPTION OF body for a given waveiength, i.e..J, as~

ENERGY FROM THIE, FIREBiALL a function of wavek'-igth for any spe,--

cified tr .r~e since J, is related toI

7.73 Spectroscopic studies made in Eh by

the course of weapon. ts.. rs have s hown j -c E, (7.74.1) t hat the fireballI does not behave #. -acl A) 4 A

like a black body, i.e., as a peifect

rtdi.-forr Generally, the proportion of where J, is in units of energy (ergs) per

radiatior.s of iinger wav-21ength~ (greater unit area (cm 2

) per uoiit time (sec) per

than 5,500 A) corresponds to 4igher unit wavelength (A). The i'esults of such

black body tempera~ures than does fthe calculations fo7 'tmperatuares ranging

shorter wave emission. The assunmption from 100 mil~ion (I19~ degrees to

of black body !,ehavioi for the fireball, 2,0000 K are shown in Fig. 7.74. It is

however, werves as a reasonable ap- seen that the total radiant power, which

proximat ion .in interpreting th': thermal is given by the a.-ea under each curve,

radiati,)n emissiont chiaraclieristics. For a decreases greatly as the temperature is

black body, the d',iribution of radiant decreased.

energy over the spectrum can be related 7.75 An imnportao- qorect of F~ig.

to the surface temperature by Planck's 7.74 is the change 'n Jo: 4tion )f the

tadiation equation. If Et-JX denctes the curves with tempc:"ture. in other

energy density, i.e., energy pet unii words, the spectrum of the radiant en-

,Alume, in the wavelength inverval ergy varies with the temperature. At

to X--d>,, then, high temperatures, radiations of short

8 Trhc Iwavelength predominate, but at low

E, X hclX kT_ teraperaturts those of long wavelength

e 1 (7731 make the major contribution. F~or ey.-

(7.7. 1)ample, in the exploding weapon. before

where c is the velocity of light. hz is the formation of the fireball, the temn

Planck's quantum of action, k is Bolt0- perature is several tens of million demann's constant, i.e., the gas consirint grees Kelvin. Most of the (primary)

per molecule, and T is the absolute thermal radiation is then in the wavetemperature. It will be noted that hc/X\ is length range f roin about 0. 1 to 100) A.

the energy of the photon of wavelength i.e., 120 to 0.12 kilo-electron volts

X\ (§ 1. 74). (keV) ener~yy, corresponding roughly to

7.74 Froin the Plank equation 'It is the soft X-ray rcgion (Fig. 1 .74). This is

possible to calculate the rate of energy the basis of the statk-ment made earlier

emission (or radiant power.) of a black that the primary thermal radiation from

141,- remaining w.,tions of thii chapker may he omirttid withoul loss of conhirluity.
306 THERMAl. RADIATION AND ITS EFFECTS

PHOTON ENERGY

I MEV 0.1 ME/ 10 KEV I KEV 0.1 KEY !0 EV I EV

.028__ - _ __ T • I

1024 . . .... I0

IB

6_____;__-

10 .. .. L_

£E

0 10

rj 1018 R_

01, A

N, 16r

U 160 - -G

cr 160_

Y.

I0

r-- O 12" . . .

(r 1010. .. .. __ _

0

101.. ,---- •' ...---Ž .

2 - - .

10-2 1O"- I 10 !0 2 1o3 104

WAVE LENGTH (ANGSTROMS)

Figure 7.74. Radiant power of a blac'k body as a fznctioai of wavelength at various 4

ternpe'atures.

A
TECHNICA' A.SPECTS O- THERMAl. RADIATION 307

a nuclear eyFlosion consists largely of X wilere C is a constant, equa, to 2 90 x

rays. These radiations are absorbed by 10" angstroins-degrees K. This expresthe surroundirig air to form the fireball sioii is known as W~cn's displacement

from which the effecti-,e thermal radia- law.

tion of present interest is emitted in the 7.78 The temperature at which the

u iraviolet, visible, and infrared regions maximum in the radiant power distribuof the sp.:ctrum. The dimensions of the tion from a black body should just fall

firebali in which the thermal X rays are into the visible spc-ctrum, i.e., waveabsorbed depends on the ambient air length 3,850 A, is found from equation

density, as wil' Ze seen shortly. (7.77.1) to Le about 7,500"K. This

7.76 1: will be recalled tha: the happens to be very close to the maxthermal radiation received at :he eaih'L. imum surface temperature of the ..rchail

surface differs to some extent from that after (he minimum, .. during the secleaving the fireball. The reason is that ,ad radiation pulse (Fig. 2.39). Since

the radiations of shorter wavelength, the apparent surface temperati:;e generi.e., in the ultraviolet, are more readily ally does not exceed ,,000°K and th.

absorbed than the others by the atmas- average is considerably less, I, is ev,-

phere between the burst Doint and the dent that the thermal energy emitted in

earth's surface. The ther.mal radiation the second pulse should consist mainly

received a( a distance from a nuclear of visible and infrared rays. with a

explosion is fairly characteristic cl a smaller proportion in the ultr,"violet rebiack body a, a tcmperature Af about gion of the spectrum. This has been

6,000 to 7,000°K, although somewhait found to te the case in actual tests, eve.1

depleted in the ultraviolet and other though the fireball deviates appreciably

shorter wavelengths. Even if the deto- from black body behavior at this stage.

natior. occurs at very high altitudes, the 7.79 The mean free path (§ 2. I 13)

thermal radiation from the low-density in cold air, at sea-level density, o' X-ray

firebal! must pass through the denser photons with energies from abou, 0.5 to

atmosphere before reaching the ground. i5 LeV is given by the approximate

The OTective thermal radiation received relationsh;1⁄4

oil the earth's surface in -his case is, E3

therefore, also composed of the longer Mean free path -- cm, (7.79. 1)

wavelengths.

7.77 An expression for the wavelength (X,,) correspondiag to the max- where E'is the photon energy itn keV. in

imuii in the radiait power as a function order to make son'me oider-of-magritude

of the black body ternper,,t're can be calculations of the distances in which

ohtaincd by differentiating equation thermal X rays from a nuclear explosion

(7.74. 1) with respect to wavelength and -ire absoibed ir. air, a convenient roundequating the result to zero. it is !hen nuurber temperalure of 107 d,&grees

found that Kelvin will be used for simplicity. From

S- 7.77.1 equation (7.77. :), the wavelength at

"T '7which the rate of emission of radiaticn

&
308 THERMAL RADIATION AND ITS EFFECTS

from a black body at this temperature is hence at 155,000 feet (approximately 30

a maximum is found to be 2.9 A. Ac- miles), for example, the density is about

cording to equaLion ( 1.74.2) this corre- 10 of the sea-level value. The mean

sponds to a photon energy of 4.3 keV. free path of the photon varies inversely

and from equation (7.79 i) the mean as the density, so that for nuclear exfree patrr of these photons in normal air plesions at an altitude of about 30 miles,

is about 15 cm. In traversing a distance the region of the air heated by X rays,

of one mean free path the energy of the which is equivalent to the fireball, e:-

radiiations decreases by a factoi" of e, tends over a radius ot sonie thousands of

i.e., approximately 2.7, hence 90 per- feet. In spite of the lower density, the

cent ot the energy will be deposited mass of heated air in this large volume is

within a radius of 2'.3 mean free paths. It much greater than in the fireball assois seen, therefore, that 4.3-keV radia- ciated with a nuclear explosion a" lower

tion will be largely absorbed in a dis- altiIuIes, and so the temperature attance of about 35 ni, i.e., a little over I tained by the air is lower.

foot, in a sea-level atmosphere.

7.80 The primay thermal radia- THERMAL POWER AND ENERGY

tioris from a nuclear explosion cove1s a FROM THE FIREBALl.

, ide range of wave;engths, as i:. evident 7.82 According to the Stefanirom Fig. 7.74. B0t to obtain -. rough

indication of thre initial si",c ot the fire- Boltzmann law, the toal amount of enhall, the wavelength (or energy) at ergy (o. all wavelengths), J, radiated per

which the radiant power forr, a b-.1Ck square centimeter per second by a black

body is a maximum may be taker~ as body in all directions in one hemisphere

typical. !t foi!-;w.vs, therefore, from the is related to the absolute temperature, T,

results given ahove that :I'e therma! X by the equation

rays from a nuclear explosion will 'e J = (rTP, (7.82.1)

ahi~ost completely absorb0 !y abaut a wihere (Y is the Stefan-Boltzmann confoot of i;r at rormal den~sity. The ox- stant. The value of J can 'lso be ohygen and nitrobt,-. in the air in the vi- taied by integration of -quation

cinity of he explosicn arc coiisiderably (7.74 i) over all wavelengths from zero

ionized, and the ions do not absorb as t7.74 ov I t ao e n n th at

eirectively as do neutral molecules.

Ncvertheless, in a nuclear explosion in (T = 27rrk4/15h c'

the at,-'osphere where the air density = 5.67x 10 'erg cm 2sec 'deg 4

does •iot differ greatly from thL sea-level = 1.36 × 10 '-2 cal cm-2 sec'i

,alue, most of the X rtys, which con- deg 4.

stitute the primary thermdl radiation,

will be absorbed wilhin a few feet of the With o known, the total radiant energy

explosion. It is in this manner that the intensity from the fireball behaving as a

initial fireball is formed in an air burst. black body can be readily calculated for

7.81 With increasing altitude, (he any required temperature.

air density decreaseý; roug,!y by a factor 7.83 In accordance with the definiof ten for every 10 miles (see § 10. 124); tion of J, given above, it follows that the
TECHNICAl. ASPECTS OF THERMAL RADIATION 309

total rate )f emi:ssion of radiant energy purposcs this may be taken as th..' C,

from thL. fireball can be obtained upon plosioa time.

multiplying the expression in equation

(7.82. 1) by the area. If R is the radius of TH-RMAL EN[ERGY IRoM AN AIR

the fireball, its area is 41TR2. s-, that the BUIRST

total rate of thermal energy emission (or

total radiant power) is (rT4 )e 4.n.R2. 7.85 In order to make the power

Representing this quantity by the symi- time curve specific for any particular

bol P, it follows that explosion energy yield, it is necessary to

know the appropriate values of P and

P -- 47rr¢rT1&fm t . Theoretically. these quantities

=- 1.71 X 0 l1 T4R2 cal/sec, should depend on the air density, but

experimental evidence indicates that the

where Tis in legrecs Kelvin and R is in dependence is small for air bursts at

centimeter,;. Aliernatively. if the radius, altitudes below 15,00) feet, in this altiR. is expressed in fect, then tude range. P,,, and t are related

approximately to the yield, W kilotons.

P = 1.59 x 10 1 T4R2 calisec. in *• following manner!

(7.83. )

P. 3.18 W1 1' kilotans'sec

7.84 Complex interactions ot hy- i 0,04i7 W, 4 -sec.

drodynamic and radiation faca ors govern "M"X

the variation of the apparent size and For heights of burst above 15,0()0 ;feet

temperature of the fireball with time. the data are sparse. Theoretical calculaNevertheless, the fireball thermal rower tions indicate that the ,-orrespoding recan be calculated as a function of time lationships are as follows:

based upon theoretical considerations

modified by experimental measure- 3.56 W" 5 kilotons/sec.

ments. The results ar. conveniently ex- "'n [p(h)/p]O 45

pressed as the scaled power, i.e., PP

versus the scaled time, i.e., t/tmu,; P is t,•= 0.038 Wh44jp(h)/ 0

)jI I,' sec.

the thermal power at any time t after the

explosion, and the P is the maximum In these expressions p(h) is the ambient

value of the thermal power at the time, air density at the burst aititude and p,, is

t n,, of the second temperature maxi- the normal ambient air density at sea

mum (§ 2.125). The resulting (left level (taken !o be 1.225 x 10

,:cale) curve, shown in Fig. 7.84, is then gram/cmi). Values of p(h)/p1, are given

of general applicability 'irrespective of in Ta''. 85 ,fr .- -dtl . "

the yield of 1he explosion. Changes in of the preceding equations resalts ir a

yield and altitude can affect the shape of discontinuity at 15,000 feet. For heights

the power pulse; however, the values in of burst at or near that altitude, values

Fig. 7.84 are reasonably accurate for should be calculatcd by both sets of

most air bursts below 100,000 feet. The equations, and the appropriate result

zero of the ,caled time axis is the time of should be used depending on whether

the first maximum, but for all practical offensive or defensive conservatism is

(Text continued on page 3"•3.)

a .-.. r.w- . .--
310 THERMAL RADIATION AND ITS EFFECTS

The curves in Fig. 7.84 show the Example

variation with the scaled time, tr/tm, of

the scaled hreb-,l power, P/P (left Gieen: A 500 KT burst at 5,000 feet max altitude ordinate) and of 'he percent of the total Finde

thermal energy emitted, EIE,,,, (righ( Find: r.(ate (a) The of emission of

ordinate), in the thermal pulse of an air thermal energy, (b) the total amount of

burst. thermal energy emitted, at I second

Scaling. In order to apply the 'ata after th- exl:'osio,1.

in Fig. 7.84 to an explosion of any Solution: Since the explosion is

yield. W ki!otons, the following ex- b ow =5 0.,0 5eet.

pressitns are used for bursts below tMa= 0.0417 x (500)44 -0.64

15,000 feet: sec, and the normalized time at I sec

after the explosion !s

P 3 . 1 '6' W O k ilo to n s! /,e c t I

(i.0417 W!'-4 sec. tmax 0.64

For bursts above 15,0(, feet, the fol- (a) From Fig. 7.S4, the value of PIP

lowing expressions are used: at this scaled timc is 0.59, and since

3.56 W'S P 3.18 X (500)1156 = 103 kilop - kilotons/sec. I"" f ( h)/Ip ]" 4 tons/sec, o ss

it follows that t = 0.038 W,•*LI)~h)/P,] s.

P = 0.59 x 103 = 60.8 kilotons/sec "In aill c as es F = = 60.8 x 10 12 cal/sec. A nswer.

1,; these expressions th i. the rtime (b) For a yield of 500 KT and a burst

after the exp!o~on for the temperature altitude of 5,000 feet, f (. - ,,/I IV) is

maximum in -he second thermal pulse, found from Table 7.98 o be about 0.35;

P is the maximum rate (at t,) of hence,

emission of ther-nal energy from the

fireball, E,,,, is the iotal thermal energy E(, = 500 x 0.35 = 175 kilotons.

emitted by the ffir&iail, f is 'h ! thermal At the scaled time of 1.56, the value of

partition (Table 7 .

8e8), and p(h)/p, is BE,,,, from Fig. 7.84 is 40 percent, i.e.,

ratio of the ambient air density at bai) st 0.40, so that

altitude to that at sea !evel ('Fable 7.85).

E = 0.40 x 175 = 70 kilotons

= 70 X 1012 cal. Answer.

Reliability: For bursts below

15,000 feet, the data in Table 7.88 to- .

gether with the curves in Fig. 7.84 are

accurate to within about J 25 percent.

For bursts between 15,000 and 100,000

feet, the accuiacy is probably within ±

5C percent. Explosions above 100,000

feet are described in § 7.89 et seq.

!I
TECHINICAL ASPECTS OF THERMAL RADIATION 311

0 (iN3083d) 031i1V43 A983N]3 1VV¶J3Hi

o 0 0 0 0

- N 0

E

CD E E

LhJ

__I - - ! -- CL)

w *

/00, cl N

LL

C?~~' W ~ __ - c; 

Xou'Y__' H3r~ NOIlVY
312 THERMAL RAD;ATION AND ITS EFFECTS

Table 7.85

ATMOSPHERIC DFNSITY RATIOS

Altitude Ratio, Altitude Ratio.

dle t ) p( h) p, (feet) pt h)),,

IS (M0) 03 00.(10) () t195

20.00) 0.53 h5.(XX) 0.075

25,(MN) 0.45 70).(XX) (1 ()5)

30.0(M) 0.37 75.(XM) 0,046

35 (MN) (). 31 O.(MM) 0036

40,0(X) (024 95,(MM) 0.02S

45.N(X) 0 19 Q0,0WM) 0.022

50,(0X) 0.15 ,)0A.0M) 0.017

55,0X) 0 12 I0, .H X) 0.014

desired. For a contact surface burst versus It, up to tha time. The resuts.

(§ 2.127 footnote) the fireball develops exprcsed as EIE,,,, (percent) versus

in a manner approaching that for an air t/t,,. are shown by the second curve

burst of twice the yiel6, because the (right scale) in Fig. 7.84, where E,, is

blast wave energy is reflected back from the total thermal energy emitted by the

the surface into the fireball (§ 3.34). fireball. It is seen that at a time equal to

Hence, t,, may be expc,'ted to be larger 10 t ... about 80 percent of the thermal

than for an air burst of the same actual energy will have been emitted: bemceyield. this tim" may he taken as a rough mea

7.86 The thermal power curve in sure oi the effective du,ation of thI

Fig. 7.8,4 (k-f' scale) presents some fea- thermal puls,e for an air burst. Since f,,,,,,

tures of special interest. As is to be incre.sas with the explosion energy

expected, the thermal powei (or rate of yiel,', so also does the pulse length.

ermissioi, of radiant energy) of the fire 7.87 The fact that the thermal pulse

ball rises to a maximum, just as does the length iacreases with the wcap(ýn yield

teinpeiature in the second radiation has a bearing on the pos:,ibility of peopulse. However, since the thermal ple taking evasive action aga'nst the,,mal

power is roqghly proportional to T4, it radiation. Evasive action is expected to

increases and decreases much more have greater relative effectiveness for

rapidly than does the temperature. This explosions of higher than lower yield

accounts for the sharp Ilse to the max- because of the longer thermal pulse duimnum in the P/P, curve, followed by a ration. The situatior, is indicated in ansomewhat less sharp drop which tapers other way in Fig. 7.87, which shows the

off as the fireball approaches its final thermal energy emission as a function of

stages. The amount of thermal energy, actual time, rather than of// , for four

E, emitteu by the fireball in an air burst different explosion energy yields. The

up to any specified time can be obtained dala were derived from the ,'orrespondfrom the area under the curve of PIP,,,,, ing curve in Fig. 7.84 by using the

qI
TECHNICAL ASPECTS OF THERMAL RA.DIATION 313

appropriate calculated value of t for by the symbol f. Estimated values of f

each yield. At the lower energy yields are given in Table 7.88 for air bursts

the tl-ermal radiation is emitted in such a with yields in the range from I kiloton

short time that no evasive action is pos- to 10 megatons at altitudes up to

sible. At the higher yields, however. 100,000 feet (19 miles). The data for

exposure to much of the thermal racia- heights of burst up to 15,000 feet were

tion could be avoided if evasive action obtained primarily from experimental

were takeL within a fraction ot v, second results. For higher bursts atitudes, the

of the explosion tim'?. It must be re- values were obtained by calculations.

membered, of ,t arse, that even during various aspects of which were checked

this short period a very considerable with experimental results. They are

amount of thcrrval energy will have con:;idercd to be fairly reliable for yields

been emitted from an explosion of high I .tween ! kiloton and I megaton :.t

yield. altitudes up to 50,000 feet (9.5 tmiles)

Outside this range of yields .- d alti7.88 The fraction of the explosion tudes, the data in Table 7.88 may be

energy yield in the form of thermal used with less confidence. Values of f

radiation, i.e., E,,/,i', is called the for burst altitudes above 100,(X) feet

"thernkal partition" and is represented are given in § 7.90 (see also K 7.104).

Table 7.8h

I1HERNAI, PARTITrON FOR VAR;(O)S EXPLOSION YIEILI)S AT IVI'FERENT

AI.TITUI)ES

Hllight of 'l'o1al Y'lId (kilolo o)

Burst

(kih lI))) 10 1()W I .(mX) I(0,(H)

UP to 15 t0' 5 ' Ii ) 5 0 ;5 0. ;S 0) 15

2') (0.35 (0 ,6 (I '0 1() .41 (0 413

30 0.35 0. 3,6 0 it) 041 0,41

40) 1)35 0 16 0 is 0.40) 0 4-1

50 (0 35 03 6 01.38 (.40 0.42

60 0.35 0 17 0 Is 0 40 ) 42

71) 0) 36 0.37 0, IQ) ()41) 0.42

80 0 ;7 0 18 () 0 ') 0 41 0 43

910 0.39 0 W9 01.41 0) 1 1 4.43

1I8) 0 401 0 .0(1 0 41 1) 42 0 15
314 IHI-RMAI RADIATION AND) I.', SI!,"--S(I,

KT )O KT MT

i 1 

(I

9 i

TIME SE CONDS)'•

Figure 7.91. Percentage of therm~al energy emitted as a function of t"ime for air bursts of

various yields.

THERMAL RADIAlI ION IN rain~mum (§§ 2.39, 2. 125), to increase

HIGH-AL.TITUDE EXPL.OSIONS andi for the minimum to be less marked.

Up to an altitude (of about 100,000 ,feet,

7.89 Th~e re:;uits described above these changes are small and so also are

are appl~caH.q to. detonations at altitudes those in the second themfial pulse. The

below about 100,000 feet (19 miles) normalized plot (Fig. 7.84) is thus ai

where the density of the air i:• sti!! ap- satisfactory representation in this altipreciable. At higher altitudes, the fire- tude range. However, betwt"en 100,O000

ball phenomena change, as described in and 130,000 feet (2.5 miies), the pulse

Chapter UI, and so also do the thermal .shape changes drastically. The first

pulse characteristics, such, as shape and minimum observed at lower altitudes

length, and th~e thermal partition. With disappears and essentially all the therincreasing altitude, t~here is a tendency meal radiation is emitted as a single pulse

for the relati, e duration of the first (§ 2. 132). The thermdlemission rises to

pulse. i.e., up to the first temperature a maximum in ai extremely sbort time

I/
IIt IINI• \1 %SiI( I1 S0W I [iI RNII R\1IRI\Ml\I ", 315

and then declines steadily, at first rap- roughly 260,000 feet (49, miles). At still

idly and later more slowly. For an ex- higher altitudes there is a :hange in the

plosion in the megaton range at an alti- firebal! behavior (§ 2. 135) and the thertude of 250,000 feet (about .47 mtes), mal partition decreases very rapidly

the duration of the thermal pulse is less with increasing altitude of the explothan a second compared with a few sion.

seconds for a similar burst below 7.91 At heights of burst abovt

I00,00() feet (cf. Fig. 7.87). Scaling ot about 270,(00 feet. only the primary X

the pulse length with respect to the ex- rays traveling downward are absorbed

plosion yield at high altitudes is very and the energy depositiot. leads to the

complex and depends on a variety of fownation of the incandescent X-ray

factors. However, the duration of the pancake described it, 'hapter II. Ths

thermal pulse is probably not strongly heated region then reradiates i's energy

dependent on the total yield. At altiiudes at longer wavelengths over a oeriod of

above roughly 270,90W feet (51 miles), several seconds. The altitude and dithe pulse length increases because of the mensions of the pancake depend to

larger mas;s and lower temperature of some extent on the explosion yield btul,

the radiating region (§ 7.91). as stated in § 2.134, reasonable average

7.90 At high altitudes shock waves values a'e 30,000 feet for tre thickness,

form much less readily in the thinner air 270,000 feet for the mean altitude, and

and consequently th. firehall is able to the height of burst minus 270,000 feet

radiate thermal e:.ergy that would, at for the radius at this altitude. The alti1,'wer altitudes, have been transformed tude and thickness of the reradiating

to hydrodynamic ert'rgy of the blast region are essentially independent of the

wave. Furtheimore, the thinner air height of burst above 270,000 feet, but

allows the primary thermal radiation (X the mean radius increases with the burst

rays) from the explosioi to travel much height. The shape of the region thus

farther than at lower leve!s. Some of this approaches a thick disk (or frustum)

radiation travels so far from the source centered at about 270.000 feet altitude.

that it makes no contribution to the en- 7.92 Not more than one-fourth of

ergy in the fireball. Between about the X-ray energy from the explosion -s

100,000 and 160,000 feet (30 miles), absorbed in the low-density air of the

the first factor is dominant and the pro- reradiating region, and only a small

portion of energy in the blast wave de- fraction, which decreases with increas.

creases; consequently, the thermal en- ing height of burst, is reradiated as secergy increases. In this altitude range the ondary radiation. Consequently, only a

thermal partition, f, is about 0.6, comn- few percent of •he weapon energy is

pared with 0.40 to 0.45 at 100,000 feet emitted as thermal radiation capable of

(Table 7.88). Above 160,000 feet, causing damage at the earth's surface.

however, !he second factor, i.e., escape In fact, for bursts at altitudes exceeding

of thermal ( rays, becomes increasingly some 330,000 feet (63 miles), the therimportant; the thtrmal partition de- mal radiation from a nuclear explosion

creases to about 0.25 at 200,000 feet (38 even in the megaton range is essentially

miles) and remains at this value up to ineffective so far as skin burns, ignition,

I _.
316 THERMAl. RADIA';ON ..\NI) i FFFF-•"IS

etc. . arc :;oncerned. However, the very short puls,- of thermal energy that

early-time debris, which separates from can cause eye injury to individuals

the X-ray pancake (§ 2.135), is at a looking directly at the explosion

fairly high temperature and it emits a (§ 32.79 et seq.).

RADIANT EXPOSURE-DISTANCE RELATIONSHIPS

AIR BURSTS the energy received per unit area normal

to the direction of propagation, at a

7.93 The following procedure i,; distance D from the explosion, it folused to calculate the dependence of the lows that

radiant exposure of a target (§ 7.35) E

upon its distance from an air burst of Q 7 -- 4,r l. e (7.94.1)

specified yield. As seen earlier in this

chapter, such infoimation, which is 7.95 When scattering of the radiagiven in Fig. 7.42, combined with the tion occurs, in addition to absorption,

data in Tables 7.35 and 7.40, permits the coefficient K changes with distance

estimates to be made of the probable and other variables. The simple exporanges for various thermal radiation ef- nential attenuation factor in e4uation

fects. (7.94.1) is then no longer adequate. A

7.94 If there is no atmospheric at- more useful (empirical) formulation is

tenuation, then at a distaice D from the

explosion the thermal radiation energy, Q = E , (7.95.1)

E,,, may be regarded a, being spread 4-rrD1Y2

uniformly over the surface of a Fpt;.ere of

area 4,rr/Y. If the rad;ating fireball is where the transmittance, T, i.e., the

ateated as a point scurce, the energy fraction of the radiation (direct and

received per unit area of the sphert, s,.attered) which, is transmitted, i,; a

would be E,,,,/4irr-2. If attenuation were complex function of the visibility (scatdue only to absorption in a uniform terina), zb.,orption, and distance.5

atmosphere, e.g., for a. air burst, this 7.96 Since E,,,, = fW, equation

quantity would be multiplied by the (7.95. 1) for the radiant exposure from

factor e -D, where K is at, ,bso;ption an air burst of yield Wean be expressed

coefficient averaged over the whole as

snectrum of wav,.lengths. Hence in

these circumstances, using the symbol fWr*

Qto Q iD (7.96.1) rcpreseot the radian: exposure, i.e., = ,D- 79.

'Scattemed radiption does not caise permanent danage to the retina of the cyc. Hence, to determine the

effective radiant exosure in this connection equation (7.94. I ) should be used; iý is about ('.03 km I for a

.!sibility of 80 km (50 miles), 0.1 km , for 4G 'ir, (25 ni:es) and 0.2 km ý for 20 km (12.4 miles).

Scattered radiation can. hov ever, contribute to dashblindness, resulting from the dazzling effect of bright

;ight (§ 12.83).
'RI'lAN ! I-POX(L";IJRI--I)IS IAN(! iR I *\JI1)NSIIPIIS 3 17

By utili/; ng the fact that I kiloton ol radiation from the source. "lransmit -

TNT is equivalent to 10' calories, tance data for these conditions are preequ;lion (7.96. 1) for an air burst be- ,,ented in Fig. 7Q.X in t;:rnis of burst

comc'• allitude a'ud distanct, ,I' a surface target

from ground zero for a cloudhless at0 (cal/cm "2) _ - /WT (7.9g•.1) mosphere with a visihilitN of 12 nile.,. 4 •ID- Since actual visibilities in cities are

often less, the values in Fig. 7..99 are

where D is in cenitimeters and W, is tn conservative.

kilotons. If the distance. D, from the

explosion to rane, the s target. epresedinki~fee i.e.. ormilsFig. the slant 7.99 7.98 Th wc.,e I tsmitta use'd, in conjunct ncie ionn

range, is expressed in kilofeet or mIles, with equation (7.96.4) and the thermal

equation (7.96.2) reduces approxi- partitions fromii 'e.88. to obtain the

niatly todata from which the curves in Fig. 7.42

"D in kilofeet: Q (cal,'crn2) iie 6 (, fWT' were ,constructedL If H is the height of

D' burst and d is (he dista'ce from ground

(7.90.3) ,.ero of a given point on 'he surface, the

"D in miles: () (cal/cm2) 3.07 fWT. corresponding slant range for use in

DI equation (7.96.4) is D - (d' + h'-). A

(7,96.4) height of burst of 200( W" 4 feeb, with W

7.97 In nuclear weapons tsts, it Is in kilotons, was used for the cahkula-.

possible to measure Q and W, and tions, but the resuiis in Fig. 7.42 are since raoal cu t o i ussa n reasonably accuiate for air bursts at ,m:y

,he distance D from the explosion is altitude up to some 15,M(X) feet.

known the magnitude of the product JT

can be determined from the equations in 7.100 Linder unusual conditions

§ 7.96. Ht-nce, to obtain " and T indi- and especially for cities at high-altitude

vidually, one of these two quantities locations, the visibiiity might be greater

must be determined independently of than at sea level and the transmiatance

the oiher. The method 'ised is to obtain f would be larger than the values given in

for different conditions from calcula- Fig. 7.98. The curves show that mo-t

tions checked by observations, as stated attenuation of radiation occur!; within a

in § 7.88. The values ot T are then few thousand feet of th-z surface, thus,

derived from nieasuremerns of f-r made the much clearer ai- at higher altitudes

at a large number of weapons tests. has less effect. For bursts above about

"7_9R The tranqmittarpco -r fnr ,nv 15000M feet (09 miles). the transmitg!vern atmospheric ondition depe;ids cn tance changes slowly with the altitude.

the solid angle over which scatteied ra- Experimental data indicate that multidiation can reach a particular exposed plying the transmittance by 1.5 corrects

object. For the present purpose it will be approximately for the effect of reflection

assumed that the target is such, e.g., an from a cloLd layer o-er *he Durst. The

appreciable flat area, that scattered radi- same correction may be made for a

ation is received from all directions snow-covered ground surface. If the

above, in addition to the direct thermal burst and target are both between a

~ - -. -. I
318 THERMAL RADIATION AND ITS EFFECTS

0 w t1.oo

N II

0

crrC

LjJ

z v

77I> :u

C) C

0 0 00

(.L33.d0lI)4) lSdWMl jO J.H913H
RADIANT EXPOSURE-DISIANTE REVATIONSHIPS 319

cloud layer and a snow covered surface. Based upon experir.rintl data, contact

the correction is 1.5 x 1.5 = 2.25. surface bursts can be represented fairly

well by a , effective thermal partition of

SURFACE BURSTS 0.18. Values ol' the thetmal partition for

other surface bursts are shown in Table

'7.101 For a surface burst, (he radi- 7.10j; they have been derived by asant exposures along the earth'.i ,•*rface signing a thermal partition of 0.18 to a

will be less than for equal distances contact surface burst and interpolating

f:om an air burst of the same total yield. between that value ard the air burst

This difference arises Q?,tiy, a. Itdt- thermal partition values in Table 7,88.

cated in § 7.20, from the decreased

transmittance of the intervening low air VERY- HIGH-ALYtTUDE BURSTS

layer due to dust and water vapor produced by the explosion. Furthermore, 7.102 In the calculation of the therthe normal atmosphere close to the mal radiation exposure at the surface of

.arth's surface transmits less than at the earth from very-high-altitude uuhigher aititudes. In order to uiliie the car explosions, two altitude regions

r ,uations in § 7.96 to determine radiant must be considered because of the

v, ,osure for surface bursts, the concept change in the fireball behavior that

o. in "effective thermal partition" is occurs at a!tiudes in the vicinity of

used, together with the normal !trans- about 270,0!,"i fcet (§ 7.9!). At burst

mitance, such as given in Fig. 7.9,1;, for heights from roughly 160,000 to

the existing atmospheric conditions. 200.000 feet (30 to 38 mile,;), the therTOble 7. ! 31

EFFECTIVE THERMAL, PARTITIGN FOR SURFACE IURSTS

Thermal Partition

Height of Total Yield (kilotons)

1, u r N I. .. .. . .. ....-

(feet) I 1) 1(iX) I .0(MO

20 0i 114 *' 40 0.21 .1.*

70 0.21 t).021. * *

I(M 0 26 0.12 0. 2 0

2MX 0.35 0.25 0,21 0,:9*

4() 0.3 0.25 0. W *1 I Q

7 0 28 0.24 0.21

I ('M ) *0 ).34 0.26 0.22

2.0(X) *0* ** **4 0.20

4.0(H) ** ** *3 ** 0)33

7.0(X) ** *. 0** 035

*These may he treated as contact surface burts., with f 0.18.

**Air ihursis: for values of f see Trahle 7.88
,20 ~THERMANL l(ADIATION AND ITS FFF.F('IS

mat energy capable of causing damage with the rned'Jar' radius at 6n altitude cf

at the surface of the earth drops shiarp'ly 27'0.,(}W feet-, this is indicated] hy the

from about 60 percent to ahout 25 per- point S in Fig. 7.103. Hence, for the

cent, i.e., f-om f= 0 60 t.of= 0.25. As ta-&et point X, the appraptiate slant

the height of huwst is increased above rarige is gwven approximately by

200,0W0 feet, the thermal partition remains about 0.25 up to a height of burst D (kilofect)

of appiox-mately 260,000 feet (49

mileýs). Since a ni,,ary sphe-ical frhl (7) H 20 I

forms hithir this latter altitude regior.,

eqL ation (7.93.3) becomecs (7 103.0)

Q (cal/cm 2) = ' D2 4W (7. 102.1I) with (d and 1i in kilofeet. This expr.-sD2 sior nolds evcn when d is greater than

111!- 270), althoug~h fth qwu'ntity in

where D is the slant ranpac in kilofetet, the square brackets is then negative, the

and W is the 3yiek( in kiloions. A linear square is P-)sitive. The_ slant -

Tange. Q,~

interpolation of the variation of thermal tor girkuud zero is obtaiined by setting d

partition .-ith burst altitude may b% pcr- in elluation (7 103. 1 ) eqlual to Zero:

formed for bursts between 160,000) feet thus,

and 260,.000 feel, however, in view of

the uncertainlces in high-altitude burst D.) (1kihofce0t-=(270)'± 11( t 270)?;I 1

phenomenology, it ma-' be desirable to

us,, the high (0.60) or 'he low (0.25) If the distance d is greater than the

valutt throughout this hurst altitude re- height of burst, the equivalent point

&ion, depending or. the u.gree of con- source may he taken to be approxiservelism desired. r'iately at the center of the radiaiting disk

7..03 At bur-. altitudes of ioughly at 271),00 feet altitude, then

270,000 fec, and above, the thermai D(ilet)-[27)±(21

radj'ation is emitted from the thick X-ray D(ioet ý1202+t2

pancake at a rnean altitude of about 7.104 For the heights of r- 's undfer

270,000 feet, eys,,ni i~i:' inaecipedent of consideration, it is. assumeoa *&' the

the Yawt ;ia of burst (§ 7.91 > In fraction 6.8 of the total yield is emitted

order to use the equation;ý in § 7.96 to as X-ray energy and that 0.25 oi this

calcula'- Wradiant exposures at various cnergy is absorbed in the radiating disk

ý.;stances from the burst, the approxi- revior.. Hence, (1.8 x 0.25 = 0.2 of

mation is mrade of replacing the disklike the te'al yield is~ -bsu~rbed. Fer caiculatradiating region by an equi'valent souitee ing the radiant e::posure, the totai yield

point defined in the following manner. If W in the eq'ý.-uois, in § 7.96 is c-;nsethe distance d from ground zero to thetý quently replaced by 0.2W. Furthertarget positirn where Q is to ve calcu- miore, the equive4 '-nt of the thermal parlated is less thin t4,- height of burst, H, tition is ca!:-d the 't!herm.al

the source may be regarded as beir~g efficiency," - j, defined as the effective

located at the closes! point on a circle fraction of the absorbed energy that iss
RADIANT EXPOSURE--!SIANCE RELATIONSHIPS 322

A BURST PON 7.105 With the information given

above, it is possible to utilize the equatons in § 7.9( to calculate the approxI /- 270 imate radiant exposvre. Q. for points on

the earth's surface at a given distance.

2701SfH- id, from ground zero. for a prescribed

PADIATING REGION height of burst, - for explosions of ________SMIDDLE 0' hegtfr ""''

essentially all burst altitudes. If dand H

are specified, the appropriate slant ,ange

can be dctermnined. Tables 7.88 and

I 7 101 and Fig. 7.104 are used to obtain

the requite-i tnermal partition or thermal

,, efficiency, and the transmittance can bt

o estimated from Fig. 7.(8 for the known

d and H. Suppose, however, it is requircd to reverse the calculations and to

SuRFACIL 1 ., find the slan! range to a :;urface target (or

GF thtt corres.ponding distance frot ground

Fludivaln radiwý %n height~r ~ zero for a specified height of burs;t) at

nmedianl radio,,s •he i he ighi

of hur,!t exceed,, dktanc (if which L particular value ot Q will be

the taryt. V. frorii grouind attained. The situation is then much

":cH more difficult becausc r can he estireradiated. F-cnce equation (7.96.3), for mated only when the sak-ri raire Or

example, becomes distance from ground zero i.; kmrown.

17. 1 ~One appioach would be to prepare CigQ (ca .12-&) D-2 ures ;ike Fig. 7.42 for scvenra heights ot

bunt- an J to interpolate among them for

where D iii kilof.!et is determined in aay other 1'wrst height. Another possiaccordancc with the conditions de. bility is to make use of nit ir,:eration

scribed in the preceding paragraph. The' procedure by guessing a value of T,

values ot F given in Fig. 7 104 as a eg., - = I, to determine a first apfunction of height of burst and yield proxirnation to D. With tiis value of D

wire obtained by theoretical calcula- anid the known height of burst, an irn-

'tons.', fne transmittance may be esti- proved estimate Of T car' be obtained

mai.d from Fig. 7.98 but no serious from Fig. 7.98. This is then utilized io

e:10r woud be tiovolved by setting it derive a beIkU app-oxinmatiwn to D, and

equal to unity for the large burst heights so on iintil cenw.'r~gence is attained.

involved.

"The caiulalions at.: aciu:flIy for I., fraction o' the ansorbed X-ray energy reradiated within I0

se,.otids; for estimating ,:fect: on :he grojud, the suhsequent rc'-diation car he ncgle,'tcd.
3 22 FHF RMAI RADLNTA ON ANDI ITS FFFF- U- S

2-~

-o

0~ 0 v~I 1 c. 

(13z_114 isin J- 1HO13H
RAD)IAN-[ ',XPCSURE-DISTAN(CE RFt ATIONSHIPS 323

BIBLIOGRAPHY

*B Ri , H. A., eI al . "Bla, Wave,'' U.niver- sponsc of Miaterials.- Office of Ci'. iiIefens.'

~iof California, I m, AlanmosScijentific I.abo- and Mobilization, 1 957. WT II 9X

ratory. March 1958. LA -2NX). NtiSRi I S. B . '"The Role of Fire in Nuclear

11,t~ I_. L..*"eview of Nuclear Weapons Warfare, An InterpretIative Review of the CuriEffects - At-~ 1i'i'. Nuclear Sci. 18. rent Technology for Evaluating the Incendiary

I 53( 1969). Consequences of the Strategic and Tactical

CII AND It F C'. C.. el al- "Predicticn oif Fire I 'ws of No~lear Weapon%;, U RS Rcsearch

Srire.'d Following Nuclear Explosions." Pacific Co ., S~an Matco. California. August 1974,

Solithwi-st Forest and Range Experiment Sta- DNA 2091F.

lion. Berkeley. California, 1963. 11 S. Forest Mtt)ft t.ioN. W, E.. ~Vis'on Through the AtSer-vice Paper PSW-5. niosphere." University of Toronto Press, 1 958

(InttONS, M.rC_"ransniissivity of the Atmos- P.Nsstii . T. 0., and R. 1. Mtt I i:R. 'Radiative

phere for rhermal Radiation from Nuclear Transfer from Nuclear D~etonationis Above

Weapons.' U.S. Naval Radiological L;,hora 50-Kmn Altitude.-' Fire Research Abst~ract, and

tory. Auaust 1966, U;SNRDL TR 1060. Reviews,s 6, 99 ( 144), National Acadcmyý i)f

G041A I.T., "Effects of Air Blast on Urhan Sciences-National Research Council.

Fires.'" URS Res~arch Co.. Blirlingarne. Cali- *RANt)AI I. P. A.. "Dar-ras 'c to Conventional

fiirnia. December 1970, OCI) Work Unit and Special Types of Residences Eyposed to

25341. Nuclear Effects,'' Office of Civil Defense arid

"(hi ss, A. W., arid R, M. CItIv'MAN, 'RC- Mobilization, March 1961, WT-I 194.

flection of Point Source Radiation Itom a ILani- *VIS1tKAN Is. R.. "Heat Transfer in Thermal

her' Plane onto a Plane Receiver,' Air Force Radiation Absorbing and Scattering Material,'

Cambridge Research Center, TR-5'/.253, [.i Argonne National Laboratory. May 1960, ANi.

hiary Of Congress. Washing'ora. I.C., 1957. 6170.

**HARt)V, J D., "Studies on Thermal Radia- WILRSMA, S. J._ and S. B. M-sttIIN, ''Evaluation,'' Cornell University Medical College. PB tion ot the Nuclear r,.Threat it, Urban,

1 54--803, Library of Congress. Washington. Areas.'' Slariford Research histitwte, Menlo

D).C., 1952. Park. California. September 1973. SRI IIYU

*I.At,(1ti IN. K. P.. ''Therma; Ignititon and Re- 110St

Tliese do~urnenis miay be pun..Iascd fioiri[lie N-'atioiii TLct;nical Information Scrvice. Dcpartrocrit of

Commerce. Springfield, Virginia. 22161.

"*These documents may be obiaized from the Lihrary of Congress. Washington. D.C. 20402.
CHAPTER VII1

INITIAL NUCLEAR RADIATION

NATURE OF NUCLEAR RADIATIONS

NEUTRONS AND GAMMA RAYS rics. namely, initial and residual

(§ 1.02). The line of demarcation is

8.01 As stated in Chaptcr I, one of somewhat arbitrary, but it may be taken

the special features of a nuclear explo- as about I minute after the explosion,

sion is the emission of nuclear radia- for the reasons given in § 2.43, The

tions These radiations, which are quite initial nuclear radiation, with -,hich the

different from the thermal radiation dis- presen' chapter will ibc concerned, concussed in the preceding chapter, consist sequently refers to the radiution emitted

of gamma rays, neutrons, beta particles, within I minute of the detonation. For

and a small proportion of aloha part;- underground or underwater explosioi.s.

cles. Most of the neulrons and part of it is less meaningful to separate the

the gamma rays are emitted in the fig- initial from the residuai nuclear radiasion and fusion reactions, i.e., simul- tion (§ 2.82, 2. '"-), although the distaneously with the explosion. The re- tinction may be made if desired.

mainder of the gamma rays are 8.03 The ranges of alpha and beti,

produced in various secondary nuclear particles are comparatively short and

processes, including deciy of the fission they camiot reach the surface ,)f the

products. The beta particles are also earth from an air burst. Even when the

emitted as the fission products decay. fireball touches the ground, the alpha

Some of the alpha particles resu!t i•om and beta particles are not very importhe normal radioactive decay of the nra- tant. The initial nuclear radiation may

nium or plutonium which has escaped thus be regarded as consisting only of

fission in the weapon, and others (he- the gamma rvys and r, xutrons produced

lium naclei), are formed in lusion reac- during a period of I minute after the

tions (§ 1.69). nuclear expiosion. Both of these nuclea,

8.9J2 Because of the nature of 'he radiations, although different in characphenomena associated with a nuclear ter, can ti-avel considerable distances

explosion, either in the air or near the through the air. Further, both gamma

surface, it is convenient, for practical rays and neutrons can produce harmful

purp-oses, to consider the nuclear radia- effects in living organisms (see Chapter

#ions as being divided into two catego- XII). It is the highly injurious nature of

324

. - - -. . . .
N ATItRL.. 01: NU(CI V.AR R. '.I)I A VIIONS 325

these nuclear rqdiations, combined witi, not !rue for gamma rays und neutrons.

their long range, that makes them such a For exampile. at a distance of I mile

'ý;-nificant aspect of nuclear explosions, from a I-mnegatrn explosion, the initial

The energy of the initial gamm" rnys nuclear radiation would probably prove

and neutrons ii only about 3 percent of fatal to a large proportion of cxposed

the total ?xplosion energy compared human beings even if surrounded by 24

with some 35 to 45 percent appearing as inches of concrete- however, a much

thermal radiation in an air burst, but the lighter shield would provide complete

nuclear radiations can cause a consider. protection from thermal radiation at the

able proportion of the casualties, Nu- same location. The problems of shieldclear radiation can also damage cert.hin ing from thermal and nuclear radiations

electronic equipment, as will be seen are thus quite distinct.

later in this chapter. 8.06 The effective injury ranges of

8.04 Most of the gamma rays ac- these two kinds of nuclear weapon radicompaning the actual fission process are ations may also differ widely. For exabsorbed by the weapon materials and plosions o! moderate and large eneig)

are thereby convertd into other forms yields, thermal ra'diation %:an have

of energy. Thus, only small proportion harmful consequences at appreLiably

(about I percent) of this gamma radia- greater distances than can the initi;,l nution succeeds in pcnetrating any dis- clear radiation. 3eyond about 1 /4 miles,

tance from the exploding weaporn. but the initial nuclear radiation from a 20-

there are several other sources of kiloton air burst, for instance, would not

gamma radiation that contribute to the cause observable injuty even without

initial nuclear radiation. Similarly, proic,:tive shielding However, Cxpomany of the neutrons produced in fis- sure to thermal radiation 6t this distance

sion and fusion reactions (§ 1.69) are could produce serious skin burns. On

reduced in energy and captured by the the other hand, when the energy of the

weapon residues or by the air through nuclear explosion is relatively small,

which they travel. Nevertheless, a suf- e.g., a few kilotons, the initial nuclear

ficient number of high-energy neutrons radiation has the greater effective range.

escape from the explosion region to 8.07 In the discussion of the

represent a significant hazard at consid- characteristics of the initial nuclear raerable distances away. diation, it is desirabhc to consider thf!

neutrons and the gamma rays sepa

COMPARISON Or NUCLEAR WEAPON rately. Although tiieir ultimate effects

RADIATIONS on living organisms are much the same,

the twe kinds of nuclear radiations differ

S.05 Although shielding from ther- in many respects. The subject of gamma

mal radiation at distances not too close rays will be considered in the section

to the point of the explosion of a nuclear which follows, and neutrons will be

weapon is a fairly simple matter, this is discussed in § 8.49 e: seq.
326 INITMAl. NUCL('l. AR IRADIATION

GAMMA RAYS

SOURCES OF GAMMA RAYS excess energy as gamma rays. This type

of interaction of a fast neutron with a

8.08 In addition to the gamma rays nucleus is called "inelastic scattering"

thai actually accompany the fission and the accompanying radiations are reprocess, contributions to the initial nu- ferred to as "inelastic scattering gamma

clear radiations are made by gamma rays.'"' The fast neutrons produced

ray-, from other sources. Of the neutrons during the fission and fusion reactions

produced in fission, some serve to sus- can undergo inelastic scaitering reacfain the fission chain rcaction, others tions with atomic nuclei in the air as

escape, and a large number are inevil- well as with nuclei of weapon materials.

ably captured by nonfissionable nuclei. 8.10 During the fission process,

Similar interactions occur for the neu- certain of the fission products and

trons produced by fusion. As a result of weapon products are formed as

nIkutron capture, the nucleus is con- ioomers.2 Some of the isomers decay

verted into a new spccies known as a initially by emitting a gamma ray. This

"compound nucleus," which is in a is generally followed by emission of a

high-,nergy (or excited) state. The ex- beta particle that may or may not be

cess energy may thetu be ermitted, almost accompanied by additional gamma rays.

insantancotusly, as gamma radiations. The initial gamma rays emitted by such

These ate called. "captuie gamma isomers may be cons.dered an indepcnrayN." because they arc' the result of thz, dent source of gamma rays. Those

capture .f a neut;on by a nucleus. The gamma rays that may be emitted subpOT~cSS is correspondingly referred to as sequently are generally considered to be

"radiative capture." part of the fission product decay.

8,09 "he interaction of weapon 8.11 Neutrons produced during the

reutron: with certain atomic nuclei pro- fission and fusion processes can undergo

vide, an,'ther source cf gamma ray:;. radiative captrtre reactions with nuclei

When a "fast" ieutron, i.e.. one hay- of nitrogen in the surrounding atmosing a large amount of kinetic energy, phere as well as with nuclei of various

collides with such a nucleusý, the ne.utron ma 'rials present in the weapon. These

ita, tr:tnsfer some (of ius energy to the reaictions wre accompanied by (seconnucleus, leaving h'.he latter in an excited daryi gamma rays which form part of

(high energy) stal,. The excited m'clcus the initial nuclear radiation. The incan ther, return to its normai energy (or teraction with nitrogen nuclei is of parground) state by the emission of the ticular importance, since somc of the

the eirltn "scautering," (cf. § 7. 10) is used hecaus'., after interacting with the nucleus, ;he tneuimon of

lower encrly gen-rally inove., off in a direction different froil that in which the original neutron waý. l.iuhriv, helore the collkision

In an iso•i r o, a particular nuclear species the nuclei are ir, a high-energy (or uxcited) slate with aii

appreciable half-life. "Jhcf isomers of interest here are those that decay rapidly, with a half-life oi about

0t1t,: housandth of awc.ttl. or less, by the emission of the extcess (or exci;atiol) encligy wi. gijllilta

radiation.
GAMMA RAYS 327

gamma rays thereby produced have very hypothetical nuclear weapon is sho, n in

high energies and are, consequently, Fig. 8.14. The energy rate is expressed

much less readily ittenuated than the in terms of million electron volts

other components of the initial gamma (§ 1.43) per second per kiloton of exradiation. plosion energy. The gamma rays ti-at

8.12 The gamma rays produced result from neutron capture in nitrogen

Airing fission and as a result of neutroij occur at late tir,,es relative to some of

interactions with weapon materials form the other sources because the probability

a pulse of extremely short duration, of capture is much greater for low-enmuch less than a microsecond (§ 154 ergy neutrons, i.e., those that have lost

fotrte). For this rea,,;on, the radiations ener,•,y by multipfle scattering reactions.

froro: these sources are known as the The dashed lines in Fig. 8. 14 show the

"'prompt" or "instantaneous" gammi. gamma-ray source as it would exist in a

rays. vacuum, e.g., from an explosion above

8.13 The fi,,sion fragments and the noimal atmosph':re. The gamma

many of their decay products are radio- rays that result from inelastic scattering

ac, ve species, i.e.. radio,lucl des of neutrons by nuclei of air atoms and

1§ 1.30), which emit gamma radiations capture in nitroger, would be absent

(se,y Chapter 1). The half-lives of these from such an explosion.

radioactive species range from a fraction 8.15 The instantaneous gamma rays

of a s,,e:orid to many years. Neverthe- and the portion of the delayed gamma

less, since the decay of the fission frag- ray ; included in the initial radiation are

ments commences at the instant of fis- produced i. nearly equal amount., but

sion and since, ini fact, ther rate of they arc by no means equal fractions of

decay is greatest at the beginninig, there the initial nuclear radiation escaping

will be an appieciable liberation of from the exploding weapon. The inganinia radiation from these radionu- stanlaricous gamma rays are produced

clides durinag the first minute after the almost entirely before the weapon has

explosion. In other words, the gamma completely blown apart. They arc,

rays emitted by the fission prodicts therefore, strongly absorbed by the

nw;:ke a significant contribution to the densc weapon material,;, and only a

initial nucl ar radiation. However, since small proportion actually emerges. The

tbc radioactive decay proLcss is a con- delayed gamma rays, on the other hano,

tinuing (or gradual) oice, spread over a are mostly enitted at a later stage in the

period of time which is long compared explosion, after the weapon matwrials

to that in which the instantaneous rad;a- have vriporized and exparijed to form a

tiot is prduced, the resulting gamma tenuous gas. These radiations thus sufradiations, together with part of the fer little or no absorption before emerpgaimma radiations that arise from initial ing into the air. The net result is that, at

isomeric decays and interactions of a distance from an air (or surface) burst,

neutrons with nuclei of the air, are re- the delayed gamma rays, together with

ferred to as "delayed" gamma tays. those produced by the radiative capture

8.14 The calculated time depcn- of neuttons by the nitrogen in th-e atdence of the gamma-ray output of a mosphere, contribute about a hundred

- . , -- 
328 INITIAL NUICI FAR RADIATION

1030

10 29 DROMPT

1028

10 27INELASTIC SCATTERING OF NEUTRONS

BY NUCLEI OF AIR I.TOMS

10 2b 

.

25

"• 1025

w ISOMERIC DECAYS

> 24

w 10

w •NEUTRON CAPYURE

10- l3 IN NITROGEN

cr 2 uz Lh 10? -- -_ - - -

z

w

i021 _

FISSION PRODUCT

1020 -

1019

-0 e - 7" 6~ -7 - 5" -0 4 -0 3 - 2z 0 " -O 2 I 2

I)10 10 166t 1 C7 c 0- 10- 10' 1 10 tO

TIME (SEC)

Figure 8. It. Calculated lime dependence of the gamnma-ray energy outputi per k:Iol,,

energy yield from a hypo!hetica& nuclear explosion. The dashed line refers to

an explosion at very high altitude.

- . .J.* * - . m . . . , . . . -
GAMMA RAYS 329

times more energy than the prompt passat~t through matter, as desck abed in

gamma rays to the total nuclear radia- § 1 .38. In1 simple terms, a roentgen is

tion received dur~ng the firs, minute the qu.kntitty of gamma radiation (or X

after detouiation (§ 8.47). rays) thal will give rise to the formation

8.16 There is another posýsible of 2.08 x 101, ion pairs per cubic centisource of ganima rays which may be meter of dry air at S.T.P., i.e., at

ment'ioned. If - nuclear explosion standard temperature (00

C and pressure

oc~urs near the earth's surface, the (1 atmosphere). This is equivalent to the

emitted neutrons cani cause what is release of about 88 ergs oif energy when

called "induced radioactivity" in the I gram of dry air under S.T.P. condimaterials prcsent in the ground (or tiotis is exposed to I roentgen of gamma

water). 1'hiý- mray be accompanied by the radiation.

emission of gamma rays which -will 8.18 The roentgen is a measure of

commence at the timne of the explosion expos. 're to gamima rays (or X rays)

aad will continue thereafter. However, The effect on a biclogical system, such

excep: near ground zero, where the in- as the whole body or at particular organ,

tensity of gammia rays from other or on a material, e.g.. in electronic

sources 's very high in any event, the equipment, however, is related to the

contribution of' induced radioactivity to amorit of energy absorbed as a result of

the initial gamma radiation is small. exposure to radiation. The unlit of enConsequently, the rndioactivity induced ergy absorption, which applies to all

in the earth's surface by neutrons will be kinds of nuclear r:- 'iations. including

treated in the next chapter as an aspect alpha and beta part, es and neutrons its

of the residual nuclear radiation (§ 9.31 well ats g-,inimia rays, is the "'rad." The

et s.eq.). rad represents the deposition of I MX ergs

oif radiation energy per gram of the ahRADIATION DOSE AND D)OSE 1I.ATE sorbing material. In stating the quantity

(or dose) of a particular radiation 'in

8.17 Gamma rays are electromag- rads, the absorbing matorial must he

ne-tic radiations analogous to X rays, specific-d since the extent of energy dehut, generally of shorter wave length or position depends on the nature (". the

higher pioton energy (§ I1.74). A inca- material. In tissue at or near the surface

suremnen, unit that is useJ speciticafly of the body, the gamma (or X-ray', cxfor gammia rays (and X ray: ) is called posure of I roentgen results in an abth roentgen."' It is based on the abii- sorption of .ipproximately irad)1 but

ity of the!;e radiations to cause ioflhza- ¶his rough equivalence does not neceslion and p.iduce ion pairs, i.e., sepa- sarily apply to other materials. Furtherrated electrons and positive ions, in their more. the rellitionship does not hold (or

'Accord~ngto the official d-tinifio~n. I rocnigen produce's electrons (in ion pairs) wiih a iotal charge of

2.58 x 10(1 t~oulonh in i Uioqrain of dry air.

4The r'.ugh equivalence between a gamma (or X-ray) -xpostire of I roenitgen and the absorpt ion ni

body tissue of I rad holds for photons of intermediate energies (0. 3 to I MeV t. For pholon energies

outside the range fri ai 0.3 io 3 McV , the exposure in roentigens is no loniger ,imply rclate,. to the

ahsorpiioun in rads.
330 I 1 I \ " t( I I \l IA IION

absorption in tissue in the interior of thc for the detection and measurement of

bodN. 1-owever. in describing the hio- variois nuclear radiations. Sonic of the

l,)gical elfects of nuclear radiation,, in in,,truments described below resrond to

thi, hook, the eln-rgy absorption (in neutros (to a tertain extent) as well as

rads) refers to that in tissuc -it (or close to gamma rays. For gamma-ray meato) the body surface nearest to the ex- surement, the instrument would have to

plosion (§ 12.108). he -,hiclded from neutron:+. The basic

8.19 There are two basic types of operatialg principles of the instruments

nuclcar radiation mea.*urement both or are described below and their use for

which ae important for biological cf- determining either doses or dose rates is

F,_cts, and damage to materia.s. ( i,.' is indicated in §§ S.229, 8.30.

thl total "exposure" in roentgens of 8.21 Norm'Jl)y a gas wilI not con-

,i.Inina rays or the total absorbed duct electricity to any appreciable ex-

"dose" in rads of any radiation accu- tenit. bu! as a result of the formation of

inulated over a period of time. The other ion pairs, by the passage of nuclear (or

is the "exposure rate" or the "dose ionizing) radiations, e.g., alpha part:-

rate". respectiveiy: the rate is the ex- ties, beta particles or ganima rays, the

posure or the absorbed dose received gas becomes a reasonably good conper unit time. Exposure rates may tic ductor. Several types of ioniz-ation inexpressed in roentgens per hour or. for struments, e.g., the Geiger counter and

lower rates, in milliroentgens per hour, the pocket chamber (or dosimeter), for

where I milliroentgen is one thousandth thc measurement of gamma (and other)

part of a roentgen. Absorbed dose rates radit'ions, are based on the formation of

can be given correspondingly in rads per electrically charged ion pairs in a gas

hour or millirads per hour. In connec- and its consequent ability to conduct

tion with damage to electronic equip- electricity.

ment. the exposure rates are generally 8.22 Senticondi,'tor (solid-state)

stated in roentgens per second and the detectors depend on ionization in a solid

absorbed dose rates in rads per second. rather than in a gas. These detectors

consist of three regions: one is the n (for

MEASUREMENT OF GAMMA negative) region, so called because it

RADIATION has an excess of electrons available for conducting electricity, the second is the

8.20 Thermal radiation from a nu- p (for positive) region which has a deficlear explosion can be felt (as heat), and ciency of such electrons, and the third is

the portion in the visible region of the neutra!. In the detector, the neutral respectrum can be seen as light. The gion is located between the n and p

human senses, however, do not respond regions. A voltage from a battery is

to nuclear radiations except at very h:igh applied across the detector to balance

intensities (or dose rates), when itching the normal difference of potential beand tihigling of the skin are experienced. tween the outer regions and there is no Special instrumental methods, based on niet flow of current. When exposed to

the interaction of these radiations with nuclear radiation, ionization occurs tn

matter, have therefore been developed the neutral region and there is a pulse of
(iAM,A% RANS 33!

current proportional to the radiation in- stance commonly used in radiation dotensity. Semiconductor detectorsý for simetetrý i'€ iithium fluori& containing a

operatior at normal temperat'vre are stn: 1 qiiantity of manganese 't he total

made :,ý silicon which is either puXc light emission from radio-photolumine-

(neutrai region) or contains regulated s.,ent and thermnhiminescent dcsimcters

amouilts of inpurities, L.g.. arsenic o0 is a rnea:;ure of the absorbed dose in the

antimony (n region) or ýoron or alum>- sensitive material.

nunr. kp region). 8.25 In mosi materials, the energy

Fi.23 Another type of interaction of of the absorbed radiation ultimately apnuclear iadiations with matter, .ither pears in the form of beat. Thus, the hea'

s'lid. ;'quid, or gas, cal~ed Ax:ita- generated by the passage of radiation is

Jeio,"- is also used in radiation mea- a meaýsure of the absorbed dose This

suremem. Instead of the electron being fact i. u¢..,ed in a special calorineter

removed completely from an atom. as it d. ?.s,,, e ter consisting of a thin sample of

is in ionization, it acquires an additional ah-.orbing material. The energy depoamount of energy. As a result, the atom ý'ited by the radiation can :hen be deteris converted into a high-energy (or cx- mined fro'm the mea.,ured temperature

cited) electronic state. When an atom rise and the known he'd capacity of th!s

(or molecule) becormes ,'-lect,,_nically material.

excited, it will generally give off the 8.26 Indirect effects of nuclear ýaexcess (on excitation) energy within diations, notably chemical changes,

about one-millionth of a second. Certain have also been used for measurement

mate'ials, usually in the solid or liquiu purposes. One example is the blackenstate, are able to lose their electronic ing (or fogging) of photographic film

ex'citation eneigy in the form of visible which appcars after it is 4L-eloped. Filn

flashes of light or scintillations. In smin- badgrs for the mez,,u!,em.nt of nuclea.Ir

tillation detectors, the scintillations are radiations generally contain two or threc

counted by means of a photomultiplier pieces of film, similar to those used b,/

tube and associated electronic devices, de•tists for taking X rays. They ar,

8.24 In radio-photoluminescent do- wrapped in paper (or other thin material)

simeterv, irradiation produces stable wl-ich is opaque to light but is readily

fluore,,,;,nce centers which can be sti- penetrated by gamma rays. The films are

mula'ed by subsequent ultraviolet illu- developed and thn degree of fogging

minv ion to emit visible light. For ex- observed is a measure of the gamma,-ray

;,mpk!, after exposure to gamma (or X) exposure.

rays, a Alver metaphosphate glass rod or 8.27 Other optical density dosiplate system emits a phosphorescent meters depend on the production by raglow when subjected to uhiraviolet light, diation of stable color centers which

the glow can b- measured by means of a absorb light at a certain wavelength. An

photoelectric detector. In thermolumin- example is a device that measures radiescent dosimeters metastable centers are ation by a change in the transmission of

produced by radiation, and these centers light through a cobalt-glass chip. A lead

can be induced to emit light by heating borate glass containing bismuth has also

:he material. A thermoluminescent sub- been developed for the measurement of
332 1,i, I..i.- NA 'I.,\K RA. t \l] ION

high levels of radiation, specifically for in pulses of very short duration as well

use in mixed gamma-neutron e.viron- as of the total dose.

nicnts Other materials that are utilized 8.30 Dose (or exposure) rates are

in instruments for the measurement of usually dctermincj by what are caited

radiation by color changes include dyed ", _rvey meters - They may be ion

plastics, such as blue cellophane and chambers, Geiger-Mueller tubes, or

'cinenioid" film, i.e., a celluloid-like scintillation detectors, together with asfilm containing a red (lye. sociated electronic counting circuit-y. In

8.28 In practice, measuring instcu- general, these survey meters ar: p, tments do not determine the exposure in able aiid battery powered. ThJ i.tc roent s or the alý-iorbed dose in fads measurement may be converted inio the

roengen bsobeddosein orthe ads total radiation dose by multiplying the

directly. One or other of several ob- popel radad dos e by t he toa

servable effects, such as current pulses properly averaged dose rate by the total

produced by ionization, scintillation:., time of exposure

chang,'s in optical res;ponse, or temperature rise, sc-ves as the basis for the GAMMA-RAY DOSE DEPENDENCE. ON

actual determination. The instruments YIEDI.[ AND DISTANCE

can indicate the exposure in roentgens 8.31 The biological effects of

or the dose in rads after being calibrated -doses wil b

witha stndar gma-ra sou%ýevar-ious gammaý-radtationdoe i h with a standard gamma-ray sourace considered more fully in Chapter XII.

uually a kte wri quantity of a radioac- However, in order to provi'e some ;

tive material that emits a ganma ray of d.ica:ion of the significance of the

the appropriate energy at a known rate numbers given below, it may be stated

8.29 Somerk instruments can reccrd that a single absorbed dose of gamma

both the total radiation d'ose (or expo- rays of less than 25 rads (in bojy tissue)

sure) and the (lose (or exposure) rat.P, will produce no detectable clinical efbut most radiation measuring devicL:s fects in humans. Larger dos3c have inare designed to indicate either the total creasingly more serious cortsequences

or the r-ite. Total radiation doses (or and whole-body doses of i.000 rads

exposures) are measured by personnel would probably prove fatal in nearly all

dosimeters worn by individuals who cases. although death would not occur

may be exposed to unusual amounts ot until a few days later

nuclear radiation in the course ' eir 8.32 As is tc bc expected, the

work. Examples of such instruments are gamma-ray dose 41 a piticular location,

pocket ion chambers, optical density resulting from a nuclear explosion, is

devices (especially film badges), and less the farther that location is from *be

photoluminescent, thermoluminescent point of burst. The relationship of the

and color-change dosimeters. Calor radiation dose to the distance is depenmeters also measure total radition doses. dent upon two factors, analogous to

The cha~ge collection time in semicon- those which apply to thermal radiation.

ductor dctectu, s is so short that these There is, first, the general decrease due

instruments lend themselves to the to dl~e spread of the radiation over larger

measurement of gamma-ray dose rates and larger areas as it travels away from
3,000 , ------

2,500 --- . . ...

i,500 4

1;I000-/ -..... ...

500 __..

z/

I-i z!

2 5 0I 20 50 MC)

EXPLOSION V',ELD (KTj

Figure 8.33a. Slant r, rgc, i'gsr specified gamma-ray doses for targets nmar the ground as a

function of energy yield of air-burst fission weapons, oased on 0.9 sea-level

air density. (Reliability factor from 0.5 to 2 for most fission weapons.)

the explosion center. As with thermal have also been performed of the transradiation (§ 7.07), the dose received i:s port ef Pimma rays through the air.

inversely proportionl to the square of These c."Iculations have been correlated

the distance from the burst point, so that with measurements, of the gamma-ray

it is said to be governed by the "inverse transport from known sources a:id with

square" law. Second, there is an atten- observations made at nucleat explotiation factor to allow for the decrease in sions. The results obtained for ."ir bursts

intensity due to absorption and scatter- are summarized in the form of two

ing of gamma rays by the intervening graphs: the first (Fig. 8.33a) shows the

atmosphere. relation between yield and slant range

8.33 The gamma-radiation doses at for various absorbed gamma-ray doses

known distances from explosions of (in fissue neai" the body surface, see

different energy yields have beer mer.- § 8.18) for fission weapons; the second

sured at a number of nuclear weapons (Fig. 8.33b) gives similar information

tests. Extcnsive computer calculations for thermonuclear weapons with 50

r1
334 INITIAl NLJC( FAR RADIATIO0N

7,000 - I 1 1 I 7

6,000-4

S4,000 -

z

Ct

t- 3,000

2,00000

"E7KOSIO YIELD (KT)

F;g ui 8.33 h. Slant ranges for specified ga.-nma-ray doses for targets near the ground as a

function of energy yield of air-burst thermonuclear weapons with 50 percent

fission yield, based on 0.9 sea-level air dei.sity. (Reliability factor frornt 0.25

to 1 .5 for mnost thermonuclear weapons.)

Perceunt of their yield from fiss- within a factor of 0.5 to 2 for mlost

ion(§ 1 .72). The data are b;tseJ on -in fixssion weapons, whereas the reliability

average density of the air in the trans- factor for Fig. 9. 33b is from 0, 25 to 1 .5

tmission path between the burst point for most thermonuclear weapons. Interand the targot of 0.9 o;f thc normal polation may be used1 for doses othcý

sca-kvel density.' Because of variations than those shown on the figures.

in weapon design and for other reasons 8.34 The u,;e of the gamma-ray

(§8.127Th the gamola-ray dloses calcu- dose curves may be illustrate] by dc*--rlated from Figs. 81.33a and b are not mining the absorbed dose received at a

exact for all sittiaiions that may arise, distance of 2,000 yards from a 50-kiloFigure 8.33a is considered to be reliablo'- ton low air burst of a fission weapon.

-rhe density reterred to here (anJ stiIheq .*:ntIy ., ifia of the air before it is di%turhod by the cxplciori

(ct § 8.36).
CAMAA RAY', 335

From Fig. F.33a. the dose for the case reach distant points until the shock wave

.;pecified is seen to be somewhat less has passed and the air density has dethan 300 rads. A reasonable interpolated creased. There is consequently less atvalue would appear to be about 250 wenuation of the fission pv-oduct gamma

rads. rays by the air than at lower energy

8.35 The cata in Figs. 8.33a and b yields. This effect is; known as the "hyare dependent upon the density of the air drodynamic enhanceme..nt" of the

between the center of the explosion and gamma-ray dose.

the point on the ground at which the

radiation is received. This is so because 8.37 The foregoing figures were

the air absorbs some of the gamma ra- calculated for heights of burst oi

diation in the course of its transmission; 290 W04 feet and the conclusions are

the dense air near the surface absorbs reasonably applicable provided the

more than the less dense air at higher height of byr,:t exceeds about 300 feet,

altitudes. If the actual average density is even though the fireball may touch the

higher )r lower than 0.9 oi the normal earth's surface. For a contact surfacc

sea-level value for which the curves burst (§ 2. 127 footnote) the dose for a

were drawn, the gamma-ray dose will specified explosion yield and range may

be decreased or increased, resptictively. be obtained upon multiplication of the

8.36 It will be noted, especially in corresponding dose in Fig. 8.33a or b by

Fig. 8.33b, that for a specified dose, the a factor which depends to some extent

slant range increases more rapidly ;n the on both yield avd range. The factors in

higher explosion yield range, i.e., the Table 8.37 for some specific yields are

slcpe of the curves becomes steeper. averages which provide a fair approxThe cause is the sustained low air den- imation for distances of interest. The

sity following the passage of the posi- factors for intermediate yields may be

tive phase of the shock wave 1§ 3.04), obtained by interpolation. Interpolation

particularly for explosions of high en- between unity vnd the tabulated factor

ergy yield. The emission of gamma rays may also be used to obtain the approby the fission products is delayed priate factors for bursts between about

(§ 8. 13) and so these radiations do not 300 feet and the actual surface.

Table 8.37

CORRECTION FACTORS FOR CONTACT SURFACE BURSTS

Fig. X,33a Fig. 8 33b

Yi.id Factor Yield Factor

I to 50 KT 2.3 10W K1 I

I1W KT I 3(X) KT I'A

700 KT I

2 MT 2

5 to 20 MT 3

9/.,
336 I Nul lxl NUUI.F~R RADIAl'HON

SI-iiELDIING AGAINST GAMMA RAYS location where the tissue dose is 50h)

rads, e.g.. of initial gamma radi;'rion.

8.38 Gamma'. rays are absorbed (,or ,with no shielding. the introduction of

atten'jated) to so)me extent in the course the appropriate ten~th- value thickness of

of their passage through any material, any substance would decrease the dose

As a rough rule, tl~e decrease ir the to (approximately) 50 rads. Thec addition

radiation intensity :.• dependent upon the of a second tenth-value thickiuess would

nmass (per unit area) of material that result in another decreas,' by a factor of

,,,,_: .......... +,,,;: bet~wccn the., ...... .. , ..- A, + the ten, so that the dose received wo'uld he

rays and •he point of observation. This (approximately) 5 rads. E'nch ,•uceet:,.-

means that it would require a greater ing tettt'n-value thickness would bring:

thickness of a substance of IA,,,,,-,.2_.sity,.' about a fuither reduction by a factor of

e.g., water, than o~le of high density,. ten. Thus. one tenth-value thickness

e.g., iron, to attenatae the tadiations by decreases the rad~ation dose by a faitor

a specified amount. Strictly speaking, it of (approximately) 10: two tenth-val'e

is no! possible to absorb gamma rays thicknesses by a factor of IC; × 10. i e..

completely. Nevertheless, if a sufficient 100; three tenth--value th'icknesses by a

thickness of matter is interposed be- factor of 10 × 10 × 10. i.e , I,.00': nd

tween the radiation source, such as a:, so on."

exploding nuclear weapon. and an dind- 8.40 In shielding again:it gamnma

vidual, the dose received care be reduced radiations from a nuclear explosion the

to negligible proportions. conditions leading to the tenth-value

8.39 The simplest case of gamma- thickne:;s concept do not exist. In the

ray attenuation is that or a narrow beam first, place the gamma-ray energies

of monoencigetic radiation, i.e.. radia- cover a wide range, the radiations are

tion having a siigle energy,, passing spread over a large area, and thick

through a relatively thin layer of shield- shields are necessary in regions; of ining material. In these special (and hy- terest. Evaluation of the efl'ecti-'cness of

pothetical) circumstances, theoretical a given shield material is then a complex

considerations lead to the concept of a problem, but calculations have been

"'tenth-value'" thickness as a measurecof made with the aid of electronic cornthe 'ffectiv,-ness of the material in at- puters. It has been found th'at, beyond

tcnuating gamma rays of a given energy the first few inches of a shielding mate-

(cf. § 8.95 et .seq.>. A tenith-value rial, ,he radiation attenuation can be

thic'! ness i', defined as the thickness of expressed with fair accuracy in many

the specified material which induces the cases in ternis of an efllective tenth-value

radiation dose (or 'dose rate) to one tenth thickness. T'his useful result apparently

03f that falling upon it: in other words, arises from the fortuitous cancellation of

one tenth-value thickness of the material factors which have opposing effects or, '3.

would decrease the radiation b a facto-r the simple situation considc."ed in

of ten. Thus, if a person were in a § 8.39. In the first few inches of the ::

"The ''half-value thickness" s son,_'iin.es used:, it is deL'tmeU as the thickness of a ,given maiterial which .

reduces th,_ do~se of i ipi iging ra.diatiir.J to ( .ippros imalely ) rne half. Tw'o such thickic,,, c,, decrease Ihnc.

dose to, one fourth: three thicknessc: to on: eighth. etc. i
GAMMA RAYS 337

shie!d the attenvation is generally 8.42 The second column for each

greater than indicated by the effective type of gamtrný radiation. designateo D

tenth-value thickness and so use of the x Td(l/sq ft), gives !he product of the

latter would be coxiaervaltve. density, D, of the ram-,terial (in lb/cu ft0

8.41 The effective tenth- value and the tenth-vali~e thickness. T (in

thicknesses of some materials of interest feet). It will be noted that D x T is

in radiation shielding are given in Table roughly constant for a given gamma

9.41,7 for broad beams of gamma rays radiation. This is the basis of thc stateemitted by the fission products in the rnent in § 8.38 that gamma-ray attenuafirst minute after the detonation and for tion is determined approximiately by the

those (%econdary gamma rays) accom- mass (per unit area) of the shielding

panying the capture ot' neutrons by ni- material. If the tenth-value thickness tor

trogen in the air (§ 8. 11 ). These partic- a p;irticular material is not known, but

ular radiations were chosen because. the density is, a fair estimate can be

they are represenitative of the main con- made by assuming D X T to he 1 30

stituiens .); the initial gamma rays. The lb/sq f! for fission p)rodoct gamma ;ays

thickoess of an), material required to and 200 lb/sq ft for nitrogen capture

decrease the nitrogen capture (secon- gamma rays. To determine (he etlectidary) gamma r.ivs to one-tenth is about veness of it given shield as it protection

50 percent greater than for the fission against the initial radiation from a nuproduct -amnia rays, thi.; is because the clear explosion, it, is recomrnendcd that

former have a considerably higheýr en- the higher of these values be employed.

ergy. The result will indicate a smnal~r degree

Table 8.41

APPROXIM~kTE EFFECTIVE TENTII1-VAIJIET C KNESSES, FOR FISSION PRODUICT

ANI) NITROGEN (CAPTURE (;AMNIA RAYS

Fission Plroduct Nitrogen ('ai11urc

Tenth- TenthValuie Value

D~ensity Thickness I') x T Thickness, I) '

Material (lh/cu ft) (inches) 0hi fo (inchs,) lh s~ft)

Steel t0ron) 490 5. 1.35 4 3 176

Concrete 146 1 1 34 10 19

Earth ItS Mb 0 ..3 .24 IM5

Witter 62.4 -)4 125 39) 2(101

Wood 40) 18 117 0.3 2101

The tenth-value thicknesses are for gammna rays that are incideit perper.dicularly on the dlah of

material. If the rays make an angle It with the perpenidicular. the tenth-value thickness is ban(

apteroximately hy inultiply'iri the %alues in the tahk v bcosine 0. provided 0 is, less t hav 45
3 18 INill\l N'(I I F\R R.A\I)I\IION

of protection than can actually be oh- person taking shelter behind a single

tai , ilh l it it better to be conse'rvativye wall, an embanknment. or a hill will he

in this respect than to overes!Imate the shielded, to some exten', from the direct

etlct.clivenoss of the shiel.l, gamimia rays. but vill still be exposed to

8.43 A more accurale estimake of the scattcred radiation (or skyshine), as

the protection that call he provided bv a shown by the broken lines in Fig. 8.45a.

particuiar shield between the source of Adequate protection from gamma rays

the radiation and the targol c . g., a per- can be secured only if the shelter is one

son. can be maac by taking a number of which surrounds the individual, so that

factors into considerat ica Th.se in'- ne can be shielded from all directions

Cludc the energy distribipiion of th, (Fig. 8.45b). In this case. both direct

anmina radiatllov falliing on the shield, alnd scattered radiations can be attenthe angle of incidence of the radiation. uited. The variation in the amounts of

1tid the geomct;y (or form) of the radiation received at a target from difshielding material. Such conside; ations ferent directions is called the 'angular

niak, it n'ccessary to uLst' comptuter distribution." It has been found that the

methods !o calculate the shielding pro- angular distribution of the initial gamma

vided by even simple strucLure:s. Esti- radiation is relatively insensd ive to the

mates of the effectiveness of some type of weapon and to the distance of

common sh-:lters in shielding from ini- the target from the explosion point.

lial gamma radiation (and neutrons) are

given in Table LRATF 8.72. (Data for these OF' IE',IVFRY OF: INITIAL,

same structures for residual (fallout) GAMMA RAYS

gamma rays will Ie f',und in Table

9.120.) 8.46 Radiation dose calculations

8.44 In a vacuum, gamma rays based on Figs. 8.33a and h involve the

travel in straight lines with the speed of assumption that the exposure lasts for

light. However. i:i its pass,-ge through the whole mirute which was somewhat

the atmosphere, gamma radiation, like arbitrarily set as the period in which the

thermal radiation, is scattred, espe- initial nuclear radiation is emitted. It is

ciaily oy the oxygen and nitrogen in !he important to know, however, sonielhinS

air Consequently, gamma rays will about the rate at which ,he radiation is

reach a pirticular target on the ground delivered from the exploding weapon. If

from many directions. Most of the dose this information is available, it is possireceived will come from the direction of ble to obtain some idea of the dose that

the explosion, but a considerable would be received if part of the radiation

amount of radiation will airive from could be avoided, e.g., by taking shelter

other direcdions. The gamma radiation within a second or two of observing the

reaching a target as a result of scattering luminous flash of the explosion.

in the air is called "skyshine." 8.47 The rate at which gamma-ray

8.45 The fact that gamma rays can energy is released from a weapon is

reach a target from directions othr than shown ii Fig. 8.14. but ine rate at

that of the burst point has an important which this energy is received at a distant

bearing on the problem of shielding. A target depends upon a number of facIi'
(;A NAMA R A NS 339

0

SCATTE iED RAD:ATION

Figure 8.45a. Target exposed to scattered gamn;, radiation.

*00

Figure 8.45b. Targei shielded from scattered gamma radiation,

71,
340 INI II \I N '(I V AR RA.,I)I..\IION

tors' the most sgnilicant are the energy 8.47. One curve refers !o a distance of

yield of the explosi(In and the distance 00()0 yards from a 20-kiloton ail hurst

from the burst point. These two quanti- and the other to 2,500 yards from a

ties affect the relative importance of the 5-megalon explosion. It i., seen that in

several components of the initial gamma the former case about 65 percent and in

radiation. The larger the ) ield and the the latter case about 5 percent of tle

greater the distar.e, the greater will bc total initial gamma radiation dose is rethe hydrodynamic enhancement of the ceived during the first second after the

fission product garnma rays (§ 8.36). As detonation.

this enhancement is increased, the relalive importance of the fission product 8.48 If some shelter could be ohgamma rays is increased. Thus, for tained, e.g., by falling prone behind a

larger yields and greater distance,, the substantial object. within a second of

fission product gamma rays, which are seeing the explosion flash, in certain

important at late times relative to the circumstances it might make the difother cc;mponents of Ihe initial gamma ference between life and death. The

radiation, provide a larger percentage of ciur"!,, c Fig,.. '.17 show thait aoidancc

the total dose. The percentage of the of part of the initial gamma ray dose

total dose received up to various times would be more practicable for explofor two differen, cases is shown in Fig. sions of higher energy yields.

NEUTRONS

SOURCES OF NEUTRONS released either in the fission or fusion

process (§§ I.4.2, 1.69). All of the ncu8.49 Although neutron; -,,'e nuclear trons fro'n the latter source and over 99

particles of appreciable mass, whereas percent of the 'ission neutrons are progamma rays are electromagnetic waves duced almoct immediately, within less

(§ 8. 17), their harmful effects on the than a millionth of a second of the

body and their ability to damage certain initiation of the explosion. These are

materials are similar in character. Like referred to as the -prompt- neutrons. In

gamma rays;, only very large doses of addition, somewhat less than I percent

neutrons may possibly be detected by of the fission neutrons, called the "dethe human senses. Neutrons clan pent- layed" neutrons, are emitted subsetrate a considerable distance through the quenly. The majority of these delayed

air and constitute a hazard that is greater neutrons are release• within the first

than might be expected from the small minute, and so constitute part of the

fraction (about I percent) of the explo- initial nuclear radiation. At distances

sion energy which they carry. greater than about 2,000 yards from a

8.50 Essentially all the neutron:: multlmegaton explosion, the dose from

accompanying a nuclear explosion are delayed neutrons can exceed that from
N1i; I RONS 34!

100 1 7 I Ir [ __ 1 I I I T so

80 _JW

U/

- .--- I . ..

0) wo I•

0 -

0.01 0,02 005 0.1 0.2 05 I 2 5 10 20

TIME (SECONDS)

Figure 1.47. Percentage of inilial gamma - radial ion dose receiveJ as a luncli n of le for

20-klioton and 5-megaton air bursts,

prompt neutrons, because the delayed st,.ond. At Jistances from the hurst

netirous are subject lo hydrodynamic where they represent a hazard, nearl. all

enhancement (§ 8.36) whereas the of the neLtroris are received within a

prompt neutrons are not. Both doses second of the explosion, that is, before

are, however, much Icss than the the arrival of the fission product gamma

gamma-ray dose for high-yield weap- rays. 'The evasive action described in

ons. Neutrons are adso proouced by the § 8.48 for gaimma rays thus has littll

action of high-energy gamma rays on effect on the neutron dose received.

the weapon mate-iais, but their contri- 8.52 The neutrons produced in the

hution is miror. fission process have a range of energies,

8.51 Despite their almost instanta- but they are virtually all in the region of

neo'us release, the prompt fission neu- high energy. Such high-energy neutrons

trons are slightly delayed in escaping are the fast neutrons referred to in

from the environment of the exploding § 8.09, their energy being kinetic in

w.:apon. Th:; delay aiises from the ru- nature, i.e., energy of motion. In the

merous scat-ering collisions suffered by course of scattering collisions with

the neuoons with the nuclei present in atomic nuclei, there is an exchange of

the weapon residues. As a result, the energy between the fast neutrons and the

neutrons traverse a complex zigzag path nuclei. Withirt Oie weapon itself, where

before they finally emergt. However, heavy nuclei, e.g., of uranium, are

they move so fas, that the .elay in the present, some of the neutrons lose enesca~r of tre prompt rietitroths is much ergy as a result of inelastic -cattering,

.ýss than a ta-tOousandth part of a the energy removed being emitted in the

I V
342 INI IA1. NU(CI F.AR RA[)IVY 1ON

form of gamma radiation (§ 8.09). In ing which removes energy from the

other collisions, especially with light neutrons and is a subs!antia! source of

nuclei, th2re is a simple transfer of ki- gamma radiation (§ 8.09, FHg. 8. 14).

netic energy from the fast neutron to the Inelastic scattering of high-energy neustruck nucleus: these arc "elastic colli- trons by oxygen also resulis in encrg3

sions'" and are not accompanied by removal and provides a less implortant

gamma ri;diation. P..cause of the variety source of gamma radiation (§ 8. 107).

of collisions which occur with different 8.54 hI, some collisions, particunuclei, the neutrons leaving the region larly with nitrogen nuclei, the neitrons

of the explosion have speeds (or ener- can he captured (§ 8. 11 ). so that they

gies) covering a wide range, from fast are completely removed. The probabilthrough intermeliate to slow. The ne-. ity of capture is greatest with the slow

trons of lowest energy (or speed) are (low-energy) neutrons. Consequently,

often called "thermal" neutrons be- in their passage through the air, frorn the

cause they are approximately in thermal .veapon to a location on the ground, for

(or temper:ture) equiliorium with their example, there are rminy interactions

surroundings. involving the neutrons. There is a tf n8.53 As a consequ,!nce of the dency for the fast (high-energy) neuvarious interactions described above, trons to lose some of their energy and to

the ncutroits that ciucrge from the region be s~owcd down. At the same time, the

of the explosion have a very difTerent slower neutrons have a greater chance of

energy distributio,, ;.e., "neutroin en- beitg captuiLd and eliminatted, as suLh,

ergy spectrum," than when they were from the nuclear radiation, although the

formed in the fission and fusion reac- capture usually leads to the emis:ion (of

tions. Furthermore, the energy spectrum gamma rays.

may change as the neutrons travel 8.55 It is Imporoant in connection

through the air For example, the neu- with the measurement of nuclear

trons leaving the weapon environment veapon neutrons and the study of their

undergo scattering collisions with nuclei biological effects to know something of

(of nitrogen, oxygen, and other elcments the neutron energy spectrum and its

in the atmosphere. These collisions are variation with distance from the exploless frequent than within the weapon sikn. From measurements made during

because of the lowei density and t'maller nuclear tests in the field, measurement,

ccrncentration (f nuclei. Nevertheless, with laboratory calibrated sources, and

!he results of the collisions are impor- extensive computer calculations, it apvant. In (he first place, the fractional pears that (he neutron Lnergy spectrun,

decrease in neutron entugy per elastic for fission weapons remains essentially

scauering, collision is, on the average, 1he same for a given weapon over the

greatest for light nuclei. The nuclei of range of distances that are of biological

oxygen and nitrogen are relatively light, interest. This condition is referred to as Aý

so that the neutrons are appreciably ar. "equilibrium spectrum." 4

,dowed down by elastic scattering coili- 8.56 The occurrence of an equilibsios in the air. Some of 'lie collisions rium spectrum is related to a combinawith ni(rogen result in inelastic scatter- tion of circurnlances which arise duriag

!4
NEPUTRONr S 343

passage of the neutrons through the air, vents the occurrence of an equilibrium

the loss of the :lower neutrons by cap- spectrum until the neutrons have trayture, e.g., by nitrogen nuclei, is corn- ,cled long distaaces in air (§ 8.117 ,'t

pensated by the slowing down of fast seq.).

neutrons. Consequently, the proportion

(or fraction) of neutrons present in any MEASUREMENT OF N:Ti.!,rRON FLUX

particular energy range appears to be

essentiall'/ constant at all distances of 8.58 Neutrons. being electrically

interest The total number of neutrons neutral particles, do not produce ionizareceived per unit area, however, at a tion or excitation directly in their pasgiven location is less the farther that sage through matter. They can, Lowpoint is from the explo:'ion, because, in ever, cause these effects indirectly as a

addition to being spread over a large je ult of their interaction with certain

area (cf § 8,32), sonic of the neutrons light nuclei. When a fast neutron colare removed by capture. lides with the nucleus of a hydroge:n

8.57 The thermonuclear reaction atom, for example, the neutron may

between deuterium and tritium results in transfer a large part of its energy to that

the liberation of neutrons with energies nucleus. As a result, the hydrogen nuof 14. I MeV. This energy iF. consider- cleus is freed from its associated elecab!y greater than thn!, of essentially all ton and moves off as a high-energy

the fission neutrons awil is also mu..h proton. Such a proton is capable of

greater than the energy of the ne'ilrons producing a considerable number of ion

prodaced by the other thernmonuclear pairs in it,, passage through a gas or it

reactions (§ 1.69). These neutrons of can cause electronic excitation. Thus,

very high energy undergo reactions the interaction of a fast ncutron with

wiihin the exploding weapon similar to hydrogen (or with any substance conthose described in § 8.52. Consequently taining hydrogen) can cause ionization

some of the high-energy neutrons arc or excitation to occur indirectly.8 The

emitted from the region of the explosion interaction of neutrons with hydrogen

with mnergies lower than 14.1 MeV. thus makes it possible to use both ionNevertheless, suficient quantities of ization and scintiflation counters as

energetic neutrons emerge from a 'her- neutron detectors. For example, if a

monuclear weapon !(? cause a peak in hydrogenous material is impregated

tMe neutron spectrnm at energies in the with a ,:ubstance diat is capable of prorange of 12 to 14 MeV. This peak is in ducing scintillations, protons released

contrast to the continuous decrease in by neutrons interacting with hydrogen

the number of neutrons with increasing atoms cau:;e the excitation of the scinneutron energy observed for iission tillation material.

weapons. The existence of the high-en- 8.59 Neutrons in the slow and

ergy peak in the neutron energy spec- moderate speed ranges can prodace

trum from thermonuclear weapons pre- ioiization and excitation indirectly in

HThe ionization and cxcitation resulting from the iiPteractiom of fw, neutrons with hydrogen in tissue is

considered to hb, the main cause of biologics, injury by neurOrls,.

A

8~ __
344 1INIFA1 NUCI tFAR RAiDIATION

other ways. When such neutro-ns are dose in rads (tissue) can be determined

captured by the ligh:er isotope of boron in this manner.

(boron-l(), two electrically charged 8.61 In addition to the procedures

particles-a helium nucleus (apha par- described above, "foil act:vation"

ticle) and a lithium nucleus-of high methods liave been extensively used in

energy are formed. Neutrons also can b,' the detection and measurement of neucaptured in the lighter isotope of lithium trons in various energy ranges. These

(lithium-6) to produce a tritium nucleus methods are based upon the fact that

and an alpha particle (§ 1.70), or the ce:'tain elements become radioactive as

neutrons can be captured by nitrogen a result of the capture of neutrons

nuc!ei and high-energy particles are (§ 8. 16). Under appropriate conditions,

emitted (§ 8. 10). In each of these re- the extent of the radioactivity, as meaactions, the resulting chargcd particles sured by the rate of emission of radiacan produce ion pairs or excitation. In- tion (beta or gamma or both), is related

direct ionization by neutrons can als,, to the 'integrated flux," or "fluence, *

result from the fission of plutonium or of incideit neutrons, i.e., the product of

uranium isotopes. Ihe fissien fragmnets the lux and time, expressed as neutrons

are electrically charged particle.; (ions) per square centimeter (neutrons/cm2 ).

of 1,igh energy which leave consiJerat,!e Hence, by the use of appropriate conionization in their paths. version factors, neutr( a fluence can be

8.60 All of the foregoing indirect calculated." In practice thL lements are

ionization or excitation processes can be used in the form of thin sheet or foil, so

used to dctc't and measure neuiron in- that they produce a minimum disturtensities. The quantity determine-: ei- bance of the neutron field. The techther di.-ectly or indirectly, ik calk.', •ie nique is referred to a:; "activation de-

"neutron flux"; it is the product ot the tection" and the materials emp!oyed are

neutron density, i.e., the number per known as "activation detectors." An

unit volume, and the a~erage velocity, activation detector which has an appre-

"The instruments emplo, ed for the mea- ciable probability of reaction only when

surement of neutron thx, such as boron the energy of !he neutron exceeds a

counters and fission chambers, are particular (threshold) value is called a

somewhat similar, in general principle, "threshold detector." The procedure is

to the dose rate (survey) meter, com- then described as the "threshold det',r,-

moniy u-ed for gamma r'idiations tor technique" and is oised to determine

(§ 8.30). ''Tis'.,ue equivalent'' the number of neutrons with energies in

chambers have been developed in which; excess of the threshold value.

,he ionization produced indirectly by 8.62 The "fission foil" method, as

neutrons is related tc the energy which its name implies, makes use of fission

would be taken up from these neutrons reactions. A thin layer of a fissionable

by animal tissue. Thus, the absorbed material, such as an isotope of uranium

"•The neutron fluence (at a give'% energy) is, in a sense, a measure of the neutron exposure fat that

energy). The absorbed dose can be derived from the fluence by allowing for the energy deposited by the

neutrons in a specified material.
NEUTRONS 345

or plutonium, is exposed to neutions. cannot be correct for all situations that

The fission products formed are highly might arise. It is with this limitation in

radioactive, emitting beta particles and mind that the curves in Figs. 8.64a and

gamma rays. By tneaur,.g the radioac- b are presented; the former is for fi.'sion

tivity produced in this manner, the weapons and the latter for thermonuamount of fission and, hence, the neu- clear weapons with 50 percent of their

tron fluence to which the fissior,able yield from fission. The estimated relimaterial was expo.ed can be deter- ability factors are the same as given in

mined. § 8.33 for Figs 8 33a and b, fespectively. The curves give absorbed neuNEUTRON DOSIE DEPENDENCE ON tron doses in tissue close to the surfa-e

YIELD AND DISTANCE of the body received near the ground for

low air bursts. The data are based on an

8.63 A basic difficulty in expressing average air density in the transmission

the relation between the neutron dose, path of 0.9 of the normal sea Ievel denyield, and the distance from a nuclear si~y. If the actual average air density is

explosion is the fact that the results vary higher or lower than this, the neutron

significantly with changes in the dose will be decreased or increased.

characteristics of the weapon. The ma- respectively.

tzrials, for example, have a considerable 8.65 When comparing or combininfluence on the ex!ent of neutron cap- ing neutron doses with those from

ture and, consequently, on the number gamma rays (Figs. 8.33a and b), it

and energy distribution of the fission should be noted that the biological efneutrons that succeed in escaping into fetts of a certain number of rad, of

the air. Further, t

he thermonuclear re- neutrons are often greater thmn for the

action between deuterium and tritium is same number of rads of gainia rays

accompanied by the liberation of neu- absorbed it: a given tissue (§ 12.97). As

trons ot high energy t§ 8.57). Hence, it fo," gamma rays, the neutron dose (leis to be expected that, for an explosion creases with distance from the explosion

in which part of the energy yield arises as a result of the inverse square law and

from thermonuclear (fusion) processes, attenuaion b) absorption and scattering

there %i!! be a larger proportion of i.i the atmý,spilere. However, since the

high-energy (fas:) neutrons than iroin a prompt neutroi !; are emitted during a

purely fission explosion, shor, time (§ 8.3 I), and since those of

8.64 In view of these considera- major biological significance travel

tions, it .,, evident that the actual number much faster than twe blast wave. there is

of ncuton; emitted per kiloton of ex- no hydrodynamic 'ýnhancement of the

plosion energy yield, as well as their (prompt) neutrons dose as there is for

energy distribution, may differ not on!y fission product gamma rays. This is one

for weapons of different types, i.e., fis- reason 'vhy the gam.na-ray dose in-

,ion and fusion, but also for weapons; of creases more rapidly v;;th the energy

the same kind. Hence, any curve which yield than does the neutron dose. The

purports to indicate the variation of data in Figs. 8.64a and b; may be reneutron dose with yield and distance garded a., applying to air !'ursts For
346 1NI I I ~I NAI I VAR~ R,\[)!,\ ION

2,500 - VV fT 7 V F

2,00

1,0

z

z ,0

1 2 510 20 50 'CO

EXPLOS:ON YIELD (KT'

Figure 9.64a. Slant ranges for speci'ied nettilOn dose:; Tor taigels near *,he ground as a

function of enlergy yield of air- burst fiss~on weapons. based on 0i.9 sea- level

air d.-nsity. (Relia~iI::y fa',tcr fr()M 0.5 Io 2 fir most fission weapons.)

contact surface bursts, the prompt neu- good gamma-ray shields because of

tron dose may be taken as one-half the their high density. These elemnents

value for a corresponding air ourst. For alone, however, are not quite as satisheights of burst Weow 300 feet, the dose tactory for neutron shielding. An iron

may be e -limaled by interpolation be- shield will attenuate weapon neutrons to

tween the values for an ý'ir burst and i some extent, but it is less effective titan

contact surface burst. some of the typ.-s described below.

8.67 The attenuatmei of neutrons

SHIELDING AGAINST NEUTRONS from a nuclear explosion involves several different phe~iwmena Firs(, the very

8.66 Neutron shielding is a dif- fast neutrons must be slowed down ir~to

ferent, and more difficult, problem than the moderately fa,-t rarige:, this requires a

shiielding against gamma rays. As far as suitable (inelastic) scattering material,

the latter are concerned, it is merely a such as one containing barium or iron.

mnatter of interposing a sufficient mass of Then, the moderately fast neutrons have

material between the source of g.irnma to be decelerated (by elastic scattering)

radiations anOi the recipient. Heavy into the slow range by mnans of an

metals, such as iron and lead, make elemept of low atomic weight (or mass
NIV U I ICONS 347

-2,5000

2 ,0 -LJ

500 - I0 1 -- t

10 2 5 IC0 2 5 a 2

EXPLOSION YIELD (KT)

Figure 9.64h. Slant ranges for specified neutron doscs for targets near the g:ouno :is a

function of energy yield of air-burst thermonuclear weepons based on 6.9

seý,-levcl air density. (Reliability factor 0.25 to 1.5 for most thermonuclear

w~eapons.

numbe:r). Water is very satisfactory in minimize the escape of the gamma rays

this respect, since its two zonstitu't-nt from the shield.

clemcnis, i.e.. hydrogen and oxygen, 8.68 In geveral. concrete or damp

both have low atomnic weights. The slow earth v'ould represent a fair compromise

(thermal) neutrons must then be ab- for neutron, as well I-s for gamm~a-ray

sorbed. 'This is not at difficult matter shielditig. Although these materials do

since the hydrT gen tia water will serve not normally contain elements of high

the purpose. However, neutron inelastic atomic weight, they do have a fairly

scattei ir.g reactions and most rio'utron large proportion of hydrogen to slow

capture reqctions are accompanied by down and capture neutrons, as well as

the emission of gamma rays (§§ 8.53, calcium, silicon, and oxygen to absorb

8.54). Consequently, sufficient gammna- the gamma radiations. A thickness of 12

attenuating matetieI must he induded to inches of concrete, for example, will
348 iNIlal N tA C( FAR RAi)iAION

,ecrease the neutron fluence from a that, because of the scattering experithermonuclear weapon by a factor of enced by gainMa rays, an adequate

about 10, and 24 inches by a factor of ::nield must provide protection from all

roughly 100. The high energy initial directions. Somewhat the same situation

gamma radiation wouid be decreased to applies to neutrons. As seen earlier,

a somewhat lesser extent (see Table neutrons undergo extensive scattering in

8.41), but, in suffiient thickness, con- the air, so that, by the time they reach

crete could be u,,ed to provide shielding the ground, even at a moderate distance

againsi both neutrons and gamma rays from the exp!osion, their directions of

from a nuclear explosion. Damp earth motion are almost randomly aistributed.

may be expected to act in a similar Partial protectiorn from injury by neumanner, although abouw 50 percent trons may be obtained by means of an

greater thickness wvould be required. object or structure that provides shield8.69 An increase in the absorption ing only from the direction of the exof the nuclear radiations can be achieved plosion, although better proiection, as in

by using a modified ("heavy") concrete the case of grxnma rays, woukd be given

made by adding a cornsiderablc propor- by a shelter which shields in all direction of an iron (oxide) ore, e.g., linion- tions.

ite, lo the mix and incorporating small 8.72 In addition to the complexities

pieces of iron, such as s;teel punchings. introduced by the arrival of neutrons at a

Alternatively, the mineral barytes, target from many directions, the distriwhich is a cumpound of barium, rry Ie bution in energy from each direction

included in the concrete. The pt ice makes it impractical to c-6culate the

of a iheavy element improves bollý -he shielding effectiveness of even simple

neutron and gamma-ray shielding prop- structures without ,esert to complex

erties of a giien thickness (or volume) computer code:s. Estimates of the

of the material. Attenuation of the neu- shielding afforded by various structures

tron fluence from a thermonuclear are given in Table 8.72 in terms of a

weapon by a factor of 10 requires about "dose transmission factor", this is de7 inches of this heavy concrete. fined as the ratio of the dose received

8.70 The presence of boron or a behind the shield to the dose at the same

boron compound in neutror shields has location in the absence of shielding.

certain advantages. The lighter (boron- Some of the transmission factors were

10) iso.ope 3f the element captures slow obtained by measuremer.ts at weapons

neutrons very readily (§ 8.59), the tests or are extrapolations from such

process beinr_ accompanied by the measurements. Others were obtained by

emission of gamma rays of modvirate relatively detailed calculations, whereas

energy (0.48 MeV) that are no, diffiLult still others are mere estimates. Ranges

to attenuate. Thus, th,- mineral cole- of values aie giveii for the dose transmanite, which contains a 1hrge propor- missio, faci., for two reasons: uncertion of boron, can be iecorporated into taintGes in the estimates themselves and

concrete in order to improve its ability variations in the degree ' • shielding that

to absorb neutrons. may be obtained ai different loc.th-ns

8.71 It was pointed out in § 8.45 within a structurc.
IRANS I I Nr-RA )IAD.ViION 1II 1(S ON II I LI RONR( S (I Rt-1 349

Table 8.72

D)OSE TRANSMISSION FACTORS FOR V'ARIU),1S STRUICTU'RES

Initial

Sricture (Gamma Rays Neutrons

Three feet underground ()X()2 0.(X)4 0.(X)2 0) 01

I-rame House (0.s 0 ()33 )

Basement 01) 0.6 0 I 0 5

Multistory building

(apartment type):

Upper stories 0 5 0.)t t) q I (0

Lower stories ,) 0.6 0.1 ()0

Conciete hlockhousi. shelt!,r:

9-in. walls 0. I 0.2 0.3 0.5

;2-in. walls 0.05 ()I 1)2 -0.4

24-in. walls 0 (X)7 0.02 0. 1 0.'

Shelter, partly

above gradeWith 2 ft earth cover 0.03 0.07 0,02 0 8

With 3 f0 earth cover 0.(X)7-0.02 (01 0,.05

TRANSIENT-RADIATION EFFECTS ON ELECTRONICS (TREE)

GENERAL. CHARACTERISTICS OF 8.74 ypplied'he name commonly 

TREF to the class of effects under considera8.73 The initial ni-clear radiation, tion is "transe~it-radiation effects on

specificz1ly ganima ra)s ,rid -.'utrons, electronics," commonly abbreviated to

can affect materiai, such a., those used the acronym TREE. In generai, TREE

in electronics systems, e g., radio and means those effects occuiring in an

radar sets, gyroszopes, inertial guidance electronicsi system as a result o:f expodevices, computers, ctc. The response sure to the tranient initial radi.-:tion

of such systInns to radiation from a from a nuclear weapon explosion. The

nuclear explosio;- depends on the nature adjective "transient" applies to the raof the radiation absorbed and also on the diation !,ince it persists for a short :eme,

specific componeut and often on the i.e., less than I minute. The response,

operating state of the sysiem. The actual however, is not necessarily transient. In

effects are determined by the charac- order to study the effects of nuclear

teristics of the circuits contained in the radiatik ns on electronics systems and

electronics package, the exact compo- components, the transient radiation

nents present in the circuits, and the from a veapon is sinmulated in the labospecific construction techniques and ratory by means of controlled sources of

materials used in making the compo- both steady statr and transient radianems. tions.

a
350 INITIAI Nt(CI FAR RAI)!AIlIN()N

8.75 The term '%lectronics" as OBSERVED EFFECTS ON

used in TREE may refer to any or all of EILECTRONICS COMPONENTS

the following: individual electronic Solid-Stote Devices

component parts, component parts assimbled into a circuit, and circuit!. 8.77 Solid-state devices, such as

combined to form a complete system. diodes, transistors, and integrated cirTREE studies may also include electro- cuits, are widely used in electronics

mechanical components connected to sy,,sems. They consist of semiconducLor

the electronics, c.g , gyros, inertial iI- materials that are quite sensitive to nustruments. etc. Purely mechanical or clear radiations. Temporary effects arc

structural components are excluded the production of spurious current

sinme they are much less sensitive to pulses caused by gamma rays absorbed

radiation thin are comporents or sys- in the solid. This phenomenon is turned

tems that depend on electrical currents to advantage in the serniconductol de-

(or voltages) for their operation. tectors of nuclear radiation (§• 8.22).

8.76 Radiation effects on elcc The strength of the current pulse is protronics may he temporary or more-or- portional to the dose rate of the radiation

less permanent. Even though the cifects and is much larger in a transistor than in

on a par!icular component, e.g., a tran- a diode because the primary current resistor, may be temporary, these effects suiting from ionization produces an ammiy result in permanent damage to plified secondary current in the transissome other part of a circuit. The corn- for.

ponent response: of short duration ar,- 8.78 Some of the changes caused

usually the result of ionization caused hy atomic displacements in a semiconby gamnma radiation and are dependent ductor disappear or "anneal" (§ 8.142)

upon the dose rate, e.g., in rads per in a short time but others remain. Persecond, rather lhan the dose. The more manent changes in the physical properpermanent effects are gererally---but ties of materials affect the oper-ting

not always--due to the displacement of characteristics of the diode or transistor.

atoms in a crystal lattice by high-energy The latter ire usually more sensitive to

(fa:!) neutrons. In such cases the extent radiation :-,ind so ihe discussion here will

of damiage ik, determined by the neutron be restricted to transistors. In most

Iluence, expressed in neutrons/cm 2 cases, degradalion in, the current ampli-

(§ 8.61 ). When a permanent effect is tication (or gain) of transistors is the

produced in an ;eicctronic component by critical factor in determining the usefulgamma radiation, the important quantity ness of electronic systems containing

usuall', is th.' dose in rads. A brief solid-st,,te components.

description of the responses of some 8.79 There is a wide variation in the

components of electronics system- arc response of transistors to radiation, even

given below: the mechanisms of the among electronic devices designed to

interactions with nuclear radiations are perform similar tunctions. The decrease

explained later (§ 8.133 et seq.). in gain may beco-ne unacceptable at
TRANSIENi -RADIATION EFFECTS ON FIE('TRONICS (IRFR ) 351

fast-neutron fluences as smali as 10'1 or u Tut'S and 7hvratrons

as large as I0'1 (or more) neutrons/cm2 .

(Fast-neutron fluences referred to in this 8.81 The orincipal transient effect

section are fission neutrons with ener- in vacuum tubes arises from thc

gies exceeding 10 keV, i.e., 0.01 'Compten) electrons ejected by gamma

MeV).I' The structure of the device has rays (§ ?,.89) from the structural parts of

an important influence on the radiation the tube into the evacuated region.

resistance of a transistor. As a general These electrons are too energetic to be

rule, a thin base, as in high-frequency significantly influenced by the electric

devices, and a small junction area favor fields; in the tube. However, their impact

radiation resistance. For example, dif- on the interior surfaces of the tube profuse-junction transistors are signifi- duces low-energy secondary electrons

cantly r-moe resistant than alloy-junction that can be affected by the existing

devices bccause of the smaller junction electric fields, and as a result !he

area. Junction and especially thin-film operating characteiistics of the tube can

field-effect tansistors car, be made that be altered temporarily. The gril is parar. quite resi,ýtant to radiation. Certain ticularly sensitive to ,his phenomenon:

types of the latter have remained opera- if it suffers a net loss of elections, its

tGonal after exposure to a fast-neutron voltage will become more positive and

fluence of 1O01 neutrons/cm2 , there is a transient increase in the plate

8.80 Damage in MOS (metal-oxide current. Large fluences of thermal neusemiconductor) field-effect transistors is trons, e.g., 1011, neutrons/cm 2 , can cau:.4e

caused primarily by gamma radiation permanent damage to vacuum tubes as a

rather than by neutrons; lhence, the ef- consequence of mechanical failure of

fects are reported in terms of the dose in the glass envelope. But at distances

rads (silicon). The most se,|sitive pa- from a nuclear explosion at which ,:Uch

rameter to radiation in these devices is fluences might be expericnced, blast and

the threshold voltage, i.e., the value of fire damage would be dominant.

the gate voltage for which curient just 8.82 Gas-filled tubes (thyratror.s)

starts to flow between the drain and !he exposed to gamma radiation exhibit a

source. In general, gradual degradation, transient, spurious firing due to partial

i.e., a shift of about 0.5 volt in the ioni,:ation of the gas, usually xenon.

threshold voltage, begins at aboLt l0Y Additional ionization is caused by collirads (silicon) and proceeds rap.Jly at sions between ions and neutral molehigher doses. The sensitivity of MOS cules in the gas. As with vacuum tube.,

transistors lo radiation is, however, de- large fluences of therricl neutrons can

pendent on the impurities in the gatc cause thyratcons to become useless as a

oxide. With improvements in the tech- result of breakage of the glass envelope

nique o,,r producing the oxide, the de- oi failure of glass-to-metal seals.

vices are expec.ted to survive doses of

i(Y rads (siiicon)

"F'Or 1lh dependent.L! of neuir,%n fluences at ,ariou,2 energies on the 'nergy yield anti distance from r

nuclear explosion. see Figs. X I 17a and h.

ti
352 INITIAl NUCLEAR iA-PIATION

Capacitors. Resistors. and Batteries

8.83 Nuclear radiation aftects the causirng a change in the resistivity of the

electricW! properties of capacitors to material.

some extent. Changes in the capacitance 8.85 Batteries are affected much

value, dissipation factor, and leakage less by radiation than other components.

resistance have been observed as a con- The effects of radiation on nickel-cadsequence of exposure. The effects are mium batteries appear to be insignifigenerally not considered to be severe for cant at gamma-ray dose rates up to 1 07

fast-neutron fluences less than 1015 neu- rads (air)/sec. No radiation damage was

trons/cm2. During a high-intensity pulse apparent in a number of batteries and

of nuclear radiation, the most pro- standard cells that were subjected to 101'

nounced effect in a caxacito; is a tran- fast neutrons/cm 2 . Mercury batteries can

sient change in the conductivity of the withstand fast neutron fluences up to

dielectric (insulating) material with a 101, neutrons/cm 2 .

corresponding increase in the leakage

currents through the capacitor. Cables and Wiring

8.84 Radiation effects in resistors

are generally small compared with those 8.86 It has been recognized for

in semiconductors and capacitors and some time that intense pulses of radiaare usually negligible. However, in cir- tion produce significant perturbation in

cuits requiring high-precision carbon electrical cables and wiring, including

resistors transient effccts may be signif- coaxial and triaxial signal cables. Even

icant at gamma-ray dose rates of 107 with no Aoltage applied to a cable, a

rads (carbon)/sec" and at tast-neutr-rn signal is observed when the cable is

fluences of '014 neutrons/cm2. The tran- exposed to a radiation pulse. The cursient effects are generally attributed to rent associated with this signal is degamma rays that interact with materials fined ar a replacement current, since it is

to produce electrons; however, ener- a current in an external circuit ,hat is

getic neutrons can also cause significant apparently necessary 'to replace elccionization by re. )iling nuclei. The tran- trons or other charged particles that arw

sient effect. on resistors include (I) a knocked cut of iheir usual -osi:ions by

change in the efiective resistance due to the radiation. In addition there is a sigleakage in the insulating material and nal, atributed to what is called the conthe surrounding medium, and (2) in- duction current, which varies with the

duced current that is the result of the voltage applied to the cable. It is

difference between *he emission and ascribed to the conductivity induced in

absorption of secondary electrons by the the insultating dielectric by the radiaresistor materials. The permanent ef- tio,1 Howcver, the conductivity current

fects are generally due to the displace- may also include substantial contriburnzAt of atoms by neutrons, thereby tiors from changes in !he dielectric ma-

'' In this and other cases the damae is determined by the dose ;ate (rather than the dose) of gamma

radiation.
TECHNICAI ASPF.CTS OF INITIAI NUCLEAR RADIATION" 353

teriai. These can usually be identified by changes in the electrical properties of

their gradual disappearance (saturation) the insulating materials. When such

after repeated exposures and by their damage becomes appreciabkl, e.g.,

reappearanc, after additional expo'ures when the resistance is reduced severely,

in which the,- is i considerable change electrical characteristics mr-y be afin the applied voltage, e.g., it is re- fected. The extent of the damage to

moved or reversed, insulating materials increases with the

8.87 Nuclear radiation can have neutron fluence (or gamma-ray dose),

both temporary and permanent effects humidity, and irradiation temperature.

on the insulating material of cables. If Ccrtain types of insulation are quite su1•,iizatior. occurs in the material, the sceptible to permanent damage. For exfree electrons produced contribute to its ample, silicon rubber is severely

conductivity. Hence, insulators are ex- cracked and powdered by a fluence of

pected to have a temporary enhancement 2 x 10", fast neutrons/cm-. The apof conductivity in ar ionizing radiatien proximate gamma-radiation damage

environment. Conduction in the insula- thresholds for three common types of

tor is frequently characterized by two cable insulation are: polyethylent,

components: (I) for very short radiation I x 101 rads (carbon): Teflon TFE,

pulses, a prompt component whose I x 104 rads (carbon), and Teflon FEB,

magnitude is a function of only the in- 2 x 104 rads (carbon). On the other

stantaneous exposurz rate, and (2) fre- hand, some irradiated polyolefins are

quently at the end of the short radiation capable of withstanding up to 5 x 10"

exposure, a delayed component having rads (carbon). A coi siderable degree of

approximately exponential decay, i.e., recovery has been observed with respect

rapid at first and then more and more to insulation resistance; this implies the

,lowly. possibility of adequate elecirical servi8.88 Permanent damage effects in ceability after moderate physical damcables and wiring are apparent as age.

TECHNICAL ASPECTS OF INITIAL NUCLEAR RADIATION'_

first of the these is called the "Compton WITH MATIOER effect." In this interaction, the gammaray (primaiy) phot)n collides with an

8.89 There are three important electron and some of the energy of the

types of interaction of gamma rays with photon is transferreu to the electron.

matter, as a ,esult of which ihe photons Another (secondary) photon, with less

(§ 1.74) are scattered or absorbed. The energy, then moves off in a new direc12The remaini:ig sections of this chapter may hr omitted without Ios.; of .:ontinflity.
354 INI I I\I N11( I FAR RADIX I(N

ticn at an angle to the direction of mo- -pair production." When a gammnra-a\y

lion of the priary photon. Conse- photon with cricrgy kn excess of I.0)2

quently. Comnpton interaction results in MeV passes near the nucleus of an

a change of direction (or scattering) of alom, the photon may be converted into

the gamma-ray photon and a degrada- matter with the formation of a pair of

tion ir. its energy. The electron which, particles, namely, a positive and a negafter colliding with the primary photon, ative electron. As with the photoelectric

recoils in such a manner as to conserve etiecl, pair production results in the

energy and( momentum is called a disappearance of the gamma-ray photon

Compton (recoil) electron, concerned. However, the" positive eclc8.90 The total extent of Compton tron soon interacts with a negative elecscattering per atom of the material with tron vith the formation of two photons

which the radiation interacts is propor- of lower energy than the original one.

tional to the irumber of electrons in the The occurrence of pair production per

atom. i.e.. to the atomic number atom, as with the other interactions,

(§ I .09). It is, consequently, greater per increases with the atomic number of the

aton for an element of high atomic material, but it also ir.,creases with the

number than for one of low atomic energy of the photon in excess of 1.02

number The Compton scattering de- MeV.

creases with increasing energy of the 8.93 In reviewing the three types of

gamma iadiadon for all materials, irre- interaction described above, it is seen

spective of the atomic number. that, in all cases, the magnitude per

8.91 The second type of interaction atom increases with increaing atomic

of gamma rays and matter is by the number (or atomic weight) of the mate-

"photoelectric effect." A photon, with rial through which the gamma rays pass.

energy somewhat greater than the bind- Each effect, too, is accompanied by ciing energy of an electron in an atom, ther the complete removal of photons or

transfers all its energy to the electron a decrease in thei. energy. The net result

which is consequently ejected from the is some attenualion of the gamma-ray

atom. Since the photon involved in the intensity or dose rate. Since there is an

photoelectric effect loses all of its en- approximate parallelism between atomic

ergy, it ceases toexLst. tn this,respect, it weight and density, the number of

differs from the Compton effect, in atoms per unit volJme does not var,

which a photon still remains after the greatly from one substance to another.

interaction, although with decree.s'd Hence, a given volume kor thicknes;s) (,'

energy. The magnitude of the photo- a material containing elements of hig"i

electric effect per atom, like that of the atomic weight ("heavy elements") will

Compton effect, increases wiih the be more effective as a gamma-ray shield

atomi: number of the material throitgh than the same volume (or thickness., of

which the gamma rays pass, and de- one consisting only of elements of low

creases with increasing energy of the atomic weight C"ligh. elements"). An

photan. illustration of this difference in behavior

8.92 Gamma radiation can interact will be given below.

with matter in a third manner, called 8.94 Another important point is that

Ij
TF(HNICAI ASPEC'US OF INITIAl NUCIEAR RADIATION 355

th2 probahilities of the Compton and without having undergone any interacphotoelectric effects (per atom) both tions can be represented by the equation

decrease with increasing energy of the , (X,)5 1

ga:mma-ray photon. However, pair productior., which starts at 1.02 MeV, in- where i. is called the "linear attenuation

creases with the energy beyond this coefficient." The distance .% :., usually

value. Combination of the various at- expressed in centimeters, so tha: the

tenuating effects, two of which decrease corresponding units for IL are reciprocal

whereas one increases with increasing centimeters (cm ý). It can be seen from

photon energy means that, at some en- the equation (8.05. I that, for a given

ergy in excess of 1.02 MeV, the ab- thickness x of material, the intensity I

sorption o' gamma radiation by a par- of the emerging gamma rays will be less

ticular material should be a minimum, the larger is the value of It. In other

"Chat .uch minima do exist will be seen words, the linear attenuation coefficient

shortly. is a measure of the shielding ability of

definite thickness, e.g., I cm, I fo-ot, or

other thickness, or any material for a

GAMMA. RAY ATTENUATION collimated beam of monoenergetic

COEFFICIENTS gamma rays.

8.96 The value of p., under any

8.95 When a narrow (or collimated) given conditions, can be cbtained with

beam of ganmma rays passes through a the aid of equation (8.95. 1) by determaterial, photons are remved as a re- mining the gamma-ray intensity before

suit of the Compton scattering intcrac- (I,) and after (U) passage through a

tion as well as by the photoelectric and known thickness, x, of material. Some

pair-production interactions. In other of the data obtained in this manner, for

words, the scattered photons are re- mon;,'nergetic gamma rays with energarded as being lost from the beam, gies ranging from 0.5 MeV to 10 MeV,

although only part of their energy will are recorded in Table 8-96. The valvrs

have been deposited in the material. If given for concrete apply to the common

such a collimited beam of gamma r:ys form with a density of 2.3 grams per

of a specific energy, having an• initial cubic centimeter (144 pounds per cubic

inter.Aity (or flux) (;' /, photons pet foot). For special heavy ý,,ncretes, con-

-quare centimeter pcr sec.)nd, traverses taining iron, iron oxide, or b'arytes, the

a :hickness of xol a givea material, the coefficients are increased roughly in

intensity, I, of the rays which emerge proportion to the density.

IIn this etuu4tion, the intensity is the r, mber of (uncollided) photons per sqvaie centimeter per

second. A similar equation, with ihe "linear energy absorption coefficient" replacing; the linear

atienuation coclficient, is applicable when the iiitensity is; expressed in terms of the total onergy of the

photons per sqjare centimeter per second.

a._____

L ~ . -- --- ---- ---- --- -- ~- ,~-- ---
356 INMTIAI NUCI FAR RADIATION

Table 8.96

LINEAR ATTENUATION COEFFICIENTS FOR 'AMMA RAYS

I.incar A *tenuation Coefficient (R) in cm

Gammia-ray Energy

(McV) Air Wtier Concre'e Iron Lead

0.5 1.11 • 10 0.047 0.22 066 1 6.'

1.0 0.81 x 10 i.071 0.15 0.47 0.80

20 0.57 I0 1 0.049 0,11 (V33 0 52

J.) 0.46 x 10 0,040 O,)58 0.28 0.47

... 0 041 x 10 9134 0.078 0.2h 0.48

.0 0.35 x 10 0.030 0.071 0.25 0.52

10 0,26 x 10 0.022 0.00) 0.23 0.55

8.97 By suitable measurements and cess of 1.02 MeV, pair production

theoretical cakculations, it is possible to begins to make an increasingly signifidetermine the separate contributions of cant contribution. Therefore, at ,uffithe Compton elfect (p.), of the'pho'- ciently high energiest"6*•i6ttdnua'iioncoelectric effect (L, ), and of pair produc- efficient begins to increase after passing

tion (LPP) to the total linear attenuation through a minim.rn. This is apparent in

coefficient as functions of the gamma- Fig. 8.97a, as well as in the la:;t column

ray energy. The results for lead, a typi- of Table 8.96, for lead. For elerrents of

cal heavy element (high atomic number) lower atomic weight, the increase does

with a large attenuation coefficient, are not set in until very high gamma-ray

given in Fig. 8.97a and those for air, a energies are attained, e.g., aoout 17

mixture of light elements (low atomic MeV for concrete and 50 MeV for

number) with a small attenuation coef- water.

ficient, in Fig. 8.97b. Except at ex- 8.98 The fact that the attenualion

tremely low energies, the photoelectric coefficient decreases as the gamma-ray

effcct in air is negligible, and hence is energy increases, and may pass through

not shown in the figure. At the lower a minimum, has an important bearing on

gamma-ray energies, the linear attenua- the problem of shielding. For example,

tion coefficients in both lead and air a Thield intended to attenuate gamma

decrease with increasing energy because rays of I MeV eiiergy will be much less

of the decrease in the Compton and effective for radiations of 10 MeV enphotoelectric effects. At energies in ex- ergy because of the lower value of the
II( IINI( \I ASPI"( IS ()I- IN Ii* \I NIt(I !!., R..\I)I \IION, 357

2.0 -

I 

I

E

1.)

: 1.5 . .. .. t

1,--

z

L 10

F- 0.

w

I'-

0

t- -

z

0 2 4 68 10

GAMMA RADIATION ENERGY (MEV)

Figure 8.97 a. i~ncar attenuation coefficient of lead as function of uamma-ray energy.

2.0

7

E

0

x 1.5

z

C'- 1. PP-___ ______

w

5 10

0 -A

0 0.5 _4_ I

F- 0

024 6 810

GAMMA RADIATION ENERGY (MEV)

Figure 8.97b. Linear attenuation coefficient of air as function of gamma-r:y er,'rgy.

..........................- w~- -.--
358 INITIAL. NUCLEAR RADIATION

attentuation ccefficient, irrespective of for iron is about 0.027 in the same units

the material of which the shield is corn- (g/cn- 2 ).

posed. 8.101 If the symboi p is used for the

8.99 An examination of Table 8.96 density of the shield mateial, then

shows that, for any particular energy equation (8.95. 1 ) car. be rewritten in the

value, the linear attenuation coefficients form

increase from left to right, that is, with 1 = e e ,', (8.101.1)

increasing density of the material. Thus.

a given thickness of a denser substance where 1/1, is the transmission factor of

will attenuate the gamma radiation more the shield of thickness x cm. and p./p is.

than the same thickness of a le,'s dense by definition, the mass attenuation comaterial. This is in agreement with the efficient. Taking p./p to be 0.023 g/cm2

qualitative c(:ncept that a small thick- for initial gamma rays, it follows from

ness of a substance of high density will equadon (8.101.1) that

make as effective a gamma-ray shield as Transmission factor

a greater thickness of one of lower den. U I (.

sity (§ 8•,38 et seq.).

In the absence of better information, this

expression may be used to provide a

MASS ATTENUATION COELFFICIENT rough idea of the dose transmission factor, as defined in § 8.72, of a thickness

8.100 As a very rough approxima- of x centimeters of any material (of

tion, it has been found that the linear known density) of low or moderate

attenuation coefficient for gamma rays atomic weight.

of a paricular energy is proportion'tl to 8.102 The simple tenth-value

the density of the absorbing (shield) thickness concept described in § 8.39 is

material. That is to say, the linear at- based on equation (8.95.1 ). For such a

tenuation coefficient divided by the thickness the transmission factor is 0. 1

der0;ity, giving what is called the "mass and if the thickness is represented h,

attenuation coefficienm," is approxi- Xo 1. it follows that

siately the same for all substances for a 0. I = e ,'..

specified gamma-ray energy. This is

especially true for elements of low and or

medium atomic weight, up to that of 30

iron (about 56), where the Compton xV( - cm. (8.10.. 1

effect makes the major contribution to

the attenuation coefficient for energies

up ito a few million electron volts (cf. If p/p is taken to be 0.023 g/cm2 for the

Fig. 8,97b). For the initial gamma r:tys initial gamma radiation of higher energy

of higher energy, the effective mass at- then, as a "rule-of-thumb" approximatenuation coefficient (§ 8.104) is close tion,

to 0.023 for water, wood, concrete, and

earth. with the densities expressed in I(cm) 1 00

grams per cubic centimeter. The value p(g/cm')

Ai
FT('HNICAL ASPE-CTS OF INITIAL NUCLEAR RADIATION 359

or the equivalent and the energy of the impinging rzdfia203 -tion: thus. equation (8.95.1) is now

T(f D(-f- (8. 162.2) written as D(Ib/ft,)

where, as in § 8.42, Tis the tenth-value

thickness in feet and D is the density of Values of the buildup factor for a variety

the material in lb/ft' . It follows, there- of conditions have been calculated for a

fore, that for the less-dense materials, number of elements from a theoretical

for which pI/p is close to 0.023 g/cm-,2 consideration of the scattering of phothe product D × T should be equal in tfns by electrons. The fact that these

about 200 lb/ft2 for gamma rays of values are frequently in the range from

higher energy. This is in agreement with 10 to 100 shows that serious errors

the values in the last column of Table could arise if equation (8.05. 1) is used

8.1I for nitrogen capure (secondary) to determine t?.e attenuation of gamma

gamma rays. The D x T foi iron (or rays by tLick snields.

steel) is smaller than for the other mate- 8.104 It will be apparent, therefore,

rials because p/p is larger, namely about that equation (8.95.1) and other,;

0.027 g/cm 2

, for the gamma rays of derived from it, such as equaions

higher energy. (8.101.2) and (8.102.1), as well as the

simple tenth-value thickness concept.

THICK SHIELDS: BUILDUP FACTOR will apply only to monoer-ergetic radiations and thin shields, for which the

8.103 Equation t8.95.1) is strictly buildup factor is unity. By taking the

applicable only to cases in which the mass attenuation coefficient to be 0.023

photons scattered in Compton interac- for less dense materials (or 0.027 for

tions may be regarded as having been iron), as given above, an approximate

removed from the gamma-ray heam. (empirical) allowance has been made for

This situation holds reasonably well for both the polyenergetic nature of the

narrow beams or for shields of moderate gamma radiations from a nuclear explothickness, but it fails for broad beams or sion and the buildup factors due to multhick shields. In the latter circum- tiple scattering of the photons. The restances, the photon may be scattered suits are, at best, applicable only to

several times before emerging from the shields with simple (slab) geometries.

shield. For broad radiation beams and Furthermore, practical radiation shields

thick shields, such as are of interest in must absorb neutrons as. well as gamma

shielding from nuclear explos~ons, the rays, and the gamma radiation produced

value of I, the intensity (or dose) of the in the shield by inelastic s*cattering and

emerging raoiation, is larger than that radiative capture of the neutrons may

given by equation (8.95.1). Allowance produce a greater intensity inside the

for the multiple scattering of the radia- shield than the incident gamma radiation is made by inclutirg a "buildup tion. Consequently, any problem infactor," represented by 8(x), the value volving gamma radiation shielding.

of which deptnds upon the thickness x especially in the presence of neutrons, is

of the shield, the nature of the material, complex, even tor relatively simple

I!
360 INITIAl NUCLEAR RADIATION

structures. appropriate computer codes determine the gamma-ray spectrum. are

are thus necessary to obtain approxima- complex, it is possible to calcula!e the

tions of the attenuaton. In the absence spectrum :it various distances from :t

of ,.tter information, however, the ef- nuclear explosion. Compuwations o1f this

,ective tenth value thicknesses, as given kind have been used to estimate

in Table 8.41 or derived from equation gamma-ray doses, as will be seen later

(8.102.2). can be used to provide a (§ 8. 125 et seq.). As an example. Fig.

rough indication of gamma-ray shield- 8. 106 shows the spect:um of the initial

:,ng. gamma radiation received at a distance

of 2,(M) yards from the explosion of a

TVHE INITIAL. GAMNIA-R/.Y tission weapon with an energy yield of

SPECTRUM 20 kilotons. At this range. some 70

percent of the gamma-ray photwns have

8.105 The major proportiin of the energies less than 0.75 Me"I. It ihould

initial gamma radiation received at a be remembered, however, that the phodistance from a nuclear explosin arises tons of high energy are the most hazfrom the interaction of neutrons with ardous and also are the most diflicult io

nuclei, especially nitrogen, in the at- attenuate.

nmospherc and from the fission products

during the first minute after the burst. !NTERAcTONS OF NEUTRONS WITH

Gamrna rays from inelastic scattering MATTER

and neutron capture by nitrogen have

ei'ective ene:gies ranging up to 7.5 8.10)7 The modes of interaction of

NMeV (or more) and those fro.:m the fis- neutrons with matter are quite -'iflerent

sion products are mainly in the I to 2 from tho I :7.-rienced by gaitiona-ray

MeV range. After passage through a photons. Unlike photons. neutrons are

distance in air, some of the photons will little offectcd by electrons, but they do

have been removed by phc.toelectric and interact in various ways with the nuclei

pair-production effects and others will of atoms present in all foinis of matter.

have had their eneigies decreased as a These neutron-nucleus interactions are

result of successive Compton scatter- of two main types, nam,.ly. scattering

ings. There will consequently be a and absorption. As aheady seer., scatchange in the ganima-ray energy distri- iering reactions can be either inelastic (§

bution, i.e., in the spectrum. ".09) or elastic (§ 8.52). In inelastic

8.106 Information concerning the -cautering part of the kinetic energy of

gamma-ray spectrum of the initial radi- the neutron is converted into internal (or

ation is important b:ecause !he suscepti- excitation) energy of the struck nucleus.

bility of living organisms and of various this energy is theii emitted as gamma

electronics component,,, ,he attenuation radiation. For inelastic scattering to

properties of air and shielding materials, occur, the rteutron must initially have

and the response of radiatiom detectors sufficient energy to raise the nucleus to

are dependent upon it. Although the an excited state. The magnitude of this

interactions of both neutrons and en,.:rgy depends on the nature of the

gamma rays with the atmosphier',ý which nucleus and varies greatly from one el

-------------------- i----- ... -,wi - oi----
TECHNICAL ASPECIS OF INITIAL NUCLEAR RADIATION 361

100

C,.-

0

F- 60

CL

0~

LJ1

<'hLAh 6040[

w I

I-z

LL) 20

C-)

a-

__ _-I

0 0.75 2 4.5 8 12

GAMMA- RAY ENERGY (MEV)

Figure Si. 106. Spectrun, of initial gamma radiation 2,(X)O yards .rom a 20-kilo:on explosion.

er.ent to another. Howev,:r, a rough wiei, a nucleus is equivalent !o a collig&ýneral rule is that for many,. but not all. sion between ;wo billiard balls: kinetic

hevvy or moderately heavy nuclei, e.g., energy is conserved and is merely

iron and uranium, inelastic scatiering transferred from one partice to the

may ot,'ur for neutrons with energies other. None of the neution energy is

ranging from a few tenths MeV to as transformed into exc'tation enery of

low as a few tens of ktV. For lightei !he nucleus and there is n- accompanynuclei, inelastic scattering iý possible ing gamma radiation. In contrast with

only whetp the neutrons have higher en- inldastic scattering. elastik scattering

egies. Significant inelastic scattering cart take place with neutions of all enoccurs only for neutron energies above ergies and any nucleus. For a given

about 1.6 MeV for nitrogen and about 6 angle of impact, the fraction of the kiMeV for oxygen. Neutrons with erter- netic energy ot the nezjt•on that is hansgies below the appropriate threshold ferred to the nucleus in a collision is

values for the nuclei present ini the me- dependent only on the mass of the latter.

dium cannot undergo inelastic scatter- The smaller tIe mass of the iuclkus th'.

ing. greater ':s Ine 5action of th~e neutron

8.108 When elastic scattering energy it ziin remove. Theoretically, the

occurs, the interaction -4 the neutron whole of the kine',c energy of a neutron

{t
3612 IAtl-I NCI I ~R RADI1A I t10N'

coulld he tr,.isferned to a hNvdroi-wn nn~- emits thec excess energy as a IQarnrna-rav

cleu (nroton) in it sInf ., head ' .col! il- photor' This t,,pe of react ion uIsuallV

,,Ion. IIn faci. ;iydrogcn. the lighitest ek'- OCCUrs wvith light nuclei and fast neuii.cnt. offers the best weans for rapidly troils, although there are a few in

degrading f&st neu~trons %i Oh eriirgie,ý stances eq.g.. lithium-6 and boron- 10,

!e,ýs than about 0.5 McV. It is for this where it also taikes place with slow neuicason that hydrogen., Ii.g, wate: . Is trenm . Nitrogen interacts with fast neu-

-in important const ituent (of neutron trons In at !1cas! two ways in which

shieIlds (§ S .67) For neutrons of higher char,'ged particles are emitted (§§ 1) 4.

energy than 0.5 N~eV. it is. better to take 9.44): one leads to the formation of

advarniage of ine, ast ic scatteri rig to slow rad~ioactive carboni- 14 (plus. a proton)

down the neutrons. Tbh- h-'avy element and the other, to tritium. the riýJioacti'le

in the special concretes de-,wrihcd In isotope, o" hydrogen (plus stable carX.69 serve'. th.S purpose. hon-I 12.

8.109 The second fundamental type 8.111 Fission, is (,, course, also a

Of interaction of neutrons. with matter foriji of 'Interaction between neutrons

involves cornplete removal of the neu- and rnalvtr. But since i! is restricted to a

Iron by capture. Radiative icapture (§ small number (if nuclear species and has

8.09) is the most comminon kind of cap- beeci considered in detail in Chaplte I. it

lure reaction, it occurs to some extent. wilnot b-- distussed fur~her hertc.

at least, with ncarly all nuclei.Th, 8. 21 rz he rate of interaction oit

probability of capture is greater for slow. neuirons with nuclei carn be described

neutrorns than for those of high energy. quantitatively in term,; of the Concept of

M, st ligzht nuclei. e.g.. carbon and ox- aucleaT *roses' Sectidow;, - The cross

ygen have little tendency to undergo section may boe regarded as 1h,- effective

ýhe radiative ;;-apture reaction with neu- target area of a particular type of nuIron:.. With nitrogen. howe-ei. the zen- dlets for a specific reaction and is a

Jcncy is significan. (§ S. I1 1. hut rot measure of the probability that this regreat. For other nuclei. especially some action -will occur between a neutron. of

of :mediumn or high mass, .. cad- given energy. and that nucleus. Thus.

miu.n. lthe rakdi~live captiore reaction each nuclear species has a specific scatoccurs very readily. In certain cd.s i, the tering cross section. a capture cross

reacticon product i- radioactive (§ 8.61 ). section, and so on. for given neul'on

this is of importance in some aspects of eneigy, the total cross section for that

weapons eff'-cts, as will be seen in energy is the sumn of the specific Lross

Chapter IX. sections for the individual intera,.tions.

8.110 Nnother type of reaction is Both specific and total cross sections

that in which the incident neutron enters vary withi the energy o! the neuitron,

the target i.ucleus and tiue compound often in a very complex manner.

nucleus so formed has enough excila!;ion F.1113 The nuclear cross sections for

energy t.., permit the expulsion of an. neutron-nucieus interactions are analoother (charged) particle. e.g , a proton, gous to the linear attenuation coeffi-j

deuteron, or alpha particle. The ;ez~idual cients (for gamma rays) divid-A by the,

nucleus is often in an excited state and nujmber of nuclei in unit vo!ume o& ihe
I1 .(H ',NI(CAI ASP F.CTS 0F INITIAl NU(II fAR R.A1I) 1AI()1 363

medium. In fact, an expression similar was, therefore, made to measurements

to equation (8.95. 1) can he employed to of neutron flkui within , few specified

describe the attenuation of - narrov, energy ranges: from the res'ilts a general

beam of monoenergetic neutrons in their idea of the spectrum was obtained.

-assage through matter. However. be- Measurements of this kind were made

cause the neutrons in the initial nm. .. , by the use of threshold detectors of

radiation are far from monoenergetic activated foil or fission foil type (§k

and the cross sections are so highly 8.61. 8.62).

dependent on the neution energy. (he 8.11I Neutrons are liberated during

equivalent of equation (8.95. I ) must not the fission ari1 fu,;ion processes. but the

be .ised to calculate neutron attenuation neutrons of interest here are those that

for shieldiig purposes Shielding calcu- escape from the exploding weapon.

lations can be made by utilizing cross Bath the iota! number of neutrons and

sections, the neutron energy distribution tiier spectrum arc altered during transit

in space and direction, and other data, through the weapon material;. Output

but the calculatins require the use of ,?ectra that might be considered illuscomputer codes. Such calculations are trative (,f fission and thermonuclear

too complicated to be described here. weapons are shown in Figs. 8.116a and

b, respectively. As mentioned preTIHI NEU.TRON ENERGY SPECTRUM viously, ,he neutron source can he defined properly only by considering the

8,114 The energies of the neutrons actual design of a specific weapon.

received at some distance from a nuclear Hence, the spectra in these figures. are

explosion cover a very wide range. from presented only as examples and should

several millions down to a fraction of an not be taken to be generally applicable.

electron volt. The determinatien of the 8.117 Passage of the neutrons

complete energy spectrum (§ 8.53), ei- through the air, from the exploding

ther by experiment or by calculation, is weapon to a distant point, is accompanvery difficult. However. it is possible to ied by interactions with nuclei that resul:

divide the spectrum into a finite number in attenuaion and energy changes.

of energy groups and t(* calculate the Hence, the neutron spectrurn. a' a disneutron flux in each eticigy g:oup at t ice may differ from the output specvarious distances from the explosion trbm of the weapon. Extensive results of

point. These calculations can ther 'e computer calculatiors of neutron

checked by measuring the variation of fluences at (or near) the earth's surface

flux with distance from known neutron are now available and these have been

sourres that are repiesentative of each used to plot the curves in Figs. 8.1 17a

e, .rgy group. and b, for fission and thermonuclear

8.115 Prior to *he cessation of at- weapons. respectively. The figures

rnospheric testing of nucleaw weapons, show the neutron fluences per kiloton of

neither the extremely large and fast energy release for a number o" energy

computers nor the sophisticated mea- groups as a function of slant rang--. The

surement instruments that are now uppermost curve in each case gives the

available were in existence. Recoure total fluence (per kiloton) of neutrons
36•4 INITIAL NUCLEAR RADIATION

Io _ I I7I ! 1 l I! 

2

122

i~z

I0 5-

(X

W

z

I--

2

10

2

i~° 1 1 L1 11 I I Ii lI ______

0.1 0.2 0.5 I 2 5 !0 20

ENERGY INTERVAL (MEV)

Figure 8. 1 16a. Neutron spectrum for a fission weapon per kiloton total energy yield.

vith energies greater than 0.0033 MeV. means that the fluence in each energy i.e., 3.3 keV. group decreases with increasing dis8.118 It is apparent from Fig. tance frxin the expios:on, but the pro8.1 ! 7a that for ý, fission weapon the portions in the various groups do not

cirves for the different energy gronps all change very inuch; that is to say, the

have roughly the same slore. This neutron spectrum does not vary signifi-
I[ (' INI"'AI ASP!IC("S OF iNI ,i *I Nt l I I- .\R K. API I 1()N, , 365

10 23 7 T-7T -7

54

2

22

-10

0 5 -

n,-

z

o 5

a-"C w 10 '

5

10 20 1 1 1 I .. Lj. I IJI I I IJ I _IJ

0.1 0.2 0.5 1 2 5 10 20

ENERGY INTERVAL (MEV)

Figure 8.1 16h. Neutron spectrum for a thermonuclear wearKrn per kiloon total energy

yield.

cantly with distnce. Furthermore, al- Fig. 8. 116a. This accounts for the equithough it is not immediately apparent librium neutron spectrum from a fission

"from Fig. 8.1 1Ia, the spectrum is al- explosion mentiou1ed in § 8.55. The

most the same .is the source spectrum in spectrum does change at much lower
366 INITIAL NUt I.EAR RADIAl ION

5

12

2 •L-CURVE MeV

1 8.18 to 10.0

2 6.36 8.18

3 4.05 6.36

4 2.35 406

5 i. 11 2.35

6 0.111 I1.1

lo,__ _17 0.0033 r'. I1I -- I. 8 Total above 6.- •

-- \

2 N

1010 ______

z

0, 5 -

I- - --I

WI 2

z7

z

J --

Li.

2

53

22

21- II

0 400 800 I P, 0 1600 12000 2400

SLANT RANGE (YARDS)

Fkgure 8. 1 17a. N~eutron flunre per kiloton energ. yielJ incider:t on a target located on or

near the carth's surface from the fission spectrL.m shown in Fig. 8. 1-16a.
TF.CHNI('AI. ASPETS OF INITIAl NU('I.EAR R[ADIATION 367

14 -c ' 7

5-

2

i013 _ _ CURVE MeV 10 - -_ 

I 12.2 to 15.0

5 2 10.0 12.2

3 , 18 10.0

4 6.36 8.18

2 X 5 4.06 6.36

6 2.35 4.06

10 12 7 I.II 2.35

8 0.111 1.11

--9 0.0033 0.111 - 5 -10 Totol obove 3.3keV -

[ ~10 2

I--

z\

0 5 - _--

La - _ _ _ _ _ _ _ _ _o_ _ _-

Uj 2 I0~10

I~i i 1012 9"1

- ________ - 10 ,... ----. . ~ r~ ,

U ,

z-L

!O7 1ý 2 .. J' • ,• _ _ • __ _L

2 6

11
368 INITIAL NUCLEAR RADIATION

neutron e,,ergies, but this is no: impor- compared to fluence-; at corresponding

tata. distances In an infinite air medium. For

8.119 Examination of Fig. 8.1 17b source-target separation distances less

for thermonuclear weapons reveals a than about a relaxation lengtn,'-, localdifferent behavior. Curves 5 through 9, ized reflect~or. from the ground generi.e., for neutron energies from 0.0033 to ally tends to increase the intensity of

6.36 MeV, are almost parallel, so that in high-energy neutrons- however, at such

this range the spectrum does not change short distances, the initial nuclear radimuch with distance. But at higher ener- atit)n is of interest only for very low

gies, especially from 8.18 to 15 MeV, yields, since tor higher yields other

the slopes of the curves are quite dif- weapon effects will normally be domrferent. Of the neutrons in groups I, 2, nant (cf. § 8 06). At longer distances,

and 3, those in group I, which h.ve the the high-energy neutron intensit) ,--a)

highest energies, predominate at a slant be reduced by a factor of five or I tore

range of 400 yards, but they are present compared to infinite air when both the

in the smallesi proportion at 1,600 source and the target i,'e at or near the

yards. During their passage through the ground surface, e.g. a surface or nearair, the fastest neutrons are degraded in surface burst. These effects have been

energy and their relative abundance ;s included in the calculations from which

decreased whereas the proportions of the figures given above were derived.

the somewiat less energic neutrons is

increased. The neutron spectrum thus INITIAL RADIATION DOSE IN TISSUE

changes with distance, especially in the

high-energy range. The peak that exists 8.121 Simplified, but reasonably

at 12 to 14 MeV of the source spectrum accurate, methods have been developed

in Fig. 8.116b becomes lower and the to predict the initial iadiation dose to

valley between about 6 and 12 MeV persons located en or near the surface of

disappears with increasing slant range. the earth. These methods are described

At very long ranges, when the high-en- separately for neutrons, secondary

ergy neutrons have lost much of their gamma rays from radiative capture and

energy, an equilibrium spectrum would inela:tic sca'tering in the atmosphere (§

be approached. 8. II ). and fisioa product gamma rays.

8.!20 Figs. 8. 17a and b provide The contribution of the primary gamma

estimates of neutron fluences and spec- rays from fission to the radiation dose at

tra from low air bursts fot taigets on or a distance is small enough to neglect (§

near the surface of the ground. As a 8.04). In all cases, the data are based on

result of reflections and absorption by the assumption that the average density

the ground, an air-ground interface can of the air in the transmission path, beincrease or decrease the neutron teen the burst point and the target, is

fluences by as much as a factor of ten 0.9 of the normal sea-leve! density.

"A rtlaxalion length may be takcin as tke distance in whi:h the radiatiom inlen'/ily in a speciltkd

ma.erial is decreased by a factor of e, where e is the base of the natural logarithms (about 2.7 v). The

relaxation length in a given material depends on the !'eutron energy ar I on whether the direct fluence

only or the total (direct plus scattered) fluence is being considered.
TECHNICAL ASPECTS OF INITIAL NUCLEAR RADIATION 369

Ini:ial Neutron Absorbed Do~w fission weapons, there are two curves in

8.122 With spectra such as those each part, they do not necessarily repshown in Figs. 8.116a and b to serve as resent the extremes in neuitron dose that

sources, a neutron transport computer might result from differernt weapon decode may be used to calculate the neu- signs, but the dose frcom most fission

tron dose resulting from a nuclear ,ex- weapons'should fall between the two

plosion in a specified geometry, i.e., curves. It is .;uggested that the upper

burst height, target height, and ai, der,- curve of each pair in Fig. 8.1 23a be

sity. The latter is taken to be the average used to obtain a conservative estimate o'

density of the air between the burst and the neutron dose from ission weapons

the target before disturbance of the air for defensive purposes, and that the

by the blast wave, since the neutrons of lower curve be used for a conservative

interest depart from the region of 'he estimate for ofiensive purposes.

explosion before formation of the blast 8.124 In order to determine t'ie

wave and are deposited at the target neutron dose received from an air burst

prior to its arrival, of W kilotons energy yield, the dose for

8.123 Results of such calculations, the given distance as obtained from Fig.

which have been corro'borated by test 8.123a or b is multiplied )y W. For a

data, are given in Figs. 8. 123a and b, contact surfacý- burst, the valuesi from

for fission and thermoi'rclear weapons. Figs. 8 123a and b should be multiplied

respectively. In each case the absorbed by 0.5. For expjosicmns above the surface

neutron dose (in tissue) received by a but bel,,w about 300 feet, an approxtarget on or near the surface of the earth imate value of !he neutrOn dose may bc

is shown as a function of slL at range per obtained by low, i- :nterpolatior,. b-Pet' ,c

kiloton energy yie!d for explosions at a the values, Jor a cý%:tact surface burst and

height of about 300 feet or more. For one at 7,,X) feet or above. The

convenience of representation, the fense" curve of Fig. 8. 123a was ased to

curves are shown in two parts: the left generate the data for Fig. 8.64a, and the

ordinate scale is ','or shorter ranges and curve in Fig. 8. 1 23b was used for Fig.

the right is for loager distances. For 8. 64b.

1 'ex! connlivid on page ),7 4, 1
370 INl I-IIý INLT; F; XR RAI)IA lION

The curves in Fig-, X.123a and h hM(aph'

show the neutron dos, in tic per Given: A 10 KT lission weapon is

kdoton vield as a Furnction of lAani radgc exploded at a hcight of 3(N0 feet,

from a hurst at a height of 300 feet or

more for fission weapoms anid thermo- Fihnd: The neutron dose at a slant

nuclear weapoos respeciively. range of I .5X) yards that is conserv2Itive

S(ing. In order t apply t data '1 from the defensive standpoint.

Figs. 8 ?23a and b to ;n explosion of So!utiin: Sjiict: ihe height of burst

,my energy. VAr' k'Ih tons, niultip!y the 301) feet, no height correction is necesvaluic (or the kiven distan.2e a,. obtained sary. From the upper "edclense") curve

frow Fig Il. 1.23a or h ,y iV. For a in Fig. 8. 12 ýa, the neutron dose per

Contact slirface burst, multip!y the dose kiloton yicid at a slant range of I S(()

obtained from Fig . 8.123a or h bs 0.5. yards from an explosion is I) rads. T'he

For burs(,; beIreek, te surface and corrsponding dose. ),. from a I0 K r

about 3",Y) feel, at; approxI.m:re 'a llc of explosion is

the neutron dose ma\ be obtained by l() x 16 16) rads. Answer

linear interpolation bo'ween a surface

hurst ard one at 3W) feet ,r above.

It

II, -... .
-II(HNI(AI ASIFL'I-(.S M)' INITIAI NU'CI FAR RAI) IIAI(ON 371

105

10 4 I0

55

103

w

U10

0

w

'An

(LO

VI

z

0

w

10 

2- 

10

'

0 1,000 ?,000 3,f)00 4000

SLANT RANGE MRijM F.XPLOSION (YARDS)

Figure 8. 1 23,.. Initial neutron dos,:' jr kilooln total yield as a function of slant range fromr,

fissiovi weap)n air hur,,ts, based or. 0.9 normal sea-leve' air density.

3⁄4i - ', .". . . , •-• ,,• • 0 ._ .. .,• .. , jr. 
372 INITIAL NUCLEAR RADIATION

105

! F

2 - - . . 5; IC4 10'

I-- 5

V) 103 10 LAJ

t

C,)

102

5 . -,

2 - " 2

1,000 2,000 3,000 4,Qr 0

SLANT PANGE FROM EXPLOSION (YAROS)

Figure 9. 123b. Initial neutron dose per kiloton total yield as e function of slant range from

thermonuclear weapon air bursts, ba.;ed on 0.9 normal sea-level air densi!y.

Fif

4

*1

II
I I( IfN I( \1 *\SPI1 ( I S Mi IN*ýI I I \i %I.t( I I \R R \0l \ I[(t)\ .37.

Sct ,tt ( )mh ( rP, iPi a- R( i .% Abs Pvl 'lw I~p~ . the seco.t1nd~ar%~ 'anl ma ras s recwh a khl

8.125 The sccondatr\ (or air NeCOnI tant tareet befo~re the hlast , s h&s

dary ganmmu ra'ss, i.e.. the gamma ir.-J tras C Ilcd s cr% t ,r Ie ,cc~ Fig X .11

pri dueedi h. variousl i nteract i low oif N. 12-7 Some Of 11he result i alr

neutron,, with at mospheric nuclei . must Lit ions of secondar\ ý.hs orhed t2AIitM.1

he considered separately fromt the tis raý doses (in tvisue). ot~hatned II diith

sion product gamnma rays to provide a manne1r1 rid icMted laho e arc sho'sin III

generall/.cd prediction scheme since the Figs. .4. 1 27a and h, w,%hich correspont' to

relative 'importance of the two depends the neutron dose cuts es in Figs 1% 2,111

oin several factors. Including the total and h, respectivelN . T[he condi; ions ot~

yield, the fraction of the total yield appi icahi I it (if ihe tigurc s. such J, air

derived fromn 1ission, the height of hurst. hurst or contact surface hurst, target

and the slant range from the explosion to location, o)tiensie o~r iees s

the target. Since measuremciis at at- etc. are the samne ats givenl Inl § . 2

mospheric tests have provided only the X 124, In order ito he consisitent, if either

total gammna radiation dose as a fun~ctioni the ''otlense" or ''deterise- curse In

of distance from the source, computer Fig,. 8 1 23a Is used ito ohtain the necutronl

calculations have been used to obtain dos-:ý for a given %-ituation, the corre-

.he doses from the two Individual sponding curve in Fig. 8 1 27a should he

gamma-ray sources. The results of the used for the secondary gammfia-ray dose

calculations of air-secondary gammaray dosies (and the total doses) predictd Vi-sis m Pr1)'lii I (wnma-Ru, -Vs,0oci're

by the calculations have been comnpared

with measurements performed at nuclear weapon tests. For bursts in the 8.128 In order to est innate the

lower atmospheie. the gam-ma rays fromt gammna-ray dose front fission Products,

isomeric decay provide such a small the radiation transport com~puter code

firiction o)f the tc~tal gamma-ray ene:rgy must be supplemented with a Code that

that the), can be neglected in the cal- describes the evolution and rise of the

culation of total dose in tissue."S radioactive cloud containing the fission

8.126 By using neutron spectra, products. Since the fission product radli

such as those shown in Figs. 9.11 O6a and ation is emitted over a sutliciently long

b, the secondary gamma-ray source can period of time, the hydrodynamic effect

be calculated. The latter is then utilized (§ 8.36) of the blast wave on the averto com~pute the secondary garnmmi-ray age air density between the source and

dose resulting from a nuclear explosion the target must be considered. The hyin a specified geometiy. As is the case drodynamic enhancement becomes

for rieutr-)ns, the all den~sity is taken to more important at high energy yields

be the average density of the air betweeTn and also at greater ranges because of the

the burst and the target before distur- larger volume of low-density air behind

bance of thc air by the blast wave, Once tne shock front.

lt sho~uld be noted that the ordinates in Fig. 8.14 are the energy emission ratesý the total cnergy

would then be obta'ried by integration over the effective emission time. This time is vay much shorter for

isomeric decay gamima rays than for fission protducts.
374 INITi. I NU('i FA R R.NI)iA I ION

",he irves in Figs. 8.127a and h ExapIh'

sho'v the secondary gamma-ray dose in

tissue per kiloton yield as a function of Giexln: A 2 KT 'isufon eapon is

,,lant range from a burst at a height of exploded on the surface.

3(00 feet or more for fission weapons and Find: The secondary gamma-ray dose

ih.rmonuclear weapons. respect'vely. at a slant range of I .(JX) yards thai is

Sc.allng. In order to apply the data ia conNerva'ive frOm the olt,,nsive standFigs. 8.127a and b to anl explosion of point.

an) energy, W kilotons, multiply the Soluiomn: Since this is a coitact survalue for the given distance as obtained face burst, a correction factor of 0.5

from Fig. 8. 1 27a or b by W. In the case must he applied to the value obtained

of a c)ntact surface burst, multiply the fromn Fig. 8.1 27a. From the lower

dose obtained from Fig. 8. 1 27a or b by "ollense"• curve in Fig. 8. 127a, the

0.5. For bursts between time surface and secondary gamma-ray dose per kiloton

about 3() feet, an approNImate value of yield at a slant range of I ,(X) yards

the secondary gamma-ray dose may t, from an explosion at or above 3W1) feet is

ohtained hy linear interpolation. 30 rads. The corrsponiing dose. DI.

from a -urface burst 20 KT explosion p;

O , 20 -, 0.3 _;, 30 .-0X) rads. Answer

'0
I t-.HNI(AI ASPt( VS (01- I'1I I 1AI N '( I V-• R RA I)I A I ION 375

V

0

0

IP D

•4

z

0

w

iC•-4

0 .0 90 3)0? C

CLANT RANGE FROM EXPLOSION (YARDS)

Figure K. 127:a. Air-secondary gamma-ray component of the initial nucdear radiation dose

per kiloton yield as a function of slanw rangc from fission weal,on air bursts,

based on 0.9 normal sea-level .iir den:it;.'.

• :: ...
376 INITIAL NUCLEAR RADIATION

'0 10

V)

05 5 .. . .. . .. .

2 .........- 1------------2

Lii

o 10 ... - 1-- 0

CF 5 . ....... .

z 102 .. ..... ... .. - .

. ... .... 02 2 4_

0 1,,00 2,000 3,000 4,000

SLANT RANGE FROM EXPLOSION (YARDS)

Figure 8. 127b, Air-secondary gamma-ray component of the initial nuclear radiation dose

pet kiloton yield as a function of slant range from thermonuclear weapon air

bursts. based on 0.9 normal sea-level air density.

8.129 With minimal hydrodynamic reduce the dose from fission product

enhancement, as is the case for very gamma rays relative to that from seconlow-yield weapons, the fission product dary gamma rays with increasing disgamma rays and the secondary gamma tance from low-yield explosions. For

rays contribute approximately equal explosions of higher yield, however,

doses at slant ranges up to about 3,000 hydrodynamic enhancement may cause

yards. However, the average energy of the fission product gEmma-ray dose to

the former gamma rays is considerably exceed the secondary gamma-ray dose,

less than that of the latter, and the an- particularly at longer ranges.

gular distribution of the fission product 8.130 The calculated fission prodgamma rays is diffused by the rise of the uct gamma-ray dose in tissue per kiloton

cloud. Each of these factors tends to of fission energy yield received V a

:7
TECHNICAL ASPECTS OF INITIAL- NUCLEAR RAOIATION 377

target on or near the surface of the earth amic enhancement depend on the total

as a function of slant range from a energy release. Interpolation may be

nuclear explosion is shown in Fig. employed to obtain the effective yield

8. 1 30a. In order to determine the fission for slant ranges that are not shown. The

product gamma-ray dose received in the curves in Fig. 8.130b were calculated

initiO! radiation from an air burst of a for a scaled height of burst of 200 WO4

fission weapon of W kilotons energy feet, where W is the total weapon enyield, the value for the given distance as ergy yield in kilotons. For a given slant

obtained from Fig. 8. 130a is multiplied range the curve is terminated at the yield

by the "effective" yield, determined at which the height of burst is equal to

from Fig. 8. 130b. The use of the effec- that slant range.

tive yield instead of the actual yield 8.132 The dawa for the effective

provides the necessary corrections for yields in Fig. 8.132 are similar v) those

the differences in cloud rise velocity and in Fig. 8.130b but are applicable to

tie hydrodynamic enhancement, each of contact surface bursts. There is no simwhich is a function of total energy yield. pie method to interpolate or extrapolate

these curves for fission-product gamma

8.131 For thermonuclear weapons, rays to other heights of burst; however,

the dose for a given distance as obtained Fig. 8. 130b may be taken to be reasonfrom Fig. 8 130a must be multiplied by ably accurate for most low air bursts,

the fraction of the total yield that results and Fig. 8. 132 may be applied to nearfrom bsion, c.g., 01.5 fur a weapon with suirfatce as well as to contact surface

50 percent fission yield, prior to multi- bursts. The results presented in Fig.

plying by the effective yield as obtained 8.33a are based on the upper curves in

from Fig. 8. 130b. It should be noted Fig. 8. 127a (for secondary gamma rays)

that Fig. 8.130b is always entered with and the curves in Figs. 8. 130a and b.

the total energy yield of the weapon to The results in Fig. 8.33b are based corobtain the effective yield, since the re';pondingly on the curves in Fig.

cloud rise velocity and the hydrodyn- 8.127b and those in Figs. 8.130a and b.

Cex conlinuid on page 38.1

*1 _ ___ _ ., . . . * .-. -- . . . . . . . . .*. fltw. . . . . . ,,~v*.;-
378 INITIAl. NUCLEAR RADIATION

The curves in Fig. 8.130a show the Evunple 2

initial radiation, fission product Given: A I MT thermonuclear

gamma-ray dose per kiloton fission yield weapon with 50 percent of its energy

as a function of slant range from a yield derived fr)mn fission is exploded at

nuclear explosion. j height of 3,20 feet.

,ý(-jf1ng. In order to apply the data in Find: The total initial nuclear radiaFig. 8. 130a to a fission explosion of any tion dose at a slant range of 4,000 yards.

energy, V' kilotons, multiply the value

for the givert distance as obtained from Solution: The total initial nuclear raFig. 8. 130-1 by the effective yield, WL' diation dose is the sum of the initial

kilotons, from Fig. 8. 130b for a low air neutron dose, the secondary gamma-ray

burst or from Fig. 8.132 for a surface dose, and the fission product gamma-ray

burst. For a thermonuclear weapon, tht dose. From Fig. 8.123b, the neutron

value obtained from Fig. 8.130a shoulj dose per kiloton yield, is 1.2 x 10 4 -ad

be multiplied by the fraction of the yield at a slant range of 4,000 yards from a

that results from fission as well as oy low air burst. The corresponding dose

W•: for the total yield. from a I MT explosion is

xvanple / DOI = 1.2 x 10 ' x 10' = 0.12 rad.

Given: A 20 KT fission weapon is From Fig. 8.127b, the secondary

exploded on the surface. gamma-ray dose per kiloton yield is 1.8

x 10 1 rad at a slant range of 4,000

Find: The fission product gamma-ray yards from a low air burst. The corredose at a slant range of 1,.000 yards. sponding dose from a I MT explosion is

Solution: From Fig. 8. 130a, the ini- D = 1.8 X 10 x 103 = 1. rads.

tial radiation, fission product gammaray dosý per kiloton yield at a slant From Fig. 8.130a, the fission product

range of 1,000 yards is 75 rads. From gamma-ray dose per kiloton fission yield

Fig. 8.132, the effective yield at a slant at a slant range of 4,000 yards from the

range of 1,000 yards from a 20 KT explosion is 3.2 '" 10 4 rad. The height

explosion on the surface is 45 KT. The of burst, 3,200 le.t, is sufficiently close

fission product gamma-ray dose for the to the scaled height of 200 W"-, i.e.,

desired conditions is therefore 3,170 feet, that Fig. 8.130b should provide an accurate value of the effective

D= 75 x 45 3,375 rads. Answer yield. From Fig. 8.130b, the effective

(This is more than ten times the secon- yield at a slant range of 4,000 yards

dary gamma-ray dose determined pre- from a low air burst I MT explosion is 4

viously for the same conditions, but the X 104 KT (or 40 MT). Since only 50

relative values will change with varia- percent of the total yield is derived from

tions in total and fission yields and fission, a correction factor of 0.5 must

height of burst.) be applied. The fission product gammaray dose is

.Ail I

WIWI
TECHNICAL. ASPECTS OF INITIAl. NUCLEAR RAI)IATION 379

-- - - -4 . . . ... . , .. .. t ... .... ......:..... -. .

2 2

2 -3

-- \ X I - -

w - \ I I I\I,,1

w, I i ' , I

2 2-.

o

_ 2 2

- I5

01

z

0 52 2,,Ii2) 2 _ _. . --'- - ------ 4-

L - 6

0 2,000 4,000 6,000 7,090

SLANT RANGE FROM EXPLOSION (YARDS)

V•, Figure 8. 130a. Fission product gamma-ray component of the initial nuclear radiation dose

per kiloton fission yield as a function of slant range from a auclear k, explosion, based on 0.9 normal sea-level air density.

at.•
380 INITIAL NUCLEAR •'%ADIATION

ON, = 0.5 x 3.2 x 10 4 x 4 x 10( In adding the doses, it should be re-

= 6.4 rads. called that I rad ef neutron; may not be

The total initial nuclear radiation dose is bologically equivalent

gamma rays (§ 8.64).

D=D,,+ D + D.,

= 0.12 + 1.8 + 6.4

8.3 rads. Answer

""
TI('IINI('AI ASPECT'S (•F INITIAl NI'I.-AR RADI)IOvI'N 381

1- 11T7 -T7-T17

2 ~SLANT RANG~E

8 8 -- ----- 6,000 YARDS

I ,000

- I 

I0 =_ -- /-I --

2 3,000 1.

IO -, -

0z

0 2 2000

-J I - l lI I I I l l ,I 1 I 1

5: 2

~ 2 - 5 0 70I77Iz2 . 0 2xO

LaL

10.

2_ 500

2-

1 2 5 10 2 5 102 2 5 103~ 2 3 le2x'04

ACTJAL EXPLOSION YIELD (KILOTONS)

Figure 8.130b. Effective yield as a function of actual yield for the fission product

gamma-ray dose from a low air burst, based on 0.9 normal sea-level air

density.
382 INITIAL NUCL.EAR RADIATION

HO ! I l, ii I 7 I--iI 

: SLANT RANGE

QB61 40 YARDS - : ' / ] 6,000 Y

---1 -- 2,000 ! I - .4 ~ i

10 7 i---4 -- -- I- .. .-- :.. .... . . . " . - - . .t, -4 0 O . -. .

1-000

-A I , I,; • /•

. 2

w 1050

10-2V.

5 -. .... . ; , - . . . .... .

,o - -- ... . . .. -I . . :

, / , , ,,, 1.i.... ..

1 2 5 102 5 102 2 5 103 2 5 104 2 x 104

ACTUAL EXPLOSION YIELD (KILOTONS)

Figure 8.132. EFlective yield as a function of actual yield fEr the fission product gamma-ray

dosc from a contact surface burst, base;d on 0.9 normaI qea-level air density.

S...... . ...... . .... •.." .. .• .. . .. . , ,, - :. .. ... - .'",,, " . ... -'"- ,-. -- . • ','..... ............- ":
TECHNICAL ASPECTS OF INITiAL NUCLEAR RAOIATION 383

MECHANMSMS !N TREE: iONIZATION an adjacent material, the former will

8.133 Two basic interactions of nu- acquire a positive charge and the latter a

clear rauiation with rinatter are important negative charge. Consequently, a difin connection with the transient-radia- ference of potential will exist between

tion effects on electronics (TREE); they the two materials. The most obvious

are ionization and atomic displacement effect of this potential difference is a

(§ 8.76). The charged particles, i.e., flow of current through an electrical cirelectrons and ions, produced by ioniza- cuit connecting the two materials, and

tion eventually combine but the accom- this current will produce electrl'. and

panying changes in materials may be magnetic fields. If there is matter in the

more or less permanent. Some aspects space between the two materials, the

of TREE depend on the relative dura- charge transfer may cause ionization

tions of the radiation pulse and the re- ai J hence conduction if there are local

covery time. If the pulse duration is the electric. fields. Finally, if the charge eiloager, the effect is observed promptly. ther originates or embeds itself in an

The magnitude of the effect is usually a insulator, a long-lived local space

function of the density of charged par- charge may result. The effects of charge

ticles created by ionization and thi,- is transfer may thus be temporary or

determined by the rate of energy ab- senipermanent.

sorption, i.e., by the dose rate. On the 8.136 The free charge carriers proother hand, if the pulse length is short duced during ionization respond to an

relative to the recovery time, the effect applied electric field by causing a net

will be delayed. The amount of damage drift current; there is consequently a

is then usually a function of the total transient increase in conductivity. This

energy absorbed, i.e., the dose. Thus, effect is particularly important for capaboth absorbed dose and dose rate must citors, since the ability to retain or rebe considered in assessing the effects uf store electrical charge is dependent on

nuclear radiation orn electronics, in the ýow conductivity of the dielectric. In

many cases, the dose rate is the deter- an ionizing environment the increase in

mining factor. The persistence of the the bulk conductivity results in a deeffect is related, in general, to the re- crease of the stored charge in a capacicovery time. tor.

8,24 The chief manifestations of 8.137 In semiconductor devices,

ionization include (1) charge trn isfets, such as transistors and diodes, there are

(2) bulk conductivity increase, (3) ex- both positive (holes) and negati'.e

cess minority-carrier generation, (4) (electron) charge carriers, either of

charge trapping, and (5) chemical which may be in the minority. The efchange. These effects will be examined fect of ionization in producing addiin turn in the following paragraphs. tional minority carriers is of prime con8.135 Charge transfer results from cern in many semiconductors and is

the escape of some elections produced usually the most imporamit manifestaby ionization from the surface of the tion of ionization in TREE. Seme of the

ionized material. If the net flow of these che'racteristics of semicoi ductor devices

e~lectrons is from the ionized material to depends upon the instantaneous con-

TECHNICAL ASPECTS OF INITIAL NUCLEAR RADIATION 385

ties of a semiconductor material are di- (number of defects present) to the damrectly related to the total number of age remaining after a long time is called

defects. Thus, the neutron flue.ce is an the "annealing factor"; it depends on

important consideration in assessing the observation time as well as on the

damage to a semiconductor caused by temperature and the electrical condition

atomic displacement. of the material. The maximum number

of defects created at early times follow8.142 Some of the defects produced ing a fast-neutron burst is frequently

by the displacement proceý,s are perma- important to the performance of elecnent but others are temporary. The teni- tronics systems. The maximum annealporary defects are annihilated by re- ing factor of a component indicates tbe

combination of the vacancy-interstitial peal, damage that must be tolerated

pairs, i.e., by the movement of an in- above the permanent damage if that

terstitial atom into a vacancy, by corn- component is to continue to function.

bination with pre-existing lattice de- 8.144 The lattice dainage caused by

fects, or they may eventually escape atomic displa'icemnent degrades the elecfrom a free surface of the material The trical characteristics of semiconductors

gradual disappearance of some defects isadcalledisannearince ofd tme raeofes by increasing the number of centers for

trapping, scatering, and recombination

annealing can he increased by raising of charge carriers. The increase in trapthe temperature. The degree of dis- ping centers results in removal of charge placement damage in a crystalline carriers and thereby decreases the cur-

:semiconductor increascs rapidly with rent flow. The additional scattering

time, reaches a peak, and then decreases --nters reduce the capability of the

as annealing becomes increasingly ef- charge carriers to move through the

fective. The annealing process may lead semiconductor material. Finally, the

to either an improvement or further additional recombination centers dedegradation of the irradiated material, crease the time during which the minorbecause in some ca=es thermally stable defetssut. ay Tesedefctsmay ity charge carriers are available for

defects may rlesu tse defects may electrical conduction. The last effect,

be more or less effective than the unst- i.e., the reduced lit'etime of the m*nority

z ble ones in changing a particular prop- carriers, is the most imporftnt factor in

erty. determining the performance of a semi8.143 A'rneaing processes fall conductor device in an environment of

roughly into two time frames. Rapid (or radiation that can cause atomic disshort-term) annealing occurs in hun- placement. The minority carrier lifetime

dredths of a second, whereas long-term is very roughly inversely proportional to

annealing continues for times of the the neutron fluence at large values of the

order of tens of seconds. At ambient fluence that are likely to cause damage

temperature, annealing of temporary to semiconductors. At sufficiently large

damage will be essentially complete fluences, the lifetime becomes too short

within about half an hour. The ratio of for the semiconductor device to function

the damage observed at early times properly.

A-
386 INITIAL NUCLEAR RAD!ATjION

)i BLIOGRAPHY

Atimo i i , . S , ''Shielding Against Initial Ra1di- lPenetrattig Radiation of Nuclear fixolosiorns."

ations from Nuclear Explosions.'' Oak Ridge English translation. Joint Publications Research,

National L a oratorv, JtulN 1 973. OR N I Service, U.S. D.leriartment of Commerce, Julk

RSIC 36. 1971. JPRS 53498.

'At:A t-R J. JA .. a et(i.. 'Nuclear Weapons Free- L.\mtN, F.. ''Radiation Effects in Semicojoluctor

Field Environment Recommended for Initial Devices." John Wiley and Sons. Inc , 1968.

Radiation Shielding Calculations.'' Oak Ridge N1.ARSII. I . J. D.. and M. 13. Wuit s. "The

National Laboratory. February 1972, ORNI, Effects of Cut-Off En'-rgy on Monte Cat lo CalTrM 3396. culated Gammna-Ray Dose Rates in Air." Ra-

"Basic: Radiation Protection Criteria -NCRP diation Research Associates. Fort Worth.

Report No. 39. National Council on Radiation Texas, 1966, RRA - M07.

Ptotection. Washington. D.C., 1971. MOONtF', L. G., ''Calculations of Weapo~n Ralit it -RIN tON, H1. (Ed. t. ''Nuclear Engineering diation Doses in Single-Compartment AboveHandbook," McGraw-Hili Book Co., Inc., Ground Concrete Structures." Radiation Re1958. search Associat':s, Fort Worth. Texas.

FRI;NC1t. R. L., "'A First-Last Collision Model of November 1969. RRA-M93.

the Air'Ground Interface Effect,., on Fast-Neu- National Bureau of Standards. ''Measur.mient oif

tron IDis~ri hut ions,"' NucI'ajr Sci. and Fng.. 19, Absorbed Dose of lNeuatrons and Mixtures of

151 (19641. Neutrons and Gamma Rays.'' NCRP Report

FRENClH. R. L., and L. G. MoONEY. "Initial No. 25. U.S. Govcrr'ment Printing OJffice.

Radiation Exposure from Nuclear Weapons.'' 1961 , National Bureau of Standards Handbook

R,.diation Research Associates, Foit Worth. 75,

Te:as, July 1972. RRA T'7201. "Protection Against Neutron Radiation." NCRP

*FRrrFtt/(ii., A. E.. N. Ei. LORIMtI"t, and Z. G. Report No. 38, National Council on Radiation

BURSON, ''Measured Low-Altitude Neutron Prot,:ction, Washington, D. C.. 1971.

and Gamima Dose IDistrihutions Due to a 14- "Radiation Damage tind Detects in SenniconducMeV Neutron Source,'' E. G., and G.. Inc., tors," Conference Series, No. 16. July 1972.

Las Vegas. Nevada, 1969, ECYG 1183-1449. The Institute of Physics (London). 1973.

*FRtr/S(.tM: ',A. E., N. E. LoRIMIIER, and Z. G. "Recommended Techniques for the Meaisuremnent

BUIRSON. ''Measured High-Altitude Neutron of Selected Nuclear Radiation Effects (-n Elecand Gamma Dose Distributions Due to a 14- tronic Components.'' IBM Electronics Systems

MeV Neutron Source," E. G., and G., Inc.. Center, Owegc,. New York, August 1967.

Las Vegas, Nevada, 1969, EGG 1183-1438. DASA 627. Vol. 11.

GWYN, C. W., D. L. S('HARFET1 ER. and J. L.' *S,.HAEFFR, N. M. (Editor), "Reactor Shielding

WIRTH, "The Analysis of Radiation Effects in for Nuclear Engineers," U.S. AEC Report

Semiconductor Junction Devices," Sandia TID-2595l, 1973.

Corporation, Albuquerque, New Mexico, July *S5j(.KF , R E. A., "Time-Dependent Neutron

1967. SC-R-67--l 158. and Secondary Gamma-Ray Transport in an

JONFS, 1'. D., and F. F. HAYWOOD, "Trans- Air-Over-Ground Geometry. Volume 11. Tabumission of Photons Through Common Shield- l&eted Data," Oak Ridge National Laboratory,

ing Media." Oak Ridge National Laboratory. September 1968. ORNL 4289.

October 1974, ORNL-TM-4728. *S-1 RAKEx, E. A.. "Status of Neutron Transport

*Kt;TtH, J. R., and F. H. SHELTON, "Neutron in the Atmosphere." Oak Ridge National LabTransport in Non-Uniform Air by Monte Carlo orato~y. July 147O7, ORNL-TM-3065.S

Calculations, Volume I.- Kaman Nuclear, Co- VoOK, F. L. (Editor), "Radiation Effects in

lorado Springs, Colorado, January 1969, Semiconductors," Proceedings of the Santa Fe

DASA 2236-1. KN-774-69-l. Conference on Radiation~ Effects in Semicon-

*KUKHTEVICH, V. 1L, -,I al., "Protection from ductors, Plenum Press. 1968.

* These publications rrniy be purchased from the National Technical Information Service, Department

of Commcrce, Springfield, Virginia. 22161.
CHAPTER IX

RESIDUAL NUCLEAR RADIATION AND FALLOUT

SOURCES OF RESIDUAL RADIATION

INTRODUCTION high-energy neutrons are produced (§

1.72), so that the residual radiation from

9.01 The residual nuclear radiation fusion weapons will arise mainly from

is defined as that which is emitted later neutron reactions in the weapon and its

than I minute from the instant of the surroundings, if the fission yield is siifexplosion (§ 8.02). The sources and ficiently low.

characteristics of this radiation will vary 9.02 The primary hazard of the rein accordance with the relative extents sidual radiation results from the creafion

to which fission and fusion reactions of fallout particles (§ 2.18 et seq-)

contribute to the energy of the weapon. which incorporate the radioactive

The residual radiation from a fission weapon residues and the induced activweapon detonated in the air arises ity in the soil, water, and other materials

mainly f:om the weapon debris, that is, in the vicinity of the explosion. These

from the fission products and, to a lesser particles may be dispersed over large

extent, from the uranium and plutonium areas by the wind and their effects may

which have escaped fission. In addition, be felt at distances well beyond the

the debris will usually contain some range of the other effects of a nuclear

radij,.ctive isotopes formed by neutron explosion (§ 9.113). A secondary hazreactions, other than fission, in the ard may arise from neuron induced acweapon materials. Another source of tivity on the earth's surface in the imresidual radiation, especially for surface mediate neighborhood of the burst point

and subsurface bursts, is the radioact- (Q 8.16). Both the absolute and relative

ivity induced by the interaction of neu- contributions of the fission product and

trons with various elements present in induced radioactivity will depend on the

the earth, sea, air, or other substances in total and fission yields of the weapon,

the explosion environment. The debris the height of burst, the nature of the

from a predominantly fusion weapon, surface at the burst point, and the time

on the other hand, will not contain the after the expiosion.

quantities of fission products associated 9.03 As mentioned in § 2.28, it is

with a fission weapon of the same en- convenient to consider i;re fallout in two

ergy yield. However, large numbers of paris, nameiv, early and delayed. Early

387

I
388 RESIDUAL NUCIFAR RADI)IATION AND FAI I Ot;

(or lo.al) f;rliout is defined as that which and residual nuclear radiations is n:.t as

reaches the ground during the first 24 definite. Some of the radiations fiom tile

hours following a nuclear explosion, weapon residues will be within range of

The early fallout from surface, subsur- ihc earth's surface at all times, so that

face, or low air bursts can produce ra- the initial and residual categories merge

dioactive contamination over large areas continuously into one another (§§ 2.82.

and can represent an immediate biolog- 2. 100). For very deep underground 4nd

ic•l hazard. Delayed (or long range) underwater bursts the initial gamma rays

fallout, which is tMa ieaching the and neutrons produced in the fission or

ground after the first day, consists of fusion process may be ignoeed since

very fine, ipvisible particles which settle they are absorbed by the surrounding

in low concentrations over a consider- medium. The residual radiations, from

able portion of the earth's surface. The fission products and from radioactive

radiation from th:- fission products and species produced b, neutron interaction,

other substances is greatly reduced as a are then the ,-1ly Y'ind of nut:".1⁄2- radiaresult of radioactive decay during the tions that need be considered. in a surrelatively long lime the delayed fallout face burst, however, both initial and

remains suspended in the atmosphere. r.,,idual nuclear radiations must be

Consequently, the r'adiations from most taken into account.

of the delayed fallout pose no immediate

danger to health, although there may be EARLY FALLOUT

a long-erm hazard. The biological effects on people, plants, amd animals of 9.06 The radiological characteristhe radiations from early and late fallout tics of the early fallout from a nucklar

art described in Chapter XII weapon are those of the fission products

9.04 In the case of an air burst, and any induced activity produced. The

particuiarly when the fireball is well relative importance of these two sources

above tne earth's surface, a fairly sharp of rcsid.tal radiatior depends apon the

distinction can be made between the percentage of the total yield that is due

initial nuclear radiation, considered in to fission, and other factors mentioned

the preceding chapter, and the residual in § 9.92. There are, however, two

radiation. The reason is that, by the end additional factols, namely, fractionation

of a minute, essc'"te.l.y all of the and saltiag, which may affect the activweapon residues, in the forii, of very ity of the early fallout; these will be

small particles, will nave risen to such a described below.

height that the nuclear radiations no 9.07 As the fireball cools, the fis.-

longer reach the groind in significant sion products and other vapors are

amounts. Subsequently, the fine parti- gradually condensed on such soil and cles are widely dispersed in the atmos- other particles as are sucked up from

pliere and descend to earth very slowly, below while the fireball rses in the air.

9.05 With surface and, especially, For detonations over land, where the

subsurface explosions, or low air bursts particles consist mainly of soil minerals,

in weather involving jrec;pitation (§ the fission product vapors condense onto

9.67) the demarcation between initial both solid and molten soil parttices and

~~"I

<. 1*•
SOURCES 01: •IESIDUAI. RADIATION 389

also onto other particles that may be process is the separation of the fission

present. In addition, the vapors of the product elements in the ascending firefission products may condense with hall and cloud as they condens, at difvapors of other substances to form fei.nt times, coriesponding to their difmixed solid particles of small size. In ferent condensation temperatures. Thus

the course of these processes, the corn- the refractory elements can condense at

position of the fission products will early times in the nuclear cloud, when

change, apart from the direct effects of the temperature is quite high, onto the

radioactive decay. This cbange in corn- relatively larger particles which are

position is called "fractionati:n." The more abundant at these times. Conoccurrence of fractionation is shown, ersely, volatile elements, with low

for example, by the fact that in a land condensation temperatures, cannot consurface burst the larger particles, which dense until later, when the cloud has

fall out of the fireball at early times and cooled and when the larger particle sizes

are found near ground zero, have dif- will be depleted. Refractory elements

ferent radiological propertie., from the ar: expected to be relatively more

smaller particles that leave the radioac- abundant in the close-in early fallout.

tive cloud at later times and reach th,. representing the larger particles, and to

ground some distance downwind, be relatively depleted in the more di,-tant

9.08 The details of the fractionation portion of the early fallout deposited by

process are not completely understood, smaller particles. T'hc reverse wil! ce

but models have been developed that true for the more volatile elements. The

represent the phenomena reasonably sa- particle size distribution in the nuclear

tisfactorily. Fractionation can occur, for cloud varies with the surface material

example, when there is a change in and hence the latter will have an effect

physical state of the fission products. As on fractionation.

a result of radioactive decay, the gases 9.10 For explosions of large energy

krypton and xenon form rubidium and yield at or near the surface of the sea,

cesium, respectively, which subse- where the condensed particles consist of

querntly condense onto solid particles, sea-water salts and wate,, fractionation

Consequently, the first particles to fall is observed to a lesser degree than for a

out, near ground zero, wil! be depleted land surface burst. The reason is that the

not only in krypton and xenon, but also cloud must coo, to 10°C (212'F) or less

in their various decay (or daughter) before the evaporated water condenses.

products. On the other hand, small par- The long cooling time and the presence

ticles that have remained in the cloud for of very small watet droplets permit resome time will have rubidium and ce- moval from the radioactive (loud of the

sium, and C'ieir daughters, strontium and daughters of the gaseous krypton and

barium, condensed upen them. Hence, xer-.n along with the other fission prodthe more distant fallout will be relatively ucts. In ýLhis event, there is little or no

richer in those elements in which the variation in composition of *he.radioacclose fallout is depleted. tive fallout (or rainout) with distance

9.09 An additiona! phenomenon from the explosion.

which contributes to the fractionation 9.11 The composition of the fallout
390 RESIDUAL NUCLEAR RADIATION AND FALI.OUT

can also be changed by ".;alting" the grations per second, i.e., almost 3 x

weapon to be detonated. This consists in 10." curies (§ 9.141). The level of acthe inclusion of significant quantities of tivity even from an explosion of low

certain elements, possibly enriched in yield is enormously greater than anyspecific isotopes, for the purpose of thing that had been encountered prior to

producing indu:edl radioactivity. There the detonation of nuclear weapons. By

are several reasons why a weapon might the end of a day, ,le rate of beta. particle

be salted. For example, salt;ng has been emission will have decreased by a factor

used in some wcapons tests to provide of about 2,000 from its I-minute value,

radioactive tracers for various purposes, and there will have been an even larger

such as the study of the paths and rela- decrea'e in the gamma-ray energy

tive compositions of the zarly arid de- emission rate. Nevertheless, the ralayed stages of fallout. dioactivity of the fission products will

still be very considerable.

ACTIVITY AND DECAY OF EARLY 9,14 It has been calculated (§

FALLOUT 9.15(5;, thai if fallout particles were

spread uniformly over a smooth infinite

9.12 The fission products constitulcf plane surface, with the radioactivity

a very complex mimxture of more than equal to that of all the fis.;ion products

3(0) differnt forms (isotopes) of 36 ele- from ]-kiloton fission energy yield for

ments (§ 1.62). Most of these isotopes each square mile, the radiation dosc rate

are radioactive, decaying by the emis- at a height of 3 feet above the plane

sion of beta particles, frequently ac- would be approximately 2,900 rads (in

companied by gamma radiation. Ab,'ut tissue) per hour at I hour after the

3 X 1023 fission product atoms, weigh- explosion." In actual practice, a uniform

ing roughly 2 ounces, are formed per distribution would be improbable, since

kiloton (or 125 pounds per megaton) of a larger proportion of the fission prodfission energy yield. The total radioac- ucts would Le deposited near ground

tivity of ihe fission products initially is zero than at farther distances. Hence,

extremely large but it falls off at a fairly the dose rate will greatly exceed the

rar~d rate as the result of radioactive average at points near the explosion

decay. center, w'.ereas at ,nore remote loca9.13 At I minute after a nuclear tions it will usually be less. Moreover,

explosion, when the residual ,mclear the phenomenon of fractionation will

radiation has been postulated as begin- cause a depletion of certain fission

ning, the radioactivity of the fission product isotopes in the local fallout, this

products from a I-Kiloton fission yield will tend to lower the theoretically calexplosion is of the order of I021 disinte- culated dose rate. Finally. the actual

, The actual value depends on :he nature ti the fissionable material al, other weapon variahles, but the

number qui•ted here is a reasonable average (§ 9.159). -Fallout radiation measurements (and calculatio's) have ccminonIy been made in terms of gamma-ray

exposures Wo, rates) in roenigen,;. For consistency with other chapters, however, all data in this ch;.ter,

are 6iven as lie equivalent doses (or rates) in rads absorbed in tissue near the surface of the body 1.f. §

9. 1). The quatlff ation "'in tissue" will be omitted subseque:-lly .:,ncc it applies throughout the chaN'r.

. .P-,,- ., ..... 1.. ..... .
SOURCES OF RESIDUAL. RADIATION 391

surface of the earth is not a smooth of induced activities make the approxplane. As will be discussed :;ubse- imate rule useful only for iliestration

quently (§ 9.95). the surface roughness and some planning purpose:;. Any

will cause 'i further decrease in the dose change in the quantity of fallout, arising

rate calculated for an infinite smooth from the continuing descent or the replane. In spite of these reductions, ex- roval of particles or from multiple dettremely high dose rates have been ob- onations, would affect the dose rate.

served within the first few hours fol- Hence, in any real fallout situation, it

lowing surface bursts. would be necessary to perform actual

9.15 The early fallout consists of measurements repeated at suitable inparticles that are contaminated mainly, tervals to estabiish the level and the rate

but not entirely, with fission products, of decay of the radioactivity.

Ali indication of the manner in which 9.16 The decrease of dose rate from

the dose rate from a fixed quantity of the a given amount of the early fallout,

actuea. mixture decreases with time may consisting of fission products and some

be obtained from the following approx- ot"er weapon residues (§ 9.32), is indi..

imate rule: for every sevenfold increase cated by the continuous curves in Figs.

in time after the explosion, the dose rate 9.16a and b, which were calculated in

decreases by a factor of ten, For exam- the manner describeo in § 9.146. In

pie, if the radiation dose rate at 1 hour these figures the ratio of the approximate

after the explosion is taken as a refer- radiation dose rate (in rads per hour) at

ence point, then at 7 hours after the any time after the explosion to a conveexplosion the dose rate .vill have d.- nient reference value, ca!-Pd the "unitcreased to one-tenthI at 7 X7=49 hours time refeIrence dose rate," is poitied

(or roughly 2 days) it will be one-hun- against time in hours.' The use of the

dredth; and at 7X7X7 =343 hours (or reference dose rate simplifies the repieroughly 2 weeks) the dose rate will be sentation of the results and the calculaone-thousand2.a of that at 1 hour after the tions based on them, as will be shown

burst. Another aspect of the rule is that below. The following treatment refers

at the end of I week (7 days), the only to external radiation exposures

radiation dose rate will be about one- from gamma-ray sources outside the

tenth of the value after I day. This rule body. The possibility should be borne in

is accurate to %ithin about 25 percent up mind, however, that some fallout could

to 2 week, or so and is applicable to enter the body, by inhaiation and mnges.,

within a factor of two up to roughiy 6 tion, and so give risc to internal radiam,,iths after the nuclear detonation. tion exposures (§ 12.163 et seq.). The

Subsequently, the dose rate decreases at major hazard in this respect is probably

a much more rapid rate than predicted radioactive iodine, which cari readily

by this rule. The complications intro- enter the body by way of milk from

duced by fractionation and the presence cows that have eaten forage contami-

'The significance of the Jashe'i lines, marked ''t I-%- will K- de-.:crih,:d in § 9.1146 el seq., where the

physical meaning of the unit-time reference dose rate will be explained. For the present, the dashed lines

may be ignored.
392 RESIDUAL NUCLEAR RA1I3ATION AND FALLOLT

4I

I _ _

r 4

- 2- --

X 0

10-4

7

WII DYIW O

i 0-O -t I i I I II i I | il I il I t il

i0_ -1.472 4 7 0

z 2

UJ W1 - - -- 2

00 7 2r 4i2 4

TIM~E AFTER EXPLOSION (HOURS)

Figure 9. 16a. Dependence of dose rate from early fallout upon time after explosion. j

nated with fallout. Because the internal rate is 4.0 rads per hour (rads/hr). From 4 doses are highly dependent upon the the curve in Fig. 9. 16a (or the data in

circulmstances, they are not predictable. Table 9.19), it is seen that at 15 hours4 9.17 Suppose, for example, that at after the explosion, the ratio of the aca given location, the fallout commences tual dose rate to the reference value is i

at 5 hours after the explosion, and that at 0.040; hence, the reference dose rate

I5 hours,, when the fallout has ceased to must be 4.0/0.040= 100 rads/hr. By

descend, the observed (external) dcs•e means of this reference value and the

1

!4
SOURCES OF RESIDUAL RADIATION 393

-3

I I S7 

o 2 - - - -- -- - , -

-4

2

2 -------

I-- 0 \NI

, LJ 0--

iW

7 TI

I-T0

'TM FEREPOIO HUS

40-2L - -- 11 1 1- 1 1

2- 2- - - 7- - - - - - - - - - - 4 7 2 4-

10 100 CYR 15YR II 2 00Y

T IKA AFEREXPLOS ION (HOURS)

Figure 9.16b. Dependence of dose tatc from early fallout upon time afei .:Aplosion.

decay curves in Figs. 9.16a and b, it is zoztal axis. Upor moving upward vcr..

possible to estimate the actual dose rate tically until the plotted (continuous) line

at the p~ace under consideration at any is rea';hed. it is seen that the required

,irne after fallout iý. complei,: Thus, if dose f-ate is 0.023 multiplied by the

ihe value is required at 24 hours after the unit-time reference dcse rat,,-, i.e.,

cxpl(c.ion, Fig. 9.16a is entered at the 0.023x 100=2.3 rads/hr.

,. point representing 24 hours on the hori- 9.18 If the dos;e rate at any time is

I¢

" 41
394 RI.SIDUAl NU('I FAR RADIA [ION AND [.AI I O)[ V

Tabk 9.19

RELATIVE THEORETICAl. DOSE RATES FROM EARLY FAuLi)uT AT VARIOUS

TIMES AFTER A NU(CLEAR EXPLOS!ON

Relative Relative

"Time (hours) dose rate Time (hours) (1ose rate

I .(0) 36 15

1 /2 610 48 1(0

2 400 72 6.2

3 230 1iW, 4.0

5 130 2(W) 1.7

6 i(1) 4(W) 0.69

10 63 6(W) 0.40)

15 4) 8W() 0.31

24 23- 1,(xx1 0. 24

known, by actual measurement, ihe taole If the actual dose ,ate at 1 hour (or

value at any other time can be esti- any other time) after the explosion is

maied. AlI that is necessary is to coin- known, the value at any specified time,

pare the ratios (to the unit-time refer- up to 1,000 ,iours, can be obtained by

ence dose rate) for the two given times simple proportion.-

as obtained from Fig. 9.16a or Fig, 9.20 It should be noted that Figs.

9.16b. For example, suppose the dose 9.16a aid b and Table 9.19 are used for

rate at 3 hours after the explosion is calculations ot dose rates. In order tc

found to be 50 rads/hr; what would be determine the total or accumulated radithe value at 18 hours? The respective ation dose received during a given

ratios, as give-n by the curve in Fig. period it is necessary to multiply the

9.16a, are 0.23 and 0.033, whh respect average dose rate by the exposure time.

to the unit-time reference dose rate. However, since the dose rate is steadily

Hence, the dose rate at 18 hours after decreasing during tie exposure, approthe explosion is 50x0.033/0.23=7.2 priate allowance for this must be made.

rads/hr. The results of the calculations based on

9.19 The restdfts in Figs. 9.16a and Fig. 9. 16a are expressed by the curve in

b may es.. represented in an alternative Fig. 9.20. It gives the total dose reform, as in Table 9.19, which is more ceived from early fallout, between I

convenient, although somewhat less minute and any other specified time after

complete. The dose rate, in any svitable the explosion, in terms of the unit-time

units, is taken as 1,000 at I Lour after a reference dose rate.

nuclear explosion; the expected dose 9.21 To illustrate the application of

rate in the same units at a numbet of Fig. 9.20, suppose that an individual

subsequent times, for the same quantity becomes exposed to a certain quantity of

of early fallout, are then as given in the gamma radiation from early fallout 2

"Devices, similar to a slide rule, are available for making rapid calculations of the decay of fallout

Jose rates and related matters.

S.... . .. .. - ...... • '• i i .I ii - 1 'I1 *'IIl ii~~i i ! N.i
SOURCES OF RESIDUAL RADIATION 395

U 04

Li70 0

C: _I- _ - iiE

LL

75

w f Ii - ID 0 v

(H C I) 31U3I-3NN .3 341l~

_Z(M ISO ivo.10wnin
396 RESII)UA!. NUCLEAR RADIATION AND FA.LLOUT

hours after a nuclear explosion and thi sequent 12 hours, i.e , by 14 hours after

dose rate, measured at that time, is the explo::ion? The f~rst step is to deterfound to be 1.5 Fads!hr. What wiil be the mine the unit-time reference dose rate.

total dose accumulated during the sub- From Fig. 9. 16a it is seen that

Dose rate at 2 hours after explosion - 0.40

Unit-time reference dose rate

and, since the dose rate at 2 hours is from Fig. 9.20, it is found that for 2

known to be 1.5 rads/hr, the reference hours and 14 hours, respectively, after

value is 1.5/0.4G=:3.8 rads/hr. Next, the explosion,

Accumulated dose at 2 hours after expl,'sion = 5.8

Unit -time reference dose rate

and

Accumulated dose at 14 hours after explosion 7.1.

-Unit-time reference dnse 'at.,

Hence, by subtraction

Accumulated dose between 2 and 14 hours after exp!osion = 1.3.

Uait-tirre reference dose rate

The unit-time reierence dose rate is 3.P or part is iumoved, 'fable 9.2"? would

rads/hr, and so the :acc'.mulated dose not he appli'able.

received in the 12 1ourF. between 2 and 9.23 If an individual is exposed to a

14 hours after the explosion, is ceiain amount of e,:rly fall"ut during

3.8X 1.3=4.9 rads. the interva., from 2 hours to 14 hours

after the explosion, the percentage of

9.22 The percentage of the accu- the infinite time dose received may bic

mulated "infinity dose" or "infinite obtained by subtracting the respective

time dose" that would be received firc-n values in (or etimated from) Table

a given quantity of early fallou: :rom- 9.22, i.e., 76 (for 14 hours) minus 62

puted from 1 minute to various times (for 2 hours), giving 14 percent, i.e.,

after a nuclear explosion, is shown in 0. 14, of the infinite time d,.se. The acTable 9.22. The calculated infinite time tual value of the infinite time dose comdose is essentially equal to the done that puted from I minute after detonation, is

would be accumulaied as a result of 9.3 times the unit-time reference dose

exposure to a fixed quantity of fallout rate (in rads/hr), as indicated by.= • in

for many years. These data can be used Fig. 9.20. Hence, if the reference value

to determine the proportion of the infi- is 3.8 rads per hour as in the above

nite time dose received during any spe- example, the accumulated dose received

cified perici following the complete de- between 2 hours and 14 b'mrs after the

position of the early fallout. Of course, burst is 0.14x9.3x3.8=4.9 rads, as

if the deposizion of fallout is inctimplete before.

- -. -. . . . . . ..- W - - ~ e -
SOURCI-S OF RESII)UAI RADIA1 M0N 39 7

Table 9.22

PERCI,'NTA(;ES OF INFINITE TIME RESIDUAL RADIATION DOSE RECEIVED FROM I

"V'INUTE UP To VARIOUS TIMES AFTER EXPLOSION

Percent of Percen, of

'imne (,hours) infinite time dose Time (hours) iniinie time dose

1 55 72 86

2 62 1(X) 88

:1 69 200 kX)

6 71 5(X) ') 1

12 75 1'000 95

24 'O 2A,0X) 97

,8 10,000 99

9.24 With the aid of Figs 9.16a other time at the same location, assumand b and Fig. 9.20 (or the equivalent ing there has been no change in the

Tables 9.19 and 9.22) many differont fallout other than natural radioactive

types o .alculations relating to radia- decay. The same nomo-raph can be

tion dose ratfs and tolti a ,c. (tilized, . ;-,*oived alternatively. to determine the

from early faliout can bI.% made. The time after the explosion at which the

procedures can be siruphiied, however, dose rate will have attained a specified

by means of special charts, as will be value. The nomograph iE based on the

shown below. The results, like those straight !ine marked "t 1." in Figs.

already given, are applicable to a par- 9. 16a and b which is seen to deviate

ticula:" quantity of fallout. If there is any only slightly from the continuous decay

change in the situation, either by further curve foi times less than 6 months or so.

contamination or by decontamination, It is thus possible to obtain from Fig.

the conclusions will not be valid. 9.25 approximate dose rates, which are

9.25 If the radiation dose rate from within 23 percent of the continuous

eaay fallout is known at a given loca curve values of Figs. 9.16a and b for the

"* * ticn, the nomograph in Fig. 9.25 may be first 200 days after th, nuclear detona-

*t , used to determine the dose rate at any tion.

* (Text continoed on page 404.)

,ii____
398 RESIDUAL NUCLEAR RADIATION AND FALLOUT

T'he nomograph in Fig. 9.25 gives an explosion at which the dose rate is I

approximate relationship becween the rad/hr.

dose rate at any time after the explosion Solution: By means of a ruler (or

and the unit-time reference value. If the straight edge) join the point representing

dose rate at any time is known, that at 8 rads/hr on the left scale to the time 6

any other time can be derived from the hours on the right sc'tle. The straight figure. Alternatively, the tittme after the line intersects the middle scale at 69 explosion at which a specific dose rate is rads/hr; this is the unit-time reference

attained can be determined approxi- value of the dose rate.

mately. (a) Using the straight edge, connect

For the conditions of apolicablitv of this reference point (69 rads/hr) with

Fig. 9.25, see § 9.30. that representing 24 hours after the explosion on the right scale and extend the

Example line to read the corresponding dose rate

on the left scale, i.e., 1.5 rads/hr. AnGiven: The radiation dose rate due to swer

fallout at a cei tain location is 8 rads per (b) E.,tend the straight line joining the

hour at 6 hours after a nuclear explo- dose rate of I rad/hr on the lft scale to

sion. the reference value of 69 rads/hr on the

middle ,;r 01

e oil to the right scale. This

Find: (a) The dose rate at 24 hours is intersect-d at 34 hours after the exafter the burst. (b) The time after the plosion. Answer

.3

- . - . ~ . .- -. . . .. .. .NVi .
SOURCES OF RESIDUAL RADIATION 399

1,000 1,000

700 7I'0

400 400

200 200

UNIT-TIME REFERENCE

100 DOSE RATE (RADS/HR) 100

70 10,000 70

7,000

40 4,000 40

2,000

1,000

20 700 020

DOSE RATE 400 TIME

(RADS/ HR) 10" 200 -10

100

47- 70 -7

40

4 20 "4

107

2t 47 -2

24

f4

t 0.7

0.7- 0.4 0.7

0.2

0.4 -0.4

0.07 , 0.04

0-2 {- -0.2 c•. t0.02

,2.' 10.01

". n p a r0.1 .fc 

,:Figure 9.2:i Nomograph for calculating approximate dose rates from early i'a.'out.
400 RESIDUAL NUCLEAR RADIATIJN AND FALLOUT

From Fig. 9.26 the total accumulated From Fig. 9.25, a straight line coimectradiation dose received from early fail- ing 6 rads/hr on the left scale with 4

out during any specified stay in a con- hours on the right scale intersects the

laminated area can be estimated if the middle scale at 32 rads/hr; this is the

dose rate at some definite time after the value of R,.

explosion is known. Alternatively, the (a) Enter Fig. 9.26 at 6 hours after the

time can be calculated for commen,=ing explosion (horizontal scale) and move

an operation requiring a specified stay up to the curve representing a time of

and a prescribed total radiation dose. stay of 2 hours. The corresponding

For conditions of applicability of Fig. reading on the vertical scale, which

9.26. scc § 9.30. gives the multiplying factor to convert

R *to the required total dose, is seen to

Example be 0. 19. Hence, the accumulated dose is

Given: The dose rate, at 4 hours after a 0. 19X32=6. I rads. Answer

nuclear explosion is 6 rads/hr. (b) Since the accumulated dose is Find:) (a)c Thhea accumulated dose i

Find: (a) The turital accumulated dose given as 4 rads and R, is 32 rads/hr, the

received curing a period of 2 hours multiplying factor is 4/32=0.125. Encornencirtg at 6 hours after the explo- tering Fig. 9.26 at this point on, the

sion. (b) The time after the explosion vertical scale and moving across until

when an operation requiring a stay of 5

the (interpolatedj curve tor 5 hours stay

hours can be started if the total dose is to ihe te crespondn ri on

b, 4 ads.is reached, the corresponding re-vding on

, 4 rads. the horizontal scale, giving the tme

aiftcr the explosion, is seen to be

Soiution: The first step is to determine

the unit-thime reference dose rate (Rd). 21 hours. Answer

,i
SOURCES OF RESIDUAL RADIATION 401

c-- -- .,I? - 1,K- - --- N 2 -

a. 0

0 Tz

am 00

cz: .0

U,,

- A ___ V -- -~ - -

__ #~'./1_

0 -dirnw3.V8SO3NI 1 11 N
402 R1.,S1) L;.A1 N L I-',,R R A 1)1 ArVI0oN A ND , I 1u(t1r

From ihe chart ;n Fig. 9.27, the total pioslort on the horizontal scale and

accumulated radiation dose received move up to the curve representing a time

from early fallout during any specified of stay of 2 hours. The multiplying

stay in a contaminated area can be es- factor for the aose rate at the time of

timated if the dose rate a! the time of entry, as read from the vertical scale, is

entry into the area is known. Alterna- seen to be 1.9. Hence, the total acc'itively, the time of stay may be evaluated mulated dose received is

if the total dose is nr-rscribed.

For conditions of applicability of .rdig.

9.27, see § 9.30. (b) The total accumulated dose is 20

Example rads and the dose. rate at the time of

cntry is 5 rads/hr: hence, the multiplyGiven: Upon enter~ng a contaminated ing factor is 2,.5 = 4.0. Enter Fig.

area at 12 hours after a nuclear explo- 9.27 at the point corresponding to 4.0

sion the dose rate is 5 rads/hr. on the vertical scale and move horizonFind: (a) The total accumulated radi- t-tlly to meet a vertical line which starts

ation dose. received fo' a stay of 2 hours. from the point rýpresenting 12 hours

(b) The .lime of stay for a total accumu- after the explosion on the horizontal

lated dosc of 20 rads. scale. The two lines are found to in+,erSolution: (a) Sta't at the point on Fig. sect at a point indicating a time of stay

9.27 represeniing 12 hours after the e'- of about 4/2 hours. Answer.

'13

C'[•
SOURCES CF RESIDUAI. RADIATION 403

0

-J

o W

P~~ -- r__ 

0 (/0

UJ

0 CC N

I--

ujw

CAV0

xl

8010~VJ DNIAld~irlm~ 31V8U 3SOGI 3Vfl-AUA,'N3

'XV '
404 RESIDUAL. NUCLEAR RADIATION AND FALLOUT

9.26 To determine the total accu- 9.29 It is evident that the first day or

-..ulated radiation dose received during a so after the explosion is the most hazspecified time of stay in an area con- ardous as far as the exposure to residual

tamrinaied with early fallout, if the dose nuclear radiation from the early fallout

rate in that area at any given time is is concerned. Although the particular

known, use (s made of Fig. 9.26 in values given above apply to the case

conjunction with Fig. 9.25. The chart specified, i.c., complete early fallout

may also be employed to evaluate the arrival 6 hours after the explosion, the

time when a particular operation may be general conclusions to be drawn arc true

comme:nccd in a contaminated area in in all cases. The radiation doses that

order not to exceed a specified accumu- would be received during the Crst day or

lated radiation (lose. two a.e considerably greater thait on

9.27 Another type of calculation of subsequent days. Consequentiy, it is in

radiation dose in a contaminated area the early stages following the explosion

(from a fixed quantity of fallout) is that protection from fallout is most imbased on a L..o.!,,dgc of the dose rate at portant.

the time when exposure, commenced in 9.30 It is essential to understand

that area, The procedure described in that the tables and figures given above,

the examples facing Fig. 9.26, which and the calculations of radiation dose

:Iso requires the use of Fig. 9.25, may rates and doses in which they are used,

then be applied to determine either the are based on the assumption that an

total dose received in a specified time of individual is exposed to a certain quanstay or the time required to accumulate a tit), of early fallout and remains exposed

given dose of radiation. The calculation continuously (without protection) to this

may however, be simplified by means same quantity for a period of time. In an

of Fig. 9.27 which avoids the necessity actual fallout situation, however, these

for evalupting the unit-time reference conditions probably would not exist.

dose rate, provided the dose rate at the For one thing, any shelter which attentime of entry (or fallout arrival time) in uates the radiation will reduce the exthe contaminated area is known. posure dose rate (and dose) as given by

9.28 If the whole of the early fallout the calculations. Furthermore, the ac-.

reached a given area within a short time, tion of wind and weather will generally

Fig. 9.27 could be used to determine tend to disperse the fallout particles in

how the total accumulated radiation some areas and concentrate them in

dose received by inhabitants of that area others. As a result, there may be a

would increase with time, assuming no change in the quantity of early fallout at

protection. For example, suppose the a given location during the time of exearly fallout arrived at 6 hours after the posure; the radiation dose rate (and

explosion and the dose rate at that time dose) would then change correspondwas R rads per hour; the total dose ingly. The same would be true, of

received would be 9 R rads in I day, 12 course, if there werL. additional fallom,

R rads in 2 days, and 16 R rads in 5 from another nuclear explo:,ion.

days. 5
St)UR(TiS OF Ri..•II)iAI R.\lI.\ I IN 405

N!tUTRON-INDUJCD) ACTIVITY Oxygen-16, for example, reacts to a

slight extent with fast neutrons, but the

9.31 The neutrons liberated in the product, an isotope of nitrogen, has a

f fission process, bui which are no: in- half-life of only 7 seconds. It ',,.ill thus

volved in the propagation of the tission undergo almniot Lomnploetc decay within a

chain, are ultimately captured by the minute or two.

w,eapon residues th.ough which they 9.34 The produc. of neutron inrn,.!st pass before they can escape, by teractio,| with nitrogen-14 is carbon-14

nitrogen (especially) and oxygen in 'he (§ 8.110), which is radioactive, it emits

atmosphere, and by various materials beta particles of low energy but no

present on the earth's surface (§ 8.10). gamma rays. Carbon-14 has a long

As a result of capturing neutrons many half-life (5,730 years), so that it decays

substances become radioactivc. They, and emits beta particles relatively

consequently, emit beta narticles, fre- slowly. In the form of carbon dioxide it

quently accompanied by gamma radia- is readily incorporated by all forms of

tion, over an extended period of time plant life and thus finds its way into the

following the explosion. Suvh neutron- human body. The carbon in all living

induced activity, thereiore, is part of the organisms contains a certain proportion

residual nucicar radiation, of carbon-14 resulting from the capture

9.32 The activity induced in the by atmospheric nitrogea of neutrons

weapon materials is highly variable, from naturally occurring cosmic rays

since it is greatly dependen-i upon the and froin weapons tests The total re,-

design and structural characteristics of ervoir of carbon-14 in nature, including

the weapon. Any radioactive isotopes oceans, atmosphere, and biosphere (livproduced by neutron capture in the resi- ing organisms), is normally from 50 to

dues will remain associated with the 80 tons; of this amount, about J ton is in

fission products. The curves and tables the atmosphere and 0.2 ton in the biosgiven above have been adjusted to in- phere. It is estimatd that before Sepelude the contribution of such isotopes, tember 1961 weapons testing had proe.g., uranium-237 and -239 and nep- duced an additional 0.63 (short) ton of

tunium-239 and -240. In the period from carbon-14 and about half had dissolved

20 hours to 2 weeks afte: the burst, in the oceans. As a resulh of the large

depending to some extent upon (he number of atmospheric nuclear tzsts,

weapon materials, these isotopes can many of high yield, conducted during

contrib,;: op 10 40 percent um i' t,-1 1961 and 1962, the excess of carbon-14

,cufivity of the weapon debris. At other in the atmosphere rose to about 1.6

times, their activity is negligible in (short) tons in the spring of 1963. By

comparison with tha. of the fission mid-1969, this excess had fallen to

products. about 0.74 ton. In the course of time,

9.33 When neutrons interact with more and more of the carbon-14 will

oxygen and nitrogen nuciai present in enter the oceans and, provided there is

the atmosphere, the resvting radioacti- no great addition as a result of weapons

vity is of little or no sigificance, as far as tests, the level in the atmosphere should

the ear'y residual radiation is concerned, continue to decrease. If the rate of deIT.71
406 REFIDUAL NU,2-'I.EAR R,\DIATION AND FAI.!.OUi

crease of excess carbon-14 in !he at- formation of radioactive silicon-31.

mosphere observed between 1963 and This isotope, with a half-iife of 2.6

1969 were to continue, the level should hours, gives off beta particles, but

fall to less than I percent above normal garnma rays are emitted in not more

in 40 to 80 years. than aLout 0.07 percent of the disinte9.35 An important contribution to grations. It will be seen later that only

the residual nuclear radiation can arise in certain circumstances do beta partifrom the aýivity induced by neutron cles themselves constitute a serious Iacapture in certain elements in the earth diation hazard. Aluminum, another

and in sea water. The extent of this common constituent of soil, can form

rmdioactivity is highly variable. The el- the radioisotope alumirium-28, with a

ement which probably deserves most half-life of only 2.3 minutes. Although

attention, as far as cnvironmental neu- isotopes such as this, with short halftron-induced activity is concerned, is lives, contribute greatly to the high inisodium. Although this is present only to tial activity, very little remains ,within

a small extent in average soils, the an hour after the nuclear explosion.

amount of radioactive sodium-24 9.38 When neutrons are captured

formed by neutron capture can be quite by the hydrogen nuclei in water (11,0),

appreciable. This isotope has a half-life the product is the nontradioactive

of 15 hours and emits both beta par- (stable) isotope, deuterium, so that there

ticles, and more important, gamma rays is no resulting activity. As seep in §

of relatively high energy.- 9.33, the activity induced in the oxygen

9.36 Another source of induced ac- in water can be ignored because of the

tivity is manganese which, being an very short half-life of the product,

element that is essential for plant However, substances dis;solved in the

growth, is found in most soils, even water, especially the salt (sodium chlothough in small proportions. As a result ride) in sea water, can be sources ,i

of neutron capture, the radioisotope considerable induced activity. The somanganese-56, with a half-life of 2.6 dium produces sodium-24, as already

hours, is formed. Upon decay it gives mentioned, and the chlorine yields

off several gamma rays of high energy, chdorirz-38 which emits both beta parin addition to beta particles. Because its ticles and high-,'nergy gamma rays.

half-life is less than that of sodium-24, However, the half-life of chlorine-38 is

the manganese-56 loses its activity more only 37 minutes, so that within 4 to 5

rapidly. But, within the first few hours hours its activity will have decayed to

after an explosion, the manganese in about I percent of its initial value.

soil may constitute a serious hazard, 9.39 Apart from the interaction of

greater than that of sodium. neutrons with elements present in soil

9.37 A major constituent of soil is and water, the neutrons from a nuclear

silicon, and neutron capture leads to the explosion may be captured by other nu-

'In each act of decay of sodium-24, there are produced two gamma-ray photons, with energies of 1.4

and 2.8 MeV, respectively. The mean energy per photon from fission products at I hour after fornation'

is about I MeV.

S. . . ..-. • +,
SOURCES OF RESIDUAL RADIATION 407

clei, such as those contained in struc- represent a serious external .1azard,

tural ari other materials. Among the Evea if they actually come in contact

metals, the chief sources of induced with the body, t'he alpha particles emitradioactivity are probably zinc, copper. ted are unable to penetrate the unbroken

and manganese, the latter being a con- skin.

stituent of many steels, and, to a lesser 9.42 Although there is negligible

extent. iron. Wood and ciothingy are un- danger from uranium and plutonium

likely to develop appreciable activity as outside the body, it is possible for dana result of neutron capture, but glass gerous amounts of these elements to

,-ould become radioactive becaiuse )f the enter the body through the lungs, the

large proportions of sodium and silicon. digestive' system, or breaks in the skin.

Foodstuffs can acquire induced activity, Plutonium, for example, tends to conmainly as a result of neutron capture by centrate in bone and lungs, where the

,odium. However, at such distances prolonged action of the a!pha particies

frou; a nuclear explos ion and under such can cause serious ha:rn (Chapter XII).

L )nditions that this activity would be 9.43 At one time it was suggested

significant, the food would probably net that the explosion of a sufficiently large

be fit for consumption for other reasons, number of nuclear weapons might result

e.g., blast and fire damnage. Some ele- in such ai extensive distribution of the

mients, e.g., boron, -,bsorb neutrons plutonium as to represent a worldwide

without becoming radioactive, and their hazard. It is niow realized that the fission

presence will decrease thz induced ac- products-the radioisotope strontiumtivity. 90 in particular--are a more serious

hazard than plutonium is likely to be.

Further, any steps taken to minimize the

danger fiom fission products, which are

9.40 The uranium and plutor.ium much easier to detect, will automatically

which may have ecaped fission in the reduce the hazard from the plutonium.

nuclear weapon rprepent a further possible source of residual nuclear radia- TRITIUM

fion. The common isotopes of these elements emit ,lpha particles and elso 9.44 The interaction of fast neusome gamma rays of low ener-ý. How- trons in cosmic rays with nitrogen nuclei

ever, because of their very long half- in the air leads to the formation of some

lives, the activity is very small com- tritium in ,he normal atmosphere; this

pared with that of the fission products. radioactive isotope of hydrogen has a

9.4i The alpha particles from ura- half-life of about 12.3 years. Small

nium and plutonium, or from radioac- amounts of tritium are formed in fission

tive sources in general, are compieic!y but larger quantities result from the exabsorbed in an inch or two of air (§ plosion of thermonuclear weapons. The

.1.66). This, together with the fact that fusion of deuterium and tritium prothe particles canrnMt penetrate ordinary ceeds mauch more rapidly than the other

clothing, indicates that uranium and thermonuclear reactions (§ 1.69) so that

plutonium depositeu on the earth do not most of the tritium present (or formed in

•.4 :.,.. .•• ~ - - -" . ....... ...
408 RESIDUAL NUCLEAR RADIATION AND FALLOUT

the D-D and Li-n reactions) is con- the atmosphere. As a general rule, the

sumed in the explosion. Nevertheless, tritium (and other weapons debris) must

some residual quantity will remain. Tri- descend into the troposphere before

tium is also produced by tL.e interaction scavenging by rain or snow can be efof nitrogen nuclei in the air with high- fective (§ 9.135).

energy neutrons released in the fusion 9.46 When tritium aecays it emits a

reactions. Most of the tritium remaining beta particle of very low energy but no

after a nuclear explosion, as well as that gamma rays. Consequently, it does not

produced by cosmic rays, is rapidly represent a significant external radiation

converted into tf-itiated water, HTC- hazard. In principle, however, it could

is chemically similar to ordinary be an internal nazard. Natuim! water is

(H20) and differs from it only in the relatively mobile in the biosphete and

respect that an atom of the radioactive any tritiated water present will be rapisotope tritium (T) r,'places one atom of idly dispersed and become available for

ordinary hydrogen (H). If the tritiated ingestion by man through both food and

water should become associated with drink. But the hazard is greatly reduced

natural weter, it will move with the by the dilution of the tritiated water with

latter. the large amounts of ordinary water in

9.45 The total amount of tri'ium on the environment. On the whole, the inearth, mostly in the form of tritiated ternal radiation dose from tritium is relwater, attained a maximum in 1963, atively unimportant when compared

after atmospheric testir.g by the United with the external (or internal) dose from

States and the U.S.S.R. had ceased. fission products (§ 12.199)

The amount was then about 16 to 18

times the natural value, but this has been CLEAN AND DIRTY WEAPONS

decreasing as a result of radioactive

decay. By the end of the century, there 9.47 The tervis "clean" and

will have been a decrease by a factor of "dirty" are often used to describe the

eight or so from the maximum, provided amount of radioactivity produced by a

there vre no more than a few nuclear fusion weapon (or hydrogen bolab) relexplosions in the atmosphere. A portion ative to that from what might be deof the t-itium produced remains in the scribed as a "normal" weapon. The

lower atmosphere, i.e., the troposphere, lattcr may be defined as one in whicl. no

whereas the remainder ascends into the special effort has been made either to

stratosphere (see Fig. 9.126). The tri- increase or to decrease the amount of

tiated water in the troposphere is re- radioactivity produced for the given exmoved by precipitation and ku times, nr, plosiorn yield. A "clear," weaoon would

1958 and 1963, following extensive nu- then be one which is designed to yield

clear weapons test series, the tritiated significantly less radioactivity than an

water in rainfall briefly reached values equivalent normal weapon. Inevitably,

about 100 times the natural concentra- however, any fusion weapon will protion. Tritium in the stratosphere is re- duce some radioactive specizs. Ever if a

moved slowly, ,..; that substantial pure fusion weapon, with no fission,

amounts are still present in this region of should be developed, its explosion in air
RADIOACTIVE CONTAMINATION FROM NUCLEAR EXPLOSION 409

would still result in the formation of so that upon detonation it genera.cd

carbon-14, tritiu.n, and possibly other more radioactivity than a similar normal

neutr -_n-induced activities. If special weapon, it would be described as

steps were taken in. the design of a "dirty " By its very nature, a fission

fusion device, e.g., by salting (§ 9. II), weapon must be regarded as being dirty.

RADIOACTIVE CONTAMINATION FROM NUCLEAR EXPLOSION

AIR BURSTS of the contamination wil! depend on the

characteristices of the weapon, e.g., tu94 takng air burst, by definition, i sion and fission energy yields, the height

ote taking tlace at srcia height above of burst, and the composition of the

the earth that no appreciable quantities surface material. The residual radioacof surface materia!s are taken up into the tivily which would arise in tlhis manner

fireball. The radioactive residues of the will thus be highly variable, but it is

weapon then condense into very small probable that where the induced activity

particles with diameters in the range of is substantial, all buildings except

0.01 to 20 micrometers (see § 2.27 strong underground structures would be

footnote). The nuclear cloud carries destroyed by blast and fire.

these particles to high altitudes, determined by the wc.apon yield and the at- LAND SURFACE AND SUBSURFACE

mospheric coi ditions. Many of the par- BURSTS

ticles are so small that they fall

extremely slowly under the influence of 9.50 As the height of burst degravity, but they can diffuse downward creases, earth, dust, and oher debris

and be deposited by atmospheric turbu- from the earth's surface are taken up

lence. The deposition takes place over into the fireball; an increasing proporsuch long periods of time that the par- tion of the fission (and other radioactive)

ticles will have become widely distrib- products of the nuclear explosion then

uted and their concentration thereby re- condense onto particles of appreciable

duced. At the saine time, the size These contaminated particle: range

radioactivity will have decreased as a in diameier from less than I micron to

cesult of natural decay. Consequently. several mnillimeters; the larger ones

rin the absence of precipitation, i.e., rain begin to fall back to earth even before

or snow (§ 9,67), the deposition of early the radioactive ,.loud has attained its

fallout from an air burst will generally maximum height, whereas the very

not be significant, smal!est ones may remain suspended in

9.49 An air burst, however, may the atmosphere for long periods. In

produce some induced radioactive con- these circumstances there will be an

tamination in the general vicinity of early fallout, with the larger particles

ground zero as a result of neutron cap.. reaching the ground withini 24 hours.

ti e by elements in the soil. The extent Photographs of typical fallout particles

"Now "
410 RESIDUAl. NUCiFIAR RADIATION ANIý FAI ItOUr

arc shown in Figs. 9.50a through d. The craier formation. Much of the radioacdistribution of the radioactivity of the tive material will remain in the crater

particles is indicatf.d by the autoradio- area, partly because it does noi escape

graphs, i.e., self-photographs produced and partly because the larger pieces of

by the radiatiolks. As a general rule the conraminated rock, soil, and debris

contamination is confined to the surface thrown up into .he air will descend in

of the particle, but in some cases the the vicinity of the explosion (Chapter

distribution is uniform throughout, in- VI). The finer particles produce.:d didicating that the particle was molten rectly or in ime forn of a base surge

when it incorpoi'ated the radioactive (§ 2.96) will remain suspended in the

material, air and wiil descend as fallout at ,onmie

9.51 The extent of the contamina- distance from ground zero.

tion of the earth's surface due to the

residual nuclear radiation following a WATER SURFACE AND

hind surface or subsurface burst depends UNDERWATER BURSTS

primarily on the location of the burst

point. There is a gradua! transition in 9.53 The parlicles entering the atbehavior from a high air borst, at one mosphere from a sea water surface or

extreme, where all the radioa':.ive res;- shallow subsurface burst consist mainly

dues am injected into the atmosphcrc, wo of sea salts at.', water drops. When dry,

a deep subsurface burst, at tha other the particles are generally smaller an~d

extreme, where the radioactive materi- lighter than the fallouw particles from a

als remain below the surface. In neither land burst. As a consequence of this

case will there ..e any significant local diffe;rence, sea water bursts produce less

fallout. Between these two extremes are close-in fallout than do similar land

surface and near-surface bursts which surface bursts. In particular, water surwill be accompanied by extensivc con- face and shallow underwater bursts are

tamination due to early fallout. A shal- often not associated with a region of

low subsurface burst, in which part of intense residual radioactivity near strthe fireball emerges from the ground, is face zero. Possible exceptions, when

essentially similar to a surface burst. such a region d(,ss occur, are water

"Th" distribution of the early fallout from surface bursts in extremely humiu atsurface and related explosions is deter- mospheres or in shallow water. If the

mined by the total and fission yields, humidity is high, theo hygroscop-,,, i.e.,

and the depth or height of burst, the water-absorbing, nature of the s,qa salt

nature of the soil, and the wind and particles may cause a cloud seeding efweather conditions. These matters will feet leading to a local rainout of rabe discussed in snme detail later in this dioactivity.

chapter. 9.54 The early residual radioacti9.52 For a subsurface burst that is vity from a water burst can arise from

not too deep, but deep enough t-,) pre- two sources: (1) the base surge if

vent emerugcnce of the fireball, a con- formed (§ 2.72 et seq.) and (2) the

siderable amount of dirt is thrown up as radioactive material, including induced

a column in the air and there is also radioactivity, remaining in the water.

_-JA
RADIOACTIVE CONTAMINATION FROM NUCLEAR EXPLOSION 411

A 1/2 MM

Figourc 9.50a. A typical fallout particle ftom a tower shot in Nevada. The particle has a du~ll,

metallic luste. and shows numerous adhering small particles.

1/2 rnrrt

Figure 9.50b. A fallout particle from a tower shot in Nevz.da. The particle is spherlmzl with

a brilliant, glossy surface.

4A
412 RESIDUAL. NUCLEAR RAD'A-i ION AND) FALLOUT

1/2 mm 1/ 2mm n

Figure 9.50:-. Photograph (left) and autoradiograph (right) of a thin section of a spherical

particle from a ground-surface' shot at Eniwetok. The radioactivity is uiniformrly distributed thioughout the particle.

Figure 9.50d. otiotgraph (left) and autoradiograph (riyhot of a thin section of an irregular

particle from a ground-surfact! shot at Bikini. The radioacti\I Ay is concentrated on the surlace of the particle.
RAI)IOACTIVIE CONTAMINATION FROM NUCk-EAR !-.Xi%.!OSION 413

The base surge is influenced strongly by sonnel on board the ships used in the

the wind, moving as an entity at the test, they would have been subjected to

existing wind speed and direction. lni- considerable doses of radiation if th,ý

tially, the base surge is highly radioac- fallout were not removed immediately 6

tive, but as it expands and becomes Since the BAKER shot was fired in

diluted the concentration of fission shallow water, the bottom material may

products, etc., decreases. This disper- have helped in the scavenging of the

sion, coupled with radioactive decay, radioactive cloud, thus adding to the

re:;ults in comparatively low dose rates contamination. It is expected that for

from the base surge by about 30 minutes F,.allow bursts ir very deep water the

after the burst (§ 2.77 et seq.),. fillout from the cloud ill be less than

9.55 The radioactivity in the water observed at the test it Bikini lagoon.

is initially present in a disk-like "pool," 9.57 An indication of the rate of

usually not more than 300 feet deep, spread of tie active material and the

near the ocean surface which is moved decrease in the dose rate following a

by the local currents. The pol gradually shallow underwater burst is provided by

expands into a roughly annular form, the data in Table 9.57, obtained after the

but it reverts to an irregular disk shape at Bikini BAKER test. Although the dose

later times. Eventually, downward mix- rate in i;e water was still fairly high

ing and horizontal turbulent diffusion after 4 hours, there would be considerresult ir. a rapid dilution of the radioac- able attenuation in the interior of a chip,

tivity, thus reducing the hazard with -;o that during the time required to cross

time. the contaminated area the total dose re9.56 In the Bikini BAKER test ceived would be small. Within 2 or 3

(§ 2.63), the contaminated falicut (or days after the BAKER test the radioacrainout) consisted of both solid palticles tivity had spread over an area of about

and a slurry of sea salt crystals in drops 50 square miles, but the radiation dose

of water. This contamination was diffi- rate in the water was so low that the

cult to dislodge ard had there been per- regi..-n could be traversed in safety.

Table 9.57

DIMENSIONS AND DOSE RATE IN CONTAMINATED WATER AFTER THE

20-KILOTON UNDERWATER EXPLOSION AT BIKINI

Contaminated Mean Maximum

Time after area diameter dose rate

explosion (hOw rs) (square miles) (miles) (rads/hr)

4 16.6 4.6 3.1

38 18.4 4.8 0.42

62 48.6 7.9 0.21

86 61.8 8.9 0.042

100 70.6 9.5 0.025

130 107 11.7 0.008

200 160 14.3 0.0004

",The techtique of washdown of ships, by continuous flow of water over exposed surfaces to remove

fallout as it settles, was developed as a result of the Bikini BAKER observations.

Iq

- - -
414 PRFSIDUAL NUCLEAR RADIATION AND FALLOUT

9.58 Th,ý residual radi:.lti,,n dose vetncity. Consequently, the residual .arates and doses from the base :;t-rge and diation distribution associated with an

pool resulting from an underwater nu- underwater burst is complex, and there

clear explosion vary significantiy with is no simplified prediction system suitweapon yield and burst depth, proximity able for general application, such as has

of the ocean bottom to the point of been developed for land surface bursts

detonation, wind velocity, and current (§ 9.79 et seq.).

FALLOUT DISTRIBUTION IN LAND SURFACE BURSTS

DISTRIBUTION OF CONTAMINATION the delayed tallout, most of which tindergoe:; substantial radioactive decay

9.59 More is known about the fall- and, hence, decreases i:M activihy before

out froih land surface and near-surface it eventually reaches thL ground many

bursts than for other types of explo- hundreds or thousands c' miles away

sioiis. Consequently, the remainder of (§ 9.121 et seq.).

ihis chapter will be concerned mainly 9.60 The distribution on the ground

with the radioactve contamination re- of the activity from the early fallout,

suiting from bursts at or near (he ground i.e., the "failout pattern," even for sirmsurface. The proportion of the total ra- ilar nuclear yields, also shows great

dioactivity of the weapon residues that variability. In addition to the effect of

is present in the early fallout, sometimes ,i'ind, such tactors as the dimensions of

called the "early fallout fraction," the radioactive cloud, the distribution of

varies from one test explosion to an- radioactivity within the mushroom

other For !and surface bursts the early head, and the range of p:ticle sizes

fallout fraction, which depends on the contribute to the uncertain'?v in attempts

nature of the surface material, has been to predic. :he f)Ilout pattern.

estimated io range from 40 to 70 per 9.61 The spatial distribution of racent. Values somewhat higher than this dioactivity within the cloud i•s not

are expected for shallow underground known accurately, but some of the gross

bursts. For water surface bursts, how- features have been derivecd fron, obserever, the fraction is generally lower, in vations and theoretical cor,.;iderations. It

the neighborhood of 20 to 30 percent, is generally accepted tha(. of the total

for the reason given iu § 9.53. Some activity that is lofted. the mushroom

variability is expected in the fallout head from a contact land-surface burst

fraction for a given type of burst due to initially contains about 90 percent with

variations in environmental and meteor- the remainder residing in the stem. The

uuilu.al ýoiidiiions. Nevertheless, it proportion of activity in the stem may be

will be assumed here that 60 percent of even less for a water :,urfac. burst and

the total radioactivity from a land sur- almost zero for an air buist However, it

fnfe burst weapon will be in the eariy appears that some radioactive particles

fallout. The remainder will contribute to from ihe mushto;om head fall or are

Id
FALLOUT I)ISTRIBUTION IN LAND SURFACE BURST 4!5

transported by subsiding air currents to Pacific. Hewever, in the absence of any

lower altitudes even before the cloud definite evidence to the contrary, it is

reaches its maximum height. In addition generally assumed that the fallout paito the radioactivity in the mushroom tern for a surface burst in a large city

head and the stem, a considerable wi!l not differ greatly from those assoquantity of radioactivity from a surface ciated with surface and tower shots in

burst is contained in the fallback in the the Nevada desert. This may atA bc the

crater and in the ejecta scattered in all same as the patterns observed at test. in

directions around ground zero (Chapter Pacific Ocean atolls.

VI). There is some evidence that, for

explosions in the megaton range, the

highest concentration of radioactiviiy AREA OF CONTAMINATION

initially lies in the lower third of the

head of the mushroom cloud. It is p.ob- 9.64 The largest particles fall to the

able, too, that in detonations of lower ground front the radioactive cloud and

yield, a layer of reiatively high activity stem shortly aftci the explosion and

exists somewhere in the cl,-ud. The lo- hence are found within a short distance

c.ation of the peak concentration appears of surface zero. Smaller particles, on the

to vary with different detonaticns, per- other hand, wifl require many hours to

haps as a function of atmospheric con- fall to earth. During this period they

ditions. may be carried hundreds of miles from

9.62 Because particles of different the burst point by the prevailing winds.

sizes descend at different rates and carry The very smallest particles have no apdifferent amounts of radioactive con- preciable rate of iall and so they may

tamination, the fallout pattern will de- circle the earth many times before

pend markedly on the siz.., distribution reaching the ground. generally ip preof the particles in the cloud after con- cipi'ation with rain or snow.

densation has occurred. In general, 9.65 The fact that smaller particles

larger particles fall more rapidly and from the radioactive cloud may reach

carry more activity, so that a high pro- the ground at consideraHle distances portion of such particles will lead to frrn the explosion meant thit! fallout

greater contamioation near ground zero, from a surface uurst cc,; pmoduce serious

and less at greater distances, than would contamination far beyond 'he rage of

be the case if small particles predomin- other effects, such as blast, shock, therated. mal radiation, and initial nuclear radia9.63 The particle size distribution tion. It is irue that the longer the cloud

in the radioactive cloud may well de- particles remain suspended in the air,

pend on the nature of the material which the lower w.ll oe their activity when

becomes engulfed by the fireball. A they reach the ground. However, the

surface burst in a city, for example, total quantity of contaminated material

could iesult in a particle size distribution produced by the surface burst of a meand ,onsequent fallout pattern which gaton weapon with a high fission yield is

would differ from those produced under so large that fallout may continue to

test conditions either in Nevada or in the arrive in hazardous concentrations up to

- -
416 RESIDUAL NUCLEAR RADIATION AND FALLOUT

perhaps 24 hours after the burst. Radio- does not normally produce any early

active. contamination from a single det- fallout, precipitation in or above the

onation may thus affect vast areas and so nuclear cloud could, however, cause

fallout must be regarded as one of the significant contamination on the ground

major effects of nuclear weapons. as a result of scavenging of the radioac9.66 An important factoi determini- tive debris by rain or snow. Precipitaing the area covered by appreciable tion can also affect the fallout from a

fallout, as well as its distribution within surface ot subsurface burst, mainly by

that area, is the wind pattern from the changing the distribution of the local

ground up to the top of the radioactive contarrinaion that would occur in any

cloud. The direction and speed of the event. F1allout from the cloud stem in a

wind at the cloud level will influence the surface biurst of high yield should not be

-i-otio: and extent of the cloud itself. In greatly influenced by precipitation,

alidition, the winds at lower altitudes, since the particles in the stem will fall to

whi-h may change both in time and earth in a relatively short time regardless

space, will cause the fallout particles to of whethe' there is precipitation or not.

driit one way or another while they 9.68 A number of circumstances

descend to earth. The situation may be affect the extent of precipitation seafurther complicated by the effect of rain venging of the stabilized nuclear cloud.

(see below) and of irregularities in the The first requirement is, of course, that

terrain. These, wý well as nonuniform the nuclear cloud should be within or

distribution of activity in the cloud and below the rain cloud. If the nuclear

fluctuations in the wind speed and dii- clot'd is above the rahi- cloud, there will

rectior., will contribute to the dcvelop- be no scavenging. The altitudes of the

ment of "hot spots" of much higher top of rain (or snow) clouds range from

activity then in the immediate sur- about 10,000 to 33,000 feet, with

roundings. lighter precipitation generally ieing associated with the lower altitudes. Thc

bottom of the rain clon:d, fromn which the

DEPOSITION OF RADIOAC'TIVE precipitation emerges, is commrronly at

DEBRIS BY PRE( ,iFATION an altituie of about 2,000 feet. Precipitation from thunderstorms, however.

9.67 If the airborre debris from a may originate as high as 60,900 feet.

nuclear explosion should encounter a For low air or surface bursts, the height

iegion where precipitation is occurring, and depth of the nuclear cloud may be

a large portion of the radioactive par'- obtained from Fig. 9.I6 and these data

ticles may be brought to earth with the may be used to estimate. the fraction of

rain or snow. The distribution of the this cloud that might be intercepted by

.aslout on the ground will then probably precipitation. For -xplosion yielhs up to

be more irregu.ar than ir, the absence of about 10 kilotons essentially all of the

piecipitatiou, with heavy showers pro- nucicar cloud, and frw yields up to 190

ducing local hot spots within the con- kilotons at least par! of the cloud could

laminated area. Although an air burst be subjec: to scavenging. For yields in

TI

. : 1,
FALLOUT DISTRIBUTION IN LAND SURFACE BURST 417

excess of about 100 kilotons, precipita- 9.71 If the nuclear cloud should

lion scavenging should be insignificant, enter a precipitation region at some time

But if the nuclear cloud should en- after the burst, the surface contaminacounter a thunderstorm region, it is tion caused by scavenging will be depossible that all of the cloud from ex- creased. In the first place, while the

plosions with yields up to several hun- cloud is drifting, the radioactive nudred kilotons and a portion from yields clides (§ 1.30) decay continuously.

in the megaton range may be affected by Thus, the longer the elapsed time before

piecipitation. the nuclear cloud encounters precipita9.69 If the horizontal diameter of tion, the smaller will be the total amount

the rain cloud is less than that of the of radioactive maferial present. Furthernuclear cloud, only that portion of the more, the nuclear cloud, especially from

latter that is below (or within) (he rain a low-altitude burst, tends to increase in

cloud will be subject to scavenging. If size horizontally with time, due to wind

the rain cloud is the larger, then the shear and eddy diffusion, without draswhole of the nuclear cloud will be tic change in the vertical dimensions,

available for precipitation scavenging. un'1-ss precipitation scavenging should

The length of time during which the occur. This increase in horizontal dinuclear cloud is accessible for scaveng- mensions will decrease the concentraig will depend on the relative direc- tion of radioactive particles available for

tions and speed of ,.ravel of the nuclear scavenging. Finally, the particle,,; that

and rain clouds. ? e 'scavenged will not be depositt., on

9.70 The time, relative to the burst the ground immediately but will fall

time, at which the nuclear cloud en- vwith the precipitation (typically 800 to

counters a region of precipitation is ex- 1 200 feet per minute for rain and 200

pected to have an importai. influence on feet per minute for snow). Since the

the gcound contamination resulting from particles are scavenged over a period of

scavenging. If the burst occurs during time and over a range of altitudes, horiheavy precipitation or if heavy precipi- zontal movement during their fall will

tation begins at the burst location during tend to decrease the concentration of

the period of cloud suabifization, a radioactivity (and dose rate) on the

smaller area on the ground will be con- ground. The horizontal movement durtarainated but the dose rate will be ing scavenging and deposition will rehigher than if the nuclear cloud encoun- suit in elongated surface fallout pattered the rain cloud at a later time. Even terns, the exact shape depending on the

for such early encounters, the dose rates wind shear.

near ground zero will be lower than after 9.72 After the radioactive particles

a surface burst with or without precipi- have been brough: to the. ground by

ration. If the rainfall oz light, the sca- scavenging, they may or may not stay in

venging will be less efficient, and the place There is a po~sibility that water

ground distribu!ion pattern will be elon- runoff will create hot ,pois in some

gated if the nuclear cloud drifts with the areas while decreasing tle activity in

wind but remain:: in the pre.ipitation others. Some of the radioactive material

system, may be dissolved out by the rain and
418 RESll)UAI. NU(I.-AR RADIATION AND FAt : I OU I

will soak into the ground. Attenuation 9.74 Two types of precipitation

of the radiations by tine soil may then scavenging have been treated in this

reduce the dose rates above the ground oianner: "rainout" (or "snowout"),

surface. when the nuclear cloud is within the rain

9.73 Much of what has been stated (or snow) cloud, and "washout" when

concerning the possible ,ffects of rain the nuclear cloud is below the rain (or

on fallout from both surface and air snow) cloud. The rainfall rate appears to

bursts is based largely on theoretical have little effect on ra-nout bat washou'

considerations. Nuclear test operations is affected to a marked extent. The data

have been conducted in such a manner in Tables 9.74a and b give rough esas to avoid the danger oi" riJiiout. The timates of the amounts of rainfall, exfew recorded cases of rainout which pressed as the duration, required for the

have occurred have involved very low removal of specified percentages of the

levels of radioactivity and the possibility nuclear cloud particles by rainoun and

of severe contamination under suitable washout, the terms Hight, moderate, and

conditions has not been verified. Never- heavy in Table 9.741) refer to 0.05,

theless, there is little doubt that precipi- 0.20, !,nd 0.47 inch of rain per hour,

tation scavenging can affect the fallout respectively, as measured at the surface.

distribution on the ground from both air Thus, it appears that washout is a less

and surface bursts with yields in the effective scavenging mechanism than

appropriate range. Because of the many rainout, The tabulated values are based

variables in precipitation scavenging, on the assumptior. that the nuclear and

the extent and level of surface contami- rain clouds remain in the same relative

nation to be expected are uncertain, positions, with the rain cloud at least as

Sone estimates have been made, how- large as the nuclear cloud (§ 9.69). It

ever, of the amounts of rainfall neces- should be noted that the times in Tables

sary to remove given percentages of the 9.74a and b are those required for the

iidioactive particles f-rom a nuclear radioactive debris to be removed by the

cloud. These estimates are based partly rain; additional time will elapse before

on field experiments with suspended the radioactivity is deposited on the

particles and partly on mathematical ground. The deposition time will demodels for use with a computer; the pend on the altitude at which the debris

results are thus dependent on the details is sLavenged and the rate of fall of the

of the model, e.g., particle size distri- rain.

bution.

:1
FALLOUT DISTRIBUTION IN LAND) SURFACE BURST 419

Table 9.74a

ESTIMATED RAINFALL DURATION FOR RAINOLIT

Perceth

of Cloud Duration of Rainfall

Scavengod (hours)

25 0,07

50 0.16

75 0. 32

90 0.53

99 1.1

Table 9.741)

ESTIMIATED RAINFAI .t DURA'riON FOR WASHOUT

Duration oi Rainfall

Percent (hours)

of Cloud - -

Scavenged Light Moderate Heavy

258 1.6 0.8

50 19 3.8 1.9

75 38 7.7 3.6

90) 64 13 6.4

99 128 26 13

FALLOUT PATTERNS at the Eniwetok Proving Grounds. Since

the fallout descended over vast areas of

9 '15 Information concerning fallout the Pacific Ocean, the contamnination

di!;iribution has been obtained from ob- pattern, of a large area had to be inferred

servations made during nuclear weapons from a relatively few radiaticn do.ae

tests at the Nevada Test Site and the measurements (§ 9. 105). Furthermore,

Eniwetok Proving Grounds. 7 However, the presence of sea water affected the

ther are many difficulties in the analysis ýesuiý3, as will be seen below.

and interpretation of the res~ilts, and in 9.76 Nuclear tests in the atmostheir use to predict the situation that phere in Nevada have been confined to

might arise from a land surface burst weapons having yields below 100 kiloover a large city. This is palticulat y !he tons and most of the detonations were

case for the megaton-ranvc dc'zonations from the tops of steel towers 100 tzo 700

~The Eniwetok Proving Grounds, called the Pacific Proving Ground before 1955, included test sites on

Bikini and Eniwetok Atolls and on Johnston and Christmas Islands in the Pacific Ocean.
420 RESIDUAL 'UCLEAR RADIATION AND FALLOUT

feet high or from balloons at levels of drawn to the hot spot, some 60 miles

400 to 1,500 feet. None of these could NNW of the northern boundary of the

be described as a true surface burst and, Nevada Test Site, that was observed in

in any event, in the tower shots there is connection with the BOLTZMANN

evidence that the fallout was affected by test. This area was found to be seven

the tower. There have been a few sur- times more radioactive than its immediface bursts, but the energy yields were ate surroundings. The location was diabout I kiloton or less, so that they rectly downwind of a mountain range

provided relatively little useful ihfor- and rain was reported in the general

mation concerning the effects to be ex- vi,•inity at the time the fallout occurred.

pected from weapons of higher energy. Either or both of these factors mny have

Tests of fusion weapors with yield, up been responsible for the increased raio 15 megatons TNT equivalent have dioactivity.

been made at the Pacific Ocean test 9.78 Measurement of fallout activsites. A very few were detonated on ity from iniegaton-yield weapons in the

atoll islands, but mos cf the shots in the Pacific Ocean area has indicated the

Bikini and Eniwetok Atolls in 1958 presence of marked irregularities in the

were fired on barges ini the lagoons or on overall pattern. Some of these may have

coral reef,(. In all cases, however, con- been due to the difficulties involved in

siderable qu.nntities of sea water were collecting and processing the limited

drawn into the iradioactive cloud, so that data. Nevertheless, there is evidence to

the fallout was probably quite different indicate that a hot spot some distar':e

from what would have been associated (50 to 75 miles) downwind of the burst

with a true land surface burst. point may be typical of the detonations

9.77 The irregular nature of the at the Eniwetok Proving Grounds and,

fallout distribution from two tests in in fact, some fallout prediction methods

Neva6a is shown by the patterns in Figs. have been designed to reproduce this

9.77a and b; the contour lines are drawn feature. The o'ccurrence of these hot

through points having the indt, a!ed dose spots may have been a consequence of

rates at 12 hours after the de!onation the particular wind structure (§ 9.66).

time. Figure 9.77a refers to the The times for most explosions at the

BOLTZMANN shot (12 kilotons, 500- Eniwetok Proving Grounds coin.cided

foot tower) of May 28, 1957 and Fig. with complex wind stiuctures from the

9.77b to the TURK shot (43 kilotons, altitude of the stabilized cloud to the

500-foot tower) of March 7, 1955. Be- surface. The large directional changes in

cause of the difference in wind condi- the wind served to contain the fallout'

tions, the fallout patterns are quite dif- more locally than if !he wind were

ferent. Furthermore, attention should be blowing in one direction.
FAL.IO)UT DISTRIITTION IN IAND) SURFACI- BURST 421

I MRAD/10r•

10

OLTz4 ANN

TEST

0 20 40 SITE

I LES

Figure 9.77a. Early fallout dose-rate contours from the BOLTZMANN shot at the Nevada

Test Site.

TURK I MRAD/HR

10~

1000 1000

C_[.•• O0TEST

SITE 0 20 40

MILES

Figure 9,77b. Early fallout dose-rate contours from the TURK shot at Nevada Test Site.

,14

• - . *-
422 RESIDUAL. NUCLEAR RADIATION AND FALLOUT

FALLOUT PREDICTIONS FOR LAND SURFACE BURSTS

PREDICTION OF FALLOUT PATTERNS methods. Apart from a few instances,

less detailed mathematical mode!s,

9.79 Several methods, of varying which do not require digital computers.

degree of complexity, have been devel- have been used to predict fallout disoped for predicting dose rates and inte- tribution patterns during nuclear tests.

grated (total) doses resulting from fall- 9.81 The analog technique, which

out at various distances from ground (or is essentially a comparison process, uti-

:surface) zero. These methods fall into lizes a pattern chosen from a catalog of

-four general categories- they are, in de- fallout contour pat,erns covering a wide

creasing order of complexity, and hence range of yields and wind conditions.

detail, the mathematical fallout model, The choice is determined by the sittithe analog method, the danger sector larity between the yield and wind in the

forecasi, and the idealized fallout pat- given situation and those in the catalog

tcr: Each of these techniques reuircs, pattern. Fhe cawalog can consist of acof coursce, a knowledge of the total and tual fallout patterns and others interpofission yields of the explosion, the burst lated and extrapolated from these, or of

height, and the wind structure to the top patterns obtained by calculation from a

of the ,-adioactive cloud in the vicinity of mathematical fallout model.

the burst. The more complex pi'ocedures 9.82 The danger sector forecast rerequire a forecast of the winds and quires a minimum of detailed informaweather in the locality over a period of tion in order to give a qualitative picture

several hours to a few days after the of the general fa!lout area and an ideas of

exolosion, In making these forecasts, the arrival times. AMthough it provides a

the considerable seasonab(e variations rough indication of the relative degree

in wind patterns must be kept in mind. of hazard, there is little or no informa9.80 In the fallout model method, lion concerning the actual dose rates to

ai, attempt is imade to describe fallout be expected at various locations. The

mathenmatically and, with various inher- method yields a prediction quickly and

ent assumptions, to predict the dose-rate simply and is p,'ob.bly as accurate as the

distribution contours resulting from a explosion yield and meteorological inparticular situation. The most reliable formation will justify in an ,perational

procedures are very complex and re- (field) situation. The fourth prediction

quire use of a large digital computer in method, based on the use of idealized

their application to a variety of circi,:n- fallkut distribution patterns, is described

stances. "lhcy are, consequently, em- in some detail below. Such idealized

ployed primarily in theoretical studies of patterns are derived from a detailed

the fa~lout process, in making planning mathematical model, as described in ,

estimates, and in the preparation of § 9.80, based on average or most probtemplates fo.r use with analog prediction able conditions.

- ..- ..- . . .. , ..... , ,- ,.. . ..... ...-.--- .. • . .. ... • , -. ,- ,,,t--- . ' - .,-. ,--.-..', •'
FALLOUT PREDICTIONS FOR LAND SURFACE BURSTS 423

IDEALIZED FALLOUT PATTERNS shortly. But if the wind direction

changes with altitude, the fallout will 9.83 Idealized fallout contour pat- spread over a wider angle, as in Fig.

terns h~ive been developei which repre- 9.77a, and the activity, i.e., the radia3ent the average fallout field for a given tion dose (ate, at a given distance from

yield and wind condition. No attempt is ound (or made to indicate irregularities which creased because the same amous of rawill undoubtedly occur in a real fallout dioactive c.ontamination will cover a

pattern, because th~e conditions deter- larger area. Lower wind speeds will

mining such irregularities are highly make the patterin shorter in he downvariable and uncertain. Nevertheless, in wind direclion because the particles will

spite of their limitations, idealized pat- not travel so far before descending to

ternis are useful for plannitig purposes, earth; the activity at some distance from

for example in estimating the overall the burst point will be lower and the

effect of fallout from a large scale nu- high dose rates immediately downwind

clear attack. Although they will un- of ground zero will be increased. If the

doubtedly underestimate the fallout in wind speed is higher, the contaminated

some locations and overestimate it in area will be greater and the radicacothers, the evaluation of the gross fall- tivity will be higher 4t large distances

out problem over the whole area af- from surface zero and lower immedifected should not be greatly in error. ately downwind of ground zero.

9.84 For a detailed fallout distribution prediction, the winds from the sur- DEVELOPMENT O FALLOUT

face to ali levels in the radioactive cloud PATTERN

must be considered. However, for the

idealized patterns, the actual complex 9.86 Before showing an idealized

wind system is replaced by an approxi- fallout distribution pattern it is impormately equivalent "effective wind." tant to understand how such a pattern

Various methods have been used to de- develops over a large area dui ing a

fine the effective wind, i.e., speed and period of several hours following a surdirection, for the genleration of idea!izeJ face burst. The situation will be illus-

, patterns. The effective wind that is ap- trated by the diagrams in Figs. 9.86a

,.ropriate for use with the idealized pat- and b, which apply to a 2-megaton externs described below should be ob- plosion with 50 percent fission yield.

tained by first determining the average The effective wind pneed was taken as

wind from the ground to the b,,se and to 15 miles per hour. Ftg. 9.86a shows a

the top of the stabilized cloud (§ 2.15). number of contour lines for certain (arThe effective wind is then the mean of bitrary) round-number values of the

these two average winds, dose rate, as would be observed on the

9.85 By assuming little or no wind ground, at 1, 6. and 18 hours, respecshear, that is, essentially no change in tively, after the explosion. A series of

wind direction at different altitudes, the total (or accumulated) dose contour

idealized fallout contour patterns have a lines for the same times are given in Fig.

regular cigar-like shape, as will be seen 9.86b. !, will be understood, of course,

EW' I !~

I" •a .• lm l•,,t• .- ',¢-•",,.r ",• ., .•" ''- .. -•r....•.•••,:....... .r-• .-.,.•,..: .'am• • .,,•,-. ..
424 RESIDUAL NUCLEAR RADIATION AND FALLOUT

that the various dose rates and doses hours about 5 lads per hour. The fallout

change gradually from one contour line commences at somewhat more than 6

to the next. Similarly, the last contour hours after the detonation and it is esline shown does not represent the limit sentiily complete at 9 hours, although

of the contamination, since th:2 dose rate this cannot be determined directly from

(and dose) will continue to fall off over a the contours given. The total accumugreater distance. lated dose, from Fig. 9.36b, is seen to

9.87 Consider, first, a location be zero at I hour after the e:xplosion,

about 20 miles directly downwind from less than I rad at 6 hours, and about 80

ground zero. At I hour after the deto- rads at 18 hours. The toial (infinite time)

nation, the observed dose rate is seei, to dose will not be as great as at locations

be roughly 3 rads/hr but it will rise closer to ground zero, because the

rapidly arid will reach a value over 500 quantity of fission products reaching the

rads/hr sometime between ! and 2 ground decreases at increasing distances

hours. The dose rate will then decrease from the explosion.

to about 20Y3 rads/hr at 6 hours; at 18 9.89 In general, therefore, at any

hours it is down to roughly 50 rads/hr. given location at a distance from a surThe increase in dose rate after I hour face burst, some time will elapse bemeans that at the specified location the tween the explosion and the arrival of

fallout was not complete at that time. the fallout. This time will depend on the

The subsequent decrease after about 2 distance from giound zero and the efhours is then due to the natural de•cay of fective wind velocity. When the fallout

the fission products. Turning to Fig. first arrives, the dose rate is small, but it

9.86b, it is seen that the total radiation inr.reases as more and more fallout dedose rece>-ed at the given locatiorn by I scends. After the fallow,t is complete, the

hour after the explosion is small, be- radioactive dec, f the fission products

cause the fallout has only just started to will cause the dose rate to decrease. a

arrive. By 6 hours, the total dose has Until the fallout commences, the accureached more than 1,000 rads and by 18 mulated dose will, of course, be small,

hours a total dose of some 2,000 rads but after its arrival the total accumulated

will have been accumulated. Subse- radiation d-,,,e will increase continquently, the total dose will continue to uously, at first rapidly and then some•-

increase, toward the infinite tune value, what more slowly, over a long period of

but at a slow rate (see Table 9.22). time, extending for many months and

9.88 Next, consider a point lOG even years.

miles downwind from ground zero. At 1 9.90 The curves in Figs. 9.90a a:nd .

hour after the explosion the dose rate, as b illustrate this behavior qualitatively;

indicated in Fig. 9.86a, is zero, since they show the variation with time of the

the fallout will not have reached the dose rate and tfhe accumulated dose from

specified location. At 6 hours, the dose fallout at points near and far, respezrate is about I rad per hour and at IF, tively, in the downwind direction from a

I'
FALLOUT PREDICTIONS FOR LAND SUJRFACF BURSTS 425

280 I RAD/HR 18

- 16

240

z

-. Wa 14

• 200 U

U. 12 '}

•oo N 3.0

o 160 to j

CL: EE

o 120 ,L M, 0

LLU L. I RAD/HR

z 10

S 84

40 2

3 RADS/R 10

30 0

1000

20 0 20 20 0 20 20 0 20

UIISTANCE FROM GROUND ZERO (MILES)

I HOUR 6 HOURS 18 HOURS

Figure 9.86a. Dose-tate contcors from early fallout at I, 6, and 18 hours after a surface

burst with a total yield of 2 megatons and I megaton fission yield (15 mph

effeciive wind speed).

*1
426 RESII)UAI. NU(CI FAR PADIA lION AND FAI I 011 V

280 18

r• 16

240 z

3:

S-) 14

" 200 I0 RADS

WW 0

N F a 160 30 I0 J

0n.

0 120 U.

U- .U

z 10 RADS 600 6

eo 30

80 .100

3 4

300

300 "'

40 1

10 RADS

1.• 000

0(•- .- 0

20 1 1 1 1.J....1J

20 0 20 20 0 20 20 0 20

DISTANCE FROM GROUND ZERO (MILES)

I HOUR 6 HCURS 18 HOURS

Figure 9.86b. Toial-dose contours from early fallout at I, 6, and 18 hours after a surface

burst with a total yield of 2 megatons and I-megaton fission yield (15 mph

effective wind speed).

S.... ,-,p'

1 • • . ... == =
FALLOUT PREDICTIONS FOR LAND SURFACE BURSTS 427

surface burst. Both ihe dose rate and the and accumulated dose curves, of the

dose are zero until the fallout particles form of Figs. 9.86a and b, for all times

reach the given locations. At these times following a nuclear detonation would

the dose rate commences to increase, obviously be a highly complicated nrttreaches a maximum, and subsequently ter. Fortunately, the situation can be

decreases, rapidly at first as the radio- simplified by utilizihg an idealized tliisotopes of short half-life decay, and out pattern in terms of the unit-time

then more slowly. The total accumu- reference dose rate, mentioned in § 9.16

lated dose increases continuously from et seq. By means of the curves given

th. time of rrival of the fallout toward earlier in the chapter (Figs. 9.16a and b

the limiting (infinite time) value, and Fig. 9.20) it is then possible t,)

9.91 Since tlh- mushroom cloud estimate dose rates and total doses from

grows rapidly in radius and reaches its fallout at any given time for a specified

stabilized altitude before the winds can distance downwind from the burst point.

act on it significantly, the time of arrival The calculations are valid only if all the

of the fallout at a particular l,,cation is early fallout has descended at that time.

measured by the distance from the por- 9.93 The general form of the ideation of the -loud nearest to that location lized ,nit-0me reference dose-rate conand the speed of the effective Wind. "he tours for land surface bursts is shown in

time of arrival is equal to the distance Fig. 9v,93. cohe dimensions that define

from ground zero to the po'nt of interest the various contours are indicated for

minus the radius of the cloud, divided the l-rad per hour contour. In a real

by the effective wind speed. For the situation all contour lines would be

S p~esent purpose the radius of the stabi- closed in the upwind direction as shown

lized cloud as a function of yield may be for the I -rad per hour contour. The

obtained from Fig. 2.16. The radius is scaling relationships, for ca!.:ulating the

affected to some extent by the p.operties downwind distance, the maximum

of the atmosphere, in particular by the width, the ground-zero width of the

height of the tropopause. The curve in idealized unit-tie dose-rate contour,

Fig. 2.16 represents a reasonable aver- for contact surfice bursts (§ 2. 127 footage for mid-latitudes. The radius of the note) of W kilotons yield are sumstabilized cloud is only important in marized in Table 9.93. The effective

calculating the time of arrival for loca- wind is 15 milez per hour in each case

tions relatively close to ground zero and with wind shear of 150. The upwind for large, yield weapons. If the cloud distance depends on the cloud radius; it

radius is small in comparison with the is estimated to be approximately onedistance from ground zero to the point half the groind-zero width, i.e., the

of interest, e.g., for low yields or large upwind contours may be represented

distances, the cloud radius may be neg- roughly by semicirclks centered at

lected in calculating fallout arrival ground zero. The contour scaling relatimes. tionslips are depender, upon the nature

of the surface; the values in Table 9.93

UNIT-TIME REFERENCE DOSE RATE are applicable to most surface materials

in the continental United States (cf.

*9.92 The representation of dose rate § 9.63).

t*,

_ _
428 RESIDUAl. NUCLEAR RADIATION AND FALLOUT

0 _S

TI ME "IME

(LINEAR SCALE\, (LINEAR SCALE)

a b

Figure 9.90a. Qualitative rcpresentat ion of dose rate and accumulated dose from fallout as a

function of time after explosion at a point not far dowvnwind from groLund

zero.

Figure 9.9Ob. Qualitative representation of dose rate and accumulated dose from fallout as

a function of time after explosion at a point far downwind from ground zero.

9.94 Idealized contour shipes and any event, the locations of such high

sizeC2 are a function of the total yield of reference values will be within the areas

the weapon, whereas ,:he dose-rate con- of complete devastation from other eftour values are determined by the fission fects.

yield. Thus, in order to obtain idealized 9.95 Thle idealized reference dose

fallout patterns for a weapon that does rates obtained by the methods described

not derive all of its yield from fission, above appiy to doses that would be

the dose-.rate values of the contour !ines received in the open over a completely

for a weapon of the same total yield smooth surface. Such surfaces provide a

should be multiplied by the ratio of the conveniient reference for calculations,

fission yield Co the total yield. For ex- but they do 1int occur to any great extent

an'iple, for a weapon having a total yield in nature. Even the surf ace roughness in

of W kilotons with 50 percent of the relatively level terrain will make the#

energy derived from fission, the contour actual values smaller than •he idealized'

dime~nsions are first determined from values. A reduction (or terrain shieldTable 9.93 •or a yield of W kilotons, ing) factor of about C.7 is appropriate

The unit-time reference dose rates are under such ci,'cumstances. A reduction•

then multiplied by 0.3. Except for iso- factor of 0.5 to 0.6 would be more "

lated points in the immediate vicinity of suitable for rough, hilly terrain. Any

ground zero, observations indicate that shelter would decrease the dose received

unit-time reference dose rates greater from early fallout (§ 9.120).

than about 5,000 rads/hr are unlikely. Tn

". W .. iI

• ... , ., , ,,., .. .•. , . . .. ..... . . ., . .. .• • _.j"?. ,.. ... : -'*.'• '• * • "•W t• - *'' "y i'•m, .•"''r ' .n ... • • • .... .m " .
FAI-LOUT PREDICTIONS FOR LAND SURFACE BURSTS 429

2I.

-o

LE

Z II.)

3

w

I-.

z

o

,11,-4

€,A
430 RESIDUAL NUCLEAR RADIATION AND FAI.IOUT

Table 9.93

SCALING RELATIONSHIPS FOR UNIr-TIME RE:FERENCE DOSE-RATE CONTOuRS

FOR A CONTACT SURFACE BURST WITH A YIELD OF W KILOTONS AND A 15 MPH

WIND

Reference Downwind Ground zero

dose rate distance Maximum width width

(vads/hr) (statute miles) (statute miles) (statute :-iiles)

3.000 0.95 Wi145 0.0076 W) M, 0,026 Ws

1.0() 1.8 W14' 0.036 W1"' I 0.060 1"'"

300 4.5 W' 4 0.13 W) - 0.20 W, '

103 8.9 W1)4 0.38 WV",' 0.39 W,':

30 16 W) 45 0.76 W,' " 0.53 VW"1 4

10 24 W4o'4 1.4 W'.,' 0.08 V..', 41

3 30 W1,V 2.2 WV" ' 0.89 W14,1

I 40 W"1 ' 3.3 s 114"! 15 W" 41

SCALING FOR EFFECTIVE WIND within the cloud to reach the ground at

twice the distance from ground zero, so

9.96 The effective wind speed and that they are spread over roughly twice

direction vary with the heights of the top the area. However, particles of many

and bottom of the stabilized cloud differert sizes will arnive at any given

(§ 9.84). For a weapon of given yield, point on the ground as a re:;ull of the

these heights will depend upon many different travel times from different

factors, including the density and rela- points of origin in the large nuclear

tive humidity of the atmosphere and the cloud. Consequently, Aimple scaling realtitude of the tropopause. Neveitheless, lationships for wind speed are not poswithin the accuracy of the idealized sible. Examination of test osata and the

unit-time reference dose-rate contours, results of calculations with computer

approximate values of the cloud heights codes suggest the following approximay be used. The curves in Fig. 9.96 mate scaling procedure: for effective

are based on the same model as was wind speeds of i, miles per hour, the

used in deriving the dose-rate contours downwind distances derived from Table

and scaling relationships in § 9.93. 9.93 are multiplied by the factor F,

They may bt: taken to be representative where

of the average altitudes to which nuclear

clouds from surface (or low air) bursts 15

of various yields migh, be expected to 60

rise in the mid-latitudes, e.g., over the

United States. for effective wind speeds greater than . 5

9.97 If there is no directional shear, miles per hour, and

then doubling the effective wind speed

would cause the particles of a given size , 30

that originate at a particular location 30

S44

• "" II
FALLOUT PREDICTIONS FOR LAND SURFACE BURSTS 431

120-

,0 U. 0 --•-- - - --- -- - I-I

I..- I ,

l,,.I .

o 80 ..... -t. ......... 4- . ..-. . ...-

T 771TO

o

40

""1 . . .. 10 1. 2.. 0 - .0 3.. 4

YIELD IKILOTONS)

Figure 9.96. Altitudes of the stabilized cloud top and cloud bottom as a function of total

energy yield for surface or low air bursts.

for wind speeds ioss than 15 miles per 9.98 As the downwind distance for

hour. These relations hold reasonably a given unit-time reference dose-rate

well for simple whid structures, i "., for contour increases with increasing wind

winds with very little directional shear, ;peLd, the maximum width of that conand for effective wind speeds between tour will decrease somewhat. Con-

•tbout 8 and 45 miles per hour. As de- versely, a decrease in downwind dis-

,ined in § 9.84, effective winds with tance of a given contour with decreasing

speeds greater than 45 miies per hour wind speed will be accmpanied by an

are not common, and speeds less than 8 increase in maximum width .'• that conmiles per hour generally result from tour. For an increase in wind speed,

large changes in directional wind shear within the limits of the simple wind

with increasing altitude. The fallout structures and wind speeds for which :he

* patterns would then be too complex to ideali',ed contours apply, the changes in

be represented by idealized dose-rate maximum width of a given contour will

contours. be small., and wiad scaling may be igIlKI! 4-A
432 RESIDUAL NUCLEAR RADIATION AND FALLOUT

nored. This may also be done for the idealized unit-time reference dose rates

upwind Jistances and hence for the are in the range of 300 to 3,000 rads/hr.

ground-zero widths. An increase in the For a total yield of 10 MT, i.e., W =

wind speed will tend to decrease upwind 104 KT, and an effective wind of 30 mph

distances by causing the particles to drift (F = 1.25 'ron,. § 9.97), the following

toward grctnd zero as they fall. At the downwind distarnces are obtained from

lower 1-h(,vi reference dose rates, e.g., Table 9.93.

100 rads/hr or less, the upwind distances Dose rite 3,000 1,000 300 radsibr

will in fact decrease with increasing Distance 75 142 355 miles.

wind speed. However, the larger particles, which are mainly responsible for Interpolation indicates that the unit-time

the close-in high dose rates, descend refetunce dose rates are 1,800 rads/h. at

very quickly and the high dose-rate 100 miles, 620 rads/hr at 20W miles, and

contours will not be greatly affected by 360 rads/hr at 300 mniles. (The best

the wind speed. Consequently. since method of interpolation is to plot the

simple wind scaling is not possible and known points on logarithmic paper and

the upwind distances are relatively to read the desired values from a smooth

short, a conservative approach is to as- curve connecting the points.) The cor-

;iunie that wind speed has no effect on responding idealized reference dose

upwind distances (and ground-zero rates for 50 percent fission yield would

widt!-s). then be 900, 310, and 180 rads/hr at

FALLOUT EXAMPilE 100, 200, and 300 miles, respectively. Answer.

Given: A 10-megaton surface burst, From Fig. 2.16, the cloud radius for a

50-percent fission yield, with an effec- 10 MT explosion is about 21 miles; this

tive wind speed of 30 miles per hour. should t~e subtracted from the distances

Find: The idealized unit-time refer- from ground zero in order to determine

ence dose rate, the fallout arrival time, the fallout arnival (or entry) timles. For a

and the dose accumulated by an exposed 30-mph wind, these are (100-.21)/30 =

person during the first week following 2.6 hours at 100 miles, (200-21)/30 = 6

fallout arrival at points 109, 200, and hours at 200 miles, and (300-21)/30 =

300 miles directly downwind from 9.3 hours at 300 miles. Answer

ground zero. Within the accuracy of the idealized

Solution: Preliminary estimates, unit-time dose-rate contours, the entry

based on Table 9.93, indicate that the times for Fig. 9.26 may be rounded off

l~l .

im__
FALLOUT PREDICTIONS FOR ILAND SURFACE BURSTS 433

to 3, 6, and 10 hours, respectively. The specified downwind distance from

multiplying factors for an exposure I ground zt2,o for a given effective wind

week after arrival of the fallout are ,ben speed would then be smaller than prefound to be about 2.3 at 100 miles, 11.6 dicted. The crosswind values at certain

at 200 mi~es, and 1.4 at 300 mile.•. The disiances would, however, he inapproximate total ý,ccumulated doses at creased. in some cases of extreme shear

the required distances would then be as the pattern wit' rmtc~nd from g&ound zero

follows: in two or more directions. In these

cases, it is imp,;ssible to define a downwind direction, and idealized contours

100 900x 2.3 =2,070 are of little value in describing the shape

200 310xl1.6 = 496 of the pattern (cf. Fig. 9.77b),

J0 0 180x 19.100 1.4 = 252 In order to emphasize the

Answer limitations of the idealized fallout patterns, Figs. 9. 100a and b are presented

These doses would be reduced by the here. The former shows the idealized

appropriate surface roughness (or terrain unit-time reference dose-rate contours

shielding) factor (§ 9.95). for a 10-megaton, 50-percent fission

surface burst and an effective wind

LIMITATIONS OF IDEALIZED speed of 30 mdles per hour. In Fig. LCONTOURS 9.100b an attempt is made to indicate

what the actual situation might be like as

9.99 Both the idealized 15-mile per a result of variations in local meteorohour pattern dimensions and the wind logical and surface condition:.. Near

scaling procedure tend to maximize the grournd zero the wind is from the southdownwind extent of the dose-rate con- west but the mean wind gradually

tours siace they involve the postulate changes to a westerly and Ihen a norththat there is little widd shear. This is riot westerly diectiov over a distance of a

an unreasonable assumption for the few hundred miles. These changes in

continental United States, since the the mean wind are reflected in Fig.

wind shear is generally small at altitudes 9. 100b, but, since the idealized pattern

of interest from the standpoint of fall- is based on a single effective wind, the

out. If there is a greater v.,ind shear, changes in the mean wind do not affect

e.g., 200 or more between thie !op and Fig. 9. 100a. The total contamination of

bottom of the mushroom head, the fall- the area is about the same in both cases.

out pattern would be wider and ihorter but the details of the distribution, e.g.,

than that based on Table 9.93. Tile ac- the occurrence of hot spots, which are

tual unit-time reference dose rate at a shown shaded in Fig. 9. 1Ob, is quite
434 RESIDUAL NUCLUAR RAD)IATION AND) [At LOUT

30 RADS/HR

100

100 N'LFS

Figure 9, 10O0a. Idealized unit-time referenco dose-rate contours for a lO-t-egator.. 50-percent fission, surface burst (30 mph effective wind speed).

30C1

c ý30 RADj/HR

'0'S.

Figure 9. 1 W~b. Corresponding actual dcse-rate contours (hypothetical).4
FALIOUT PREDICTIONS FOR LAND SURFACE :5lJRSTS 435

different. The pattern in Fig. 9. 100b is percent of those predicted for a smooth

hypothetical and not based on actual su'rface. In a city, buildings, trees, etc.-

observations: its purpose is to call at- will reduce .he average intensity still

tention to the defects of the idealized further.

fallout pattern. But sinc• the factors 9.102 The rate ef decay of the early

causing deviations from th:ý ideal vary fallout• radioactivity, and hence the total

from place to place and eve,- from day dose accumulated over a period of time,

to day, it is impossible to kno v them in will be affected by weathering. Wind

advance. Consequently, the L,'st that may transfer the fallout from ,.e locacan be done here is to give an idcolized tion to another, thus causing local varipattern and show how it may be us .1 to ations. Rain, after the fallout has deprovide an overall picture of the c-ri- scended, may wash the particle.- into ihe

tamination while, at the same time, ii,. soil and this will tend to decrease the

dicating that in an actual situation there dose rate observed above the ground.

may be marked differeeces in the detai's The extent of the decrease will, of

of the distr;bution. ourse, depend on the climatic and surfaie conditions. In temperate regions in

FACTORS AFFECTING FALLOUT the absence of rain, the weathering efPATTERNS fect will probably be small during the

first n onth after the explosion, but over

9.101 It must be emphasized thai a perio'l of years the fallout dose rate

(he procedures described above for de- would -. crease to about half that which

veloping idealized fallout patterns are would otherwise be expected. intended only for overall planning. 9.103 in attempting to predict the

There are several factors which will af- time that must elapse, after a nuclear

fect the details of the distribution of the explosion, for the radiation dose rate to

early fallout and also the rale of de- decrease to a level that will permit recrease of the radioactivity. Near ground entry of a city or the resumption of

zero, activity induced by neutrons in tie agricultural operations, use may be

soil may be significant, apart fron tha' made of the; (continuous) decay curves

due to the fallout. However, the extent in Figs. 9.16a and b or of equivalent

of the induced activity is very variable data. It is inadvisable, however, to deand difficult to estimate (§ 9.49). The pend entirely on these estimates because

existence of unpredictable hot spots will of the uncertainties mentioned above.

also affect the local radiation intensity. Moreover, even if the decay curve could

Furthermoie, precipitation scavenging be relied upen completely, which is by

will have an important effect on the no means certain, the actual composifallout pattern (§ 9.67 et seq.). The data tion of the fallout is known to vary with

presented in the preceding paragraphs distance from ground zero (§ 9.08) and

are applicable to very smooth surfaces the decay rate will vary accordingly. At

of large size. As mentioned in § 9.95, 3 months after a nuclear explosion, the

even grour.d roughness in what would dose rate will have fallen to about 0.91

normally be considered flat countryside percent, i.e., one ten-thousandth part,

might reduce the dose rates to about 70 of its value at 1 hour, so that almost any
436 RESIDUAL NUCLEAR RADIATION AND FAI.I.OUI

contaminated area will be safe enough sible- one, for example, ascribes the

to enter for the purposes of taking a large radiation doses on the northeril

measurement wi:h a dose-rate meter, islands of Rongelap Atoll to a hot spot

provided there has been no additional and brings the 3,000-rad contour line in

contamination in the interim, much closer to Bikini Atoll. because of

the absence of observations frcvn large

THE HIGH-YIELD EXPLOSION OF areas of ocean, the choice of the fallout

MARCH I 1954 pattern, such as the one in Fig. 9. 105, is

largely a matter of guesswork. Never9.104 The foregoing discussion of theless, on, fact is certain: there was

the distribution of the early fallout may appreciable radioactive contamivation at

be supplemented by a description of the distances downwind of 300 miles or

observations made of the contaminaiion more from the explosion.

of the Marshall Islands area following 9.106 The doses to which the conthe high-yield test cxplosion (BRAVO) tours in Fig. 9.105 refer were calculated

at Bikini Atoll on March 1, 1954. The from instrument record-i. They represent

total yield of this explosion was ap- the maximum possible exposures that

proximately 15-megatorts TNT equiva- would be received only by individuals

lent. The device was detonated about 7 who remained in the open, with no profeet above the surface of a coral reel' and tection against the radiation, for the

the resulting fallout, consisting of ra- whole time. Any kind of shelter, e.g.,

dioactive particles ranging from about within a building, or evacuation of the

one-thousandth to one-fiftieth of an inch area would have reduced the dose rein diameter, contaminated an clongated ceived, On the other hand, persons rearea extending over 330 (statute) miles maining in the trea for a period longer

downwind and varying in width up to than 96 hours after the explosion would

over 60 miles, In addition, there was a have received larger doses of the residseverely contaminattd region upwind ual radiation.

extending some 20 miles from the point 9.107 A radiation dose of 700 rads

of detonation. A total area of over 7,000 over a period of 96 hours would probasquare miles was contaminated to such bly prove fatal in the great majority of

an extent that avoidance of death or cases. It would appear, therefore, that

radiation injury would have depended followirng tike test explosion of March 1,

upon evacuation of the area or taking 1954, there was sufficient radioactivity

protective measures. from the fallout in a downwind belt

9.105 The available 4ata, for the about 170 mi!es long and up to 35 miles

estimated total &.oses accumulated at wide to have seriously threatened the

various locations by 116 hours after the lives of nearly all persons who remained

BRAVO explosion, are shown by the in the area for at least 96 hours followpoints in Fig. 9.105. Through these ing the detonation withoit taking proroints there have been drawn a series of tective measures of any kind. At discontour lines which appear to be in tances of 300 miles or more downwind,

moderately good agement with the the number of deaths due to short-term

data. However, other patterns are pos- radiation effects would have been negli-

• , _
437

IC 0

0

U)C)

0-

0

0) _ 0

> 0

q in oo~ 

0 0 E

OD 0r ; > N(0 -

0

LAi C, ~ o0

LL N~ z 0, LL w 0w .

(~U)

W / 0

LOr

DL -j4-

00o

2~2 2

CDYK
438 RESIDUAL N'UCIEAR RADIATION AND FAIl.OUT

gible, although there would probably only 220 rads. Tne inhabitants of Ronhave been many cases of sickness re- gelap Atoll weit: in this area, and were

sultng in temporary incapacity, exposed to radiation dosages up to 175

9.108 The period of 96 hours after rads before they were evacuated some

the explosion, for which Fig. 9.105 44 hours after the fallout began

gives the accumulated radiation doses, (§§ 12.124, 12.156). The maximum

was chosen somewhat arbitrarily. It theoretical exposures in these two areas

should be understood, however, as has of the atoll for various time ntervals

been frequently stated earlier in this after the explosion, calculated from the

chapter, that tie radiations from the decay curves given earlier in this

fallout will continue to be emitted for a chapter, are recorded in Table 9.109.

long time, although at a gradually de- 9.110 It must be emphasized that

creasing rate. The persistence of the the calculated values in Table 9.109

external gamma radiation may be illus- iepresent the maximum doses at the

trated in connection with the BRAVO given locations, since they are based on

test by cor idering the situation at two the assumption that exposed persons redifferent locations in Rongeiap Atoll. main out-of-doors for 24 licurs each day

Fallout began about 4 to 6 hours after and that no measures are taken to rethe explosion and continued for several move radioactive contamination. Furhours at both places. 1hermore, no allowance is made for

9.109 The northwestern tip of the v, eathering or the possible dispersal of

atoll, 100 miles from the point of dto- the particles by winds. For example, the

nation, received 3,300 fads during the dose rates, measured on parts of the

first 96 hours after the fallout started. Marshall Islands on the 25th day folThis was the heavie3t fallo'it recorded at lowing the explosion were round to be

the same distance from the explosion about 40 percent of the expected values.

and may pessibly have represcrnted a hot Rains were known to have occurred

spot, as mentioned above. About 25 during the second week, and these were

miles south, and 115 miles from ground probably responsible for the major dezero, the dose over the same period was crease in the contamination.

Table 9.109

CALCULATED RADIATION DOSES AT TWO LOCATIONS IN RONGELAP ATOLL

FROM FALLOUT FOLLOWING THE MARCH 1, 1954 TEST AT BIKINI

Accumulated dose in thts period

(rads)

Inhabited Uninhabited

Exposure period after the explosion location location

First 96 hours ............................... 220 3,300

96 hours to I week 35 ;............................ 530

i week to I month .......... .................. 75 1,080

i knonth to I year. ................................... . 75 1 ,19

Toal to I year ....... ........................... 405 6,010

I year to infinity ..... .. .................... Ab ut About 115I

.- -, . - . ... ... .. . . . ,... . . . .. . . ".. w ' - •r- ... J .L I... ' " " '
ATh NI ' 'VION OF RESIDUAI. NIJ(I FAR RADIA [ION 439

9.111 In concluding this section, it high fission-yield weapon. The general

may be noted that the 96-hour dose direction in which the fallout will trove

contours shown in Fig. 9.105, repre- can be estimated fairly well if the wind

senting the fallout pattern 'n the vicinity pattern is known. But the total and fisof Bikini Atoll after the high-yield ex- sion yields of the explosion and the

plosion of March 1, 1954, as well as the height of burst, in the event of a nuclear

idealized unit-time reference dose-rate attack. are unpredictable. Consecont:ours from Table 9.93, can be re- quently, it is impossible to determine in

garded as more or-less typical, so that advance how far the seriously contamithey may be used for planning purposes. nated area will extend, although the

Nevertheless, it should be realized that time at which the fallout will commence

they cannot be taken as an absolute at any point could be calculated if the

guide. The particular situation which effective wind speed and direction were

developed in the Marshall Islands was known.

the result of a combination of circum- 9.113 In spite of the uncertainties

siances involving the energy yield of the concerning the exact fallout pattern,

explosion, the very low burst height there are highly important conclusions

(§ 9.104), the nature of the surface to be drawn from the results described

below the point of burst, the wind sys- above. One is that the residual iuclear

tern over a large area and to a great radiation from a surface burst can, under

height, and other meteorological cowixi- some conditions, represent a serious

tions. A change in any one of these hazard at great distances from the exfactors could have affected considerably plosion, well beyond the range of blast,

the details of the falout pattern, shock, thermal radiation, and the initi,,l

9.112 In other words, it should be nuclear radiation. Arather is that plans

understood that the fallout situation de- can be made to minimize the hazard, but

scribed above is one that can happen, such plans must be flexible, so that they

but is not necessarily one that will hap- can be adapted to the particular situation

pen, following the surface burst of a which develops after the attack.

ATTENUATION OF RESIDUAL NUCLEAR RADIATION

ALPHA AND BETA PARTICLES The range of an alpha particle depends

upon its initial energy, but even those

9.114 In their passage through mat- from plutonium, which have a moderater, alpha particles produce considerable tely high energy, have an average range

direct ionization and thereby rapidly of only just over I1/2 inches in air. In

lose their energy. After traveling a cer- more dense media, such as water or

tain distance, called the "range," an body tissue, the range is less, being

alpha particles ceases to exist as such.5 Obout one-thousandth part of the range

KAn alpha particle is identical with a nucleus of' the elemen: helium (§ 1.65). When it has lost most of

its (kinetic) energy, it captures two electrons and becomes a harmless (neutral) helium atom.
440 RESIDUAL NU( !.EAR RADIATION AND FAlI "•)LT

in air. Consequently, aipha particles etrate considerable distances through air

from radioactive sources cannot pene- and into the body. Shielding will be

trate even the outer layer of the unbro- req,,ired in most fallout situations to

ken skin (epidermis). It is seen, there- reduce the radiation dose to an accept.

fore, that as far as alpha particles arising able level. Incidentally, any method

from sources outside the body are con- used to decrease the gamma radiation

cerned. attenuat;on is no problem. will also result in a much greater atten9.115 Beta particles, like alpha uation of both alpha and beta particles.

particles, are able to cause direct ion- 9.118 The absorption (or attenuaization in their passage through matter. tion) by shielding materials of the reBut the beta particles dissipate their en- siducl gamma radiation from fission

ergy less rapidly and so have a greater products and from radioisotopes prorange in air atid in other materials. duced by neutron capture, e.g., in soMany of the beta particles emitted by dium, manganese, and in the weapon

the fission products traverse a total dis- residues, is based upon exactly the same

tance of 10 feet (or hiore) in the air principles zs were described in Chapter

before they are absorbed. Fowever, be- VIII in connection with the initial

cause the particles are continually de- gamma radiation. Except for the earliest

flected by electrons and nuclei of the stages of decay, however, the gamma

medium, they follow a tortuous path, rays from fallout hive much less enand so their effective (or net) range is ergy, on the average, than do those

somewhat less. emitted in the firs! minute after a nuclear

9.116 The range of a beta particle is explosion. This means that the residual

shorter In more dense media, and the gamma rays are more easily attenuatea;

average net distance a particle of given in other words, compared with the inienergy can travel in water, wood, or tial gamma radiation, a smaller thickbody tissue is roughly one-thousandth of ness of a given material will priuce the

that in air. Persons in the interior of a same degree of atteruation.

house would thus be protected from beta 9.119 Calculation of the attenuation

radiation arising from fission products of the gamma -adiation from fallout is

on the outside. It appears that even difierent and in some ways more cornmoderate clothing provides substantial plicated than for the initial ,adiations.

attenuation of beta radiation, the exact The latter come from the explosion

amount varying, for example, with the point, but the residual radiations arise

weight and number of layers. Only beta from fallout particles that are widely

radiation from material ingested or in di.stributed on the ground, on roofs,

contact with the body poses a hazard. trees, etc. The complication stems from

the fact that the effectiveness of a given

GAMMA RADIATION thickness of material is influenced by the

fallout distribution (or geometry) and 'I

9.117 The residual gamma radia- hence depends on the degree of contions present a different situation. These tamination and its location relative to

gamma rays, like those which form part the position where protection is desired.

of the initial nuclear radiation, can pen- Estimates of the attenuation of residual

,~I.

'.4
ATTENUATION OF RESIDUAL NUCLEAR RADIATION 441

radiation in varicus structures have been mobiles, buses, trucks, etc.. the transmade, based partly on calculaions and mission factor is about 0.5 to 0.7.

partly on in.asurements with simulated Rough eslimates can, thus be made of the

tallout. shielding from fallout radiation that

might be expected in various situations.

9.120 Some of the results ,f these Depending upon his location, a person

estimates are given in Table 9. 120 in in the open in a built-up city area would

terms of a dose-transrinssion factor receive from about 20 to 70 percent of

(§ 8.72). Ranges of values are given in the dose that would be delivered by the

view of the uncertainties in the estimateýs same quantity of fallout in the absence

themselves and the variations in the de- of the builaings. An individual standing

giee of shielding that may be obtained at against a building in the middle of a

different locatiornv within a structure. block would receive a ruch smaller

(Shielding data for the same structures dose than one standing at the interser;-

for initial ,tuclear radiation are given in tion of two streets. In contaminated agTable 8272.) All of the structures are ricultural areas, the gamma-ray dose

assumed to be isolated, so that possible above the surface can be reduced by

effects oi adjacent buildings have been turning over the soil so as to bury the

neglected. For vehicles, such as auto- fallout particles.

Table 9.120

FALLOUT GAMMA-RAY DOSE TRANSMISSION FACTORS FOR VARIOUS

STRUCTURES

Dose tralsmnission

Structure factor

Three feet underground 0.0002

Frame house 0,3-0.6

Ba,.enent 0.05-0, I

Multistory buiiding

(apartmeni type):

Upper sMories 0.(0)1

Lrwer stories 0. I

Concrete. blckhouse

shelter:

9-w. walls 0.007-0.09

12-.in. walls 0.OOt-0.03

24-in. walls 0.0001-0.002

Shelter, partly

above grade:

With 2 ft earth cover 0.005-0.02

With 3 ft earth cever 0.001-0.005

- J -..- ~ - - . ~ - - . -'- . r .~
442 RESIDUAL NUQLLEAR RADIATION ANI FALLOU'r

DELAYED FALL.,UT

INTRODUCTION they have ascended in the nuclear cloud.

The very fine particles, e.g., those with

9.121 There is, of course, no sharp radii of a few micrometers or lecs, fall

change at 24 hours after a nuclear ex- extremely slowly. Consequently, they

plosion when, according to the arbitrary may remain suspended in the atmosdefinition (§ 9.03), the early fallout phere for a considerable time and may

ends and the delayed fallout com- be, carried over great distances by the

mences. Nevertheless, there is an im- wind. Ultimately, however, the partiportant difference between the two types cles are bNought to the ground, primarily

of fallout. The principal early fallout by precipitation scavenging (§ 9.67 et

hazard is from exposure to gamma rays seq.), and the resulting delayed fallout

from sources outside the body, although will be spread over laige areas of the

there is also a possibility of some inter- earth's surface.

nal exposure (§ 9.16). A, secondary 9.123 Much (if not all) of the debris

hazard would arise from beta particles from low air and surface bursts with

emitted by fallout in contact with the yields less than about 100 kilotons does

skin. The delayed fallout, on the other not rise above 30,000 feet or so (Fig.

hand, is almost ex-lusively a potential 9.96) and it soon becomes accessible to

internal hazard that would be due to the removal by precipitation. Should this

ingestion of iodine, strontium, and re- occur within the first few weeks after the

sium isotopes pio-sent in food, especially explosion, as it often will, the fallout

milk. Bolh early and delayed fallout can will still contain appreciable amounts of

have long-term genetic effects, but they radioisotopes with fairly short halfare probably of less significance than lives, as well as those with long halfother expected consequences. These and lives. The main poiential hazard then

related biological aspects of fallout are arises from the ingestion of iodine- 131,

discussed in Chapter X1I. which has a half-life of 8 days; like all

9.122 Essentially all of the residues isotopes of iodine, when it enters the

from an air burst contribute to the de.- body this isotope tends to become con.

layed fallout, for ;n an explosion of this centrated in the thyroid gland (§ 12.169

type there is very little early (or local) et seq.). Iodine- 131 has been detected in

fallout. For land surface bursts, about rainfall and in milk from. cows which

40 percent of the radioactivity -A' !he have eaten contaminated forage at disweapons residues remains in the atrnn.s* tanccs several thousand miles from but

phere after the early fallout and for in the same hemisphere as the burst

water surfacc bursts the proportion has point. With increasing yield, a smaller

been estimated to be roughly 70 percent proportion of the weapon debris remaii:s

(§ 9.59). The time required for the in the atmosphere below 30,000 to

debris particles to descend to earth and 40,000 feet, from which it can be rethe distance they will have traveled moved fairly rapidly: but this may be

during this time depend on the size of sulfcient to produce significant deposithe particles and the altitude to which tion of iodiua 131 on the ground, espe-
DELAYED FALLOUT 443

cially if the total fission yield is large. nation nearly as much as that of the

9.124 For explosions of moderately early fallout. What is .uore important is

high and high yields, most of the radio- the manner in whicih the contaminated

active residues en;er the stratosphere particies enter the upper atmosphere. In

irom which removal occurs slowly. The order to undzrstand the situation, it is

small particles in the stratosphere are necessary to re-,iew some of the characeffectively held in storage for a few teristic features of the atmosphere.

months up to a few years, as will be

secn shortly (§ 9.135 et seq.). During STRUCTURE OF THE ATMOSPHERE

this time., the radioisotopes of short and

moderate half-life will have decayed al- 9.126 One of the most significent

most complely. Radioactive species aspects oi the atmosphere is the variaw ilh intermediate half-liv•'s, from about tion in temperature at different altitudes

a month to a year, have been detected on and its dependence on latitude and time.

the ground within a few months after a In ascending into the lower atmosphere

nucloar test series. But the major bio- from the surface of ihe earth, the temlogical hazard of the delayed fallout is perature of the air falls steadi~y, in gernfrom the long-lived isotopes strontium- eral, toward a minimum value. This

90 (half-life 27.7 years) and cesium-137 region of falling temperature is called

(half-life 30.0 years) which might ente4 the "troposphere" and its top, where

the body in food over a period of years, the temperature ceases t3 decrease, is

Strentium-90 can accumulate in thc: known as the "tropopause." Above the

bone from which it is removed slowly troposphere is the "stratosphere,"

by radioactive docay and by natural where the temperature remains more or

elimination processes; it can thus repre- less constant with increasing altitude in

sent a prolonged internil hai:ird the temperate and polar zones, Although

(§ 12.188 et seq.). Not .-aly do these all the atmosphere immediately over the

isotopes of strontium and cesium decay tropopause is commonly referred to a-&

slowly, they constitute relatively large the stratosphere, there are areas3 in

fractions of the fission p.,xlucts; thus, which the structure varies (Fig. 9.126).

for every 1,000 atows undergoing fis- it. the equatorial regions, the temperasion there are eventually formed from ture in the stratosphere increases with

30 to 40 atoms of strontium-90 and from height. This inversion also occurs at the

"50 to 60 of cesium- 137. Moreover, both higii-r altitudes in the temperate and

rf these isotopes have gaseous precur- polar regions. In the "riesosphere" the

sors (or ancestors), so that as a result of temperature fvlis off igain with increasfractionation (§ 9.08) their proportions ing height. At still higher altitudes is the

in the delayed tallout will tend to be "thermosphere" where t'ie temperature

greater, at least for surface bursts, than rises rapidly with height.

in the fission products as a whole. 9.127 Most of th,; visible phenom9.125 The ultimate distribution of ena associaied with weather occur in the

the delayed fallout over the earths sur- troposphere. The high moisture content,

face is not affected by the particular the relatively high temperature at the

viind conditions at the time of the deto- earth's 'wurface, and the convective
444 RESIDUAL NUCLEAR RADIATION AND FALL.OUT

+ 2500% -I

THERMOSPHERE.j

IONOSPHERE

250-4 MESOPAUSE ......... 75:.:C:................C.. .... . ............... .......

....... E..SPHER.......................

o150- STRATOPAUSE -+.....OC 0

100 STRA-TOSPHERE

(I) (INVERSION)

0. cc

STRATOS PHERE ' z

(LJSO TH-ERMA L 1 .. .0 * *..,

-55 C ,...*,-

K., JT~EAL~ STRATOSPHERE .

.7 ISOTHEML

x~ PO

C, 25- TROPOSPHERE opo P4 S

aPOLAR FROWiS

+1%+300C -0 C

90 60 30 0 3 60 90

N S

DEGREES LATITUDE

Figure 9.126.. &tr~.cturc of the atmosphere during July and August.

movemnent (or instability) of the air 9.126). In thest: regions. the average

arising from temperature differences rainfall is high.

prornotf the formation of clouds and 9.128 The tropopause, that is the

.ainfall. In the tempeike latitudes, at top of the troposphere, is lower in the

about 45' in the summuer and 300 in the polar and temperate zones than in thc

winter, where the cold polar air mecýts tropics; Ats height in the former regions

the warm air of the tropics, there are varies from 25,000 to 45,000 feet, deformed meandering, wavelike bands of pending on latitude, *ime of ycar, and

storm fronts called "polar fronts" kiFg. particular conditions of the day. In gent
DELAYED FALLOUT 445

eral, the altitude is lowcst in the polar erable convective mixing of the air to

regions. The tropop . may disappear great heights.

entirely at times i oolar winter

night. In the tropt•, e tropopause ATMOSPHERIC PATHS OF DELAYED

usually occurs near . ")00 feet at all FALLOUT: TROPOSPHERIC

seasons. It is more sharply defined than FALLOUT

in the temperate and polar regions be- 9.130 The fallout pattern of the

cause in the tropics the temperature in- very small particles in the radioactive

creases with height above the tropo- cloud which remain suspended in the

pause instead of remaining constant. atmosphere depends upon whether they

Therc is a marked gap or discontinuity were initially stabilized in the troposin the tropopause in each temperate phere or in the stratosphere. The diszone, as may be seen in Fig. 9.126, that tribution of the radioactive material beconstitutes a region of unusual turbu- tween the troposphere and the

.lence. Each gap moves north and south stratosphere is determined by many facseasonally, following the sun, and is tors, including the total energy yield of

usually located near a polar front. It is the explosion, the height o0 burst, the

believed that considerable interchange environment of the detonation, and the

of air betwecn the stratosphere and tro- height of the tropopause. Additional

posphere takes place at the gaps. A jet complications arise fronm scavenging by

stream, forming a river of air moving dirt and precipitation and from fractionwith high speed and circulating about ation in sorface bursts. Scavenging will

the earth, is located at the tropical edge tend to d,&Lrease the proportion of raof the polar tropopause in each hemi- dioactive debris remaining in the cloud

sphere. while increasing that in the early fallout,

whereas fractionation will result in a

9.129 Because of its temperature relative increase in the amounts of

structure, there is very little convective strontium-90 and cesium-137 that remoiion in the stratosphe-e, and the air is main suspended. Consequently, it is not

exceptionally stable. This is especially yet possible to predict the quantitative

noticeable in the tropics where the ver- distribution between troposphere and

tical movement of the radioactive cloud stratosi ere, athough certain quaitafrom a nuclear explosion has sometimes tive ce ',isions can be dr',wn.

been less than 2 miles in three trips 9.U In general, a larger proporaround the globe, i.e., approximately tion of tue weapon debris will go into

70,000 miles. This stability cunfinues the stratosphere in an air burst than in a

up to the mesosphere were marked tur- surface burst under the same conditions;

bulence is again noted. The polar for one thing, there is essentially no

stratosphere is less stable than that in the local or early fallout in the former case

tropics, particularly during the polar and, lor another, surface material taken

winter night when the stratospheric up into the cloud tends to depress .he

temperature structure changes to such at. height attained in the latter case. In the

extent that the inversion may disappear. temperate and polar regions, more of the

When this occurs there may be consid- radioactive debris enters the strato-
446 RESIDUAL NUCI.EAR RADIATION AND FALLOUT

sphere from an air burst than for an about 30 days. During the course of *ts

equivalent burst in the tropics. The rea- residence in the atmosphere, the !ropo.ison is (hat the tropopause is lower and pheric debris is carried around the earth,

the stratosphere is less stable in the by generally westerly winds, in perhaps

nontropic regions. For low-yield expio- a month's time. The bulk of the fallout

sions, most of the radioactive material on the average is then confined to a

remains in the troposphere, with little relatively narrow belt that spread& to a

entering tlH,- stratosphere. But since the width of about 300 of latitude.

altitude to which the cloud rises in- 9.134 Since uniform winds and

creases with the explosion energy yield, rainfall are not very probable, the trothe proportion of debris passing into the pospheric fallout patterns, like those of

stratosphere wilt increase correspond- the early fallout, will vary and probably

ingly. will be quite irregular, In view of the

9.132 The small particles remaining .;trong dependence of tropospheric fallin the troposphere descend to earth out distribution on the weather, and in

gradually over a period of time up to particular on precipitation, it is not

several months; this constitutes the practical to provide an idealized repre-

"tropospheric fallout." The most im- sentation of the possible distribution.

portant mechanism for causing this fallout appears to be the scavenging effect STRATOSPHERIC FALLOUT

of rain and snow. The fine particles may

be incorporated into the water droplets 9.135 The radioactive debris that

(or snow crystals) as they are formed enters the stratosphere descends much

and are thus brought down in the pre- more slowly than does the tropospheric

cipitation. Except for unusually dry or fallout. This is mainly due to the fact

wet regions, the amount of delayed that vertical motions in the stratosphere

fallout deposited in adjacent areas is are slow, as stated above, and little

closely related to the amount of precipi- moisture is available to scavenge the

tation in those areas during the fallout particle". It appears that almost the only

period. Dry fallout has been recorded, way for the removal of the radioactivity

but it probably represents a minor pro- from the stratosphere is for the air

portion of the tropospheric fallout in masses carrying the particles to move

most instances, first into the troposphcre, where the

9.133 The rate of removal of mate- particles can be brought down by prerial from the troposphere at any time is cipitation. There are at least three ways

roughly proportional to the amount still in which this transfer of air from the

present at that time; consequently, '.he stratosphere to the troposphere can

"half-residence time" concept is use- occur, they are (1) direct downward

ful. It is defined as the period of time movement across the tropopause, (2)

required at a given location for the re- upward movement of the tropopause or

moval of half the suspended material. If its reformation at a higher altitude, and

the cloud particles originally reached the (3) turbulent, large-scale meandering

upper part of the troposphere, the half- horizontal circulation through the troresidence time for tropospheric fallout is popause gaps. The relative importance

I9
DELAYED FALLOUT 447

of these mechanisms depends upon the: season in each hemisphere after a delay

altitude, latitude, and time of year at of about one year from the time of

which the injection into the stratosphere injection. If the injection occurs in the

takes place. The first method may be stratosphere below 70,000 feet, the

important during the arctic winter and major influx of debris into the troposthe second in the lowei' polar strato- phere will begin during the first winter

sphere in the early spring. The third or spring season following the injection.

mechanism is particularly applicable to At this lower aititude in the stratomaterial in the lower stratosphere near sphere, transfer between the hemithe gaps. Very little debris crosses the spheres takes place at a much slower

tropopause in equatorial regions. rate. Most of the radioactive debris

9.136 The rielatively complicated tends initially to become a narrow band

structure of the stratosphere and the girdling the globe more or less at the

varied modes by which contaminated latitude of injection, since the winds in

particles may leave it, make it impossi- the stratosphere below 70,000 feet are

ble to assign a single half-residence time predominantly unidirectional, i.e., eifor all stratospheric debris However, ther easterly or westerly, depending on

semiempirical models have been devel- the place and the time. The band soon

oped t,-' -" ,ermit the calculation of stra- spreads out as a result of diffusion and in

tosphei erntories, concentrations in the winter and spring there is a poleward

air neat ,ne surface, and deposition of and downward transfer of the debris.

debris injected into the stratosphere, 9.138 In the lower stratosphere,

mesosphere, or higher levels. The below 70,000 feet, the half-residence

model used here has successfully pre- time for transfer between hemispheres is

dicted the fallout from several specific roughly 60 months, whereas the halfinjections of radioisotopes from atmos- residence time for transfer to the tropheric nuclear tests conducted since posphere is about 10 months. Since the

1961. It also predicted the fate of the half-residence time in the troposphere is

substantial amount of plutonium-238 only a month (§ 9. i33), it is apparent

released in the burnup of the SNAP-9A that weapon residues entering the lower

generator in a satellite launch-vehicle stratosphere in a particular hemisphere

failure in 1964. will tend to fall out in that hemisphere.

9.137 The model divides the strato- Most nuclear tests have been conducted

sphere of eaAh of earth's (north and in the Northern Hemisphere and most of

south) hemispheres into two compart- the debtis injected into the stratosphere

ments: the region above 70,000 feet and did not reach altitudes aboe 70,000

that below 70,000 feet. For an injection feet. Consequently, the amount of deof radioactive debris at an initial altitude layed fallout on the ground in this

above 70,000 feet, rapid transfer be- hemisphere is considerably greater than

tween the hemispheres is assumed to in the Southern Hemisphere. On the

take place, based on what is known of other hand, in the upper stratosphere,

air circulation in the tinper atmosphere. above 70,000 feet, the Iransfer between

The debris will g,,,gin to arrive below hemis'iheres is much more rapid than in

70,000 feet during the winter or spring th~e lower region and entry into the tro-

.4!
448 RESIDiAL NUCLEAR RADIATION AND !-*ALLOUT

posphere is delayed, Hence, in the few unit called the "curie." It is defined as

injections that have o-curred above the activity (or quantity) of any radio70,000 feet there has been a wore even active substance undergoing 3.7 x I,()"

distribution of the fallout between the disintegrations per second. (This partichemispheres. ular rate was chosen because it is close

9.139 Regardless of where it is in- to the rate of disintegratio, of I gram of

jected, the major poition of the stratos- radium.) Where large amounts of active

pheric fallout will reach the earth in the material are involved, the '"negacurie"

temperate latitudes. This is mainly due unit is employed; this is equal to I

to high-rainfall regions near the polar million curies and corresponds to disinfronts (§ 9.127). Since the half-resi- tegralions at the rate of 3.7 x 1016 per

dence time in the troposphere is so second. A megacurie 6f strontium-90 is

short, air coming down through the tro- that quantity of this isotope which emits

popause gap or on its poleward side and 3.7 x 10", beta particles per second."

moving toward the equator will be de- 9.142 Since 1954, a number of

pleted of its contaminated particles by sampling networks have been estab- scavenging before it can reach the trop- lished in various parts of the world to

ics. Consequently, stratospheric fallout determine the amounts of radioactive

in the equatorial zone is low in spite of contamination in tropospheric and strathe heavy rainfall, tospheric air and in rainwater and soil,

arising from weapcns tests. The results

DELAYED FALLOUT FROM NUCLEAR obtained have shed a great deal of light

WEAPONS TESTS on the possible mechanisms of the de- layed fallout. The information so ob9.140 For making estimates of de- tained, coup!ed with biological studies

layed fallout, it is the general practice to to determine the concentrations of cerdetermine the amount of strontium-90, tain radioisotopes in the diet and in

for several reasons. It i'0as a long half- human beings and animals, has permitlife compared with the residence time in ted an evaluation to be made of the

the stratosphere, so that it does not possible worldwide hazard (see Chapter

decay to any great extent prior to its XII).

deposition on the earth; it is produced in 9.143 TVe plots in Figs. 9.143a and

relatively large quantities in fission, and b show the variations ove, a period of

it is fairly easy to identify and measure years of the megacuries of strontium-90

by standard radiochemical techniques, present in the total stratospheric invenFurthermore, the concentration of tory, i.e., the activity still remaining in

strontium-90 is of special interest be- the stratosphere at various times, and

cause it provides a measure of the haz- the ground inventory, i.e., the activity

ard from delayed fallout, deposited con the ground. The extensive

9.141 The activity of strontium-90, atmospheric nuclear tesi programs conas of radioactive materials in general, is ducted by the U.S. and the U.S.S.R.

conveniently expressed in terms of a during 1961 and 1962 are reflected by

YOne megaton of fission yield produces about 0. II megacurie of F'rontium-90.

II
DEI. %YED FALLOUT 449

7- j 44 4# -7 1 1 1 -7-77

I i

-- * I * . 4 * 4

w4 -I0 L I

*' t, I ' '

" ! I , ;*I i 

1951 .955 1960 196. 1970 1974

YEAR

Figure 9.143a. Stratospheric burden (or inventory) of stronlium-90.

4~I. I . ',

10

- I

,., ji - i

S a1 6

I,.- z.-. .

o -- I I

1953 1955 1960 1965 L 197l 1974

YEAR

Figure 9.143b. Surface burden (or inventory) of strontium-90.

* .. ,'
4.50 RESIDUAL NUCLEAR RADIATION AND FALLOUT

the large peak in the stratospheric in- atmospheric testing were discontinued.

ventory (Fig. 9.143a) which reached a the surface inventory should decrease

maximum toward the end of 1962. The steadily.

sharp increase in the ground inventory 9.145 Alter strontium-90, the next

(Fig. 9.143b), which began in 1962 and most important radioisotope from the

continued through 1965, reflects the de- biological standpoint in the worldwide

posi ion of the strontium-90 during fallout is cesium-137. Fission products

those year,,. contain, after a short time, roughly 1.5

9.144 The maximum amounts of times as many cesium-137 atoms as

strontium-90 on the earth's surface will strontium-90 atoms (§ 9.124). Since

be attained when the rate of natural there is essentially no fractionation relradioactive decay just begins to exceed ative to one another of these two isothe rate at which the isotope reaches the topes and they have half-lives which are

ground in delayed fallout. The atmos- not very different, the activity of cepneric tests conducted by France and sium-137 on the ground can be deterChina during the late 1960's and carly mined, to a good approximation, by

1970's have not caused a significant multiplying the values for strontium-90,

increase in. the surface inventory, and if e.g., Fig. 9.143b, by 1.5.

TECHNICAL ASPECTS OF RESIDUAL NUCLEAR RADIATIONM°

RATE OF DECAY OF FALLOUT with the nature of the weapon, but the

ACTIVITY values plotted in Figs. 9.16a and b are

reasonable averages for situations in

9.146 The continuous curves in which the "a!lout ..ctivity arises mainly

Figs. 9.16a and b, which represent the from fission products. It is seen that the

decrease in dose rate due to gamma decrease in the dose rate with time canradiation from radioactive fallout, have not be representea ny a simple equation

been obtained by summing the contri- which is valid at all times, but it can be

butions of the wore than 300 isotopcs in approximated by the dashed straight

the fission products and of the activity lines labeled "t-', for times between

induced by neutrona in the weapons 30 minutes to about 5,000 hours (200

materials for various times after fisdion. days) after the explosion, to within 25

The effects of fractionation, resulting percent. For times longer than 200 days,

from the partial loss of gaseous krypton the fallout decays more rapidly than

and xenon (and their daughter elements) indicated by the t-1. 2 line, so that the

and from other circumstances, have also continuo, curve may be used to estibeen taken into account (§ 9.08). The mate dose rates from fallout at these

dose rates calculated in this manaer vary times.

1oThe remaining sections of this chapter may be omitted without loss of continikity.

ii

" •I
TECHNICAl. ASPECTS OF RESIDUAL NUCLEAR RADIATION 451

9.147 During the interval in which so that a logarithmic plot of RIR,

' he approximation is applicable, the against t should give a straight line with

decay of fallout activity at a given loca- a slope of - 1.2. When t = 1, i.e., I

tion may be represented by the simple hour after the explosion, R, = R. or

expression R,/R, = I; this is the basic reference

R ==Rt2, (9.147 1) point through which the straight line of

R, Rslope -1.2 is drawn in Figs. 9.16a and

where R, is the gamma radiation dose b.

rate at time t after the explosion and R, 9.150 The total accumulated dose

is the dose rate at unit time; this is the received from a given quannity of fallout

unit-time reference dose rate whichl nas can he dctermined fiom Fig. v.20 using

beeii used earlier, e.g., in Figs. 9.16a the method described in § 9.21. The

and b, and Figs. 9.20 and 9.25. The curve in Fig. 9.20 was obtained by nuactual value of R, will depend on ,he merical integration over time of the acunits in which the time is expressed, tual dose-rate (continuous) curve in

e.g., minutes, hours, days, etc. In this Figs. 9.16a and b. However, for times

chapter, time is generally expressed in between 0.5 hour (30 minutes) and

hours, so that the unit time for the ref- 5,000 hours (200 days) after the exploerence dose rate R, is 1 hour."I sion, an approximate analytical expres9.148 It should be clearly under- sion for the dose received during a given

stood that equation (9.147.1) is appli- time interval can be obtained by direct

cable provided there is no change in the iategration of equation (9.147.1); thus if

quantity of fallout during the time inter- D is the total dose accumulated between

val under consideration. It cannot be the times t,, and t

h, then

used, therefore, at kuch times that the

fallout is still descending, but only after D R R' t-. 2 dt

it is essentially complete at the particular location. If fallout material is removed in any way, e.g., by weathering = 5R1 (t-0.2- t-0.2).

or by washing away during the time t, or

if additional material is brought to the (9150.1)

given point by wind or by another nu- Hence if the unit-time reference dose

clear detonation, equation (9.147. 1) rate R, is known or is determined, e.g.,

could not be employed to determine tht- from Fig. 9.25 and tVe measured dose

rate of decay of the fallout activity, rate at any known time after the explo9.149 By rearranging equation sion, the total (or accumulated) dose for

(9.147.1) and taking logarithms, it foi- any required period can be calculated,

lows that provided the fallout activity decays in

accordance with the t-1. 2 relationship

log - 1.2 log t, (9.149.1) during this period. R

"Physically the unit-time reference dose rate is the dose rate that would be received from the given

(constant) amount of fallout at unit time, e.g., I hour after the explosion, although this quantity might

41 actually be ;n transit at that time and would not have ieached the location under consideration.

4t
452 RESIDUAL NUCLEAR RADIATION AND FALLOUT

9.151 Measurements made on ac- R,. This can be obtained from equation

tual fallout from weapons tests indicate (q. 149. 1), if the dose rate, R,, is meathat, although the t 1 2 decay represents sured at any time, t, after the explosion,

a reasonable average, there have been e.g., at the time of entry. The results

instances where exponents in the range can be cxpre.;sed graphically as in Figs.

of -0.9 to -2.0, rather than -1.2, are 9.26 and 9.27.

required to represent the rate of decay. 9.153 In principle, equation

in fact, different exponents are some- (9.150. 1) could be usý,d to estmate the

times needed for different times after the total accumulated dose received from

same explosion. These anomalies ap- fallout in a contaminated area, provided

parently arise from the particular cir- the whole of the fallout arrives in a very

cumstances of the explosion and are short time. Actually, the contaminated

very difficult to predict, except possibly particles may descend for several hours,

when a large quantity of neutron-in- and without knowing the rate at which

duced activity is known to have been the fallout particles reach the ground, it

produced. Furthermore, fallout from is not possible to make a useful calculatwo or more explusions occurring at tion. When the fallout has ceased, howdifferent times will completely change ever, equations (9.149.1) and (9 150.1)

the observed decay rate. In general, too, may be employed to make rough estiover a long period of time after the mates, of accumulated radiation doses

burst, weathering will teno to alter the over moderate periods of time, up to

dose rates in an unpredictable ma.~Aer. about 200 days after the explosion, proConse'uently, in an actual situation vided one mea;urement of the dose rate

following a nuclear detonation, esti- is available.

mates based on either the t- 1.2 dec..v rule

or even on the continuous curves in RADIATION DOSE RATES OVER

Figs. 9.16a and t must be used with CONTAMINATED SURFACES

caution and should be verified by actual

measurements as frequently as possible. 9.154 It was seen in § 9.141 that

9.152 Within the limits of applica- the curie and megacurie are useful units

bility of the t-12 decay relationship, for expressing the activity of radioactive

equation (9.150.1) can be used to es- material, and they will now be emtimate the time which an individu9l can ployed in connection with the contamistay in a location contaminated by fis- nation of areas. Because, as far as the

sion products withoui accumuia-ting external radiation dose is concerned, the

more than a specified dose of tadiation. gamma rays are more significant bioloIn this case, the accumulated dose is gically than the beta particles, the early

specified; i,, is the known time of entry fallout attivity may be stated in

into the contaminated area and th is the gamma-megacuries, as a measure of the

required time at (or before) which the rate of emission of gamma-ray photons,

exposed individual must leave. In order where I gamma-megacurie represents

to solve this problem with the aid of the production of 3.7> 1016 photons per

equation (9.150.1), it is necessary to second.

know the unit-time reference dose rate 9.155 If an area is uniformly con-
TECHNICAL ASPECTS OF RESIDUAL NUCLEAR RADIATION 453

taminated with any radioactive material altitude of the aircraft. if the dose rate

of known activity (in gamma-mega- near, i.e., 3 feet above, the ground is

curies) at a given time, it is possible to known, then the value at any specified

calculate the gamma-radiation dose rate altitude can be obtained upon dividing

at various heights above the s,.rface, by the attentuation factor for that altiprovided the average energy of the tude. On the other hand, if the dose rate

gamma-ray pholons is known. The re- is measured at a known altitude, mulsuits of such caiculations, assuming a tiplication by the attenuation factor

contamination density of I gamma- gives the dose rate at about 3 feet above

megacurie per square mile, for gamma tho ground at that tirile.

rays having vrious energies, are repre- 9.158 A Dossible use of the curve in

sented in Fig. 9. '55. if the actual con- Fig. 9.157 is to determine the dose rate

tamination density differs from I mega- near the ground and contamination dencurie per square mile, the ordinates in sity from data obtair.ed by means of an

the figuwe would be multiplied in pro- aerial survey. For example, suppose a

portion. radiation measuring instrument sus9.156 The calculations upon which pended from an aircraft at a height of

Fig. 9. 155 is based take into account the 1,000 feet showed a radiation dose of

effects of bui!dup in air (§ 8.103). Fur- 0.24 rad/hr and that, from the known

thermore, it is assumed that the surface time after the explosion, the average

over which the contamination is distrib- energy'of the gamma-ray photons was

uted is perfectly smooth and infinite in estimated to be 0.8 MeV. The attenuaextent. For actual terrain, which is mo- tion factor for an altitude of 1,000 feet is

derateiy rough and may have a variety approximaieiy 27 and so the dose rate at

-A radiation shielding, the dose rate at a 3 feet above ground at the time of the

specific height above the ground would observation is roughly

be less than for an infinite, smooth 0.24 x 27 = 6.5 rads/hr. It is seen

plane. The actual reduction factor will, from Fig. 9.155 that for a contamination

of course, depend on the terrain featurcs density of I megacurie per square mile

and the extent of the contaminated area. and a photon energy of 0.8 MeV, the

A terrain shielding factor of 0.7 is com- dose rate 3 feet above the ground would

monly applied to the dose rates ebtained be about 5.9 rads/hr. Hence, in the

from Fig. 9.155 to obtain approximate present case, the (.ontamination density

average values for a moderately rough -of the ground is approximately

terrain (§ 9.95). 6.5/5.9 = 1. 1 gamma-megacurie per

9.157 The dose rate at greater square mile.

heignts above the ground, such as might 9.159 The gamma-ray activity from

be observed irt an aircraft, can be es- the fission products will vary depending

timated with the aid of Fig. 9.157. The upon the nature of the fissionable matecuive gives approximate values of the rial; however. 4t has been calculated that

attenuation factor for early fallout radi- a reasonable average would be about

ation as a function of altitude. It applies 530 gamma-megacuries per kiloton fisin particular to a uniformly contami- ,Aon yield at I hour after the explosion.

nated area that is large compared to the The average photon energy also depends
454 RESIDUAL, NUCLEAR RADIATION AND FAII.OUT

10

I0 662I 43

4 1 

6

4 0 721 45

HEIGHT ABOVE PLANE (FEET)

Figure 9. 155. Dose rates above an ideal plane from gamma rays of various energies for a

contamination density of I gamma-megacurie per square mile.

on the fissionable material, but at 1 hour 9.160 If all of the radioactivity in

after the explosion an average energy of the weapon debris were deposited uniabcut 0.7 MeV is a reasonable approx- formly over a smooth surface of area I

imation. Thus, if all the (unfractionated) square mile, the 1 hour dose rate above

fission products from 1-kiloton fission this area would thus be about 2,900

yield were spread uniformly over a rads/hr per kiloton of fission yield. If the

smooth plane I square mile in area, the same residues were .pread uniformly

radiation dos( received at a point 3 feet over a smooth SArface of A square miles

above the plane can be estimated from in area, the !-hour dose rate would be

Fig. 9.155 as 5.3 X 530 i.e., approxi- 2,900/A rads/hr; consequently, the

mately 2,800 rads/hr. Activity induced product of the I-hour dose rate and the

by neutron capture in the weapon mate- area in square miles would be equal to

rials may add about 100 rads/hr to this 2,900 in units of (rads/hr) (miles) 2

/kt

figure, making a total of 2,900 rads/hr a-t fission. If all the residues from I-kiloton

I hour after the er.plosion.12 fission yield were deposited on a smooth

i2The best values reported in the technical literature range from roLghly 2.700 to 3,100 rads/hr fur

different fissionable materials and neutron energy spectra. The dose rate given here is considered to be a

good avervge.
TECHNICAL ASPECTS OF RESIDUAL NUCLEAR RADIATION 455

104

7

7 _7

7= - _/__......... ---.. ]__ -....- _--. -

C.)

IL- 2

z

0

Z 7 Uj 1&

I2 - _ _....- --....... . . .I ........ 2/

I0

4 --------- .---.

-7

I L , il .. L ..

"0 800 !,600 2,40Q 3,200 4:000 4,800

HEIGHT ABOVE GROUND (FEET)

Figure 9.157. Altitude attenuation factor for early fallout radiation dose rate relative to the

dose rate 3 feet above the grounrd.

w?..
456 RESIDUAL NUCLEAR RADMATION AND FALLOUT

surface in varying concentrations typical shielding factor is taken to be 0.7

of an early fallout pattern, instead of (§ 9.156), the I-hour dose rate area inuniformly, the product of the dose rate tegral that would be measured over an

at I ijour and the area would be replaced ideal smooth plane, with no shielding,

by the "area integral" of the l-hcur would be 1,300/0.7, i.e,, approximately

dose rate defined by 1,900 (rads/hr) (miles)2 /kt fission.

9.162 The ratio of 1,900 rads/hr to

Area Integral R ICRdA, the theoretical 2,900 (rads/hr) A (miles)2/kt fission indicates that about 6(0

JA percent of the total gamma-ray activity

where R, is the I-hour dose rate over an of the weapon residues is deposited in

element of area dA and A square miles the early fallout from a land surface

is the total area covered by the residues. burst (§ 9.59). This value must bc recHence, tegardless of the concentration ognized as an estimate because the data

pattern, the area integral of the I-hour upon which it is based are both limited

dose rate over a smooth surface would and variable. For example, it depends to

always be 2,900 (rads/hr) (miles)2/kt some extent on the nature of the surface

fission, assuming that the fallout had materiil. Furthermore, as the hurst

been completely deposited at that time. height increases, the fraction of the

9.161 Measurements after several weapon debris deposited as local fallout

nuclear tests have given a wide range of will decrea:se until the fireball no longer

values, but a reasonable average is intersects the earth's surface.

about 1 000 (rads/hr) (miles)2/kt fission.

These measurements were made with RATE OF PARTICLE FALL,

radiation monitoring instruments at

various times after the explosions. This 9.163 The time at which particles of

value differs from the 2,900 (rads/hr) a given size and density will arrive at the

(miles) 2/kt fission given above for two ground from specified heights in the

main reasons: first, only part of the nuclear cloud may be calculaied from

radioactivity of the weapon residues ap.- aerodynamic equations of motion. The

pears in the early fallout, and second, effects of vertical air motions are genercorrections must be applied to the raea- ally ignored since they cannot be presured value for instrument response and ditted. especially as they are believed to

terrain shielding. Typical ionization-, be generally small for particles which

chamber monitoring instrumentis that fall within 24 hours. However, field test

were used in the surveys, calibrated in data sometimes indicate times of arrival

the usual manner, will read about 25 which are quite different from those

percent too low as a result of a nonlinear predicted by the theoretical calculations;

response to gamma rays of various en- hence, it is probable that vertical wind 4

ergies, directional response, and shield- components and oither factors may

ing provided by the operator. This cor- sometimes significantly influence the

rection increases the "obser"ed" area partirle fall. One such factor is precipiintegral from 1,000 to about 1,300 tation (§ 9.67 et seq.), but this will be

(rads/hr) (miles) 2/kt fission. If the terrain disregarded here.

I4O
TI'ECHNICAL. ASPE.CTS OF RESIDUAL. NUCLEAR RADIATION 457

9.164 Some typical results of time extreme, particles less than 20 tLm in

of fall calculations are shown in Fig, radius carry 12 percent of the activity.

9.164. The curves give the times re- This distribution of activity is known as

quired for particles of different sizes to "log-normal" because it obeys tiwý norfall to earth from various initial alti- mal (Gaussian) distriblu.ior, law witt" the

tudes. The density of the fallout material logarithm of the particle radius as the

is taken to he 2.5 g/cm3⁄4. which is variable. It may not be strictly valid in

iughly that of dry sand, the falling any giver, case, since the activity disparticles are assumed to be spherical. tribution var-es with the type of burst.

their radii being given :n micrometers the nature of the terrain at ground zc.ro,

(ýml). Actual fallout particles are some- etc. Nevertheless. it is characteristic of

times quite irregula,' and angular in the activity distributions assumed for the

shape, although a large percentage tend theoretical analysis of fallout.

to be fairly smooth and globular since 9.166 The method for est;imating

they result from the solidification of the arrival lime of t.he fallout at a

fused spherical droplets of earth and of downwind location was dcscribe6 in

weapon debris (see Figs. 9.50a thrugh § 9.91. Suppose that the time of arrival

d). Even if the particles are irregular, is 20 hours at a downwind distance of

they can be assigned an effective radius 300 miles from the explosion. If the

and then treated as spheres for calcu!at- nuclear cloud stabilizes at 60,000 feet,

ing times of fall. !hen it follows from Fig. 9.164 that, at

this time, all particles with radii !ess

9.165 The percentages given in Fig. than about 30 IL will still be present, and

9.164 represent estimates of the propor- lhat they carry Toughly 28 percent of the

tions of the total activity deposited by total activity deposited in the early fallparticles with sizes lying between pairs out. It is evident that, in spite of the

of lines. Thus, particles with radii larger decay which will have occurred in tranthan 200 pLrm carzy 1 percent of the sit, fallout of appreciable activity may

activity; those between 150 and 260 Rim be expected 300 miles downwind at

carry 3 percent, and so on; at the other about 20 hours after the detonation.

i7

J $
458

CN

0-C

00

0

rr

___-j N Z

EE

00

II- I0

N 0 N

(133 ~O ONV~lOH) ~OlhI.1V 1II.

ge

Uily 0;
rECP.NICAL ASPECTS OF RESIDUAL NUCLEAR RADIATIJN 459

BIBLIOGRAPHY

BUNNEY, L. R., and D. SAM. "Gamma-Ray Coordin'ators. "Precipitation Scavenging

Spectra of Fractionated Fission Products,- (1970)," AEC Symposium Series No. 22, U.S.

Naval Ordnance Laboratory. June 197! , Atomiic Enerf~ Commission. December 1970.

NOLTR 71-103. Fuituv, H. W., et al., "Final Report on Project

BURsoN. Z. G., "Fallout Radiation Protection Stardlust. V--.umcs I through III,- Isotopes. A

Provided by Transportation Vchicles," EG & Teledyne f'ompany, 'Westwood. New Jersey.

G, Inc., Las Vegks. Nevada. October 1972, October 1967, DASA 2166-1 through, 2166-3.

EGG -I 18 3-1560. FtIRhE~ti, G. J., "Distribution of Radioactivity

C7ýAWFORD, T. V.. "Pccip,..ation Scavenging with Height in Nuc!ear Clouds."~ Proceedings

and 2BPUFF.'' University of California, of the Second Conferer-ce sponsored by the

Lawrence Livermore Laboratory, December Fallout Studies Branch, U.S. Atomic Energy

1971, UOPKA 71-14. Commission. Nov.ember 1965.

CROCKER, G. R., "Fi%.ioin Product Decay FRF.WiNo, E. C.. and N. E. BAt LOU, "Nmure of

Chains: Schematics with Branching Fractions, Nuclea.- Debris in Sea Water,'' Natiure, 195.

Half-Lives, and Literature References,- U.S. 1283 (1962).

Naval Radiological De~cense Laboratory, June KNOX, J, B.. T. V. CRAVVFORD), and W. K.

1967, USNRDI.-TR-67-l 11. CRANDAll, "Poteritial E-posures fram LowCROCKER, G. R., and T. TURNER, "Calculated Yield Free Air Bursts.'' Uriiver-sity ;f4 CaliforActivities, Exposure Rates, and Gam-ia Spec- mia, Lawrence Livermot,ý Laborrlory. Detra for Unfractionated Fission Prvilucts." U.S. cember 1971i. IJICRL-51164

Naval Radiolog-ýPý4i rDeferise' Laboratory. De- *KREY. P. W., and B. KoRAEwS.W. "HASI.

cember 1965, 'JSNRDL-TR-itV)9. Mvdel (if Atmospheric Trantsport,' HWalth and

CROCKER, G. R.. and M. A. CGNNORS. Safety Laboratory, U.S. Atomic Er~erg'! Com-

"Gamnia-Emissi'rn Data for the Calculation of mis~ion. New York. N.Y., Septemnber 1969.

Fxposure Rates fromt Nuclear Debris. Volumne HASL-2 15.

1. Fission P~roduct%," U.S. Naval Radiological KitiFY, P. W.. and B. KRAJFWS114. "COMp~arison

Delfanse La boratory. June 1965, USNRDL- of Atinospberic Transport Mndel Calculations

TR-876. with Observations ot Radioactive Debris.'" J

CROCKER, (J. R, i. D). O'CoNwcR, and E. C. GeophYs. R~es-. 75. 2901 Wl'.70),

Fm#EIl ING, "Physical and Radiochemical *KREY, P. W., M. SCII~ONHPI;, and L.. TOON-

?roperties and Fallout Pa. ,icles," U.S. Naval KEL., "Updating Stratospheric inventories to

Radiological Defense Laboratory, June 1965. April 1974." Fallout Program Quarterly SumIJSNRDL-TR-899. -nary Report. Health and Safety Laboratory.

"Dcr'artment of Defens-e Land Falloolt Prmdiction I I.S. Energy Research and Development AdSystem," Defewtc~ Atomic Support Agen'q, 'inistration, New York, N.Y., July 1975.

Washington.,.. U.S. Army Nuclear De- H.\SL-294.

tense laboratory-, U.S. Naval Radiological De- LEE. H. P. W. WoNG. and S. L. BitoWN,-

fcnse Labarattq: Technicai' Operations Re- "SEER II: A New Damage Assessment Fallout

search, B~urlington. Massachusetts., 1966, Mocel." Stanford Rcsiarch Institute, Menlo

DASA 1800-1 throuigh l1(OO-VlIL Park, Californiz. 'May 1972, DNA 3009F.

DOLAN. P. J., "Gamma Spectra of U.-aniunt-23i MARTIN, J. R., and J. J. KORAND)A. "The ImFisaion Produjcts at Various Times After F~s. orts.'ý of Tritium in the Cisil Defense Consion," krmed Forces Speeial Weapons Proj.-ct, texj,"- Uni'6crsity of California, Lawrence LiWashington, D.C., March 1959, AFSWP 524. v~rmore Laboratory, March 1971

DokLAN, P. J.. "C3lculation of Abundances and UCRL-73085.

Activilies o1 the Preclucts of, High-Energy Neu- National Academy of Sciences, Advisory Corn

tron Fitssion of Uranium-238," Deiensc Atomic mittee on Civil Defense, Subcommittee on

Support Agency. Washington. D.C., May Fallout. 'Responsc Io DCPA Questions on

1959, DASA 525. F.allout," Defense Civil Preparedness Agency,

Doi.AN, P. J., "Gamma Spectra of Uranium-238 Researca, Report No. 19, May 1973.

Fission Products at Various Times After Fis- PET.ERSOI'4 "An Empirical Model for Estimating

sion, 'Defense Atomic Support Agency, W.,,rd-Wide Deposition from Atmospheric NuWashington, D.C., May 1959, DASA 526. clear Detonations." Health Phyvsics, 18. 357

*ENGLEMANN. R. J., and W, G. N. StIANN. (1970).
460 RESIDUAL NUCLEAR RADIATION AND FALLOUT

*S.INN, W. G. N , "Aerosol Particle Size De- Safety Laboratory, U.S. Atomic Energy Compendenc- of the Rainout Rate," Battelle Pacific mission, New York, N.Y.. April 1973,

Northwest Laboratories, AEC Research and HASL-273 Appendix.

Development Report, June 1971, BNWL-1551 Vot.cHoK H. L., "Strontium-90 Deposition in

Vol. I1, Part 1. New York City." Science, 156, 1487 (1967).

STEWART, G. L., and R. K. FARNSWORTH. *VoI-cHoK, H. L., "Worldwide Deposition of

"Uniied States Rainout and Hydrologic Impli- -0Sr Through 1974," Fallout Program Quarterly

cation," Water kesources Research, 4. 273 Slimmary Report, Health and Safety Labora-

(1968). tory, U.S. Enrgy Research and Development

*"Sr-.90 and Sr-89 in Monthly Deposition at Administration, New York, N.Y., October

World Land Sites," Fallout Program Quaiterly 1975. HASL-297.

Summary Report, Appendix A, Health and

*Thase publications may Se purchased from the National Technical Information Service, Department of

Commerce, Springfield, Virginia 22161.

•' ,
CHAPTER X

RADIO AND RADAR EFFECTS

INTRODUCTION

RADIO BLACKOUT discussion of the disturbances produced

10.01 The transmission of electro- by nuclear bursts at various altitudes.

magnetic waves with wavelengths of I Consideration will then be given to the

millimeter or more, which are used for effects of these disturbances on the

radio communications and for radar, is propagation of electromagnetic waves in

often dependent upon the electrical different frequency ranges. Apart from

properties, i.e., the ionization (§ 8.17), the effects that can be ascribed directly

of the atmosphere. The radiations from to changes in ion.zation, radio com. the fireball of nuclear explosion and munications and radar signals can 6L

from the radioactive debris can produce degraded in other ways, e.g., by nclse,

marked changes in the atmospheric ton- distortion, changes in direction, etc.

ization. The explosion can, therefore, These disturbances, which cannot be

disturb the propagation of the electro- treated in a quantitative manner, w'ill be

magnetic waves mentioned above, discussed briefly.

Apart from the energy yield of the explosion, the effects are dependent on the ELECTROMAGNETIC PULSE

altitudes of the burst and of the debris

and on th wavelength (or frequency) of 10.03 Another consequc~ice o. a

the electromagnetic w'.ý,es. In certain nuclear explosion that may ,-ause ,emcircumstances, e.g., short-wave (high- porary interference with rad,.) ane radar

frequency) communic', ions after the signds is an electrical (or .lectro-nagexplosion of a nuclear weapon at an neti-:) pulse of short dur,,,ion emitted

altitude above about 40 miles, the elec- froin the region of the bu,'t. The mosil

tromagnetic signals may be completely ser ous potential effects of this pulsc are

disrupted, i.e., "blacked out," for sev- dainage to electrical anid electronic

eral hours. equipmen', rather ihzn t,, the propaga,

10.02 In this chapter, the normal ii(,n of electromagnetic ivaves. Hence,

ionization of the atmosphere will be th! electremagnetic pub,, will be condescribed and this will be followed by a sicered separately in Cli~pter XI.

461
462 RADIO AND RADAR EFFECTS

ATMOSPHERIC IONiZATION PHENOMENA

EFFECT OF IONIZATION ON or ions) in the air, they will reradiate

ELECTROMAGNETIC WAVES electromagnetic energy of the same fre10.04 Ionization, that is, the for- quency, but with a slight time delay.

mation of ion pairs consisting of sepa- Thus, the energy is restored to the wave

rated electrons and positive ions, can be without loss, but with a change in phase

produced, either directly or indirectly, (§ 10.82 et seq.). If, however, the air

by the gamma rays and neutrons of the density is appreciable, e.g., more than

prompt nucJl'.ar radiation, by the beta about one ten-thousandth (10 4) of the

particles Faid gamma rays of the rcsidual sea-level value, as it is below about 40

nuclea: radiation, by the X rays and the miles altitude, collisions of electrons

ultraviolet light present in the primary with neutral particles will take place at a

thermal radiation, and by positive ions significant rate. Even above 40 miles.

in the weapon debris. Hence, after a collisions between electrons and i"'ns

nuclear explosion, the density of elec- are significant if the electron density is

trons in the atmosphere in the vicinity is abnormally high. In such collisions,

greatly increased. These electrons can most of the excess (coherent) energy of

affect electromagnetic (radio and radar) the electron is transformed into kinetic

signals in at least two ways. First, under energy of random motion and cannot be

s.uitable conditions, they can remove reradiated. The result is that energy is

energy from the wave and thus attenuate absorbed from the wave and the electhe signal; second, a wave front travel- tromagnetic signal is attenuated.

ing from one region into -another in 10.06 Other conditions being the

which the electron density is different same, maore energy is absorbed from an

will be refracted, i.e., its direction of electromagnetic wave by an ionized gas

propagation will be changed. It is evi- as the wavelength of the signal is indent, therefore, that the ionized regions creased, i.e., as its frequency decreases.

of the atmosphere created by a nuclear This may be regarded as being due to

explosion can influence the behavior of the longer time interval, as the frecommunications or radar signals whose quency is decreased, between success•-

transmission paths encounter these re- ivw alternations (or reversals) of the

gions. oscillating electromagnetic field

10.05 When an electromagnetic (§ 1.73). When the accelerating influwave' interacts with free electrons, enct, ,f tb,, wave is applied for a longer

some of the energy of the wave is time, a given electron will attain a

transferred to the electrons as energy of higher vibrational velocity during each

vibration. If the electrons do not lose cycle of the wave, and will dissipate a

this energy as the result of collisions greater amount o' energy upon colliwith other particles (atoms, molecules, sion.

,As used in tnis chapter, the term "electromagnetic wave" refer,; to radiations of wavelength of I

mi!limeter or more, such as are used in radio and radar, and not to the enti,,e spectrum described in § 1.74

et seq.

4
ATMOSPHERIC IONIZATION PHENOMENA 463

10.07 Posidve and negative ions ally oe refracted back toward the earth

can also absorb energy from an elec- (Fig. 10.08). Th's process is commonly

tromagnetic wave. Because of their referred to as "reflection," although it

larger mass, however, the ions attain is not the same as true reflection, in

much lower velocities than electrons which there would be no penetration of

and so they are less effective in absorb- the ionized layer of air. True (or speing energy. Thus, the effects of ions cular) reflection, as from a mirror, does

may ordinarily be neglected. However, occur to some extent especially with

for some situations in the denser (low- electromagnetic waves of the iowest

altitude) portion of the atmosphere, iidio frequencies.

where ions can persist for an appreciable

time, or for frequencies low enough for IONIZATON IN THE NORMAL

the ions to nave time to acquire signifi- ATMOSPAFRE

cant velocity be-ore reversal of the

elect.'omagnetic field, the effect of ions 10.09 In order to understand the efmay be important. fects of iree electrons on radio and radar

10.08 A radio or radar wave travel- systems, it is necessary to review briefly

ing upward from the ground begins to be the ionization in the normal, undisbent (refracted) when an increase of turbed atmosphere. Below an altitude of

electron density is encountered. In- about 30 miles, there is little ionization,

creased electron density causes the wave but above this level there is a region

path to bend away from the region of called the "ionosphere," in which the

higher electron density toward the re- density of free electrons (and ions) is

gion of lower density (§ 10.85). As the appreciable (see Fig. 9.126). The ionelectromagnetic wave penetrates farther osphere consists of three, more-or-less

into a regior where the electron density distinct, layers, called the D-, E-., and

increases toward a peak value, more and F-rc.:6ions. Multipie layers, which

more bending occurs. For certain com- sometimes occur in the E- and Fbinations of the angle of incidence regions, may be disregarded for the

(angle between propagation direction

and the vertical), the electron density, 350 "

and the frequency, the wave may actu- 300 I

;; 250

W/

IONiZED F-REGION -

T MRECRI ON

t•[C1O DDATYY', CRNSC s

1.50 -NICHT

100~

0-R EGION IO

50

o' ý-REG1 4 1 0 1

TRANSMITTER RECEIVER

Figure 10.08. Rcflectio,, of a radio (or

radar) wave by successive Figure 10.09. Typical electron densities in

refractions in an ionized D-, E-, and F-regions of the

region of the atmosphere. ionosphere.

4
464 RADIO AND RADAR EFFECTS

oiesent purpose. Typical variations of of their effect in the F-region. In some

electron density with altitade and with latitudes, the maximum electron density

time of day are illustrated in Fig. 10.09. in the ionosphere during a magnetic

The approximate altitudes of the three storm nuly decrease to some 6 to ,0

main regions of the ionosphere are given percent of its normal value.

in Table 10.09. 10.12 Apart from these major

changes in electron density, the causes

Tabie 10•69 of which are known, there are other

variations that are not well understood.

APPROXIMATE ALTITUDES OF Sometimes an irregular and rapidly

REGIONS IN 'TE IONOSPHERE varying increase in the electron density

Approximate Altitude is observed in the E-region. Apparently

Region (miles) one or more layers of high electron

dens,•>:j are formed and they extend oer

D 30-55 distances of several hundred miles. This

E 55..95 is referred to as the "sporadic-E" pheF Above 95 nomenon. A sominwhat similar effect,

calied "spread-F," in which there are

10.10 Although the D-, E-, and F- rapid changes of electron density in

regions always exist in the daytime and space and tCme, occurs in the F-region.

the E- and F-regions at night, the details The areas affected by spread-F are gerof the dependence of the electron den- erally much smaller than those assosity on altitude, especially in the F- ciated with sporadic-E.

region, vary with the season, with the

geographic latitude, with the solar (son- CHARACTERISTICS OF THE

spot) activity, and with other factr.rs. IONOSPHERE

The curves in Fig. 10.09 are applicable

to summer, at middle latitudes, around 10.13 The composition of the atthe time of mnaximurri sunspot activity. mosphere, esperially at the higher altiThe effects of the variable factors men- tudes, varies with the time of day and

tioned above are farly well known, so with the degree of solar activity; howthat the corresponding changes in the ever, a general description that is applieectron density-altitude curve can be cable to daytime conditions and mean

predicted reasonably accuraiely, sunspot activity is sufficient for the

10.11 in addition to these system- present purpose. Near the earth's sur..

atic variations in the electron density, face, the principal constituents of the

'here are temporary changes arising atmosphere are molecular nitrogen (N,)

from special circumstances, such as and molecular oxygen (02). These diasolar flares and magnetic storms. Solar tomic gases continue to be the dominant * 2

flares can cause a ten-fold increase in the ones up to an altitude of approximately

electron density in the D-region, but that 75 miles. At about 55 miles, ultraviolet

in the F-region generally increases by no radiation from the sun begins to disso

more than a factor of two. Magnetic ciate the oxygen molecules into two

storms, on the other hand, produce most atoms of oxyger. (0). The extent of

-0
ATMIOSPHE'RIC IONIZATION P~HENOMENA 465

dissociation increases with aZtitude. so tudes. whe-re molecular nitrogeni and

that above 120 miles or so, oxygen oxygen are !he main components of the

atoms are the dominant species in the atmosphere.

low-pressure atmosphere. This con'li- 10.16 At altitudes below about 30

tion persists up to an altitude of somec mi!C5, i.e. , below the D-regiOn, VA.

6(0) miles. Ozone (0~) and nitric oxide the air is relatively dense, file pre/babil-

(NO) are formed in the lower atmnos- ity of' interaction between rrce electirons

phere by the action of solar radiations or'. and neutral melecuies is large.. The few

the oxygen and nitrogen. Although the electrons that are produced by shootamounts of' ozone and nitric oxide ,ire wavelcngth solar radiation that penequite sin!l, they are iniportant b.ecause trates so low Into the atrnosphn'rý are

each absorbs radiation and enters into thus rapidly removed by attachment.

chemical reactions in a characteristic The density of freeý elect~rons mn the ;1'-

manner. mosphere below abciat 30 ni~les Is con10.14. The electroni (and positive sequcaity -.o srr-2ll that it caa be negions) in the normal ionosphere are pro- !-"led.

duced vtbe inteinactioris of solar radia- .10 '7 In the altilude rwligc from

tions of short waveiengt1P with the roughly 30 to 55 wiles (D-regici; of the

*various iiiolecuiar and atom-ic -pecics iork; sphere), the density of neutaral parpresent in the atmesphert., In llhe D- tidles i% relatively low, between about

* cgkon, !he ions tire almostI exclusively 10 1arid 10 5 of th- sea-level density

NO, , a! I the.ie ic.is vrc also the most Becauseý uf this low 'icnsitv, the wl.- ei

importart in the E-rcgioik-: in the latter ititachm2!ul 'is not iarge -and e.)eurons

region, howeve., thetc. are. in addition. remain free for severaii minutes. The

abo.' as2ryO jn-tr o averag-: lifetiime varies w.-th iocation and

Atomi~c oxyqeo ium,,. (,)+, begin to ap- the time of the year. but it is long

pear hin ile upper parts of the 7_-:egion, enough for the radiation from the sun to

and their proportion ircreases witii alti- ~maintain a pea;k density between about

tltde. 1r the F-tegion. the proportion of 102 a.rnd 10', elections per cubic centiNO' and 0,; ions decreases, whereas, meter (electrons!crný) in the daytime. At

tht'.t of 04 increases steadily. Above an nivŽht, whb'.i electrot~s a-e no longer

altitude of ab~out 120 niilrs. (lip to 60O being generateýd by sola.' radiations, th,ý

mi~es), 01 ions are domina.:-t. ýFre-e electrons in the D-tegion disappear.

10. 15ý The actuw'i electroni deasity at A10houigh thee density of Yneutral particles

in,.- altitude deienmJs on the r.~e of for- is smiall enough to peimit the electrons

mn~ticn of electroas as a result of ion- Oýn tie daytime) to have an appreciable

izi:iof ard their rate of removal, Zither average life, it is nevertheless suffiby tecombinatior. with po-,tive ions oý riently larg.- .Or collisions to cause conby attachrivrnt to nieutral particles (mol- sidorabie attenuafion of electromagnietic

tcule" or atomis). Rerombination tends waves in the manner described in

to be thae more im.portanit removal pro~c- W.~0O5.

;SS at -)igh aititudes (low atmosrpreri-. 10.18 In the E-region of :h-% ionospircssurc), whe:Zs attach-,nent to neilral ph.-M (55 to 95 miles altitude), the air

*particles p!_edominates at lower. alti- density is quite low, about 10-1 to 10 8
466 RADIO AND RADAR EFFECTS

of the sea-level value, and the average small, despite the high electron density.

lifetinme of electrons is even longer than because of the very low electron-neuin the D-region. The daytime electron tral collision frequency; however, redensity is about 10 to 105 elec- flection effects (§ 10.08) make the retrons/crnl, but most of the ionization, as gion important.

in the D-region, disappears at night. 10.20 Normally, the low electron

However, because of the very low den- densities in the D-region are sufficient to

sity of neutral particles, the frequency of reflect back to earth only those electrocollisions between them and electrons is magnetic waves with frequencies below

so small that there is relatively little about I million hertz, j.e.. I megahertz

attenuation of electromagnetic signals in (§ 1.74), provided the angle of incithe E-region. If sporadic-E conditions dence is small. At larger angles, the

exist, radio signals are reflected limiting frequency for reflection by the

(§ 10.08) in an erratic manner. normal D-region is increasingly less

10.19 The F-region extends upward than I megahertz. 'Waves of higher frefrom an altitudc of about 95 miles. Here quency pass through the D-region, with

the neutral-particle density is so low that ,;ome refraction (bending) and aitenuafree electrons have extremely long life- tion, and penetrate into the E-region or

times. At about 190 miles, the peak into the F-region if the frequencies are

electron density in the daytime is ap- high enough. Reflection may then occur

proximatelv 10" electrons/cm', decreas- in the E- or F-regicm, where the electron

ing to about 10.1 electrons/cmn at night. densities are higher than in the DDuring the day there are various layers region. For a given angle of incidence,

of ionization in the F-region. which tend the electron density required for reflecto merge and lose their identity at night. tion ;ncreases with the frequency of the

The aititude of peak ionization may also electroinagnetic wave. The smaller the

shift at night. Other factors causing angle of incidence, i.e., the more nearly

changes in the F-region were referred to vertical the direction of propagation, the

earlier (§ 10.12). Attenuation of elec- higher the frequency that will be retromagnetic signals in ihe F-,egion is flected by a given electron density.

IONIZATION PR9DUCED BY NUCLEAR EXPLOSIONS

INT.RO(DUCTION ations from a low-altitude nuclear exL0.21 UP to three-fourths of the plosion arc much jiaore intense within a

energy yield of a nuclear explosion may limited volume of space, i.e., in and

be expended• in ionizing the atmosphere. near the fireball, than the changes proThe resuilting changes are characteristic ductd naturally, e.g., by solar flares.

of the given weapon and of the burst and N,•.ciear explosions at high altitudes may

debris altitudes. The ionization effects z.(fect a considerable portion of the ton•-

caused by the imciear and thermal tad'- osphere in ways somewhat similar to

i'
IONIZATION PRODUCED BY NUCLEAP EXPLOSIONS 467

changes in solar activity: however, the around the fireball is ionized in varying

mechanisms and details of the interac- degrees by the initial thermal and nutions with the atmosphere are quite dif- clear radiaticns and by the delayed

ferent. Because of the complexities of gamma rays and beta particles from the

these interactions, descriptions of "typ- radioactive debris. The chemistry of the

ical" changes to be expected from a atmosphere may be modified signifinuclear explosion are often not applica- cantly, thus making predictions of elecble or even very meaningful. A caretui tron persistence difficult (and greatly

analysis of each situation, with the con.. complicating the problem of analyzing

ditions stated fairly explicitly, is usually mJiltiple-burst situations). For near-surnecessary. face explosions, the density of the air

10.22 Atmospheric ionization and prevents radiation from escaping very

disturbances to the propagation of elec- far from the fireball, and the ionization

tromagnetic signals caused by a nuclear is both localized and short-lived due to

explosion can be described in terms of very rapid attachment of free electrons

four spatial regions: (1) tl'e hot fireball, to neutral particles. As the detonation

(2) the atmosphere surrounding the fire- altitude is increased the radiation can

ball, (3) thu D-region, and (4) the high- ,scape to greater distances, and the

altitude region which includes the nor- electron density will reach values at

mal E- and F-regions of the ionosphere. which electromagnetic signal propaga10,23 Fireballs from explosions at tion can be afected.

low altitude are relatively smll 1,.25 When prompt or delayed ra-

(roughly, a I-megaton explosion at sea diation from tle explosion can reach the

level pnoduces a fireball of about 0.6 D-region, the electron density of that

mile diameter at I second). The air region is enhanced. Most of the wideinside the fireball is at a temperature of spread and persistent absorption of

many thousands of degrees. Electron electromagnetic waves then takes place

density and collision frequency are ia and near the D-region of the normal

high, and the absorption of electromag- ionosphere. For e'cctromagrtetic waves

netic waves is so large that the fireball is in the radio and radar frequency ranges,

considered to be opaque. At intermedi- circumstances are such that the maxiate bur.t altitudes (up to about 50 or 60 mum attenuation usually occurs within a

miles•. the early fireball is larger in size, layer I0 miles deep centered at an altibut it is still defined as it hot, ionized tude of about 40 miles (§ 10.128).

mass of oir which ýs Gpaqne to radio aad Hence, most of the subsequent discusradar signals for many seconds With sion pertaining t- D-region ionization

increasing altitude the characteristics of will be in terms of the free electron

the region of energy absorption change. density at an altitude of 40 miles.

At burst altitudes above about 190 10.26 In the E- and F-regions of the

miles, the atmosphere is very thin and ionosphere, the frequency of electronthe ecrgy from the nuclear explosion neutral particle collisions is low, and

can spread over very large distances. refractior. rather than absorption is gen10.24 When the burst point is erally the predominant effect. When the

below th, D-region, the atmosphere burst or debris altitude is high enough

4i
468 RADIO AND RADAR EFFECTS

for prompt or delayed radiation to reach with decreasing altitude, interct',ons of

the E- and F-regions, the electron den- the atoms anO molecules with the radiasity of those regions may be increaseJ. tion take pla,-. at rapidly increasing

On the o:her hand, nuclear explosions rates and energy is removed from the

sometimes cause a decrease of electron radiation.

dcnsity in the E- and F-regions, largely 10.29 The concept of -stopping aldue to traveling hydrodynamic and hy- titude" provides a useful approximate

dromagnetic disturbances 2 and to niodel for treating the interaction of

changes in air chemistry (§ 10.71 et ionizing radiation and the atmosphere ii,

seq.). which the density changes with altitude.

10.27 Increased ionization in the The stopping altitude for a given type of

D-region may occur not only in the radiation is the level in the atmosphere

vicinity of the nuclear explosion, but to which that radiation coming from

al,;o at its magnetic conjugate in the above will penetrate before losing so

earth's opposite herisphere (§ 2.143). much of its energy that it produces little

Charged particles, especially beta par- further ionization. The radiation is then

ticles (ele,-trons). resulting from the ex- said to have been "stopped." Most of

plosion will spiral along the earth's the energy will actually be deposited

magnetic field lines. Upon reaching thte within a few miles of the stopping alticonjugate region, the beta particles will tude. Only a small proportion of the

cause ionization similar to that produced energy is absorbed at the higher altinear the burst point. tudes where the air has a lower density

and is relatively transparent to the radiENERGY DEPOSITION ation, and little energy remains to be

given up at lower altitudes. Different

10.28 A detailed analysis of energy types of radiation deposit their energy in

deposition, the starting point for exa- the atmosphere in different way:. and

mining the effects of nuclear explosions thus have different stopping altitudes.

on the propagation of radio and radar Table 10.29 shows approximate stopsignals, is very complicated. The fun- ping altitudes for various ionizing outdamental principles, however, are well puts from a typical nuclear exploe-ion.

known and relatively simple. Consider The altitude quoted for debris ions refers

ionizing radiation entering the earth's to ionization that results from the ranatmosphere from a nuclear explosion at Joun (thermal) motion of these ions. The

high altitude or, as it normally does, debris mass can, however, be carried to

from the sun. As it travels downward, greater heights by the rising fireball and

the radiation at first encounters air of cause ionization by the emission of desuch low density that very few interac- layed radiations.

tions occur with atmospheric -toms and 10.36 For detonations btlow 15

molecules. Hence, very little ionization miles altitude, 'he minimum siopping

is produced. As the air density increases altitude in Table !0.29, the air is cssen-

:A hydrodynamic disturbance of the 'itmosphere is a direct result of the shock wave. The air is ionh'ed

and so its motion is affected by the earth's magnetic field. The combination of hydrodynamic ant,

magnetic effects leads to h,,.yromagnetic (or magnetohydrodoiyrnmic) disturbances.
IONIZATION PRODUCED BY NUCLEAR EXPLOSIONS 469

Table 10.29

APPROXIMATE STOPPINC ALTITUDES FOR PRINCIPAL WEAPON OIUTPUTS

CAUSING, IfNIZATION

Stopping Altitude

Weapon O-zput (miles)

Prompt radiation

X rays 35 it, 55

Neutrons and gamma rays Is

Iebr;s ions 7()

Delayed radiation

Gamma rays 15

Beta particles ,5

tially opaque to all ionizing radiatic.ns. are more laborious. F-or a disturbed at..

The radiation wlll penetrate only a fairly mosphere, calculations of the penetrashort distance into the atmosphere be- tion distance are difficult and not very

fore most of its energy is absorbed in reliable.

causing ionization (or is transformed

into other kinds of energy). As the alt- LOCATION OF RESULTANT

tudc of !he explosion increases to 15 IONIZATION

miles and above, the radiation can

escape to increasingly greater distances. 10.32 The region of maximum enOnce the stopping altitude for a given ergy depositioa is ¶he location where

ionizing radiation is reached, the at- ion-pair production is the greatest, but it

mosphere above the burst is relatively is not always the !ocation of the maxtraisparent to that radiation, which can imum densily of free elections. At altithen travel upward and outward to great tudes below about 30 miles, i.e., at

distances. relatively high air densities. removal

10.31 Below the stopping altitude, processes are so rapid thiat the average

in a region of uniform density, the no- lifetime of a free electrotn is a fraction of

minal penetratior distance of ionizing a second. An extremely high ion-pair

radiation of a particular kind and energy production rate is then required to susis inversely proportional to the air den- tain even a few free electrons per cubic

si:y (The penetration distance is often centimeter. But in the D-region (starting

expressed in terms of the mean free at about 30 miles altituJe) removal

path, as described in § 2.113.) For a processes are not so rapid and higher

particular radiation of a single energy electron densities are possible. For the

traveling thr.ugt% an undisturbed region delayed gamma rays, for 'example. the

of constant density, the penetration dis- stopping altitude, i.e., the region of

tance (or mean free path) can be cal- maximum energy deposition and ionculeted relatively easily. For a radiation pair production rate, is 15 miles- ho,-

spectrum covering a range of energies ever, the resultant electron density tends

and for complex paths along which the to t maximum at a higher altitude in the

air densi(/ changes, the ,omputations D-,•-gior.
470 R A D10 A NtD R ADA R :.* F CV~S

10.33 To understand the ionization beta radiation from the radJioactive

resulting foio nuclear explosions, it is debris wiffhin the fireball may sustain the

helpful to examine four detonation alti- iow-'ation level fo-. ipt o3 or 4 m1-inutes.

tude reogmes separately, they are: (i) Thus. the fireball region will be suffibelow 10 miles, (2) between 10 and 40 ciently ionize.'d to absorb elctrornagnemiles, (3) between 40 and 65 miles. and tio signals for a period of -tt least 10

(4) above 05 miles. Different mecha- seconds and possible for as long as 3 oi

nisnis associated with various burst 4 ininutes:, however, the spatial extent

heights will be considered. but it should of the ionization will t'e small.

be understood that these altitude re- 10.35 Trhe firebail will be spherical

gimres are somewhat arbitrary and are in shape initially. After a few seconds,

chosen for convenience in bringing out as the hot fireball rises upward

the change- in be:havior that occur wilth buoyantly (§ 2.120), it will take the

burst height. Actually, there are tio lines form of a torus. Thc torus, having lost

of demarcation beiweecn the variojis al- its 11minous qualities, wil! coalesce: into

titude ranges. ihe ch'inges are conltiu- a flattened cloud snape. The transition

ous. and one typc of rinechaiiismr gradu- from a fireball or torus to a debris cloud

ally supers,,de:; anoiacr and becomes is% indefinite, but at late enough' timesdomina~a. The four spalial regions after a few minutes-the fireball as such

where therc may be si.-nific-rit ceflccs will ceak~e to exist, and only k deaud of

(§ 10. 22) also shift in importancp as the radiuactive debris wiil remain. This

altitudes of the detonation ai.d cf t-he cloud will reach a fic~af stabilization alradoacivederischa-e titude in about 5 minutes. It 'vill then be

spread by wbatever winds prevail at that

DETONATIONS BELOW 10 MILES altitude range. Typically, the average

ALTITUDF. spieading velocity is about 35 feei per

secoW i.

10.34 For nucieqr eplo.;i~ms at at- 10.36 The atmospinere surrounding

titudes below 10 mniiev (ani ,;orrewhai th,: fireball will he ionized by prompt

higher), most of the energy iz. depo.;ited nvutrons and by prompt gamma radiain the atmospherý: in the iin.r~ediate vi- tion, but the frce electrons thus formed

cinity of the detonation, -esulting in the will Ixrsikt less than a second. The a-ir

formation of the firebll and the air blast will alko be- ionized by the delayed rawa-e, as 'Jescribec; in Chapter II. The diation emitted cont-nuously fromn the

electron density within the in, radioactive debris within the fireball.

tially at least equa! ýo &~e partcle den- Close to the fir--ball, the continuous

sity (about lION/cin1). v. ill remain above --mission from the adjacent gamma-ray

about 108 electrons/cm' ior times tip t,- 3 sourre will result in a hig~h electron

anid 4 minutes, depending on the aature der~sity in spite of~ the- fairly !apid remoof the weapon. For about 10 suconds the val of elIectrons by attachment of air

firebcLl temperature will be high enough particles at the low altitudes under coný'above 2,5000 Kelvin) 'to cause signifi- sideration. Thus, for detonations below

cant ionization of the air by the thermai 10 miles, there will be a region surradiation (§ 10.04). After tbis period. rounding the fireball which will absorb
IONIZArION PROI)UCIED BY NUCI EAR EXPI OSIONS 471

electromagoetic waves appreciably for r:idiation from a nuclear exphtmion

tens of seconds. This effect will be neg- belovw, 10 miles, except possibly by the

ligiole for most radiofrequency systems. rising debris from a high-yield burt (cf.

but it may be signifcant for radars with § 10,41) However, perturbations in the

highiy directional beams that pass fairly refractive properties of the F-region

near (in addition to those passing have been noted following explosion:- in

tnrough) the fireball, this altitude tegime. Traveling distur10.37 In the atmosphere around the bances (§ 10 26) that move outward in

region referred to above, the electron the E- and lowcr F-regions appear to

density wi!l be much lower because the result from the initial blast wave.

gamma rays a:c somev.hat attentuated

by the air, and the electrons that are DETONATIONS AT 10 TO 40 MILES

formed are removed rapidly by attach- ALTITUDE

ment. Hence. the number of free electrons is not expected to be as large, 10.40 If the explosion occurs in the

neither will they be as widely distiih- altitude regime of roughly 10 to 40

uted. as in the region around the fireball miles, thermal energy radiated as X rays

for bursts at higher altitudes (§ 10.43 et will be deposited in the vicinity of the

seq.). Refraction of radar ,:ignals burst, as at lower altitudes with sub-

(§ 10.118) and clutter (§ 10.120) may sequent reradiation to form the familiar

then be more significant than absorp- fireball. Ionization by debris ions or by

tion. These effects are also important if beta particles within the fireball may

1he signals pass through or near the stem sustain the electron density after the

ur cloud of a burst that is sufficienitly low temperature has fallen it) the 2,5(IX'

for debris from the surface to be carried Kelvin ,equired for significant thermal

aloft ionization by 'i.r. The fireball region will

10.38 The D-region is not affected bt. ionized to high levels--more thai, 10'

to arny great extent by prompt radivtion electrons per cubic centimeter-for a

from nuclear explosions below 10 period of a! least 30 seconds and iossimiles, ,ince the burst is below the stop- bly for longer than 3 minutes. The spaping altitude for X rays, neutrons, and tial extent of the ionizatirn will be larger

gamma rays (Table 10.29). Ioniz4tion in than for detonations at th,• lower altitude

the D-region may be increased, how- considered previously.

ever by delayed radiation, if the radio- 10.41 The fireball will be &pherical

active debris is carried upward by the in shape initially, with the transition

rising fire;bali above 15 miles, the stop- from sphere to torus occurring later than

ping aititude for gamma radiation. for bursts at lower altitudes. FurtherThere may be addit.onal ionization due more, the debris, most of which is carto beta particles if the debris rises as tied upward by the hot, rising firebali,

high as 35 miles, but this is expected may reach considerably greater heights.

only for weapons of large yield (see Fig. Multimegaton weapons detonated near

10. 158c). the upper limit of the iO to 40 miles

10.39 Ionization in the E- ana F- altitude regime will begin to exhibit the

regions is not changed significantly by effects of an initial ballistic impulse,
472 RA i1) 1 \NI) R.ADAR V :.F-.F.i S

caused by pressure gradients across the fast neutrons and the inelastic scattering

large ver:ical diameter of the hIreball gamna rays are !;pread over a large

(§ 2. 129). As the fireball and debris rise ,,olume, so that the resulting electron

into thini,er air, they continue to ex- dens'y is low. Most of the neutron-inpand. The ballistically rising fireball can duccdt (plompt) ,onization arises irow

reach altitudes far above the detonai-,t: elastic scattering of the neutrons. The

point. Because of the rapid upward mio- nuclei that recoil from the scattering

tion ef the fireball and the decrease in process have sufficient energy to proatmospheric density with altitude, the duce ionization by interaction with atdeosity of the fireball may be greater mospheric atoms and molecules

than that of the surrounding atmosphere. 10.44 The persistent ionization in

Overshoot then occurs, and aher reach- the air is caused mainly, however, by

ing maximum altitude, the fireball de- delayed gamma radiation. Most of the

scends until it encounters air of density beta partic 1 ':s from the rWdioactive

comparable to its own. debris are absorbed within the fireball,

10.42 When the cloud of debris but the gamma rays can travel great

stabilizes in altitude. its horizontal distances when the debris is above their

spread will be infltuenced by diftision stopping altitude (15 miles). The size of

and by the prevailing winds. A spread- the ionized region surrounding the fireing velocity of 165 feet lpr :iecond is a ball can then be quite large. Calculation

reasonable e,;timate for debris at alti- of the electron densities is fairly cointudes between about 50 and 125 miles, plicated since it depends on the attenuathe spread is, however. moic.: complex tion of the gamma rayF by the amosthan is implied by such an assumption of phere and the electron loss mechanisms

a uniform expansion. which change with altitude.

10.43 For bursts in the: 10 to 4) 10.45 Ionization in the D-region

miles altitude regime, the X rays are from delayed gamma rays and beta parlargely confined within the fireball, ticles will be much more important for

especially at the lower altiludes. Even detonations in the 10 to 40 miles altitude

though the prompt gamma rays canry regime than for those below IC miles. If

only a smali proportion of the explosion the debris attains an altitude above 15

energy (§ 10.138), they will cause ion- miles, the delayed gamma rays can

ization in the surrounding air for a very reach the D-region and produce ionizasnort time. However, the main source of tior there. When the debris is below 35

prompt ionization in the surroundingair m-les, the stopping altitude for beta

(and also it the D..region foir detonations particles, the energy of these particles is

above 15 mi!es) appears to be the fast deposited close to or within the debtis

neutrons. There are three important in- cloud. The ionization is thus restricted

zeraction processes of such neutrons to this region.

with atomic nuclei in tl.e atmosphere 10.46 For the beta par-icles to cause

which can It-ad to ionizatian; they are ionization in the D-region, the debris,

ab,;orption, inelastic scatt:ering, and must be above 35 mileE. Be'cause of

elastic scatte.inrg (see Chapter VIII). their electric charge, the spread of the

The amount cf absorption is small for beta particles is largely prevented by the
IONiZATION PRODUCLD BY NUCLEAR EXPi.OSIONS 473

BE TA PARTICLES

GEOMAGNETIC

FEDLINES

GAMMA OZORIS

RAYS

BETA PARTICLES-,

BETA-PARTICLE ADGAMMA- RAY

IONIZATION GAMMA-RAY BETA- PARfICLE

AND.GAMMA-RAY." -GAMMA-RAY IONIZATION

* IONIZATION

* * ~................. ..... . . . . . . . . . .

., :! "':(::•.. .. . " : i.'. .. :,.:..:.:.:.:.:.. ---.. .. ,.............. ....... ,....., ... ... .... ,

..:!,. .. ,,• .. ; ....:.:. ..... ...:, ..:.:.:.:.:.: ....'. .......... :. . ..... ....... .. ............ .............. .. ...... ... .. ." ,

...... .................... ..........

Figure 10.47. Location of beta and gamma ionization regions when the debris from an

explosion ;n the northern hemisphere is above 40 m~les altitude.

earth's magnetic (geomagnetic) field, gamma rays are not affected by the

The area over which the beta particles geomagnetic field and they can therefore

produce ionization ini the D-region is spread in all directi..ns. If the debris!

thus essentia~lly the same as the area of rises above 40 mdles, the delayed

•he debris whea "'•,. initial expansion has gammas can produce ionization over a

ceased. lai gc are." in the D-region. The ioniza10.47 If the debris rises above 40 tion is not restricted by the tube of--

,arieCs, the beta particles will travel back magnetic field lines con'aining the

and forth along the geomagnetic field debris, as is that from the beta particles.

liles. They will then cause ionization in The D-region ionization caused by the

the local D-region and also in the mag- delayed gamma rays is thus mo•re ei:-

netic conjugate region in the opposite tensive in area although usually less

hemisphere of the earth (Fig. 10.47). If intense than that due to the beta parthe radioactive debris is uniformly dis- ticles.

tributed over a horizontal plane, the 10.49 Since the beta particles ate.

eiectrcn density ia the D-region due to largely prevented from spreading by the

the beta particles will be about the same geomagnetic field, the ionization they

in both hemispheres. In practice, at- produce (in the D-region) is not greatly

mospheric winds and turbulence and affected by the altitude to which theI

geomagnetic anomalies cause the dfstri- radioactive debris rises, provided it is

bution of the debt is to be nonuniform, ahov'e 40 miles. For the accompanying

but a uniform distribution is generally gamma radiation, however, th= intenassumed for estimating electron densi- sity, and hence the associated ionizaties resulting from nuclear explosions. tion, decreases the higher the altitude of

10.48 Unlike the beta particles, the the debris above the D-region. The areal
474 RADIO AND RADAR EFFECTS

extent increases at the same time. ing a field line into the atmosphz.ýre,

Gamma-ray ionization in the magnetic either in the viciiaitv of the explosion or

conjugate region will be much smaller at the magnetic conjugate. The ionizaand will arise from such debris ions as tion levels produced by neutrons in this

have traveled along the geomagnetic manner are low, but they have been

field lines and reached the vicinity of the detected at distances of several thousand

[)-region in the other terrestrial hemi- miles from the burst point. From the

sphere (§§ 2.141, 10.64). times at which the effects were ob10.50 There are two other sources served, they covld hhve been caused

of ionization in the conjugate region, only by neutrons.

namely, Compton electrons and neu- 10.52 Thermal X rays begin to

trons. Gamma rays lose part of their escape from the fireball for detonations

energy in the atmosphere by Compton in the upper po.rtion of the 10 to 40 miles

scattering (§ 8.89). If the Compton altitude regime and can cause apprecielectrons are formed above about 40 able ionization in the E-region above the

miles, they will either deposit their en- burst point. Ionization in the E- and

ergy (and cause ionization) locally in the F-regirns will be perturbed by traveling

D-reion or be guided by the geomag- disturbances to a greater extent from

netic field to the conjugale region. Since detonations in this altitude regim.' than

delayed gamma rays are spread over a from explosions of similar yield below

fairly large volume when the radioactive 10 miles. A high-yield detonation near

debris is above about 15 miles, Comp- 40 miles altitude may produce a region

ton electrons can produce widespread of severe electron density depletion

ionization. The space affected is larger (§ 10.71 et seq.). Fireballs rising above

than that in which beta particles cause 65 miles and beta particles escaping

ionization in both conjugate regions. from fission debris above 40 miles also

Althou, gh the ionization from Compton Increase the electron density in the Eelectrons in the magnetic conjugate re- and F-regions.

gion is net large, the effects on 'he

propagation of electromagnetic waves, DETONATIONS AT 40 TO 65 MILES

especially those of lower freq'aencies, ALTITUDE

can be important.

10.51 Many of the neutrons pro- 10.53 X rays ionize a region of

duced ini a nuclear cxplosior. above 15 considerable extent around a detonation

miles will travel upward, escaping to in the 40 to 65 miles regime. The

high altitudes. Since neutrons are not mechanism of fireball formation

affected by the geomagnetic field, they changes appreciably in this range

spread over a large region. A free neu- (§ 2.130 et seq ), since at 65 miles he

tron disintegrates spontaneously, with a X-ray stopping altitude has been exhalf-life of about 12 minutes, into a ceeded, and the radiations can spread

proton and an electron (bhta particle), very widely. Starting at about 50 m;les

The latter will be trapped by the ge,''- altitude, the interaction of the expanding W

magnefic field lines and will produce weapon debris with the atmosphere beionization in the D-region after follow- comes the dominant mechanism pro- A
IONIZATION PRODUCED BY NUCLEAR EXPLOSIONS 475

du::ing a fireball. Above about 50 miles, estimates of debris motion for stabilizathe geomagnetic field will influence the tion altitudes between 50 and 125 miles.

location and distribution of the late time If more than a rough estimate is refireball, as will be seen shortly. The 40 quired, upper-altitude wind information

to 65 miles altitude regime is also a must be used to calculate the spreading

transitional one for deionization mecha- ,,,locity.

nisms in the fireball, and for the dy- 10.56 The region identified for

namic motion of the rising fireball. lower altitude bursts as that around the

10.54 Above about 40 miles, the fireball now merges into the D-. and E-.

temperature of the fireball is no longer and F-regions. Hence, it will not be

the governing factor in ionization. The discussed separately here or in the next

electron density changes only in ac- section which is concerned with detocordance with the increase in volume of nations above 65 -niles altitude.

the fireball, thus causing a wider dis- 10.57 The D-region is more widely

tribution of the free electrons in space. influenced by prompt radiation from

Recombination of electrons witn posi- detonations above 40 miles than from

tive atomic ions, produced by the high detonations below that altitude, since

temperatures in the fireball, is the main both X rays and neutrons have lc,:ger

removal process. This is, however, penetration distances at the higher &%

much slower than the recombination tudes. For detonations above 40 roi!es,

with molecular ions which predominates X rays produce essentially all the

in the normal D- and E-regions. Elec- prompt ionization in the D-region. As

tron densities greater than 108 elec- indicated in § 10.43, fast neutrons are

trons/cm' can then persist for tens of apparently the main source of prompt

seconds, resulting in significant attenu- ionization in this region 'or detonations

ation and refraction of electromagnetic ai somewhat lower altitudes.

waves. The persistence depends on how 10.58 Continuivg ionization of the

rapidly the fireball volumi" increases and D-region by delayed gamma rays and

on the detailed chemistry of the fireball beta particles is of major importance

gases. when the burst altitude is between 40

10.55 For explosions of high and and 65 miles. The situation is similar to

moderately high yields at altitudes near that described in § 10.47 for the case in

the upper limit of the regime under which the debris rises to a height of

consideration, the fireball may rise to more than 40 miles. The beta-particle

heights of hundreds of miles (see Figs. ionization is restricted to areas, in ihe

10.1 58b and c). At these heights, the D-regions of both hemispheres of the

fireball and debris regions wiJ1 be af- earth, which ire each roughly equal to

fected by the geomagnetic field lines the area of the debris. The delayed

(§ 10.63 etseq.). For smaller yields, the gamma rays spread in all directions,

fireball generally rises buoyantly and however, and the ionization in the Dsmoothly to a nominal stabilization alti- r-egion near the burst point is consetude, with no overshoot (Fig. !0. 158a). quently more extensive in area but is

A ;preading velocity of 165 feet per less in~ense than that due to the beta

second is frequently used to make rough particles. The upward motion of the

AU

*ft Av
476 RADIO AND RADAR EFFECTS

debris can aliow the gamma rays to noted after subsequent high-altitudL, exirradiate areas of the D-region several plosions.

hunidred miles in radius. It is apparent

that the electron densities resulting from DETONATIONS ABOVE 65 MILES

such widespread irradiation will generally be low. i0.62 The mechanisms of fireball

10._'. Compton electrons from de- formation and growth contintue to

layed gamma rays and beta particles change as the detonatio,,i altitude informed by the spontaneous disintegra- creases above 65 miles. At these altition of neutrons can cause widespread, tudes, X rays travel great distances in

althot'gh relatively weak, ionization in the very low-density atmosphere and do

the D-region near the burst point and not produce a normal fireball. Below

also at its magnetic conjugate. The gen- about 190 miles, depending &n the

eral effects are simila-i to tihose described weapon yield, the energy initially apin §§ 10.50 and 10.51 for nuclear deto- pearing as the high outward velocity of

nations at lower altitude. debris particles will still bl deposited

within a fairly short distance. This re- 10.60 Detonations above 40 miles, suits in the formation of a heated and

and particularly those above 50 or 55 ionized region. The apparent size of this

miles, will irradiate the E-region ex- so-called "fireball" region may depend

tensi, ly with X rays. Consequently, on the manner in which it is view.d.

there will be prompt ionization, with the The optical (or radiat;ng) fireball may

usual fairly long E-region recovery not coincide with the radar fireball, i.e.,

time, in addition to tlat caused by the the region affecting radar signals, and

continuing radiations from the radioac- the fireball boundary may not be well

tive debris. Ionization effects in the E- defined. Pecause of the large dimenregion, similar to sporad-c-E (§ 10.12), sions, times of the order of a iew sechave been noted following detonations onds may be required before the initial

above 40 miles. motion of the debris is reduced signifi10.61 Strong F-region distur- cantly.

bances, involving an initial increase 10.63 The geomagnetic field plays

followed by a decrease in electron den- an increasingly important role in consity, were observed over an area of more trollinf debris motion as the detonation

than a thousand miles in radius for many altitude increases. Above about 300

hours after the TEAK megaton-range miles, where the density of the atmosburst at about 48 miles altitude (§ 2.52). phere is very low, the geomagnetic field

The proposed explanation for these dis- is the dominant factor slowing the outturbances is given in § 10.71 et seq. ward expansion of the weapon debris.

There also appiared to be an effect sim- This debris is initially highly ionized

ilar to spread-F (§ 10. 12) which ended and is consequently a good electrical

at sunrise, and some tilti g of the nor- conductor. As it expands, it pushes the

real ionospheric stratification which al- geomagnetic field out ahead of it, and

tered the path of reflected radio signals. the magnetic pressure caused by the

Similar but less severe effects were deformation of the field can low down

- *",'•.. . • . . . . -• ' "• ". .. ..-... : ......... .' .'- ,•.rr'..,-.' in,• p,w, ,x•,, w•l• .-, •.-- .f ...-- . ..........- " • '
ION!ZATION PRODUCED BY N4UCIAEAR EXPLOSIONS 477

and stop the debris c,'pansion. The reduced air density above 65 miles, the

debris may expand h n-.!reds of miles initizl ionizatioa within the fireball is

radially before beýt stopped by the less than for detonit~ons at lower altimagnetic pressune. The problem of the tudes. Ho-vever, ii expansion is largely

expansion of ionized debris against a along the geomi-agnetic field lihies. demagnetic field is quite complex. Insta crease in election density due to volume

bili!ies in dhe interface between the ex. expansico may be relativety slow. D*-

panding debris and the geomagneti, mensions across the geomagnetic ficld

field cati cause jetting of debris across are typically a few hundred miles after a

field lines, and sonic debris can escape few minutes.

to great distances. 10.67 As stated in § 10.54, electron

10.64 Debris initially dirccied recombination wii'h positive atomic ions

downward will be stopped by the denser will proceed slew!y, and electron denait telow the burst point at an altitude of sities in the fireball high enough to proabout 70 miles. whereas upward-di- duce attenuation of radar nignals nay

rected debris travels for long distances. last up to a oew minutes. Electron denIf, in being stopped by the atmosphere, sities sufficient to affect electromagnetic

the downward-directed debris heats and signals of lower frequency may persis;t

ionizes the -ir, that heated region will much longe.. The formation, location.

subsequently rise and expand. Some and extent of !he ionized regions are

upward-directed, ionized debris will dependent both on weapon characterisfollow geomagnetic field lines and will tics and atmospheric composition and

reach the conjugate region in the other are difficult to predict.

hemisphere of the earth. )0.68 Apart irom the ionization

10.65 The geomagnetic field will within the firebali region due to the

also play an important role in determin- kinetic energy of the debris ions, the

ing the continued growth ai Ad location of radioactive debris causes ionization (in

the ionized region once it has formed. the D-region), after the initial expansion

Expansion along the. field lines can con- has ceased. This ionizatior results from

tinue after expansion across the field has the emission of beta particles and destopped. Arcs (or tubes) of charged layed gamma rays. Hence, the location

partic'es, mainly beta particles, may bc of the debris after the initial expansion is

formed, extending froir. one hemisphere important.

to the other. Ionization will then occur 1,.69 Neutrons and X rays travcIin the upper atmosphere in each con.- ing C- -nwaid from a burst above about

jugate region. This may happen even for 65 rniv~s altitude ;,il irradiate large

detonations below 65 miles if the fire- areas of the D-re•,_'t,. 3Sme widespread

ball is still highly ionized after it reaches ionization of low atknts..y wilt dlso be

alitudes of a fe•w 1undred miles. caused by the decay of neutrons in the

10.66 Within thje fireball, the rap- earth's magnetic field, as described in

idly moving debris ions cause ionization § 10.51.

of the air; each such ion -an ionize 10.70 The debris that is initially dimany air molecules and atoms before rected upward or jets across the field

losing its kinetic energy. Because of the lines will be in a position to release beta
478 RADIO AND RADAR EFFECTS

particlci in locations and directions then decreased well below normal until

suitable for trapping in the earth's mag- local sunrise (§ 10.61). Change's in the

netic ie~d. These paiticles. traveling chemistry of the atmosphere may have

back and forth along the field lincs and been parly responsible for the decrease

drifting eastward in longitude around in electron density.

the earth, will spread within a few hours 10.73 A% the shock wave dows

to form a sheli of high-energy beta par- down, it eventually becomes an ac,.,ustic

ticles, i.e.. electrons, c_,ompletely (or sound) wave, often called a giavity

around the earth (§ 2.247). acoustic wave because it is propagated

in a medium (the atmosphere) w;,ose

INDIRECT EFFECTS OF density variation is determiaed by gray-

"HIGH-ALTITUDE EXPLOSIONS ity. Acoustic waves travel thousands of

10.71 The electron density in the E- miles from the bursi point and can cause

and F-regions of the ionospheie may b;e perturbations in the E- and F-regions at

changed by t.ffects associated with a great distances. These perturbations are

nuclear expiosion other 1han direct ion- evidently hydromagnetic in nature,

ization. The most importan, of there since 1he electron densities, which are

effects are hydrodynamic (shock) and diffictito calculate, are apparently dehydromagnetic disturbances (Fee pendent on the direction of propagation

§ 10.26 footnote) and changes in air of the acoustic waves relative to the

chemistry. As the shock wave from the local geomagnetic field lines.

detonation propagates through the at- 10.74 As well as causing ionizamosphere, 'he air in a given region ex- tion, X rays from a nuclear explosion,

perie,1ces first a compression phase and like gamma rays, can produce excited

then a suction phase (§ 3.04). During states (§ 8.23) of atoms and molecules

the compression phase, the density of of the air in the E- and I--regions. These

the ,ir, and hence of the electrons pros- excited nettral particles can undergo

ent, increases because of the aecrease in chemical reactions which affect electron

volume. However, the comb, red effect densities. If the detonation aititude is

of heating by compression and of ex- above about 200 mi!es, the resulting

pansion of the air during tl~e suction changes can be widespread and may last

phase may be a decrease in the electron for several hours. The moderate dedensity below the normal value, crease in electron density in the F

10.72 The TEAK high-altitude shet region, observed out to more than 600

produced a shock wave which propa- miles from the burst point after the

gated for several hundred miles from the STARFISH PRIME event (1.4 megaburst point. As !he shock passed a par- tons at 250 miles altitude), has been

ticular location, the electron densities in attributed to changes in air chemistry

the E- and F-regions first increased and caused by X rays.

'7;
F FFF.C-S ON RADIO AND RADAR SIGNALS 479

"EFFErTS ON RADIO AND RADAR SIGNA!_S

SIGNAL DEGRADATION or missed targets for radars. As the

1G. 75 Nuclear explosions can de- result of a nuclear explosion, the siggrade, i.e., attenuate, distort, or inter- nal-to-noise ratio may be decreased by

fere with, signals from radar, comrnun- attenuation of the signal strength or by

;cation, navigation, and other s ;ters increase in noise (or by both).

employing electromagnetic waves pro- 10.77 Detailed analysis of system

pagated through the atmosphere. In performance requires consideration of

general, systems that depend on the many factors. These include the follownormal ionosphere for propagation by ing: the geographic and geomagnetic

resection or scattering, as will be de- locations of the burst point and of the

scribed in due course, can be affected propagation paths; time variations of the

over large areas for periods ranging etectromagnctic transmission properties

from minutes to hours following a single along these paths, i.e., propagation

burst at high altitude. Electromagnetic channel characteristics- the effect of

waves that pass through the ionosphere, these characteristics on the desired sigbut do not rely on it for propagation, nal, on noise generated within the ree.g., satellite communication and some ceiver, and on undesired signals reachradar systems, can also be affected, but ing the receiver; the signal processing

usually only over localized regions and used; the system mission; and criteria of

for periods of seconds to minutes. Sys- system performance.

tems which use waves that propagate

below the ionosphere, 4!ong lines-of- SIGNAL ATTENUATION

sight between ground stations or between ground stations and aircraft, will 10.78 Absorption of energy from

not, in general, experience signal deg- the electromagnetic waves is the major

radation. source of signal attenuation following

10.76 The signal strength required the detonation of a nuclear weapon. In

for acceptable systems performance is general, the absorption produced by a

usually given in terms of a signal-to- certain electron density is related invernoise ratio. The term "noise" refers to sely to the square of the wave frequency

random signals that may originate (§ 10.130); hence, absorption is more

within the receiver itself or may arise important for low- than for highfrom external sources, usually thunder- frequency systems that use the ionosstorms and other electrical disturbances phere for long-range transmission. The

in the atmosphere. Nuclear expibsions extent of absorption depends strongly on

can also generate noise. When the sig- the location of the transmission path

nal-to-noise ratio falls below a mini- relative to the burst point and to the time

mum acceptable level, system degrada- after the 'burst. Shortly after the explotion occurs in the form of increased sion, absorption may be so intense that

error rate, e.g., symbol or word errors there is a:. blackout and communication

for communications systems and false is impossiblhe. This will be followed by a
480 RADIO AND RADAR EFFECTS

period of reduced system performance is known as -synchrotron radiation."

before fairly normal conditions a-,- res- This covers a range of trequencies, but

tored. The duration of the blackou.. is much more intense at low than at high

particularly for systems operating below frequencies. Synchrotron radiation

about 30 megahertz, is generally long in picked up by an antenna will produce

comparison with that of reduced per- noise in the receiver. However, the

formance. Absorption may also affect noise level is relatively weak and is not

received noisc levels if the noise reaches significant except for very ý.ensitive,

the receiver via the ionosphere. low-frequency systems with the antenna

10.79 When the electron densities beam at right angles to the geomagnetic

are decreased by the effects of a nuclear field lines.

explosion, signal attenuation especially

in the frequency range between 3 and 30

megahertz, can result from loss of reflection (due to refraction) from the Eand F-region. Signals which would nor- 10.82 In free space, the phase vernally reach the receiver by reflection locity of an electromagnetic wave, i.e.,

from the ionosphere may then be only the rate of propagation of a plane of

weakly refracted so that they continue constant phase, is equal to the velocity

into space. of light in a vacuum. In an ionized

mediunm, however, the phase velocity

NO.SE exceeds the velocity of light by an

anmount which depends on the frequency

10.80 Two noise sources from a of the wave and the electron density of

nuclear detonation are thermal radiation the medium. if an electromagnetic sigfrom the fireball and synchrotron radia- nal traverses a region that has become

lion from beta particles traveling along ionized by a nuclear detonation, it will

the geomagnetic field lines. The fireball consequently suffer phase changes. A

may remain at temperatures above communication system that uses phase

1,9000 Kelvin for a few hundred sec- information will thus be affected. Furonds and may produce considerable thermore, because the phase velocity

noise if the antenna is pointed at the varies with the wave frequency, a signal

fireball. Thermal noise generally will be consisting of waves of several frequensignificant only for systems with low cies, as is commonly the case, will be

(internal) receiver noise. The actual distorted because the phase relationships

noise received will depend on the pruip- between the waves will be changed.

erties of the fireball, e.g., whether or not 10.83 If the propagation path passes

it is absorbing at the frequency of inter- through regions of varying electron

est, the amount of attenuation outside deusities, that is to say, if the electron

the fireball, and the directivity of the densities encountered by the signal vary

receiving antenna. with time, a frequency shift (Doppler

10.81 Beta particles spiraling along shift) occurs. For wide-band communithe geomagnetic field lines radiate elec- cations systems there may then be intromagnetic ei~ergy in the form of what terference between adjacent channels.

- -- N ., -iN~,-.-MT,
EFFECTS ON RADIO AD RADAR SIGNALS 481

As a result, the effectiv0 (or useful) ing electron density, i.e., of decreasing

bandwidth would be decreased. refractive index, the conti:ued refrac10.84 Although the phase velocity tion may cause the wave to return to the

of electromagnetic waves is greater in region of low electron density from

an ionized medium than in free space, which it originally came. The wave is

the group velocity, i.e., the velocity then said to be reflected. By increasing

with which the signal energy is trans- the electron density in the ionosphere, a

mitted, is less than the velocity of light, nuclear detonation will change th'! reThe group velocity is also dependent on flection altitude of electromagnetic

the wave frequency and the electron waves coming from the earth. Thus,

density of the medium. A signal passing systems that rely on reflection froin the

through an ionized region thus suffers ionosphere for long-range communicafrequency-dependent time delays as tions can be adversely affected by the

compared with propagation through free detonation. Even if reflected signals are

space. This will cause various errors in not normally used, unwanted reflected

radar systenis, as will be seen in signals may cause interference with the

§ 10.119. desired direct signals.

10.87 When an electromagnetic

wave encounters patches (or blobs) of EFFECTS irregular ionization, successive refractions may lead to more-or-less rEEdom

10.85 The ohase change of an elec- changes in the direction of propagation.

tromagnetic wave in an ionized medium Thlis is referred to as "scattering." The

is related to the refractive index of the term "forward scattering" is used when

wave in this medium (§ 10.125). The the propagation after scattering is in the

index of refraction in free space is unity, same general direction as before scatbut in an ionized region it is less than tering. !f the electromagnetic wave is

unity by an amount that increases with scattered toward the location from

the electron density, for waves of a which it came, the effect is described as

given frequency. As a result, the direc- "backscattering."

tion of propagation of an electromagne- 10.88 Reflection and scattering of

tic wave is changed in passing from free electromagnetic waves from ionized respace, i.e., the nonionized (or very gions produced by a nuclear explosion

weakly ionized) atmosphere, into a re- can result in abnormal propagation paths

gion of significant ionization. This is the between transmitter and receiver of a

basis of the refraction (or bending) of radio system. Multipath interference,

electromagnetic waves by an ionized which occurs when a desired signal

medium described in § 10.08. The wave reaches the receiver after traversing two

is always bent away from the region of or more separate paths, produces fading

lower refractive indeAt (higher electron and signal distortion. Interfering sigdensity) toward that of higher refractive nals, due to anomalous propagation

index (lower electron density). from other radin transmitters, can in10.86 If an electromagnetic wave is crease noise levels to such an extent that

propagated through a region of increas- the desired signal might be masked. In

ri
482 RADIO AND RADAR EFFECTS

radar systems, changes in the propaga- weapon yields and detonation altitudes

tior, direction due to refraction can cause which were not necessarily those that

angular errors. Moreover, if a radar would maximize the effects on cornsignal is scattered back to the receiver, it munications systems.

can mask desired target returns or, de- 10.91 It is convenient to discuss

pending on the characteristics of the radio system effects in accordance with

scattering medium, it may gcnerate a the conventional division of the radiofalse target (§ 10.120 et seq.). frequency spectrum into decades of frequency ranges. These ranges, with asRADIO COMMUNICATIONS SYSTEMS sociated frequencies and wavelengths,

are given in Table 10.91. Radar sys10.89 The general category of radio tems, which normally employ the fresystems of interest includes those in quency ranige of VHF or higher, are

which electromagnetic waves are re- treated separately in § 10. 114 et seq.

flected or scattered from the troposphere

(§ 9.126) or the ionosphere. Such sys- VERY-LOW-FREQUENCY RANGE (3 to

tems are used primarily for long-dis- 30 kHz)

tance communications; however, other

uses, e.g., over-the-horizon radars, also 10.92 The frequencies in the VLF

fall in this category. band are low enough for fewer than 100

10.% Detailed analysis of corn- free electrons/cm3 to cause reflection of

munications systems, even for the nor- the signal (§ 10.20). The bottom of the

mal atmosphere, is difficult and depends ionosphere thus effectively acts as a

largely on the use of empirical data. sharp boundary which is not penetrated,

Measuremeats made during nuclear anu the electromagnetic radiation is

tests have shown that both degradation confined oetween the earth and the ionand enhancement of signals can occur. osphere by repeated reflections. The reThe limited information availible, suiting "sky wave," as it is called, may

however, has been obtained in tests for be regarded as traveling along a duct (or

Table 10.91

RADIOFREQUENCY SPECTRUM

Name of Range Frequency Range* Wavelergth Range

Very Low Frequency VLF 3-30 kHz 107-106 cm

Low Frequency LF 30-300 kHz I0W-105 cm

Medium Frequency MF 300-3,000 kHz 105-104 cm

High Frequency HF 3-30 MHz 10'-l C10• c4n

Very High Frequency VHF 30-300 MHz 103--102 cm

Ultra High Frequer.cy UHF 300-3,000 MHz 102-10 cm 4

Super uligh Frequency SHF 3-30 GHz 10- 1 cm

Extremely High Frequency EHF 30-300 GHz 10- 1 mm

*The abbreviation kHz, MHz, and GHz refer to kilohertz ('0 3 cycles/sec), megahertz (106 cycles/ sec),

..,J gigahertz (109 cycles/sec), respectively.

ftI

gi
EFFECTS ON RADIO AND RADAR SIGNALS 483

guide) whose boundaries are the earth where both ground and sky waves are

and that level in the atmosphere at received, the change in phase of the sky

which the electron denisity is aboul 100 wave may result in mutual interference

'lectrons per cubic centimeter. There is of the two signals. There will then be a

also a "ground wave" whereby the sig- reduction in the strength of the pro.

nal is transmitted along the surface of cessed signal. Over relatively short

the earth and tends to follow its curia- !ransmission paths. when only the

ture. Global VLF broadcast communi- ground wave is normally used, the

cations ond maritime and aerial naviga- change in reflection altitude may cause

tion systems use the long propagation the sky wave to be received. This may

distances that are possible because enhance or interfere with the ground

ground wave attenoation is relatively wave, according to circumstances. For

low and the sky wave is reflected at the long-distance VLF communications.

bottom of the ionosphere with |iivile ab- when oniy the sky wave is important, a

sorption. nuclear explosior, can cause large phase

10.93 The m:.Jor effect of nuclear changes even a' a distance. Thus, after

the TEAK and ORANGE high-altitude detonat;ons is to cause ionization i e., shots (§ 2.52). the 18.6-kilohertz signal

an increase in electron density, which transmitted from the Naval Radio Stamay lower the ionospheric reflection al- tion at Seattle, Washington, to Camtitude. Theoretical analyses and experi- bridge, Massachusetts, suffered an

mental data indicate that the major con- abrupt phase shift. The entire path was

sequences are phase anomalies and at least 3,000 miles from the burst

changes in signal strength and in the points.

noise from distant thunderstorms. These pn. 10.96 Distant thunderstorms proefects are expected to persist longer in duce some atmospheric noise in the

the daytime than at night because of the VLF band, the noise level depending on

slower decay of the electron density, the ionospheric reflection height.

assuming the same weapon yield and Hence, a change in this height can affect

burst altitude. the signal-to-noise ratio. The system

10.94 Phase changes may be large degradation or improvement following a

and rapid, e.g., 1,000 degrees or so nuclear detonation will depend on the

within a millisecond, and they are fol-, relativ. geographic locations of the siglowed by a slow recovery of a few nal source, the noise source, the ionizadegrees per second. Such phase changes tion produced, and the propagation

may be significant for navigation, syn- path. Reduction of the signa:-to-noise

chronous communications, and phase ratio appears to be significant primarily

modulation systems. VLF systems for long transmission paths with ionosoperating over short, medium, or long pheric reflection. A single high-altitude

distances can be affected by the phase explosion or multiple explosions which

changes that result from the ionization produce ionization affecting appreciable

produced by a nuclear explosion, portions of a propagation path will result

10.95 On paths of medium length, in maximum degradation,

Mi
484 RADIO AND RADAR EFFECT'%

LOW-FREQUENCY RANGE (.10 TO 300 when ionization produced by the detokil-)nation affects appreciable portions of the

10.9 Asthe leroagneic ave propagation path. Furthermore, large

frequency is increased above 30 kilo- phssifscnour

hertz, the normal ionosphere behkwes

much less as a sharp boundary. The MEDI UM -FREQUENCY RANGE

wave penetrates several miles before (300kHz TO 3 MHz)

being reflected back toward the earth. 109 No-a-poqaini h The altitude to which the wave perle- prp "aioni h trats atenuaionnwrnllyex- ad th MI band is cr'aracterized by. iergc atpcrienc-!d depend s~rongly on the limitengomuiation of sywvsuinhe datime. t

nitude and the rate of vertical change, lmtngc mucaontschtfa5o

i~e. th grdiet, f elctrn dnsiy ~ ground waves. Increase of ionization in

te.,temo gatheientosphereelectrndsiona the D-rtgior from high-altitude nuclear

extends the iiwcfui range of propagation, fxplosion wilauese, ute a ttenupa ationwa

particularly at night when ionization in o MF sy wvs n rpgto a

~~he' 'v. ~'ini . .onay abet be, limited to the ground wave during Atten V-t. o i a skyi wav increalyases nt rJUh day and night. In regions nee the

Athenu dayt ý0 e, eskeay fwrate higcrerssi burst (or its magnetic conjugate) the sky the daenccme becaspel for thehirgreaer wave may be blacked out for hours.

penetration. AltKUigh ground waves are Sincatospheric nisea princpalsure o!

commonly used 'lar LF transmissions, uiospeesaprnilsureo

sky waves Gften provide acceptable si-interference, absoipt-on in the D-region

nals a few thousand w~es from the my improve gru~-~ereception for

transmittin-7 station. some paths. However, the limiting sig- C nal-lo-noise ratio is determined pri- 10.98 Ionization from wuiwA,ýr ex.. marily by local t~understorin activity.

plosions will generally not dcjaacd iflc Reduction of noi'se from distant hiunperformance of LF systems which nor- derstormis w-ill thus not improve marrrn3lly depenct anly on the groiind wave ginal reception.

unless the change in reflection -altitude

causes the sky wave to be i-cceived. As IHFEUNYR GE3TO0

with VLF, this may enhatnce or interfere MHz)-RQEC RNE( O3

with the ground wave accord~ing to the

circumstances, however, reception of 10.A00 The HF band is used exthe sky wpv~e is less likely for LF than tensively for long-range communlicafor VL-F. Systems which .-ely on sky- tioris; the frequencies aie high enough to

wave propagation may experience at- permit transmission of informxation at a

tenuation lasting from a few minutes to rapid rate and yet are sufficiently low to

several hours. For a given yih,-d and be reflected by the ionosphere. Tihe sigburst height, the duration of the distur- nals are !nropagated from the transmitter

bance may be expec'ted to be greatest in to a receiver by succ-essive reflections

the daytime. The most severe attewiua- from the E- or F-region and the surface

ticn appears to occui for Lng paths, of the eafth. Electromagnetic wa,,%e,"
EFFECTS ON ':,ADIO AND RADAR SIGNALS 485

with frequencies toward the lower end distance of about ,500 miles from the

of the HF ran.ie are normally reflected burst point. Recovery would requIre

from the E-region of the ionosphere from a few h,,ndred to a few thousand

after suffering some attenuation by ab- seconds, dcnding on the explosion

sorption in the D--egion. Reflection at yield, the signal frequency, and the

the upper end of the range requires number of traversals of the D-region

higher electron uunsities and occurs made by the electromagnetic wave in its

from the F-region (§ 10.135). successive reflections from transmitter

10.101 If a nuclear explosion in- to receiver.

creases the electron density in the D- 10,104 The signal degradation due

region above its usual maximum ,alue to delayed radiations also varies with the

of about 101 e~ecironsicm', signal atten- explosion yield and altitude. For weapuation by absorption will be increased. ons detonated at low altitudes, in which

Furthermore, the increase in electron the radioactive residues do not rise

density may lower the reflection altitude above 15 miles, the effects on [IF sysand thus change the propagation path of tems will generally be small, except for

the siglial. Communication: (and other) propagation paths close to the burst

systems using the HF range can thus be point. If the debris reaches an altitude

seriousl,ý degraded. Disturbances re- above 15 miles but below about 35 to 40

sulty' from an increase in the D-region miles, the D-region above the debris

electron derinity will persist longer in the will be ionized by delayed gamma rays

daytime than at night, but decreases in and possibly by beta particles (§ 10.46).

the E- and F-regions may reverse the Should the debris rise above 40 miles,

:,ituation (§ 10.105). the beta parlcles will cause ionization

10.102 Both prompt and dtlayed both in the burst region and in the magradiations from a nuclear buist can pro- netic .onjugate region. In the low-altiduce sufficie.nt ionization to cause tude detonation of weapons of large

blackout of HF signals, lasting from a yield, the debris may rise above 15

few seconds to several hou~.s. The re- miles and significant attenuation of HF

covery time depends, among oWher signals can occur for propagation paths

things, on the weapon yield and the within several huidred miles of the

detonation altitude. Th-e period during burst point. For high-altitude dctonalion

which the system is degraded is greater of such weapons, blackout may persist

for lower than for higher frequencies, for many hours over regions thousands

because a higher electron density is re- of miles in diameter. Even kiloton-yield

quired in the latter case, and it increases detonations at very high altitudes may

with the number of times the propaga- cause daytime blackout of HF systems

Zion path traverses the region of en- over considerable areas for periods of

hanced ionization. minutes to tens of minutes.

10.103 The effect of prompt radia- 10.105 Nuclear explosions may

tion is greatest for high-altitude explo- also affect HF communications by a

sions. This, a negaton burst at a height decrease in the electron density in the Eof 200 miles in the daytime would be and F-regions which changes their reexpected to disrupt HF systems out to a flection characteristics. Following the
486 RADIO AN[) RA.DAR E.FFECTS

TEAK shot (in th,. D-region), the max- VERY-MiGH-FREQUENC'ý RANGE (30

irnum usable frejluency for long-dis- TO 3(X) MHz)

tance communica ion was ccdu,'" over

an area some thoisands of mes in ra- pe10.108 Signals in the VHF range

dius for a perioc lasting• from shortly penetrate the normal ionsphere and

after midnight u.itil sunrise (cf. escape from the ea prih. iynsequentdy, § 10.72). Such § 1072) ~-ver Suh chnge inthe this frequcncy range is primarily used ,--%/ere cl~anges in the

reflection properlies of the ionosphere for line-c'-sight communications ovewere not noted, hov ever, during the short distances, e.g., commercial teleFISHBOWL hi ph-altilde te.;t series vision channeis and FM radio, but

(§ 2.52). Nevertheless, electron depleý i(,',,-range communication is possible

tion in the "-- an:l F-regions is expc-.td by making use of the small amount of

to be a significant degradation factor transmitted energy ti-w is scattered back

following large-yield detonations above to earih in a torv ird direction by

about 65 miles during the nighttime. p;tches of unusually ýntcnse ionization.

Restoration of tfae normal electron den- Forward propagation ionospheric scatter

sity following a daytime explosion of (FPIS) systems are inefficient, since

the same type ihould occur more rap- only a minute fraction of the energy of

idly. the transmitter reaches the receiver, but

they make additional portions of the

10.106 For three events at the electromagnetic spectrum available for

highest altitudes in the FISHBOWL fairly reliable communication between

series, a number of new propagation ground stations at distances up to 1,500

modes were noted; in some cases the miles apart.

use of exceptionally high frequencies, 10.:09 Normally, VHF signals

well into the ",HF range, became possi- scatter from ionization irregularities

ble. When such modes were in exis- caused by meteor trails or by turbulence

tence, in addition to the tiormal modes, in the upper part of the D-region. Since

considerable nultipath propagation was scattering from meteor trails occurs at

experienced. The usefulness of the new altitu-es of about 60 miles or more, the

modes depends markedly on the relative propagation path must traverse the regeometry of the transmitter and re- gion of maxinmum absorption (around 40

ceiver, and on the reflection mechanism, miles altitude) caused by delayed

10.16i7 It is important to mention ua•nma and beta radiations from a nu-,

that, although HF communications can ,iear burst. Meteor-scatter circuits norbe degraded seriously by a nuclear ex- mally opnrate with fairly small signal

plosion at high altitude. radio systems margins, and so absorption effects can

operating in this band may still be able be important.

to perform substantia' portions of their 10.110 Signals in FPIS systems

mission in some circumstances. It is by scattered from irregularities in electron

no means certain. for example, that HF density caused by turbulence may be

systems will be blacked out completely enhanced by the increased ionization

if the transmission path is at some dis- from a nuclear explosion. However,

tance from the burst point, absorption will reduce the signal return

: - -- - '- - ... .-~ . . .. *..-.--' . . ~-* - y,- 7- ,
EFFECTS ON RADIO AND RADAR SIGNALS 487

from normal scatter heighis to negligible propagation due to increased ionosmr.gni.udes for only a siiort period of pheric ionization appears unlikely.

time. New propagation modes, pro- 10.113 Line-of-sight propagation

duced by reflection from increased ion- through the ionosphere, such as is used

ization in the F-region or by fireball by UHF satellite links, can be degrad-d

ionization, can cause a multipath condi- if the propagation path paý.c,-s th,•oug% or

tion w),ich wi!i reduce the effective cir- near the fireball. Ionization by delayed

cuit bandwidth. Following the KING- radiation, especially beta particles, can

FISH event (submegaton yield in the produce absorption lasting a few minE-region), the Midway-to-Kauai ionos- utes over rcgions of from tens of miles

pheric-scatter circuit in the Pacific was to a few hundred miles in radius. If the

required to operate on a reduced band- ground-to-satellite propagation path

width for 21 minutes. Pacific FPIS sys- moves rapidly, the degradation period

tems alsc experienced about 30 seconds will depend primarily or) the relative

of blackout following the STARFISH geometry of the path and the disturbed

PRIME te.t (§ 10.74). region. Wide-band satellite signals can

10.111 Line-of-sight propagation be degraded by signal distortion.

traversing the D-regioi,, e.g., satellite

communications, can be degraded Dy RADAR SYSTEM EFFECTS (VHF AND

absorption due to an increase in electron ABOVE)

density arising from delayed radiation.

The degradation may last fcr tens of 10A,14 Radar systems are similar to

minutes over regions of huadreds of radio communicationis systems in the

miles in radius. Attenuation and signal respect that a transmitter and receiver of

distortion caused by fireball regions electroniagnctic waves are used. Howabove about 60 miles may also affect ever, in radar the receiver is located near

communicatio-: systems operating in the the transmitter and may use the same

VHF band. antenna, which typically is highly

directional. The transmitted signai,

S ULTRA-IlGH FREQUENCY RANGE consisting of a series of pulses, is in part

,(300 Mtz TO 3 GHz) reflected back to the receiver, like an (T3echo, ty obiecs i,. the path of the

10.112 In the UHIF bandi (and 0he pulsed beam. From the direction of the

upper pvrt of the VHF band), forward antenna, the travel time of the signal,

scattering by neutral molecules and and its speed of propagation, informasmall particles in the troposphere (below tion can be obtained concerning the !oabout 12 miles) is used to extend prop- catiorL and movement of the source of

agation beyond the line of sight. Weap- the echo. Frequencies normally emSons detonated above the troposphere are ployed in Ihis connection are in the VHF

not expected to affect tropospheric range and above. There is little effect of

propagation paths. Bursts at lower alid- ionization on signals of these frequentude may cause degradation for a few cies provided both the radar and the

•o ) seconds if the fireball rises through the target are below the ionosphere.

propagation path. Significant multipath 10.115 If the signal must pass
488 RADIO AND RADAR EFVFECTS

through the ionosphere, however, the detonations at lower altitudes (§ 10.36).

interference from nuclear detonations The degree and areal extent of ti.e abbecomes important, Radar signal; tra- sorption can be calculated with reasonversing the ionosphere will, like radio able reliability but lengthy computations

signals, be subject to attenuation. Al- are required.

though any additional attenuation is un- 10.118 Although absorption is gendersirable, the amount which can be erally the main source of degradation of

tolerated varies widely with the type of radar systems, there are a number of

radar and the purpose sAd feit of the system. In is other mechanisms which may be imI

search radars, for examp'M, whereiti otninsmcaeFrxmpth desired to detect each target at the portant in some cases. For example, the

gesirea possilerag, otest i ge. tas sn signal path may be bent by refraction

greatest possible range, i.e.,mjust as soon when the electromagnetic wave tCaas the target return becomeh observable verses a medium in which 11ke electron against the background n'iise, even the density changes along the path length. smallest additional signal loss results As a result, directional errois can occur.

directly which in shortening of the ratige at This effect may be significant if the a given target can be detected. A Thseecmabeigfcntfte wi w ,-, signal pas';es close to the fireball, but track,1 or guidance radar ina outside the region in which absorption

system, on the other hand, usually takes predominates, where the electron gra- over its target, well inside i~s mnaximum redmntsnhr h lcrnga deritectioaraget, wrom anothe itsemarc) dients are large, or if the signal traverses rdarechio 

radar which h hasge, has arem already adyoth~er dete.cted (and and the E-region where the electron 'lensity

.racked the object. In this case the signal is high and the rate of collision with

can be attenuated to a muzlh greater other particles is low (§ 10.137).

degree before the. radar lose,; its ability 10.119 The velocity of propagation

to acquire .:r track. of the radar signal that is detected is

10.116 A large amount of aenua- equal to the group velocity of the election by absorption occurs when the tromagnetic wave described in § 10.84;

propagation path traverses a firebaV!. this de.ermines the travel time of the

The. attenuation is determined by the signal from the transmitter to the target

properties of the fireball and these are and back. C1 anges in the group velocity

stioigly dependent on altitude. In gen- as a result of propagation through an

eral, it can be said that fireballs wvill be ionized medium will change the signal

opaque to radar signals operating at fre- travel time and will introduce an error in

quencies of 10 gigahertz (104 mega- estimating the range of the target. Since

hertz) and .,elow, for periods of tens of the change in the group velocity vwries

seconds to a few minutes. with the wave frequency, radar system.,

10.117 The ionized atmosphere using wide bandwidths will have difsurrounding the firebail will absorb ferent travel times over the range of

radar frequencies below a few giga- frequencic2 present in the signal. The

hertz, i.e., a few thousand megahertz, return signals will then arrive at difwhen the fireball As above about 10 ferent times, leading to what is called

miles. A smaller region tdjacent to the "dispersion." The phenomenon is

fireball will have the same effect for characteristic of transmission through 

a

'S.
TECHNICAL ASPECTS OF RADIO AND RADAR EFFECTS 489

highly ionized medium and causes sub- periences forward scattering through

stantial range errors. small angles, the signals reaching the

10.12') The fireball .:nd the charged receiwer will fluctuate both in phase and

particles in the tube enclosed by the amplitude. The resulting effect is regeomagnetic kield lines (§ 10.65) may ferred to as "scintillation." The phase

reflect or scatter radar waves, thus rro- fluctuations arc equivalent to fluctuaducing spurious signals which may be tions in the angle of arrival of the sigconfused with target return signals. This nals, so that the apparent position of the

effect, known as "clutter," may occur target will appear io move someiwhat

by reflection from rapidly changing gra- randomiy. The ampliude iuctuations

dients of electron density or as back- make target identification difficult for

scatter from irregular patches of ioniza- the signal processing systrem

tion or from particulate matter thrown

into the air when a fireball touches the

surface. Clutter returns. may be so in- SUMMARY OF NUCLEAR

tense as to affect radars in the same way DETONATION EFFECTS

that terrain features sometimes cause

difficulties by reflecting energy back to 10.122 The general effects of nuthe receiver thereby masking weak tar- cleaf detonations on the various radiogets. frequency ranges used in r,,dio and radar

10.121 If part of the energy of the systems are summarized in Table

radar pulses returning frot a '.aget ex- 10.122.

TECHNICAL ASPECTS OF RADIO AND RADAR EFFECTS 3

DENSITY OF THE ATMOSPHERE AND tion of the ai" change with altitude, the

scale height is not a,-tually a constant.

10.123 The decrease in, density of However, below about 60 mih s, use of

the atmosphere with increasing altitude a constant density scale height of 4.3

can be represented approximately by the miles in equation (10.123.1) gives a

equation fairly good representatikn of the change

in atmosot~heric density wi'th aititude. For

V (h) -pe-h/Hp g CM3 , (10. 123.1) higher ahlitudes the density scale height

where p (h) and p0 are the densities, in increases, i.e., the density varies more

g/cmr at height h and at sea level, re- slowly with altitude, but since altitudes

spectively, and H is called the scale below 60 miles are of primary interest

"height; h and H must be expressed in for the present purpose the simple ex-

"the same units of length, eg., miles. ponential relationships with constant

Because both temperature and composi- scale h'ight will I, emrployed.

JThe riomaining sections of this chapter may be omitted wi'thout loss of continuity.

.Xi Z
490 RADIO AN~D lRADAR EFFECTS

>~ > m u4)

0 C 0u.) ;l . E -0 C

0-u 0 0ch

0d 0 .0 V 8C

4) j CA

>0 0

0 0 r~0-

.-. 3 - i i ~ 0 C >C U

eq j .~p-wom0m
TECHNICAL. ASPECTS OF RADIO AND RADAR EFFEC'TS 491

14•.124 By setting H in equation to the effects of nuclear explosions on

(10.! 23.1) equal to 4.3 milcs, the result the ionization of the atmosphere.

is 10.126 Attenuation of electromag-

(h3 (netic (and other) signals is commonly

S(h) oe-4 (10.124.1) staled in terms of decibels; thus,

and this expression, with h in miles, will

de used later. If the base of the exponent Attenuation in decibels = 10 log P - U I

is changed from e to 10, where 0U,

e ;-10-• ?, theii where P, is the signa! power (or

p (h) ;- plo0-i,4. 3 x 2.3 .- pl10-h o0 strength) before attenuation and Pot is

that after attenuation. An attenuation of

it follows, the'efore, that in the altitude 10 decibels implies that the signal

range of interest, the density of the at- strength has been reduced to iO-t , 20

mosphere decreases approximately by a decibeis to 10-2, 30 decibels to 10-3,

factor of 10 for every 10 miles increase and so on, of the original strength. A

in altitude. Thus, at an" altitude of 40 decrease of 20 to 40 decibels, depending

miles the air density is abou, 10-4 and at on the uriginal signal power and the

60 miles roughly 10-6 of the sea-level no:se level, will generally result in

density. serious degradation of comn.-unications.

M, a rough guide, it may be taken that

an attenuation of 30 decibels will reduce

ATTENUATION AND REFRACTION 0F substantially the effectiveness of a radio

ELECFROMAGNETIC WAVES or radar system.

10.127 From the theory of" the

10.125 The propagation of electro- propagation of electromagnetic waves

magnetic waves of a given frequency through an ionized mediim, it i's found

through omedium can be described in that the signal attenuation, a, in decibels

terms o• a "complex" index of refrac- per mile of 'ravei path, is given by

tion, consisting of a real part and an

imaginary part. The real part is a phase a = 7.4 >< 104 xl,..

factor which determines the phase shift W2 + v2

and ordinary index of refraction, i.e., decibels pet mile, (10.1'27.1)

the ratio of the pLase velocity of the

electromagnetic waves in a vacuum to where N, is the electron density, i.e.,

that in the given medium. The imagi- m'mber of electrons per cubic centimenary part, on the other hand, is related to ter, v is thl number of collisions per

the attenziation of the waves by absorp- second which an electron makes with

tiov in the medium. From the equations ions, molecules, or atoms, and W is the

of motion of electromagnetic waves, it (angular) frequency of the wave (in reis possible to derive expressions for the dians per second) h follows from

index of refraction and for the attenua- equation (10. 127 1) that if the collision

tion in ap ioaized medium. Appropriate frequency v is small then, for a given

forms of these expressions are given and wave frequency, a will he sma.ll because

discussed below, ',with special referene of ihe v in the numerator. On ihe other

".!A6
492 RADIO AND RADAR EFFECTS

hand, if v is very large, a will again be frequencies greater than -hout lI me

small becau:,e of the p,

2 in the denomi- gahertz, v-2 at an altitude of 40 miles

nator. Thus, the attenuation passes may be neglected in comparison with W2

through a maximum for a particula" in the denominater of equation

value of the electron collision fre- (10.127.1), this equation then reduces

qaency. to

10.128 Since the collision fre- Nv, N

quency is proportional to the deisity of a 7.4xl04 ---A- decibels per mile,

tie air, it will decrease exponentially (10.130.,)

with altitude. It is to be expected,

therefore, that the values of Y f,.- which

attenuation of signals is important so that the attenuation (in decibels) is

would occur only within a relatively approximately proportional to the elecnarrow altitude region. Theoretical tron collision frequency. At 40 miles

studies show that the attenuation of altitude, the latter is roughly 2 X 107

radio and radar signals caused by nu- per second. Upon inserting this value

clear explosions occurs mainly within a for v in equation (10.130.1) and conIG -mile range centered about an altitude verting the wave frequency from radians

of 40 miles. Hence, by confining aiten- per second to megahertz, the result is

tion to the situation in the neighborhoodN

of a 40 rit. altitude, it is possible to a - 4 X 10-2 - decibels per mile,

avoid jomplexities and yet pr.sent a

reasonably accurate picture of dwe effects of the burs; on -lectronaagnct,.; where j is zhe wave frequency iJ mega-

,ionals. hertz, i.e., 10-6w/2T". If the signal beam

W0.129 There aie two exceptions to has an angle of incidence i, referred to

the foregoing generalizations: (i) atten- the vertical, and the ionized region is 10

uation wi.iin or close to the fireball or miles thick, the total attenuation, A, is

debris regions, and (2) righttime atten- N

uation by ionization resulting from A - 0.4 - sec i decibels,(10.130.2)

prompt radiation. In the former case, the

altitude of the region of maximum at- for frequencies greater than about W0

tenuation is goverrned by the altitude and megahertz.

size of the fii,.;ba-l or debris region. In JO.131 The collisiin frequency

the second case, the altitude e'" peak used above is for electron collisions

attenuation is about .5 miles, but since with ieutral particles, since these prethe electron density due to delayed ra- dominate at 40 miles altitude. For elecdiation is dominant at niight after only a tron denisities greater than about I04

few seconds, the prompt ionization can electrons/crn. collisions of electrons

be ignored. The present trreatment wil' with ions cati be important, particularly

therefore,, be mainly concerned with the within a fireball at or above 60 mi!es

10-mile range of the atmosphere cen- altitude, where. the neutral particle dentered at an altitude of 40 miles. sity is low and electron-neutral collision

10. 30 For electromtrgnetic wave frequencies are small, But for attenua-
† . . †. ..† † † † † † † † a†† , W

TECHNiCAL ASPECTS OF RADIO AND RADAR EFFECTS 493

tion of electromagnetic signals in the f is the wave frequency in megahertz:

D-region at some distance from the Upon inserting the cuu`erx:IJ values for

fircball, equation (10.130.2) is applica- e and m, it is found that

ble.

10. 132 For operational HF circuits, - 0.8 N 2

the value of sec i is about 5 undttr n- 4 2

normal conditions. It follows then from

equation (10.130.2) that, for a fre- Since electror densities are riot known

quency of 10 megahertz, a 10-mile thick very accurately, this result may be aplayer with an zlcctron density of about proximated to

1.5 x 103 electrons'cin3 at 40 miles al-

,itude. will pr.oduce 30 decibels of signal n (10!133.2)

attenuation. For a frequency of 30 me-

.gahertz, the same atteimation will result

from an electron density of about 10-134 If an electromagitic wave

L.4 X 104electrons/cm3. These electron crosses a plane interface where the

densities may be taken as indicative of index of refraction changes sharply from

the values required to degrade HF sys- I to n, a beam will be bent by an alnount

tems. Since radars usually operate zt given by the familiar Snell's law, i.e.,

frequencies greater than 30 megahertz

and sec i generally will be less than 5, :>ia i

'Jensities exceeding 10.5 electrons/cm3 sin r

are necc.-sary to cause serious attenuation when the signals pass threugh the where i is the angle of incidence and r

D-region of the ionosphere. the angle of refraction. If the index of

10.133 Consideration will now be refraction is such that n = sin i, then

given to the ptnse aspects of the propa- sin r = 1, i.e., r = 90', and critical

gation of electromagnetic waves reflectior occurs; the refraction is so

through an ionized medium. Provided large that the signal is unable to penethe electron collision frequency, v, is trate 1he medium. The conditiorn for

small in comparison with the wave fre- critical reflection by an ionized redi'Am

quency, w, as has been assumed above, is obtained by setting n in equation

the ordinary (rca;) index of refraction, (10.133.2) equal to sin i; the result obn, is given by tained is

Si rr NO e2 1'2 f 10 -<N sec i

(for critical reflection). (10.134.1)

- 12 e-"m -2 , (10.133.1) For reflection of an electromagnetic signal encountering a given ionized medium, with electron density N,, the frewhere e is mne charge (4.8 x 10-10 quency must be less than that expressed

electrostatic unit) and m is the mass by equation (10.134.1). Alternatively,

(9.1 X 10-28 gram) of the electron, and for reflectioo of a signal of specified

S., . -. ' ,;
494 RADIO \ND RADAR EFFI (S

frequency f. the electron density of the waves can be both attenuated and reionized medium must b. greater than fracted by the ionized medium. The efthat given by this equation.- fect that predorainates depends oi the

10.135 As in § 10.132, sec i may ratio of the electuon density grauient to

be taken to be about 5 for an operational the electron collision frequency. If this

HF system. Hence, for a signal of 5 ratio is large, then the wave will be

megahertz. at the lower end of the band, refracted, but if it is small the main

to ve reflected, the electron density must effect will be attenuation. in most cirexceed 10W clectrons/cm'. For a fre- cumstances associated with a nuclear

quency of 30 megahertz, the minimum explosion, attenuation around 40 miles

density for reflection is 3.6 X 10- elec- altitude predominates. ,t altitudes

trons/cml. These densities are normally above about 60 miles, however, where

attained in the F- and F-reg;,ns of the the collision frequency is small and the

ionosphere, respectively. A change in electron density gradient moderately

the electrun density arising from the large, refraction may be important.

effects; of a nuclear explosion can alter Also, near the fireball but outside the

the altitude at which an electromagnetic absorbing region, refraction of electrowave in reflectcd and can consequertly magnetic waves Lip io high frequencies,

affect communications systems, as seen such as radar signals, is possible

earlier in this chapter. (§ 10,37). Although (he collision fre10.136 Equation (10.134.A) is ap- quency is large, the high electron denplicable only when a nonionized me- sity gradient is here the dominant factor.

diti-a is separated from an ionized one Within the fireball itself, however,

by a sharp boundary at which the change electiomagnetic waves are always

in refractive index, from I to n, occurs strongly absorbed.

over a distance small in comparison to a

wavelleagth at the propagating frequLncy. This condition does not exist

either in the normal ionosphere or after PROMPT RADIAUCTIONS

it has been disturbed by a nuclear detonation. The refractive index does not 10.138 Consider a nuclear explcchange sharply and there is a gradual sion of W kilotons yield and iet k be the

bending of the transmitted wave. In fraction of the yield radiated at a oarticsuch situations, both the electron den- ular energy, i.e., as monochromatic rasity and its gradient deiermine the phase diatior.. For a point source of such radi.

(refraction) effects. ation, assuming negligible scattering

10.137 When the quantity Ne/P is and no reradiation, the energy deposited

sufficiently large, electromagnetic (or absorbed) per unit volume of air, ED,

'The quantity 10-2/vN megahertz or, miore exact[-,, (4nirNtein) radian,i per second, is called the "critical frequency" or "plasma frequency" of ar iou.ized medium, i.e., a plasma. It is the frequency for

which the :ndcx of -efraction of the given medit~m is zero. It is also t•ne 1owest frequency of an

electromagnetic wave that ca- penetrate into the medium, and then oniy for notma! incidence, i.e., for

i=0.

a,,•
TECHNICAL ASPECTS OF RADIO AND RADAR EFFECTS 495

at an "observation" point at a slant pairs, i.e., 3 x I 4 electrons, are prodistance D from the exolosion is duced for each million electron volts of

energy absorbed in air (about 34 elecE kW -it M tron volts are required to produce an ion

-4 - D2 ,epair). Consequently, about 8 x !0.C?

(10.138.1) electrons are produced for each kiloton

of energy deposited in the air. Hence,

where p is the air density at the obser- the number of free electrons per unit

vation altitude, .L,, is the mass (energy) volume, N, is obtained from equation

absorption coeMicient in air of the given (10 138. 1), with W in kilotons, as

radiation,' and M is the penetrationi

mass, i.e., the mass of air per unit area N4. 2.4 X< 101s

bctween the radiation source and the k W - M' M i 0.139. 1

observation point. This equation maybe D2 cm ,0.31

used for all forms of prompt radiation,

using the appropriate value of k given in with p in grams per cubic centimeter, IL,

Table 10.138. The fraction of the en- in square centimeters per gram, M in

ergy radiated as prompt gamma rays is grams per square centimeter, and D in

small and its contribution to the electron miles.

density is generally less than th,ý for 10.140 An expression for Mmay be

other radiations. If the energy deposited obtained in the following manner. Let

in the air is reradiated or if the source Ht (Fig. 10. 140) be the altitude of the

photons or neutrons are scattered and explosion poi.: and H that of the obserfollow a random path before depo3iting vation point whicr. is at a distance D

all their energy, equation (10.138.1) from the burst. Then if El represents

must be modified (§ 10. 142). any position between the explosion and

the observation point, and h is the corTable 10.138 responding altitude, the value of M in

FRACTION OF EXPLOSION ENERGY appropriate units is given by

AS PROMPT RADIATIONS

.f9D

Radiation 4 f p(U)dD'

X rays 0.7

Gamma rays 0.003 D I

Neutrons 0.01 - p(h)dh,

H-Ho J Ho

10.12q Acco'ding to Table 1.45, 1

1y; kilotwn TNT equwvalent of energy is where, in deriving tie second form, the

equal to 2.6 x 1025 million electron curvature of the earth has been negvolts. Furthermore, about 3 x 104 ions lected. !f p(h) is now represented by

'The mass absorption coefficient is similar to the mass attenuation coefficient defined i. § 8. too,

except that it involves the energy absorption coefficient, referred to in the footnote to equation (3.95.!).

. ' :." -* ',. ' ' " + , - *' • . . . . . "†, J
496 RADIO AND RADAR EFFECTS

equation (10.124. 1), it is found that for X-ray photons (of lower energy) for

which the mass absorption coefficient is

M = 6.8 × 10- -D PO appi'c'Iimately inversely proportional to

the cube of the energy. Furthermore, the

(e-H,!4.3 - H14.3 situation is complicated as a resut ofe g crn 2 , energy changes that occur when the

(10.140.1 1 photons are scattered. For neutons, the

highest electron densities eeise from

where D, H, and HI) are in miles and p(, elastic scattering (§ 10.43) and the nein grams -per cubic centimeter; the factor cessity for summing over multiple scat6.8 x 10.1, which is the density scale tering angles makes the calculations

height in centimeters (slightly less than difficult, especially in an (inhomogen4.3 miles), is introduced to obtain the eous) atmosphere of changing Uýensity.

required units (g/cm2) for M. 10.142 Allowance: for the effects of

scattering and of the energy spectrum of

. - /EXPLOSICN the radiation can be made approximately

S, H,7 by modifying equation (10.139.1) to

// /take the form

h N 2.4 X 1018 k A)

H , D ) cm7

OBSERVATION (10.142.1)

POINT

where F (M) is an effective mass absorption coefficient which is a function

of the penetration mass, M. Values of

F(M)/K, where K ;s a normalization

GIROUIN factor that permits F((M) for various

Figure 10. 140. Quanti',es used in defining radiations to be plotted on a single diathe penetration mass (M). gram, are given in Fig. 10. 142. The

values of K tsed are shown in the insert.

10.141 In general, the energy ra- 10.143 The electron d.nsities prodiated fbom a nuclear explosion as duced by the total promnpt radiation

gamma rays and X rays is not mono- (neutrons and X rays) are obtained by

chromatic but covers a range of photon summing the conttibutions of the indienergies. Hence, integration over the vidual radiations as given by the approemergy spectrum is necessary. For the priate forms; of equation (10.,142.1). In

range in which most of the gamma-ray this manner, the ,urves in 1,wig. 10.143

energy is radiated, the mass absorption for electron dersities at a height of 40

coefficient of air, PI.,, can be considered miles as a function of horizontal dis- A

to be constant. But this is not the case tance 6 were derived for a i-megaton 11

6The term "horizontal distance," as used here and later, refers to the distance parallel io the earth's

surface.

___
TECHNICAL ASPECTS OF RADIO AND RADAR EFFECTS 497

11 

G A MMA RAY SX

0-I _ _ _ _NFKUTkONS -

1 I ( (ELASTIC S SCATTERING)

"•" ' BETA

IO-Z• . PARTILLE\S

R0 A__ 0!_AT_1_N

,C4.

10 RA 4 x 10 3

8'T9 Z

GAMMA O.C25

NEUTRON 0.015 L - -I

10-6 -_ 

-o7 -o6 -b" o-'• , • -" -I" o 02 o

167 10 0 ICb 1(510 10 10 10, 10.

PENETRATION MASS, 1.f (GRAMS/CM2

Figure 10.142. Values of F (M) f.:r %Iarious radiation source:;.

explosion at various altitudes. Since the that at low burst altitudes, up to aborit

electron density is proporfional to the 20 iniles, the ionization from pro,..t

energy yield, W. of the weapon, the radiation is relatively small except at

results for other yields can be readily short distiaces, At higher burst alliobtained from Fig. 10. 143. In comput- tudes, not only does the electron density

ing M for this figure, the effects of a (at 40 miles adtitude) for a given horicurved earth and a variable density scale zontal distance increase, but the range

height were included. The calculations foý a given electron density, especially

show that below abow' 40 miles, ion- above 10- electro.s/cm3 , increases

izatioij due to neutrons predominates, markedly. These densities ar. sufficien'

hut for nuclear detonatins at higher to cause blackout of HF systems that use

altitudes the X rays produce essentiall) the sky wave for lo,. -distance propaall the additional elec:rons from prompt gation. However, i will be seen

ionization in the D-region. (§ 10.152) that the blackout woui.- be of

10.144 It is seen from Fig. 10. 143 relatively short duration.

it

'I- ..'*•• . .t... , -- -,- -, • .--•- • -

S-,.'. j
498 RADIO AND RADAR EFrECTS

The curves in Fig. !0. 143 show the Example:

initial electron denmities at 40 miles a!-

titude produced by the prompt radiation Given: A 500 KT detonation at an

from a 1-megaton exploion as a func- altitud&', of (a) 20 miles, (b) 60 miles.

tion of distance, for various burst alti.- Find: In each case, the horizonti

trades. distanrce at ar, altitude of 40 miles at

Scaling. For auy specifier combi- which the initial electron density from

nation of burst height and distance, the prompt radiations is I0-G electrons/cm.1 or

initial electron densiiy at 40 miles "i- more.

tude is directly proportional t& the yield Solution: The corresponding elec- in megatons, i.e.,Sotin Thcorsndgel- tron density for I NIT is

N(W) = VN (I MT), N(W)

where N (I MT) is the value of the N( NT)0.5

initial electron density at 40 miles alti- = 2 x 105 electrons/cm3

iude and the desired distance from a I

MT explosion at the desired altitude, From Fig. 10. the prompt radiaand N( W) is the corresponding initial tion from a I MT exolosion will produce

electron. density for ,. MT. initial eiectro, densities of 2 'x 10-

electrons per cubic centimeter at an altitude of 40 miles

(a) to a horizontal range of about

190 miles, if burst is at an altitude of 20

miles. Answer.

(b) to a hotizointal range of about

550 miles, if burst is at an altitude of 60

miles. Answer.

I4 4

-. ~ -'7 ' - '711 Z7 ,
TECHNICAL. ASPECTS OF RADIO AND RADAR EFFECTS 499

ý11111 1 I ilfili 11'I lll 1 1 I1 

0

- -.-- 1---- A4

0 t

o >

t*I - L4

ý( W

4 L.2

117 ____, o.- 4`

*D 0 0 U0D 

(~V~SN~-313) -JINON~313

&ýWN60 .IN0N80
500 RADIO AND RADAR EFFECTS

RATE OF DISAPPEARANCE OF FREE where S, the .detachinent rate coeffiELECTRONS PRODUCED BY PROMPT cient, is related to the detachment

RADIATION source strength. In the daytime, S is

10.145 Free electrons are removed approximately 0.4 sec-1 above about 35

either by attachment to neutral particles miles altitude. Below about 35 miles the eitherlby atthmoent tox ne l prtiles value of S is uncertain but apparently it

(usually molecular oxygen in the Dý-islwrbseeaodrsfy is lower by severl'a orders of magnitude. region) or by recombination with posm- tive ions. The electron loss by recom- At night, detachment is negligible at

bination is proportional to the number altitudes less than about 50 miles.

densities of electrons, N., and of posi- 10.148 Negative ions formed by attive ions, N+, so that tachment of electrons to molecular c,-

ygen can also react with positive ions to

dN P N N (10.W. 14 ) form neutral molecules. Since the negadt tN ive and positive ion densities affect the

electron density, the ion loss by recomwhere cd is the recombination coeffi- bination must be considered. The rate of

cient. Below an altitude of about 60 milent, Beow appromaltuely o2 a 10-7 t positive ion loss by recombination with miles, e -1 dcis approximately 2 -dcm 3 negative ions is proportional to the

10146 Electron loss by attachment number densities of both ions; thus,

to molecular oxygen is proportional to dN, N N, (10.148.1)

the square of the atmospheric density dt - ( and the number density of elec.trons; thus, where ap, usually known as the mutual

dN neutralization coefficient, is equal to

-"__ = -1p 2 N, (10.146.1) about 3 X 10-8 cm3 sec-' above 30 dt miles. Below 30 miles, a, is .pproxiwhere 13 is an attachment coefficient mately proportional to the atmospheric

appoximatcly equai to 4 X 101.3 cm 6

g- 2 density and is 4 X 10-6 cm.3 sec-I at sea

sec-1. The quantity [.p 2 is often called level.

the attachment rate coefficient, K; it

decreases from 6 × 107 sec-' at sea ELECTRON DENSITIES FROM

level to about 2 X 10-- sec-' at 55 miles PROMPT RADIATIONS

altitude.

10.147 After electrons are attached 10.149 The differential equations

to molecules to form negative ions, they describing the time history of electron

may become detached by solar radiation and ion densities do not have a closedor by collisional processes. The rate of form solution. However, a number of

free electron production by detachment approximations are available, and nuis proportional to the number density of merical solutions have been obtained

negative ions, N_, and the detachment with the aid of computers for particular

source strength, i.e., cases. An approximate solution, which

dtN gives reasonable results for many condt SAT = ,(10.147.1 dt =( 4 ditions, is the so-called "equal.-alpha"

dt_ ___....___ __

- . . . . . . . . . y yI..
TECHNICAL ASPECTS OF RADIO AND RADAR EFFECTS 501

approximation. When ad is taken equal for times more than a few seconds after

to a1,, the electron density, N(t), as a the burst ;n the daytime, and

"function of tine following a pulse of

prompt radiation, can be represented by Nt) at 55 miles

NN (0) _ cm 3 (nighttime) N (0) 1 --2 x 1,0 -7Vf,(0) t

) + aN,(0)t (10.150,.2)

S+Ke-(K + S)t

S + K + K ( 10.149.) for nighttime conditions.

10.151 Calculations of the decay of

electron densities from ionization prowhere N.,(0) is the initial electron den- duced by prompt radiations from a nuusity, given by equation (10.142.1). a is clear detonation have been made with a

an effective recombination coefficient, computer using numerical solutions that

and t is the time after the burst. do not involve the equal-alpha approx10.150 Approximate values of a, imation. The results for daytime condiS, and K in centimeter-gram-second tions at a height of 4.0 miles are shown

units are given in Table 10.150 for an in Fig. 10.151; they are reasonably

altitude of 40 miles in ihe daytime and consistent with equation (10.150.1)

55 miles at night. These are the alti- provided the electron density is appretudes, for day and night, respectively, at ciably larger than the normal value ,i

which maximum attenuation of electro- the ionosphere. Natural ionization

magnetic signals is to be expecied sources must be con•sidered when the

(§ 10.129). Upon inserting the appro- electron density resulting from prompt

priate values into equation (10.149. 1), radiation has decayed to values compathe time history of electron density at rable to those normally existing at an

the altitude of maximum attenuation is altitude of 40 miles.

Fnund to be 10.152 There are two aspects of

N() at 40 miles Fig. 10.151 that are of special interest.

3 First, it is seen that when the initial

N,(0) cm 3 (daytime) electron density, Nf,(0), is greater than

I + 10 7N,,(0)t 107 electrons/cm3, the electron density,

(10.150.1) N,(t), at any time more than about I

.1 4 Table 10.150

APPROXIMATE VALUES OF a, S, and t'• IN CGS UNIrS

40 Miles 55 Miles

Coeflicient (daytime) (nighttime)

.a ILx 2x 10

S 0.4 2 x 10

K 0.8 2 x I'

_ __ _ _.___., ,___ ,,.... _
502 RADIO AND) RA1)AR EFFECTS

The curves in Fig. 10. 151 show the tude layer at 4 horizontal distance of 125

electron density from prompt radiation miles from the burst.

at 40 mile!: a!titude in the daytime as a Solutiot.: From Fig, 10.!43, the

function of timc after burst, for various initial electron density at c horizontal

values of the ;nitial electron de.,sity. distance of 125 miles from a 1 MT

These curves together with those in Fig. e,.plosior. at an altitude of 30 miles is

10.143 can be used to estimate the about 5 x l10 electrons/cm-. From Fig.

electron density at 40 miles altitude in 10. 151, this initial value will have de

the daytime for various combinations of cayed to about l10 electrons/crn3 by 30

explosion yields and burst altitudes. seconds after the burst. By use of equation (10.130.2), the attenuation is

Example: N10-1 A 0.4 N seci = 0.4 -1x 6

Given: A I MT explosion in the l ×6

daytime at an altitude of 3G miles. = 24 decibels. Answer.

Find: Thc one-way attenuation of a Note: The attenuation determined

100-MViHz radar system that would result above is d'le only to prompt radiation.

from D-region ionization at 30 seconds The effect of delayed radiation should

after the burst; the radar beam makes an also be investigated to estimate the

angle of 80 degrees (sec i - 6) with the overall effect on the system (§ 10. 154 et

vertical and intersects the 40 mile alti- seq.).

$

j ____

_ _ _ _ .1
TE(. HNICAL ASPE1- 1- OF RADIO AN~D RADAR EFFECTS 503

10- ' 1 I-- - .-- _ __ __ 10 107 INITIAL ELFCTRON DENSITY -S 5

U)0

o 00

Li

0 2 2 2 0 2 ~ 1 ~ 1 0

0~ -0
504 RADIO AND RADAR EFFECTS

second after the burst (in daytimne) is fission products but including activity

independent of the initial value. This induced by neutrons in the weapon macondition is referred to as a "saturated terial (§ 9.32), is represented by

atmosphere." It is to be expected from + + 0 1 2, (10.154.1)

equation (10.150.1), since when N(0)

is more than 107 and t is at least a few where I, `s the rate of energy emnission at

seconds, the quantity 10- 7 N,(O)t in the t seconds after the detonation and I, is

denominator of the equation is greater the value after 1 second. 7 The total beta

than unit-. Hence, the latter can be and gamma energy emitted is obtained

neglected and equation (10.150.1) re- (approximately) by integrating between

duces to zero time and infinity; thus,

(t) X I 1 10-7 M Total energy 3 x0-t -I

so that the eectron density at time t is I,(1 + 0-'.-dt = 51,

independent of the initial value.

10.153 The other matter of interest 'Ihe fraction of the delayed radiation

is that, regardless of the initial value, energy emited per second at time I is

the electron density in the daytime will then

have decreased to 103 electrons/cm3

within an hour (or so). This fact is

apparent from Fig. 10.151 or it can be 1(1 + t)-.2 = 0.2 (1 + t)-I.2

derived from equation (10.150.1). It 511

follows, therefore, that significant degradation of HF or radar systems as the 10.155 About 7 percent of the fisresult of ionization by prompt radiation sion explosion energy is radiated as dewill nol persist for more than an hour or layed beta particles and gamma rays,

so in the daytime. At night, decay is with approximately half carried by each

faster, as is apparent from equation kind of radiation. Hence, for an explo-

(t0.150.2), and effects on electromag- sion of WF kilotons fis:ion yield,

netic waves of the prompt radiations can roughly 0.007 (1 -t- t-. 2 WF kilotons of

usually be neglected. As will be seen energy per second are radiated by beta

later, the effects of 'he delayed radiation particles and the same amount by

may persist for longer times. gamma rays.

10.156 The rate of production of

RATE OF ELECTRON PRODUCTION ion pairs (and hence of electrons) by

BY DELAYED RADIATIONS delayed gamma rays car be estimated

from an expression similar to that used

10.154 The rate of energy emission to determ. -te the electron density arising

as delayed (beta and gamn..a) radiation from the prompt radiatioi,. Thus, if kW

from the radioaciive residues of a nu- in equatiori (10.142.1) is replaced by clear explosion, consisting mainly of 0.007 (1 +,,)-I.2Wr, the result, assureSFor times that are long in comparison with I second, equation ( 10. 154. 1) reduces io the same fo;rm as

equation (9.147. 1).

i i
TECHNICAL AjPiFCTS OF RADIO AND RADAR EFFECTS 505

ing a point source for the gamma raysi the rep!acement of the area 4,TrD 2 in

(cf. § 10.138), is equation (IC.156.1) by 2A in equwdion

(10.157. 1) and sin q) is required because

q•(t) = 1.7 x 10' of the motion of the beta particles along

p.(H)F(M cm . sec the field lines. The 'unction F(M) is

D2(1 + t1 51 evaluated from Fig. 10.142 for (10.156.1)

M . rM (h) dA

where qv(t) cm- 3sec-l is the electron sin (P H hI 

production rate at time t seconds after

the nuclear detonation, as observed at a 6.8 x 10. 2

slantl distance D miles at an altitude of H sin qp

miles (see Fig. 10.140). The function / H/4.3 - Hc)/4.3

F(M) can be obtained fromFW. 10.142 e -e gc -r,

with Mdefined by an equation similar to \

equation (10.140.1), except that the (10.157.2)

detonation altitude Ho is replaced by the where H. is the debris altitude in milesdebtis altitude HD. in this expression the curvature of the

10.157 The radial motion of the earth is neglected.

bet particles is largely prevented by the 10.158 In order to use equations

geomagnetic field lines. The area of the (10.156.1) and ("0.157.1) it is necesD-region at an altitude of 40 miles sary to know the altitude, H., and rawhere the beta ionization occurs is then dius, R, of the weapon debris. Deterapproximately the same as the area of mination of these quantities requilres an

the debris (Fig. 10.47). If the latter rises understanding of the processes taking

abo,/e 40 miles, roughly half of the place as the debris cloud 'ises and

energy is deposited in the iocal D-region spreads horizontally. The actual procand half at the magnetic conjugate. The esses are very complex, but a simple

total area over which the beta-particle model which parallels the gross features

energy is deposited is thus twice the of the debris motion has been develdebris area. If the debris is assumed to oped. The debris height and radius, as

be uniformly Aistribited over an area A, they change with time, fzr various burst

which may be taken to be 'rrR 2, where R altiticdes as ýý.btained from this model are

is the debris radius, the electron pro- showu in Figs. 10. 158a, b, and c, for

duction rate from ionization due to oeia energy yields of 10 and 100 kilotons and

particles in each D-region is then I megaton, respectively. For interpolation between these yields, W13 scaling

q(0 = 2.1 X 1017 - -l. may be used, at least for the first few 2A(I + t). 2 sin (p minutes after tfi.- explosion. The ex-.

p (H)IF(M) cm- 3 sec- - reme left-hand end of each curve indi-

( 0.157.1) cates the altitude of the explosion and

where ýp is the local magnetic di1> ingle the initial size of the fireball. It should

and A is in square miles. The ch-ange in be noted that when using Figs. 10.158a,

the ntrnerical factor (by 4'rr) arises from b, and c that W is the total energy yield

- . .... . .- *-- --- , . -r.-t--. . . * tr~r-..,--. n,...-- - r___
506 R-IDIO AND RADAR EFFECTS

1000

500

200L

I MIN HOURS]

BURST ALTITUDE * mn * ~ c .

20 F52 0_-

10 __ 10 __ _ _ __ _

3 6

2 ATMOSPHERIC WINO

8.1 02 Q 10 50 20 020 SO10

RADIUS (MILES)

Figure 10. 158a. Fireball/debris altitude and horizontal radius for 10-kiloton explosions at

various altitudes.

of the explosion. For thermonuclear delayed beta particles an~d gamma rays,

weapon'F, the fissinon yield W. in equa- respectively, were obtained in this gentioris ,10,156.), and (10.157.1) is gen. eral manner for an alt~tude of 40 miles,

erally taken to be half of the total yield. where m'iimum attenuation of electromagnetic signals due to ionization froin

ELECRONNSIIES ROMdelayed radiations occurs both during

ELECRON ENSIIES ROMday arnd nipht. In computing the curves,

DELAED RDIATONSan accurate treatment for the energy 10.159 The actual election density, :ipectra of the radiations was used to

NV;(t), arising from the delayed radia- evaluate the rate of formation of dclction.; at a particular location and time trons; remova! rates were calculated

can be calculated by assuming that, along the lines indicated in § 20. 145 el

soon after the detonation, a transient seq., with detailed consideration of all

steady state e,;Osts at any instant. The irniortant loss mechanisms. The values

value of NU!) is then obtaincd by shown in Fig. 10. 159a were computed

equating q,(t) or qy(t) at any time t to the for a magnetic dip angle of 600; howrate of loss of electrons by various re- ever, they provide reasonable estimates

combination and attachment processes. for dip angles between about 450 and

TV.,: curves in Figs. 10. 159a and b, for 750, i.e., for mid-latitudes.

(Text confinut'd on pagc 511.)
TEICH-NICAL ASPECTS OF RADIO AND *iADAR EF-FECTS 507

1000 I

500

200 MIN 5 HOURS

3 I

bcSEC - 5

U) BURST ALTITUOEI

50 (MILES) 5nw3 15 1 3

50mmni m m50

50~in m

5 ~ MIN2

2 SEC 1 E EPNSCN U TO

ATM[ rIERiC WINDS

0.1 0.2 05 1 2 5 Ic, 20 50 ICO 200 500 1000

RAOI US (MILES)

Figure 10. 158b. Fireball/debris altitude and horizontal radius for 100-kiloton explosions at

various altitudes.

100 0 . .... ................ I 

500 GEOMAGNETiC FIELD EFF.CTS, DEBRIS

DISTRIBUTED ALONG iIELO

MIN HOURS

200-

10BORST ALTITUDE SEC t0 - (MILES) \, 0

38 5o 1

50 101I 60IS a

MINM M MEMM I I

5 2

30 M NU EXPANSION DUE 10

2 SCATMOSPHERIC WINOS

11.2j

0.1 0.2 06 1 2 5 10 2V 50 100 200 500 1000 2000

V11, RADIUS (MILES)

Figure 10. t 58c. Fireball/debris altitude and horizontal radius for I -megaton explosions at

various attitudies.

Mro1
508 RADIO AND RADAR EFFECIS

The curves in Figs. 10. 159a and b (a) ýnterpolation of Fig. 10. 15Sc

show the electron densities at 40 miles !wggests that by 5 minutes the debris

altitude due to beta particles (for debris will have reached an altitude (H4) of

above 40 miles) and delayed gamma about 60 miles, ,;th a horizontal radium

rays (for debris .bove 15 miles), re- of about 30 miles. Since the beta parspectively. Only the attenuation result- tides follow the geomagnetic field lines,

ing from the highest electron density, the ionization they cause at an altitude

which may arise from prompt radiation:, of 40 miles (H) will be centered about a

(Figs. 10.143 and 10.151), delayed point that is displaced a distance d horigamma radiation, or beta particles, need zontally from the center of the debris,

iev considered. The densities, and h',nce where d is given (approximately/) by

the attenuations, cannot be addde4 S di- d - ( - H

rectly. Figures 10.158a through c may (60 - 40) tan 60' = 35 miles.

be used to estimate the position and size

of the debris for use with Figs. l0.159a The radial extent of the ionized region

and b. The curves of Fig. 10. 59a (for will be approximately equal to the

beta particles) are for a magnetic dip debris radius (30 miles). Thus, at 5

angle of 600, but they provide "rvdson- minutes after the explosion beta ionizaable estimates for dip angles between tion will not affect a point that is located

about 450 and 7'.- The possible effect of at a horizontal distance of 250 miles

the earth's curvature on Fig. 10.159b from the burst. Hence, at this tiP only

(gamma rays) is obtained from Fig. the ionization caused by delayed gamma

10.162. rays need be considered.

The distance V. from the debris to the

Example: point of interest is about 250 miles and

Givea: A 1 MT explosion during the the time is 300 seconds. Since the total

night at an altitude of 25 miles and a yield is I MT, the fission yield, Wb,

location in the northern hemisphere may be taken to be 500 kilotons; hence,

where the magnetic dip angle is 60'.

Find: The electron density in tC• D- 1)2(l + t)1 (250)2 (301)1.2

region at a horizontal d;,tance of 250

miles north of the buirst point (a) 5 8 x 10-6'

minutes after the explosion. and (b) 2

hours after the explosion. The debris altitude (60 miles) and the

horizontal distance (250 miles) are such Solution: Since it is nighttime, anyin Region I of

promp! ionization will have died away ta t c0.162o

by the times of nterest and can be ig 62, so that Fig. 10. 159b is Sneglected (§ 10. 153). applicable. The electron density due to

ne lce (§* 10 153).. **~ .. ~*~
TECHNICAL ASPECTS OF RADIO AND RADAR EFFECFS 509

IU

z

0

o -O

CDAY

40 i

I 

0

0 0'

I- ? 

I- 

-

LU

I~d 2 -IGHT I I0 

I0"9 5 10"62 5 10F 2 10"6 I0- i 5 loI"? 5 10-5 ' 5 I0-, ? " i0" 4

wr

Figure 10. 159b. Electron density at 40-mile altitude due to delayed gamma rays (for debris

above 15 miles).

SF
510 RADIO AND RADAR kF'||E(CVS

delayed gamma rays is then found to be W, _- 500

10W e!,;ctrons/,zm3⁄4. Answer. A(! + t), 2 T-(250)2 (7201)1 2

(b) At 2 hours after the explosion, the 6 X 10 8

debris will still be at an altitude of about

60 miles, but interpolation of Fig. The electron density due to beta parti10. 158c suggests that it will have spread cles is found from Fig. 10. 159a to be

to a radius of about 250 miles. Since the about 2 X 103 electrons/cml. The eleccenter of the beta ionization will be tron density from the delayed gamma

displaced about 35 miles farther north, rays was estimated above to be 103

the point of interest will be contained electrons/cm.3 at 5 minutes after the exwithin thz beta ionized region.8 At that plosion, and so it will be much less at 2

time, i.e., t 7200 sec, hours. Hence, the ionization dve to the

gamma rays can be neglected, Answer.

•It is assumed that the debris expands uniformly about a stationary center once it has ceased to rise,

Motion of the debris caused by atmospheric winds introduces many uncertainties in the predic:ion of

ionization at times more than a few minutes after the burst.

_ _ _ _

. *.• *- C-C -- ... ,--•-' -"1 z * .. -

S*i~------------~-------
TECHNICAL ASPECTS OF RADIO AND RADAR EFFEC S 511

10.160 The curves in Fig. 10.159a the gamma rays will be largely abfor the electron density resulting from sorbed. For the conditions in Region i

ioniza;ion by delayed *beta particles are of Fig. iO. 162. the straight line from the

based on the assumption that the debris debris (center) to the observation point

has risen above 40 miles. The particle at 40 mniies altitude does not intersect the

energy is then equally distributed be- stc.ping altitude for gamma rays, and

tween the local D-region and the one at the ele.i:tron densities in Fig. 10. 159b

the magnetic conjugate. The electron are applicable. But in Region 2, most of

densities given in the figure are those to the rays will intersect a volume of air

be expected at the 40-mile altitude in below the stopping altitude before

each region. If the debris is below 35 reaching the point of interest. As a result

miles, the delayed beta particles cause of the gamma-ray absorption, the elecessentially no ionization in the D-r4..gion tron densities will be substantially

(§ 10.45); at altitudes of 35 through 40 below those given .,i Fig. 10.159b. In

miles, the ionization in this region is the intermediate (unshaded) region of

intense, but the electron densities are Fig. 10.162, part but not all of the

difficult to cilculate. Because beta par- gamma rays will encounter the stopping

ticles follow the geomagnetic field lines, altitude and the electron densities will

the ionization they productc at any alti- be somewhat lower than in Fig.

tude is not affected by the earth's cur- 10. 159b. When using this figure to devature. Gamma rays, on the other hand, termine the expected effezts of a nuclear

travel in s.raight lines and may be so explosion on a radar system, for examaffected (§ i0.162). ple, a conservative approach would be

10.161 The stopping altitude to, the to assume that the unshaded portion ii

delayed gamma rays is about 15 miles; Fig. 10.162 is part of Region I for the

hence, the results in Fig. 10.15.b are user's radar, but that it is part of Region

applicable onily if the debris rises above 2 for tCe opponent's radar.

this' altitude. The principal source of 10.163 As for prorapt radiations (§

error in !he figure is that the gamma rays 10. 149 et seq.), an approximate solution

are assumed to origiiuate from a point to the problem of calculating election

source at the center of the debris cloud, densities arising from the delayed radiSince the atmospheric absorption of ations, which is consistent with Figs.

gamma rays is negligible above the 10. 159a anti b, can be obtained by using

stopping aititude, t',e straighi-line path the equal alpha approxim,.tion to deterfrom the tebriso the point of interest in raine the loss rate at any instant. The

the D-regon (40 mi!es altitude) can lie result can be written in the form

in any direction, provided it does n-,t t, q(t)

pass through the stopping altitude. Ne(t) -

10.1-2 As a consequence of the S + C"L(_

curv4l.,re of the earth, the path of the S + K + VU(t)

gamma rays, for sufficiently large dis- (10.163.1)

tances, may intersect the stopping alti-

"fude, evei; when the debris rises above where q(t) is either the value for beta

.5 miles. If this occ:urs, the energy of particles from equation (10.157.1), or

;1;

i . ~ tWI.jm 'zi 
512 RAD13 AND RADAil EFFECTS

160L

140

120 /

800........

40

20

0 ?00 400 600 Soo IC0O0 1200

HORIZONTAL 0DWANCE %'MILES)

Figure 10. 162. Effect of earth's ~.urvaturu on delayed gamma-ray ionization ait 410 ini!Zs I altitude.

for gamma rays hiorn equation 10.164 For electron production

(10. 156. 1); the coe.11cients oL, S, and K -.,ates less than 106 electrons cm sec-',

hae hesar-ji;'iance as before. B,- equation (10. 163. 1), with the values of

using the al.eiopriate values of these a, S, and K giv-n in Table 10. 150 for

coefficients for different altitudes, it hzs a-1 altitude of 40 miles in the daytime

been found that the electron densities reduces to

peak around an altitude of 40 miles for

boih daytim.i an.6 nighttiijhe conditions 1Mjt) at 40 miles

for slant distances more than 30 miles -103 -',p(t) CM- 3 (daytime).

from the burst point. This is aiso the

aitiiude foCr th maximum attenuiation of At night, the values of a., S, and K at an

alecti'omnagrietic signals ty the ioiiiza- altitude of 40 miles are 3 x 10-8, 0, and

lion from. delayed radiations (§ 10. 159). 6.8, respectively.. and then

Fo, smaller d'stances from the burst

point, the electron density peaks 'near N()at- 4.9 miles

the altitude of the debris region. q(t) cm -3 (nighttime),
TECHNICAL ASPECTS OF RADIO AND RADAR EFFFCTS 513

for production rates less than about 1O6 for both daytime and nighttime. This

electrons crf: -I sec-. For production result is consistet1 , with Figs. 10. 159a

rates of about ITY (or more) eiectrons and b, in which the curves for day ard

cm-- 3 sec-1, the electron density at 40 night coinc.ide when the circumstances

miles t, given approximately by are such as to lead to high electron

densities. The conditions of applicabilNe(t) at 40 miles ity of these figures, as described in

3 × 103 ývlq(t) cm , § 10.160 et seq., also apply to the ex-

'.ressions given above.

BIBLIOGRAPHY

CnRi's~itii.oS, N. C., "The Argus Experi- on the Artificial Wadiation Belt, 68, 605 et se:q.

went," J. Geophys. Res. 64, 869 (1959). (1963).

CRAIN, C. M., "Decay of Ionization Impulses in KNAPP, W. S.. C. F. Mi.Yfl4, and P. G. FisHER,

the D and E Regions of the Ionosphere," J. "Introduction to the Effccts of Nuclear ExploGeophys. Res., 68, 2167 (1963). sions on Radio and Radar Propagation," GenCRAIN, C. M., "Ionization Loss Rates Below 9(0 eral Electric Co., TEMPO, December 1967,

kim," 1. Geophys. Res. 65, 1117 (1960). DASA-1940.

CRAIN. C. M., and P. TAMARKIN, "A Note on LATTER, R., and R. E. LEiLEvIER, "Detection of

the Cause of Sudden hIoization Anomalies in Ionization Effects froJi- Nulear Explosions in

Regions Remote from High-Altitude Nuclewc Space," J. Geophys. Re.. , 68. 1643 (1963).

IBursts," J. Geophys. Res., 66, 35 (1961). New Zealand Journal of Ge,!ogy and Geophysics,

CUMMACK, C. H., and G. A. M. KING, "Dis- Special Nuclear Explosions iisc,,;,S, 4i8 erseq.

turbances in the Ionospheric F-Regior. Follow- (1962).

ing a Johnston Island Nuclear Explosion," New Proceedings of the IEEE, Special Issue on Noclear

ZealandJ. Geol. and GeopAys., 2, 634 (1959). Test Detection, 53, 1813 et seq. (1965).

DAVIS, K., "Ionospheric Radio Propagation," SAMSON, C. A., "Radio Noise Anomalies in

National Bureau of Standards, Monograph 80, August 1958," J. Geophys. Res., 68, 2719

April 1965. ( 963)

HOFRI IN, H., "United States High-Altiwude Test SKOt.NIK, M. I., "lntr,"duction to Radar Sys--

Experiepces," University of California, Los tems ' McGraw-Hill Book Company, 1962.

Alamos Scientific Laboratory," October 1976, STEIGER, W. R., and S. MATSUSHITA, "PhotoI.A-6405. grapi-: ')f the High-Altitude Nuclear Explosion

Journal oj Geophysical Research, Special Issue TEAK," .1. Ceopvs. Res., 65, 545 (1960).

L ii-- - *~- -. --
CHAPTER XI

THE ELECTROMAGNETIC PULSE AND ITS

EFFECTS

ORIGIN AND NATURE OF THE EMP

INTRODUCTION ing was halted in 1962. Subsequently,

11.01 Explosions of conventional reliance has been placed on underhigh explosives can produce electro- ground testing, analysis of existing at'.

magnetic signals and so the generation nospheric test data, nonnuclear simulaof an electromagnetic pulse (EMP) fron, tion, and t._-'orctical calculations.

a nuclear detonation was expected. Extended cfforts have been made to imHowever, the extent and potentially prove theoretical models and to 6evelop

serious nature of EMP effects were not associated computer codes for predi,'-

realized for several years. Attention tive studies. In addition, simulators

slowly began to focus on EMP as a have been developed which are capable

probable cause of malfunction of elec- of producing reprcsen:ative pulses for

'ronic equipment during atmospheric system coup2ing and responsc studies.

nuclear tests in the early 1950's. In- 11.03 Nuclear explosions of all

duced currents and voltages caused un- types - from underground to high aitiexpected equipment failures and subse- tudes - are accompanied by an EMP,

quent analysis disclosed the role of EMP although the intensity and duration of

in such failures. Finally, around 1960 the pulse and the area over which it is

the possible vulnerability of various ci- effective vary considerably with the lovilian and military electrical and elec- cation uf the burst point. The strongest

tronic systems to EMP was recognized. electric fields are pioduced near the

At about the same time it became ap- burst by explosions at or nea,' the earth's

parent that the EMP could be used in the surface, but for those at high altitudes

long-range detection of nuclear detona- the fields at the earth's surface are strong 4

tions. enough to be of concern for electrican

11.02 For the foregoing reasons, and zlectronic equipment over a very

theoretical and experimental effort3 much larger area.

havc been made to study the EMP and 11.04 The nuclear EMP is a timeits effects. A limited amount of data had varying electromagnetic radiation which

been gathered when abovegrourid test- increases very rapidly to a peak and then

14
ORIGIN AND NATURE OF TH!L EMP 515

decays somewhat more slowly. The ra- hundredth part of a microsecond (§ 1.54

diation has a very broad spectrum of footnote).

frequencies, ranging ftcvn very low to 11.06, If the explosion occurred in a

several hundred megahertz but mainly perfectly homogeneous (cor.stant denin the radiofrequency (long wavelength) sity) atmosphere and the gamma rays

region (Fig. 1.74). Furthermore, the were emitted uniformly in all directions,

wave amplitude (or strength) of the ra- the electric field would be radial and

diatior, varies widely over this fre- spherically symmetric, i.e., it would

quency range. Be3cause the EMP is a have the same strength in all directions

very complex phenomenon dependent outward from the center (Fig. 11.06a).

upon the conditions of the burst, the There would thern be no electromagnetic

descriptions given in this chapter are energy radiated from the ionized deposlargely qualitative and sometimes over- ition region. In practice, however, such

simplified. They should, however, pro- an ideal si.uation does not exist; there is

vide a general indication of the origin inevitably some condition, such as difand possible effects of the EMP. ferences in air density at different levels,

proximity of the earth's surface, the

noauniform configuration of the ex- DEVELOPMENT OF AN ELECTRIC ploding weapon (including auxiliary FIELD

equipment, the case, or the carrying

11.05 The instantaneous tor vehicle), or even variations in the water

prompt) gamma rays emitted in the nu- vapor content of !he air, that will interclkar reactions and these produced by fere with the symmetry of the ionized.

i , witit w,,.'u -CS01- e ,f thW:t burs! o.. ur a! er ne.ar !he

dues or the surrounding medium (Fig. earth's surfact., the departure from

8.14) are basically responsible for the spherical symmetry wiii clearly be conprocesses that give rise to EMP from siderable. In all these circumstances,

bursts in the lower atmosphere. The there is a net vertical electron current

gamma rays interact with air molecules generated within the ionized deposition

and atoms, mainly by the Comptcn ef- region (Fig. I 1.06b). The time-varying

fect (§ 8.89), and produce an ionized current results irn the ieanission of a short

region surrounding the burst point (§ pulse of electromagnetic radiation

8.17). In EMP studies this is called the which is strongest in directions perpen-

"deposition region." The negatively dicular to the current; this is the EMP.

charged elect•ons move outward faster In a high-altitude explosion, the EMP

than the much heavier positively arises in a somewhat different manner,

charged ions and as a result there is as will be seen shortly.

initially a separation of charges. The

region '•: nearer to the burst point has a net NATURE CF THE EMP

positive charge whereas that farther

away has a net negative charge. This 11.07 After reaching its maximum

separation of charges produres an elec- in an extremely short tinre, the electric

tric field which can attain its maximum field strength falls off a~id becomes quite

value in about 10-8 second, i.e., one small in a few tens of microseconds. In
516 THE ELECTROMAGNETIC PULSE AND ITS EFFECTS

RADIAL

ELECTRIC

FIELD

GAMMVA,4 RAYS •.'

DEPOSITION-,

(SOURCE)

REGION

Figure 11.06a. Only a symmetric radial electron field is produced if the ionized deposition

region is spherically symmetric; there is no net eiectron current.

NET

ELECTRON

CURRENT ,2N,

/l'k •\." ),EM

RADIATION

Figure 1 1.06b. Disturbance of symmetry results in a net electron current; a pulse of

electromagnetic radiation is emitted which is sirongest in directions perpendicular to th- net current.

spite of the short duration of the pulse, it collector may thus suffer severe damcarries a considerable amount of energu:, age. The consequences could be serious

especially if the exploding weapon has a for any system that relies on such

yield in the megaton range. As it travels equipment, e.g., commercial electric

away from the burst point at the speed of power geneIration and distribution sys--

light, as, do all electromagnetic waves tems, telecommunications, i.e., radio,

(§ 1.73), the radiation can be collected radar, television, telephone, and teleby metallic and other conductors at a graph systems, and electronic comdistance, just as radio waves are picked puwerm.

up by antennas. The energy of the radi- 11.08 In a Lýude serse, the EMP

ation can then be converted into strong radiations ar- somewhat similar to the

electric currents and high voltages, familiar radio waves, although there are

Electrical and electronic equipment some important differences. Radio

connected to (or associated with) the transmitters are designed io produce
ORIGIN AND NATURE OF THE EMP .517

electromagnetic waves of a particular about them and about air bursts (§ 11 .66

frequency (or wavelength), but the et seq.).

waxes in the EMP have a wide range of

frequencies and amplitudes. Further- EMP IN SURFACE BUIRSTS

more., the strength of the electric fields

associated with the EMP c~n be millions 11.10 The mechanism of EMP forof times greater than in ordinary radio mation is different in explo-,ions at (or

waves. Nevertheles3, in each case, the near) the surface .nd at high altitudes.

energy of electromagnetic waves is col- In a surface burst, those gamm,' r.,,ys

lecred by a suitable antenna (or conduc- that travel in a generally d'wnward ditot) and transferred to attached or adja- rection are readily absorbed in the upper

cent equipment. The energy from the layers of the ground and there ;s cssenEMP is received in such a very short tially no charge separation or electric

time, howevei, that it produces a strong field in this direction. The gamma rays

electric current which could damage the moving outward and upward, ho"',ever,

equipment. An equa! amount of energy produce ionization and charge separaspread over a long period of time, as in tion in the air. Consequently, there is a

conventional radio reception, would net vertical electron current (I ;g.

have no harmful effect. 11 . 10). As a result, the ionized depo,, it11.09 The characteristics of the ion (source) region is stimulated to en it

EMP depend to a great eztent on the much of its energy as an electromagnt -

weapon yield and height of burst. For tic pulse in the radiofrequency spec.

explosions in the atmosphere at altitudes trum.

of a few miles. the deposition region 11.11 Since the ground is a relawill have a radius of about 3 mites, but tively good conductor of electricity, it

i: will increase to roughly 9 miles with provides an alternative path for the

increasing height of the burst point up to electrons to return from the outer part of

attitudes of approximately 19 miles. In the deposition region toward the burst

this altitude range, the difference in air point where the positively charged ions,

density across the vertical dimension of which have been left behind, predomithe deposition region will not be large nate. Electric currents thus flow in the

and so the EMP effect will be moderate. ground and generate strong magnttic

In addition to the EMP arising from air fields iu, the region of the suirface burst

density asymmetries, a short pulse is point.

emitted in a manner similar to that dc- 11.12 The electric field produced in

scribed in § 11.14 for high-altitude a surface burst is very strong but the

bursts. The electric fields produced on radiated field falls off with inrreasing

the ground from air bursts between a distance from the deposition region, at

few miles and about 19 miles altitude first quite rapidly and then somewhat

will be less than those radiated from less so. The potential hazare to electrisurface (or near-surface) and high-alti- cal and electronic equipment from the

tude explosions. These latter two types EMP will thus be greatest within and

of nuclear explosions will be considered near the deposition region which may

briefly here, and more wi!l be said later exiend over a radius around ground zero
518 THE EI.ECTROMA,riN-TIC PULSE. AND I-IS EFFF[CTS

DEPOSITION

(SOURCE)

REGION NET E'.ECTRON

CURR'NT

.,,, \¶e 7 \IEM /\ 

/ / NRADIATION / / '

(NL

I \ /

74

.*.. ~ IGROUND .. ,. . *.-.... . 1*•,-.

,- MAGNETIC

FIELD IN AIR ELLCTRONS

MAGNETIC FIELD RETURN

IN GROUND

Fgurt 11. 10. Schematic representation of the EMP in a surface burst.

of about 2 to S rimes, d&pending cn the sorbed. On the other hand, the gamma

explosion yield. In this area, structures rays emitted from the explosion in a

in which eq'Iipment is housed may suf- generally downward direction will ei;-

fer severe damage, espec-ally fiom counter a region where the atmospheric

high-yield explo:;ions, unless they are density is increasing. Thesz gamma rays

blast resistant. However. the threat to will interact with the air molecules and

electrical and electronic systems from a atoms to form the depotsition (or source)

surface-4urst EMP may extend as far as region for the EMP (Fig. 11. 13). This

the distance at whicb the peak over- roughly circular region may be up to 50

pressure from a I-megaton burst is 2 miles thick in the center, tapering

pounds per square inch, i.e., 8 miles toward the edge, with a mean altitude ef

(see Chapter III). The degree of dam- about 25 to 30 miles. It extends horiage, if any, will depend on the suscep- zontally for great distances which intibility of the equipment Pnd the extent crease with the energy yield and the

of shie.lding (§ 1.33 ctse4'.). height of the burst point (see Figs. 11 .70a dnd b).

EMP WN HIGH-ALTITUDE BURSTS 11.14 In the deposition region th ,

gamma rays produce Compton electrons

11.13 If the nuclear burst is at an by interactions in the air; these electrons

altitude above about 19 miles, the are deflected by the earth's magnetic

gamma rays moving in an upward di- field and ere forced to undergo a turning

rection will enler an atmosphere where motion about the field lines. This motior,

the air density is so low that the rays causes the electrons to be subjected to ,

travel great distances befoic being ab- radial acceleration which results, by a

4
ORIGIN Aj'.;D NATURE OF THE EMP 519

NUCLEAR

E•E>'LOSi ON

GAMMA RAYS .

DEPOgTION (SOURCE) ,EGiON

- EM RADIATION

GROUNDi

ZERO

HORIZON FROM BURST POINT

(TANGENT POINT)

Figure 1 . 13. Schematic representation of the EMP in a high-altitude burst, (The extent of

the deposition region varies with the altitude aivd the yield of the explosion.)

complex mechanism, in the generation 11.15 For an explosion of high

of an EMP that moves down toward the yield at a sufficient altitude, the area

earth. The pulse rises to a peak and then covered by the high-frequency EMP

decreases, both taking place more rap- extends in all directions on the ground

idly than for a surface burst; as a result as far as the lihe-of-sight, i.e., to the

more of the electromagnetic energy ap- horizon, from the burst point (see Fig.

pears hi, the higher frequcn.y range (§ 11. 13). The lower frequencies will con11.63). The strength of the electric field stitute a significant pulse extending even

observed at the surface fi-om a high-al- beyond the horizon. For a nuclear extitude expiosior, is from one-tenth to a plosion at an altitude of 50 miles, for

hundredth of the field within the source example, the affected area on the ground

region from a surface buist. However, would have a radius of roughly 600

in a surface burst the radiated field miles and for an altitude of 100 miles

strength drops off rapidly with distance the ground radios would be about 960

outside this region and is then sinaller miles. For an explosion at 200 miles

than for a high-altitude burst. In the above the center of the (conterminous)

latter case, the radiated .,-Ad does not United States, almost the whole

vary greatly over a large area o, the country, as well as parts of Canada and

ground or in the atmosphere above the Mexico, could be affected by the EMP.

ground. The electric field is influenced Thus, for a high-altitude burst, the

• by the earth's rragnetic fieid, but over damage could conceivably extend to

most of the area affected by the EMP, distances from ground zero at which all

tho electric field strength varies by not other effects, except possibly eye .njury

more than a factor of two for explosions at night (§ 12.79 et seq.), would be

with yields of a few hundred kilotons or negligible. Fui'thermo,'e, because the

more (§ 11.73). radiations travel with the speed of lighl:,

S•.!!row
520 THE ELECTROMAGNETIC PULSE AND ITS EFFECTS

the vhcle area could be affected almost lectoi, the EMP energy can be coupled

simultaneously by the EMP from a sin- in other ways (§ 11.27). For example it

gle high-altitude nuclear explosion, is possible for an electric current to be

induced or for a spark to jump from the

COLLECTION OF EMP ENERGY conductor which collects the EMP energy to an adjacent conductor, not con11.16 For locations that are not nected to the collector, and !hence to a

within or close to the deposition region piece of equipment.

for a surface or air burst, both the 11.17 The manner in which the

amount and rate of EMP energy re- electromagnetic energy is collected

ceived per unit area on or near the from the EMP is usually complex, beground will be small, regardless of the cau3e much depends on the size and

type of nuclear explosion. Hence, for shape of the collector, on its orientation

damage to oz'cur to electrical or elec- with respect to the source of the pulse,

tronic systems, it would usually be nec- and on the frequency spectrum of the

es-ary for the energy to be collected pulse. As a rough general rule, the

over a considerable area by means of a amount of energy collected increases

suitable conductor. In certain systems, with the dimensions of the conductor

however, sufficient energy, mainly from which serves as the collector (or anthe high-frequency components of the t~nna). Typical effective collectors of

EMP, may be collected by small me- EMP energy are given in Table 11.17.

tollic conductors to damage very sensi- Deeply buried cables, pipes, etc,, are

tive components (§ 11.31). The energy generally less effective than overhead

is then delivered from thz collector (an- runs because the gound provides some

tenina) in the form of a t~rong current shielding by absorting the high..

and voltage surge to attached equip- frequency part of the energy (see, howment. Actually, the equipment does not ever, § 11.68).

have to be attached directly to the colTable 11.17

TYPICAL COLLECTORS OF EMP ENERGY

Long ru:is of cable, piping, or conduit

Large antennas, anter';a feed cabics, guy wires, antenna support towers

Overhead power and telephone lines and support towers

Long runs of electrical wiring, conduit, etc., in buildings

Metallic structural components (girders), reinforcing bars, corrugated roof,

expanded meta! lath, inetallic fencing

Ra;lroad trackls

Alurminum aircraft bodies

been studied by means of simulators

SUMMARY OF EMIP DAMAGE AND PRO EcTirON which generate sharp pulses of electromagnetic radiation ( § 11.41 et seq.).

11.18 The sensitivity of various The results are not definitive because the

systems and components ýo the EMP has amount of EMP energy delivered to a

"",V- lit

.. ... , ..
ORIGIN AND NATURE 01 THE EiMP 521

particular component would depend on vent access of the radiation, good

the details of the circuit in which it is grounding to divert the large currents,

connected. Nevertheless, certain gen- surge arrestors similar to those used foeral conclusions seem to be justifiable. lightning protection, and proper wiring

Computers and other equipment haviiig arrangements. Finally, componepts that

solid-state components are particularly are known to be susceptible to damage

sensitive. Since computers are used ex- by sharp pulses of electromagnetic entensively in industry and commerce, in- ergy should be eliminated. A further

cluding electrical distribution and com- discussion of these procedures is given

munications systems, the consequence later in this chapter ( § 11.33 et seq.).

of operational ailure could be very 11.20 Except for locations close to

seriou's. Vacuum-tube equipment (with a surface burst, where other effects

no solid-state components) and low- would dominate in any event, 6'w EMP

current relays, switches, and meters, radiation from a nuclear explosion is

such as are used in alarm and indicator expected to be no more harmful. io peosyriers, are less susceptible The least ple than a flash of lightning at a dissusceptible electrical components are tance. Tests on monkeys and dogs have

motors, transformers, circuit breakers, shown that there are no deleterious efetc., designed for high-voltage applica- fects from pulses administered either

tions. The threat to any component, re- singly or repetitively over a period of

gardless of its susceptibility to opera- scveral mon~hs. However, a person in

tional upset (temporary impairment) or contact with an effective collector of

damage, is increased if it is connected EMP energy, such as a long wire, pipe,

(or coupled) to a large collector. Con- conduit, or other sizable metallic object

vcr,;e!-, the dang r is ddminmshed, if the listed in Table I !17, might receive a

collector is small. Thus, although tran- severe shock.

sistorized circuits are generally sensitive

to the EMP, portable (battery operated) SYSTEM-GENERATED EMP

radios with very short "whip" or ferrite

core antennas are not readily damaged 11.21 In addition to the EMP arisunless they are close to a collector. ing from the interaction of gamma rays

Disconnection of a piece of equipment from a nuclear explosion with the atfrom the electric power main supply will mosphere (or the ground), another type

decrease the energy collected, but this is of electromagnetic pulse, called the

not always feasible because it would "system-generated EMP'' (or

deny use of the equipment. SGEMP), is possible. This term refers

11.19 Various means are possible to the electric field that can be generated

foi protecting or "hardening" equip- by the interaction of nuclear (or ionizment against damage by the EMP. Such ing) radiations, particularly gamma rays

protection is generally difficult for ex- and X rays, with various solid materials

isting systems, but it can be built into present in electronic systems. The efnew systems. Some of the approaches to fects include both forward.- and backhardening which save bee.n pr,-pPsed scatter emission of electrons and exterare the following: metal ,hields to pre- nal and internal -urrent generation.

4pe4gnrain
522 THE ELECTROMAGNETIC PULSE AND ITS EFFECTS

11.22 The system-generated EMP fields 

- about 100,000 to a million

is most important for electronic compo- volts per meter 

- can occur near the

nents in satellites and ballistic systeras, interioi walls. At higher gas pressures,

above the deposition region, which howew'r, the electrons cause substantial

would be exposed directly Ito the nuclear ionization of the gas, e g., air, thereby

radiations from , high-aftitude burst releasing low-energy (secondary) tlecThe system-generated EMP can also be trons. The relatively large number of

significant for surface and modera'e-al- secondary (conduction) electrons form 

a

titude bursts if the system is within the cuirent which tei;ds to cancel the elecdeposition region buw is not subject to tric field, thus enabling the high-energy

damage by other weapons effects. This electrons to move across the cavity more

could possibly occur for surface systems easily.

exposed to a burst of relatively low yield 11.25 The electric fields generated

or for airborne (aircraft) systems and near the walls by direct interactions of

bursts of higher yield. ionizing radiations with the materials in

11.23 The system-generated EMP an eletronic system can induce electric

ohenomenon is actually very complex, currents in components, cables, ground

but in simple terms it may be considered wires, etc. Large currents and voltages,

to be produced in the following manner. capable of causing damage or disrupThe solid material in an electronic sys- tion, can be developed just as with the

tern or even in the shielding designed to external EMP. Because of the complexprotect the system froin the external ity of the interactions that lead to the

EMP contains atoms which are heavier system-generated EMP, the effects are

than those present in the air. Conse- difficult to predict and they are usually

quently, interaction with gamma rays determined by exposute to radiaii,'n

and high-energy X rays w.11 produce pulses from a device designed to simuelectrons by both the Compton and late the EMP radiation from a nuclear

photoelectric effects ( § 8.89 et seq.). explosion (§ 11.42).

These electrons can, in turn, interact

with thz- solid material to release more EMP EXPERIENCE IN HIGH-ALTITUDE

electrons, called secondary electrons, TESTS

by ionization. Such electrons as are 

4

produced, directly or indirectly, close to 11.26 The reality of damage to

and on both faces of the solid material :Iectrical and electronic equipment by

ahid have a velocity component perpen- the EMP has beeii established in various

diculai to the surrace, will be emitted nuclear tests and by the use of EMP

from the surface of the material. As a simulators. A number of failures in ciresult, an electric field is generated near vilian electrical systems were reported

the surface. There arc other effects, but to have been caused by the EMP from

they need not be considered here. the high-altitude test explosions con11.24 If the component has a cavity durted in the Johnston Island a"ea of the

(or space) in wHich the gas pressure is Pacific Ocean in 1962. One of the best

very low, less than about 10-3 milli- authenticated cases was the simultameter of mercury, very high electric neous failure of 3(0 strings (series-con-
EMP DAMAGE AND "aoWrECTION 523

nected loops) of stree! lights at various "hundreds" of burglar alarms in Honlocations on the Hawaiian island of olulu began ringing and that many cir-

)P,,l at a distanc, of some 800 miles cuit breakers in power lines were

frtn ,round zero. The failures occurred opened. These occurrences probably rein devices called "fuses" which are sulted from the coupling of EMP energy

installed across the secondaries of to the lines to which the equipment was

transformers serving these strings; the connected and not to failure of the depurpose of the fuses is to prevent dam- vices themselves. No serious damage

age to the lighting system by sudden occurred since these items are among

current surges. Similar fuses -asociated the least susceptible to the EMP (§

with individual steet lights were not 11.18).

affected. it was a',c- reported that

EMP DAMAGE AND PROTECTION'

COUPLING OF EMP ENERGY scribed, the conductor forms an alterna11.27 There are 4bree basic modes tive conducting path and shares the curof coupling of the EMP energy with a rent with the medium.

conducting system; they are electric in- 11.28 if the EMP wave impinges

duction, magnetic induction, and resis- upon the ground, a part of the energy

tive coupling (sometimes referred to as pulse is transmitted through the airdirect charge deposition). In electric in- ground surface whereas the remainder is

duct'on a current is induced in a con- reflt-cted. An aboveground collector,

ductor by the component of the electric such as an overhead power line or a

field in the direction of the conductor radic antenna tower, can then receive

length. Magnetic induction occurs in energy from both the direct al.d reconductors that form a closed loop; the flected pulses. The net effect will decomponent of the magretic field pee- pend on the degree of overlap between

pzndicular to the plane of the loop the two pulses. The EMP transmitted

causes current to flow in the loop. The into the ground can cause a current to

form of the loop is immaterial and any flow in an underground conductor either

connenied conductors, even the rein- by induction or by resistive coupling.

forcing bers in concrete, can constitute a 11.29 The coupling of electromagloop in this respect. Resistive coupling netic energy to a conductor is particucan occur whemi a conductor is immersed larly efficient when the maximum diin a conducting medium, such as ion- mension is about the same size as the

ized air, salt water, or the ground. If a wavelength of the radiation. The concurrent is induced in the medium by one ductor is then said to be resonant, or to

of the coupling modes already de- behave as an antenna, for the frequency

'This section (§§ 11.27 through 11.59) is of particular interest to electrical and electronic engineers.

. i~ * 9$f 
524 THE ELECTROMAGNETIC' PULSE AND ITS EFFECTS

corresponding to this wavelength. Since component and also on the nature of the

EMP has a broad spectrum of frequen- semiconductor materials and fabrication

cies, only a portion of this spectrum wili details of a solid-state device. In gencouple most efficiently into 1 specific eral, however, the components listed in

conducter cenfiguration. Thus, a partic.. Table 1 1.31 are given in order of deular collection system of interest must creasing sensitivity to damage by a

be examined with regard to its overall sharp pulse of electromagnetic energy.

configuration as well as to the compo- Tests with EMP simulators have shown

nent configuration. Most practical col- that a very short pulse of about l0-1

lcctor systems, such as those listed irt joule may be sufficient to damage- a

Table 11.17, are complex and the de- microwave semiconductor diode,

termination of the amount of EMP en. roughly 5 X 10-2 joule will damage an

ergy collected presents a very difficult audio transistor, but 1 joule would be

problem. Both computer methods and required for vacuum tube damage. Sysexperimental simulation are hK:ing used tems using vacuum tubes only would

to help provide a solution. thvs be much less sensitive to the EMP

than those employing solid-state comCOMPONENT AND SYSTEM DAMAGE ponents. The minimum energy required

to damage a microammeter or a low11.30 Degradation of electrical and current relay is abmt the same as for

electronic system performance as a rie- audio transistors.

suit of exposure to the EMP may consist

of functional damage or operational Table 11.31

upset. Functional damage is a catastrophic failure that is permanent; examples ELECTRONIC COMPONENTS IN ORDER

are burnout of a device or component,

such as a fuse or a transistor, and in- Microwave semiconductor diodes

ability of a component or subrsystem to Field-effect transistors

execute its entire range of functions. Radiofrequency trnnsistors

Operational upset is a temporary im- Silicon-contro!kd rectifiers

pairment which may deny use of a piece Audio transistors

Power rectifier semiconductor diodes

of equipment from a fraction of a second Vacuum tubes

to several hours. Change of state in

switches and in flip-flop circuits are ex- 11.32 As seen earlier, the EMP

amples of operational upset. The threat to a particular system, subsystem,

amount of EMP energy required to or component is largely determined by

cause operational upset is generally a the nature of the collector (antenna). A

few orders of magnitude smaller than sensitive system associated with a poor

for functional daimage. collector may suffer less damage than a

11.31 Some electronic compoients system of lower sensitivity attached to a

are very sensitive to functional damage more efficicat collector. Provided the

(burnout) by the EMP. The actual sen- EMP energy collectors are similar in all

sitivity will often depend on the charac- cases, electrical and electkonic systems

teristics of the circuit containitig the may be classified in the manner shown

._ _ _ __ _ _ __ _ _
EMP DAMAGE AND PF"OrECTION 525

in Ta?-5e 11.32. However, the amount of may require consideration of ',perational

energy collected is not always a suffi- upset and damage mechanisms iw iddicient criterion for damage. For exair..le, tion to the energy collected.

an EMP surge can sometimes serve as a

trigger mechanism by produciag arci'-g ROTECTIVE M.EASURES

or a change of state which, in turn,

allows the- normal operat-lag voltage to 11.33 A general approach to the

cause damage to a piece of equipml~ent. examination of a system with regard to

Thus, analysis of sensitivity to EMP its EMP vulnerabillity might include the

Table 11.32

DEGREES OF SUSCEPTIBILIT/ TO THE EMP

Most Susceptible

Low-power, high-speed digital computer, either transistorized or vacuum tube ýoptrationzl

upset)

Systems employing transistors or semicorductor rectifiers (either silicon or selenium).

Computers atid power supplies

Semiconductor components terminating long cable runs, especially bctwccn sites

A!arm systems

Intercom sysiem

Life-support system controls

Some telephene equipment which i3 partially trmnsistori'ed

Trmnsistorized receivers anc, transm"tters

Transistorived 60 to 400 :ps converters

Transi.torized process control. systems

Power system controls and communication links

Less Susceptible

Vacuum-tube equipment that does not include semiconductoi rectifiers:

Transmitters Intercom systems

Receivers Teletypc--telephone

Alarm systems Power Supplies Equipment employing low-current switches, relays, meters:

Alarms Panel indicators and status

Life-support systems boards

Power system control Process controls

A panels

Hazardous equipment containing:

Detonators Explosive mixtwes

Squibs Rocket fuels

Pyrotechnical devices

Other:

Long power caje runs employing dielectric insulation

Equipment associated with high-energy stcrage capacitors

Inductors

Least Susceptible

I-igh-voltage 60 cps equipment:

Transformers, motors Rotary converters

Lamps (filament) Heav'-duty relays,

Heaters circuit breakers

Air-ins,.lta;ed power cable runs

", ... ..
526 THI: F.LCTROMAGNETIC PULSE ANt) 11 S EFFE,7TS

following steps. First, information con- nents or small subsystems ,s ge:ierally

ce'ning the system components and de- not practical because of the complexity

vices is collected. The information is cf the task. Good shielding practice may

categorized into physical zones based on include independent zone shields, sevsusceptibiiity and worst-case exposure eral thin shields rather than one thick

for these items. It must be born2 in mind one, and contikwous joints The shield

in this connection that energy col'.ected should not be used as a ground or return

in one part of a system may De coupled conductor, and sensitive equipment

directly or indirectly (by induction) to should be kept away from shield

other parts. By usiug objective criteria, corners. Apertures in shields should be

problem areaG are identified, analyzed, avoided as far as possible' doors should

and tested. S.'itable changes a-e made as be covered with metal sheet so that

necessary to cocrect deficiencies, and when close! they form a continuous part

the modified system is examiiaed and of the whole shield, and ventilation

tested. The approach may be followed openings, which cannot be, closed,

on proposed systems or on those already should be protected by special types of

existing, but experience indicates that sc;eens or weveguides. In order not to

the cost of retrofitting EMP protection jeopardize il e effectiveness of the

may often be prohibitive. Consequently, shielding, p,,cautions must be taken in

it is desirable to consider the vulnera- connection with penetrations of the

bility of the system early durir.g the housing by conductors, such as pipes,

dc, ign stage. conduits, and metal-sheathed cables

11.34 A few of the practices that (§ 11.59).

may be employed to harden a system 1 i.36 Recommendations for circuit

-,ainst EMP damage are described !ayout include 0he use of common

below. The discussion is intended to ground points, twisted cable pairs. sysprovide a general indication of the tech- tem and intrasystem wiring in "tree"

niques rather than a comprehensive format (radial spikes), avoiding loop

treatment of what is a h-ghly technical layouts and coupling to other circuits,

and specialized area. Some of the use of conduit or cope trays, and

methods of hardening against the EMP shielded isolated transformers. The

threat are shielding, proper circuit avoidaaice of ground return in cable

layout, satisfactory grounding, and shields is also recommended. Some

various protective devices. If thes procedures carry over from communimeasures do not appear to be adequate, cations and power engineering whereas

it may be advisable to design equipnent othet s do not.

with vacuum tubes rather than solid- 11.37 F'rom the viewpoint of EMP

state components, if this is compatible protection, cable desigla iepresents an

with the intended use ef the eqipnent. extension of both shielding alld circuit

11.35 A so-called "electromagne- practices. Deeply buried (more dian 3

* tic" shield consists ot a continuous feet underground) cables, shield layer

metal, e g., steel, soft iron, or copper. t;ontinuity at splices, and good junction

sheet surroanding the system to be pro- box contacts are desirable. Ordinary

tected. Shielding of iidividual compo- braid shielding should ae avoided.

i;

,-i
EMP DAMAGE AND PROTECTION 527

Compromises are often made in this con-controlled vectifier clamps, and

area in the interest of economy, but they other such items are built into circuit

may prove t-,, be unsatisfactory. boards or cabinet entry panels.

11.38 Good grounding practices 11.40 Few of the devices men

will aid in decreasing the susceptibility tioned above %re by themselves suffiof a system to damage by the EMP. A cicnt as a complete solution to a specific "ground" is commonly thought of as a problem because each has some limitapart of a circuit that has a relatively low tion in speed of response, voltage ratimpedance to the local earth surface. A ing, power dissipation capacity. or reset

particular ground arrangement that sa- time. Hence, most satisfactory protectisfies this definition rma,,,, however, not tive devices are hybrids. For example, a

be optimum and may b,. 7. orse than no band-pass filter may be used preceding a

ground for EMP pmot-culon. In general, lightning arrester. Tihe filter tends to

a ground can be ide.1-ified as the chassis stretch out the rise time of the EMP,

of an electronic circt.•t, the "low" side thus providing sufficient time for the

of an antenna system, a common bus, or arrester to become operative. In general,

a metai rod driven into the earth. The a hybrid protection device must be delast depends critically on local soil con- signed specially for each application.

ditions (conductivity), and it may result

in resistively coupled currents in the TESTING

ground circuit. A good starting point for 11.41 Because of the complexities

EMP protection is to provide a single of the EMP response, sole reliance canpoint ground for a circuit cluster, not be placed on predictions based on

usually at the lowest impedance element analysis. Testing is essential to verify

Sthe biggest piece of the system that is analysis of devices, components, and

electrically immersed in the earth, e.g., complete systems early in the design

the water supply system. stage. 'resting also is the only known

11.39 Various protective devices method that ,;an be used to reveJl unexmay be used to supplement the measures pzcted effects. These may include coudescribed ab ye. These are related to pling or interaction modes or weakthe nriýans commonly employed io pro- nesses that were overlooked during the

tect radio and TV transmission artennas design. In some simple systems, nonfrom lightning strokes and power lines linear interaction effects can be analyzed

from current surges. Examples are ar- numerically, but as a general rule tea. .ng I iresters, spark gapý,, band-pass filters, is necessary to reveal them..As a result

amplitude limiters, circuit breakers, and of the test, many of the original apS fuses. Typically, the protective device proximations can be refined for future

would be found in the "EMP room" at analysis, and the data can improve the

the cable entrance to an underground analytic capability for more complex

f, installation, in aircraft antenna feeds, in problems. Testing also locates weak or

telephone lines, and at power entry susceptible points in components or

panels for shielded rooms. On a smaller systems early enough for economic imscale, diodes, nonlinear resistors, sili provement. After the iLtprovements,

' "I
528 THE ELECTROMAGNETIC PULSE AND ITS EFFECTS

testing confirms that the performance is the time domain. Both types of tests

brought up to standard. A complete should be considered for a complete

system should be t.ested to verify that it analysis.

has been hardencd to the desired level; 11.44 Large-scale simulators are

subsequent periodic testing will indicate required for the final test of large sysif any degradation has resulted from tems. The two principal kinds of large

environmental or human factors. simulators are metallic . ir,'ctures that

11.42 Since the cessation o;" atmos- guide an electromagnetic wave past A

pheric weapons tests, heavy reliance has lest object, and antennas that radiate an

been placed on simulation to test the electromagnetic field to the object. Each

EMP hardness of systems. The classes type of simulator may use either pulse

of EMP tests include: (1) low-level cur- generators (time domain) or CW signal

rent mapping; (2) high-level current in- generators (frequency domain). Pulse

jection; (3) high-level electromagnetic generators themselves can be either

fields. Low-level current mapping high-level single shot or low-level reshould be used at the beginnii.g of any petitive.

test program. With the system power 11.45 The essential elements of a

turned off, the magnitudes and signa- guided-wave or transmission-lir:e simutures on internal cables are determined lator include a pulser, a transition secin a low-level field. This provides an tion, working volume, and a terminainsight into the work that must follow. tion. An electromagnetic wave of

After indicated improvements are made, suitable amplitude and wave shape is

a high-level current can be injected di- generated by the pulser. This wave is

rectly into the system with the system guided by a tapered section of transmispower on to explore for nonlinearit~es. sion line (the transition section) from the

and to uncover initial indications of small cross-sectional dimension of the

system effects. If subsystems maifunc- pulser output to the working voiume.

tion, it may be desirable to conduct The working volume, where the test

extensive subsystem tests in the labora- object is located, should be large

tory. Finally, test in a high-level elec- enoug>" to provide a certain degree of

tromagnetic field is essential. field uniformity over the object. This

11.43 The type of excitation must condition is satisfied if the volume of the

be defined in any type of test. The two test object is about one-third (or less)

principal choices are: (I) waveform that of the working volume, depending

simulations, which provide time- on the degree of field perturbation that is

domain data, and (2) continuous wave acceptable. The termination region pre-

(CW) signals, which provide fre- vents the reflection of the guided wave

quency-domain data. If the intent is to back into the test volume; it consists of a

match a system analysis in the fre- transition section that guides the inci- M

quency domain to measured system re- dent wave to a geometrically small response, CW signals may be the more sistive load whose impedance is equal to

suitable. If the tet.t results were being the characteristic impedance of the

compared 'o known electronic thresh- transmission line structure.

old.,, it is frequently necessary to test in 11.46 The basic types of radiating

L~ _ - __
!MP DAMAE(, ANt) PROTF'I-TION 529

simulators are long wire, biconical di- EMP AND ELECTRIC POWER

po'.e, or conical monopole. The !ong SYSTEMS

wire is usually a long dipole oriented 11.49 Some indication of the pcssiparallel to the earth's surface. It is sup- ble threat of tht- EMP to commercial

ported above the ground by noncon- electric power system 1ray be obtained

ducting poles with high-voltage insula- by considering the effects of lightning

tors. The two arms of the dipole are strokes end switching surges. In power

symmetric about the center and con- systems, protection against lightning is

structed from sections of lightweight achieved by means of over-head

cylindrical conductor, such as irrigation "ground" wires and lightning arresters

pipe. Pipe sections decrease in diameter of various types. By providing an ef

with increasing distance from the iective shunt, an overhead ground can

center, and resistors are placed between di2vert most of the lightning surge from

the pipe sections to shape the current the phase conductors. Such grounding,

wave and to reduce resonances. The two however, would afford only partial proarms of the dipole are oppositely tection from the EMP. Furthermore, alcharged, and when the voltage across though there are some similarities bethe spark gap at the dipole center tween the consequences of lightning and

reaches the breakdown voltage, the gap those of the EMP, there are differences

begins conducting and a wave front in the nature of the current (or voltage)

propagates away from the gap. pulse which make the ligHtning arres'ers

'1.47 Conical and biconical an- in common use largely ineffective for

tennas use pulsers, such as Marx gener- the EMP.

ators or CW transmitters, instead of re- 11.50 The general manner of the

lying on the discharge of static surface growth and decay of the current induced

charges. The antennas consist of light- by the EMP from a high-altitude burst in

weight conducting surfaces or wire an overhead transmission line is indigrids, cated by the calculated curve in Fig.

11.48 Electromagnetic scale mod- 11.50. The details of the curve will vary

eling may sometimes be an important with the conditions, but the typical feaalternative to full-scale testing of a sys- lures of the current pulse are as shown: a

tem. Because of the difficulty in intro- very rapid rise tj a peak current of

ducing minute openings or poor bonds several thousand amperes in a fraction

into models, and since these often con- of a microsecond followed by a decay

trol interior fields, the usefulness of lasting up to a millisecond for a long

modeling ordinarily is limited to the transmission line. The current surge in

measurement of external fields, volt- an overhead power line caused by a

ages, and currents. Once these param- lightning stroke increases to a maximum

eters are known for a complex structure, more slowly and persists for a longer

perhaps having cable runs, analysis can time than for the EMP. As a xesul1,

often provide internal field quantities of older conventional lightning arresters

interest, are less effective for the EMP from

.. t
530 THE ELECTROMAGNET!C PULSE AND ITS EFFECTS

12

0

I.-

E

z

Lji

0

Figuae 11.50. Typical form of the current pulse induiced by the EMP from a high-altiude

nuclear explosion in a loog overhead power line. (The actual currents and

times will depend to some extent on the conditions.)

hiAgil.-altitude explosions than for light- protection, the surge voltages on overning, Modern lightning arresters, how- head power lines produced by the EMP

* ever, can piovide protection against could cause insulator flashover, particuT EIMP in many applications and hybrid larly on circuits of medium and low

* arrester-3 (§ 11 .40) are expccted to e votge. (The components of high-volteven better. age tranlsmission systems should be able

11.51 In the absence of adequatc to withstand the EMP surge voliages.) If
EMP DAMAGE AND PROTECTION 531

flashovers occur in the event of a high- EMP AND RADIO STATIONS

altitude burst many would be experi. 11.54 Unless brought in underenced over a large area. Such simulta- ground and properly protected, power

neous multiple flfhovers could Yead to and telephone lines could introducc

system instability, substantial amounts of energy into radio

11.52 Switching surges occur when (and TV) stations. A major collecto; of

power lines are energized or de-cnei- this energy, however, would be the

gized. In systems of moderate and low transmitting (or receiviig) antennas

voltage such surges can cause breakers since they are specially designed for the

in thu switching circuit to operate er- transmission and reception of electroroneously, but the effect of the EMP is magnetic energy in the radiofrequency

uncertain because the current rise in a region. The energy collected from the

switching surge is even slower than for EMP would L e mainly at the frequencics

lightning. In extra-high-voltage (EHV) in the vicinity of the antenna design

lines, i.e., 500 kilovolts or more, frequency.

switching surges are accompanied by a 11.55 Antenna masts (or towers)

rapidly increasing radiated electromag- are freqtvently struck by lightning and

netic field similar to that of the EMP. spark gaps are installed at the base of the

The currents induced in control and tower to protect the station equipment.

communications cables are sufficient to But the gaps in common use, like those

cause damage or malfunction in asso- in power lines, are not very effective

ciated equipment. The information ob- against the EMP. Actually, when an

tained in connection with the develop- antenna is struck by lightning, the supment of protective measures required for porting guy wires, rather than the spark

EHV switching stations should be ap- gaps, serve to carry most of the ligiftplicable to EMP protection. ning current to the ground. Although the

11.53 There is a growing move- guy wires have insulitors along their

ment in the electric power industry to length, arcing occvrs across them

substitute semiconductoi' devices for thereby providing continuity for the

vacuum tubes in control and communi- current. This flashover of the insulators

K cations circuits. Solid-state components would not, however, provide protection

are, however, particularly sensitive to against the EMP. In fact, the guy wires

the EMP. Even a small amount of en- would then serve as additional collectors

ergy received from the pulse could re- of the EMP energy by induction.

sult in erroneous operation or temporary 11.56 In spite of protective devices,

failure. Computers used for automatic both direct and indirect, damage to radio

load control would be particularly sen- stations by lightning is not rare. The

sitive and a small amount of EMP en- mosi commonly damaged component is

ergy, insufficient to cause permanent the capacitor in the matching network at

damage, could result in faulty operation the base of the antenna; it gt.nerally

o" temporary failure. Special attention is suffers dielectric failure. Capacitors and

thus required in the protection of such inductors n the phasor circuit are also

equipment. subject lo dacz.age. It is expected that

IR
532 THE ELECTROMAGNETIC PULSE AND ITS EFFECTS

high-voltage capacitors would be sensi- limited protection against the EMP untive to damage by the EMP. Such dam- less suitably modified. Steps are being

age could result in chorting of the an.. taken to improve the ability of the longtenna feed line to the ground across the distance telephone network in the

capacitor, thus precluding transmission United States to w ithstar.d the EMP as

until the capacitor is replaced. Experi- well as the other effects of a nuclear

ence with lightning suggests that there explosion.

may also be damage to coaxial trzns- 11.59 In a prnperly "hardened"

mission lines from dielectric flashover. system, coaxial cai-fles are buried unSolid-state components, which are now derground and so also are the main and

in common use in radio stations, would, auxiliary repeater or switching centers.

of course, be susceptible to damage by In the main (repealer and switching)

the EMP and would need to be pro- stations, the buildinig is completely entected. closed in a metal I'MP shield. Metal

11.57 Radio transmitting stations flashing surrounds each metallic line,

empioy various means to prevent inter- e.g., pipe, corduit, )r sheathed cable,

ference from their own signals. These entering or leaving th., building, and the

include shielding of audio wiring and flashing is bonded to he line and to the

components with low-level signals, sin- shield. Where this is iot possible, progle-point grounding, and the avoidance tectors or filters are ust d to minimize the

of loops. Such practices would be useful damnage potential of •he EMP surge.

in decreasing the EMP threat. Inside the building, ci'nnecting cables

are kept short and ire generally in

EMP AND TELEPHONE SYSTEMS straight runs. An emr gency source of

11.58 Some of the equipment in power is available to pc (imit operation to

telephone systems may be susceptible to contihue in the evern of a failure (or

damage from the EMP energy collected disconnection) of the c( mwercial p•ower

by power supply lines and by the sub- supply. The auxiliary (repeater) stascriber and trunk lines that carry the tions, which are also tndergrur4d, do

signals. Various lightning arresting de- not have exterior shield ng but the elecvices are commonly used for overhead tronic equipment is pr, itected by steel

telephone lines, but they may provide cases

THEORY OF THE EMP2

DEVELOPMENT OF THE RADIAL explosion are such that, n air, Compton

ELECTRIC FIELD scattering is the dominant photon in11.60 The energies of the prompt teractikn (see Fig. 8.97b). The scan!ered

gamma rAys accompanying a nuclear photon frequently retairs sufficient en2The remainder of this chapter may bc .mittcl withow.t loss of continuity.

j.. I
THEORY OF THE EMP 533

ergy to permit it to repeat the Compton. saturation sooner and is somewhat

process. Although scattering is scme- stronger than at points farther away.

what random, the free electrons pro.- 11.62 In a perfect!y homogeneous

duced (and the scattered photons) iend, medium, with uniform emission of

on the average, to travel in the radial gamma rays in all directions, the radial

direction away from the burst point. The electric field would be sphericafly symnet movement of the electrons consti- metrical. The electric field will be cuntutes an electron current, referred to as fined to the region of charge separation

the Cornpton current. The prompt and no energy will be radiated away. In

gamma-ray pulse increases rapidly to a a short time, recombination of charges

peak value in about 10-8 second or so, in the ionized medtum occurs and the

and the Compton current varies with Jectric field strength in all radial directime in a silnilai manner, tions decreases within a few microse11.61 When the electrons are conds. The energy of the gamma rays

driven radially outward by the flux of deposited in the ionized sphere is then

gamma rays, the atoms and molecule,, degradeA into thermal radiation (heat).

from which they have been removed, If the symmetry of the ionized sphere is

i.e., the positive ions, travel outward disturbed, however, nonradial oscillamore slowly This results in a partial tions will be initiated and energy will be

separation of charges and a radial elec- emitted as a pulse of electromagnetic

tric field. The lower energy (secondary) radiation much of which is in the radioelectrons generated by collisions of the frequency region of the spectrum.

Compton electrons are then driveni back Since, in practice, there is inevitably

by the field toward the rosit've charges. some disturbance of the spherical symConsequently, a reverse electron current metry ir a nuclear explosion, all such

is produced and it increases as the field explosions are accompanied by a rastrength increases. This is called the diated EMP, the strength of which de-

"conduction current" because, for a pends on the circumstances.

given field strength, itf magnitude is

detcrmined by the electrical conductiv- GENERAL CHARACTERISTICS OF THE

ity of the ionized medium. The conduc- EMP

tivity depends on the extent of ionization which itself results from the 11.63 The radiation in the EMP

Compton effect; hence the conductivity covrs a wide range of frequencies with

of the medium will increase as the the maximum determined by the rise

Compton current increases. Thus, as the time of the Compton current. This is

radial field grows in strL-igth so also typically of the order of 10-1 second and

does the conduction current. The con- the maximum frequency for the mechaduction current flows in such a direction nisni described above is then roughly

as to oppose this electric field; hence at a 108 cycles per second, i.e., 108 hertz or

certain tirme, the field will cease to in- i10) megahertz. Most of the radiation

crease. The electric field is then said to will, however, be emitted at lower frebe "saturated." At points near tht quencies in the radiofrequency range.

burst, the radial electric field reaches The rise time is generally somewhat

",W ,''•
534 THE t-I.F.CTROMAGNETRI( PULSE Al, .) ITS EFFECTS

shorter for high-altitude bursts than for ure intermediate between medium-altisurface and medium-altitude bursts: tude and surface bursts. At burst altihence, the EMP spectrum in high-alti- tudes below about 1.2 miles, the ratude bursts tends toward higher fre- diated pulse has the general

quencies than in bursts of the other characteristics of that from a surface

types. burst.

11.64 The prompt gamma rays

from a nuclear explosion carry, on the MEDIUM-ALTITUDE AIR BURSTS

average, about 0.3 percent of the explosion energy (Table 10.138) and only 11.66 In an air burst at medium

a fraction of this. on the order of ap- altitude, the density of the air is someproximately 10 2 for a high-altitude what greater in the downward than '11

burst and 10 1 for a surface burst, is the upward direction. The diiference in

r•,diated in the EMP. For a l-megaton density is not large, although it inexplosion at high altitude, the total en- creases with the radius of the deposition

ergy release is 4.2 X 1022 ergs and the (or source) region, i.e , with increasing

amount that is radiated as the EMIP is altitude. The frequency of Compton

roughly 1018 ergs or 101, joule-;. Al- collisions and the ionization of the air

though this energy is distributed over a will vary in the same manner as the air

very large area, it is po:ssible for a col- density. As a result of the asymmetry,

lector to pick up something on the order an electron current is produced with a

of I joule (or so) of EMP energy. The net component in the upward direction,

fact that a small fraction of a joule, since the symmetry is not affected in the

received as an extremely short pulse, azimuthal (radial horizontal) direction.

could produce either permanent or tem- The electron current pulse initiates

porary degridation of electronic de- oscillations in the ionized air and energy

vices, shows that the EMP threat is a is emitted as a short pulse of electroserious one. magnetic radiation. The EMP covers a

11.65 Although all nuclear bursts wide range of frequencies and wave

are probtibly associated with the EMP to amplitudes, but much of the energy is in

some degree, it is convenient to con- the low-frequency radio range. In addisider thi'ec more-or-less distinct (or ex- tion, a high-frequency pulse of short

treme) types of explosions from the duration is radiated as a result of the

EMP standpo;nt. These are air bursts at turning of the Compton electronis by the

medium altitudes, surface bursts, and earth's magnetic field (§ 11.71).

bursts at high altitudes. Medium-alti- 11.67 The magnitude of the EMP

tude bursts are those below about 19 field radiated from en air burst will demiles in which the deposition region pend upon the weapon yield, the height

does not touch the earth's surface. The of burst (whica influences the as~mradius of the sphere ranges roughly from metry due to the atmospheric density

3 to 9 miles, increasing with thie Sursfi gradienw), and asymmetries introduced '

altitide. The EMP characteristics of air by the weapon (including auxiliary

bursts at ýower altitudes, in which the equipment, the case, or the carrying 4

dcposition region d,)es touch the earth, vehicle). At Foints ou:side the deposit-
THEORY OF THE EMP 535

ion region, for the lower-frequency ihe air ard there is a net electron current

EMP arising from differences in air with a strong component in the upward

density., the radiated electric field E(t) at direction. Further, the conducting

any specified time t as observed at a ground provides an effective return path

distance R from the burst point is given for the electrons with the result that

by current loops are formed. That is, elecR trons travel outward from the burst in

E(t) = 0- Et) sin 0, the air, then return toward the burst

R(11.67.1) point through the higher conductivity

ground. These current loops generate

where R0 is the radius of the deposition very large azimuthal magnetic fields that

region, E0(t) is the radiated field strength run clockwise around the burst point

at the distance R0 , i.e., at the beginning (looking down on the ground) in the

of the radiating region, at the time t, and deposition region, c~pecially close to

0 is the angle between the vertical and a the ground (Fig. I .10). At points very

line joining the observation point to the near the burst, the air is highly ionized

burst point. It follows from equation and its conductivity exceeds the ground

(11.67.1) that , as stated in § 11.06, the conductivity. The tendency for the conEMP field strength is greatest in direc- duction current to shift to the ground is

tions perpendicular to the (vertical) therefore. reduced, and the magnetic

electron current. Values of E0 (t) and R( fields in the ground and in the air are

are determined by computer calculations decreased correspondingly.

for specific situations; Eo(t) is com- 11.69 Large electric and magnetic

monly from a few tens to a few hundred fields arc developed in the ground which

volts per meter and R0 is from about 3 to contribute to the EMP, in addition to the

9 miles (§ 11.09). The interaction of the fields arising from the deposition region.

gamma rays with air falls off roughly As a result of the number of variables

exponentially wilh distance; hence, the that can affect the magnitude and shape

deposition region does not have a pre- of the fields, it is not possible to describe

cise boundary, but R0 is taken as the them in a simple manner. The peak

distance that encloses a volume in which radiated fields at the boundary of the

the conductivity is 10-7 mho per meter deposition region are ten to a hundred

or greater. dines stronger in a direction along the

earth than for a similar air burst. The

SURFACE BURSTS variation with distance of the peak radiated electric field atong the earth's

11.68 In a contact surface burst, the surface is given by

presence of the ground introduces a

strong additional asymmetry. Compared E = E0 , (11.69.1)

with air, the ground is a very good R

absorber of neutrons and gamma rays where E0 is the peak radiated field at the

and a good conductor of electricity, radius R0 of the deposition region and, E

Therefore, the deposition region con- is the peak field at the surface distance R

sists approximately of a hemisphere in from the burst point. For observation

R
536 [HE- E. ,E CTR010A GN FTI C PUJI S F AN!1) 1 TS E 1:FE (TS

KAILES

90 100 200 300 400 5( 600 700 800

70

E 40 1~30

4 U HOB 50 km 1-106 100km H08:Ž00Ikm HB0

0 (31 miles) (62 miles) (124 miles) (186 miles) 202

0 200 400 c00 800 1000 1200 1400

DISTANCE PARAL.LEL TO SURFACE ( krr.)

Figure 11. 70a. Deposition regions for 1-PAT explosions at alhtudes of 31, 62, 124. and 186

miles.

MILES

100 200 300 400 5Q0 600 700 800 90 1~-----~-----~-----~

80 IO1MNT -50

E 70

zt60H0=30 m4

W

C0 50 16mls

F- 40- lOB'50km HOB 100 km HIOB -200 km _j

00

0 200 400 600 800 1000 1200 1400

DISTANCE PARALLEL TO 5ýURVACE Ckmn

Figure 11 .70b. Deposition- regic its for Il0-Mi' explosions at altitudes of 3 1, 62, 124, 186

miles.

points above the surface the peak ra- earth's surface from ground zero. The

diated field tails off rapidly with in- curves were computed from the esticreasing distance. As stated in § 11. 12, mated gamma-ray emissions from the

Ro is roughly 2 to 5 miles, depending or explosions and the known absorption

the explosion yield;, E0 may be several coefficients of the air at various densities

kilovolts per meter. (or altitudes). At small grourid distances, i.e., immediately below the

HIGH-ALTITUDE BURSTS burst, the deposition region is thicker

than at larger distarce because rhe

11.70 The thickness and extent of gamma-ray intensity decreases with

half of the deposition region fer bu.-sts distance from the burst point. Since the

of I and 10 megatons yield, respec- gamma rays pass thro-ugh air of increastively, for various heights of burst ing density as they travel toward the

(HOB) are shown in Figs. 11 .70a aind b. gr')und, most are absorbed in a layer

The abscissas are distances in the at- between altitudes of roughly 40 and 10

mosphere measured parallel to the miles.
THEORY OF THE EMP 537

11.71 Unless they happen to be Table 11.72

ejected along the liiaes of :he geomag-.

netic field, the Compton electrons re- GROUND DISTANCE TO TANGENT POINT

suiting from the interaction of the

gamma-ray photons with the air mole- Burst Altitude Tangent Distance

cules and aroms in the deposition region 1miles (miles)

wili be forced to follow curved paths

along the field lines.3 In doing so they 62 695

93 850

are subjected to a radial acceleration and 124 980

the ensemble of turning electrons. 186 1,195

whose density varies with time, emits 249 1,370

electromagnetic radiations which add 311 I.520

coherently. The EMP produced ini this

manner from a high-altitude burst-and its amplitude) at the earth's surface from

also to some extent from an air burst-is a high-altitude burst will depend upon

in a higher frequency range than the the eplosion yield, the height of burst,

EMP arising from local asymmetries in the location of the observer, and the

moderate-altitude and surface bursts (§ orientation with respect to the geomag11.63). netic field. As a general rule, however,

11.72 The curves in Figs. 11.70a the field strength may be expected to be

and b indicate the dirnf-nsions of ihe tens ot kilovolts per meter over most of

deposition (source) region, but they do the area receiving the EMP radiation.

not show the extent of coverage on (or Figure 11.73 shows computed contours

near) the earth's surface. The EMP does for Ek,,, the maximum peak electric

not radiate solely in a direction dowt, field, and various fractions of Ea., for

from the source region; it also radiates burst altitudes between roughly 60 and

from the edges and at angles other than 320 miles, assuming a yield of a few

vertical beneath this region. Thus, the hundred kilotons or more. The diseffect at the earth's surface of the tances, measured along the earth's surhigher-frequency EMP extends to the face, are shown in terms rf the height of

horizon (or tangent point on the surface burst. The spatial distr.,; ution of the

as viewed from the btirst). The lower EMP electric field depends on the geofrequencies, however, will extend even magnetic field and so varies with the

beyond the horizon because these elec- latitude; the results in the figures apply

tromagnetic waves can follow the generally for ground zero between about

earth's curvature (cf. § 10.92). Table 30' and 60O north latitude. South of the

11.72 gives the distances along the sut- geomagnetic equator the directions inface from ground zero to the tangent dicating magnetic inorth and east i~a the

point for several burst heights. figure would become south and west,

11.73 The peak electric field (and respectively. It is evident from Fig.

'At higher altitudes, when the atmospheric density is much less and coilisions with air ,,torr and

molecules are less frequent, continued turning of the electrons (beta particles) about the field lines leads

t, to the helical motion referred to in §§ 2.143. 10.27.

":. . --,•,, , . .-.-.. . ........... ..... . .. .. . ....---- . --- I- -": - . -. .... .- . . . -, .
538 THE ELECTROMAGNETIC PULSE AND ITS EFFECTS

0.5 E Max 0.5 E m(,x //

GROUND DISTANCE GROUND DISTANCE

TO TANGENT POINT TO TANGENT POINT

MAGNETIC NORTH

i

-IX 1108

S\GRO U N 1

0,75 E max 0.5 Ema i X HOB ZERO/

0.5 Emx I,

GROUND DISTANCE

0.7 5 E max

Figure 11.73. Variations in peak electric fields for locations on the earth's surface for burst 4

altitudes between 60 and 320 miles and for ground zero between 30' and 600

north latitude. The data are applicable for yields of a few hundred kilotons; or

more.
[HEORY OF THE EMP 539

1 1.73 that over most of the area affected be a point of zero field strength ir the

by the FMP the electric field strength on center of this region where the Compton

the gro;-id would exced 0.5E.max For electrons would move directly along the

y'e!ds of less than a few xlundred kilo- held lines without turning about them,

tons, this wot:id not necessaiy b, true but other mechanisms, such as oscillabecause the field strength at the earth's tions within the deposition region, will

tangent could be substantially less than produce a weak EMP at the earth's sur0.5 E-,1 •. face. The other variations in the field

strength at larger gretind ranges are due

11.74 The reason why Fig. 11.73 to differences in the slant range from the

doet, not apply at altitudes above about explosion.

320 miles is that at such altitudes the 11.76 The contours in Fig. 11.73

tangcnt range rapidly becomes less than apply to geomagnetic dip angles of

four times !he height of burst. The dis- roughly 500 to 70'. Although E ,,, would

tance scale in the figure. in terms of the probably not vary greatly with the burst

HOB, then ceases to have an)y meaning. latitude, the spatial distribution of the

For height' of burst above 320 miles, a peak field strength would change with

set of contours similar to those in Fig. the dip angle. At larger dip angles, i.e..

11.73 can be plotted in terms of frac- at higher latitudes than about 600, the

tions of the tangent distance. contours for Ema and 0.75 Ek. would

11.75 The spatial variations of tend more and more to ,.ncircle ground

EMP field strength arise primarily from zero. Over the magnetic pole (dip angle

the orientation and dip angle of the 90'), the contours would be expected

geomagnetic field, and geometric fac- theoretically to consist of a series of

tois related to the distance fiom the circles surrounding g:ound zero, with

explosion to the observation point. The the field having a value of zero at ground

area of low field strength slightly to the z-ro. At lower dip angles, i.e., at latinorth of ground zero in Fig. 11.73 is tudes less than about 30', the tendency

caused by the dip ia the geomagnetic for the contours to become less circular

field lines with reference to the horizon- and to spread out, as in Fig. 11.73,

tal direction. Theoretically, there should would be expected to increase.

BIBLIOGRAPHY

BLOCK. R., et a!., "EMP Seal Evaluation," *"Electromagnetic Pulse Probtems in Civilian

Physics international Ci.. San Leandro, Cali- Power and Communications," Summary of a

fornia. January 1971. seminar held at Oak Ridge National Laboratory,

BRIDGES, J. E.. D. A. MILLER, and A. R. August 1969, sponsored by the U.S. Atomic

VALENT!NO, "EMP Directory for Shelter De- Energy Commission and the Department of

sign," Illinois Institute of Technology Research Defense/Office of Ci',il Defense.

Institute, Chicago, Illinois, April 1968. "Elec'romagnetic Pulse Sensor and Simulation

*BRIDGES, 3. E., and J. WEYER, "EMP Threat Notes, Volumes 1-10," Air Force Weapons

and Countermeasures for Civil Defense Sys- Laboratory, April 1967 through 1972, AFWL

tems," Illinois Institute of Technology Re- EMP 1-1 through 1-10.

search institute, Chicago, ll!inoi3, Novcntber -EM!7

1 Proection fot Emergency Operating

1968. Cc.:ors,-" Department of Defrnse/Offle of

,.I:,••
540 THE ELECTROMAGNETIC PUL.SE AND ITS EFFECTS

Civil Defense, May 1971, TR-61-A. tr~cal Standards Division 2412, Sandie, Labora.

"EMP Protective Systems," Department of De- tory, Albuquerque, New Mexico, November

fense/Office of CiNvil Defense, Novemiber 197 1, 1967.

TR-6 I1-B. MINDEL, I. N., Progrurn Coordinator, "DNA

"EMP Protection for AM Radir' Broadcast Sta- EMP Awareness Course Notes," 2nd ed., Iliitiois," Department of Defenre/Office of Civil nois Institute of Technology R4-5search Institute,

Defense, May 1972, TR-61--C. Chicago, Illinois, August 1973, DNA 2772T

Foss, J. W., and R. W. MAYO, "Operation *NELSON, D. B., "Effects of Nuclear EMP on

Survival," Bell Laboratories Record, January AM Broadcast Statiokis in the Emergency

1969, page 11. Bzoadcast System.," Oak Ridge National LaboGILINSKY, VI., arid G. 'ý'E'LES, "The Develop- ratory, July 1971,. ORIVL-TM-2830.

ment of a Radioj Signal from a Nuclear Explo- NELSON, D. B., "EM? Impact on U.S. Desion in the Atrnosplteor," J. Geophys. Res., 73, fenses," Survive, 2, No. 6, 2 (1969).

405 (1968). NELSON, D. B., "A Program to Counter Effects

HIRSCH, F. G., and A. BRL2'.:Z-., -At.ýence of of Nuclear EMP in Commercial Power SysElectromagnetic Pulse Effects on Mcnkeyt- Rnd tems," Oak Ridge National Laboratory, OcDogs," J. Ocrupational Mfedicine, 14, 380 tober 1972, ORNL-TM-3552.

(1972). RICKETTS, L. W., et at., "EMP Fadiation and

KARZAS, W. J, and R. LATTER, "Detecti-rn of Protective Techniques." Wiley-Interscience,

Fiectromagnetic Radiation from Nuclear Ex- 1976.

plosions in Space," Phys. Rev. 137, Bl:S69 *SARGis, D. A., et al., "Late Time Source for

(i465). Close-In FMP," Science Applications, La

LE~iiOX, C. R., "Experimental R~esult- of Test- Jolla, California, August 1972, DNA 3064F,

irg Resistors Under Pulse Conditions," Elec- SAI-72 .556-L--J.

",These documents muay be purchased from the Nationial Technical information Service, Department of

Commerce, Springfield, Virginia 22161.
CIHAPTER XH1

BIOiLOGICAL EFFECTS

•NTRODUCTION

TYPES OF INJURIES ries due to a nuclear explosion is exceptionally high. Most of these are, flash

12.01 The three main types of burns caused by direct exposure to the

physical effects associated with a nu- pulse of thermal radiation, although inclear explosion, namely, blast and dividuals trapped by spreading fires may

shock, thermal radiation, and nuclear be subjected to flame burns. Ir, addition,

radiation, each have the potentiality for persons in buildings or tunnels close to

causing death and injury to exposed ground zero may be burned by hot gases

persons. Blast injuries may bz. direct or and dust entering the structure even

indirect; the former are caused by the though they are shielded adequately

high air pressure and the latter by mis- from direct or scattered thermal radiasi!es and by displacement of the body. tion. Finally, there are potential harmful

For a given overpressure, a nuclear de- effects of the nuclear radiations on the

vice is more effective in producing body. These represent a source of cadirect blast injuries than is a conven- sualties entirely new to warfare.

tional, high-explosive weapon because, 12.03 A nuclear explosion in the air

as will be seen, the human body is or near the ground will inevitably be

sensitive to the duration of the pressure accompanied by damage and destruction

pulse and this is relatively long in a of buildings, by blast, shock, and fire,

nuclear explosion unless the yield is over v considerable area. Consequently,

much less than 1 kiloton. On the whole, a correspondingly larger number cf perindirect blast injuries, especially those sonal casualties is to be expected.

caused by missiles such as glass, wood, However, the actual number, as well as

debris, etc., are similar for nuclear and their distribution among the different

conventional weapons. Howe',zr, be- kinds of injuries mentioned above, will

cause of its longer duration, the blast be greatly dependent upon circurnwave from a nuclear explosion produces stances. As a general rule, for bursts of

missile and displacement injuries at a given type, e.g., air, surface, or submuch lower overpressures than does a surface, the range of each of the major

chemical explosion, immediate effects-blast, thermal radi12.02 The frequency of burn inju- ation, and initial nucleai' radiation-in541
542 BIOLOGICAL EFFECTS

creases with the explosive yield of the and debris are sucked up into the radioweapon. But the relative importance of active cloud the hazard from the residual

the various effects does not remain the nuclear radiation in the early fallout insame. The initial nuclea' radiation, for creases. For an underground burst at a

example, is much more significant ii moderate depth, the injuries from blast

comparison with blast and thermal radi- and from thermal and initial nucdear

ation for nuclear explosions of low en- radiations would be mud& less than from

ergy yield than it is for those of high an air burst or even from a surface burst

yield. In other words, although the total of the same yield. On the other hand,

number of casualties will increase with the effects of ground shock and the dethe energy of the explosion, under sim- layed nuclear radiation hazard would be

ilar circumstances, the percentage of greatly increased. In the case of a deep

injuries due to initial nuclear radiation (completely contained) underground

may be expected to decrease whereas burst, casualties would result only from

the proportions of blast and thermal in- ground shock.

juries will increase. 12.06 Apart from the explosion

12.04 All other things, including yield and burst conditions, local enexpo'ure conditions, being the same, vironmentl circumstances can be a sigthe number and distribution of casualties nificant factor in the casualty potential

of various kinds for a nuclear explosion of a nuclear weapon. Conditions of terof given yield will be determintd by the rain and weather can influence the injutype of burst. Moreover, for an air ries caused by blast and by thermal

burst, the height of burst will have an radiation. Structures may have a.1 imimportant influence. With other factors portant, although variable, effect. For

constant, there is an optimum height of example, the shielding in ordinary

burst which maximizes the range on the houses may markedly reduce the range

ground for a given overpressure in the over which significant casualties from

blast wave (§ 3.73). This optimum flash burns can occur. This is particuheight differs for each yield and for each larly the case for heavier structures exvalue of the overpressure. Similarly, tending below as well as above ground;

thcre are particular heights of burst, persons properly located in such buildusually different from that for blast ings could be protected from blast and

damage, which maximize the ranges for initial nuclear radiations as well as from

either thermal radiation Gr the initial thermal radiations. On the other hand,

nuclear radiation. It is evident, there- in certain buildings the frequency of

fore, that considerable variations are indirect blast injuries may be greatly

possible both in the number and in the increased by the presence of large

nature of the injuries associated with an numbers of missiles.

air burst. 12.07 As regards direct injuries re12.05 The effects of a surface or of sulting from the overpressure of the air

a shallow subsurface burst will not be in the blast wave, the effects of a stucgreatly :Jifferent from those accompany- ture are also quite variable. In some

ing a low air burst. However, as in- situations it is known that the magnitude

creasing amounts of contaminated earth of the peak overpressure inside a strucS.1

">.?1
INTRODUCTION 543

ture can be appreciably less than the sions. Almost any kind of nuclear exfree-field (open terrain) value. On the plosion in a populated area, except perother hand, there is a possibility that, as haps one deep under the surface, would

a result of reflection at walis, etc., the be accompanied by a large number of

air overpressure in the interior of a deaths and injuries in a short interval of

building may be increased twofold or time, but the actual number of casualties

more, depending on the geometry in- and their distribution between blast (and

volved (see Chapter IV). There will also shock), thermal, and nuclear radiation

be changes in wind velocity inside effects could vary markedly with the

structures, so that the magnitudes may circumstances.

differ markedly from those existing in 12.09 The data in Table 12.09 are

the free field as the blast wave spreads the best available estimates I for civilian

outward from the burst point. Never- casualties resulting from all effects of

theless, provided people do not lean the explosions over Hiroshima and Naagainst the walls or sit or lie on the gasaki. The population estimates are

floor, there is generally a lower proba- only for civilians within the affectea

bility of injury from direct overpressure area in each city and do not include an

effects inside a structure than at equiva- unknown number of military personnel.

lent distances on the outside. This re- Three zones, representing different disqults from alterations in the pattern of tances from ground zero, are considthe overpressure wave upon entering the ered: the first is a circular area of 0.b

structure. mile radius about ground zero, the second is a ring from 0.6 to 1.6 miles from

JAPANESE CASUALTIES ground zero, and the third is from 1.6 to

3.1 miles from ground zero. In each

12.08 The only direct information case there is given the -total population

concerning human casualties resulting in a particular zone, the pop,".ation

from a nuclear explosion is that obtained density, i.e., number per square mile,

following the air bursts over Japan and and the numbers of killed and injured, in

this will be used as the basis for much of that zone. Also included are the total

the discussion presented here. It should population "at risk"' in the city, the

be pointed out, however, that the Japa- average population density, and the total

nese experience applies only to the par- numbers of killed and injured. The

ticular heights of burst and yields of the standardized casualty rates are values

weapons exploded over Hiros.,ima and calculated by proportion on the basis of

Nagasaki (§ 2.24), and to the weather, a population density of one person per

terrain, and other conditionG existing at 1,000 square feet (or about 28,000 per

the times and locations of the explo- square mile) of vulnerable area.

'Comi.'rued from data in A. W. Oughterson and S. Warren (Editors), "Medical Effects of the Atomic

Bomb in Japan," McCraw-Hill Book Co., Inc., Chapter 4, 1956. For further information, see also

"Medical Effects of the Atomic Bomb," Report of the Joint Commission for the Investigation of thc

Effects of •he Atomic '3omb in Japan. Office of the Air Surgeon NP-3041; "Medical Report on Atomic

Bomb Effects," T.ie Me4ical Section, Special Committee for the Investigation of the Effects of the

Atomic Bomb, National Research Council of Japan, 1953; and the U.S. Strategic Bombing Survey.

"The Eff-cts of Atomic Bombs on Hiroshima and Nagasaki," 1946.

• I.
544 BIOLOGICAL [-FFECTS

Table 12.09

CASUALTIES AT HIIP.OSHIMA AND NAGASAKI

Density

Zone Population (per square mile) Killed Injured

Hiroshima

0 to 0,6 mile 31,200 25,800 26.700 3,000

0.6 to 1.6 miles 144,800 22,700 39,690 53,00

1.6 to 3. miles 80,300 3,500 1,700 20,000

Totals 256,300 8,500 68,000 76,000

Standardized Casualty Rate: 261,000 (Vulnerable area 9.36 square miles).

Nagasaki

0 to 0.6 mile 30,900 25,500 27,300 1,900

0.6 to 1.6 miles 27,700 4,400 9,5W() 8.100

1.6 to 3.1 miles 115,200 5,100 1.300 11,000

Totals 173,800 5,800 38,000 21,000

Standardized Casualty Rate: 195,000 (Vulnerable area 7.01 square miles).

12.10 It is important to note that, area and degree of destruction are

although the average population densi- greatly increased. Second, because of

ties in Hiroshima and Nagasaki were the high energy yields, the dura.ion of

8,500 and 5,800 per square mile, re- the overpressure (and winds) associated

spectively, densities of over 25,000 per with the blast wave, for a given peak

square mile existed in areas close to overpressure, is so long that injuries

ground zero. For comparison, the aver- occur at overpressures which would not

age population density for the five be effective in a 'chemical explosion.

boroughs of New York City, based on Third, the proportion of the explosive

the 1970 census, is about 24,700 per energy released as thermal radiation is

square mile and for Manhattan alone it very much greater fo0 a nuclear weapon;

is 68,600 per sqnare mile. The popula- hence there is a considerably larger intion density for the latter borough during cidence of flash burns. Finally, nuclear

the working day is, of course, much radiation injuries, which are completely

higher. The ten next largest U.S. cities absent from conventional explosions,

have average population densities rang- add to the casualties.

ing from 14,900 to 3,000 persons per 12.12 The data in the table also

square mile. show that more than 80 percent of the

12.11 The numbers in Table 12.09 population within 0.6 mile (31 10 feet)

serve to emphasize the high casualty from ground zero were casualties, In

potential of nuclear weapons. There are this area the blast wave energy, thermal

several reasons for this situation. In the exposure, and initial nuclear rad;atiol,,

first place, the explosive energy yield is were each sufficient to cause serious

very much larger than is possible with injury or death. Beyond about 1.6

conventional weapons, so that both the miles, however, the chances of survival
INTRODUCTION 545

were very greatly improved. Between would have been wearing more exten0.6 and 1.6 miles from ground zero a sive clothing. Both the number of peolarger proportion of the population pie and individual skin areas exposed to

would probably have survived if imme- thermal radiation wouid then have been

diate medical attention had been avail- greatly reduced and there vo'!ld have

able. Although the particular distances bccn fewer casualties from flash burns.

mentioned apply to the yield and condi- 12.15 None of the es.imnatcs of the

tions of the Japanese explosions, it is to causes of death bear directly on the

be expected quite generally that close to incidence of those blast effects which

ground zero the casualty rate will be result in early death, e.g., air (emboli)

high, but it will drop sharply beyond a in the arteries, lung damage, and heart

certain distance which scales with the injury which tolerate very little post-inenergy yield of the explosion, jury activity, various bone fractures,

severing of major blood vesselk by sharp

CAUSES OF FATALITIES missiles, violent impact, and others.

One of the difficulties in assessing the

12.13 There is no exact information importance of injuries of various types

available concerning the rclative signi- lies in the fact that many people who

ficance of blast, burn, and nuclear radi- suffered fatal blast injuries were also

aLion injuries as a source of fatalities in burned. As seen earlier, within about

the nuclear bombings of Japan. It has half a mile of ground zero in the Japabeen estimated that some 50 percent of ness explosions, either blast, burns, or

the deaths were caused by burns of one nuclear radiation injury alone was lethal

kind or another, but this figure is only a in numerous instances.

rough estimate. Close to two-thirds of 12.16 As a result of various cirthose who died at Hiroshima during the cumstances, however, not everyone

first day after the explosion were re- within a radius of half a mile was killed

ported to have been badly burned. In immediately. Among those who suraddition, there were many deaths from vived the first few days after the explkburns during the first week. sions at Hiroshima and I'agasaki, a

12.14 The high incidence of flash number died two or more weeks later

burns caused by thermal radiation with symptoms which were ascribed to

among both fatalities and survivors in nuclear radiation injuries (see § 12.113

Japan was urndoubtedly related to the et seq.). These were believed to reprelight and scanty clothing being worn, sent from 5 to 15 percent of the total

because of the warm summer weather fatalities. A rough estimate indicates

prevailing at the time of the attacks. If that about 30 percent of those who died

there had been an appreciable cloud at Hiroshima had received lethal doses

cover or haze below the burst peint, the of nuclear radiation, although this was

thermal radiation would have bcen at- not always the imnmediate cause of

tenuated somewhat and the frequency of death.

flash burns would have been muck less. 12.17 The death rate in Japan was

Had the weathei been cold, fewer peo- greatest among individuals who were in

ple would have been outdoors and they the open at the time of the explosions; it

,,/
546 BIOLOGICAL EFFECTS

was less for pe:sons in residential has been obtained of the distribution of

,wood-frame and plaster) structures and the three types of injuries among those

least of all for those in concrete build- who became casualties but survived the

ings. These fccts emphasize the influ- nuclear attacks. The results are qt'•ted

ence of circumstances of exposure on in Table 12.18; the totals add up to more

the casualties produced by a nuclear than 100 percent, since many individuweapon and indicate that shielding of als suffered multiple injuries.

some type can be an important *for in

survival. For example, within a range of

0.6 mile from ground zero over 50 percent of individuaas in Japanese-type DISTRIBUTION OF TfPES OF INJURY

homes probably died of nuclear radia- AMONG SURVIVORS

tiun effects, but such deaths were rare Percent of

among persons in concrete buildings Injury Survivors

within the same range. The effectiveness of cokv:rete structures in providing Blast (mechanical) 70

protection from injuries of all kinds is Burns (flash ind flame) 65

apparent from the data in Table 12.17; Nuclear radiation (initial) 30

this gives the respective average dis- 12.19 Among survivors the proporlances from ground zero at which there ,ion of indirect blast (mechanical) injuwas 50-percent survival (for at least 20 ries due to flying missiles and motion of

days) among the occupants of a number other debris was smallest outdoors and

of buildings in Hiroshima. School per- largest in certain types of industrial

sonnel who were indoors had a much buildings. Patients were treated for lachigher survival probability than those erations received oUt to 10,500 feet (2

who were outdoors at the times of the milcs) from ground zero in Hiroshima

explosions, and out to 12,500 feet (2.2 miles) in

Table 12.17 Nagasaki. These distances correspond

AVERAGE DISTANCES FOR roughly to those at which moderate

50-PERCENT SURVIVAL AFTER damage occurred to wood-hiame

20 DAYS IN HIROSHIMA houses, including the shattering of winApproximate dow glass.

Distance 12.2i0 An interesting observat;on

(miles) made among the Japanese survivors was

the relatively low incidence of serious

Overa~l0.8 Concrete buildings 0.12 mechanicai injuries. !or example, frac- School personnel: tures vere found in only about 4 percent

Indoors 0.45 of survivors. In one hospital there were

6utdoors 1.3 no cases of fracture of the skull or back

and only one fractured femur among CAUSES OF INJURIES AMONG 675 patients, although many such inju- SURVIVORS ries must have undoubtedly occurred.

1218 From surveys made of a large This was attributed to tie fact that pernumber of Japanese, a fairly good idea sons who suffered st,'.%re concussion or

_ __ _ _ _ _
INTRODUCTION 547

fractures were rendered helpless, par- shieiding against the initial nuclear raticularly i7" ieg injucies occurred, and, diation and particularly from the thermal

along with those who were plined be- pulse.

neath the wreckage, were trapped and 12.22 In two concrete buildings

unable to seek help or escape in case fire closest to ground zero, where the morensued. Such individuals, of course, did tality rate was 88 percent, about half the

not survive. casualties were reported as being early

and the other half as delayed. The

CASUALTIES AND STRUCTURAL former were attributed to a variety of

DAMAGE direct and indirect blast injuries, caused

by overpressure, structural collapse,

12.21 For people who were in debris, and whole-body translation,

buildings in Japan, the overall casualties whereas the latter were ascribed mainly

were related to the extent of structural to burns and initial nuclear radiation.

damage, as well as to the type of struc- Minor to severe but nonfalal blast injuture (§ 12.17). The data in Table 12.21 ries no doubt coexisted and may have

were obtained from a study of 1,609 contributed to the delayed lethality in

Japanese who were in reinforced-con- many cases. At greater distances, as the

crete buildings, between 0.3 and 0.75 threat from nuclear radiation decreased

mtile from ground zero, when the nu- more rapidly than did that from air blast

clear explosions occurred. At these dis- and thermal radiation, the proportion of

tances fatalities in the open ringed from individuals with minor injuries or who

about 90 to 100 percent, indicating, were uninjured increased markedly. The

once more, that people were safer inside distribution of casualties of different

buildings, even when no special protec- types in Japanese buildings was greatly

tive action was tiken because of the lack influenced by where the people hapof warning. There may have been an pened to be at the time of the explosion.

increase of casualiies in buildings from Had they been forewarned and knowldebris etc., but this was more than edgeable about areas of relative hazard

nompensated by the reduction due to and safety, there would probably have

Table 12.21

CASUALTIES IN REINFORCED-CONCRETE BUILDINGS IN JAPAN RELATED TO

STRUCTURAL DAMAGE

Percent of Individuals

Serious ZJght

Injury Injury No

Killed (hospital- (no hospi- Injury

Structurnl Damage Outright izaiion) talization) Reported

Severt damage 88 11 -1

Moderate damage 14 18 21 47

.Light damage 8 14 27 51

A4i
548 BIOLOGICAL E FECTS

been fewer casualties even in structures mind in considering the data in Table

that were badly damaged. 12.21. Although the table indicates a

general correlation between structural

12.23 The shielding effect of a per- damage and the frequency of ,asualties,

ticular building is not only different for the numbers cannot be used to estimate

blast, the thermal pulse, and nuclear casualties from the degree of structural

radiation, but it may also depend on the damage. In an actual situation, the efdistance from the explosion and the feCts w:uld depend on many factors,

height of burst. Furthermore, the loca- inc!uding the type of structure, the yield

tions and orientations of individuals in of the nuclear explosion, the height of

the building are important in determin- burst, tne distance from the explosion

ing the extent of the shielding. Hence, point, the locations and orientation- of

the protection offered by structures is people iii the building, ncnd the nature of

quite variable. This fact must be kept in prior protective action.

BLAST INJURIES

DIRECT BLAST INJURIES: body being rapidly engulfed and subBIOLOGICAL FACTORS jected to severe compression. This continues with decreasing intensity for the

12.24 Blast injuries are of two main duration of the positive phase of the

types, namely, dircet (or primary) inju- blast wave. At the same time the blast

ries associated with exposure of the wind exerts a drag force of considerable

body to the environmental pressure magnitude which contributes to the disvariations accompanying a blast wave, placement hazard.

and indirect injuries resulting from im- 12.26 The sudden compression of

pact of penetrating and nonpenetrating the body and the inward motion of the

missiles on the body or as the conse- thoracic and abdominal walls cause

quences of displacement of the body as rapid pressure oscillations to occur in

a whole. There are also miscellaneous the air-conlaining organs. These effects,

blast injuries, such as burns from the together with the transmisv'ior. of the

gises and debris, and irritation and pcs- shock wave through the body, produce

sibly suffocation caused by airborne damage mainly at the junctions of tisdust. The present section will treat ,-ues with air-containing organs and at

direct injuries, and indirect blast effects areas between tissues of different denwill be discussed later. sily, such as where cartilage and bone

12.25 The general inrteractions of a join soft tissue. The chief consequences

human body with a blst wave are are hemorrhage and occasional rupture

somewhat similar to that of a structure of abdominal and thoracic walls.

as described in Chapter IV. Because of 12.27 The lungs art. particularly

the relatively small size of the body, the prone to hemorrhage and edema (accudiffraction process is quickly over, the mu!ation of fluid causin, swelling), andP f

A
BLAST INJURIES 549

if the injury is severe, air reaches the hemorrhage has been reported as long as

veins of the lungs and hence the heart 5 to 10 day;; after injury. In view of such

and arterial circulation. Death can occur facts and overwhelming disruptive efin a few minutes from air embolic ob- fects of the Japanese bombings on medstruction of the vessels of the heart or ical and rescue services, it can be conthe brain or from suffocation caused by cluded that individuals with significant

lung hemorrhage or edema. Fibrin em- direct blast injuries did not survive.

boli in the blood may also affect the Those with relatively minor blast injubrain and otier critical organs. The em- ries who did -,urvive, did so without

boli, apparently associated with severe getting into medical channels, or if they

hemorrhagic damage to the lungs, are a did require medical care it was for postconsequence of the disturbance of the blast complications, e.g., pneumonitis,

blood-clotting mechanism. Damage to or for causes other than blast injury to

the brain due to air blast overpressure the lungs. For these reasons primary

alone is improbable, but indirect dam- blast effects, except for eardrum rupage may arise from injury to the head ture, were not commonly seen among

caused by missiles, debris, or displace- Japanese survivors.

mer.! of the body. Bodily activity after 12.29 Many petsous who apblast damage to the heart and lungs is parently suffered no serious injury reextremely hazardous and lethality can ported temporary loss of consciousn.-ss.

result quick!y where recovery might This symptom can be d'ie to the direct

otherwise have been expected. The action of the blast wave, resulting from

direct blast effect was not specifically transient disturbance of the blood cirrecognized as a cause of fatality in culation in the brain by air emboli.

Japan, but it no doubt contributed sig.- However, it can also be an indirect efnificantly to early mortality even though feet arising from impact in'ury to the

most o" the affected individuals may head caused by missiles or by violent

also have received mortal injury frcm displacement of the body by the air

debeis, displacement, fire, or thermal pressure wave.

and nuclear rfdiations. 12.30 A number of cases of rup12.28 Primary blast casualties have tured eardrums were reported among the

been reported after large-scale air at- survivors in Hiroshima and Nagasaki,

tacks with conventional high-explosive but the incidence was not high even for

bombs, mainly because of the provision those who were fairly close to ground

of medical care for those who otherwise zero. Within a circle of 0.31 mile (1,640

would have suffered the early death that feet) radius about 9 percent of a group of

is characteristic of serious blast injury to 44 survivors in Nagasaki had ruptured

the lungs. However, persons who spon- eardrums, as also did some 8 percent of

taneously survive for 24 to 48 hours in 125 survivors in the ring from 0.31 to

the absence ef treatment, complications, 0.62 mile from ground zero. In Hiroand ether injury usually recover anw shima the incidence of ruptured earshow little remaining luag hemorrhage drums was somewhat less. In both cities

after 7 to 10 days. In very severe inji- very few cases were observed beyond

nies under treatment, recurring lung 0.62 mile.

"swam
550 BIOLOGiCAL EFFECTS

DIRECr BLAST INJURIES: PHYSICAL sures. As a consequence, the injury

FACTORS caused by a certain peak overpressure

depends on the rate of increase of the

12.31 Tests with animals have pressure at the blast wave front. For

demonstrated that five parameters of the wave fronts with sufficiently slow presblast wave can affect the extent of the sure rise, the increase in internal presdirect injuries to the body, they are (1) sure due to inward movement of the

the ambient pressure, (2) the "effec- body wall add air flow in the lungs keeps

tive" peak overpressure, (3) the rate of pace (to some extent) with the external

pressure rise (or "rise time") at the pressure. Consequently, quite high inblast wave front, (4) the character and cident overpressures are tolerable. In

"shape" of the pressure pulse, and (5) contrast, if the rise time is short, as it is

the duration of the positive phase of the in nuclear explosions under appropriate

blait wave and the associated wind (see terrain and burst conditions, the damagChapter ill). These parameters will be ing effect of a given overpressure is

considered below as they arise, greater. The increase in internal pres12.32 The biologically effective sure of the body takes a finite time and

peak overpressure depends on the ori- the response is then to the maximum

entation of the individual to the blast possible pressure differential. Thus, a

wave. If the subject is against a reflect- sharply rising pressure pulse will be

ing surface, e.g., a wall, the effective more damaging than if the same peak

overpressure for direct blast injury is overpressure is attained more slowly. In

equal to the maximum reflected over- precursor formation (§ 3.79 et seq.), for

pressure, which may be a few times the example, the blast pressure increases at

incident peak overpressure. On the other first slowly and then quite rapidly; the

hand, in the open at a substantial dis- injury potential of a given peak overtance from a reflecting surface, the ef- pressure is thus decreased.

fective overpressure is the sum of the 12.34 An individual inside a buildpeak incident overpressure and the as.. ing but not too close to a wall would be

sociated peak dynamnc pressure if the subject to multiple re,,ections ot thisubject is perpendicular to the direction blast wave from the ceiling, floor, and

of travel of the blast wave and to the walls as well as to the inciLrnt wave

peak overpressure alone if the subject is entering the structure. Since the rep;rallel to this direction. Consequently, flected waves would reach him at diffor a given incident overpressure, the ferept times, the result would be a step

blast injury is expected to be greatest if loading, although the rise time for each

the individual is close to a wall and least step might be quite short. In such cases,

if he is at a distance from a reflecting where the initial 5last pressure is tolerasurface and is oriented with his body ble and the subsequent pressure increase

parallel to the direction in which the is not too great or occurs in stages (or

blast wave is moving, slowly), a certzain peak overpressure is

12.33 The body, like many other much less hazardous than if it were

structures, responds to the difference applied in a single sharp pulse. Apbetween the external and internal pres- parently the reason for the decreased

I€ -- - - . . . . . .- - . ".-- 
BLAST INJURIES 551

blast injury potential in these situations size. it is only the magnitude of the

is that the early stage of the pressure overpressure that is important. The dupulse produces an increase in the inter- ration of the positive phase, for a given

nal body I essure, thereby reducing the peak overpressuv'e, varies with the enpressure differential associated with the ergy yield and the height of burst

later portion of the pulse. In a manner of (§ 3.75 et seq.). But for most condispeaking, a new and higher "ambient" tions, especially for energy yields in

pressure is imposed on the body by the excess of about 10 kilotons, the duration

early part of the pressure pulse and tol- of the positive phase of the blast wave is

erance to the later rise in overprr,ýsure is so long-approaching a second or

enhanced. A higher peak overpressure is more-that the effective peak overpresthen required to cause a certain degree sure is the main factor for determining

of blast injury, the potential for direct injury from a

12.35 Clearly, for a given peak in- fast-rising pressure pulse.

cident overpressure, the geometry4 in 12.37 A given peak pressure in the

which an individual is exposed inside a blast wave from conventional high exstructure may have a significant effect plosives is less effective than from a

on his response to air blast. A location nuclear explosimn-except perhaps at

against a wall is the inost hazardous unus ally low yields-mainly because

position because the effective peak of the short duration of the positive

overpressure, which is the maximum phase in the former case. From obserreflected overpressure, is high and is vations made with small charges of

applied rapidly in a single step. A loca- chemical explosives, it has been estidon a few feet from a wall is expected to mated that deaths in humans would redecrease the direct blast injury, although quire sharp-rising effective overpresthe hazard arising from displacement of sures as high as 200 to 490 (or more)

the body may be increased. Apart from pounds per square inch when the posithe effects just deseribed, oscillating tive phase durations are less than a milpressures, for which no adequate bio- lisecond or so. These pressures mzy be

medical criteria are available, often compared with values of .-oughly 50 (or

exist inside structures due to reveiberat- less) to about 100 pounds per square

ing reflections from the inside walls. inch, with positive phase durations of

12.36 The duration of the positive the order of a second, for nuclear exphase of the blast wave is a significant plosions.

factor for direct blast injuries. Up to a 12.38 Tentative criteria, in terms of

point, the increase in the duration in- effective peak overpressure as defined in

creases the probability of injury for a § 12.32, for lung damage, lethality, and

given effective peak overpressure. eardrum rupture caused by a fast-rising

Beyond this point, which may be of the pressure pulse of long duration (0.1

order of several tens to a few hundred second or more) are givenr, in Table

milliseconds, depending on the body 12.38. The values for lung damage and

'The word "geometry" is used here as a general term to describe the location of an individual in

relation to the details of the environment that may affect the blast wave characteristics.
552 BIOLOGICAL EFFECTS

lethality are average pressures obtained at which impact occurs, and the size,

by extrapolation from animal data to shape, density, mass, and nature of ihe

man; the variability of the results is moving objects. Furthermore, considerindicated by the numbers in parenthe- ation must be given to the portion- of the

ses. Rupture of the normal eardrum is body involved in the missile impact, and

apparently a function of the age of the the events which may occur at and after

individual as well as of the effective the time of impact, namely, simple

blast pressure. Failures have been re- contusions and lacerations. at one excorded at overpressures as low at 5 treme, or more serious penetrations,

pounds per square inch ranging up to 40 fractures, and critical damage to vital

or 50 pounds per square inch. The vai- organs, at the other extreme.

ues in Table 12.38 of the effective peak 12.40 The hazard from displaceoverpressures for eardrum rupture are ment depends mainly upon the time and

based on relatively limited data from distance over which acceleration and

man and animals. deceleration of the body occur. Injury is

more likely to result during the latter

INDIRECT BLAST INJURIES phase when the body strikes a solid

object, e.g., a wall or the ground. The

12.39 Indirect blast injuries are as- velocity which has been attained before

sociated with (1) the impact of missiles, impact is then significant. This is detereither penetrating or nonpenetrating mined by certain physical parameters of

(secondary effects), and (2) the physical the blast wave, as mentioned below, as

displacement of the body as a whole well as by the orientation of the body

(tertiary effects). The wounding poten- with respect to the direction of motion

tial of blast debris depends upon a of the wave. The severity of the damnage

number of factors; these include the depends on the magnitude of the impact

impact (or striking) velocity, the angle velocity, the properties of ihe impact

Table 12.38

TENTATIVE CRITERIA FOR DIRECT (PRIMARY) BLAST EFFECTS IN MAN FROM

FAST-RISING, LONG-DUkATION PRESSURE PULSES

Effect Effective Peak Pressure (psi)

Lung Damage:

Threshold 12 ( 8-15;

Severe 25 (20-30)

Lethality:

Threshold 40 (30-30)

50 percent 62 (50-75)

100 percent 92 (75-115)

Eardrum Rupture: Threshold 5

50 percent 15-20 (mote than 20 years old)

30-35 (less than 20 years old)

i

- - -.. . ,. - , A- - - . .. '. --
BLAST INJURIES 553

surface, and the particular po:ftion of the thus not too sensitive to the duration of

body that has received the deceierative the overpressure and winds, but depends

impact, e.g., head, back, extremities, largely on the effective peak overpresthoracic and abdominal organs, body sure (cf. § 12.32). As a consequence of

wall, etc. this fact, it has been found possible to

relate the velocities attained by the

DISPLACEMENT VELOCITIES fragments produced by the breakage of

glass window panes to the effective

!2.41 Because the effects of both overpressure. The results for glass panes

missiles and body displacememtt depend of different thicknesses can be expressed

on the velocity attained before impact, it in v fairly simple graphical manner as

is convenient to conside" the relation- will be shown in § 12.238.

ships between displacement velocity 12.43 The variations of the overand the blast parameters for objects as pressure and dynamic pressure with

small as tiny pieces of glass and as large time (§ 3.57 et seq.) at the location of

as man. The significant physical factors interest also have a bearing on the bein all cases are the magnitude and dura- havior of a displaced object. Data were

tion of the blast overpressure and the obtained at nuclear weapons tests under

accompanying winds, tide acceleration such conditions that the blast wave was

coefficient of the displaced object.' approximately ideal in behavior. Soine

ground shock, gravity, and the distancc of the median velocities, masses, and

traveled by the object. The latter is im- spatial densities (number of fragments

portant because, as a result of the action per square foot) of window glass, from

of the blast wave, the velocity of tý)e houses exposed to the blast, and of natobject increases with the time and dis- ural stones are summarized in Table

tance of travel until it attains that of the 12.43. For glass, the velocities refer to

blast wind. Subsequently, the velocity those attained after 7 to 13 fe-t ot tr3vel;

falls because of negative winds or im- for the stones the distances are not

pact with the ground or other material, known, but the velocities given in ihe

12.42 As a result of the interaction table may 1Y.- regarded as applicable to

of the various factors, large and heavy optimum distances of missile travel.

objects,ý gain velocity rather slowly and 12.44 Studies have also been maue

attain a maximum velocity only after of the displacement of anthropomorphic

most of the blast wave has passed. The dummies weighing 165 pounds by the

velocity is consequently determined by blast from a nuclear explosion. A

the duration of the overpressure and dummy standing with its back to th,.

winds. In contrast, small and light ob- blast attained its maximum velocity,

jects reach their maximum velocity about 21 feet per second, after a disfairly quickly, often after a small pro- placement of 9 feet within 0.5 second

portion of the blast wave has passed After the arrival of the blast wave. The

over them. The maimum velocity is free-fiekd overpressure at the test loca-

'The acceleration coefficeist is the product of the projected area presented to the blast wave and the

drag coefficient (§ 4.19) divided by the mass of the object.
55-4 BIOLOGICAL EFFECTS

Table 12.43

VE' CITIES, MASSES, AND LVENSITIES OF MISSILES

Pcak Median M.edian Maximumn

Overpressure VeckWity Mass Numbewr per

Mi'sile (psi) (ftlsec) (granvi Sq Ft

Glass 1.9 108 1.45 4.3

Glasis 3.8 168 0.59 151)

Gla5;s 3.9 140 0.32- 108

Gilass ~ 5 0 170) 0.13 398

Sim-e 8.5 286 0.22 40

tion was 5".3 pounds per square inch. relationship was found to represen( the

The dummy traveled 1 3 feet before stopping distance as a function of vestriking the ground andI then slid or locity applicaNbi: to thie animals over a

rolled another 9 feet. A pronie dummy, wide range of mass (§ 12.239). Oneý

however, did not move unde; t.,c same reason~ for the consistency of the data is

condi'ions. The foregoing results were probably ffhat all the animals assumed a

obtained in a situation where the blast rolling position aboot their long axis

wave was nearly ideal, but in another regardless of fth initial orientation. The

test. at a kxak overpr~essure of 6.6 animals remained relatively low to the

pounds pter square inch, where the blast ground and bounced very iittle, Ay

wave was nonideal (§ 3.79), both contrast, stones andi concrete blocks

standing and protie dummies suffered bounc.ed many times before stapp,"g.. Iconsiderably greater displa'cements. the data were not sensitiv'e tv mass,

Ever. in such circumstances, however, depended mom' on o~ienvttion, and were

the displacement of over 125 feet for the more variable than the resulu obtained

prone dummy was much le-ss than that with animals. On the wholu, the stcpof about 250 feet for the standing one. ping distances of the blocks and stones

The reason for ihe g-,eater displacement were greater for a given initial velccity.

of the standing dummy is that it ac- One of the conclusions dri'wn from~ the

quired a higher vclocitv. foregoing tests was that a person tumn12.45 In order to stady the dis- bling over a -,mooth surface, free from

place..ientp of moving objects, field tests i-ocks and other hard irregularities,

have been mar't by dropping animal m'ýght survive, even ii the mritial veloccadavers, including guinea pigs, rab- ity is quite high, if he could avoid head

bits, goats, enJl dogs, and stones and injury and did not Plai! his limbs. I concrete block:- onto a fiat, hard %urface

f rom a vehicle traveling between 10 and MIS~SILE AND DISPLACEMENT

60 miles per hour (14.7 to 88 feet per NUYCIEA

second). For a giveip initial velocity, the

stopping distance for the animials in- 12.46 Velocity criteria for the procreased somewhat with the mass, and a duction of skin lacerationG by penetrat-
BLAST INJURIES 555

ing misiles, e.g., glass fragments, are value for skin lacerations is recorded as

not known with certainty. Some reliable 50 fcet per second and for serious

informiation is available, however, con- wounds it is 100 feet per second.

cerning the probability of penetraiion of 12.48 Little is known concerning

'he abdominal wall by glass. The impact the relationship between mass and veve'ocities, for glass fragments of dif- locity ot nonpenetrating missiles that

ferent masses, corresponding to 1, 50. will cause injury after impact with the

and 99 percent penetration probability bdy. Studies with animals sbowed that

are recorded in Table 12.46. fairly high missile velocities are re12.47 The cstimatcd impact veloci- quired to produce lung hemorrhage, rib

ties of a 10-gram (9.35-ounce) glass fructur.,s, and early mortality, but

missile required to produce skirn lacera- quantitative data for man are lacking.

tions and serious wounds arc sum- No relationship has yet been developed

roarized in Table 12.47. T11h threshold between mass and velocity of nonpeneTable 12.46

PROBABILITIES OF GLASS FRAGMENTS PENETRATING ABDOMINAL WALL

Probability o! Penetration

Mass of Glass (percecrt)

Fragments

(graras) I 50 99

Impact 'klocity (fl/sec)

0.1 235 410 730

0.5 160 275 485

1.0 140 245 430

10.0 Its 180 355

Table 12.47

TENTATIVE CRITERIA FOR INDIRECT (SECONDARY) BLAST EFFECTS FROM

PENETRATING 10-GRAM GLASS FRAGMENTS,

Impact Velocity

Effect (f:/sec)

Skin laceration:

Threshold 50

Sef;ous wounds:

Threshold I 0

50 percent 180

Near I00 percent 30C

Figures represent impact velocities witm unclothed skin. A serious wound is .rbitrarilv defined as a

laceration of the skiri with missile penetration into the tissues Z- e' depth of I cm (about 0.4 inch) ,r more.
556 BIOLOGICAL EFFECTS

trating missiles that will cause injury as pact velocity of 10 feet per second is

a result of impacts with other parts of unlikely to be associated with a signifithe body wall, particularly near the cant number of serious injuries; between

spine, kidney, liver, spleen and pelvis. 10 and 20 feet per second some fatalities

It appears, however, that a missile with may occur if the head is involved; and

a mass of 10 pouiids striking the head at above 20 feet per second, depending on

a velocity of about 15 feet per second or trauma to critical organs, the probabilimore can cause skull fracture. For such ties of serious and fatal injuries increase

missiles it is unlikely that a significant rapidly with increasing displacement

number of dangerous injuries will occur velocity. Impact velocities required to

at impact velocities of less than 10 feet produce various indirect (tertiary) blast

per second. The impact velocities of a effects are shown in Table 12.49. The

10-pound missile for various effects on curves marked "translatior near structhe head are given in Table 12.48. tures" in Fg. 12.49 may be used to

12.49 Although there may be some estimate ground distances at which I

hazard associated with the accelerative percent and 50 percent casualties would

phase of body displacement (translation) be expected, as functions of height uf

by a blast wave, the deceleration, par-. burst, for a 1-kiloton explosion.5 Based

ticularly if impact with a solid object is on tests with animals, the criteria for I

involved, is by far the more significant. and 50 perceri casualties were someSince a hard surface will cause a more what arbitrarily set at impact velocities

serious injury than a softer one, the of 8 and 22 feet per second, respecdamage criteria given below refer to tively. Thie results in Fig. 12.49 may be

perpendicular impact of the displaced extend:.,1 to other burst heights and

body withl a hard, ilat object. From yields by using the scaling law given in

variou~s data it is concluded that an im- the e!. ample facing the figure.

Table 12'248

TENTATIVE CRITERIA FOR INDIREC-t BLAST EFFECTS INVOLVING

NONPENETRATING Ib-POUND MISSILES

impact Velocity

Effect (ft/sec)

Cf.rcbral Concussion:

Mos"y "safc" 10

Threshold 15

Skull Fracture:

Mostly "safe" 10

Threshold 13

Near 100 percent 23

in this connection, a casualty is defined ..s an individual so injured that he would probably be a burdei,

o-, ot:ers. Some of the casualties woula J-rove fatal, especially in the absence of medical care. W
BLAST INJURIES 557

Table 12.49

TENTATIVE CRITERIA FOR INDIRECT (TERTIARIY) BLAST EFFECTS INVOLVING

IMPACT

Impact Velocity

Effect (ft/sec)

Standing Stiff-Legged Impact:

Mostly "safe"

No significant ctfect < 8

Severe discomfort 8-10

Injury

Thrmshold 10-12

Fracture threshold (heels. feet. and legs) 13-.16

S.:ated hnpect:

Mostly "safe"

No effect < 8

Severe discomfort 8-14

:njury

Threshold 15-26

Skull Fracture:

Mostly "safe" 10

Threshold 13

50 percent 18

Neor 100 percent 23

Total Body Impact:

Mostly "safe" 10

Lethality threshold 21

Lethality 50 percent 54

Lethality near 100 percent 138

12.50 Evaluation of human toler- tumbling are still not adequate. The iniance to decelerative tumbling during tial velocities at which I and 50 percent

translatiori in open terrain is more diffi- of humans are expected to become cacult than for impact against a rigid stir- sualties as a result ef decelerative turnface described above. Considerably bling have been tentatively estimated to

fewer data are available for decelerative be 30 und 75 feet per second. respectumblipg than for body impact, and tively. The curves in Fig. 12.49 marked

there is virtually no human experience "translation over open terrain" are apfor checking the validity of extrapola- proximate, but they may be ised to

tions from observations on animal ca- provide a general indication of the range

davers. Tests have been made with within which casualties might occur

goats, sheep, and dogs, but for humans from decelerative tumbling due to air

the information required to derive reli- Hlast from surface and air bursts.

able hazards criteria for decelerative (Text continued on page 560.)

.- ¶, 7
558 BIOLOGICAL EFFECTS

The curves ia Fig. 12.49 show 50 Eample

percent and 1 percera casualties resulting from translation near structure and Given: A 50 KT explosion at a

over open terrain as a function of grtound eight of 860 feet over open terrain.

distarnce and height of burst for a KTr Find: The ground distance at which

explo,,;ion in a standard sea-level atmos- tr(nslcio ualtes woul prode 50

phere. The results apply to randomly per ent casualties among prone personoriented, prone personnel exposed to the nel.

blast wave in the open. The curves for Solution: 'ghe corresponding burst

transiation over open terrain (decelera- height ior I KT is

tive tumbling) are approximate h h 860 180 feet.

(§ 12.50). WO- (50)04

areScaling. The required relationship-. From Fig. 12.49, at a height of burst of

180 feet. the ground distance at which

d = h = WO.4 50 percent casualties among personnel

di hi in the open will occur is roughly 660

feet. The corresponding ground distance

where d, and hi are the distance from for 50 KT is then given approximately

ground zero and height of burst, re- as

spectively, for I KT; and dand hare the

corirsponding distance and height of 3 1 1W0 f 60 s()0

burst for W KT. = 3,150 feet. Answer

I

1'
PLAST INJURIES 559

0-2

0t IM 0 w

0

_ _ o

LAz .

0

ci

_ _ _ _ _ _CID

(0 0

2~~~ (.L3.0 H~ 0Sfl <1 
560 BIOLOGICAL EFFECTS

BURN INJURIES

CLASSIFICATION OF BURNS ciently high or does not persist for a

sufficient length of time, pain will cease

12.51 Thermal radiation can cause and no injury will occur. The amount of

burn injuries either directly, i.e., by pain is not directly related to the severity

absorption of the radiant energy by the of the burn injury, but it can serve a

skin, or indirectly by heating or ignition useful purpose in warning an individual

cf clothing, or as a result of fires started to evade part of the thermal pulse from a

by the radiation. The direct burns are nuclear explosion.

often called "flash burns," since they 12.53 First-degree burns, whic.i are

are produced by the flash of thermal the mildest, are characterized by immeradiation from the fireball. The indirect diate pain and by ensuing redness of the

(or secondary) burns are referred to as affected area. The pain continues even

"contact burns" or " flame burns"; they after the temperature of the skin has

are identical with skin burns that result returned to normal. The first-degree

from touching a hot object or those that burn is a reversible injdry; that is to say,

would ac~ ompany (or 6e caused by) any healing is complete with no scar formalarge fire no inatter what it;,- origin. In tion. Sunburn is the classic example of

addition, individuals ir, buildings or first-degree burn.

tunnels close to ground zero may be 12.54 Second-degree burns result

burned from hot debris, gases, and dust from skin temperatures that are higher

(§ 12.02). and/or of longer duration than those

12.52 A skin burn is an injury causing first-degree skin burns. The incaused by an increase in skin tempera- jury is characterized by pain which perture resulting from direct absorption of sists, and may be accompanied either by

thermal radiation, which varies with no immediate visible effect or by a vaskin color, or from the transference of riciy of skin changes including blanchheat through clothing. The severity of ing, redness, loss of e!asticity, swelling,

the burn depends on the amount of the and development of blisters. After 6 to

temperature increase and on the duration 24 hours, a scab will form over the

of the increase. For example, a skin injured area. The scab may be flexible

temperature of 70°C (155°F) for a frAc- and tan or brown, if the injury is modtion of a second will produce the sanme erate, or it may be thick, stiff, and dark,

type of burn as a temperature of 480C if the injury is more severe. The wounds

(1 180F) for a few minutes. Skin burns will heal within one to two weeks unless

are gen-.; ally classified as first, secona, thcy are complicated by infection. Secor third degree, in order of increasing ond-degree burns do not involve the full

severity of the burn. Pair asso,,i.atpd thickness of the skin, and the remaining

with skin burns occurs whet, the tem- uninjured cells may be abie to regenerperature of certain nerve cells near the ate normal skin without scar formation.

surface is raised to 43TC (I090F) or 12.55 If sk;n temperatures become

more. If the temperature is not suffi- sufficiently high and/or are of long du-
BURN INJURIES 561

ration, third-degree burns will be pro.- therniore. there are cer~ain critica", local

duced. Pain is experienced at the pe- regions, such as the hands, where alriphera!, less in 'jured areas only, since most any degree oi burn will :Acapacithe serve endiiigs in the ccn'.-;aly burned tate the individual.

areas are damaged to the exient that they 12.58 Persons mxposed to nuclear

are unable to transmit pain iwi~pulses. e plosions of low or intermediate yield~

Immediately after suffering the burn, th-, may sustain very sev;ere burns or, their

skin may appea,. either normnall, scalded, faces and hands o~r other exposed areas

or charred, and it mnay lose its e!asticity. of the bed), as a r.-~sult of thc short pulsc,

The healing of third-degree burns takes of direc *tiy absorbed thermnal rod-ation.

several wecks and will always result -,i These burns may cause severe superfisrar formation unless new skin is cial damage simiiqr to a third-degree

grafted over the burned area. The scar burn, but the deeper layers of [he skin

results from the fact that the full thick- may be uninjuted. Such burns would

ness of the skin is injured, and the skin heal rapidly, like irniid second-degree

cells -re unable to regrenerate normal burns. Thermal radiation burns occurtissue. ring under clothing or from ignited

12.56 The distribution of buras into clothing or other tir.-er will be simila; to

three groups obviously has cw~ain limi- thcose ordinarily seen in burn injuries of

tations since it is not possible to draw. a nonnuclear origin. Bcc~wse of the

sharp line of demarlalion between first- longer durationi of the the~mall pulsc.

and second-degree, or between second- from an air burst weapo; 'In the megaton

4nd third-degree burns. Within each rnnge, fiaAh burns on e.-po.ized skir. and

clas.s the burn may bc mild, niodernte, burns of nonnuclea: origin may aiso lA.

or sevcie, so thai Lpon pi-eiiminary --x- similar,

guih etwena evee unof the sec- BURNS UNDER CLOTHING

burn. Subsequeat pathology of the in.- 12.59 SkL~n burns under clothing,

jury, however, will usuaaly inake a dis- vdhi-h depend on the zolor, thickness,

tinction po.3sible. in the following dis- and n~ature of the fabric-, can be pfocussion, reference to a particular degree duced in tho followifig ways: by direct

of burn should be tii.en to imiply a Uansmitarace through the fabric if time

mod-.rate burn of that type. latter qs thin anid mrerely acts as an at12.57 The depth of the burn is not tenuating screen; by heating the, fabric.

the only factor ~n doiermiring its effee and causirng stearm or vo. tilt. oroducts

on ýh- individnial. The oxten, of the area to impinge on ýIhe skin; by condu;,ticn

at the skin wh~ich hr bern afte-ted is from the hol fabric to the skin; m' thne

also important. I1 hus, a first-degree butrn fabric may ignite and hot vapors aod

- ~ ovef the entire body may be mo-re flames will cause burrus w.here they imserious than a third-ck.;g-ee hurn at one pinge on the skitn. Burms beaheath clothspot. Trhe, larer tho, area beruied, the ing can arise from heat transfer for.,--)me

more likely is the appearance cf symp- time after the thermal pu).be ends. TihIese

terns involving the. whole. body. Fur- burns getteralky involve deeper tissues
5 62 BIOLOGICAL EFFECITS

than the flash burns produced by the ond- oi- third-degree burns in excess of

direct ihermal pulse on hare skin. Flaniz 20 percent of the surface area of the

burns caused by ignited clothing aiso body should be considered major burns

result from longer heat application, and and will require special medical care in

thus will be more liKe burns due to a hospital. If the nose and throat are

co~~tcna onigrion.sriously involved and obstructive

12.60 Ffitst. aad second-.degree edema (§ 12.27) occurs, breathing may

burns of thc uricovered skin and burns become impossible and tracheotomy

through thin clothing occur at lower may be required as a l~ife-saving mearadiant exposures (.§ 7.33) thaii those sure.

which igni'.e clothing (TabP! 7.26). Be- 12.62 Sho-ck is a term denoting a

causeý of these factors, first- and sec- generalized state of serious ci!rculatory

orid-degree Nurns in exposed person~s inadequacy. If serious, it will result in

would involve oniy those body ateas incapacitation and unconsciousness and

that it-ace the explosion. Where the direct if untreated may cause dcarth. Third-decthermial pulse produces third-degree grec. burns of 25 percent of the body and

I -is and clothing ignition takes olace, seconJ-degrec burns of 30bw% p rcent of the

personis wearing tihina clothing would body will generally produce shock

have sucrh burns .-ver parts of the body within 30 minutes to 12 houirs and re.-

facing the burst, Persons wvearing heavy quire prompt medical treatment. Such

clothing could suffer thirel-degree burns treatment 'is ';omphacated and causes a

over' t~w whole -H-,dy if the ignited heavy dirain on medical personnel and

cloth.ing could not be removed quickly. supply resources.

This phenomenon is typically seen in

pcrsons whose Alothing catches ffire by RDA" XOUE O UN

convetio.al mans.ON EXPOSED SKIN

INCAPACrrATION FROM BURNS 12.63 The critical radiant exposure

for a skin burn depends on the du,,atiorr

!2.61 Burns of clrtain areas of the of the radiation pulse and the thevmal

bodý, even if only of t~ie first degree, energyv spectrum; both of these quantiwill freque~ntly restih in. incapacitation ties vary with the yield and height of

h-cawie of their critical lotcalon. Any burst. Hence, although the radiant exburn ;urruunding the eyes tnat ca-ises posure is known as a function of disoccludi,.d -vision, e.g., because of swet!- tanice and yield (see Chapter VII), it is

ing of the ey!1ids, wil! be incapacitat- not a simple matter to predict distances

i. urns oi the elbows, kns.es, hands, at which burns of different types may be

and feet -r-oduce iimmobility or limita- eAptcted from a given explosion. Apart

i i.,,n of rno.iun as the result of swdlfing, fro'-n radiant exposure, the probability

pain, or scab fl~rmaziun, and will causte hi1d severity of the burns will depend on

ineffiectiveness in most cases. The o,-- several factors. One of the most imporcurrenice of burns of iht face, neck, an0 tant is the absorptive properties of the

hands are prebabie because t1hese areas ski.- for thermal radiation. in a normal

are most likely to be unprotected. Sc'c- population, the iraction of the radiation

4'
BURN INJURiES 563

energy absorbed may vary by as much babilities of 18 percent and 82 percent

as 50 percent because of differences in assigned within the various ranges. For

skin pigmentation. example, from Fig. 12.65 it is expected

12.64 For thermal radiation pulses that, if a normal population is exposed

of 0.5 second duration or more, as is the to the theimal pulse from a 1-megaton

case for explosions with yields exceed- exp!osion in the lower atmo.',phere. at

ing 1 kiloton, the energy absorbed by distances where the radiant exposures

the skin, rather than the radiant expo- are between 4.5 and 6 cal/cm2 , 18 persure, determines the extent of the burn cent of the population will receive secinjury. The spectrai absorptance of the ond-degree burns and the remainder

skin, i.e.. the fraction of the incident first-degree burns to the exposed (unradiation energy (or radiant exposure) protected) skin.

that is absorbed, depends on the skin 12.66 With the aid of the yieldpigmentation. The curves in Fig. 12.64 distance relationships for various radiant

have been derived from thermal energy exposures given in Chapte'r VII, the

spectra of nuclear explosions in the curves in Fig. 12.65 may be used to

lower part of the atmosphere and mea- determine the ipproximate distances

sured values of the absorptance of dif- from ground zero at which gi'Ve,.' burn

ferent skin types. By considering ex- probabilities may be experienced. Supplosions in the lower atmosphere, the pose that, in the example given above,

height of burst variable is largely elimi- the 1-megaton weapon is detonated at a

nated. The results in dhe figure are ap- height of 10,000 feet. which is within

plicable to exposed skin wher ir.o eva- the lower atmosphere. According to

sive action is taken and there '.s no Fig. 7.42, for air bursts below 20,000

protection from structures or clothii.g. It feet and 12-mile visibility, the specified

is seen that the radiant exposure re- radiant exposure between 4.5 and 6

quired to produce a given degree of burn cal/cm 2, would be received at slant

injury varies significantly with skin pig- ranges of from 9 to 10 miles. Since

mentation. In fact, people with very these ranges are substantially greatedark skins could receive burns from ap- than the height of burst (,about 2 miles),

proximately twe-thirds the incident ra- they may be taken as the distances to

diant energy that will cause similar ground zero to the accuracy of Fig.

burns in very light-skinned people. 7.42. Hence, within the radii of 9 and

12.65 Figure 12.65 shows radiani 10 miles from ground zero, it is probaexposures for the various probabilities ble that 18 percent of an average ppuof burn occurrence, again asscming no lation subjected to the whole thermal

evasive or protective action. The solid pulse will receive second-degree burns

lines represent the conditions under and 82 percent first-degree burns to their

which it is probable that 50 percent of an exposed (unprotected) skin.

average exposed population will receive 12.67 As already noted, the burn

skin burns of the indicated degree. The criteria given above are based on the

broken lines divide the burn probability supposition that no evasive action is

distribitions into ranges for three de- taken. For air bursts with yields less

grees of burn severity with average pro- than about 100 kilotons, the main part of

. L 
564 BIOLOGICAL EFFECTS

131 II77III -- 7--777111 1 11

12 L =Li'qht skin )

M= Medium skin ThirdD Dark skin Degree

11

10 L

9M

_j SecondU Degree

LJ 0

0 6 0-

4

Degree

3 -

2

1 10 102 l 0

EXPLOSION YIELD (KILOTONS)

Figure 12.64. Radiant exposure required to produce skin burns for different skin pigmentations.
BURN INJURIES 565

eN z z t z

t~ o tO Z. 

CO co N O O w- - -0 w D C C

cr-00

-00

C c,

B -C)

N 0

(Zom 38SIX ANVO
566 t101 )OGiCAI FFI("i C'S

the thermal energy arrives too quickly Hiroshima and Nagasaki were caused by

for people to react and take some pro- flash burns. In the former city alone,

tective action. Evasion of part of the about 42,0(X) burn cases were reported

thermal energy that would be effective and of those some 24,500 were recorded

in reducing burn injuries is possible, as being serious. Unless protected by

however, for yields of 100 kiloton!; or heavy clothing, thermal radiation burns,

more in the lower atmosphere. The apart from other injuries, would have

length of the thermal pulse is then such been fatal to nearly all unshielded pertha! the pain could initiate a reaction sons in the open at distances up to 6,,M)

which, if appiopriate, might allow a feet (I.I miles) or more from ground

person to obtain sufficient protection to zero. Even as far out as 12,(X0M to

decrea,;e the severity of the pwtential 14,000 feet (2.3 to 2.6 miles), there

burn (§ 7.87). The ability to react in this were instances of such burns which

manner can apparently be improved by werc bad enough to require treatment.

appropriate training.

"I'HiRMAL RADIATION BURNS IN

BURN INJURIES IN JAPAN JAPAN

12.68 Among the survivors of the 12.70 A distinctive feature of the

nuclear explosions in Japaa. the inci- thermal radiation (flash) burns was their

dence of flame burns appeared to be sharp limitation to exposed areas of :he

very small. In fact, they constituted not skin facing the center of the explosion.

more than 5 percent of the total burn For this reason they are sometimes

injuries. This was the case because most called "profile burns" (Fig. 12.70). The

of those who suffered flame burns did phenomenon occurred because most of

not sufvie, since they were caught in the radiation received had traveled in a

burning buildings and could not escape. straight line from the fireball and so only

The character of' the flame burns was regions that wer: directly exposed were

similar to that of burns caused by other affected. A striking illustration of this

conflagrations. The clothing usually behavior was that of a maa writing becaught fire and then large parts of the fore a window. His hands were

body suffered flame burns. By contrast, seriously burned, but his face and neck,

as will be seen below, flash burns were which were not covered, suffered only

generally restricted to exposed skin slight burns because the angle of entry

areas, i.e., face, arms, hands, and legs. of the thermal radiation :hrough !he

12.69 One of the most striking window was such as to place them in

consequences of the nuclear bombings partial shadow.

of Japan was the large number of ca- 12.71 Although flash burns were

sualtie, dt•e to flash burns caused by the largely confineo to exposed parts of the

thermal radiation. The situation was ag- body, there were a few cases where such

gravated by tht; clear ak.nosphere and burns occurred through one, and very

warm weather which prevailed at the occasionally more, layers of clothing.

time (§ 12.14). It was estimated that 20 Instances of this kind were observed

to 30 percent of the fatal casualties in when the radiant exposure was large

rx
It RN INJIURIE S 567

4A'

i i

Figure 12.70. Partial protection against thermal radiation pro.Juced "profile" hurns (I .2 ,

miles from ground ,ero in Hiroshima. the radiant e.xpure %.%,vs e,,!ina.ed 1o

he 5.5 to 6 calIci). The Laj- wa, sufficient to priotect (he top of the head

agiinst flasi hu n.

enough to overcome the protective ef- i2.72). This was attributed to the refect of the particular fabric. When burns flection of thermal radiation by white or

did occur through clothing, they fre- other light-colored fabrics, whereas

quently involved regions where the materials of dark color absorbed radiaclothes were in contact with the skin, at tion, became hot, and so caused contact

the elbows and shoulders, for example. burus. In some cases black outer clothSuch burns may have been due to heat ing actually burst into flame and ignited

transmitted from the hot fabric, rather the undergarments, so that flame burns

than to the direct effect of radiation. resulted. It should be menticned, howAreas over which the clothing fitted ever, that white clothing does not

loosely, so that at air space sepawated it always necessarily provide protection

from the skin, were generally unharmed against thermal radiation. Some materiby the thermal radiation (Fig. 12.71). als of this kind transmit enough radia12.72 There were many instances in tion to permit flash burning of the skin to

which burns occurred through black occur.

clothing, but not through white material 12.73 The frequency of flash burns

wo-rn by the same individual (Fig, was, of course, greatest among persons
.38It 10 1 M; I(CA I :1: 1

A

Figurt: 12, Y11. The skin tinder (hec areas of contact wiih clothing is burnied. The protective

effect of thicker layen.; can be ween on the shoulders and across the back.

wh~o were in the open, Nevertheless, attacks on Japan, only their general G'eathere were a surprising number of such lures were reported. However, this inlb'.irns among Individuals who were n.. formation has been supplemented by

doots. This was largely because many observations riade, especially oil an

Windows, especially inl commercial esthetized pigs, both in the l~oboatory

structures, were uncurtained or were and at nucleur test explosions. The skin

wide open on account of' the summier of white pigs has been found to respond

weather. Hence, many persons inside to thermal radiation in a manner which

buildings were directly exposed i'o ther.. is in mnany respects ,;Imilar to, and c.'O

miat radiation. In addition to the protec- be correlated with, thie response o-.f

lion afford-ed by clothing, particularly if human skin.

light in color, some shiezldingy was pro.- 12.75 Severity of the flash burns in

vided by the natua1 promontories of the Japan ranged from mild erythemna ((redbody, e.g., the nose, supraorbital (eye dening) to charring of the outermlost

sock~et) ridges, and the chin. layers of thte skin, Amnong those who

were within about 6A0X) fee-t kI . I miles)

GENEAL CAR~cERISICS i'7ý fromn ground zero, the burn injurie.s were

FL EASH BU ARNS ERST depigniented lesiorii (light in c:o'or), but

ait greater distances.. fromn 6,000 to

12.74 lIn spite of the thousands of 12,M() feet 0 1 tol .3 miles), the initial

flas_.. -jurns experienced after the nuclear erythenma was followed by th?, develop-
BUI.N INJURIES 569

.;, vo"

An

Figure 12.72. The patient's rkin is burned in a pattern corresponding to the dar'n portions of

a kinono vorn at the time of he explosion.

ment oi" a walnut •.oloration of ihe Akin, cases because of the decruase in resissometimes called the "mask of Hiro- tance of the body to infection.

shima.' 12.77 Experimental flash burns

12.76 Burrs of moderate second have been produced both in the iaboradegree (and rri~der) usually healed tory and in nuclear tests which were

within four weeks, but more severe apparently quite similar to those reburns frequently became infected so that ported from Hiroshima and Nagasaki. in

the hcaling process was much more the more severe cases of circular experprolonged. Even under the best condi- imental burns there was a central

tions, it is difficult to prevent burns from charred region with a white outer ring

becoming infected, and after the nuclea',. surrounded by an area of erythema. A

bombings of Japan the situation vp,,; definite demarcation both in extent and

aggravated by inadequate care, pour depth of the burns was noted, so that

sanitation, and general lack of proper they were unlike contact burns which

facilities. Nuclear radiation injury may are generally variable in depth. The

have been a contributory factor in some su.'face of the flash burns became dry Iif
570 BIOLOGICAL EFFECTS

without much edema or weeping of Among I,900 ca.:es, chosen at random,

serum. of individuals who were in the open,

12.78 Another phenomenon, which within some 6,600 feet (1.25 miles) of

appeared in Japan after the healing of ground zero at the time of the explosome of the more severe burns, was the sions. only 42 gave a history of keratitis

formation of keloids, that is, thick coming on within the first day. Delayed

overgrowths of scar tissue. It was sug- keratitis was reported in 14 additioilal

gested, at one time, that they might have cases, with symptoms appearing at

been due to nuclear radiation, but this various times up to a, month or more

view is no longer accepted, The degree after the explosion. It is possible that

of keloid formation appears to have nuclear radiatiolb injury, which is assobeen influenced by infections, which ciated with delayed symptoms, as will

complicated healing of the burns, and be seen below, may have been a factor

by malnutrition. A secondary factor is in these patints.

the known disposition for keloid forma- 12.81 Investigators have reported

tion to occur among the Japanese and that in no case, among 1,400 examined,

other dark-skinned people as a racial was the thermal radiation exposure of

Lharacteristic. Many spectacular ke- the eyes apparently sufficient to produce

Ioids, for example, were formed after permanent opacity of the cornea. This

the healing of burns produced in the observation is not surprising s-nce the

incendiary bomb attacks on Tokyo. cornea is transparent to the major porThere is a tendency, however, for ke- ticn of the thermal energy which is reloide to disappear gradually in the ceived in the visible and longer wavecourse of time. length (infrared) parts of the spectrum.

In approximately one-quarter of the

EFFECTS OF THERMAL RADIATION cases studied there had been facial burns

ON THE EYES and often singeing of the eyebrows and

eyelashes. Nevertheless, some 3 years

12.79 It is of interest that, among later the corneas were found to be northe survivors in Hiroshima and Naga- mal.

saki, eye injuries directly attributable to 12.82 Several reasons have been

thermal radiation appeared to be rein- suggested for the scarcity of severe eye

tively unimportant. There were many injuries in Japan. For example, the detinstances of temporary blind..ess, occa- onations occurred in the morning in

sionally lasting up to 2 or 3 houri, but broad daylight when the eye pupil

only one case of retinal injury was re- would be expected to be small. Another

ported. possible explanation is that the recessed

12.80 The eye injury known as position of the eyes and, in particular,

keratitis (an inflammation of the cornea) the overhanging upper lids served to

occurred in some instances. The symp decrease the direct exposure to thermal

toms, including pain caused by light, radiation. Furthermore, on the basis of

foreign-body sensatio,, lachrymation, probability, it is likely that only a small

and redness, lasted for periods ranging proportion of individuals would be facfrom a few hours to several days. ing the explosions in such a way that the
BURN INJURIES 571

fireball would actually be in their field of mal injury that involves both the pigvision. merited layer and the adjacent rods and

12.83 Exposure of the eye to the cones, so that visual capacity is permabright flash of a nuclear detonation can nently lost in the burned area. The natproduce two possible injuries: flash- ural tendency of people to look directly

blindness and retinal burns. Flashblind- at tWe fireball would increase the inciness (dazzle) is a temporary impairment dence of retinal burns. A retinal burn

of vision caused by a bleacbin,- of the rormally will not be noticed by the

individual concerncd if it is off the cencones) light-sensitive in the retina ele~ments of the eye. (rods It may and be ta tral axis xso of vision, iin but veryysalbre small burned 

• cons) rtin n te ofthee,,. I ma be areas may be noticeable if they are cenproduced by scattered light and does not aral may b ernotieeleifthy aec- necessarily require the eye to be. focused trally located. A person generally will necesarly equie te ee tobe.focsed be able to compensate for a small retinal

on the fireball. Flashblindness will normally blank out the ertire visual field of burn by learning to scan around the

view wiC. a bright afterimage. The ef- burned area.

fects persist enly a short time and re- 12.86 Retinal burns can be procovery is complete. dured at great disthwces from nuclear

12.84 During the period of flash- detonations, because the probability of

blindness (several seconds to minutes) their occur'ence doei not decrease as the

useful vision is lost. This may precl'iac square of the distance from the detonaeffective performance of activities re- tion, as is true of many other nuclear

quiring constant, precise visual func- weapons effects. Theoretically, the option. The severity and time required for tical process of image formation within

recovery of vision are determined by the the eye should keep the energy per unit

intensity and duration of the flash, the area on the retina a cvnstant, regardless

viewing angle from dte burst, the pupil of the distance. However, meteorologisize, brightnrss of the object being cal conditions and the fact that the

viewed and its background, and the vi- human eye is not a perfect lens, r11

sual complexity of the object. Flash- contribute toward reducing the retinal

blindness would be more severe at night burn hazard as the distance is increased

since the pupil is larger and the objects between the observer and the detona..

and background are usually dimly illu- tion.

minated. 12.87 Explosions with yields of

12.85 A retinal burn is a permanent more than about 1 megaton at heights

eye injury that occurs whenever the re- greater than some 25 miles may produce

tinal tissue is heated excessively by the retinal burns as far out as the horizon on

image of the fireball focused in the eye. clear nights. If the burst height is greater

The underlying pigmented cells absorb than some 50 miles, the short pulse of

much of the light (radiation) energy and thermal energy' from the early-time

the temperature is increased in that area. weapon debris, as well as that from the

A temperature elevation of 12 to 20'C X-ray pancake, can be effective in :his

(22 to 36°F) in the eye produces a ther- respoct (§ 7.91). Bursts above 90 miles
572 BIOLOGICAL EFFECTS

z!itude probably will not cause retinal for the complete absence of flashblindbur-s in persons on the ground, unless tiess are not available and the distances

the yield is greater than 10 megatons. in Figs. 12.89a and b are those within

The eye's blink reflexes are sufficiently which a visual loss for about 10 seconds

fast (roughly 0.25 second) to provide may be expected, to a degree sufficient

some protection against weapons of to preclude the performance of a precimore than 100 kilotons yield detonated sion task under conditions of dim light,

below about 25 miles. The blink time is e.g., a piiot reading instruments at

too slow to provide any appreciable night.

protection from smaller weapons or 12.89 The flashblindness and retinal

from bursts at higher altitudes. When burn safe separation distances do not

people have adequate warning of an bear a constant relationship to one animpending nuclear burst, evasive ac- other as the yield changes. In circumtien, including closing or shielding the stances that require determination of

eyes, will prevent both flashblindness complete eye safety (bearing in mind the

and retinal burns. 10-second visual loss criterion for

12.88 Safe separation distances flashblindness), the effect that occurs at

from ground zero, i.e., distances the greater distance from the burst is the

beyond which persons on the ground critical one. For example, for a height of

would not receive incapacitating eye in- burst of 50,000 feet at night, it is seen

juries, are shown in Figs. 12.88a and b from 'j. 12.88b that for yields up to

as a function of weapon yield for two about 3 megatons, flashblindness is the

heights of burst (HOB). The curves in important factor in determining the disFig. 12.88a are for a clear day; for a tahce at which there will be no incapac!oudy day the safe separation distances Qitating eye effects. For larger yields,

would be reduced to about half. The retinal burn becomes the limiting factor.

curves in Fig. 12.88b are for night con- Wherc only permanent eye damage is of

ditions The distances for retinal burns interest and the temporary loss of vision

are those for which such burns will not from flashblindness is of little concern,

occur provided the eye can blink within the retinal burn curves should be used to

0.25 second. A faster blink time will not estimate safe distances no mat.er what

change the values appreciably, but a the explosion energy yield.

slower time would increase them. Data

r,.It
BURN INJURIES 573

10 -- I I0 ,I

.1 H08 = 10,000 feet

_ / / RETINAL BURN

-o 101 I -- ~ 0 8O = 50,000 f ee t_

S- I RETINAL BURN

z

0

•I02- \ LSBI~fe

S•HOE - 10,000 feet

F.LA0SH BFLINADN ESS

-1--

•/ -

0 20 40 60 80 100

SAFE SEPARATION DISTANCE 'MILES)

Figure 12.88a. Flashblindness and retinal burn safe separation distai.-ces for an observer on

the ground, as a function of explosion yield, for burst heights of 10,000 feet

"and 50,000 feet on a clear day.

4" / FLSBINN)

- -~• • -- / .- : .'.- I
574 BIOLOGICAL EFFECTS

104_- -7 , 7 - -0,0/ 'Io i /f- -- /// --

- FL/ASHBL INDNESSY

/ /

-HOB= 10,000 feet

o RETINAL BURN HOB 50,000 feet

-., \RE ,NAL BURN

W, 1021-- /,/

z a

:2 -/HOB 50,0OO feet

1/ FLASHBLINDNESS

•oof

0 L___ -

_/ / / - ~//

_/ //

//

o 20 40 60 80 100 120 140 i1O

SAFE SEPARATION DISTANCE (MILES)

Figure 12.88b. Flashblindness and retinal burn safe sepfration distance& for an observmr on

the ground, as a function of explosion yield, for burst heights of 0,000 feet

and 50,00) feet at night.

II,
BURN INJURIES 575

NUCLEAR RADIATION INJURY

INTRODUCTION spite of the growing awareness by both

scientists and physiciar.s of the hazards

12.90 The injurious effects of nu- inherent in many radiation sources,

clear radiations from a nuclear explo- there were some excessive exposures. In

sion represent a phenomenon which is the course of time, however, recomcompletely absent from conventional mendations for preventing overexpoexplosions. For this reason, the subject sures were adopted and radiation injuof radiation injury (or sickness) will be ries became less frequent. Nevertheless,

described at some length. It should be occasional overexposures have occurred

understood, however, that the extended among personnel ol.erating radiographic

discussion does not necessarily imply equipment, powerful X-ray machines in

that nuclear radiation would be the most industrial laboratories and hospitals,

important source of casualties in a nu- cyclotrons, and experimental nuclear

clear explosion. This was certainly not reactors, or working with radioactive

the case in Japa, where the detonations materials.

occurred at heights of approximately

1,870 feet (Hiroshima) and 1,640 feet 12.92 .he harmful effects of nu-

(Nagasaki) above the ground. Such in- clear radiations appear I) be :aused by

juries as were caused by nuclear radia- the ionization (and excitation) produced

tion were due to the initial radiation. in the cells composing living tissue. AaiThe effect of the residual radiation, in a resu!t of ionization, some of the conthe form of early fallout and induced stituents, which are e'iential to tthe norradioactivity, was negligible. However, mal functioning of the cells, are altered

as was seen in Chapter IX, the situation or destrnyed. In addition, the products

could be very different in the event of a formed may act as poisons. Among the

surface burst. observed consequences of the action of

12.91 It has long been known that ionizing radiations or. cells are breaking

exposure to r~diaiions, such as X rays, of the chromosomes, swelling of the

alpha and beta particles, gamma rays, nucleus and of !he entire cell, increase

and neutrons, which are capable of pro- in viscosity of the cell fluid, increased

ducing ionization, either directly or in- per-._eability of the cell membrane, and

directly (§§ 8.21, 8.58), can cause in- destruction of cells. In addition, the

jury to living organisms. After the process of cell division (or "mitosis")

discovery of X rays and radioactivity, is delayed by exposure to radiation.

toward the end of the nineteenth cen- Frequently, the cells are unable to untury, it becamne increasingly apparent dergo mitosis, so that the normal cell

that an element of danger was associated replacement occurring in the living orwith exposure to ionizing radiations. 6 In ganism is inhibited.

6 'he mere general expression "ionizing radiations" is often employed instead of nuclear radiations,

.since this permigs tie inclusion of radiations of nonnuclear origin, e.g., X rays. hiaving .imiiar bioiogical

effects.

a

? ,. ". .• • ,. - *, ... "*- ..... . .. • . ..... .... ..-- . ,.. . -,,,,.... ' .... , :. * ', '*. .. ,,r•.,••r• . * ._, ,, • ... .. . . - ,.
576 BIOLOGICAL EFFEC-9 S

RADIATION DOSE UNITS the energy of the radiation, the kind and

degrec. of the biological damage, and the

12.93The r adiatio uas nature of the organism or tissue under

the roentgen was described in § 8.17. consideration.

By definition, it is applicable only to 12.95 The "biological dose," also

gamma rays or X rays and not to other called the "RBE dose," that provides a

types of ionizing radiation, such as direct indication of the expected effects

alpha and beta particles and neutrons. of any ionizing radiation on the body (or

Since the roentgen refrs to a specific organ), is stated in terms of the "rem,"

result in air accompanying the passage an abbreviation of "roentgen equivaleni

of an amount of radiation through the (in) man." It is equal to the absorbed

air, it does not imply Rny effect that it dose in rads multiplied by the RBE for

would produce in a biological system. the particular radiation (or radiatiops)

The roentgen is thus a measure of the absorbed; thus,

"44exposure" to gamma rays and X rays.

The efect on a biological system, such Dose in rems = Dose in rads x RBE.

as the whole body or a particular organ, An advantage of the rem is that it is

however, depends on the amount of ra- possible to express the total biological

diation energy that has been absorbed by effect that might result from the absorpthe body or organ. The unit of absorbed tion of more than one kind of ionizing

dose, which applies to all kinds of ion- radiation. The absorbed dose in rads of

izing radlations, including alpha and each radiation type is multiplied by the

beta particles and neutrons, is the rad, as appropriate RBE and the resuis ae

defined in § 8.18. added. (In connection with radioiogical

i12.94 Although all ionizing radia- protection in pea-.etime activities, the

tions are capable of producing similar "dose equivalent" in rems is defined as

biological effects, the absorbed dose the absorbed dose in rads multiplied by

(measured in rads) which will produce a a "quality factor," and sometime- by

certain effect may vary appreciably from other modifying factors. The quality

one type of radiation to another. This factor, which depends on the nature and

difference in behavior is expressed by energy of the absorbed radiation, reineans of the "relative biological effec- places the RBE.)

tivencss" ((,r RBE) of the particular 12.96 All radiations capable of

nuclear radiation. The RBE of a given producing ionization (or excitation) diradiation is defined as the ratio of the rectly of indirectly, e.g., alpha and beta

absorbed dose in rads of gamma radia- particles, X rays, gamma rays, and

tion (of a specified energy) 7 to the ab- neutrons, cause radiation injury of the

sorbed dose in rads of the given radia- same general type. Although the effects

tion having the same biological effect. are qualitatively similar, the various raThe value of the RBE for a particular diations differ in the depth to which they

type of nuclear radiation depends upon penetrate the body and in the degree of

several factors, incluciing the dose rate, injury coiresponding to a specified

'Gamma rays feoin cobalt-60 have been commonly specified for this purpose.
NUCLEAR RADIATION INJURY 577

amount of energy absorption. As seen sary to distinguish between an "acute"

above, the latter difference is expressed (or "one-shot") exposure and a

by mearts cf the RBE. "chronic" (or extended) exposure. In

12.97 The RBE for gamma rays is an acute exposure the whole radiation

approximately unity, by definition, al- dose is received in a relatively short

'hough it varies somewhat with the en- interval of time. This is the case, for

ergy of the radiation. For beta particles, example, in connection with the initial

the RBE is also close to unity; this nuclear radiation. It is not possible to

means that for a given amount of energy define an acute dose precisely, but it

absorbed in living tissue, beta particles may be somewhat arbitrarily taken to be

produce about the same extent of injury the dose received during a 24-hour

within the body as do X rays or gamma period. Although the delayed radiations

rays.8 The RBE for alpha particles from from early fallout persist for longer

radioactive sources that have been taken times, the main exposure would be reinto the body is in the range from 10 to ceived during the first day and so it is

20, more specifically for the develop- regarded as being acute. On the other

ment of bone cancers. The RBE for hand, an individual entering a fallout

neutrons varies with the energy and the area after the first day or so and remaintype of injury. For the neutron energy ing for some time would be considered

spectrum of nuclear weapons, the RBE to have been subjected to a chronic

for immediate (acute) radiation injury is exposure.

closc to 1.0. But it is significantly larger 12.99 The importance of making a

(4 to 10) for the occurrence of opacities distinction between acute and chronic

of the eye lens (cataracts), leukemia, exposures lies in the fact that, if the dose

and genetic changes (§ 12.144 et seq., rate is not too large, the body can

§ 12.201 et seq.). For these biological achieve partial recovery from many (but

effects, a certain amount of energy ab- perhaps not all) of the consequences of

sorbed from exposure to neutrons is nuclear radiations. For example, an

much more damaging than the same acute dose of 50 rems will generally

amount of energy (in rads) absorbed cause changes in the constituents of the

from gamma rays.9 blood (§ 12 113), but the same dose

spread over a period of years (or even

GENERAL CHARACTERISTICS OF less) will produce only minor etfects on

RADIATION EFFECTS the blood cells. In an extreme case, an

acute dose exceeding 600 rems would

12.98 In considering the possible cause serious illness and in the great

effects on the body of ionizing radia- majority of instances death could occur

tions from external sources, it is neces- within a few weeks. On the other hand,

KBeta particleL, from sources on or near the body can also cause skin lesions, called "beta burns"

(§ 12.155 el seq.).

"•The curves in Chapter VIII that show the neutron dose in rads at a particular location relative to a

nuclear explosion ca-lculated by considering the contributions of nieutrons in various energy ranges at that

location for typical weapons spectra. Multiplication of these doses by the appropriate RBE gives the

corresponding biological dose in reins.

a,
578 BIOLOGICAL EFFECTS

a chronic dose of the same total magni- impossible to make detailed observatude accumulated gradually over 20 tions and keep accurate records. Neveryears might have no observable effect. theless, certain important conclusions

12.100 The injury caused by a cer- have been drawn from Japanese experitain dose (and dose rate) of radiation ence with regard to the effects of nuclear

will depend upon the extent and part of radiation on the human organism.

the body that is exposed. One possible 12.103 Information on this subject

reason is tha! when the exposure is res- has also been gathered from other

tricted, the unexposed regions may be sources. These include a few laboratory

able to contribute to the recovery of the accidents involving a small number of

injured area. But if the whole body is human beings, irradiatior used in treatexposed, many organs are affected and ing various diseases and malignancies,

recovery is much more difficult. and extrapolation to man of observa12.101 Different portions of the tions on animals. In addition, detailed

body show different sensitivities to ion- knowledge has been obtained from a

izing radiations, and there are variations careful study of over 250 persons in the

in degree of sensitivity among individu- Marshall Islands, who were accidentally

als. In general, the most radiosensitive exposed to nuclear radiation from fallcells are found in the lymphoid tissue, out following the test explosion on

bone marrow, spleen, organs of repro- March 1, 1954 (§ 9.104 et seq.). The

duction, and gastrointestinal tract. Of exposed individuals included both Marintermediate sensitivity are the skin, shallese and a small group of American

lungs, and liver, whereas muscle, servicemen. The whole-body radiation

nerve, and adult bones are the least doses ranged from relatively small valsensitive, ties (14 rems), which produced no obvious symptoms, to amounts (175 reins)

that caused prompt marked changes in EFFECTS OF ACUTE RADIATION the blood-forining system (§ 12.124).

12.104 No single source of data di12.102 Before the nuclear bomb- rectly yields the relationship between

ings of Hiroshima and Nagasaki rela- the physical dose of ionizing radiation

tively little was known of the phenom- and the clinical effect in man. Hence,

ena associated with acute whole-body there is no complete agreement conexposure to ionizing radiation. In Japan, cerning the effect associated with a spehowever, a large number of individuals cific dose or dose range. Attempts in the

rece.ved whole-body doses of radiation past have been made to relate particular

ranging from insignificant quantities to symptoms to certain narrow ranges of

amounts wh;ch proved fatal. The effects exoosure; however, ,he data are inconiwere often complicated by other injuries plete and associated with many compliand shock, so that the symptoms of cating factors that make interpretation

acute radiation injury could not always difficult. For instance, the observations

be isolated. Because of the great in Japan were very sketchy until 2

numbers of patients and the lack of weeks following the exposures, and the

facilities after the explosions, it wai people at that time were suffering from

- . '" ., ........ . - ' .. . . .,,,. " ", ... ... . , , ,-.-' '.. -- .
NUCLEAR RADIATION INJURY 579

malnutrition and pre-existing bacterial and a generalized feeling of illness. The

and parasitic infections. Consequently, onset time decreases and the severity of

their sickness was often erroneously at- these symptoms increases with increastributed to the effects of ionizing radia- ing dose. During the latent phase extion wher, such was not necessarily the posed individuals will experience few,

ca•e. The existing conditions may have if any, symptoms and most likely will

been aggravated by the radiation, but to be able to perform useful tasks. The

what extent it is impossible to estimate final phase is characterized by illness

in retrospect. that requires hospitaliztion of people

12.105 In attempting to relate the receiving the higher doses. In addition

acute radiation dose to the effect on to the recurrence of the symptoms noted

man, it should be mentioned that reli- during the initial phase, skin hemorable information has been obtained for rhages, diarrhea and loss of hair may

doses up to 200 reins. As the dose appear, and, at higher doses, seizures

increases from 200 to 600 reins, the data and prostration may occur. The finat

from exposed humans decrease rapidly phase is consummated by recovery or

and must be supplemented more and death.

more by extrapolations based on animal 12.108 With the foregoing in mind.

studies. Nevertheless, the conclusions Table 12.108 is presented as the best

drawn can be accepted with a reasonable available summary of the effects of

degree of confidence. Beyond 600 rems, various whole-body dose ranges of ionhowever, observations on man are so izing radiation on human beings. Resporadic that the relationship between suits of radiobiological studies are gendose and biological effect must be in- erally reported in terms of the (vertical)

ferred or conjectured almost entirely midline tissue dose in fads. This dose is

from observations made on animals ex- lower than the dose that would be meaposed to ionizing radiations. Such ob- sured by instruments (and the dose thal

servations have been made in recent vwould be absorbed by :issue) near the

years at extremely high doses. surface of the body by a factor that

12.106 Individuals receiving acute depends upon the energy of the radiation

whole-body doses of ionizing radiation and the size of the individual. The numay show certain signs and symptoms clear radiation data presented in

of illness. The time interval to onset of Chapters VIII and IX refer to the abthese symptoms, their severity, and sorbed dose in tissue at the surface of an

their duration generally depend on the individual that is nearest the burst, and

amount of radiation absorbed, although thus they also correspond to the exthere may be significant variations pected instrument readings. For consisamong individuals. Within any given tency, the data in Table 12.108 are the

dose range the effects manifested can be doses (in rems) equivalent to the ab-i

divided conveniently into three time sorbed doses (in rads) in tissue at the

phases: initial, latent, and final. surface of the individual. For gamma

12.107 During the initial phase, rays, these absorbed doses are essenexposed individuals may experience tially equal to the exposures in roentnausea, vomiting, headache, dizziness, gens (8 8.18). For nuclear weapon ra-

.o
580 BIOLOGICAL EFFECTS

SI : : :

E ZU

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rq ~0 U, , Vl V I

I 00

00

t> E

E~ E

SVl V1 vi

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E. , ,' =

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o 0 Cu
NUCLEAR RADIATION INJURY 581

.v

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582 BIOLOGICAL E~FFECTS

cdiationi, the midline tissue doseF for :;,ary so that the patient may receive such

average size adults would be appoxi.- trretri~nt as mnay be indicated. Up to

mnately 70 percent of the doses in the 600 terrns, there is reasonable contitable. dence in the clinical even'.s and appro12.109 As shown in Table 12. 108, priate therapy, but for (loses in excess of

below 1(X reins the response is ~Arnos1l this arnouait there is considerably uncercompletely subLtlinical, that is to say, tainty ariO variability in response.

there is no sickness requiring srpecial 12.111 Beyond I ,C00 reins, the

attention. Changes m--ay, nevertheless, popcso eoeyaes orta be occurring in the blood, a. wil be throspect of b resrctery largel so portatseen later, Between I(M and I WO re hrpymybersnitdlagl ta

is the range in which therapy, i~. liative measures. It is oC :riedical inter.

ov~r medical treatmnent, will he suc est, however, to subdivide this lethal

cesfulat he owe en an ma be range into two parts irn which the

suces~sful at the upper endan The bert characteristic major clinical effects are

symptoms oi radiation injury are nausea itretAhuhtediviigln a

and vomiting, which may crmnebeo'n somewhat arbitrarily set at 5.MX)

within about 1,5 minutes to 6 hours uf reins in Table; 12.108, human data are

exposure, depending on the dJose, a~c- s() limited that this dose level might well

companied by discurnlort (mnalaise), have usy value from 2,000 to 6,000

loss of appetite, and fatigue. The ~o'st reins. In the range from 1,.000 to

significant, although not immediately (roughly) 5,M0) reins, prthological

obvious effec in, th ag ne o- changes in tht: gastrointestinal tract,

CdraiILC istaon the hrange Ufliet which are apparent at lower doses, betissue, i.e., mie organs concevned with com-e very markced. Above 5,000 reins,

the formation of blood. An important the central nervous system also exhibits

maifestation of the chan~ges In the teconsequences of major injury,

functioning of these organs is lcuko- 12.112 The supkerposition of radia..

penia, that is, a decline in the number of tion effects upcxi injuries from other

leukocytes (white blood cells). Loss of causes may be tc,,pected to result it) an

hair (epilation) will he apparent about 2 increase in the number of cases of

weeks or so after receipt of a dose ex- shock, For example, the combination of

ceeding 300 rerns. sublethal nuclear radiation exposure and

12.110 Because of the increase in moderate thermal burns will produce

the severity of the radiation injury and earlier and more severe shock than

the variability in response to treatment would the comparable burns alone. The

in the range from 100 to 1,000 reins, it healing of wounds of all kinds will bet

is convenient to subdivide this range retarded because of the susceptibility to

into three subsections, as shown in secondary infection accompanying radi-

'Cable 12. 108. For whole-body doses ation injury arid for other reasons. In

from 100 to 200 reins, hospitalization is fact, infectons, which could normally

generally not required, but above 200 be deal', with by the body, may prove

reins admission to a hospital is rneces- fatal in such cases.
(ClARACTISRTI'CS O- ACUTE. WHOLE--13OtY RAD!ATION INJURY 583

CHARACTERISTICS OF ACUTE WHOLE-BODY RADIATION INJURY

DOSES OF 25 TO 100 REMS: NO toms at all, There may be some nausea

ILLNESS and vomiting on the first day or so

fol lcw'ng irradiation, but subsequently 12.113 Single doses in the X,:ge of there is a latent period, of up to 2 weeks

from 25 to 100 reins over the! whole

or more (§ 12.107). The usual sympbody will produce some changes in the oms, sc .17 l o etitcan mablood (§ 12. 124). These changes do not tais, may ap of but te d the

usualy ccurt~eow tis angeandare laise, may reappear, but if they do, they usually occur below this range and are aeml.Tecagsi h hrce

not rodced ons~enty ulessthe are mild. The changes in the character

not produced consirtently unless the of the blood, which accompany radiadose is 50 reis or more. Disabling tion injury, become significant during sickness does not occur and exposed the latent period anti persist for some

individuals should be able to proceed the If pere a nd co pi atio nsome

with their usual duties. time. If there are no complications, due

to other injuries or infection, there will

DOSES OF 100 TO 200 REMS: SL!GIIT be recovery in essentially all cases. In

OR NO ILLNESS gonei il, the more severe the early stages

Oif t!de radiation siclkness, the longer will

12.114 A whole-body dose in the be the process of recovery. Adequate

range of 100 to 200 reins will result in a care and the use of antibiotics, as may

certain amount of illness but it will be indicated clinically, can greatly cxrarely be fatol, Doses of this magnitude pedite complete recovery of the small

were common in Hiroshima and Naga- proportion of more serious cases.

saki, particularly au'ong persons who

were at some distan.e from the nuclear DOSES OF 200 TO 1,000 REMS:

explosion. Of the 267 individuals acci- SURVIVAL POSSIBLE

dentally exposed to fallout in the Mar-

,hall Islands following the test explo- 12,116 For doses between 200 and

sion of March 1, 1954, a group of 64 1.000 rems the probability of survivai is

received radiation doses in this range, good at the lower end of the range but

* The exposure of these individuals was poor at the upper end. [he initial sympnot strictly of the acute type, since it toms are similar to those common in

* extended over a period of some 45 radiation sickness, admely, nausea, vohours. More than half the dose, how- miting, diarrhea, loss of appetite, and

ever, was received within 24 hours and malaise. The larger the dose, the sooner

the observed effects were similar to will these symptoms deve!op, generally

"those to be ex,,ected from an acute ex- during the inidal day of the expostire.

posure of the same amount. After the first day or two the symptoms

12.115 The illness from radiation disappear and the.:' may be a latent

doses in this range does not present a period of several days to 2 weeks during

serious problem since most patients will wlich the patient feels relatively well,

suffer little more than discomfort and although importani changes are occurfatigue and others may have no symp- ring in the blood. Subsequently, there is
584 BIOLOGICAI UFFECTS

Figure 12.117. An example )f cpilatiora due to radiation exposure.

a re~urn of symptomns, including fever, techiac) are ubterved. This tendency

diarrhea, and a steplike rise in tcrypera- may be marked. Particularly common

ture which may be due to accompanying are spontaneous bleeding in the mouth

inf-,ction. and from the lining of the intestinal

12.117 Commencing about 2 or 3 tract. There may be blood ini the urine

weeks after exposure, there is a ten- due to bleeding in the kidney. The hedency to bleed into various organs, and morrhagic tetidency depends mainly

small hemorrhages Pinder the skin (pe- upon depletion of the platelets in the
CHARA,CTERISTICS OF ACUTE WHOLE-BODY RADIATION INJURdY 585

blood, resulting in defects in the blood- and degenerative changes in tcstes and

clotting mechanism (see § 12.129), ovaries. Ulceration of the mucous

Loss of hair, which is a prominent con- membrane of the large intestine, which

sequence of radiation exposure, also is generally indicative of doses of 1,000

starts after about 2 weeks, i.e., imme- rems or more, was also noted in some

diatcly following the latent period, for cases.

doses over 300 rems (Fig. 12.117). 12.121 Those patients in Jz,)an who

12.118 Susceptibility to infection of survived for 3 to 4 months, and did not

wounds, burns, and other lesions, --in succumb to tuberculosis, lung diseases,

be a setious complicating factor. This or other complications, gradually iewould result to a large degree froin loss covered, Thert was no evidence (;f peruf the white blood cells and a marked manent loss of hair, and examination of

depression in the body's immunological 824 survivors some 3 to 4 years later

precess. For example, ulceration about showed that their blood composition

the li'-s may commence after the latent was not significantly different from that

period and spread from the mouth of a control group in o city not subjected

througli the entire gastrointestrinal tract to nuclear attack.

in the terminal stage of the sickness,

The multiplication of bacteria, made

possible by the decrease in the white SURVIVAL IMPROBABLE

ce!ls of the blood and injury to other

immune mechanisms of the body, 12.122 Very large doses of wholeiO.lows an overwheiming infectioi to body radiation (approxi,.,ately 5,000

develop, reins or more) result in prompt chanpes

12.119 Among other effects ob- in the central nervous system. The

served in Japan was a tendency to symptoms are hyperexcitability. ataxia

spontaneous internal bleeding toward (lack of muacular coordination), :.,spi- .he end of the first week. At the ,game ratory .,,,,,,s, and intermittent stupor,

time, swelling and inflammation of the There is almost immediate incapacitathroat was nrot uncommon, The deve[ tion for most people, and death is ceropment of severe radiation illress tain in a few hours to a week or so after

among the Japanese was accompanied the acute exposure. If the dose is in the

by an increase in the body temperature, range from i.,C)0 to roughly 5,000

which was probably due to secondaiy rems, it is the gastrointestinal system

infection. Generally th-re was a step- which exhibits the earliest severe clinilike rise between the fifth and seventh cal effects, There is the usual vomiting

days, sometimes as early as the third and nausea followed, in more or less

day following exposure, and usually rapid succession, by prostration, diarcontinuing until the day of death. rhea, ano'exia (lack of appetitt, and dis12.120 In addition to fever, the like for food), and fever. As observed

more serious cases exhibited sevtic after the nuclear detonations in Japan,

emaciation and 6elirium, and death oc- the diarrhea was frequent and severe in

curred within 2 to 8 weeks. Examination character, being watery at first and

after death revealed a decrease in size of tending tc, become bloody later; how-

" I, .
586 BIOLOGICAL EFFECTS

ever, this may have been related to pre- the bleod of human beings (§ 12.103).

existing disease. The descriptions given below, which are

12.123 The sooner the foregoing in general agreement with the reults

:.ymnptorns o, radiation injury develop observed in Japan, are based largely on

the sooner ;s death likely to result. Al- this study.

though there may be no pain during the 12.125 One of the most strikih•;

first few days, patients experience :na- hematological changes associated with

laise, accompanied by marked depres- radiatio'n injury is in the number of

sion and fatigue. At the lower ena of the white blood cells. Among these cells are

dose range, the early stages of the se- the neutrophils, tormed 'chiefly in the

vere radiation illness are followed by !i bone marrow, which are concerned with

lateat period of 2 or 3 days (or rmore), resisting bacterial invasion of the body.

during which the patient appear.s to be During the course of certain types of

free from symptoms, althuugh profound bacterial infection, the number of neucbvnges are t•kirig plice hii the body, trophils in the blood increases rapidly to

c.,vpe,,ially in the blood-formitg tissues, combat the invading organisms. Loss olf

This period, when it occurs, is followed ability to meet the bacterial invasion,

by a recurrence of the early symptoms, whether due to radiation or any other

often accompanied by delirium or coma, injury, is a very grave matter, and bacterminating in death usually within a teria which arr. normally held iii check

few days to 2 weeks, by the neutrophils can then multiply

rapidly; the consequences are thus

serious, There are several types of white CONSTITUENTS blood cells with different specialized functions, but wb,-h have in common

12.124 Among the biological con- the general property of r-esisting infecsequences of exposure of the whole tion or removing toxic products from the

body to an acute dose of nuclear radia- body, or both,

tion, perhaps the. most striking and 12.126 After the body has received

c aracteristic are the changes which a radiation dose in the sublethal range,

take piace in the blood and blood-form- i.e., about 200 rems or les, the total

ing organs. Normally, these changes number of white blood ceil' may show a

will be detectable only for doses greater transitory increase during.: tho first 2 days

than 25 reins. Much information on the or so, and then decrease below normal

hematological response of human levels. Subsequently the white count

beings to nuclear radiation was obtained may fluctuate and possibly rise above

after the nuclear explosions in Japan and normal on occasions. During the sevalso from observations on victims of enth or €ighth weeks, the white cell

laboratory accidents. The situation count becomes stabilized at low leveis

which developed in the Marshall Islands and a minimum probably occurs at

in March 1954, however, provided the about this time. An upward trend is

opportunity for a very thorough study of observed in succeeding weeks but com-.

the effects of small and moderately large plete recovery may require several

doses of radiation (up to 175 rems) on months or more.
CHARACTERISTICS OF ACUTE WHOLE-BODY RADIATION INJURY 587

12.127 The neutrophil count paral- change in the number of erythrocytes is

lels the total white b!ood cell count, so much less striking than that in the white

that the initial increase observed in the blood cells and platele:s, escpecially for

latter is apparently due to increased radiation doses in the range of 200 to

mobilization o, neutrophils. Completc 400 reins, Whereas the response in the:;.

return of the numbcr of neutrophils to cells is rapid, the red cell count shows

normal does not occur for several little or no change for several days,

months. S'ibsequently, there is a decrease which

12.128 In contrast ,o the behavior may continue for 2 or 3 weeks, followed

of the neutrophils, the mimber of lyrn- by a gradual increase in individuals who

phocytew, produced iii parts of the lym.- survive.

phatic iissues of the body, e.g., lymph 12.131 As an index of severity of

nodes and spleen, shows a sharp drop radiation exposure, particularly in the

soon after exposure to radiation. The sublethal range, the total white cell or

lymphocyte count continues to remain neuttophil counts are of liniated usefulcCsiderably below normal for several ness because of the wide fluctuations

:•uoaths and recovery may require many and the fact that several weeks may

months or even years. However, to elapse before the maximum deptession

judge from the obsetvationt. made in is observed. The lymphocyte count is of

Japan, the lymphocyte count of exposed more value in this respect, particularly

individuals 3 or 4 years after exposure in the low dose range, since depression

was not appreciably different from that occurs within a few hours of exposure

of unexposed persons, (§ 12.224). However, a marked de12.129 A sigrnificant hematologicOa crease in the number of lymphocytes is

change also occurs in the platelets, a observed even with low dcee. s0 th,.kie

constituent of the blood which plays an is relatively little difference with large

important role in blood clotting. Unlike doses.

the fluctuating total ,'hite count, the 12.132 'The platelet count, on the

number of platelett, begins to decrease other hand, appears to exhibit a regula:

soon after exposure and fall, steadily pattern, with the maximum depression

and reaches a minimum at the end of .Eing attained at appraximately the

about a menth. The devrease in the same time for various exposures in the

number c! platelets is followed. by pat- sublethal rv',,.g. 1urthertrre. in this

tial recovery, but a normal count may range, the degree of depression from the

not be attained for several months or normal value is roughly proportional to

even years after exposure. It is the de- the estimated whole-body dose. It has

crease in the platelet count which partly been suggested, therefore, that the plaexplains the appearance of hemorrhage telet count might serve as a convenient

and purpura in radiation injury, and relatively simple direct method for

12.136- The red blood cell (erythro- determining the severity of radiation incyte) count also undergoes a lecrevse a, jury in the sublethal -ange. The main

a reiult of radiation exposure and hem- disadvantage is that an appreciable de-

,rrhage, so that symptoms of anemia, crease in tne platelet count is not appare.g., pallor, become apparent. But the ent until some time after exposure.

:1 ___
588 BIO.OGIC AL. EFFECTS

CCMBINED INJURIES

GENERAL CONSIDERATIONS and Nagasaki, among those who sur.

vived for 20 days or more, about 50

12.133 Thus far, blast, thermal, percent of the peop!e within 1.25 miles

and (ionizing) radiation injuries have of ground zero received combined injubeen considered separately, but corn- ries, whereas the incidence was roughly

bined injuries, irom two or more of 25 percrnt at distlnces from 1.25 to 3

these causes, would probably be corn. miles from ground zero.

mon as a result of a nuclear explosion. 12.135 It should be recognized that

Combined injuries might be receivcd ihe incidences of combined injuries in

almost simultaneously, e.g., from a the two Japanese cities apply only to the

single detonation withput fallout, or particular curcumnstances of the nuclear

separated in time by minutes to days, explosions. The number and types of

e.g., from a single detonation followed combined injuries will ,depend on the

by fallout or from multiple detonations, yield, height of burst, and the conditions

Injuries may. consist of any combination of exposure. Air bursts, unaccompanied

of hlast, thermal, and radiation effects, by fallout, with yields !ess than about 10

Furthermore, such injuries may be in- kilotons, would cause combinations of

fluenced by other conditions that might mec~hanical, thermal, and ioitial-radiabe expected during or after a nuclear tiozn injuries. On the other hand. larger

attack, e.g., malnutrition, poor sanita- yields would be expected to produce a

tion, fatigue, and various other en- greater proportion of combined burn and

vironmental factors, Current knowledge mechanical injuries; initi4l-radiation inconcerning combined injuries is derived juries would be less significant in the

mainly from studies of the Japanese surviving population. A nuclear explovictims of nuclear bombs and from lab- sion near (above or clow) the surface

oratory and field tests with a variety of would maximize radiation injuries due

animals, to fallout and in a large proportion of the

12.134 The contribution of corn- casualties such injuries would be combined injumies to overall mortality and bined with mechanical and thermal efmorbidity in Japan has never been de- fects. People who are outdoors and untermined adequately, but two general shielded would have a greater

impres'iions have emerged: the combi- probability of sustaining initial and/or

nation of mechanical (blast) and thernial fallout (residual) radiation injury in

injuries was responsible for the majority combination with flash burns than wouid

of deaths that occurred within the first those within buildings. In the latter

48 hours after the attacks, and delayed case, burns would be minimized and

mortality was higher and complications' combinations of mechani :al and radiawere more numerous among burned tion injuries might be dor-inant.

people exposed to ionizing radiation 12.136 No reliable criteria for incathan would have been anticipated in the pacitation are. known for persons reabsence of such radiation. In Hiroshima ceiving combined injuries. The avail- 4
COMBINED INJURIES 589

able data do indicate, however, that some anemia and the body is less able to

individuals suffering such injuries that cope with this stress if the immune

occur nearly simultaneously are unlikely mechanism and the activity of the bone

to become caalialties within a few hours, marrow are depressed by the ionizing

provided the individual injuries would radiation. The enhanced mortality from

not produce casualties if administered the thermal burns combined with radiaseparately. Consequently, it is not un- tion exposure was not observed for

reasonable to make early casualty pre- doses of 25 reins or less and it is irndictions for a singe nucleab detonation probable that the synergistic effect

on the basis of the most significant in- would occur unless the dose is large

jury. If there is a substantial probability enough to produce at least minimal efof another injury, this cou;d contribute fect on the immunologic and hematoloto combiaed injury and iiight result in gic systems. Very little information is

increased casualties at later times. available on fallout (intzrnal) radiation

12,137 The effects of combined in- in combination with thermal or any

juri.s may be synergistic, additive, or other form of injury.

antagonistic. That is to say, the overall

reswonse may be greater than, equal to,

or less than, respectively, what would

be predi,:ted based on the assumption INJURIES

tha( the various injuries act independently of one another ;n producing cL', 12.139 Mechanical and radiation

sualties. Quantitative data trom labora- injuries can be expected to tce frequent,

tory experiments suggesh that in particularly if fallout is present. Studie~s

situations where a cotnbi-aed effect has indicate that there is a delay in wound

been observed, the interaction of the healing with doses in excess of 3X)

various lorms of injury. has resulted in reins, and that wounds in irradiated

enhanccd eaily as well as delayed mor- subjects are considerably more serious if

tality, although from the limited data treatment is delayed for more than 24

available the latter seems to be ihe more hours. In addition, missile and impact

common, injuries that result in disruption of the

skin and damage to the soft tissues pro- vide a portal of entry for infecti~n, and

RADIATION AND THERMAL INJURIES thus may be extremely hazardous to

iriadiated peoo!e. Injuries that are asso12.138 Exposure of laboratory an- ciated with significant blood loss would

imals to external io)nizing radiation be more serious in those who have rewhile subjected to thermal burn has ceived a radiation dose large enough to

been found to cause a siibstantial in- interfere with normal blood clotting

crease in mortality over that t;xpected mechanisms.

from the insults received separately.

The. extent of the increase depends on 12.140 One week after exposure to

the radiation dose and the severity of the an external radiation dose which would

burn. Severely burned subjects exhibit by itself have resulted in 45 percent
590 lIOI.OGICAI. FFFE('TS

mortality within 30 days, animals (rats) THERMAL AND MECHANICAL

were subjected to a blast overpressure INJURIES

which would normally produce 5 percent early lethality. As a result, early 12.141 Burns and mechanical injulethality associated with blast-induced ries in combination are often encounhemorrhage and lung injury was in- tered in victims of conventional enplocreased four fold and the delayed tor- sions. Increased numbers of delayed

tality was almost double that expected complications, shorter times-to-death,

from the radiation alone. In these tests, and enhanced mortality rate are frequent

ionizing radiation and blast were clearly occurrences. However, few quantitative

synergistic in causing both early and data are available on this form of corndelayed mortality. bined injury.

LATE EFFECTS OF IONIZING RADIATION

INTRODUCTION cells and tissues at the time of exposure.

12.142 There are a number of con- If atn exposed individual survives the

sequences of nuclear radiation which acute reaction, ,-ell replacement may be

may not appear for some years after complete, but the cells may not necesexposure. Among them, apart from sarily be quite normal; however, the

genetic efftects, are the formrtation of causes for the late effects are largely

catar'acts, nonspecific life shortening, unknown although many theories have

leukemia, other forms of malignant dis- been proposed.

e.-se, and retarded development of children in utero at the time of the exposure. CATARACTS

Information concerning these late effects has been obtaitied from continued 12.144 The term "cataract" is

studies of various types, including those commonly used to describe any detectin Japan made chiefly under the direc- able change in the normal transparency

tion of the Atomic Bomb Casualty of the lens of the eye. Cataracts may

Commission.'M ran"ge from small lesions, which cause

12.143 The effects which occur only minor impairment of vision, to

late, in life, 'ike the acute reactions extensive opacification thlat results in

observed within a few weeks or months total blindness. The vast majority of

after irradiation, arise from changes in natural cataracts in man are of the senile

"o'The Atomic Bomb Casualty Commission (ABCC) of the U.S. National Academy of Sciences-National Pt, search Council was sponsored by the U.S, Atomic Energy Commission (now the Enr'gy .

Research and Development Administration) and administered in cooperation with the Japanese Natioi;al

Institute n! Health. One of its purposes was to .kudy the long-term effects of human exposure to nuclear

radiation. In 1975, the ABCC was superseded by the Radiation Effects Rescarcl Foundation which is ,.

supported equally by Japan and the United States.

_ _7

- -" ". ' f - . . - . - . . . -'-. . . .. ' . ~ -,...
LATE EFFECTS OF IONIZING RADIATION 591

type, it is rare in people under 40 years anese who developed eye opacities from

old and its frequency increases with age. radiation, proper correcting lenses proSufficient exposure of the eye lens to vided serviceable vision. Furthermore,

ionizing radiations can cause cataracts the opacities have apparently not bein man and it, other animal species. come worse with the passage of time- in

There is a latsnt period between expo- some cases, in fact, an improvement :)as

sure of the eye and development of an been observed. Only a small proportion

opacity ranging from a few months to of the cataracts were bad enough to

several years. The duration of the latent cause substantial diminution of central

period is shorter the greater the radiation vision. There have been very few cases

exposure. Fast neutrons, such as those of eye lens opacities in people who

from a nuclear explosion, have been received doses of less than 200 -ems of

found to be more effective than gamma ionizing radiation to the eyes. This tends

rays in producing cataracts. Studies with to support the commonly held view that

small animals indicate that fast neutrons cataract formation is a threshold phehave an RBE (§ 12.95) of about 4 to 6 nomenon, that is to say, it will not occur

for cataracts and it is commonly as- unless the eye dose exceeds a more-orsumed that similar values are applicable less definite minimum value. Not evto man. eryone receiving a radiation dose ex12.145 Eye lens opacities caused by ceeding the threslold value will

radiation from the nuclear explosions necessarily develop cataracts, but the

were first detected among the inhabi- probability of this occurring is expected

tants of Hiroshima and Nagasaki in to increase the larger the dose to the

1950, about five years after the attacks, eyes.

In nearly all cases the individuals had

suffered extensive epilation of the scalp, LEUKEMIA

so that they had probably received

whole-body doses of 300 rems or more. 12.147 Studies of mortality rates

In 1963 and 1964 eye examinations have shown that, at least prior to about

were made on some 2,500 survivors, of 1950, leukemia, a form of cancer in

whom an estimated 40 percent had re- which there is a proliferation of white

ceived radiation doses in excess of 200 cells in the blood, was a much more

rems. A significantly larger number of common cause of death of radiologists

cataracts were found among those who than of other physicians. This has been

had received the highest doses. In an- attributed to chronic exposure to modother survey, there was a suggestion of erate amounts of radiation over many

impairment of visual acuity among years. After protective measures were

children who were in utero at the time of improved, the incidence of leukemia

the bombings and whose mothers had among radiologists declined markedly.

been exposed to radiation. The sample A largei than expected frequency of

size was too small, however, for a sta- leukemia has also been observed among

tistically meaningful conclusion to be a group of people in the United King..

drawn. dora who had received large doses of X

12.146 In the great majority of Jap- ray, to the spine for the treatment of a

All
592 BIOl.OI('CAl F!FECTS

form of arthritis known as ankylosing vice. By attributing an RBE of about 5

spondylitis. Three main types of leuke- for the induction of leukemia by fast

mia are induced by radiation, namely, neutrons, the incidences (per rem) in the

acute dnd chronic granulocytic and two cities were in general agreement.

acute lymphocytic forms; the occur- The evidence from Japan, and from

rence of chronic lymphocytic leukemia othcr sources, is that the probability of

is not significantly increased by radia- the occurrence of leukemia is roughly

tion. The development of leukemia as a proportional to the whole-bdy dose,

result of an overexposure to radiation is and there is no indication of a threshold

associated with a latent period varying value. About 90 percent of the cases of

from one to 20 years or more. The leukemia among the survivors in Hirodisease is generally fatal, no inatter shima and Nagasaki received doses of

what its cause. more than 200 reins, but not all the

12.148 The first evidence of an in- people who received such large doses

creased incidence of leukemia among developed the disease. An approximate

the survivors of the Hiroshima and Na- estimate suggests that there were about

gasaki explosions appeared in 1947. 20 instances of leukemia per rem per

The occurrence of the disease reached a million population exposed at age 10

peak in 1951 and 1952 and it has been years or more and roughly twice this

declining since then. By the end of number for younger individuals.

1966, tile frequency of acute granulocytic anemia was approaching the normal value for Japan. Children who were OTHER TYPES OF CANCER

exposed to radiation when they were

less than 10 years oid were roughly 12.150 It has been established from

twice as susceptible to leukemia as older the mortality statistics of radiologists

individuals. One case of acute granulo- and of some of the spondyltic patients

cytic leukemia was discovered in 1972 mentioneJ in § 12.147, from other examong the 53 inhabitants of Rongelap posures to radiation for various medical

Atoll in the Marshall Islands who had purposes, and from experiments with

received an estimated whole-body dose animals that large doses of radiation can

of 175 rems of gamma radiation from increase the frequency of various types

fallout in 1954 (§ 12.175 et seq.). The of cancer, in addition to leukemia. The

individual, a young man, had been a same effect has been observed among

year old at the time of exposure. the survivors of the nfuciear attacks on

12.149 The occurrence of leuke- Japan. For example, after a latent period

mia, for a given estimated absorbed of about 10 years, a sig-iificant increase

dose (in rads), appeared to be greater in was observed in the incidence of thyroid

Hiroshima than in Nagasaki. Later cancer among -'1⁄4dividuals who were

studies revealed that the Hiroshima (gun within about half a mile from ground

type, uranium-235) bomb emitted a zero and consequently received large

larger proportion of neutrons, relative to doses of ionizing radiaticis. Delayed

gamma rays, than did the Nagasaki thyroid abnormalities have also been

(implosion type, plutonium-239) de- found among the inhabitants of the
LATE EFFECTS OF 1ONIZING RADIATION 593

Marshall Islands whose glands were LIFE SHORTENING

subjected to internal exposure from radioiodines in fallout, but only a small 12.152 Laboratory studies with anproportion were malignant (§ 12. 181). imals have indicated that shortening of

The frequency of thyroid cancer induced the life span, apart from the effects of

by radiation is estimated to be roughly leukemia and other forms of malignant

10 per rem per million of exposed disease, can sometimes (but not always)

adults, but substantially more for chil- result from partial or wholc-body expodreih. Provided it is detected in time, sure to radiation. Such shortening may

however, thyroid cancZr is rarely fatal in be the result of a number of factors,

chbidren and only in about 10 percent of including decreased immunity to infecadults. tion, damage to connective tiss.ies, and

12.151 A statistical study of mor- possibly premature aging. The lift

tality data, obtaiied from 1950 through shortening in a given animal, for a spe1970, or a large number of people who cific radiation dose, apparently depends

were in Hiroshima anc' Nagasaki at the on such factors as genetic constitutica

times of the nuclear explosions shows and on the age and physical condition at

an increased frequency of various other the time of the exposure.

types of cancer. The most important 12.153 It has been reported that for

sites appear to be the lung, the gas- radiologists who received fairly large

trointestinal system (other than the chronic doses of radiation ia the course

stomach), and ihe female breast. Al- of their work, before adequate prov'•cthough they are relatively rare, salivary tive measures were instituted, the avc:rgland tumors have been found to be age age at death was about five years

more common amor-g the Japanese ex- less than for other physicians. Part of

posed to radiation than in the unexposed the increase in death rate was due to

population. In a group of 109,000 sur- leukemia and other formis of cancer, but

vivors who have been studied about after allowing for these and other spe5,700 re':eived whole.-body doses of 100 cific effects of radiation, there were inrems or more. Among these, 690 were dications that ionizing radiations caused

over 50 years of age at the time of nonspecific life shortening. However,

exposure and during the period from an examination of deaths occurring from

1960 to 1970 thre were 47 deaths from 19.50 through 1970 of survivors of the

cancer, other than leukemia, whereas nuciear attacks on Japan suggests that,

about 30 would have been expected. Oi apart from various forms of cancer,

the 820 children who were under 10 there is little evidence that radiation acyears of age when exposed, there were celerated aging.

six such deaths, compared with 0.75

expected. Tiius, although the actual increase in fatal cancers was smaller RETARDED DEVELOPMENT OF

among those exposed at an early age, CHILDREN

the relative increase, i.e., actuaL/expected, was much greater than in older 12.154 Among the mothers who

persons. were pregnant at the time of the nuclear

Y4
594 BIOLOGICAL EFFECTS

explosions in Japan, and who received the first three or four months of pregsufficiently larg•e doses to show the usual nancy. Most of the mothers of the chilacute radiation symptoms, there was a dren referred to above were so close to

marked increase over normal in the grotud zero that they must have renumber of stillbirths and in the deaths ol ceivL6. ,.•orc than 200 rems of ionizing

infants witfin a year of birth. The in- radiation. Maldevelopinent of the teeth,

crease in mortality was .ignificant only attributed to injury to the roots, was also

when the mothers had been exposed noted in many of the children. Children

dcring the last three months of preg- who were conceived after the nuclear

nancy. Among the surviving children attacks, even by irradiated parents, apthere was a slight incrtease in frequency pear for the most part to be normal. The

of mental retardation and head circum- fear expressed at one time that there

fcrcrces were smaller than normal. would be a sharp increase in the occurThzse effects were most marked when rence of abnormalitics has not been

the radiation exposure occurred within substantiated.

EFFECTS OF EARLY FALLOUT

EXTERNAL HAZARD: BETA BURNS from bet;, particles which might be significant.

12.155 In most circumstances, the 12.156 Information concerning the

whole-body dose from the gamma rays development and healing of beta burns

emitted by the early fallout will repre- has been obtained from observations of

sent the major external hazard from the the Marshali Islanders who were exdelayed nuclear radiation. The biologi- posed to fallout in March 1954

cal effects are then similar to those from (§ 12.103). Within about 5 hours of the

equal acute doses of radiation (§ 12.102 burst, radioactive material commenced

et seq.). In addition, injury can arise in to fall on some of the islands. Although

two general ways from ex-ernal sources the fallout was observed as a white

of beta particles. If the beta-particle powder, consisting largely of particles

emitters, e.g., fission products, come of lime (calcium oxide) resulting from

into actual contact with th• skin and the decomposition of coral (calcium

remain for an appreciable time, a form carbonate) by heat, the island inhabiof radiatio- injury, sometimes referred tants did not realize its significance.

to as "beta burn," wil' result. In addi- Because the weather was hot and damp,

tion, in an area of extensive early fall- the Marshallcstý remained outdoors;

out, the whole surface of the body may their bodies were moist and they were

be exposed to beta particles coming relatively little clcihiia, Az a i.,sult,

irom many directions. It is true that appreciable at:tounis of fissicil product3

clothir'g will attenuate this rauiition t, a fell upon ".1c hair and -kin and remained

cons.derable extent; nevertheless, k'e there for d c,)nsiderable time Morover

whoie body couid receive a large dose since the islanders, as a rule, did not
EFFECTS OF EARLY FALLOUT 595

•'•. . . ,.

Figure 12.158a. Beta burn on neck I month after e;xposure.

wear shoes, their bqre feet were contin- oped on the exposed parts of the body

ually subjected to contamination from not protected by clothing, and occurred

fallout on 'he ground. usually in the following order: scalp

12.157 During the first 24 to 48 (with epilation), neck, shoulders, dehours, a number of individuals in the pressions in the forearm, feet, limbs,

more highly contaminated groups expe- and trunk. Epilation and lesions of the

rienced itching and a burning sensation scalp, neck, and foot were most freof the skin, These symptoms were less quertly observed (Figs. 12.158a and b).

marked among those who were less 12.159 In addition, a bluish-brown

contaminated with early fallout. Within pigmentation of the fingernails was very

a day or .wo all skin symptoms subsided common among the Marshallese and

and disappeared, but after the lapse of also among American negroes who were

a' out 2 to 3 weeks, epilation and skin in a group of servicemen stationed on

lesions were apparent on the areas of the Rongerik Atoll (Pig. 9.105). The phebody that had been contaminated by nomenon appears to be a radiation refallout particles. There was apparently sponse peculiar to the dark-skinned

no erythema, as mighl have been ex- races, since it was not apparent in any of

pected, but this may have been obscured the white Americans who were exposed

by the natural coloration of the skin. at the same time. The nail pigmentation

12.158 The first evidence of skin occurred in a number of individuals who

"d amage was increased pigmentation, in did not have skin lcsions. It is probable

the foim of dark colored patches and that this was caused by gamma rays,

raised areas (macules, papules, and rather than by beta particles, as the same

raised plaques). These lesions devel- effect has been observed in dark-skinned

.,k2
596 BIOLOGICAL EFFECTS

! ..

i~ r o *,' 0

I.k

Figure 12.158b. Beta burn on feet I month after exposure.

patients undergoing X-ray treatment in increased pigmentation. Normal pigclinical practice. mentation gradually spread outward in

12.160 Most of the lesions were the course of a few weeks.

superficial without blisteriing. Micro- 12.161 Individuals who had been

scopic examination at 3 to 6 weeks more highly contaminated developed

showed that the damage was mot deeper lesions, usually on the feet or

marked in the outer layers of the skin neck, accompanied by mild burning,

(epidermis), whereas damage to the itching, and pain. These lesions were

deeper tissue was much less severe, wet, weeping, and ulcerated, becoming

This is consistent with the short range of covered by a hard, dry scab; however,

beta particles in animal tissue. After the majority healed readily with the

formatiov of dry scab, the lesions healed regular treatment generally employed

rapidly leaving a central depigmented for other skin lesions not connected with

area, surrounded by an irregular zone of radiation. Abnorw-.d pigmentation ef-

#..
IFFECTS OF EARLY 7AI.IOUT 597

IA.

Figure 12.161a. Beta burn on neck I year after exposure (se.! Fig. 12.158a).

fects persisted for some time, and in same time, nail discoloration had grown

several cases about a year ezapsed be- out in all but a few individuals. Seven

fore the normal (darkish) skin coloration years later, there were only 10 cases

was restored WYigs. 12. 161a and b). which continued to show any effects o'"

12.162 Regrowth of hair, of the beta burns, and there was no evidence of

usual color (in contrast to the skin pig- malignant changes.

meutation) and texture, began about 9

weeks after contamination by fallout INTERNAL HAZARD

and was complete in 6 months. By the 12.163 Wherever fallout occurs
598 t3IOLOGICAt. E|:E('TS

* .

Figure 12.161 b. Beta burn on feet 6 months after exposure (see Fig. 12.1 58b).

there is a chance that radioactive mate- expo~iure of various organs and tissues

rial will enter the body through the di- from internal sources is continuous,

gestive tract (due to the consumption of subject only to depletion of th,: quantity

food and water contaminated with fis- of active material in the body as a result

slon products), through the lungs (by of physical (radioactive decay) and biobreathing air containitig fallout parti- logical (elimination) pr-ocesses. Furcies), or throiigh wounds or abrasions. thermore, internal sources of alpha

Even a very small quantity of radioac- emitters, e.g., phui'onium, or of beta

tive material if retained in the body can particles, or soft (low-energy) gammaproduce considerable injury. Radiation ray emitters, can deposit their entire

u4

i4

1/
-FFITTS O1F i:ARI Y ;:AlI MI l'T 599

energy within a small, possibly sensi- radioisotopes are potentially hazardous

tive, volume of body tissue, thus caus., for two reasons in particular; first, the

itrg considerable damage. Even if the radiations can damage the bone marrow

radioisotope remains in the body for a and thus affect the whole body by defairly short time and causes no ob,;erv- creasing blood-cell formation

able early injury, it may contribute to (§ 12.226). and second, the deposition

damage that does not become apparent of alpha- or beta-particle energy in a

for some time (§ 12.142 et seq.), small volume can cause serious bone

12.164 The situation with regard to damage, including cancer (§ 12.173).

internal exposure is sotnetimes aggra- 12.166 The extent to which early

vated by the fact that certain chemiald fallout contamination can enter the

elements tend to concentrate in specific bloodstream as ih result of iogestion,

organs or tissues, scme of which are inhalation, or a wound is .trongly inhighly sensitive to ionizing radiation, fluenced by the physical properties,

The fate of a given radioactive element e,g,, size distribution, density, and surwhich has entered the blood stream will face area, of the particles, and by ;hcir

depend upon its chemical nature. Ra- solubility in the body fluids, Whether

dioisotcpes of an element which is a the material is subsequently deposited in

normal constitutent of the body will some specific tissue or not will be defollow the same metabolic processes as termined by the chimical properties of

the naturally occurring, inactive (stable) the elements present, as indicated preisotopes of thse same element. This is the viously, Elements which do not tend to

case, for example, with iodine isotopes, concentrate in a particular part of the

all of which--radioactive and stabe- boJy are eliminated fairly rapidly by

tend to concentrate in the thyroid gland, natural processes.

12.165 An clement not usually 12.167 The amount of radioactive

found in the body, except perhaps in material absorbed from early fallout by

minute traces, will behave like oue with inhalation appears to be relatively small

similar chemical properties that is nor- because the nose can filter out almost all

mally present. Thus, among the fission particles over 10 micrometers (see

products, strontium and barium, which § 2.27 footnote) in diameter, and about

are similar chemically to calcium, 95 percent of tlose exceeding 5 miwould be largely deposited in the cal- crometers, Although particles of a wide

cifying tissue of bone. The radioiso- range of sizes will be present, most of

topes of the rare earth elements, e.g., the particles descending in the fallout

cerium, which constitute a ccnsiderable during the critical period of highest acproportion of the fission producta, and tivity, e.g., within 24 hours of the explutonium, which may be present to plosion, will be the larger ones (§ 9.50),

some extent in the fallout, aie also more than 10 micrometers in diameter.

"bone-seekers." Since they are not Consequently, only a small proportion

chemical analogues of calcium, how- of the early fallout particles present in

ever, they are deposited to a sn,aller the air will succeed in teaching the

extent and in other parts of the bone than lungs. Furthermore, the optimum size

are strontium ar-d barium. Bone-seeking for deposition in the alveolar (air) cells

Y`

Ft,
600 IlOI.OGI(CAI. FPFF.CTS

of the lungs is as small as I to 2 mi- (§ 1.63), which determines the rate of

crometers. removal by natural decay, and on its

12.168 Since many of the contami- "biological half-life," i.e., the. time for

nated particles are reatively insomuble, the amount in the body to decrease to

the probability is low that inhaled fis- half of its initial value solely as a result

sion products and other weapon residues of elimination by biological proce%.es.

present in the early fallout will reach the The combination of radioactive and biblood stream from the lungs. After de- ological half-lives leads to the "effecpositicn in the alveolar spaces of the live half-life" as a measure of the net

lungs, particles of low solubility in the rate o" the radionuclide from the

body ttuids may be retained in these body , decay and biological

spaces for long periods until they are elimination, The retention pattern of a

eventually dissolved or are removed by given element in the body represents the

mechanical means, e.g., by cellular or summation of the retentions in individlymphati," transport or in mucus. Par- ual tissues. In those cases where practititles leaving the lungs by way of the cally all the body burden is in one tissue

lymphatic system tend to accumulate (or organ), e.g., iodine in the thyroid

prinicipally in the tracheobroachial gland, the effective half-life is essenlymph node.; thereby leading to an in- tially that for this tissue (or organ). A

tensc, localized radiation dose. major c'onsideration itn assessing the inIZ. 169 Following ingestion or ternal hazard from a given radionuclide

clearance of the upper respiratory tract is the total radiation dose (in renis) deafter inhalation, the extent of absorpion livered whi.e it is in the body (or a

of fission products and other radk., ictive critical organ), The main factors in this

materials throngh the intestine- is largely respect are the effective half-life, which

dependen, upon the solubility of the determines the time the nuclide is presparticles, In the ýarly fallout, the fL;sion ent in the body (or organ), the total

prioducts as well as uranium and pluto- quantity in the body (or organ), and the

nium arv chiefly present as oxides, many nature and energy of the radiation emitof which do not dissolve to any great ted. The importance of these factors in

extent in body fluids. The oxides of various circumstances will become ap.-

strontium and barium, however, are parent in due course.

soluble, so that these elements enter the 2.171 The biological half-life of

blood stream more readily and find their the element iodine, which is essentially

wy into the bones." The element io- that in the thyroid glaiid, has an average

dine is also chiefly present in a soluble value of about 80 days, although it acform and so it soon enters the blood and tually varies from a few days in some

is concentrated in the thyroid gland. people to several years in otherý;. A

12.170 The lengthi of time a parti,' number of radioactive isotopes of iodine

ular nuclide remains in the body de- are present among the fission products,

pends on its radioactive hlif-life but most have moderate or short radioI' Even under these conditions, orly about 10 percent of the strontium oi barium is actually absorbed.
I-:I:FC:("'S 0(1" I:AARI Y I -\. l ()I IT 601

active half-lives. The effective half- fraction of the inhaled fallout partic!.s

lives, which are related to the times the contaminated with plutonium will be

various isotopes are effective in the deposited in the alveolar spaces of the

body (thyroid), are then determined lungs, If tle particles are relatively inmainly by the radioactive half-lives, soluble, they can be retained in the

rather than by the longer biological lungs for long periods with gradual re.

half-life. The heavier isotopes,, iodine- moval by niechanicnl means or by slow

132, -133, -134, etc., all of which have absoirption in the tlood, With the more

radioactive half -,ives of !eis than a day, soluble particles, residence time in the

thus have short effective half-lives, lungs will be shorter and absorption into

consequently, they constitute a hazard the bloodl stream will occur more raponly if t1clivered in sufficient amounts to idly, Plutonium that enters the hlood

the thyroid via th" blood stream, The stream tends to be deposited in the liver

injury that rnight be caused by these and on certain surfaces of the bone, the

isotopes is then largc!y dependent on the amount of plutonium present and its

quantities that reach the thyroid gland activity decrease at a very slow rate

within a short time, On" the other hand, because of the long radioactive and biothe common fission producz iodine- 131 , logical half-lives, The continuous expowith a half-life of about 8 days, has a sure for many years of a limited region

longer effective half-life and can repre- of the body, e.g., lung. liver, or Enne

sent a hazard in smaller amounts be. surface, to the short-range but high-encause it remains active in the thyroid for ergy alpha particles from plutonium can

a longer time. cause serious injury, Thus, the injection

12.172 in addition to radioiodine, o" sufficient amounts of soluble plutothe important potentially hazardous fis., nium into some animals has been found

sion products, aSsuming sufficient to cause bone malignancies whereas Mr.-

amounts get into the body, fall into two halation of plutonium dioxide particles

groups. The first, and more signdicani, may result in the formation of lung

contains strontium-89, stroxitium-90, tumors.

cesium-137, and barium-140, Yhereas 12.174 Despite the large amounts

the second consists of a group of rare of radioactive material which may pass

earth and related elements, pirticularly through the kidneys in the process of

cerium-144 and the chemically similar elimination, these organs ordinarily are

yttrium-9 1. not greatly affected by radiation. By

12.173 Another potentially hazard-, contrast, uranium can cause damage to

ous element, which may be present to the kidneys, but as a chemical poison

some extent in the early fallout, is plu- rather than because of iti radioactivity.

tonium, in the form of the alpha-particle However, the quantity of uranium cornemitting isotope plutoniun..239. This pounds found in the fallout that must be

isotope has a long radioactive half-life ingested in order to be pott-ntially poi-

(24,000 years) as well as a long biolog- soous are so large that it is not considica' half-lite in the skeleton (abnut 100 ered to be of primary concern compared

years) and the liver (about 40 years). A.: with other constituents of nuclear

with any airb.,rne particulate matter, a weapon debris.

•.5
602 BIOLOGICAL EFFECTS

MARSHALLESE EXPERIENCE activity levels of the strontium isotopes

12.175 Early iailout accompanying were more persistetit. Not only do these

the niuclear air bursts over Japan was isotopes have longer radioactive halfinsignificant and was not monitored. lives, but the biological half-life of the

Consequently, no informati in was element is also relatively long.

available concerning the potentialities of 12.178 No elements other than tofission products and other weapon resi- dine, strontium, barium., and the fare

dues as internal sources of radiation. earth group were found to oe retained in

Following the incident in the Marshall appreciable amounts in the body. EsIsland,; in March 1954, however, data uf sentially all other fission products and

great interest were obtained, Beca,,.-. weapon residue activities were rapidly

they were not aware of the significance eliminated, because of either the short

of the fallout, many ol' the inhtbitants effective half-lives of the radionuclides,

ate contaminated food and drank con- the sparing solubility of the oxides, or

taminated water from open containers the relatively large size of the fallout

for periods up to 2 days before they particles.

were evacuated from the islands. 12.179 The body burden of radio12.176 Internal deposition of fis- active material among the more highly

sion products resulted mainly from in- contaminated inhabitants of the Margestion rather than inhalation for, in shall Islands was never very large and it

addition to the reasons given above, the decreased fairly rapidly in the course of

radioactive particles in the air settled out 2 or 3 months. The activity of the

fairly rapidly, bit contaminated food, strontium isotopes fell oil somewhat

water, and utensils were used all the more slowly than that of the other ratime. The belief that ingestion was the dioisotopes, 'because of the longer rachief source of internal contaminationi dioactive half-lives and greater retentkin

was supported by the observations on in the bone. Nevertheless, even stronchickens and pigs made soon after the tium could not be regarded as a dangerexplosion, The gastrointestinal tract, its ous sotirce of internal radiation in the

con'eats, and the liver were found to be cases studied. At 6 months after the

much more contaminated than lung tPs- explosion, the urine of most individuals

sue. contained only barely detectable quanti12.177 From radiochemical analy- ties of radioactive material.

sis of the urine of the Matshallese sub., 12.180 In spite of the fact that the

jected to the early fallout, it was possi- Mar,'shallese people lived approximately

ble to estimate the body burdens, i.e., 2 days under conditions where maxithe amounts deposited in the tissues, of mum probability of contamination of

various isotopes. It was found that io- food and water supplies existo:d and that

dine- 1 -11 made the major contribution to the)y took few steps to protcct them- .

the activity at the beginning, but it soon selves, the ai.uunt of internally depodisappeared because of its relatively sited radioactivity from early fallout was

short radioactive half-life (8 days). small. There seems to be little doubt,

Somewhat the ,;amc was true for therefore, that, at least as far as shortbarium- 140 (12.8 days half-life), but thf, term effects are ,.oncerned, the radiation

J1
FFEC ,'S OF EARI.Y FALLOUT 603

injury b-v early fallout due to internal Of a total of 19 such children who were

sources can be minor in comparison on Rongelap, 17 developed abnorroaliwith tha, duce to the external radiation, ties, includ-ng one malignancy and two

However, d&elayed effects of internal ra- cases of hypothyroidism. The radiation

diation exposure, including one case of doses from radioiodine isotopes that had

leukemia (§ 12.148), became apparent been concentrated in the thyroids of

several years after the eplosion, these children were estimated to be from

12.11 Un:Il 19,53. no thyroid ab- 810 to 1,150 reins. In 1974, a lesion

was observed in one of the individuals normalitie. had been detected among who had been exposed in utero; the

The inhabitants of the Marshall Islands thyroid dose was uncertain but it must

that could be attributed to the fallout. In have have been be at wastun75rtin least 175 reins. buTht The mussix

that year, one was found among the children in the less highly exposed

people of Rongelap Atoll, but by 1966

there were 18 cases; the total number group who were on Alinginae received

increased to 22 by 1969 and to 28 by estimated thyroid doses of 275 to 450

1974. Of the Rongela perems; by 1974, lesions were observed in 1974 OftheRon ela people who were

exposed, 64 (plus one in utero) received two cases with one doubtful malignexternal doses of about 175 reins; 18 ancy. 12.183 For purposes of compariothers (plus one in utero), who were on

the neighboring Alinginae Atoll (cf. son, studies were made on 194 people

Fie. 9.105) at the time of the, nuclear who normally lived on Rongelap Atoll

test, received about 69 reihs. The but who were away on other islands and

were not exposed to the fallout. There

thyroid doses t'rom radioiodines were were nine thyroid abnormalities (none much larger, especially in children malignant), including one in 61 childreni

under 16 years of age. In 1974, there

were 22 individuals with thyroid lesions who were less than 10 years old in 1954.

An examination was also made of 157

among the more highly exposed group inhabitants of Utirik Atoll who had reand six among tne others. In the former ceived e~ternal doses of 14 reis from

group there were three malignancies and the fallout. The 58 children less than 10

two cases of atrophied thyroids (hy- years old at the time of the explosion

pMthytoidism); there were no definite received thyroid doses from radioio- malignaicie group ai. thyoi dose frome 

malignancies in the latter group al.. dines estimated to be 60 to 95 remr;, but

though there was one doubtful case. All by 1974 no abnormalities had been obother thyroid abnorma),ties were benign served. Six people in the older group of

99 were found to have thyroid lesions,

12.182 Most of the lesions occurred one of which was malignant; the estiin children who were less than 10 years mated thyroid doses were in the range of

old at the time of the expl.,sion in 1954. 27 to 60 rems.

* *

4'3
604 BIOLOGWCAL EFFECTS

LONG-TERM HAZARD FROM DELAYED FALLOUT12

CESIUM-137 ements are generally :tore ý-o, uble than

12.184 Of the fission products the corresponding coinpounds of stronwhich present a potential long-term tium and calcium and the details of the

hazard from either the atmospheric test- transfer of these two pairs of elements

ing of nuclear weapons in peacetime or from the soil to the human body are

their use in warfare, the most imncrtant quite different. The element cesium is

are probably the radioactive isotopes relatively rare in nature and the body

cesium-137 and strontium-90. Since normally contains only small traces.

both of these isotopes are fairly abun- Because of the presence of cesium- 137

dant among the fission products and in the delayed fallout, studies have been

have relatively long half-lives, they will made of the behavior of this isotope in

constitute a large percentage of any de- various biological systems and of the

layed fallout. The process of fractiona- levels of uptake and retention in man.

tion will tend to increase the proportions Regardless of its mode of entry--

of strontium and cesium still further inhalation, ingestion, or wounds-ce-

(§ 9.08). Of course, the activity level sium is soon distributed fairly uniforrmly

d&te to these isotopes at late times in the throughout the body. A preferential deearly fallout pattern in tho area close to a position in muscle results in concentra-

,;urface or subsurface burst will be con- tions that are somewhat higher than in

side.rably larger than in the delayed fall- the body as a whole, whereas in some

ow from a given explosion. However, other tissues, e.g., the lungs and skelethe special interesi in the delayed fallout ton, the concentrations are lower than

arises from the fact thzt it may occur in the body average.

significant amounts in wavry parts of the 12.186 From the studies referred to

globe remote from the point of the nu- above, the biological half-life of cesium

clear detonation, as explained in in human adults has been reported as

Chapter IX, as well as in close by areas, ranging from 50 to 200 days. Factors

12.185 Cesium..137 has a radioac- contributing to this spread of values intive half-life of 30 years and is of par- clude diet, age, sex, race, and body

ticular interest in fallout that is more weight. Because of the fairly uniform

than a year old because it is the principal distribution of cesium, the entire body

constituent whose radioactive decay is would be irradiated by both beta paraccompanied by the emission of gamma ticles and gamma rays emitted as the

rays. The chemical and biochemical cesium-137 decays. However, since the

properties of cesium resemble those of biological half-life of cesium is rela..

potassium. The compounds of these el- tively short, compared with strontium,

"12 Much valuable information on delayed fallout and related problems can be found in the published

Hearings before the Special Committee on Radiation of the Joint Committee on Atomic Energy,

Congress if 'he United States: "The Nature of Radioa'tive Fallout and its Effect' on Man," May 27 to

June 7, 1957; "Fallout from Nuclear Weapons Tests," May 5 to 8, 1959; ,nd "Biological and

Environmental Effects ol Nuclear War," June 22 to 26, 1959 (U.S. Government Printing Office).

-
LONG-TERM HAZARD FROM DELAYED FALLOUT 605

and it does not tend to concentrate sig- 3TRONTIUM-90

nificantly in any organ or tissue, the 12.188 Stontium-90, because of its

residual cesium-137 in a given amount relatively long radioactive half-life of

of delayed fallout is much less of a 27.7 yeais and its appreciable yield in

biological hazard than is the strontium- the fission process, accounts for a con90. siderable fraction of the total activity of

12.187 The amount of internal ex- fission products which are several years

posure to cesium-137 is determined by old. Strontium is chemically similar to

the quantity of this isotope in food. If calcium, an element essential to both

the major mechanism for its incorpora- plant and animal life; an adult human

tion into the diet is through the root being, for example, contains over 2

systems of plants, then the dose will be pounds of calcium, mainly in bone.

more or less proportional to the total However, the relationship between

amount of cesium-137 accumulated on strontium and calcium is; not a simple

the ground. On the other hand, if this one as will be seen in subsequent secisotoLe enters the diet mainly through tions and, because of its complex me

material deposited directly on the leaves tabolism in the body, the behavior of

of plants, the internal dose will be more strontium-90 cannot bc stated in terms

nearly proportional to the rate of descent of a single effective half-life (§

of delayed fallout. It has been calculated 12.170). "

that if the former mechanism prevails, 12.189 The probability of serious

the internal 30-year dose to the gonads, pathological change in the body of a

which is of interest in connection with particular individual, due to the effects

possible genetic effects (§ 12.201 et of radioisotopes deposited internally,

seq.), would be much higher than if the depends upon the amount deposited, the

alternative mechanism were of major energy of the radiations emitted, and the

importance. The bo'st data presently length of time the source remaitas in the

available on cesiumt-M37 levels in food body. Strontium-90 and its daughter,

suggest that, up to the present time, the yttrium-90, emit beta particies which

fallout rate has been the dominant fac- can cause serious localized d.mage folt;r; but in the future a larger proportion lowing their deposition and long-term

of the cesium may get into food via the retention in the skeleton.14 Tests with

soil, provided no considerable amounts animals indicate that the pathological

of cesium-137 are added to the atmos- effects resulting from sufficient quantiphere. ties of inhaled, ingested, or injected

" Data from strontium-90 excretion by the Marshallese people and studies in a case of accidental

inhalation indicate thtat for an acute intake the major portion of the absorbed strontium-90 is excreted with

a biological half-life of 40 days during the first year. During the next 2 years, at least, a smaller fraction

is excreted with a biological half-life of 500 days. The romaining portion (less than 10 percent) is tightly

bound to bone and is excreted very s'owly with a long biological half-life of about 50 years. In this latter

case, the effective half-life (§ 12.170) would be about 18 years. The situation for a chronic intake e.g.,

from delayed fallout, although not the same, would he similar.

'$The energy of the strontium-90 beta particles is 0.54 MeV. However, its daughter, yttrium-90.

which has the short half-life of only 64 hours, emits 2.27-MeV beta particles (no gamma rays); the decay

product is stable zirconium-90. Thus, both 0.54- and 2.27-MeV beta particles accompany the decay of

strontium-90. (The energies quoted are maxima; the average energy is about one-third of the maximum.)

"A• - •t,. • "'
606 BIOLOGICAL EFFECTS

strontium-90 include bone necrosis, and calcium, because of their chemical

bone tumors, leukemia, and other he- similarity, may be thought of as commatologic dyscrasias (abnormalities). peting for entry into the root system of

12.190 Most of the strontium-90 in plants, not all of the calcium in soil is

the delayed fallout is ultimately brought available for assimilation. Some natural

to earth by rain or snow, and it makes its calcium compounds in soil are insoluble

way into the human body primarily and are not available as plant food until

(directly arid indirectly) through plants. they have been converted into soluble

At first thought, it might appear that the compounds. Most of the strontium-90 in

ratio of strontium to calcium in man the delayed fallout, however, is in a

would be equal to that in the soil from water-soluble form. Third, in additiop,

which he obtains his food. Fortunately. to the strontium-90 which plants derive

however, a number of processes in the from the soil, growing plants retain a

chain of biological transfer of these ele- certain amount of strontium-90 from

mer.ts to the human body operate col- fallout deposited directly on the surface

lectively to decrease the relative quan- of the plant.

tity of strontium that is stored in mar. by 12.192 As the next link in the

an overall factor of two to ten. The chain, animals consume plants as food,

accumulation of strontium-90 in the thereby introducing strontium-90 into

human body by way of food is affected their bodies. Once again, the evidence

by the availability and proximity of indicates that natural discrimination

strontium to the root system of a plant, factors result in a strontium-90/calcim

strontium-90 uptake by the plant, ratio in the edible animal products that is

transfer from plant to animal (where less than in the animal's feed. Very little

relevant), and transfer from plant or strontium is retained ir ,he soft tissue,

animal to man. so that the amount of strontium-90 in the

12.191 Greenhouse experiments edible parts of the animal is negligible.

show a slight discrimination in favor of It is of particular interest, too, that the

calcium and against strontium when strontium-90/calcium ratio in cow's

these elements are taken up by most milk is much lower than that in the

plants from homogeneous soils. How- cow's feed, and thus is an important

ever, several factors make it difficult to barrier to the consumption of strongeneralize concerning the ratio of stron- tium-90 by man. This barrier does not

tium to calcium in the plant compared to operate, of course, when plant food is

that in field soils. First, plants obtain consumed directly by human beings.

most of their minerals through their root However, it appears that about threesystems, but such systems vary from fourths of the calcium, ar.d hence a large

plant to plant, some having deep roots fraction of the strontium-90, in the

and others shallow roots. Most of the average diet in the United States is obstrontium-90 deposited in undisturbed tained from milk and milk products. The N

soil has been found close to the surface, situaion may be different in areas where

so that the uptake of this nuclide may be, a greater or lesser dependence is placed

expected to vary with the root habit of upon milk and milk products in the diet.

the plant. Second, although strontium 12.193 Not all of the strontium-90

I 1I
LONG-TERM HAZARD FROM DELAYED FALLOUT 607

that enter, the body in food is deposited cancer. On this basis, it has been recin the human skeleton. An appreciable ommended that the maximum activity of

fraction of the strontium-90 is elimi- strontium-90 in the body of any indinated, just as is most of the daily intake vidual who is exposed in the course of

of calcium. But there i. L:ways some his occupation be taken as 2 microfresh deposition of calcium taking p~lace curies. Since the average amount of

in the skeletal structure of healthy indi- calcium in the skeleton of an adult

viduals, so that strontium-90 is incor- human is about 1 kilogram (or a little

porated at the same time. The rate of over 2 pounds), this corresponls to a

deposition of both calcium and stron- concentration in the skeleton of 2 mitium-90 is, of course, greater in growing crocuries of strontium-90 per kilogram

children than int adults. In addition to the of calcium. Moreover, the limit generfact that the human metabolism dis- ally considered to be acceptable for any

crim'inates against strontium, it will be individual member of the general popunoted that, in each link of the food lation is 0.2 microcurie of strontium-90

chain, the amount of strontium-90 re- per kilogram of calcium. rhe Internatained is somewhat less than in the pre- tional Commission en Radiological

vious link. Thus, a series of safeguards Protection has suggested that the conreduces deposition of strontium in centration of strontium-90 averaged

human bone. over the whole population should not

12.194 As there has been no expe- exceed 0.067 microcurie per kilogram

rience with appreciable quantities of of calcium.

stroptium-90 in the human body, the 120.195 As a result of nuclear test

relationship between the probability of explosions in the atmosphere by various

se~ious biological effect and the body countries, there has been an increase in

burden of this isotope is not known with the strontium-90 content of the soil,

certainty. Tentative conclusions have plants, and the bones of animals and

been based on a comparison of the man. This increase is worldwide and is

effects of strontium-90 with radium on not restricted to areas in the vicinity of

test animals, and on tlhe known effects the test sites, although it is naturally

of radium on human being3. From these somewhat higher in these regions becomparisons it has been eslirnated that a cause of the more ocalized (early) fallbody content of 10 microcuries (1 mi- out.1.5 The fine particles of the delayed

crocurie is a one-millionth part of a fallout descend from the stra t

osphere

curie, as defined in § 9.141) of stron- into the troposphere over a period of

tium-90 iki a large proportion of the years, and are then brought down by

pl•ulation would produce a noticeable rain and snow. Consequently, the

increase in the occurrence of bone amount of strontium-90 in the strato-

"It is to be expectcd that areas near the explosi-in will be more highly cont.:.iminated in atronlium-90

than are more distant regions, to an extent dependent upon such factors as the h:itght (or depth) of burst.

the ,tal and fission yields of the explosion, and the prevailing atmospheric conditions. Because of thu

phenomenon of fractionation, the proportion of strontium-90 in the local (early) fallout will generally be

less than that in the worldwide (delayed) fallout. It is of interest to mention, too, that the atrontium-90 in

early fallout appears to be in a less soluble fnrm, and hence probably less readily accessible to plants,

than that present in the delayed fallout.
608 M1OLOGICAL EFFECTS

.;pheie a.,•lable to fall ,)n earth is de- no gamma ra,,s. Tri:ium is a mirlor

termined by the differenc,., between the product of fission, but much larger

quantity introd'.,ced by nuclear ,.xplo- amounts are releas-ed in thermonucicar

sions and that removed by precipitation explosions (§ 9.44). The half-life of tri-

(and radioactive decay). 'This net iiurn is 12.3 years and the beta particles

amount reached a maximum at the end it emits have even a lower energy

of 1962, )fter the cessation of nuclear (average approximately 0.006 MW:V)

weapons testing in the a.mosphere by than those from carbon-14; there are

the United States anO ,ne U.S.S.R. (see also :no gamma rays.

Fig. 9.143a). Subseqvtent additions of 12.199 As a consequence of the

strontium-QO from nuclear tests made by testing of thermonuclear weapons,

Frmiice and mainland Chinu have caused starting in 1952, therc has been a large

temporary increases in :he stratospheric increase in the quantity of carbon-14 in

reservoir, the atmosphere, particularly in the

12.196 Calculations, based on stratosphere. Although ihis has been

somewhat uncertain premise3, suggest decreasing since 1963, there is still a

that, in the event nuclear weapons were significant burden of carbon-14 in the

to N- used in warfare, debris hom many stratosphere which will find its way into

thousands of megatons of fission would the lower part of the atmosphere (trohave to be added to the stratosphere posphere). Because -f its long half-life,

before the delayed fallout from these carbon-14 decays very slowly and the

weapons would lead to an average con- decrease in conceitration in the troposcentration in the human body equal to phei-e is largely due to removal of tartht, recommended maximum value for bon dioxide by gradual solution in o' ean

occupationally exposed persons, i.e., 2 waters.

microcuries of strontium-90 per kilo- 12.199 (;arbon- 14 does not tend to

gram of calcium. concentrate in any particular part of the

body and iL stributed almost uniformly

CARBON-14 AND TRITIUM throughout soft tissue; hence, the whole

12.197 Long-term radiation expo- body is exposed to the low-energy beta

sure can arise from carbon-14 and from particles. The whole-body dose from

tritium, the radioactive' isotope hy- carbon-14 in nature before 1952 was

drogen, both of these substances are somewhat less than I millirem per

normally present in nature and they are annum. By 1964, this dose had been

also produced in considerable amounts roughly doubled by the additional carin nuclear explosions. Carbon-14 is not bon-14 arising from nuclear tests in the

strictly a componeni of fallout, but it i- atmosphere. If there are no further subconvenirnt to consider it here since it is stantial additions, the dose will decrease

formed by the acdon of fast neutrons, gradually and approach normal in ane.g., from a thermonuclear weapon, on other 100 years or so. Compared with

nitrogen in the atmosphere (§ 9,34). the annual radiation, dose from stron.-

Carbon-14, with a half-fife of 5,730 tium-90, mainly to the skeleton, the

yewas, emits beta particles, with the low contribution from carbon-14 produced

average energy cf aboup 0.05 MeV, arid by thermonuclear weapons is small.
GI.NI-TIC F.:FE(CTS OF NUCILEAR R'OIATIONS 609

12.200 Tritium, in the form of tri- significant preferential concentration of

tiated water (§ 9.44), can enter 1he body tritium in any o,'gan. In spite of the large

by the ingestion of food and water, by increase in :he quantity of tritium on the

inhalation of air containing tritiated earth as a result of nuclear explosions,

water vapor, and by absorption through the annual whole-body dose was less

the skin. Since it is an isotope of hy- than 0. 1 millirem even at its maximum.

drogen, and has the same chemical Because cf the low energy of the beta

properties, tritium soon becomes dis- particles it emits and its relatively short

tributed throughout the body wherever half-life, tritium is much less of a longhydrogen i,- normally found. There is no range radiation hazard than the radioreason for believing that there is any isotopes already considered.

GENETIC EFFECTS OF NUCLEAR RADIATIONS

SPONTANEOUS AND iNDLICED cells carries a set of 23 chromosomes,

MUTATIONS one representing the characteristics of

12.201 The mechanism of heredity, the mother and the other set those of the

which is basically similar in ali sexually father. The resulting fused cell then has

reproducing plants and animals, includ- the normal complerv .;nt of 46 chrormoing man, is somewhat as follows. The somes. Subsequently, as the embroyo

nuclei of dividing cells contain a defi- develops, the cells reproduce themnite number of thread-like entities called selves and, in general, the 46 chromo-

"chromosomes" which are visible somves (and their constituent genes) are

under the microscope. These chromo- duplicated without change.

snies are believed to be differentiated 12.203 In rare instances, however,

along their length into several thousands a deviation from normal behavior occurs

(in man) of distinctive units, referred to and instead cf a chromosome duplicatas "r,,.n,ýs." The chromosomes (and ing itself in every respect, there is a

genes) exist in every cell of the body, change in one or more of the ge!,es. This

but "rom the point of view of genetics change, called a "mutation," is essen*-

(or heredity), it is only those in the germ tially permanent, for the mutant gene is

ceils, produced in the reproductive reproduced in it.,; altered form. If this

organs (sex glands), that are important. mutation occurs in a body cell, there

12.202 Human body cells normally may be some effect on the individual,

contain 46 chromosomes, made up of but the change is not passed on. But, iK

two similar (but not identical) sets of 23 the mutation occurs in a gernt cell ochromosomes each. in sexual reproduc- either parent, a new characteristic may

tion, the first step is the union of an egg appear in a later generation, although

cell, produced in the ovaries of the there may be no observable effect on the

mother, with a sperm cell, originating in individual in whom the gene mutation

the testes of the father. Each of these occurs. The mutations which arise nat-
610 BIOLOGICAL EFFECTS

urally, without any definitely assignable 12.206 As a general rule, new mucause or human intervention, are called tations, whether spontancous or induced

"spontaneous mutations." by radiation, are recessive. Neverthe12.204 The matter of immediate less, it appears that a mutant gene is

interest is that the freqtlency with which seldom completely recessive, and some

heritable mutations occur can be in- effect is observable in the next generacreased in various ways, one being by tion even if the particulat gene i-, inexposure of the sex glands (or heritcd from only one parent. Further-

"gonads"), i.e., tests or ovaries, to more, in the great majority oi cases,

ionizing radiation. This -,ffect of radia- mutations have deleterious effects of

fion has beer, observed with various in- some kind. A very few of the mutations

sects and mammals, and it undoubtedly are undoubtedly beneficial, but their

occurs also ir, human beings. The gene consequences become apparent only in

mutations induced by radiation (oi by the slow process of Hiological evolution.

,various chemicals or heat) do not differ 1U.,207 The harmful effects of a dequalitatively from those occurring leteiious mutation' may be moderate,

spontaneously. In practice. it is impos- such as increased susceptibility to dissible to determine in any p',rticular it,- ease or i decrease in life expectancy by

stance if the chaage has occirred :ztb- a fev ,nonths. or they may be more

rally or if it was~a result of ex.posure -o serious, such as deah in the embryonic

radiation. It is only the freq!;eicy wv:h mtage. Thus, individuals bearing harmwhich the mutations occur thz, if; in- ful gcnes are handicapped re!ktive to the

creased by ionizing radiation. One of rest f the population, particularly in the

the concerns about rrmdimhtiork exposure of respects that they tend to have fewer

a large population is that there may be a ý hildren or to die earlier. It ;s apparent,

substantial increase in tie overall bur.. therefore, that such genes will eventuder. of harm.ul mut.Ainns. There would a'ly be eliminated from tme population.

then be a greater than normal incidence A gene that does great harm will be

of defects in subsequen' generatiovis. eli-mnased rapidly, since few (if any)

12.205 Ail genes have the property individuals carrying such genes will

of being either "dominant" or "reces- survive to the age of reproduction. On

sive." If , gene is dominaant, ten the the other hand, a slightly deleterious

appropriete char,,cteriatic affected by routant gene may persist much longer.

that gec will appeai in the offspring and thereby do harm, although of a less

even if it is pro.duced by the gonads of severe character, to a larger number of

only one of the parents. On the other individuals.

hand, .4 particular recesý;ive gene m:st

occur in the gonads of both parents if the GENE MUTATIONS INDUCED BY

characteristic is to he apparent in the RADIATION

next generation. A recessive gene may

consequcntly be lteait for a number of 12.20)8 Since genetic effects of ragenerations, until the occasion a!is.s for diation are not apparent in expesed inihe union of iperm and egg cells both of dividt',"ls, information conct.rning muwhich contain iinis particular gene. tations can be obtained only from
GENETIC EFFECTS OF NUCI.EAR RADIATIONS 611

observations on subsequent generations. mutation frequency in these animals has

Data on radiation-induced mutations are been found to be dependent on the exavailable only from luboratory stuaies posure (or dose) rate at which the radia.

on experimental organisms with nonrt tion is received. There are definite indigeneration times. Unfortunately, these cations that some recovery can occur at

data cannot be extrapolated to man with low exposure rates and not too large

any degree of certainty. The extensive total exposure (or doses).

investigations of genetic effects of ,adi- 12.210 For exposure rates greater

ation on mice appear to provide the most than about 90 roentgens per minute, the

relevant information from which the incidence of radiation-induced mutapossible effects on man may be esti- tions in male mice appears to be pro.-

mated. Radiation can cause two general portiona! to the total (accumulated)

types of genetic change: gene (or point) gamma-ray (or X-ray) exposure to the

mutations in which the general structure gonads; that is to say, the mutation

of the chromosomes remains un- frequency per roentgen is independent

changed, and chromosome abnormali- of the exposure rate.' 6 For exposure

ties associated with gross structural rates from 90 down lo 0.8 roentgens per

changes. The former appe-ar to be the minute, however, the mutation fremore impor:ant and the subsequent dis- quency per roentgen decreases as the

cussion refers mainly to gene mutations. exposure rate is decreased. Finally,

12.209 From the earlier studies of below 0.8 roentgen per minute, the muradiation-induced mutations, made with tation frequency per roentgen once

fruitflies, it appeared that the number (or again becomes independent of the ex

frequency) of mutations in a given pop- posure rate, but the value is only about

ulation, i.e., the probability of the oc- one-third as large as at the high expocurrence of mutations, is proportional to sure rates (above 90 roenigens per minthe total dose received by the gonads of ute). In other words, a given radiation

the parents from the beginning of their exposure will produce roughly one-third

development up to the time of -'oncep- as many mutations at low than at high

tion. The mutation frequency appeared exposure rates.

to be independent of the rate at which 12.211 The exposure-rate effect in

the radiation dose was received. The feti'ale mice, for radiation exposure

implication was that the damage to the rates of less than 90 roentgens per mingonads of the parents caused by radia- ute, is even more marked thani in males.

tion was cumulative with no possibility The radiation-induccd mutation freof repair or recovery. More rer,;,t ex- quency per roentgen decreases continperiments with mice, however, have uously with the exposure rate from 90

shown that these conclusions mist be roentgens per minute downward. At all

revised, at least for mammals. When exposure rate of 0.009 rot..ntgen per

exposed to X rays or gamma rays, the minute, the total mutation frequency in

"161n the experiments with gamma and X rays, measurements were made of exposures in roentgens per

minute; hence, these units are used here. The dose rates in rads (or remn.;) per minute to the mo|e. gonads

are probably esseniially the same as the exposure rates. All conclusions concerning exposure-rate effects

thus apply equally to dose-rate effects.

""PM
612 BIOLOGICAL EFFECTS

female mice is indistinguishable from made with adult femnle mice is that a

the spontaneous frequency. There thus delay of ai Zast seven weeks between

seems to be an exposure-rate threshold e,:•posure to a substantial dose of radiabelow which radiation-induced muta- tion, either neutrons or gamma rays, and

tions are absent or negligible, no matter conception causes the mutation frehow large the total (accumulated) expo- quency in the offspring to drop almost to

sure to the female gonads, at least up to zero. In males, on the other hand, a

400 roentgens. Another important ob- lengthening of the interval between exservation is that at the same high expo- posure and fertilization of the female

sure rate of 90 roentgens per minute, the has little effect on the mutation fremutation frequency per roentgen at a quency. It is to be noted that in this as

total exposure of 50 roentgens is only well as other respects male and female

one-third of that for a total exposure of mice exhibit different responses to radi400 roentgens. The -adiation-induced ation in the occurrence of genetic mutamutation frequency in female mice thus tions. The reason is that in mice (and

decreases both with decreasing exposure other mammals) the mechanisms for the

rate and with the total exposure, in the development of male and female germ

ranges studied, cel;s are quite different.

12.212 For exposure to fission neu- 12.214 Since the reproductive systrons, no dose-rate effect has been ob- terns are basically the same in humans

served for genetic mutations in male as in lower mammals, it is probable that

mice and only a small one in females. the genetic effects of radiation in man

For large dose rates, equivalcnt to acute $Vill be at least qualitztively siminlr to

radiation exposures, the mutation fie- those in mice, as described above.

qucncy per rad of fast neutrons is five or Thus, a derease in mutation frequency

six times as great as for gamma rays. It per rad is expected at very low dose

would thul appear that a RBE value of 5 rates of gamma rays in humans, espeor 6 should be applicable for genetic cially in females. and the apparent RBE

effects due to exposure to fast neutrins; for fast neutrons should be about 5 or 6.

but this is i1ot strictly correct because the

types of mutations induced in mice by GENETIC EFFECTS OF NUCLEAR

neutron irradiation differ from those EXPLOSIONS

caused by X rays and gamma rays.

Sijice there is virtually no dose-rate ef- 12.215 In a nuclear explosion, peofect with neutrons, but a large one for X pie would be subjected to various

rays, the apparent RBE for neutrons amounts of initial ionizing radiation,

becomes quite lorge at very low dose consisting ot gamma rays and neutrons,

rates. This situation is, however, of delivered at a high dose rate, and also

limited interest in connection with possibly to the beta particles and gamma

weapons effects because neutron expo- rays froin fallout received at a very

sure can result only from the initial much lower dose rate. Because of interradiations and the dose rates are then in breeding between exposed and unexthe high range. posed persons, it is not possible to make

12.213 A significant observation accurate predictions of the genetic con-

_
GENETIC EFFECTS OF NUCIEAR RADIATIONS 613

sequences. A rough estimate is that an idly by the thyroid gland and the expoacute dose of about 50 rems to the .;ure of the gonads would be

gonads of all members of the population insifiiificam.

would result in additional mutations 12.217 Cesium-137, carbon-14, and

equal to the number occurring spontan- tritium are in a different zategcry as

eously. But this may not allow for the internal sources because they are dispossible advantage that might arise from tributed throughout the body and so can

delaying conception for some months caime irradiation of the gonads. Moro:-

after exposure to radiation. Although, to over, the decay of cesium..137 is acjudge from the observations on mice, companied by gamma rays of fairly long

this might not decrease the genetic ef- range.' 7 From the standpoint of the

fects of radiation in males, recovery in genetic impact of a patti.ular radiothe female members of the population nuclide, th-, total radiation dose to the

would bring about a substantial reduc- population over many generations must

tion in the "load" of mutations in sub- be taken into account. Hence, although

sequent generations, the annual radiation dot-e to the gonads

12.216 Gamma rays from radionu- from carbon-14 is less than from ceclides of short half-life in the early fall- sium- 137, the overall effect of these two

out on the ground or in the surroundings substances may not be very different

will be part of th4 in'tial (acute) radia- because of the murh ionger half-life of

tion dose to the gonads. Beta particles carboh-14. An additional eflect can reand gamma rays emitted from constitu- suit from the radioactive decay of carerts of the fallout that enter the body bon-14 atoms in the molecules that carry

and remain there for some time can also genetic information. Replacement of a

induce mutations. Genetic effects of carbon atom by its decay product, ni.

strontium,.90 are expected to be rela- trogen-14, would result in a change in

tively miuor. The element strontium the nature of the molecule.

tends to concentrate iii the skeleton and 12.218 The suggestion has been

because of the short range of the beta made that tritium may become concenparticles from strontium-90 in the body, trated in the genetic molecules and so

they do not pcnetrate to the gonads. represent a special hazard. There is,

Furthermore, the intensity uf the secon- however, no convincing evidence that

dary X radiation (bremsstrahlung) pro- such is the case. It appears that the

duced by the beta particles is low. Fi- increase in mutation frequency that

nally, the amount of strontium-90 in soft might arise from the presence of tritium

tissue, from which the beta particles in the gonads is not appreciably greater

might reach the reproductive organs, is than would be expected fion, the dose to

small. Radioiodines in the body would the body a. a whole. Since the whole-.

also not be important because all iso- body dose from tritium produced in a

topes of iodine are taken up quite rap- nuclear explosion is less than from car-

"1Gamma ,ays accompanying the decay of cesium-137 (and of other species of moderately long

half-life) deposited on the ground as delayed fallout, i.e., as an external source, ran make a significant

contributic.i to the gerelic dose.

I,

S. .... .. .. .. ....... . ....... . . . . .. .. .. .. . . . . .. .. " " " ..... : :• '; "7 . .. : . . ... ...
614 BIOLOGICAL ElFF•• "S

bon-14 and the effective half-life is natural background radiation, i.e., apart

considerably shorter, the gonetic effects from that due to nuclear explosions. In

of tritium should be very much less than the United States, the average dose to

those of carbon-14. the. gonads, from cosmic rays and from

12.219 In attempting to assess the radioactive isotopes in the body (espegenetic effects of internal radiation cially potassium-40) and in the ground,

emitters, it should be borne in mind is about 90 millirems per annum. It has

that, although the total radiation doses been estin.atcd that the fallout from exover many gcneiations may be large, the plosions of a few hundred megatons

dose rate is very low. In fact, it may be yield would be necessary to double the

so low that the eifects ia females, in overall mutation rate arising from back

particular, will be negligible. Further- ground radiation. This, incidentally,

more, the radiation from fallout should represents ;probably only a small fracbe compared with the gonad exposure of tion of the total number of spontaneous

all members of the population to the mutations.

PATHOLOGY OF ACUTE RADIATION INJURY' T

CELLULAR SENSITIVITY nuclear swelling, increased rytoplasmic

12.220 The discuJsion presented in visco.ity, cellular permeabiliiy, and

§ 12.90 et seq. has been concerned cellular death, are manifekted as altered

chiefly with general symptoms and the bodily functions when enough cells are

clinica! effects cf radiation injury, These affected to reduce the total function of

effects are due directly to the action of the organ made un of these cells. la

nuclear radiation upon individual organs certain instances, cells may be killed

and tissues. The changes in the periph- outright with very high doses of radiaeral blood, for example, reflect the lion (interpnase death), but more comdamage done by nuclear radiation to the monly iiradiated cells die when they

bone marrow and lymphatic tissue. The divide to reproduce (mitosis-linked

pathologic changes in other systems and death). Delayed death of this kind may

oigans caused by ionizing radiation, occnr after several cell divisions folwhich arz the basis of the clinical radia- lowing irradiation, so that the effect may

tion syndrom,, are discussed here not be obser'ved until some time after

briefly. exposure. MNIosis-linked death is ap12.221 Radiation damage is the re- parently caused by chromosomal and

suit of changes induced in individual perhaps ether nuclear abnormalities, but

cells. Morphologically demonstrable with time some of these Lbnormalities

changes, sucn as chromosome breaks, are repaired. Consequei.y, the longer

•'iThe more technical discussion in § 12.220 through § 12.239 may be omitted without loss of

continuity. A general treatmcnt of radiation effects on plants and farmi animals is given in § 12.240 et

seq.

. j'+.. ..Vft•,+
PATHOLOGY OF ACUTE RADIATION INJURY 615

the time between ccll divisions, the bombs in Japan. After damage by radigreater is thc opportunity to recover ation, the lymph nodes do not p~oduce

from radiation damage. Cells of dif- new lymphocytes for periods that vary

fercnt types and organs have quite dif- with the radiation dose. As a result of

ferent Jegrees of radiosensitivity based this cessation of production, combined

mainly on the rapidity of the cell divi- with death of circulating lymphocytes,

sion. Chromosotnal changes can also there is a rapid fall in the number of the

occur that will not result in cell death latter. This easily measurable early

but in hereditable abnormalities change in the peripheral blood has been

(§ 12.208) or in cell trans•jrmatiions found to be a useful means of prognosis

which may lead to cancer. following radiation exposure. A rapid,

12.222 Of the more common tis- almost complete, disappearance of lym.

sues, the radioiensitivity decreases phocytes implies that death is highly

roughly in the following order: lym- probable. whereas no change within 72

phoid tissue, bone marrow, gastroirates- hours it, indicative of an inconsequential

Onal epithliiurn, germinai epithelium of exposure.

tthc gonads;, embryonic tissues, corical 12.225 Atrophic lymph nodes, tontissue, enidothelial cells of th, blood sils, adenoids, Peyer's patches of the

vwssels, germinal epithelium of the skin, intestine, appendices, and spleens were

differentiated nervous tissue, collagen common findings among the radiation

and elastic tissue, aad bone and carti- casualties ir Japan.

lage. T' lymphocytes are remarkable

in that t ty are killed by relatively small BONE MARROW

acute raJivtion doses (see below).

12.226 Since all the other formed

LYMPI-10D) TI3SUE blood cells, except the lymphocytes,

arise from radiosensitive marrow cells,

12.223 Lymphoid tissue is com- the acute radiation exposure syndrome

posed of the lymph nodes, 'onsils, ,ie- is accompanied by severe changes in

"noids, spleen, and the submucosal is- cellular composition of the blood.

lands of the intestine. The lymphocytes Under normal circumstances, the maof the peripheral bloo6 arise in hese ture blood cells leave the marrow anid

various sites. Wherever these cells enter the blood stream where they reoccur, they are ihe most radiosensitive main until destr,',yed by natural proccells of the whole body. In fact, lym- esses and in defense against infection.

phocytes 4re killed outright by radiation l'he different kinds of cells have difdoses as low as 100 rems or less. ferent spans of natural life. The shorter

12.224 Under the microscope, itra- the life of a particular cell, the more

diated ly-nphocytes can be seen to be quickly will radiation darn'ge to the

undergoing pyknosis and subsequent parents of that particular cell be revealed

disintegration. As these cells die, their by a decrease in numbe, of such cells in

remnnants are removed and the lymph the c'rculation. The red blood cells,

nodes atrophy. This change was com- which have the longest life span (about

mon among the victims of the nuclear 120 days), are the last to show a reduc2, 1
616 BIOLOGICAL EFFECTS

tion in number even though their parent creased ability to produce antibodies,

cells, the erythroblasts, are almost as lowers the resistance of the body to

radiosensitive as the !ymphocyles. bacterial and viral invasion. If death

12.227 Bone marrow exhibits strik- does not take place in the first few days

ing changes soon after irradiation. There after a large dose of radiation, bacterial

is at once a temporary cessaiion of cell invasion of the blood stream usually

division, Those cells in th¢• process of occurs and the patient dies of infection.

dividing go on and complete the proc- Often such infections are caused by

ess, after which all the cells in the mar- bacteria which, under normal circumrow mature progressively. Since they stancus, are harmless.

leave the marrow as rapidly as maturity 12.230 Very often in whole-body

is reached, the marrow becomes de- irradiation the outward signs of severe

pleted at omne of both adult and less damage to the bone marrow, lymphatic

mature cells. As time passes, the mar- organs, and epithelial linings are ganrow, barring regeneration, becomes grenous ulcerations of the tonsils and

progressively more atrophic until in the pharynx. This condition (agranulocytic

final stage it con'-ists of dilated blood- ahemia) i. also found in cases of chemfilled sinuses, with gelatinous edema of ical. poisoning of the bone marrow that

the spaces left empty by the loss of resemble the effect of radiation expomarrow cells, and large macrophages sure. Such ulcerations and the pneumocontaining the debris of dead cells re- nia that often accompanies them are

moved from the circulation. Such ex- unusual in the respect that very little

treme atrophy of the marrow was com- suppuration is found because of the

mon among those dying of radiation paicity of leucocyte cells. Although

injury in Japan up to 4 months after most of the bacteria in such ulcerations

exposure. In some of these delayed ra- can usually be controlled by antibiotic

diation deaths, the bone marrow showed drugs, the viruses and fungi which also

a return of cellular reproductive activity, invade such damaged tissues are not

affected by treatment, and fatal septi- cemia is common.

HEMORRHAGE AND INFECTION

12.228 Hemorrhage is a common REPRODUCTIVE ORGANS

phenorpenon after radiation exposure

becaue the megakaryocytes, from 12.231 Cell division in the germinal

which the blood platelets necessary for epithelium of the testes stops at once

clotting are formed, are destroyed and with lethal exposure to ionizing irradiap•atelets are not replenished. If hemor- tion. The first change is pyknosis or -4)

rhage occurs in vital centers, death can nuclear death of the spermatogonia, the

result. Often the hemorrhages are so most primitive of the male germinal II

widespread that severe anemia and epithelium. Following this change, the

death are the consequences. more developed cells undergo matura12.229 The loss of the epithelial tion without further division, so ihat the

coverings of tisjues, together with the testicular germinal cells leave the testes

loss of white blood cells and the de- as adult sperm, and the most primitive
PATHOLOGY OF ACUTE RADIATION INJURY 617

cells disappear sequentially as they ma- head. In severely exposed but surviving

ture and die during cell division, cases, hair began to return within a few

12.232 Changes in the ovaries months, and epilation was never percauseu by radiation are less striking than manent.

those in the testes. The primordial ova

can be found in progressive stages of

post irradiation atrophy and degenera- 12.235 Some of the first gross

tion. In some Japanesu irradiation vic- changes noted in radiation-exposed Japtims, the ovarian follicles failed to de- anese were ulcerations of the intestinal

velop normally and menstrual lining. The mucosa of the first part of

irregularitiies resulted. There was an the small intestine is the most radiosenincreased incidence of miscarriages and sitive but usually does not ulcerate

premature births, along with an in- deeply. Ulcers are most commonly

creased death rate among expectant found after irradiation in the lymphoid

mothers. These changes were related to tissues of the lower ileum and in the

the radiation dose, as determined by the caecum, where bacterial invasion is

distance from ground zero. common.

12.233 Morphologic changes in the 12.236 Microscopically profound

human reproductive organs, compatible changes are found throughout the gaswith sterility, are thought to occur with trointestinal tract. For example, the

doses of 450 to 600 rems. Various de- acid-secreting cells of the stomach are

grees of temporary sterility were found lost. Mitosis stops in the crypts of the

among surviving Japanese men and intestinal glands and, as a result, the

women. Many supposedly sterile from cells covering the villi of the intestine

exposure to significant doses cf radia- are not replaced and the villi become

tion have since produced childr'n who swollen, turgid, and denuded. When

are normal by ordinary measurements. bacterial invasion occurs, ulcers covered by a shaggy, fecally contaminated

LOSS OF HAIR exuadate develop. Since the white blood

Y€ cells are simultaneously depleted and

12.234 Epilation was common too few in number to combat infection,

among exposed Japanese surviving these intestinal ulcerations are often the

more than 2 weeks after the explosion, point of entry of bacteria that kill !he

The onset of epilation from the head was victim of heavy radiation exposure.

between the 13th avid 14th days after

exposure in both sexes. Combing ac- NERVOUS SYSTEM

centuated this change, although copious 12.237 Although certain nerve cells

amounts of hair were lost spontaneously are among the most radioresistant cells

for about 2 weeks. The distribution of in the adult body, the nervous tissue of

the radioepilation conformed in general the embryo and some cells of the adult

with that expected from the senile cerebellum are relatively sensitive to

changes of male ancestors. The hair of radiation. Early disorientation and coma

the eyebrows, eyelashes, and beard may be induced by brain damage at dose

came ou' much less easily than from the levels of thousands of reins.
618 BIOLOGICAL EFFECTS

BLAST-RELATED EFFECTS

VELOCITIES OF GLASS FRAGMENTS relative to the advancing shock front.

12.238 Glass fragments produced From Fig. 12.238 the geometric mean

by air blas' arL. a substantial hazard and velocity of the fragments can be deterthe injuric" (hey can cause are related to mined for glass panes of any specified

the velocities attained (§ 12.42). Mea. thickness exposed to a given effective

surements have been made of the frag- peak overpressure.

ments produced from glass pnes,

mounted in either steel or wood frames, DECELERATIVE TUMBLING

when destroyed by the blast from nuclear (11 to 29 kilotons) or conventional 12.239 The results of the tests re-

(15 to 500 tons) explosions. The types ferred to in § 12.45, on the decelerative

of glass ranged from 0.25-inc. thick tumbling of various animal cadavers

plate glass, through various standard dropped onto a hard, flat surface at difthicknesses of single- and double- ferent velocities, are represented graphstrength glass, to thin nonstandard panes ically in Fig. 12.239; the possible error

0.06J inch thick. The results obtained is within the range of about ± 10 to 15

can be represented, with an accuracy of percent. The initial velocity V1 feet per

roughly ± 10 to 15 percent. by the second and the stopping distance S feet

straight line in Fig. 12.238. The geo- are scaled for the mass of the animal (m

metric mean velocity, i.e., the antilo- pounds). Scaled stopping times are also

garithm of the mean of the logarithms of shown. Thus, for a given initial velocity

the velocities, represented by V ,0 feet and animal mass, the stopping distance

per second, is modified by an empirical for decelerative tumbling may be

scaling factor for the thickness (tinches) derived directly from the linear plot and

of the glass panes. The effective peak the corresponding stopping time may be

overpressure (pounds per square inch) is determined by interpolation. Although

equal to the peak reflected overpressure the data were obtained from tesis with

if the glass is oriented face-on to the animals, it is thought that the results can

blast wave and it is the same as the be applied to the deceleralive tumbling

incident peak overpressure if the pane is of humans provided there is no signifilocated on the side or back of a structure cant bouncing.

EFFECTS ON FARM ANIMALS AND PLANTS

INTRODUCTION have similar potential for causing dam12.240 In general, the three main age to animals and plants as they do to

immediate physical effects of nuclear humans. As biological systems, larger

explosions, i.e., blast, thermal radia- animals are similar to man and would

tion, and the initial nuclear radiation, experience much the same blast, burn,
EFFECTS ON FARM ANIMAI.S AND PLANTS 619

L.L

-- 0

I in

- IJJ

v a,.o, 00

0 0

(20' - 1* Io +r. '

•,. . o

09A.

' o o o o oo° ~ o ~~o 

.... A1IOO'13A NV3VY 0181.3VI,030 03 9IV 9S

I 7,

!. Li

•;.-

'.."..- .-.-

• • ''"• - .... ....... . ;" a• .• '.. . . .. ;, -• : .. -. : .. . " . .. ""
620 BIOLOGICAL EFFECTS

o' E 

to

aU)

0) 0

9/1~~~ ~ ~ ~ ((/91 -A'0-3A-Vlll 1-l
EFFECTS ON FARM ANIMALS AND PLANTS 621

and radiation injuries, if exposed in the the possibility of serious ecological dissame manner. In fact, much information turuances. These might be caused by

concerning the expected effects of nu- large-scale fires, denuding of forests by

clear weapons on man, apart from the fallout, destructive plagues of insects

data from Japan, has been inferred from which are known to be relatively insen-.

studies on animals. Plants, on the other sitive to radiation, and so on. It is not

hand, vary greatly in the characteristics expected that such effects would be sethat determine injury from the immedi- vere enough to prohibit or seriously

ate physical effects of nuclear explo- delay recovery of food production facilsions. Consequently, for plants the ities after a nuclear attack.

range of biological responses is greater

than for man or animals. FALLOUT RADIATION EFFECTS ON

12.241 In nuclear warfare, an im- LIVESTOCK

portant need would be to assure an adequate food supply for the survivors, 12.244 As with man, fallout may

especially during the early post-attack cause both internal and external radiaperiod. The main concein would then tion exposures to animals. The external

not be with the immediate effects of the (whole-body) exposure would arise

explosions, but rather with the effects of mainly from gamma rays, and if the

the fallout on farm animals and crop fallout particles should remain on the

plants forming part of man's food chaiA skin for some time, the animals could

As a rule, the seriousness of these ef- suffer beta burns (§ 12.155). Internal

fects increases with increasing dose and radiation exposure could result from

dose rate of ionizing radiations. The tarm animals consuming contaminated

total effect of a given dose is also in- grass and thereby ingesting fallout parflueýnced by the stage of development of titles. Beta radiations from these par..

the organism and the environme'tai ticles wouid then irradiate the walls of

conditions prior to, during, and after the the intestinal tract whereas the gamta

exposure. As with the immediate effects rays would contribute to the whole-body

of a nuclear explosion, plants show a exposure. Certain radioisotopes may be

wide range of sensitivity to fallout ridi- leached from the fallout particles and

ation. enter the blood stream; they may then be

12.242 Another factor to be con- deposited in specific parts of the body,

sidered is the possible contcequences of e.g., iodine in the thyroid and strontium

the accumulation of various radioiso- in the skeleton.

topes in food supplies due to the residual 12.245 Skin injury caused by fallradioactivity in soils and water from out was observed in cattle exposed at the

deposited worldwide fallout. However, TRINITY test (§ 2.36) and also in anthese effects are of a protracted nature imals during atmospheric te;ts at the

and their importance is not well under- Nevada Test Site. Minor to severe injustood at present. ries due to beta radiation have occurred,

12.243 Another matter of interest in although none of the cattle died within

connection with the effects of nuclear 150 days of expcsure. The skin injuries

explosions on plants and farm animals is appeared to be s-milat to thermal burns

PRO.

' •-*
622 BIOLOGICAL EFFECTS

except that the latter are soon visible to gammu rays from fallout on the roof

whereas the effects of beta particles may and the surrounding ground.

nol bc seen for three or four weeks. 2. In a pen or corral: whole-body

12.246 The damage to the cattle at exposure to gamraa rays from fallout on

the TRINITY site was described as the the ground and exposure of the skin to

development of zones of thickened and beta particles. from fallout deposited on

hardened skin which appeared as the skin.

plaques and cutaneous borns. After 15 3. In a pasture: whole-body expoyears, three of the exposed cows devel- sure to gamma rays from fallout on the

oped scale-like carcinomas of the skin in ground, exposure of the skin to beta

the affected regions, but it is not entirely particles, and exposure of the gastroinclear that they were induced by radia- testinal tract from fallout on the grass.

tion. In areas les-s severely affected, The exposure to gamma rays is simuthere was some Loss and graying of the lated by means of an exterital cobalt-60

hair. The location of these cattle witl source. Skin irradiation is achieved by

respect to ground zero is not known, but attaching to the back of the animal a

it is estimated that the whole-body flexible source of beta particles. Finally,

gamma radiation dose was about 150 the internal exposure is simulated by

rems, although the skin dose may have adding to the animal's feed a material

been very much larger. There was no consisting of yttriunt-90 fused to 88-

evidence of radiation damage on the 175 micrometers particle- of sand, givlower surfaces of the body that might ing a specific activity of 10 microcuries

have been caused by exposure from per gram of sand. This product is confallout on tht. ground. sidered to be representative of the beta

12.247 Information concerning the radiation from the fallout produced by a

possible effects of fallout on faTm an- land-surface detonation.

imals under various conditions has been 12.248 Observations have been

obtained from studies with simulated made on animals exposed to wholefallout sources. Three main situations of body gamma radiation alone (barn) or in

interest, deperpding or, The location of combinacion with skin exposure (pen or

the animals, are as follows: corral) or w,th exposure of the skin and

I. In a barn: whole-body exposure the intestinal tract (pasture) at dose rates

Table 12.248

ESTIMATED LIVESTOCK LETHALITY (LD5o,6o) FROM FALL.OUT

Total Gamma Exposute (roentgens)

Animals Barn Pen or Corral Pasture

Cattle 500 450 180

Sheep 400 350 240

Swine 640 600* 550*

Horses 670 600* 350*

Poultry 900 850* 8001

* No expeimental data availible; estimates are based on grazing habits, anatomy, and plbysio? .gy of

the species.

it

.-
EFFECTS ON FARM ANIMALS AND PLANTS 623

of the order of magnitude expected from adults, but the difference appears to be.

fallout. From the results, estimates were less marked for swine than for cattle. At

made of the total gamma exposure high exposure rates, the total exposure

whicb would be fatal to 50 percent of a required to produce a certain degree of

large group of animals within 60 days lethality is smaller than when the rate is

(LD5()60); the values are summarized in low, suggesting the possibility of partial

Table 12.248. It is evident that, for recovery by the animal from radiation

cattle and sheep, which are ruminants, injury. Again, this effect is more

internal exposure can contribute sub- marked for swine than for other livestantially to the lethality of fallout. sto~ck.

12.249 The data in the table apply 12.251 The great majority of farm

to extreme conditions and are intended animals receiving an exposure of less

only to ind2icate the different sensitivities than 400 roentgens of whole-body k-adito radiation of a few animal species, the ation alone would be expected to surkinds of doses that might prove fatal, vive. However, they will show sympand the effects of combining different tonms similar to those observed in man.

types of exposures. The basic assump- The primary symptoms are those assotion involved is that the animals remain ciated with damage to the blood-formin a given situation while they accumu- ing tissues; they usually include a severe

late an exposure of a few hundred drop in the number of platelets in the

roentgens of radiation.'1 In practice, ot blood and gastrointestinal damage

course, the animals would probably be caused by failure in blood clotting. Inremoved as soon as possible from a creased permeability of the capillaries

contaminated area and, in any event, also contributes to the loss of blood

contaminated grass would soon be re- cells, plasma, and electrolytes (salts).

placed by clean fodder. Swine are nor- Most of these losses occur between 14

maily fed in a drylot ano would proba- and 30 days after exposure, at which

bly not ingest enough radioactivity to time the white-ceh count is low; fever

increase dioses above those e-pected and bacterial invasion may also occur.

trom whole-body irradiation alomie. 12.252 Cattle receiving wlhole-body

12.250 There are considerable vari- exposures in the range of 200 to 600

ations in radiation sensitivity in a given roentgens commonly experience some

animal species, just as in man, lut on loss of apoetite and slight fever for

the whole it appears, in agreement with about 24 hours. They then appear rorthe estimates in Table 12.248, that cattle mal for about 14 days (latent stage),

and sheep are more sensitive to radiation after which there is a marLed fever in

than are swvine. Furthermore, among those receiving the larger radiation exthose who survive, the recovery time is plsures: most of the latter will die

shorter in swine than in cattle and sheep. within a month' or so. Those animals

As % general rule, young animals are which survive show only a mild fever.

more sensitive to radiation than are Very few, if any, of these survivc-ý are

"gln the tests, ihe gamma-ray exposurcs were measitred in roentgc•rs and so are expressed in this form

"in the table. The ectual whole-body doses in reins would probably iot be greatly different.

A
624 BIOLOGICAl. EFFECTS

expected to suffer the serious loss of have not been exposed, but lactation

appetite and vomiting which are asso- may be reduced as a result of destruction

ciated with the gastrointestinal radiaticn of thyroid tissue by radioiodines from

syndrome at higher exposures. ingested fallout. It is possible that the

12.253 The effects of internal radi- concentrations of strontium-90 and of

ation exposures have been studIied by iodine-131 may make the milk unsuitaddiag the simulant mention..d in able for general use. Most sheep, cattle,

§ 12 247 to the feed of sheep. The ear- and swine surviving the exposure to

liest symptoms were loss of appetite, fallout, even those with gastrointestinal

diarrhea, weight loss, and fever. The tract injuries from ingested fallout,

sandy radioactive material tended to could eventually be used for food under

collect in "pockets" in the rumen and emergency conditions. Until more data

abomasum220 where the radiations are available, it has been recommended

caused ulceration and accumulation of that, for 15 to 60 days after exposure to

fibrinous exudate. No gross lesions were radiation levels that might cause some

found in the intestines of sheep under mortality, only muscle meat from surthese conditions. Loss of appetite was viving animals be used for food.

accompanied by stagnation in the rumen

which prevented the normal passage of FALLOUT RADAATION EFFECTS ON

the animal's food. This was followed by PLANTS

severe diarrhea and weight loss. Sheep

that survived usually returned to normal 12.255 Plants differ krom animals

feed consumption within 60 days, but (and man) with respect to radiation exconsiderably more time(- was required to posure from fallout; aniinais can move

recover thQ less of weight. or be moved from thr. fallout field

12.254 Whole-body exposure to whereas plants in the ground must re240 roentgens of external gammi. radia- main in the same location during their

tion, at the high exposure rate of 60 lifetime. Since food crops are harvested

roentgens per hour, affected neither the at tve end of the growing season, the

body weight nor the feed consumption toval exposure received will be greatly

of sheep and cattle. If the whole-body dependent on the stage of development

exposure was supplemented by a skin at which the fallout occurs. Thus, a

dose there was some decrease in weight, young seedling will receive a much

and an even greater decrease if there larger radiation dose than will a fairly

was also exposure of the intestinal tract. mature plant which is almost ready for

However, it appears that at radiation harves,,ing. Furthermore, the sensitivity

doses below lethal values and at dose of a plant to radiation is different at

rates expected from fallout, the effect on different growth stages. These and other

livestock production would be minor at factcrs make it impossible to present

most. As a rule, irradiated dairy cows any precise information concerning the

produce as much milk as those which expected effects of fallout on plants.

2OThe rumen is the firs' stomach (or pouch) of a ruminant and the abomasum is the fourth (or true)

stomach.

-.
EFFECTS ON FARM ANIMALS AND PLANTS 625

Nevertheless, some genera! conclusions much as a ten-fold change in apparent

can be drawn. radiosensitivity of a given plant species.

12.256 At sufficiently large doses, Significant exposures to radiation are

radiation can seriously reduce the exDet:-ed to delay flower initiation and

growth and yield of a plant, particularly fruit ripening. Hence, plants with z

if it is exposed at certain stages of de- growing season that is limited by clivelopment. In addition, there may be matic conditions, e.g., tomato, may

loss of reproductive capacity, changes survive through the grkuwing season but

in shape wnd appearance, wilting, and would produce essentially no useful

ultimately death. There may also be yield.

changes in the normal plant tolerance to 12.259 Since seeds are needed to

environmenta& stresses. The sensitivities provide the next crop, the viability of

of plants to radiation vary over a wide seeds from irradiated plants is imporrange and they are influenced by many tant. Adverse characteristics are somebiological, environmental, and radiolo- times present, although the seed appears

gical factors. The sensitivities of dif.. to be normal. Too little is known about

ferent species may differ as much as this matter for any definite statements to

100-fold or more, and there may be a be made. Seeds already formed are

50-fold range of sensitivity in a given fairly resistant to radiation and seeds in

species at different stages of growth. storage will probably remain essentially

Thus, certain stages of the development unaffected. Seed potato tubers and small

of reproductive structures, e.g., forma- onion transplants are more sensitive

tion of flower buds, are very sensitive to than ordinary dry seeds. Exposure of

radiation, but the ripe seeds are much seeds to sufficiently large doses of radimore resistant. ation is known to produce mutations,

12.257 As with animals, the re- and mutations may well appear in seeds

sponse of a plant to a given dose of from exposed plants. Although most of

radiation depends on the dose (or expo- the mutations are deleterious, a number

sure) rate, although the effect appears to of beneficial mutant forms have been

be more marked for plants. A much developed from irradiated seeds.

larger total dose is usually required to 12.260 Information on the effects of

produce a given degree of injury to actual fallout on plants is meager. At the

plants when the dose rate is low than Nevada Test Site, trees and shrubs have

when it is high. At very high and very been killed by radiation from fallout,

low dose rates, however, there is no but the plants have been close to the

observable evidence of a dose-rate ef- locations of cratering explosions. Subfect. stantial amounts of fallout particles were

12.258 Among the many important deposited on the leaves where they reenvironmental conditions influencing mained for some time because of the

the radiation response of plants are cli- small rainfall ia the desert area. No such

mate, temperature, light, soil moisture, occurrences have been observed foland cempetition from other plants. Ex- lowing contained, buried nuclear exploeluding the effects of drought, changes sions. Essentially all that is known

in environmental factors can result in as about the effects of radiation on plants

.4J-.,, mm .. . ... , . : -
626 BIOLOGICAL EFFECTS

has been obtained from tests in which the least resistant plant species, a total

plants at various stages of growth and exposure of about I,000 roentgens (or

development have been exposed to more) in the seedling stage is required to

gamma rays from an external source. kill about 50 percent of the exposed

12.261 Because of the great varia- plants, whereas for the most radioresistions in radiosensitivity even among tant plant 15,000 roentgens may be replants of the same species, the results quired. The decrease in yield of the

obtained with experimental plants are surviving plants after exposure to radiaapplicable only under the precise condi- tion follows the same order, in general,

tions of the experiments. However, an as the increase in lethality.

important conclusion hasi emerged from 12.263 Although woody plants are

these studies which should provide a not a source of food, they are of ecogeneral guide as to the expected effects nomic importance. Evergreen trees

of gamma radiation on plants. At (gymnosperms), such as pines and reequivalent growth stages and u-der lated species, are quite sensitive to rasimilar conditions, the radiosensitivity diation. Deciduous trees, which shed

of a plar.t is directly related to the size of their leaves at the end of each growing

the chromosomes, measured as the season, are much less sensitive; the exaverage volume occupied per chromo- posures that will kill about half the exsome in the cell nucleus. The larger the posed trees range from 2,600 to 7,700

effective chromosome volume, the more roentgens. However, even smaller exsensitive is the plant to radiation. In posures would have a serious effect on

other words, under equivalent condi- the economiý: value of these trees.

tions, a given total dose (or exposure) of 12.264 The results described above

radiation will cause a larger proportion refer to exposures from gamma radiaof deaths and a greater decrease in yield tion. In a fallout situation, however, the

from the surviving plants, the larger the plant would be subjected to beta radiachromo,•cme volume. Or stated in an- tion in addition. In fact, it appears that

other way, the larger the chromosome for many crop plants, which typically

volume, the smaller the radiation dose have relatively little tissue mass around

required to produce a given degree of their most radiosensitive parts and

damage to the plants. which are often in contact (or near con12.262 On the basis of chromosome tact) with the fallout particles, the dose

volume (and experimental observations from beta radiation may be greater thar,

of lethality and yield) some important from gamma rays. This would be paifood crops can be placed in an approx- ticularly the case in the early stages of

imate order of decreasing sensitivity to plant growth. Beta radiation may thus

radiation as follows: onions, small-grain make an important contribution to the

cereals, e.g., wheat, barley, oats, and injury of plants and may be the domicorn (but not rice), held peas, lettuce, nant cause of damage irn many situalima beans, potatoes, sugar beets, broc- tions. Apart from the view that beta and

coli, and rice. It is of interest that young gamma radiation have equivalent effects

seedlings of rice appear to be excep- for the, same dose in rads, information

tionally resistant to radiation. Even for concerning beta-radiation injury and the

., . . . . .. -
EFFECTS ON FARM ANIMALS AND PLANTS 627

possible synergism with gamma radia- particles that might be attached to leaf or

tion is very sparse. root vegetables. The major problem

would arise from the possible presence

12.265 Food crops harvested from in the edible parts of the plant of raplants that have survived exposure to dionuclides taken up from the soil by the

fallout would probably be safe to eat roots or from particles deposited on the

under emergency conditions, especially leaves. Because of thc. complexities inif the exposure occurred during the later volved, no generalizations can be made

stages of growth. Care would have to be and each situation would have to be

taken to remove by washing any fallout evaluated individually.

BIBLIOGRAPHY 21

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(1974). in Man," U.S. Armed Forces Medical Journal,

BELL, M. C., L. B. SASSER, J. L. WEST, and 9, 313 (1958).

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Labelled Fallout Simulant to Sheep," Radia- Bomb Survivors, Hiroshima and Nagasaki,"

tior Research, 43, 71 (1970). Radiation Research, 45, 216 (1971).

*BENSON, D. W., and A. H. SPARROW (Eds.), JABLON, S., et al., "Cancer in Japanese Exposed

"Survival of Food Crops and Liveritock in the as Children to Atomic Bombs," The Lancet,

Event of Nuclear War," Proceedings of a May 8, 1971, p. 927.

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sium Series, No. 24, U.S. Atomic Energy and Mortality, 1950-1970," Radiation ReCommissior 1971. search, 50, 649 (1972).

BROOKS, J. W., et al, "The Influence of External KATO, H. "Mortality in Chidren Exposed to the

Body Radiation on Mortality from Thermal A-Boanbs While In Utero, 1945-1969," Amer.

Burns," Annals of Surgery, 136, 533 (1952). J. Epidemiology, 93, 435 (1971).

BROWN, S, L., W. B. LANE, andJ. L. MACKIN, Kutp, J. I., A. R. SCHULERT, and E. J.

"Beta Dosimetry for Fallout Hazard Evalua- HODGES, "Strontium-90 in Man: IV,"

tion," Stanford Research Institute, Menlo Park. Science, 132, 448 (1960).

California, July 1970, EGU-8013. LANE, W. B., "Fallout Simula~at Development:

*BkUCER, M. "The Acute Radiation Syndrome: Leaching of Fission Products from Nevada

Y-i2 Accident," Oak Ridge Institute of Nu. Fallout and Properties of Iodine-tagged Simuclear Studies., April 1959, ORINS-25. lant," Stanford Researth Institute, Menlo Park,

BRYANT, F. J., ,-t al., U.K. Atomic Energy California, June 1970, SRI-7968. (This report

Authority Repxort AERE HP/R 2353 (1957); contains reference., to and summaries of pre-

"Strontium in Diet," Brit. Medical Journal, I, vious studies.)

1371 (1958). LANGHAM, W. H. (Ed.), "Radiobiological Fac2 The number of publications on the biological effects of nuclear weapons if very large; additional

* citations will be found in the selected references given here.

J.h _
628

lors in Manned Space Flight," Chapters 5 and *"Rediation Injuries and Sickness: A DDC Etib6, National Academy of Sciences-National Re- liography, Volume I, May 1957-,'ily 1970,"

search Council, Publication No. 1487, 1967. May 1971.

LAPPIN, P. W., and C. F. ADAMS, "Analysis of RUBIN, P.. and CASARETT, G. W.. "Clinical

the First Thermal Pulse and Associated Eye Radiation Pathology," Vols. I and !I, W. B.

Effects," Aerospace Medical iteaearch Labora- Saunders Company, 1968.

tories, Wright Paliterson Air Force Base, Ohi-), RUSSELL, S. R., and A. H. SPARROW (Eds.),

December 1968, AM RL-TR-67-214. "The Effects of Radioactive Fallout on Food

LoUTi r, J. F., and R. S. RUSSELL, (Eds.), "The end Agriculture," North Atlantic Treaty OrgaEntry of Fission Products int'a Food Chains," nization Report (1971).

Progress in Nuclear Energy, Seriew VI, Vol. 3., SPAR1,OW, A. H., S. S. SCHWEMMER, and P. J.

Pergamon Press, Inc., 1961. BOTr',NNO, "The Effects of External Gamma

MILLER, C. F.., and P, D. LA RIVIERIE, "In- Radiation from Radioactae Fallout on Piants

troduction to Long-Term Biological Effects of with Special Referetnce to Crop Production,"

Nuclear War," Stanford Research Institute, Radiation Botany, 11, 85 (1971).

Menlo Park, California, April 1966, MU-5779. United Nations General Assembly Official ReMitL,..R, R. W., "Delayed Radiation Effects in cords, "Report of the United Nations Scientific

Atomic Bomb Survivors," Science, 166, 569 Committee on the Effects of Atomic Radia-

(1969). tion," A/5216 (1962); A/5814 (1964); A/6314

National Academy of Sciences-Nationel Research (1966/; A/7613 (1969); A/8'05 (1972); United

Council, "The Biological Effects of Atomic Nations, New York.

Radiation," 195o and 1960; "Paih "`gical Ef- *WiiITE, C. S., et al,, ' Compa-'ative Nuclear

fects of Atomic Radiation," Publi, ation No. Effects of Biomedical Interest," Civil Effects

452, 1961; "Effects of Inhaled Radioacdive Study, U.S, Atomic Energy Commission, JanParticles," Publication No. 848, 1961; "Long- uary 1961, CEX-58.8.

Term Effects of Ionizing Radiations from Ex- WiHITE, C. S., et al., "The Relation Between

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"Effects of Ionizing Radiation on the Hu'man Variations," Space Life Sciences, 2, 158

Hem atopoietic System," Publication No. 875, (1970).

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* These publications may be puichased from the National Technical Information Servi, k,,,"!,ent

of Commerce, Springfield, Virginia, 22161. .
GLOSSARY

A-Bomb: An abbreviation for aomic bomb. See Apparent Crater: See Crater,

Nuclear weapon. Arching: In the case of a buried structure, it is

Absorbed Dose: rhe amount of energy in:- the tendency for the soil particles to lock together

parted by nuclear (or iornizing) radiation to unit in the form of an arch, with the result that part of

mass of absorbing material. The unit is the rad. the stress is traismitted around the structure

See Dose. Rad. instead of through it.

Absorption: The irreversible convei:4ion of the Atiom: The smallest (or ultimate) particle of an

energy of an electromagnetic wzve into another element tha' still retains the characteristics of that

form of energy as a result of its interaction with element. Every atom consists of a positively

matter. As applied to gamr "9 (or X) rays it is the charged central -cieus, which carries nearly all

process (or processes) resulting in the transfer of the mass of the atuin, surrounded by a number of

energy by the radiation to an absorbing material negatively charged electrons, so that the whole

through which it passes. In this sense, absorption system is electrically neutral. See Electron, Eleinvolves the photoelectric effect and pair pro- ment, Nucleus.

duction, but only part of the Compton effect. See Atomic Bomb (or Weapon). A term sometimes

Attenuation, Comptor, effect. Pair production, applied to a nuclear weapon utilizing fission

Photoelectric effect. energy only. See Fission, Nuclear weapon.

Absorption Coefficient: A number characteriz- Atomk Cloud: See Radioactive cloud.

ing the extent to which specified gamma (or X)

rays transfer their energy to a material through Atomic Number: See Nucleus.

which ihey pass. The linear energy absorption Atomic Weight: The relative mass of an atom

coefficient is a measure of the energy tiansfer (or of the given element. As a basis of reference, the

absorption) per unit ihickness of material and is atormic weight of the common isotope of carbon

stated in units of reciprocal length (or thickness). (carbon-12) is taken to be exactly 12; the atomic

The mass energy absorption coefficient is equal weight of hydrogen (the lightest element) is then

to the linear absorption coefficient divided by the 1.008. Hence, the atomic weight of any element

densit,, of the absorbing material; it is a measure is approximately the mass of an atom of that

of the energy absorption per unit mass. See element relative to the mass of a hydrogen atom.

Attenuation coefficient.

Afterwinds: Wind currents set up in the vicinity Attenuation: Decrease in intensi.y of a signal,

of a nuclear explosion directed toward the burst beam, or wave as a result of absorption and

center, resulting froni the updraft accompanying scattering out of the path of a detector, but not

the rise of the fireball, including the reduction due to geoiretric spreading (i.e., the inverse square of distance effect).

Air Burst: The explosion of a nuclear weapon at As applied to gamma tand X) rays, attenuation

such a height that the expanding fireball does not refers to the loss of photons (by the Compwn,

touch the earth's surface when the luminosity is a photoelectric, and pair-production effects) ii the

maximum (in the second pulse). passage of the radiation through a material. See

Alpha particle: A particle emitted spontan- Absorption, Inverse square law, Photon. Scateovsly from the nuclei of some radioactive ele- tcri.lg.

ments. It is identical with a helium nucleus, Atte.nuation Coefficient: A number characterhaving a mass of four units and an electric charge tizing. the extent of interaction of photons of

of two positive units. See Radioactivity. specified gamma (or X) rays in their passage

Angstrom: A unit of length, represented by A, through a material. The linear attenuation coefeqLal to 10- 8 centimeter. It is commonly used to ficient is a mcasure of the photon interaction per

Lxpress the wavelengths of electromagnetic radi- unit thickness of -naterial and is stated in units of

a~ions in the visible, ultraviolet, and X-ray re- reciprocal length (or thickness). The .nruss atten..

gions, uation coefficient is equal to the linear attenuation

629
630 GLOSSARY

cc,,efficient divided by the density of the material, Blast Scaling Laws: Formulas which permit the

it i.s a measure of the attenuation per unit mass. calculation of the properties, e.g., overpressure.

See Absorption coefficient, dynamic press'ire. time of arrival, duration, etc.,

Background Radiation: Nuclear (or ionizing) of a blast wave at any distance from an explosion

radiations arising from within the body and from of specified energy from the known variation

the suriounuings to which individuals are always with distance of these properties for a reference

exposed The main sources of the natural back- explosion of known energy (e.g., of I kih.ton).

ground radiation are potassium-40 in the body, See Cube root law.

potassium,40 and thorit, m, uranium, and their Blast Wave: A puose of air in which the pressure

decay products (including radium) present in increas:s sharply at the front, accompanied by

rocks and soil, ar.d cosmic rays. winds, propagated from an explosion. See Shock

Base Surge,: A cloud which rolls outward from waVe.

the bottom of ,he column produced by a subsur- Blast Yield: That portion of 'he total energy of 

a

face explosion. For underwater bursts the visible nuclear explosion that manifests itself as a blast

surge is, in effect, a cloud of liquid (water) (or shock) wave.

droplets with the property of flowing almost as if Bowb Debris: See Weapwi debris.

it were a homogeneous fluid. After the water

evaporates, an invisible base surge of small ra- Boosled Fission Weapon: A weapon in which

dioactive particles may persist. For subsurface neutrons produced by thiermunuclear reactions

land bursts the surge is made up of small solid serve to enhance the fission process. The iherparticles but it still behaves like a fluid, A soft monuclear energy represents only a small fracearth medium favors base surge formation in an tion of the total explosion energy. See Fi:;sion.

underground burst. Thermonuclear.

Bearing Wall: A wall which supports (or bears) Breakway: The onset of a condition in which

pait of the mass of a structure such as the floor the shock front (in the air), moves away from the

and roof systems. exterior of the expanding fireball produced by tht.

Beta Particle- A charged particle of very smad explosion of a nuclear (or atomic) weapon. Se4

mass emitted spontaneously from the nuclei of Fireball, Shock front.

certain radioactive elements. Most (if not all) of Bremsstrahlung: Literally "braking radiathe direct fission products emit (negative) beta tion." Radiations covering a range of wave

particles. Physically, the beta particle is identical lengths (and energies) in the X-ray region resultwith an electron moving at high velocity. See iný 'rom the electrical interaction of fast (highElectron. Fission products, Radioactivity. energy) electrons with atomic nuclei. BremsBeta Patch: A region of air fluorescence formed strahlung are produced by the interaction of beta

by absorption of beta particles from the fission particles with matter. See X rays.

prod-,cts in thie debris from a nuclear explosion Burst: Explosion or detonation. See Air burst,

above about 40 miles altitude. H!gh-altitude burst, Surface burst. Underground

Biological Half-Life: The time required for the burst, Underwater burst.

amount of a specified element which has entered Cleam Weapon: One in which measures have

the body (or a particular organ) to be decreased to been taken to reduce the amount of residual

half of its initial value as a result of natural, radioactivity relative to a "normal" weapon of

biological elimination processes. See Half-life. the same energy yield.

Black Body: An ideal body which would absorb Cloud Chamber Effect: See Condensation

all (and refklct none) of the radiation falling upon cloud.

it. The spectral energy distribution of a black Cloud Column: The visible column of weapon

body is described by Planck's equation; the, ai debris (and possibly dust and water droplets)

rate of emi3sion of radiant energy is proportional extending upward from the point of burst of 

a

lc the fourth power of the absolute temperature nuclear (or atomic) weapon. See Radioactive

(Ste'an-Boltzmann law). cloud.

Blast Loading. The loading (or force) on an Cloud Phenomena: See Base surge, Cloud

object caused by the air blast from an explosion column, Fallout. Fireball, Radioactive cloud,

striking and flowing around the object. It is a 4k

combination of overpressure (or diffraction) and Colum (or Plume): A hollow cylinder of water

dyn, amic pressure (or drag) loading. See Diffrac- and spray thrown up from an underwater burst of

tion, Drag loading. Dynamic pressure, Over- a nuclear (or atomic) weapon, through which the

pressure. hot, high-pressure gases formed in the explosion 

)

.j I
GLOSSARY 631

are vented to the atmosphere. A somewhat simi- vaporization of the surface material, by the

lar column of dirt is formed in an underground scouring effect of air blast, by throwout of disexplosion. turbed material, or by subsidence. In general, the

Compton Current: Electron current generated major mechanism changes from one to the next

0 rwith increasing depth of burst. The apparent as a result of Compton pULessc-. See Compton crater is the depression which is seen after the

effect, C'ompton electron. burst; it is smaller than the true crater (i.e., the

Compton Effect: The scattering of photons (of cavity actually formed by the explosion), begamma or X rays) by the orbital electrons of cause it is covered with a layer of loose earth,

atoms. In a collision between a (primary) photon rozk, etc.

an, an election, some of the energy of the photon Critical Mass: I he minimum mass of a fissionis transferred to the electron which is generally able material that will just maintain a fission

ejected from the atom. Another (secondary) chain reaction under precisely specified condiphoton, with less energy, then moves off in a tin such aste n reofte saerial andit

new direction at an angle to the direction of purity, the nature and thickness of the tamper (or

motion of the primary photon. See Scattering. neutron reflector), the density (or compression),

Compton Electron: An electron of increased and the physical shape (or geometry). For an

energy ejected from an atom as a result of a explosion to occur, the system must be supercriCompton interaction with a photon. See Comp- tical (i.e., the mass of material must exceed the

ton effect. critical mass under the existing conditions). See

Condensation Cloud: A mist or fog of minute Supercritical.

water droplets which temporarily surrounds the Cube Root Law: A scaling law applicable to

fireball following a nuclear (or atomic) detona- many blast phenomena. It relates the time and

tion in a comparatively humid atmosphere. The distance at which a given blast effect is observed

expansion of the air in the negative phase of the to the cube root of the energy yield of the

blast wave trom the explosion results in a lewer- explosion.

ing of the temperature, so that condensation of Curie: A unit of radioactivity; it is the activity

water vapor present in the air occurs and a cloud of a unit of radioactivitypeies th ich forrs. he son coudis ispeledwhenthe of a quantity of any radioactive species in which

forms. The cloud is soon dispelled when the 3.700 x 10M• nuclear disintegrations occur per piessure returns to normal and the air wa ims up second. The gamma curie is sometimes defined

again. The phenomenon is similar to that used by correspondingly as the activity of material in

physicists in the Wilson cloud chamber and is which this number of gamma-ray photons are sometime' called the cloud chamber effect. emitted per second.

Contact Surface Burst: See Surface burst. Damage Criteria: Standnrds or measures used

Contained Underground Burst: An under- in estimating specific levels of damage.

ground detonation at such a depth that none of

the radioactive residues e~cape through the sur- Debris: See Wcapon debris.

face of !he ground. Decay (or Radioactive Decay): The decrease in

Contaminstion: The deposit of radioacti"'e ma- activity of .ny radioactive material with the pasterial on the surfaces of structures, areas, objects, sage of time due to the spontaneous emission

or perso||nel, following a nuclear (or atomic) from the atomic nuclei of either alpha or beta

explosion. This material generally consists of particles, sometimes accompanied by gamma rafallout in which fission products and other diation. See Half-life, Radioactivity.

weapon debris have become incorporated with Decay Curve: The representation by means of a

particles of dir, etc. Contamination can also gr-iph of the decrease of radioactivity with rearise from the radioactivity induced in certain spect to time.

substances by the action of neutrons from a

nuclear explosion. See Decontamination, Fall- Decontamiration: The reduction or removal of

out, Induced radioactivity, Weapon debris. contamirating radioactive material from a strucCrack: The light-colored region which follows ture, mabeaoplsdby()tainthsrfe area, object, or person. Decontamination

closely behind closly th the dak dark ehid slick sickin in an a underwater unerwter may so as be to accomplished remove or decrease by (I) treating the contamination; the surface

burst. It is probably caused by the reflection of so as to mover decrease the aminaio the(2) letting the material stand so that the radioactwftivity is decreased as a result of natural decay;

Crater: The pit, depression, or cavity formed in and (3) covering the contamination so as to

4 the surface of the earth by a sitrface or under- attenuate the radiation emitted. Radioactive maground explosion. Crater formation cmn occur by terial removed in process (1) must be disposed of

.4
632 GLOSSARY

by burial on land or at sea. or in other suitable Dosimetry: The theory and applicatior of the

way . principle,: anu techniques inolved in the incaDelayed Fallout: See Fallout. surement and recording of rajiation doses and

dose rates. Its practical aspect is c micerned with

Deuterium: An isotope of hydrogen of mass 2 the use of various types of radiatior ivstrurients

units, it is sorietimes referred to as heavy hy- with which measurements are made. See Dosidrogen. It can be used in thermonuclear fusion meter, Survey meter.

reactions for the release of energy. Deuterium is

extracted from waier which iJways contains I Drag Loading: The force on an object or strucatom of deuterium to about 6,500 atoms of ordi- turc due to the transient winds accompanying the

nary (light) hydrogen. See Fusion, Isotope, passage of a blast wave. The drag pressure is the

Thermonuclear, product of the dynamic pressure and the drag

coefficient which is dependent upon the shape (or

Diffraction: The bending of waves arouid the geometry) of the structure or object. See Dyedges of objects. In connection with a blast wave namýc pressure.

impinging on a structure, diffraction refers to the Dynamic Pressure: The air pressure which repassage around and envelopment of the structure suts from the mass air r prwind) behind the

by the blast wave. Diffraction loading is the suots fromt ma air floe (o in ehind the force (or loading) on the structure during the shock front of a blast wave. It is equal to the

envelopment process, product of half the density of thk air through m pwhich the blast wave passes and the square of the

Dome: The mound of water spray thrown up particle (or wind) velocity behind the shock front

into the air when the shock wave from an under- as it impinges on the object or structure.

water detonation of a nuclear (or atomic) weapon Early Fallout: See Fcllout.

reaches the surface.

Dosage: See Dose. Effective Half-Life: See Half-life.

Dose: A (total or accumulated) quantity of ion- Elastic Range: The stress range in which a

izing (or nuclear) radiation. The absorbed dose material will recover its original form when the

in rads represents the amount of energy absorbed force (or loading) is removed. Elastic deformafrom the radiation per gram of specified absorb- tion refers to dimensional changes occurring

ing material. In soft body tissue the absorbed within the elastic range. See Plastic range.

dose in rads is essentially equal to the exposure in Elastic Zone: The zone beyond the plastic zone

roentgens. The biological dose (also called the in crater formation in which the ground is disRBE dose) in reins is a measure of biological turbed by the explosion but returns to its original

effectiveness of the absorbed radiation, See Ex- condition,

posure, Rad RBE, Rem, Roentgen. Electromagnetic Pulse: A sharp pulse of radioDose Equivalent: In radiation protection asso- frequency (long wavelength) electromagnetic raciated with peacetime nuclear activities, the dose diation produced when an explosion occurs in an

equivalent in rems is a measuie of the biological unsymmetrical environment, especially at or near

effectiveness of absorbed ionizing radiation. It is the earth's surface or at high altitudes. The insimilar to the biological dose which is used in tense electric and magnetic fields can damage

connection with the large radiation exposures unprotected electrical and electronic equipment

that might accompany a nuclear explosion. See over a large area. See Electromagnetic radiation,

Dose, Rem, High-altitude burst.

Dose Rate: As a general rule, the amount of Electromagnetic Radiation: A traveling wave

ionizing (or nuclear) radiation which an individ- motion resulting from orcillating magnetic and

ual or material would receive per unit of time. It electric fields. Familiar electromagnetic radiais usually expressed as rads (or reins) per hour or tions range from X rays (and gamma rays) of

in multiples or submultiples of these units, such short wavelength (high frequency,, through t'"e

as millirads per hour. The dose rate is commonly ultraviolet, visible, and infrared regions, to radar

used to indicate the level of radioactivity in a and radio waves of relatively long wavelength

contaminated area. See Survey meter. (low frequency). All electromagnetic radiations

A n m f m r a travel in a vacuum with the velocity of light. See

Dosimeter: An instrument for measuring and Photon.

registering the total aectmulated dosc of (or

exposure to) ionizing radiations. Instruments Electron: A particle of very small mass, carryworn or carried by individuals are called person- ing a unit negative or positive charge. Negative

nel dosimeters. electrons, surrounding the nucleus, (i.c., orbital

'i.1

*

a-
GLOSSARY 633

electrons), are present in all atoms: their number (radiation front). See Breakaway. Thermal Xis equal to the number of positive charges (or rays.

protons) in the particular nucleus. The term Fire Storm: Stationary mass fire, generally in

electron, where used alone, commonly refers to builtup urban areas, causing strong, inrushing

negative electrons. A positive electron is usually winds from all sides; the winds keep the fires

called a positron, and a negative electron is from spreading while adding fresh oxygen to

sometimes called a negatron. See Beta particle. increasc their intensity.

Electron Volt (EV): The energy imparted to an Fission: The process whereby the nucleus of a

electron when it is moved through a potential particular heavy clement splits into (generally)

difference of I volt. It is equivalent to two nuclei of lighter elements, with the release of

1.6 x 10 Q erg. substantial amounts of energy. The most imporElement: One of the distinct, basic varieties of tant fissionable materials are uranium-235 and

matter occurring in nature which, individually or plutonium 239, fission is caused by the absorpin combination, compose substances of all kinds. tion of neutrons.

Approximately ninety different elements are Fission Fraction: The fraction (or percentage)

known to exist in nature and several others, of the tot yil : fracnuclear wentwihi

including plutonium, have been obtained Ps a of the total f ield of a nuclear weapon which is due to fission, For thermonuclear weapons the result of nuclear reactions with these elements.

average value of the fission fraction is about 50

EMP: See Electromagnetic Pulse. percent.

Energy Absorption: See Absorption. Fission Products: A general term for the coinEnergy Partition: The distribution of the total plex mixture of substances produced as a result

energy released by a nuclear explosion among of nuclear fission. A distinction should be made

the various phenomena (e.g., nuclear radiation, between these and the direct fission products or

thermal radiation, and blast). The exact distribu- fission fragments which are formed by the actual

fion is a finction of time, explosion yield, and splitting of the heavy-element nuclei. Something

the medium in which the exp~osion occurs.' like 80 different fission fragments result from

roughly 40 different modes of fission of a given

Exposure: A measure expressed in roentgens of nuclear species (e.g., uranium-235 or plutothe ionization produced by gamma (or X) rays in nium-239). The fission fragments, being radioair. The exposure rate is the exposure per unit active, immediately begin to decay, forming adtime (e.g., roentgens per hour), See Dose, Dose ditional (daughter) products, with the result that

rate, Roentgen. the complex aidxure of fission products, so

Fallout: The process or phenomenon of the de- formed contains over 300 different isotopes of 36

'cent to the earth's surface of particles contami- elements,

nated with radioactive material from the radio- Flash Burn: A '-urn caused by excessivC expo.

active cloud. The term i also applied in a sure (of bare skin) to thermal radiation, See

collective sense to the cont,.ninated particulate Thermal radiation.

matter itself. The early (or local) fallout is defined, somewhat arbitrarily, as those particles Fluence (or Integratel Flux): The product (or

which reach the earth within 24 hours after a integral) of particle (neutron or pheton) flux and

nuclear explosion. The delayed (6r worldwide) time, expressed in units of particles per square

fallout consists of the smaller paiticles which centimeter. The absorbed dose of radiation (in

ascend into the upper troposphere and into the rads) s related to the fluence. See ;qux.

stratosphere and are carried by winds to all parts Flux (or Flux Density): The product of the

of the eatth. The delayed fallout is brought to particle (;ci.uiron or photon) density (i.e., number

earth, mainly oy rain and snow, over extended per cubic centimeter) and the particle velocity.

periods ranging from months to years. The flux is expressed as particles per square

Fireball: The centimeter per second and is related to the ab- luminous sphere of hot gases sorbed dose rate. It is numerically equal to thc

which forms a few millionths of a second after a sot be of r partis n geinall ectons

nuclear (or atomic) explosion as the result of the tota spher of i sing in ti os

absorption by absoptin the surrounding bythesurrundng mdiu medium of of the ite through n',etional a area sphere per of second. I square centimeter crossthermal X rays emitted by the extremely hot

(several tens of million degrees) weapon resi- Fractionation: Any one of several processes,

dues. The exterior of the fireball in air is initially apart from radioactive decay, which results in

sharply defined by the luminous shock front and change in the composition of the radioactive

later by the limits of the hot gases themselves weapon debris. As a result of fractionation, the

t.
634 GLOSSARY

delayed fallout generally contains relatively more Half-Residence 'rime: As applied to delayed

of strontium-90 and cesium-137, which have fallout, it is the time required for the amount of

gaseous precursors, than does the early fallout weapon debiis deposited in a particular part of

from a surface burst, the atmosphere (e.g.. stratosphere or troposFree Air Overpressure (or Free Field Over- phere) to decrease to half of its initial value.

pressure): The unrt,flected nressure, in excess Half-Value Thickness: The thickness of a given of the ambient atmospheric pressure, created in material which will absorb half the gamma radithe air by the blast wave from an explosion. See ation incident upon it. This thickness liepends on

Overpressure. the nature of the material-it is roughly inversely

Fusion: The process whereby the nuclei of light proportional to its density-and also on thi enelements, especially those of the isotopes of ergy of the gamma rays.

hydrogen, namely, deuterium and tritium, com- H.Bomh: An abbreviation for hydrogen bomb.

bine to form the nucleus of a heavier element See Hydrogen bomb.

with the release of substantial amounts of energy. Height of Burst: The height above the earth's

See Thermonuclear. surface at which a bomb is detonated in the air.

Gamma Rays (or Radiations): Electromag- The optimum height of burst for a particular netic radiations of high photon energy orginam- target (or area) is that at which it is estimated a

ing in atomic nuclei and accompanying many weapon of a specified energy yield will produce 

a

nuclear reactions (e.g., fission, radioactivity, certain desired effect over the maximum possible

and neutron capture). Physically, gamma rays area.

are identical with X rays of high energy, the High-Altitude Burst: This is defined, someonly essential difference being that X rays do what arbitrarily, as a detonation at an altitude

not originate from atomic nuclei, but are pro- over 100,000 feet. Above this level the distribuduced in other ways (e.g., by slowing down tion of the energy of the explosion between blast

(fast) electrons of high energy). See Electro- and thermal radiation changes appreciably with

magnetic rcdiation, Photon, X rrys. increasing altitude due to chaiges in the fireball

Genetic Effect: The effect of various agc,.ts phenomena. (including nuclear radiation') in producing Hot Spot: Region in a contaminated area in

changes (mutations) in the hereditary compo- which the level of radioactive contamination is

nents (genes) of the germ cells present in the somewhat greater than in neighboring regions in

reproductive organs (gonads). A mutant gene the area. See Contamination.

causes changes in the next generation which may

or may riot be apparent. Hydrogen Bomb (or Weapon: A term sometimes applied to nuclear weapons in which part of Ground Zero: The point on the surface of land the explosive energy is obtained from nuclear

vertically below or above the center of a burst of fusion (or thermonuclear) reactions. See Fusion,

a nuclear (or atomic) weapon; frequently abbre- Nuclear weapon, Thermonuclear.

viated to GZ. For a burst over or under water the

corresponding term is surface zero (SZ). Surface Hypocenter: A term sometimes used for ground

zero is also commonly used for ground surface zero. See Ground zero.

and underground bursts. Implosion Weapon: A device in which a quanGun-Type Weapon: A device in which two or tity of fissionable material, less than a critical

more pieces of fissionable material, each less mass, has its volume suddenly decreased by

than a c:itical mass, are brought together very compression, so that it becomes supercritical and

rapidly so as to form a supercritical mass which an explosion can take place. The compression is

can explode as the result of a rapidly expanding achieved by means of a spherical arrangement of

fission chain. See Critical mavs, Supercritical. specially fabricated shapes Gf ordinary high ex- p~osive which produce an inwardly-directed ira- ,( Hall-Life: The time required for the activity of a plosive which pde ansinarly-iete d imgiven radioactive species to decrease to half of its the center of the sphere. See Critical mass.t

initial value due to radioactive decay. The half- Supercritical. o s 

. rs

life is a characteristic property of each radioac- ueil

tive species and is independent of its amount or Impulse (Per Unit Ares): The product of the

condition. The effective half-life of a given iso- overpressure (or dynamic pressure) from the

tope is the time in which the quantity in the body blast wave of an explosion and the time during (or an organ) will decrease to haif as a result of which it act,; at a given poink. More specifically,

both radioactive decay and biological climina- it is the integral, with respect to tim,. of overtion. See Biological half-life, pressure (or dynamic pressure), the integration

C

SiA-V
GLOSSARY 635

being between the time of arrival of the blast separation occurs. In the sense used in this book,

wave and that at which the overpressure (or ionization refers especially to the removal of an

dynamic pressure) ret urns to zero at the given electron (negative charge) from the atom cr

-'oint. molecule, either directly or indirectly, leaving a

Induced Radioactivity: Radioactivity produced positively charged ion. The separated electron

in certain materials as a result of nuclear reac- and ion are referred to as an ion pair. Sec

tions, particularly the capture of neutrons, which Ionizing radiation.

are accomplinied by the formation of unstable IoniTing Radiation: Electromagnetic radiation

(radioactive) nucle. In a nuclear explosion, (gamma rays o" X rays) or particulate radiation

neutrons can induce radioactivity in the weapon (alpha particles, beta particles. neutrons, etc.)

materials, as well as in the surroundings (e.g., by capable of producing ions, i.e., electrically

interaction with nitrogen in the air and with charged particles, directly or indirectly, in its

sodium, manganese, aluminum, and silicon in passage through matter. See Nuclear radiation,

soil and sea water). Ionosphere: The region of the atmosphere, exInfrared: Electromagnetic radiations of wave- tending from roughly 40 to 250 miles altitude, in

length between the longest visible red (7,000 which there is appreciable ionization. The presAngstroms or 7 x 10-4 millimeter) and about I ence of charged particles in this region promnillimetei. See Electromagnetic radiation. foundly affects the propagation of long-waveInitial Nuclear Radiation: Nuclear radiation length electromagnetic radiations (radio and

(essentially neutrons and gamma rays) emitted radar waves).

from the fireball and the cloud column during the Ion Pair: See Ionization. first minute after a nuclear (or atomic) explosion, Isomer (or Isomeric Nuclidei): See Nuclide.

The time limit of one minute is set, somewhat

arbitrarily, as that required for the source of part Isotopes: Forms of the same el-rrent having

of the radiations (fission products, etc., in the identical chemical properties b-it differing in their

radioactive cloud) to attain such a height that atomic masses (due to different numbers of neuonly insignificant amounts of radiation reach the ,rons in thi ir respective nuclei) and in their

earth's surface. See Residual nuclear radiation, nuclcar properties (e.g., radioactivity, fission,

etc.). For example, hydrogen has three isotopes, Integrated Neutron Flux: See Fluence. with masses of I (hydrogen), 2 (deuterim), and 3

Intensity: The amount or energy of any radia- (tritium) units, respectively. The first two of

tion incident upon (or flowing through) unit area, these are stable (nonradioactive), but the third

p.rpendicular to the radiation beam, in unit time. (tritium) is a radioactive isotope, Both of the

The intensity of thermal radiation is generally common isotopes of uranium, with masses of

expressed in calories per square centimeter per 235 and 238 units- respectively, are radioactive,

second falling on a given surface at any specified emitting alpha particles, but their half-lives ate

instant, As applied to nuclear radiation. the term differcnt. Furthermc:e, uranium-235 is fissionintensity is sometimes used, rather loosely, to able by neutrons of all energies, out uranium-238

express the exposure (or dose) rate at a given will undergo fission only with neutrons of high

location, energy, See Nucleus.

Internal Radiation: Nuclear radiation (alpha Kilo-Electron Volt (or KEV): Ar. amount of

and beta particles and gamma radiation) resulting energy equal to 1,000 electron volts. See Elecfrom radioactive substances in the body. Impor- Iron Volt,

tant sources are iodine-131 in the thyroid gland, Kiloton Energy: Defined strictly as 1012 calories

and strontium-90 and plutonium-239 in bone. (or 4.2x 10", ergs). This is approximately the

Inverse Square Law" The law which states that amount of energy that would be released by the

when radiption (thermal or nuclear) from a point explosion of I kiloton (I .000 tons) of TNT. See

source is emitted uniformly in all directions, the TNT equivalent.

amount received per unit at.ea at any given dis- Linear Attenuation Ccefficient: See Attenuatance from the source, assuming no absorption. tion.

is inversely proportional to the square of that I

distance. Linear Energy Absorption Coeffirient: See

Ionization: The separation of a normally dec- Absorption.

trically neutral atom or molecule into electrically Lip Height: The height above the original surcharged components. The term is also employed face to which earth is piled around the crater

to describe the degree or extent to which this formed by an explosion. See Crater.

a
636 GLOSSARY

L~oading: The force on an object or structure or Milliroentgen: A one-thousandth r irt of a

element of a structure. The loading due to blast is roentgen. See Roentgen.

equal to the net pressure in excess of the ambient Millisecond: A one-thousandth part of a second. valtie multiplied by the area of the loaded object,

etc. See Diffraction, Drag loading. Mirror Point: A poiat at which a charged parMuch Front; See Mach stem. ticle, moving Oin a spiral path) along the lines of

a magnetic field, is reflected 6ack as it enters a

Mach Region-, The iegion on the surface at stroiiger magnetic field region. The actual loca.

which !he Mach stem has formed as the result of tion of the mirror point depends on the direction

a pa .cular exrlosion in the air. and energy of motion of the chargef! particle and

NMach Stem: The shock front formed by the the fatio of the magnetic field strengths. As a

merging of the incident and reflected shock fronts res .uit, only those pia'iicles satisfying the refrom an explosion. The term is generally used quiremencrts of the e!.,satng situation'are reflected.

with reference to a blast wave, propagated in the Monitoring: The procedure or operation of 10oair, reflected at the surface of the earth. The cating and measuc~ng radioactive contamination

Mach stem is nearly perpendicular to the reflect- hy means of survey instruments which can detect

ing surface and presents a slightly convex (for- and measure (as dose rates) ionizing radiations.

ward) front. The Mach stem is also called the The individua1l performing the operation is called

Mach front, See Shock front, Shock Hsave, a monitor.

Mass Attenuation Cco-fficient: See Attenua- Negati-ie Phait: See Shock wave.

tioni. Neutron: A iteutral particle (ie .with no elecMass Energy Absorption Coefficient: See Ab- trical charge) of approximately unit mass, p:.lssorptionl. ent ~n ail atomic nuclvi ce'cept those of ordinary

Mass Number: See Nucleus. (light) hydrogen. Ne'.ttrons are required tri initiate

the fission process, and large numbers of neuMeaid Free Path: The average path distance i trons are produc, I Lsy both fiss-oz' an-i fttsion

particle (neutron or photon) travels bef,'.-re un- reactions in nuciecir (or atomic) Cxplosions. iertAing a specified rte-action (,.lh a nucleus or Neto'Fu:SeHx

n)i i'c~ miatter. Nurn~a:SeFu~

0aule 'u m~llion cuis See Cur Nominal /Alowic Bomb: A :erm, now beccim- *~aure: iL * uris. ure. ing obsol%;`., esed to descriLe ai, atomic weapon

Megaton. F'oergy: Defiiied staictly as 1013 calo- with an eneýgy rel.aase equivalent to 20 kilotons

ries (or 4,2x X 022 eras). This is approximately the (i 7!-. 20,100 tons) of TNT. This is very approx-

;!mount of eneegy titat wvuld be. released by the imte~y the energy yield of the bombs exp~oded

expiosion of I01,0W kilotons (1,000.000 tons) of ovet Japan and in thtu Bikini test of 1946.

T'NT. See TNT equivalent. Nuciear Cloud: See Radioactive cloud.

MIEV 'or Million Electron Volt): A unit of NcetrRdai:Prtute ndecto

eýnergy commonly used ;n nuclear physics. It is mag-.ietic radiation emitted 'rom atomic ituclei An

equivalent to 1 .6X 10 1,erg. Approximately 200 various nuclear processes. The impot:ant nuclear

MeV (of energy are produced for every niucleus radiatvoris, from thp weapons standpoint, ýare thut undergoes fission. See Etctron volt. alpha and beta particles, gamma rays, and *ieu.

Micructirie: A one-ai~lionth part of a curie. See trons, All nuclear radiations are ionizing radiaCurio. tions, but the reverse is not true; X ray.. tor

example, are included among i ,nizing vadi- Micromneter: Sec Micron. tions, but they are aot nutclear ýadiations since

Micron: A one-millionth part of k, meter (i.e., they do not originatc from atomaic nu-tei. See

10 -6 m~eter or 10 A centimetee); it is roughly four Ionizing radiation, X-ray.-%

or, -ivoindred-thousanjths (4< 10 .9 of an inch. Nuclear (or Atomtic) f~~ats: Test carried cui- to

Microkttcovsd: A one-milionth part of a secoud, supply information required for the detsign and

Millon Vlt: Eectrn ee. eV.improvement of nuz'lear (or atomirc) weapons and Millon Vlt:See Eecton eVto study the phenomena and eftents associsted

Millirad: A ote-thousandth part of a rad, See with nuelIeak- (or atomi-) explosions. Many Lf the

Rail, data presented in th!3 booic are based n~n meaMllfirem: A one-thousandth part -1. a rem See surements and observations made i~t such tests.

Rem Nuclear Weapnot (ot- Blkmb): NX gencral namue
GLOSSARY 637

given to any weapon in which the explosion exce~s of 1 .02 McV in passing ne!ar the nucleus

results front the energy released by reactions of an atom is converted into a positive electron

involving atomic nuclei, either fission or fusior and a negative e.lectron. As a result, the photon

or both. Thus, the A- (or atom-cl 'bomb and the ceases to exist. See Photon.

H- (r hdroen)bom ar boh ncler wap- Photoelectric Effect: The process whereby a

ons. It would be equally tiuc to call them atomic gmary(rXry htn iheeg wearions, since it is Jhe energy of atomic nuclei gammwatreayt(r X-ray) photon idn wthe energy

thatis i nmc ivolvd cas. Hweve, ithas of an electron in ar. atom., transfers all its energy become niore-or-less customary, although it is to the electron which is consequently removed

not strictly accurate, to refer to weapons in which from the atom. Since it has lost al! its .mnergy, the

all the energy results from fission as A-bombs or photon ceases to exist. See Photon.

atomic bombs. In order to make a distinction,

those weapons in which part, at least, of the Photon: A linit or "pa~rticle" o' electromagnetic

energy results from thermonuclear (Wision) reac- radiation, carrying a quantum of energy which is

tions of the isotopes of hydrogen have been characteristic of tile riart~cular radiation. If v is

called H-bombs or hydrogen bombs. the frequency ori the radiation in cycIts pzr --ecNucleus (or Atomic Nucleus): The small, ,cen- ond and X is t'.4e wavelength in cmtimeters, the

tral, positively charged region of an atom which energy quantum of the 13hotnti ini ergs is )w or

carries essentially all the mass. Except for the hdx\, where h is Planck's constant, 6.62'x 10-2

nucleus of ordinary (light) hydrogen, which is a e rg-sczond and k- is the velocity of light

single proton, all atomic nuclei contain both (3.00 tOW cen-rtimeters pe! seccL~i). .. ot gamma

protons and neutrons. The number of protons rays, thz phot-' -nergy is usually expressed in

determines the total positive cI'arge, or atomic milo .- ctn l ( V)utsie,

number, this is the same for all the atomnic nuclei 12xO1/ hr si etmtrto

on a given chemical element. The. total number of I 24x !rG-2'X if X is in an~gstroms).

neutrons arnd pro~ons, called the mass number, is PIsitic Range: The strcss ran,..e in which a rnaclosely related to the mass (or w~ight, of tite teri,31 will not fail whey. subjected to flw- action of

atom. Thý- nuclei of !so; -pes of a given element a force, but wifi nut reccover completely, so that &

contain tlie same number of protons, but differer.i pet mane- d.Aorniation results when the force is

numbers of neutrons. n.hey ihus have thle same removed. Piastie tjefvrsration refers to dimenatomic number, and so are the same element, but sional chAanges occurring within the plastic range.

they have ditierent mass numbers (and ma~ioes). Sec Elastic range.

The nuclear properties (e.g., raJioactivity, qs Plastic Zone. The region beyond the rupture

sion, neutron capture, etc.) of an isotope of a zore associated with crater formation in which

given element u-e determin,'.d by both the numnbe-r there is no visible rupture but in which the

of neutrons and the nunther of protons. See ground is permanently deformed and compressed

Atom, Elemnent- !.2oiepe, Neurro'% Proton, to a higher density. See Crater. Binstic Zone,

* NMcllde: An atonsic species distinguiishud by the Ri2ture 7one.

comhposition Uf its HuclLUS (i.C., by the number of Plm:SeCvrn

protow! an~d the nunmber 9f r.-L:ions) In ixomeric

nuclides the itucld have the same comp)stition Positive Phasp: See Shock, wave.

bu( are in different energy stat~s. Sec Atom, PrecursoT-: An air pressure Yjave wh- J ov-;

Ne'uron, Nucleus, Pmrono. Oiead of the main 1-as: wave for ýomr lice

Cverpressureý: The transie%-i pressure, vt~uaily as v. %esult of a nucler ~o( atomic) expo iof

expre~sed in poonds vv sq'iare inch, eAetd~ng appropiiate yield and low butst heiight ,en a

the arrbient pres~zt-e, nianifcsicd in tie shozk (o- beat-absoirvir~g (rur dulty) s"r fact. Tb.- pressuie

blast) wa-ve frum an explosion. The v-iriatioa of at the precursor frant increa,;ýs m ow~ gradua'l,,

the overprei~sure with tin~tierdpnds on the energy tttntý in a true 'or ideal) -hoc., wave, so zhat thc.

yield of the explusiun, ine distance from the bchav~or ini the precursoi rcgiort is s&0d to be

point of bu~sk, -3d thle wt:diurn in vhich the nonndeal. See I~ayt wave, Shork front. Shock

weapon is detonated. The peak overpressl'e is (PC

the maximnum vahic of the ovarpmesstjre a' j Proton, A parlicie of mass 'approximately)

aivc:, location and is generally experienced at the unity carryinp a unit lyobitive charge; it is identiin.-tant the shock (or blast) w,-,,- rea~ches that cal physically with the nucln.;s of the ordinary

;ocation. See S~ock wave. (ligbt) hydrogcn atum. All atomnic nuclei cuntain

Pair Production, The process whereby a protunh. See Nu~-leus..

gamma-may (or X-raiy) photon, with energy in Quantum: See Photon.
638 GLOSSARY

Rad' A unit of absorbed dose of radiation; it which the shock wave is traveling (e.g.. air), the

represunts 'he absorption of 100 ergs of nuclear reflected pressure is positive (compression). If

(or i-nizing) radiation per gram of absorbing the reverse is true (eg., when a shock wave in

material, such as bedy tissue. the ground or water strikes the air surface) the

Radiant Enposure: The total amount of thermal reflected p.,;sure is negative (rarefaction or ten-

,'adiation encrgy reccived per unit 3rea of ex- sion).

posed surface; it is usually expressed in calries Reflection Factor: The ratio of the total (reper square eentimeter. flected) pressure to the incident pressure when a

Radiation: See Ionizing Radiation. Nuclear ra- shock (or blast) wave traveling in one medium

diation, Thermal radiation. strikes another.

Rrdiation Injury (or Syndrome): See Svn- Rem: A unit of biological Oose of radiation; the

name is derived from the initial letters of the term drome (Raaiaxion). "roentgen equivalent man (or mammal)." The

Radiosactive (or Nuclear) Cloud. kn AMI- number of reins of radiation is equal to the

inclusive term for the cloud of hot gases, smoke, number of rads absorbed multiplied by the RBE

dust, and other particukte matter from the of the given radiation (for a specified effect). The

weapon itself and from the environment, which rcm is also th,- unit of dose equivalent, which is

is carried aloft ir conjunction with the riring equal io the product of the number of rads abfireball produced by the detonation of a nucleau sorbo.1 and the -quality factor" of the radiation.

(or atomic) weapon. See Dose. Dose equivalent, Rad, RBE.

Radioactivity: The spontaneous emission cf ra- Residual Nuclear Radiation: Nuclear radiadiatior,, generally alpha or beta particles, often tion, chiefly beta particles and gamma rays,

accompanied by gamma rays, from the nuclei of which peisists for some time following a nuclear

an (unstable) isotope. As a result of this emission (or atomic) explosion. The radiation is emitted

the radiouctive isotope is converted (or decays) mainly by the fission products and other bomb

into the isotepe of a different (daughter) element residues in the fallout, anJ to some extent by

which may (or may not) also be radioactive. earth and water constitutents, and other materiUltimately, as a result of one or more stages of als. in which radioactivity has been induced by

radici~ct!ve decay, a stable (nonradioactive) end the capture of neutrons. See Fallout, Induced

product is formed. See lwc.ope. radi&rtiviy, Initial nuclear radiation.

Radio Blackout; The complete disruption of Roentgem A u.dit of exposure to gamma (or X)

radio (or radar) signals over iarge areas caused by radiation. It is defined precisely as the quantity of

the ionization accompanying a high-alt1 rade nu- gamma (or X) rays that will produce electrons (in

clear explosion, especially above about 40 mile.. .on pairs) with i total charge of 2.58 X10 4 couRrZioisotope: A radioactive isotope. See lso- lomb in I kilogrami of dry air. An exposure ,f I

tope, Radioactivity. roentgen results in the deposition of about 94

ergs of energy in t gram of soft body tissue.

Rad~onucllde: A radioactive nuc!ide (or radio- Hnce, an exposure of i roentgen is approxia..tive atomic species). See Nuclide. ,'naely equitvalent to an absorbed dose of I rad in

Rainout: The removal of radioactive partichs soft tissue. S:ee Dose. Rad.

from a nuclear cloud by p-ecipitation when thiS Rupttire Zone: The regri imnmedialely adja-"

cleud is within a rain cloud. See Washout. ceiit to the crater boundary in which the stresses

RBE (or Relative Biological Effective- produccd by the explosion have exceeded the

ness): The ratio of the number of rads of ultimate strength of the ground medium. It is

gamma (or X) radiation of a ,*eftain energy which characterized by the appearance of numerous

will produce a specified biech.glcal effect to the radizl (and other) cricks of various sizes. See

number of rads of arother radiation required to Crater, Plastic zore.

produce the same effect is ;he RRE of !he latter Sealing Law: A mathematical relationship

radiation. "which permits the effects of a nuclear (or atoniic)

P.eflcte P,'-,ssure: The total pressurc which ' explosion of given energy yield to be determined

zerilts instantaneously at the surface when a as m function of distance from the explosion (or

Flick ,e,.kts (Or blast)t blast) w -wave l av traveling the iurfoce in ont: mhedium medium from ground zero), provided, the corresponding trav(.ig ,effect is known as a function of distance for a strikes ano.iher medium (e.g, at the instant when reference explosion (e.g., of •.kiitoir energy

the front oi a blast wave in aIr strikes the ground reference e lo s ing(e , ag of be ro e o aw.

or a structare). If tte medium struck (e.g., the yield). See Blast scaling law, Cube root law.

ground or a structure) is more dense than that in Scattering: The diversion of radiation, includSIt
GLOSSARY 639

ing radio, radar, thermal, and nuclear, from its na. lic pressure is somewhat longer than for

orginal path as a result of interactions (or colli- ovLipressure, due to the momentum of the movsions) with alims, molecules, or larger particles ing a, be iind the shock front. The duration of

in the atmosphere or other medium between the the pos,.,!vc phase increases and the maximum

source of the radiations (e.g., a nuclear explo- (peak) pressure deC.reases with increasing dission) and a point at some distance away. As a tance from an explosion of given energy yield. In

result of scattering, radiations (especially gamma the second phase, the negative (suction. rarefacrays and neutrons) will be received at such a tion, or tension) phase, the pressure falls below

point from many directions instead of only from ambient and then returns to the ambient value.

the direction of the source. The duration of the negative phase may be sevScavenging: The selective removal of material eral times the duration of the positive phase.

from the radioactive cloud from a nuclear explo- Deviations from the ambient pressure during the

sion by inert substances, such as earth or water, negative phase are never large and they decrease

introduced into the fireball. The term is als' with increasing distance from the explosion. See

applied to the process of removal of fallout Dynamic pressure. Overpressure.

particles from the atmosphere by precipitation. Skyshine: Radiation, particularly gamma rays

See Rainout, Snowout, Washout. from a nuclear explosion, reaching a target from

Shear (Wind): Unless the term "velocity many directions as a result of scattering by the

shear" is used, wind shear refers to differences in oxygen and nitrogen in the intervening atmos.-

direction (directional shear) of the wind at dif- phere.

ferent altitudes. Slant Range: The distance from a given locaShear W tion, usually on the earth's surface, to the point at all - A w all (or partition) designed to wh c t e ex l s o o cu r d

take a load in the direction of the plane of the

wall, as distinct from lateral loads perpendicular Slick: The trace of an advancing shock wave

to thc wall. Shear walls may be designed to take seen on the surface of reasonably calm water as a

lateral loads as well. See Bearing wall, circle of rapidly increasing size appaiently darker

Shielding: Any material or obstruction which than the surrounding water. It is observed, in

absorbs (or attentuates) radiation and thus tends ?artvcular, following an underwater explosion.

to protect personnel or materials from the effects See Crack,

of a nuclear (or atomic) explosion. A moderately Snowout: The removal of radioactive particles

thick layer of any opaque material will provide from a nuclear cloud by precipitation when this

satisfactory shielding from thermal radiation, but cloud is within a snow cloud. See Rainot.t.

a considerable thickness of material of high den- Spray Dome: See Dome.

sity may be needed for nuclear radiation shielding. Electrically continuous housing for a facil- Stopping Altitude: The altitude in the vicinity

ity, area, or component, attenuates impinging of which; a specified ionizing radiation coming

electric uand magnetic fields. from above (e.g., from a high-altitude nuclear

Shock Front (or Pressure Front): The fairly explosion) deposits most of its energy by absharp boundary between the pressure disturbance sorption in the atmospheie. The stopping altitude

created by an explosion (in air, water, or earth) varies with the nature of the ionizing radiation,

. .anu 'the'irfilbient "atmosphdre, water, 'or earth, Stratosplierk:" A relatively' stable layer of tht

I 'spectively. It constitutes the front of the shock atmosphere between the tropopause and a height

mSor blast) wave. See Shock wave, of about 30 miles in which temperature changes

Shock Wave: A continuously propagated pres- very little (in polar and tzmperate zones) or

sure pulse (or wave) in the surrounding medium increases (in the tropics) with increasing altitude.

which may be air, water, or earth, initiated by the la the stratosphere clouds of water never form

expansion of the hot gases produced in an ex- and there is practically no convection. See Troplosion. A shock wave in air is generally referred popause, Troposphere.

to as a blast wave, because it resembles and is Subsurface Burst: See Una. ound burst, accompanied by strong, but transient, winds. Underwater bursi.

The duration of a shock (or blast) wave is distinguisi'ed by two phases. First there is the positive Supercritical: A term used to describe ihe state

(compression) phase during which the pressure of a given fission system when the quantity of

rises very sharply to a value that is higher than fissionable material is greater than the critical

ambient and then decreases rapidly to the am- mass under the existing conditions. A highly

bient pressure. The positive phase for the dy- supercritical system is essentiaol for the producX, ';4
640 GLOSSARY

tien of energy at a very rapid rate so that an In an air burst, the thermal partition (i.e., the

explosion may occur. See Critical mass. fraction of the total explosion energy emitted as

Surface Burst: The explosion of a nuclear (or thermal radiation) ranges from abcut 0,35 to

atomic) weapon at the surface of the land or 0.45. The trend is toward the smaller fraction for

water at a height above the surface less than the low yields or low burst heights and toward the

radius of the fireball at maximum luminosity (in highe, fraction at high yields or high bursts.

the second thermal pulse). An explosion in which Above 100.000 feet burst height, the fraction

the weapon is detonated actuJly on the surface increases from about 0.45 to 0.6, and then de-

(or within 5 W,' feet, whcrc W is the explosion creases to about 0.25 at burst altitudes of

yield in kilotons, above or below the surface) is 160,000 to 260,000 feet. At still greater burst

called a contact surface burst or a true surface heights, the fraction decreases rapidly with inburst. See Air burst. creasing altitude.

Surface Zero: See Ground zero. Thermal Radiation: Electromagnetic radiation

emitted (in two pulses from an air burst) from the

Surge (or Surge Phenomena): See Base surge. fireball as a conscq,,ence of its very high ternSurvey Meter: A porteble instrument, such as a perature; it consists cssen;z!ly of ultraviolet,

Geiger counter or ionization chamber, used to visible, and infrared radiations. In the early

detect nuclear radiation and to measure the dose stages (first pulse of an air burst), when the

rate. See Monitoring. temperature of the fireball is extremely high, the

ultraviolet radiation predominates; in the second

Syndrome, Radiation: The complex of symp- pulse, the temperatures are lower and most of the

toms characterizing the disease known as radia- thermal radiation lies in the visible and infrared

tion injury, resulting from excessive exposure of regions of the spectrum. For high-altitude bursts

the whole (or a large part) of the body to ionizing (above 100,000 feet), the thermal radiation is

radiation. The earliest of these symptoms are emitted as a single pulse, which is of short

nausea, vomiting, and diarrhea, which may be duration below about 270,W00 feet but increases

followed by loss of hair (epilation), hemorrhage, at greater burst heights.

inflammation of 'he mouth and throat, and general loss of energy. In severe cases, where the Thermal X-Rays: The electromagnetic radiaradiation exposure has been reletively large, tion, mainly in the soft (low-eneigy) X-ray redeath may occur within 2 to 4 weeks. Those who gion, emitted by the extremely hot weapon resisurvive 6 weeks after the receipt of a single dose due in virtue of its extremely high temperature; it

of radiation may generally be expected to re- is also referred to as the primary thermal radiacover. tion. It is the absorption of this radiation by the

ambient medium, accompanied by an increase in

Tenth-Value Thickness: The thickness of a temperature, which results in the formation of the

given material which will decrease the intensity fireball (or other heated region) which then emits

(or dose) of gamma radiation to one-tenth of the thermal radiation. See Weapon residue, X-ray

amount incident upon it. Two tenth-value thick- pancake. X-rays.

nesses will reduce the dose received by a factor

of lOX 10, i.e., 100, and so on. The tenth-value Thermonuclear: An adjective referring to the

thickness of a given material depends on the process (or processes) in which very high temgamma-ray energy, but for radiation of a partic- peatures are used to bring about the fusion of

ular energy it is roughly inversely-proplttionai to light nuclei, ssuch as-those of the hydrogen isothe dens;ty of the material. topes (deuterium and tritium;, with the accompanying liberation of energy. A thermonuclear

Tests: See Nuclear tests. bomb is a weapon in which part of the explosion

Thermal Energy: The energy emitted from the energy results from thermonuclear fusion reacfireball (or other heated region) as thermal radia- tions. The high temperatures required are obtion The total amount of thermal energy re- tained by means of a fission explosion. See

ceived per unit area at a specified distance from a Fusion.

nuclear (or atomic) explosion is generally ex- TNT Equivalent: A measure of the energy repressed in terms of calories per square centime- leased in the detonation of a nuclear (or atomic)

ter. See Radiant exposure, Thermal radiation, weapon, or in the explosion of a given quantity

Transmittance, X-ray pancake. of fissionable material, e:.pressed in terms of the

Thermal Energy Yicld (or Thermal mass of TNT which would release the same

Yield): The part of the total energy yield of the amount of energy when exploded. The TNT

nuclear (or atomic) explosion which is received equivalent is usually stated in kilotons or megaas thermal energy usually within a minute or less. tons. The basis of the TNT equivalence is that the
GILOSSARY 64!

explosion of I ton of TNT is assumed to release clarity of the atmosphere ranging from 170 miles

l(P calories of energy. See Kiloton, Megaton. (280 kilometers) for an exceptionally clear atYield. mosphere to 0.6 mile ( 1.0 kilometer) or less for

Transmittance (Atmospheric): The fraction den.,e haze or fog. The visibility on an average

(or percentage) of the thermal energy received at clear day is taken to be 12 miles (19 kilometers).

a given location after pass.ge through the at- Washout: The removal of radioactive particles

mosphere relative to that wh; '. would have been from a nuclear cloud by precipitation when this

received at the same location if no atmosphere cloud is below a rain (or snow) cloud. See'

were present. Rainout. Snowout.

Triple Point: The intersection of the incident. Weapon, Atomic (or Ndclear): See Nuclear

reflected, and merged (or Mach) shock fronts weapOl.

accompanying an air burst. The height of the Weapon Debris: The highly radioactive matetriple point above the surface (i.e., the height of rial, consisting of fission products, various prodthe Mach stem) increases with increasing dis- ucts of neutron capture, and uranium and plutotance from a given explosion. See Mach stem. nium that have escaped fission, remaining after

Tritium: A radioac.ive isotope (f hydrogen, the explosion.

having a mass of 3 units. it is produced in r:uclear Weapon Residue: The extremely hot .

reactors by the action of neutrons on lithium pressed gaseous residues formed at the iauckei, the explosion of a nuclear weapon. Tt

Tropopause: The imaginary boundary layer di- aturc is several tens of million degree..

viding the stratosphere from the lower part of the and the pressure is many millioa.i t.

atmosphere, the troposphere. The tropopause pheres,

normally occurs at an altitude of about 25.00W to

45.000 feet in polar and temperate zones, and at

55,000 feet in the tropics. See Stratosphere. cloud.

Tropospnere. Worldwide Fallout: See Fallout.

Troposphere: The region of the atmosphere, X-Ray Pancake: A layer of air, about 30,000

immediately above the earth's surface and up to feet thick at a mean altitude of roughly 270,000

the trpopause, in which the temperature falls feet, which becomes incandescent by absorption

fairly regularly with increasing altitude, clouds of the thermal X rays from explosions above

form, convection is active, and mixing is con- 270 000 feet altitude. The heated air emits thertinuous and more or less complete. mal radiation (of longer wavelengths) in a single

S True Surface Buirst: See Surface Burst. pulse of several seconds duration. See Thermal

TBrradiation. Thermal X rays.

S 2W Concept: The concept that the explosion of

a weapon of energy yield W on the earth's X Rays: Electromagnetic radiations of high en- ergy having wavelengths shorter than those in the surface produces (as a result of reflection) blast ultraviolet region, i.e., less than 10-6 cm or 100

phenomena identical to those produced by a Angstroms. Materials at very high temperatures

weapon of twice air romany the i~e, yield aay (i.e., eflctig 2 W) srfae). burst in free (millions of degrees) emit such radiations; they

air (i.e., away from any reflecting surface), are then called thermal X rays. As generally

. Ultraviolet: Electromagnetic radiation of wave produced by X-ray machines, they are bremslength between the shortest visible violet (about straLlung resulting from the interaction of elec3,850 Angstroms) and soft X-rays (about 100 trons of I kto-electron volt or more energy with

Angstroms). a metallic target. See Bremsstrahlung, ElectroUnderground Burst: The explosion of a nu- magnetic radiaion, Thermal X-rays.

clear (or atomic) weapon with its cente: more

than 5 W .1 feet, where Wis the explosior yield in Yield (or Energy Yield): The total effective kilotons, beneath the surface of the ground. See energy released in a rnuclear (or atomic) explo- ilsotonsnedunderground burst, sion. It is usually expressed in terms of the also Contained uequivalent tonnage of TNT required to produce Underwater Burst: The explosion of a nuclear the same energy release in an explosion. The

(or atomic) weapon with its center beneath the total energy yield is manifested as nuclear radiasurface of the water. tion, thermal radiation, and shock (and blast)

Visibility Range (or Visibility): The horizontal energy, the actual distribution being dependent

distance (in kilometers or miles) at which a large upon the medium in whlicl, the explosion occurs

dark object can just be seen against the horizon (primarily) and also upon the type of weapon and

sky in daylight. The visibility is related to the the time after detonation. See TNT equivalent.

... ....... .. . . . ... , ... . , .... -. O ....
642 GUIDE TO SI UNITS

Guide to S1 Units

The International System of Units (SI) has been adopted in the publications of

several scientific an6 technical societies in the United States and other countries. It

is expected that in due course that these units will come into geieral use. The SI

units and conversion factors applicable to this book are given below. For further

information, see "The international System of Units (SI)," National Bureau of

Standards Special Publication 330, U.S. Government Printing Office, Washington,

D.C. 20402.

Base Units

Quanity Si Unit Symbol

Length meter m

Mass kilogram kg

Time second s

Electric current ampere A

Temrerature* kelvin K

*(Temperatures may also be expressed in °C)

Derived Units

Quantity Unit Symbol Formula

Force newton N kg.m/s2

Pressure pascal Pa N/mi2

Energy, heat. etc. joule J N.m

Power watt W J/s

Frequency hertz Hz I (cycle)/s

Radioactivity becqueicl Bq I (decay)/s

Absorbed dose gray Gy J/kg

Conversion Factors

To convert from: to: multiply by:

Length, Area, Volume

inch meter (m) 2.540 X i0-2 -

foot meter (M) 0.3048

yard meter (m) 0.9144

mile kilometer (kin) 1.609 . centimeter meter (m) 10 2

angstroml meter (m) 0 ,0

square inch meter2 (m2) 6.452 X 10-4

square foot meter2 9.290 x 10

square mile kilometer' (km2) 2.590

cubic foot meter' (min) 2.832 x 10 2

644

, .I
GUIDE TO SI UNITS 643

Mass

pound kilogram 'kg) 0.4536

ounce kilogram (kg) 2.835 x 10 2

Energy

calorie joule (M) 4.187

erg joule (J) 1.00 x 10

MeV joule (J) '.602 x 10 1"

ton (TNT equivalent) joule (J) 4.2 x l09

Miscellaneous

density (lb/ft•) kg/m- 1.602 x 10

pressure (psi) pascal (Pa) 6.895 x 10'

radiant -.xposure (cal/cm2) J/m2 4.187 x 104

speed (ft/sec) m/s 0.3048

speed (miles/hour) m/s 0.4470

dose (rads) gray (Gy) 1.00 x 10-2

dose rate (fads/he.ar) Gy/s 2.778 x 10 -6

curie becquerel (Bq) 3.700 x 10 10

The only multiples or submultiples of SI to which appropriate prefixes may be

applied are those represented by factors of lOn or 10-, where n is divisible by 3.

Thus, kilometer (103m or I km), millimeter (10- 3

m or I mm), and micrometer

(10- 6

m or I jam). The centimeter and gram are not used in the SI system, but they

are included in the metric system proposed for adoption in the United States.

J

I!

j'i

2)...?
INDEX

Aftershocks, 2.105, 6.24-6.27 Ato'nic Bomb Casuaity Commission, 12.142

Afterwinds, 2.09, 2.18 Attenuation, radiation, see Alpha particles; Beta

Air blast, see Blast particles; Gamma rays, Neutrons; Transmission

Air burst, 1.31-1.35, 1.78, 2.03-2.17. 2.32- factors

2.51, see also High-altitude burst Aurora, artificial, 2.62, 2.142-2.145

afterwinds, 2.09, 2.18

blast wave, 2.32-2.37, see also Blast Bedl of fire, .ee Firebal!

Jamage, ;ee Damage; Structures Base surge, see Surface burst; Underground burst;

definition, 1.31 Under water burm

EMP, 11.66, 11.67 Beta burns, 12. i55-12. i62

energy distribution, 1.24-1.27 Beta particles (or radiation), [29, 1.43, 1.61-

fireball, 2.03-2.05, 2.110-2.129 1.66, 2.42, 8.01, 9.11

ground shock, 't.51, 3.52 attenuation, 2.42, 9. 115, 9.116

injuries, see Injuries and geo.nagnelic field. see Geomagnetic field

nuclear radiation, 2.41-2.45, see also Nuclea: hazard, extemnal, 12. 55-12. 12

radiation internal, 12.163-.12.172

radioactive cloud, see Cloud RBE, 1:.97

contamination, 9.48, 9.49 sources, 1.61-1.63

radio and radar effects, see Radio and radar stopping altitude, lu.i9

thermal radiation, 2.38-2.40, see also Thermal M.2ta patch, 2. 1-t*

radiation Biological effectiveness, remtive (RBY'), 12.95

Aircraft, damage, 5.94, 5.95, 5.151-5.154 Biological efiec'i of niclear tacliations, see NuAlpha particles (or radiation), 1.65, 2.41, 8.01, clear radiations

8,03, 9.40-9.42, 9.114 Biological half-lifa, 12. !70

attenuation, 2.42, 9.114 Blackout radio, see !2adio and radar

contamination, 9.42 Blast (and Bias: wave), 1.01, 1.25, 2.32-2.37,

hazard, 9.114, 12.97, 12.165, 12.173 3.01-3.85, 6,02, 6.80, 6.81, see also Dynamic

RBE, 12.97 pressure: Overpressure; Shock wave

sources, 2.41, 8.01, 9.40-9.43 altitude effect, 3.44-3.46. 3.64-3.68

Animals, nuclear explosion effects, 12.240- artiva.' time, 3.C9, 3.14, 3.63, 3.77

i2.254 atmospheric effects on, 3.39-3 43

Arch, loading, 4.62-4.66 bending of, 3.42, 3.43

Arching effect, soil, 6.96-6.99 characteristics, 3.01-3.20

Area integral, fallout, 9.160 damage, see Dfamage

ARGUS effect, 2.146, 2.147 and height of burst, 3.30-3.34

Atmosphere, density vs. altitude, 3.66, !0. 1231, development, 3.01-3.20

10.124 d.ffr3cion, 4.03, see also I co.ng

ionization, 10.09-10.12, see also Ionosphere dueation, 3.14, 3. 1, 3.63, 3.76

pressure vs. altitude. 3.66 front, 1.01, 2.32, 3.62, 3.03

properties, 3.66 and -round si,ock, 3.51, 3.52

sca!e height, 10.123 impulse, 3.49

structure, 9.126-9.129 injuries, see l'tL.ries

visibility, 7.12 interaction v. ith structures, 4.01-4.67

Atom, i.07 loading, see Loading

Atomic bomb (or weapon), I. i1. see also Nuclear Mach effect, see Mach effect

weapons and meteorological conditions, 3.39-3.43

cloud, see Cloud negative phase, 3.04, 3.05

explosien, see Nuclear explosion nonideal, 3.47, 4.67

number, 1.09 positive phase, 3.05

structrire, i.06--.09 precursor, 3.49, 3.79-3.85, 4.67

644

!F F
INDEX 645

pressure, see Dynamic pressure; Overpressure scavenging, 9.67-9.74

properties, 3.53-3.59 stabilized, 2.15, 9.84, 9.91, 9.96

height of burst cirves, 3.73-3.77 Column, in underwater burst, 2.67, 2.68

Rankine-Hugoniot relations, 3.53-3.56 Compton effect. 8.89, 8.90, 8.95, 8.97. 8.103,

reflection, 3.21-3.29, 3.78, see also Mach ef- 11.105

fect and EMP, 11.60-11.63, 11.66

irregular. 3.24 Concrete, radiation shielding, 8.41, 8.68, 8.69.

regular, 3.22 8.72, 9.120

refraction, 3.42, 3.43 structures, damage, see Damage

scaling laws, 3.60--3.63 Conjugate points (or regions), 2.143, 10.49,

and structures, see Damage; Loading 10.64, 10.65

surface (or terrain) effects, see Terrain effects Condensation cloud, 2.47-2.50, 2.66

target response, 5.08-5.18, see also Damage Contamination, radioactive, 9.48-9.113, 9. i54-

velocity, 3.55 9.162, see also Fallout; Fission products; Rawind, 3.07, 3.13, 3.55 dioactivity, induced

Blood, radiation effects, 12.124-12.132 in air bursts, 9.48, 9.49

Boltzmann constant, 7.73 decay, 1.64. 9.15-9,130, 9.146-9.153

-Stefan law, 7.82 distribution patterns, 9.75-9.113

Bone seekers, 12.!65 dose calculations, 9.15-9.30

Boosted weapons, 1.72 hot spots, 2.31, 9.66, 9.105

Breakaway, fireball, 2.120, 2.121 in surface and subsurface bursts, 9.50-9.52,

Bridges, damage, 5.127, 5.139, 5.140 9.61

Buildings, damage, see Damage in underwater bursts, 9.53-9.55

Burns, 7.32, 12.13, 12.14, 12.22, 12.51-12.89 Crack, in underwater burst, 2.65

beta, 12.155-12.162 Crater, 2.21, 2.90, 6.03-6.11, 6.70-6.79

classification, 12.51-12.58 dimensions, 6.08-6.11, 6.70-6.72

under clothing, 12.59-12.60 formation mechanism, 2.92-2.94

to eyes, see Eye injuries plastic zone, 6.07, 6.70

flame, 12.51 rupture zone, 6.07, 6.70

flash, 1.32, 12.13, 12.14, 12.18, 12.51, underwater, 6.60, 6.61

12.74-12.78 Critical mass (or size), 1.46-1.53

incapacitation from, 12.61, 12.62 attainment in weapon, 1.51-1.53

in Japan, 12.13, 12.14, 12.18, 12.68-12.73 Crops, see Plants

profile, 12.70 Cross section, neutron, 8.112

and radiant exposure, 12.63-12.69 Curie, 9.141

Buses, damage, 5.87

Damage, 5.01-5.161, 6.104-6.114

Cancer, nuclear radiatio1 a, i2.147-12.151 administrative buildings, 5.19-5.27, 5. 139-

Capture ganima rays, 8.08 5.141

Carbon-14, in nature, :2,198 aircraft, 5.94, 5.95, 5.151-5.154

in weapons residues. 12. 197-12.199 arches and domes, 6. 101

Casualties, 12.01-12.21, see also Injuries automobiles, 5.86-5.91, 5.146

in buildings, 12.17 brick stru m,'es, 5. I.,9, 5.140

i, Japan, 12.08-12.22 bridges, 5.127, 5.139, 5.140

Cataracts, nuclear radiation, 12.144-12.146 buses, 5.87

Cattle, see Animals chimneys, 5.34

Cavity, in underground burst, 2.102, 6.85.-6.88 cormercial buildings, 5.19-5.27, 5.139, 5,140

Cesium-13 7 , in delayed fallout, 9.124, 12.184- communications equipment, 5.122-5.126,

12.187 5.148

Chain reaction, see Fission concrete buildings, 5.20-5.27, 5.139, 5.140

Chimney, in underground burst, 2.103, 6.88, 6.89 diffraction-sensitive structures, 5.139-5.145

Clean weapon, see Nuclear weapons --distance relationships, 5. 140, 5.146

Cloud, condensation, 2.47-2.50, 2.66 domestic appliances, 5.114

radioactive, 2.06-2.17, 2.19, 2.43, 2.68, 2.97, drag-sensitive structures, 5.146-5.154

9.07-9.09 dwellings, see Damage, residences

dimensions, 2.16 electrical distribution systems, 5.98-5.105

height, 2.16, 9.96, 10.158 fabrics, 7.33-7.36, 7.44-7.48

rate of rise, 2,12 forests, 5.146, 5.149, 5.150, 7.60

radioactivity in, 9.61 frame buildings, 5.25, 5.26, 5.37-5.51, 5.139.

radius, 2.16 5.i40

U,
646 INIA

gas systems, 5.108-5.121 Electromagnetic pulse (EMP). 1.38, 2.46, 2.61.

houses, see Damage, residences 11.01-11.76

hydraulic structures, 6.122-6.125 and animals, 11.20

industrial buildings, 5.04, 5.28-5.51, 5.139, characteristics. 11.04, 11.07-11.09, 11.63-

5.140 11.65

in Japan, see Japan, nuclear explosions and Compton current, 11.60, 11.61

rmachine tools, 5.128-5.133 damage, 11.18-11.20, 11.26, 11.30-11.33.

masonry buildings, 5.76-5.79, 5.139, 5.140 11.49-11.59

mobile homes, 5.80--5.84 electrical systems, 11.26, 11.32, 11.33,

oil tanks, 5.155 11.49-11.53

plastics, 7.39, 7.40 electronic equipment, 11,30, 11.31

railroad equipment, 5.92, 5,93, 5.146 and electrical power systems, 11.49-11.53

residences, 5.04, 5.52-5.84. 5.139, 5.140, energy collectors, 11. 16. 11.17

7.28 coupling, 11.27-11.29

ships, 5.96, 5.97, 5.146, 6.63-6.65 high-altitude bursts, 11.03, 11.13-11.15,

smokestacks, 5.34 11.26, 11.70-11.76

storage tanks, 5.155 medium-altitude bursts, 11.66, 11.67

subways, 6.106 protection, 11.19, 11.33-11.40

transportation equipment, 5.85-5.97, 5.146, and radio stations, 11.54-I 1.57

5.147 surface bursts, 11.03, 11.10--11.12, 11.68,

tunnels, 6.109 11.69

utilities, 5.98-5.121 system-generated, 11.21-Il .25

vehicles, 5.86-.5.91, 5.146 and telephone systems, 11.58, 11.59

water systems, 5.106, 5.107 testing for rcsponse, 11.41-11.48

Decay, radioactive, 1.02, 1.62 theory, 11.60-11.76

fission products, 1.54 see also Fallout, decay Electromagnetic radiation, 1.73-1.79, see also

Decibel, 10.126 Thermal radiation

Detection ionizing radiation, see Measurement Electromagnetic waves, see Radio and radar

Deuterium fusion reactions, 1.16, 1.67-1.71 Electron, 1.08, see also Beta particles

Diffraction loading, see Loading Electron volt, definition, 1.42

-sensitive structures, 5.139-5.145 EMP, see Electromagnetic pulse

Dirty weapons, 9.47 Energy distribution in nuclear explosions, 1.22-

Dose (and dose rate), rz.diation, 8.17-8.19 1.27, 7.88, 7.101, 7.102

absorbed, 8.18, 12.94 Energy, fission. 1.43

biologically effective, 12.93-12.97 fusion, 1.69

exposure, 8.19, 12.93 Energy yield, explosion, 1.20, 1.21, 1.45 from initial radiation, 8.33, 8.64, 8.12 1-'3. 127 Evasive action, nuclear radiation, 8.48 from residual (fallout) radiation, 9.12-9.30 thermal radiation, 7.87

transmission factors, 8.72, 9 120 Explosion, atomic, see Nuclear explosion

Dosimeter, 8.21, 8.24, 8.29

Drag loading, see Loading Eye injuries, 7.32, 12.79-12.89

-sensitive structures, 5.146-5.154 cataracts, 12.144

Ductility, materials and structures, 5.14-5.18 flashblindness, 12.83, 12.84, 12.87-12.89

Dynamic pressure, 3.06-3.08, 3.13-3.20 keratitis, 12.80

decay rate, 3.07, 3.13, 3.56' retinal burns, 12.85-12.89

-distance relationships, 3.75

duration, 3.76 Fabric damage, thermal, 7.33-7.36, 7.44, 7.48

and height of burst, 3.75 Fallout, 2.18-2.31, 2.99, 9.01-9.166

loading, see Loading, drag air burst, 9.48, 9.49

Rankine-Hugoniot relations, 3.55 attenuation of radiation from, 9.114-9.120

surface effects, 3.50, 3.82 from BRAVO explos;on, 9.114-9.120

and wind, 3.07, 3.13-3.17, 3.55 cesium-137 in delaytd, 9.124, 9.145, 12.184-

12.187

Earth, shielding, 8.41, 8.72, 9.156, 9.161 contamination, 9.48- 9. 1 ! 3

Earthquakes, and underground bursts, 6.24-6.27 distribution, 9.75-9. 113

Effective half-life, 12.170 contours, see Fallout patterns ,"

Electrical and electronic equipment, EMP effects, decay, 1.64, 9.12-9.30, 9.145-9.153 t if

11.26-11.59 half-residence time, 9.133

nuclear radiation effects, 8.73-8.88, 8.133- stratospheric, 9.130, 9.131, 9.135-9.139

8.144 tropospheric, 9.130-9.134

S.AM
INDEX 647

from weapons tests. 9. i40-9.141 Fireý,. 7.49-7.70

distribution, 9.59-9.63, see also Fallout pat- in Japan, 7.61-7.80

terns mass, 7.58-7.60

dose, 9.16-9.30, 9.146-9.162 origin, 7.49-7.53

rate, area integral, 9.160 spread. 7.54-7.60

early, 2.28, 9.03, 9.06-9.30 Firestorm, 7.58. 7.71

fractionation, 9.06-9.10 Fission, 1.13, 1.14, 1.21, 1.42-1.56

hazard, to animals, 12.244--12.254 chain, 1.42, 1.46-1.50, 1.54-1.59

to humans, 12.155--12.200 energy, 1.15, 1.20, 1.21

to plants, 12.255-12.265 distribution, 1.42-1.45

and height of burst, 2.128 TNT equivalent. 1.45

hot spots, 2.31, 9.66, 9.105 explosion time scale, 1.54-1.59

iodine in delayed, 9.123 fraginents, 1.41, 1.43

local, see Fallout, early g-ner,,tion time, 1.54

particles, rate of fall, 9.163-9.166 1. 1.5, 1.26, 1.29, 1.43, 1.60-1.66,

patterns, 9.75-9.114 .G', 210. 2.11, see also Fllout, decay

idealized, 9.83-9.103 weaponi. see Nuclear weapons

limitations, 9.99-9.103 Flame burn.s see Burns, flame

wind effect, 9.96-9.98 Flash blindi,;ss, 12.83, 12.84, 12.87-12.89

plutonium in, 9.40, 12.173 Flash burns, see Burns, flash

protection factors, 9. 120 Fluorescence radiation, high-altitude burst, 2. 131,

and rainfall, 9.67-9.74 2.138-2.141

rainout, 9.74 Fog, and thermal radiation, 7.16, 7.17

scavenging, 2.30, 9.67-9.74 FoAd plants, see Plants

stratospheric, 9.130, 9.131, 9..35-9.139 Forests, damage, 5.146, 5.149, 5.150, 7.60

strontium-90 in delayed, 9.124, 9.140-9.145, Fractionation, fallout, 9.06-9.10

12. 488-12.196 Fusion reactions, 1. 13, 1.16-1.18, 1.67-1.72

surface burst, 2.23-2.31, 9.50-9.52 weapons, see Thermonuclear weapons

surface (or terrain) effect, 9.95, 9.101, 9.156,

9.161 Gamma rays (or radiation), 1.28-1.30, i.43,

tropospheric, 9.130-9.134 1.61-1.66, 1.71, 8.01, 8.04, 8.08-8.48

underground burst, 2.99, 9.05, 9.51, 9.52 attenuation, 8.38-8.42, 8.95-8.104, 9.117-

underwater burst, 2.82, 2.85, 9.05, 9.53-9.58 9.120

uranium in, 9.40-9.43 coefficients, 8.95-8.102

washout, 9.74 biological effectiveness, 12.94

worldwide, see Fallout, delayed buildup factor, 8.103, 8.104

Farm animals, see Animals capture, 8.08

Film badge, 8.26 delayed, 8.13

Fireball, 1.32, 1.36, 1.40, 2.03-2.05, 2.18, 2.36, delivery rate, 8.46-8.48

2.38-2.40, 2.54-2.59, 2.110-2.137, 7.73- dose-distance relationships, 8.31-8.37, 8.125-

7.105 8.132

air burst, 2.03-2.05, 2.106-2.129, 7.83, 7.86 evasive action, 8.48

breakaway in, 2.120 half-value thickness, 8.39

debris uptake, 2.09, 2.18, 2.19, 9.50, 9.59 hazard, 12.91-12.92

development, 2.110-2.121 hydrodynamic enhpncement, 8.36, 8.47

dimensions, 1.32, 2.05, 2.127-2.129 inelastic scattering, 8.09

high-altitude burst, 2.53-2.59, 2.132, 2.136, interaction with matter, 8.17, 8.89-8. 104 3 7.22 ionization by, .8.17, 8.21

ionization, 10.21-10.24, 10.40-10.44, 10.53- measurement, 8.20-8.30

10.55, 10.62 prompt, 8.12

shock front development, 2.115-2.120 RBE, 12.94

surface burst, 2.18, 7.20 scattering, 8.44, 8.45

thermal power, 7.82-7.85 shielding, 8.05, 8.38-8.45, 8.72, 9.120

thermal radiation, 2.38-2.40, 7.01-7.04, 7.75, skyshine, 8.44

7.76, 7.80-7.84 sources, 1.61-1.63, 8.08-8.16, 9.16

underground burst, 2.91, 7.21 spectrum, nuclear explosion, 8.105

underwater burst, 2.64, 7.21 stopping altitude, 10.29

X-ray, 2.110-2.1119 tenth-value thickness, 8.39-8.42, 8. 102-8.104

..... .7 -•
648 INDEX

transmission factors, 8.72, 9.120 Hiroshima. ,ucicar explosion, 2.24, see also

and weapon yield, 8.63, 8.64 Japan

Gas systems, damage. 5.108-5.121 Hot spots. 2.31. 9.66, 9.105

Geiger counter, 8.21 Houw' damage. see Damage, residences

Genetic effects, radiation, 12.208-12.219 Hydraulic fill, craters. 6.09

Geomagnetic field, and auroral phenomena, Hydraulic structures, damage, 6.122-6.125

2.142-2.145 Hydrodynamic enhancement. 8.36, 8.47. 8.128-

and beta particle motion, 2.143, 10.27. 10.46- 8.131

10.51 phase, fireball, 2.117

conjugate regions, 2.141, 2.143, 10.27, 10.47, separation. 2.115

10.64 Hypocenter, explosion, 2.34

and ionization, 10.46-10.51, 10.55, 10.63- Hydrogen bomb, see Thermonuclear weapons

10.66 isotopes, 1.16. 1.17, 1 ')7-1.69

and weapon debris, 10.55, 10.63, 10.64, 10.70

Glass, missile hazard, 12.42, 12.43, 12.238 Ignition, materials, 7.33-7.40

Ground motion, in surface burst, 6.12-6.17 Implosion, 1.53

in underground burst, 6.33-6.40, 6.90-6.93 Impulse, 3.59, 3.63, 3.65, 3.66

Ground shock, see Shock and structure loading, 4.54, 4.56, 4.66

Ground zero, 2.34 Incendiary effects, see Fires

Gun-barrel assembly, 1.52 Induced radioactivity, 8.16, 9.31-9.39

Industrial buildings, damage, 5.04, 5.28-5.51,

Half-life, biological, 12.170 5.139, 5.140

effective, 12.170 Initial nuclear radiation, 1.02, 1.26-1.29, 1.34,

radioactive, 1.63 1.37-1.39, 2.41-2.45, 8.01-8.72, 8.89-8.124,

Half-residence time, delayed fallout, 9. 133 9.04, see also Gamma rays; Neutrons

Half-value thickness, 8.39 Injuries, 12.01-12.239, se.r also Burns; CasualHarbor damage, see Hydraulic structures ties; Radiation injury

Height of burst and blast damage, 3.30-3.33 blast, direct 12.24-12.38, 12.239

and blast wave arrival time, 3.77 indirect, 12.39-12.50, 12.238

and dynamic pressure, 3.75 blood, see Blood

duration, 3.76 burn, 12.51-12.78, see also Burns

and fallout, 2.128 causes, 12.18

,,ptimum, 3.73 combined, 12.133-12. 143

and overpressure, 3.73 eardrums, 12.38

duration, 3.76 eye, see Eye injuries

scaling, 3.62 in Japan, 12.08-12.23, 12.68-12.78, 12.114-

Hematological effects, radiation, 12.124-12.132 12.132, 12.144-12.154

High-altitude burst, 1.24, 1.36, 1.37, 2.52-2.62, ionizing radiation, 12.91, see also Radiation

2.130-2.150 injury

auroral phenomena, 2.62, 2.142-2.145 lung damage, 12.38

beta patch, 2.141 from missiles, 12.41-12.48

blast, 3.68 nuclear radiation, see Burns, beta; Radiation

definition, 1.36, 2.130 injury

and EMP, see Electromagnetic pulse protection by buildings, 12.17

energy distribution, 1.36, 2. 130, 7.89-7.92 thermal radiation, see Burns

eye injuries, 12.87 Iodine in delayed fallout, 9.123

fireball, 2.53-2.59, 2.131, 2.136, 7.22 Ionization, 1.38, 8.17, 10.04

FISHBOWL series, 2.52 atmospheric, 10.09-10.20, see also Geomagfluorescence radiation, 2.131, 2.138-2.141 netic field

ionization, atmospheric, 10.40-10.74 and electromagnetic waves, 10.04-10.08,

and ozone layer, 2.148-2.150 10.125-10.137

phenomena, 1.36, 1.37, 2.52-2.60, 2.130- in nuclear explosions, 10.21-10.74

2.150 below 10 miles, 10.34-10.39

radio and radar !ffects, 10.89-10.121 10 to 40 miles, 10.40-10.52

shock wave, 2.136 40 to 65 miles, 10.53-10.61

thermi-r! radiation. 2.131-2.135, 7.89-7.92, above 65 miles, 10.62-10.74

7.102-7.105 Ionizing radiation, 12.91, see also Nuclear radiaX-ray pancake, 2.130, 7.91, 7.103 tion
IN D F. 649

Ionosphere, 10.09-10.20 fallout. 9.66-9.74. 9.102, see also Hot %I)ot%,

electron density. 10.09 Scavefiging

delayed radiation effects, 10. 154-10.164 fires, 7.54, 7.58, 7.71, 7.72

nuclear explosion effects, see Ionization, in Million electron volt (or MeV), 1.42

nuclear explosions Mobile homes, damage. 5.80-5-s4

prompt radiation effects, 10.138-10.153 Monitoring, ionizing radiation, see Measurement

radio and radar effects, see Radio and radar Mutations. see Genetic effects

Ion pairs, 1.38, 8.17

Iron, radiation shielding, 8.41, 8.104 Nagasaki, nuclear explosion, 2,24, se( also Japan

Isothermal sphere, fireball, 2.114-2.120, 2.!24 Neoplasms, nuclear radiation, 12.147-12.151

Isotopes, 1.09 Neutron, 1.08, 1.31, 8.01, 8.04, 8.49-8.72

hydrogen, 1.16, 1,17, 1.67-1.69 absorption (or attenuation). 8.66-8.72, 9.120

capture. 8.08. 8,11. 8,16. 8.54, 8.56, 9.31-

Japan. nuclear explosions, 2.24 4.39

casualties, 12.08-12.23 cross section, 8.112

nuc!ear radiation injuries, 12.114-12.132, delayed, 8.50

12.144-12.154 dose--istance relationships, 8.121-8.124

structural damage, 5.28-5.34, 5,52. 5.53, fast, 8.52

5.85, 5.98, 5.106-5.108, 5.127 fluence, 8.61

thermal radiation, burns, 12.68-12.'i8 flux, 8.60

incendiary effccts, 7.61-7.72 measurement, 8.58-8.62

materials effects, 7.44-7.48 hydrodynamic enhancement, 8.50

induced activity, 8.16, 9.31. 4.39

Keloid formation, 12.78 initial nuclear radiation, 8.01. 8.04, 8.49-8.72

Keratitis, 12.80 interaction with matter, 8.107-8.113

ionization, 8.58, 8.59

Leukemia, nuclear radiation, 12.147-12.149 measurement, 8.58-8.62

Lithium deuteride, 1.70, 1.71 prompt, 8.50

Loading, blast, 4.01-4.6"'. u.94-6.103 RBE, 12.97

arched structures, 4.62-4.66 scattering, 2.41, 8.09, 8.52, 8.53, 8.107, 8.108

buried structures. 6.94-6.103 shielding, 8.66-8.72, 9.120

development, 4.22-4.37 slow, 8.52

shape effect, 4 35-4.37 alowing down, 8,54

size effect, 4.31-4.34 sources, 8.01. 8.04. 8.49-8.57

diffraction, 4.03, 4.05-4.11 spectrum, 8.53. 8.114-8. 120

drag, 4.12-4.14, 4.29 equilibrium. 8.118, 8.119

nonideal blast wave, 4.67 thermal, 8.52

structures, 4.15-4.20. 4.41-4.67 from thermonuclear (fusion) reactions. 1.69,

box-like, closed, 4.41-4.45 1.72, 8.57, 8.116, 8.117, 8.119

partially open, 4.46-4.51 transmission factors, 8.72, 9,120

cylindrical, 4.57-4.16 transmissior, from source, 8.5".-8.56, 8.117--

open-frame, 4.52-4.56 8.120

Lung injuries, 12.15, 12.28, 12.38 Nitrogen, neutron reaction, 8.11, 854. 8.56,

8.110, 9.34

Mach effect, 2.33-2.37, 3.24-3.31, 3.34 Nuclear explosion, blast wave, 1.01, src al,.'

front (or stem), 2.33-2.37, 3.25 Blast; Shock

and height of burst, 3.29 casualties, see Casualties

triple point, 3.25 characteristics, 1.01-1.23

Machine tools damage, 5.128-5.133 and conventional explosicvns, 1.01 - 1.03

Marshall Islands, inhabitants, 12.175-12.183 damage, see Damage.

Masonry buildings, damage, 5.76-5.79, 5.139. description, air burst, 2.03--2.51, .ee also Air

5.140 burst

Mean free path, 2.113, 7.79 high-altitude burst, 2.52-2.62. see also

Measurement, ionizing radiation, 8.20-8.30, Hig!•-altitude burst

8.58-8.62 surface burst, 2.03-2.51. see also Surface

Megacurie, 9.141 burst

Mesosphere, 3.42, 9.126 underground burst, 2.90-2.105

Meteorological effects, blast wave, 3.39-3.43 underwater burst, 2.63-2.89

._ _. • _ _ _•.- ..
650 INDFX

fireball dcveopment, see Fireball Ozwni layer, nuclear cxp!osion e€lects, 2. 148-

incendiary effectN, see Fires 2.150

injtiries, see injurics; Radintion injury

!otrization, see Ionization iair production, ga.inia-ýay. 1-92

nuclear radiation, mee Nuclear ra~Jiation Particles, rate of fall, 9 163 -1.166

pressvres, 2 ;O7 ,talhol, jy. radiation injuly, 12.220-12.23?

pr61-iples, 1,46-1.59 Photoelectric effect, gamma-ray, 8.9l

radio and rp.dar effects, se, kadk, and radar Phuton, 1,74, 7379

shock wave, 1,01, see also Miast; Shock -!rnck Lu;ation (or theory,, 1.74, 7.73, 7.74

tcmptature%, 1,23, 2.107, 7,75 Plants, nuc;!ar explosion ceFects, 12,240-12,243,

th%, mal radtoion, see Thermal radiation 17,215- 12.265

types. I,3lII,.l, 2.01, 2.02 Plastic dMformaiion, 5.15

Nuclear radiation, 1,02, 1,34--I.'9, 2,41-2,45 Plastics, thermal damage, 7.39

from air burst, 1,33-I,35, 2,44, 2.4. Plh'stic .one, cr,ater, 6,07, 6.70

biolo;g' J effectl,, on animals, 12,241)-12.254 Platonium, fission, 1,14, 1.15, 1.18, 1.42, 1,44.

ot. man, see Radiation injury 1,45

on plant", 12,241.-12,201, 12.2W5-M2,265 hWard, 11.73

initial, see Initial nuclear radiatton in weapon.i residues, 9 40-9.43

injuries, see Radintion Iini'ty Polar front, 9,127

prompt, 2.41 Precurs;or, blast wave, 3,49, 3,79-3.85

residual, 'eýw Residual nuclear radiation loading, 4.b7

from - ,fae burst, 7.21-2.31, 8.37, 8.6, Pressure, blast and shock, see Dynamic pressure;

9.50-9.52 LUding; Overpressure

transmission factors, 8,72, 9.120 Protile burns, 12.70

from undirground burst, 1,39, 2.49, 2. 100 Protection, see Evasive action, Shielding

from underwater burst, 2. 77-2. .'9, 2.81, 2.82, factors, initial radiation, 8.72

2,89 fallout, 9,120

Nuclar wuap•,ns, 1,02, 1.11I, ,.19-4I,21, I,.51, Proton, 1,08

1.72, sec also Nucloar cxplosioens

boosled, 1.72 Qu.mum, 1.74

cloean and dirty, 9.47 tQuory, u er Planck

critikality att•,inincnt, 1.51 L.1. t

4sion, ,4d .59a 1$ :us-ior, 1.6•7.1.72, ,•ev. aJlso 1 hermc,'m,.'lear d,,1

Radar elf4tcs, see Radio and radar

wearxbns R!kli,stnl e xpou'c, 7.35 sailed, 9., I I suite, Qý I pwer, 7/74, 7-82-7.84. 7.86

tlarumonu¢|ear, see Thermonuclear weapons R o iury, I2AJO-7,2,7

yield, 1.20, 1.21 RadUlon Injury, 12.qO-12.237

Nucleus, atornic, 1.08 acute, 12.102-.12.132

Nuclide, 1.10 bloo) 12,124-12,132

rMaiodtivo, 1.30 cancer (neoplasms), 12.147-12. 151

-' larners, 12.144- 12.146

()il-ti damage, 5. 155 . Iiical phenomesa, 12.108-12.123

Overpre.,turf, 2.33, 3.01 -3,05, .,21- 3.34, delaycou, 12.142-2.154

3.5.1-3,853, se arls. Mllast; Loadih,,g Mach o~f.. from iallout,

fect early. 12-055-1l2.WI3

decay rate, 30(), 3.57 delayed, 12.184-12.200

distance rclat~onships, 3.73 genetic, 12,208-12.219

dutation, 1,7(0 pathology, 12,220-12,237

free air, 3,72 thyroid, 12.171, 12131.-12.193

and helght of burst, 3.73, 1.76 Radiation Effet,:, Research Foundation, 12.142

loading, se Ulding, diffraction Radiation, nuclear, me (3amelia rays, Neutrons.

nogative, 3,05 Nuclear raiiation

peak, 3,.2, 3.74 Radioactive capture, neitrons, 8.08

arrial tior, 3,77 Radioactive cloud, see Cloud

P.nkine-iHugon',of relations, 3.ý5, ,.56 Radioactive hilf-life, 1,63

reflected, 3,56, 3.78 Radioactivitv, 1.02, 1,28-1.30, 1,61--1,66, see

scaling, 3.65 VIso Fallout

surfikLe (terrain) ell'cets, 3,4'-3..S0, 3.79-3,85 inducad, 8.1 f, 9.31- 9.39
INDEX 651

Radioflash, .,ee Elrtromagnetic pulse Shock (ard Shock wave), 1,01I 1.33. 6.82-6.84.

Radionuclide, i,30 see also Blast

Radio and radar effects, 10.01-10. 164, see a!so fror.t, 1.01. 3.03

Ionization, in nuclear cxplo.ons in fireball. 2.155.-2.120

attenuation, signal, 10.78, 10.79 ground, in air burst, 3.51. 3.52

blackout, 10.01 damage from. 6.104-6.114

Doppler shift, 10.83 in surf•ce bur,... 6.12-6.17

d--gradation. signal, 10.75-I.77 in undergiound burst, 6.18. 6.19, see also

HF (high-freque'icy), 10.100-10. 107 Seismic effects

hydromagnetic disturbance, 10.26 ira underwater burst, 6.14-6,52. 6. 1 15-6.118

initial radiation, 10.149-10.153 Skin burns, see Burns

LF (low-frequency), 10.97, 10.98 Skyshine. gamma-ray, 8,44

MF (mediun:-freq'tency), 10.82.-10.84 Slek. irn underwater burst. 2,65

noist, 10.80, 10.61 Smoke, and thermal radiation, 7.16, 7.17

phase changes, 10,82-10.84, 10.94 Soil, vaporization in surface burst, 2.18

radar systems, 10.114-10,122 Spray dome in underwater burst, 2.66. 2.84

radio systems, 10,89-10. I13, ,10.122 Stagnation pressut-,, 4,25

residual radiation, 10. 154-10.164 Stcfan-Boltzmann law. 7,82

scattering, 10.87, 10.88 Stopping altitude, 10,29

summary, 10. 122 Storage tanP., damage, 5.155

UHF (ultrahigh-frequency), 10. 112, 10.113 Scratoszhc,, 9.126

V HF (very-high. frequenvy) t0 02.-10,111 falloui from, 9.130, 9.1 ?I, 9,135-9, 139

VLF (very- ow-frequency), 10.92-10.96 Stopping altitude, radiation, 10.29

Railroad equipment, damage, 5.92, 5,93, 5.146 Strontiurn-.90 in del'tyed fallout, 9.124, 9.140-

Rainout, 9.74 9.145

Rankine ,Hugoniot relations, 3 53-3.56 radiation hazard, 12,188-12.196

RBE (Relative biological effectiveness), 12.94 Structural damage, see Damage

Reflection, blast wave, see Blast wave', MLh Structures, see Damage; 1,oading

effeci Subsurface buwsta, see Surface; Underground;

Reinfoiced-concrete buildings, damage, 5,20- Underwater

5.27, 5,139, 5.140 Subways, damage, 6.106

Relative b.Aogical effectlveness (PBE), 12.94 Surface (and shallow uiderground) burst, 1,40,

Rem, 12,95 1,13-2.31, 2.90-2.100, 6.01-6.,18

Residences, damage, 5,04, 5,52-5,84, 5,139, air blast, 2,32-2.37, 3.34-3.74, 6,02, 6.80,

5.140, 7.28 6,81

Residual nucIea7 radiation, 1.02, 1,26--1.30, characteristics, 2,18-2.37, 2,90-2.100, 6.01-

-.3), 1.39, 9,0i-9. ioo, sce also Fallout; Ra- 6.18

diactivity, induced contact. 3.34, 3.74

Resonxse, spectrum. 6.90 crater formation, 2.21, 2.90-2.A4, 6.03-6.11,

structures, 5.08-5.18, see also Damage 6,70-6,79, see also Crater

Retinal burns, see Eye Injuries damage In. 6.28-6.31, 6.94-6,103

Roentgen, 8. 17 iLAP effect, 11.03, I110-1I. 12, 11.68, 11.69

Rupture : (w. crater, 6,07, 6.70 fallout, 2.23-2.31, 9.50-9,52, see also Fallout

fireball, 2,!8, 7.20

Scattering, see Compton emYect; Gamma radiatton; ground motion, 6.82-6,84

Thermal radiation; Neutrons ground sbock, 6. 12--6.18

Scvenging, fallo'At, 2.30, 9.67-9.74 nuclear r.viiilon, initial, 8.37, 8.65, s•u also

Scintillation counter, 8.23 Nucleai radiation

SeIhmic effects, 2.102, 2,105, 6.19-6.27 residual, 2,23-2,31, 9.50-9.52

Semiconductor detector, 8,22 radioactivr cloud, 2,19.-2.22

Semiconductor, EMP effects, 113 1,11, 32 contamination, 9.50-9.52

radiation effects, 8,77-8,80 thermal radiation, 7.20, 7,42, 7, 101

Shake, 1.54 Furface effects on blast, see Terrain effects

Shielding, grnuna rAys, 8.05, 8,38-4145, 8,72, Surface, zero, 2,34

9.120 Survey meter, 7.30

neutrons, 8,66-8,72

thermal radiation, 7. 18, 7.19 Tamper, nuclear weapon, 1I50

Ships, damage, 5,96, .1,97, 5,146, 6,63-6.65 Tenth-value tiickness, 8.38, 8,102

I,.
652 INDEX

Terrain effects, on blast, 3,35-3.38, 3,47-3.50, Time scale, fission explosion, 1.54-1.59

3.79-3.85 TNT equivalent, 1.20, 1.45

on fallout, 9.95, 9.101, 9.156. 9.161 Trailer coach, damage. 5.80-5.84

Thermal layer, 1.80 Trarsient-radiation effects on electronics (TREE).

Thermal pulses, in air burst, 2.38-2.40, 7.86, 8.73-8.88,8.133-8.144

7.87 characteristics, 8.73-8.76

in high-altitude burst, 2.132, 2.133, 7.89 effects on equipment, 8.77, 8.78

Thermal radiation. 1,02, 1.22-1.25. 1.73-1.79, mechanisn., 8.133-8,144

7.01-7.105 Transmission factors, initial nuclear radiatin,

absorption, in materials, 7,23-7,31, 7.33, 7.34 8.72

in air burst, 1.33, 2.38-2.40. 7.03-7.05, residual nuclear radiation, 9.120

7.85-7.100 Transmittance, thermal radiation, 7,95-.7.98.

and atmospheric conditions, 7.11-7.17, 7.98 7.101-7.104, 7.105

attenuation, 7,08-7.19, 7.94, 7.98 Transportation equipment, damage, 5.85-5.97,

burns, see Burns, flash 5.146, 5,147

damage, 7,33-7.40 Trinity test, 2.36, 12.245, 12.246

definition, 7,02 Triple point, 3.25, see also Mach effect

effects, 7.23-7.53 Tritium. thermonuclear (fusion) reactions, 1.67-

in Yapan, 7.44-7.48, 7.61-7.72 1.70

energy fraction, air burst, 1.25, 7.04, 7.88 in residual radiation, 12,197, 12.200

high-altitude burst, 7.22, 7.90, 7.102, 7.104 Tropcpause, 2.13, 9. t26

,urface burst, 7. 101 Tiopophere, 3.40, 9.126

evasive action, 7,87 fallouit from, 9,130-9,134

exposure-distance relationship, 7.41-7,43, Tunnels, damage, 6.109

7,93-7. 105

and fabrics, 7.27, 7.33-7.35 Ultraviolet radiation, 1,73, 1.78, 2.38, 2.39,

from fireball, 7.01-7.22. 7.73-7.92 7,75, 7.76

in high-altitude burst, 7.22, 7,89-7.92, 7,102- Underground burst (deep), 1.39, 2.90-2.105,

7,105 6.19-6.40, 6,85-6.93

ignition exposures, 7.35, 7,40 aftershocks, 2.105, 6,20.-6.27

incendiary effects, 7,49-7.72 air blast, 6,02, 6.53

in uries, 7 32, 12.51-.12.78 base surge, 2.96-2.98

materials ignition, 7.33-7.40, 7.44-7.49 cavity, 2.102, 6.85--6,88

and plastics, 7,39 characteristics, 2.90-2. 105

primary, 1.77, 7.01, 7,75, see also Thermal chimney, 2,103. 6.89

X-I ayr damage criteria, 6.104-6 114

prompt, 7,02 fallout, 2,98, see also Fallout

pulses, sce Thermal puh'cti fault displacement, 6,20-6-21

radiant exrp.,iure, 7.35 fireball, 2,91

power, 7.74, 7.82-7.84, 7.86 ground motion, 6,33 -6.40

scattering, 7.08. 7.10-7.17, 7.19, 7.95, 7.98 loading, buried stiuctures, 6,104-6,. Il1

shielding, .18, 7,19 seismic effect-;, 6.19-0.27

smoke anid fog uffects, 7,16, 7.17 shallow, se Surface burst

In surlace burst, 7.20, 7.101 shock wave, 6.18, 6.19, 6.33

transmittance, 7,95-7.98, 7,101, 7.104, 7.105 and structures, 6,33-6.40

underground burst, 2 99 Urtderwater burst, 1,39, 2.63-2.89, 6.41 6,69,

underwater burst, 2,80 6. 115-6.125

Thermal X-rays, 1,77-1,79, 7.01, 7,75, 7,80, air blast, 6.53, 6,68, 6,69

7,81, 7,90--7.92, 7 104 base surge, radioactive, 2.76 2,79

ionization, 10.53, 10.57, 10.60, 10.62, 10.69 visiblo, 2.72-.2.75

Thermonuclear (fusion) reactions, 1.17-1.19, characeristics, 2.63--2,79, 6.41-6.69

1.67-1.72 cloud, 2.69

weapons, 1.67-1.7^ column, 2,67, 2.68

fallout patterns, ', contamination, water, 9,53--9,58

gamma rays, 8.33 crack, 2,65

neutrons, 8.64. 8. 116, 4, 117, 8,119 crater formation, 6,60, 6.61

Thermosphere, 3.,43, 9.126 damnage, 6.62-6.64

Thyroid abnormallit•es, 12,171, 12.181-.12.183 deep, 2.81 -2.89
P

INDEX 653

fireball, 2.64 Wall-bearing structures. 5.27. 5.139

hydraulic structures, damage, 6.122-6.124 Wall failure, 5.!45

nuclear iadiation, 2.74-2.79, 2.81. 2.82, see Weapons. nuclear, see Nuclear weapons

also Fallout Weather effects, see Meteorological effects

overpressurc. water, 6.41 Wien's displacement law, 7.77

plume, 2.67 Wilson cloud, 2.47-2.50, 2.66

shallow, 2.63-2.8? Wind, and fallout patterns, 9.96-9.98

ships, damage, 6.58, f_63-6.69 Wind (dynamic pressure), 3.07, 3.08, 3.13, 3.14,

shock wave, 6.41-6.52, 6.62-6.69, 6. 15- 3.16

6,118 velocity, 3.07, 3.55

reflection, 6.43, 6.44-6.52 Wood, thermal radiation effects, 7.37. 7.38, 7.40.

surface cutoff, 6.43 7.14

slick, 2.65 Worldwide fallout. see Falloter, delayed

thermal radiation, 2.80

water wavcs. 2.70, 2.71. 6.,4-6.59, 6.119- X-ray fireball, 2.110

6.121 X rays, 1.73, 1 71, 1.79

Unit-time reference dose rate., 9.16-.9.23, 9.92- absorption, 2.114, 7.80, 7.81, 7.92

9.95 degrvoation, 1.78, 2.38, 7.02, 7.75

Uranium fission. 1,14, 1.15, 1.18, 1.42, 1.44, .onization, atmospheric, 10.53, 10.57. 10.60,

1.45, 1.72 10.62, 10.69

hazard, 12.174 pancake, 2.134, 2,135, 7.91, 7.103

in weapons residues, 9.31, 9.40-9.42 stoppiag altitude, 10.29

Utilities, damage, 5.98-5.121 thermal, see Thermal X-rays

Vehicle, damage, 5.86-5.91, 5.146 Yield, explosion, 1,20, 1.21, 1.45

U 8 GOVE1iNMENT PI1INTINCi OFFICE 1U77 0 213 704