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CIC-14 REPORT COLE~lON

REPRODU~lON

COPY

Classification changed to UNCLASSIFIED “

by authority of tke U. S. Atumic Energy Commissio~ #

BY REPORT LIBRARY

LAUS“ 507

SABLE

18 Date:

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M Date: 6

January31, S947 Thisdocumentcontains~ages

SFRE!IDOF RADIOACTIVECONTAMINATION

FROMA ‘i!OVUMLBURST ATOMICBOJkB

ReDortWritten By:

F. Reties

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●

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SPREAX)OF RADIOACTIVECONTAMINATIONFRO?4A TOWER-BURSTATOMIC BOMB%

F. Reines

pU1’DOSt?~. The pwpOSet Of this report is to -iew the ava~lable evidence on the spread of’radioactivecontaminationfrom an atomic bomb

burst on a tower in order to make clear the factors on which the

spread of contaminationdepends. For completenessother types of

damage are brieflydiscussed. This subject is being reopenedat

this time in connectionwith determiningthe feasibility-- from

the point of ~iew of the possibleeffect on the preservationof

American lives,well-being,and property-- of conductingphYsics

tests of atomic bombs within the continentalconfinesof the United

States. *

Tynes of Damage: In generalIt can be stated that by removingthe

test site a distance of 20 miles from the nearest populatedregion,

and by keeping the land and sky above clear of unauthorizedpersons,

then even for an explosionwith an energy release equal to that of

100 kilotons of TNT there will be at most minor glass breakage,and

this only if the ground contoursfavour focussingof the blast.

Except for the possibledepositionof radioactivematerialsand

of glass breakage,a distanceof 20 miles is more than adequateto

~–” ““”’’-’-–- ‘“

~O-insure protectionagainstdlldestructiveeffectsl~ earth shock$

~,

~%i

:=: mz ~.alrblast,prompt and delayed gammas and neutronsemitted from the

m-m ; 5—+-~~ -nuclearexplosion9incendiaryeffects9and any flying fragments.

$-o :

$~g ‘:

>@.~a ,1 With the possibleexceptior&@..tempa.raay-Qlindness if the bomb

~~em ,’vtewed at night from this d9.~ta!lc. _~&%omb gives off visible

—e radiationroughly equal to %~At&.%x=-for $ one second.

.- 1+

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Mtense irradiationconstitutethe only hazardwhich does not fall

off with distancein a reasonablypredictableway.

General Factor~on Which SJMead of ContaminationDenends:

In order to indicatethe factors on which the spreaddepends a

brief descriptionis given here of an atomic explosionin the close

proximityof the earth with specialattentionto the formationof a

crater9 the formationand ~ise of the ball of ftre and cloud, and its

subsequentdissipation. Comparisonis made between the Trinity test

with the M30-foottower and the projectedtests employing200-fo@ towers.

The nuclear explosfongives rise to an enormous incandescentball

comprisingthe vaporizedbomb, tower, and to soye extent, dtrt. The

maximum diameterreached by this ball of fire is about 2,000 fee@ $ as

given by the area fused at Trinity. A temperatureof abmt 1400°C XS

required to fuse Trinitydirt. The expanding’pressurepulse generated ~

by the tower-explodedbomb poundedupon the earth forminga compressloh

crater of about 1,000 feet in diameter,a figure which would not be .

substantiallyaltered by the increasedtower height. In the Trinity

test a surprisinglysmaZl drea of ground in the vicinity of tho tower

was disrupted. Light macadamr,’..dswere undestroyedto within approximately 150 feet of the centar. Disruptivecrateringshoulddepend

sensitivelyon the height of burst as will be discussedmore fully after

the generaldescriptionis completed. To anticipate,however,it is of

some importancethat the soil break-up be minimizedbecause of the

increasedrate at which the radioactivitytn the cloud may be expected

to settle’ifit containsstzchdust particles.

The Tower height in this case (100 ft) a$ i~a;~eoprosectedtest

(2@3 ft) fS small comparedwith the;~a:$~”o~;f~s~$ earth. LA-356.

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‘=3- 4

To continue,since the vaporize~:m~x@d&s& ~;bomb, towert and ) ● ● **● ● **● **● .

air is less dense than the surroundingair, it rises causingan enormous

updraft which sucks into the rising$ extremelyradioactivemateria19air

togetherwith whatever loose dust, dirt, and more solid debris exists

in the near vicinity. The particlesso drawn into the cloud, as the

cooling ball bf fire is called in its later stages, serve as centers

on which the radioactivenuclei condenseand deposit. These particles

of extraneous.matter become Intenselyradioactive,probablywith a

higher specificactivttythan the fused ground below the explosion.3

The cloud then assumes the shape of a mushroom,the head of which rises

to severalkilofeet,and drifts along carriedby the air currentsunti2

it is torn apart by cross-currentsand generallydiffuse$ throughoutthe

atmosphere. As it travelsalong there is a ‘traintiof radioactivedust

formed by condensation,some of which takes place on the tirt particles

sucked up into the cloud by the initialupdraft. It is expected that

# the radioactivedust particlesso formed would be larger than those

● condensingon dust nuclei present In the atmospherebefore the explosion

and hence will

expansionand

cool and hence

in. This rain

dry air on the

fall faster because in the later stages of the initial

when the updraft is still strong, the ball of fire is

not able to vaporizethe externaldust and dirt so drawn

will spread activity over a wtde area dependingin still

particlesize.

however,radioactiveparttcles

ously small region even in tile

If it rains in the conventionalway,

can easily be made to fall in a dangerabsence of large condensationnuclei.

An importantquestion arises at this point as to the subsequent

fate of’the radioactivecloud, assuming that the cloud reaches the

lower stratospherewithout appreciableactivitysettlingout. The

.

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moisture in the heated cloud compon~~t~~dy

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.

1

radioactivenuclei. The questiono~”~h~

● ●✟ ✎ ✎✎✎ ✎ .9*9 ●’-.6 .,

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n safelywide dispersionof the material

should M investigated. A difficultyin

radioactivitycenters about a lack of knowledgeof the sfzes of the

● ☛☛ —e ●

&ub&%/Y&~~”precipitationversus

by the substratosphericwinds

predictingthe fate of the

partlcloscondensingon dust particlesor other nuclei found in the air

prior t~ the explosion. Thts point mtght be investl~atedby expertment$

of the type discussedunder heading (b) except that they should be

perfomed in m atmospherecontainingvarious amounts of dust. It might

be add~!dthat the rate of settlingout of radioactivitycan certainlybe

.

alter~dby the presentsof a down draft. The results in the case of

Triniby4where no attemptwas made to keep the dust down are a cause

for ~larm. For exa?uple,a two weeks~ dose of from 5 to 10R, or, considering Lhe decreaseof intensitywith time, rough~y0.5 to 1.OR the first

day,was estimatedfrom necessarilyrough measurementas in evidence

t et a distance of 120 miles to the Meward.

~jye DetalIedConstderatluns~

●

(a) Keenln~ the dust down

.’

It seems clear that the first ftep in diminishingthe rapiddeposition of radioactivityfrom the cloud Is to prevent it from piokifigup

Mterial from the ground. Although jt is not very likely that a crater

wiil be formedby a bomb burst on tho 200-ft tower$ this point could

probablybe verified in some positivqway by small-scaleexperiments

with ordinaryhigh explosiveon the dependenceof crater formationon

. .-

the height of burst. The reason for checkingthis point is that the -

answer to the questionof whether OJInot there will be a crater governs

to some extent the treatmentwhich ;heground should recefveto help

APPROVED FOR PULBIC RELEASE

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of macadam and then lay in a criss-crossfashionas indicatedM Fig* Ia$b

a network of heavy,wooden timberswhich might be bolted togetherand

taeatedwith some fire-proofingagent.

F(G. i a m rkw FIG. fh J’/as J4EW

Such a scheme as this sn+ghtsuffice to keep the surface from breakingup.

The region outside the crater could be protected~ as learned mom

experience,with a standardmacadam surface such as previouslyused

at Trinity for roads~ If the region fr~ 15~ feet *O !$~ feet were ~~ t

surfacedand then cleanedwith a portablevacuum cleaner before the

9

shot$ dust ptckedup in the absence of the surfacingmight be eliminat@-

As seen from Trinity5,this Is importantbecause 2%$ of the dirt moved

from the region O to 1000 ft came from the region 150 to 1000 feet.

{b) ‘l’hesize of condensed Partfcles

‘Studieshave been made at Chit!aga(cFL362$II on the particlesizes

resultingfrom the condensationof vaporizedmaterials explodedby the

passage of high D-C currentsat temperaturesestimatedto

neighborhoodof 20,000°C. The particlesin a Pu-A1 smoke

like, havfng a mean diameter of#O.2 micron and a length

5 LA-3!%.

be in the

were chain6 of+l micron.

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6 Ce144 aerosolsproduc~~i~.d c&5&ti&c had a mean particlediameter

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for the rato of fall of pnrticleshaving a specificgravity > and

a diameterD microns.

Th.lsapp~oxlmatelaw i’{obeyed7reasonablywell for particlesbetw~en

~ and 3Cl}microns,althoughthe velocitydecreasesmonotonicallywith

radius,smallerparti!Lesfall more rapidly than it predicts.

Assumin/:with LA?JS-4;1?that & = z *6, the time for a particleof 5

.mlcronradius to fal; 20 kilofeet IS ~900 hours or=~40 days.

In qualitativesupportOf t~$ calculation~H*rschfelderand Mgee,

writing of the air ;hotat Bikini, saY M MMS-438: ‘~InAble shot.....

activematerialwa! depOsited ~n the water dropletswhich remained in

tte air. There w/s no evidenceof abnormal rain from the cloud or of

a trail of activ’materfal producedby a fall-out. Thfs was quite

d~fferentfrom ~hesituationat Trinitywhere active materialwas

I

depositedon ~ustPart~cleswhich fell aecerdlngto Stokefs law.”

8 If one ~~s~es t~t the partialesizes in an atomtc explosion

t{rewithin a ‘factorof lo of thomprtiuced by the Chicago group in their

tlerosolstnd.essthe radioactiveparticleswill remain aloft for many

cays. Pmhg thifitime they will become distributedthroughoutmany

lmndre~iso? even thousandsof cubic miles and so be rendered less harruful. The q~~~tionof the requireddilutionof plutoniumand fission

This }ointshould be studiedfurther to determinethe validity

f?the 8-~riorireasonableassumptionabout the similarityin particle

~.zeres~lttngfrom a bomb explosionand the vaporizationprocesses

● ,mployedby Chicngo,

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3.s not strictlyconstant:.:&WV#T ~0$116accuracyof this formulawill

sufficeffw the present”di~t?us~io~..:

b

here carefulcalculationmight

have as its startjngpoint”tMe StMhx+ mningham relation {CH-3629,pp 62-3).

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●

b

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this point regarding the

ASSIFIE9

si%e of gartlclos

which oan be picked up by filter paper, since tha successof this metlnd

cf efficiency determination at Bikini has been suggestedas evidenceof

large particlesizes. According to GH-3629, a test of a Navy-typs asbestos filter (manufacturedby A.ii.ThrxnasCo.), consisting of tcheets~ one in back of the others l?ou;~d99=9Y~of th~ gmrtf.clesin an

aerosol of mean diameter 0.1 to 0.2 m@ron oollected on the firgt sheet.

1’

‘?/ewill take this as indicative of tb smallest -particlesize effectively

caught. As seen above, such small partlmles rnmain suspended in the air

for a great lenGthof tiae during which enormousdilution can occuro

It is true, however, that in addition larger particles may have been.

cau~ht on the Bikini.filters even thugh t~ s~na~lp~rtic~~s twwed

naro sufficient fo3?the effi.clencyt.naaauromentsoIf possible,this

point should be investlgatedo

Plutonium\ Acoording to LA-591 the dally dose of plutonium which a

is safely tolerated by the body for a five-year period at eight houl’s

of exposure eaoh day is 5JC1CI”7micm~rams or an air pollution of 0.03s

counts/minute per liter of air. This extremely conservative figure

(probably by a facto??of Mo) under test conditions where unly a Um$ted

exposure would occurs corresponds to a uniform spreading of all the

unburnt plutonium over a region having a volume of approximately 200

cubic miles,

Fission Prwducts; A more serious pxwblem is that gn?esentedby ths

.

tission products. The figure accepted by the -.edlcalprofession from “

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8.

nakss for conditionsmore difficvl~~ ;~&8t%:”” ● em*:*.

4

:0

Except for a relativelysmalfi‘&G&t “&:O”/ ●:aetivity$the fission

product activityts due to YVS . These yes are emittedaccording

to a l/t1”2 law which 35 obeyedreasonablywell from secondsom

About 4 mev per fission is gtvon o~f in the form of y~a ~ 3.6 Mev coming

off in the first hour (LAMS-351)C This leaves 0.6 mev to be emitted

.

from 1 hour on.

The y source derksity~s, from an atomic explosionfrom 1 hour

ix) 3.s s z z . 6*I65 ev/cm3,where: f is the number of f’issions$

v and v the volume throughoutwhich

productsare assumed to be

uniformly distributed

for 100 kilotons,”f 2X~02~ fissions

As an ~entat~ calculationlet us assume a wtnd velocity of

20 miles/hr.so constructedthat it @kes 1 hour to spread the aotivity

uniformlyover a region 20 miles longq 10 miles wide and Y mtles high-

(Fig. 2.) JV

t 4 :- he+

The radiationflux I receivedby a person at point O will now be calculated on this assumption.

here s is taken as independentof r and the upper limit is taken

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as infinite?since mO +++~ ~.~s.~~~”l~ldst lo ma~n free paths. The

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; 5-WV Y‘S to 250 meters for~y~Swi@: a? @~g~Oo~ ~ Mev.

“:’16~“””““”‘“” Convertingto R units , R = 5~10 = 15. Allowingfor the

continuingdilutionof contamination,~ ~sition, this corresponds to an h- dose of~O.5 R (or 5 daily doses) fromyl to i=2hours,

where R/hr (at+l hours)*#”~ . Tht8 means that allowlngfor

dilution ( v~#t3, R ‘(1#) .(@*~ w@.2) ●

after a few days the daily dose under the above assumptionwill have

dropped to below 10-5 R/day.

The above result was obtainedunder somewhatartificialassumption

of uniform mixfng of the fissionproductswith air throughoutthe region

from ground level to an altitudeof some five miles, whereas it IS not

inconceivablethat most of the activity might be carried In the head

of the characteristicmushroomshaped cloud which reaches and may remain

at high altitudesfor hours or even days. The type of mixing and hence

source distributionspossiblecan only be realisticallygiven by an

I expert meteozmloglst. This mixing problem is crucial and should be “

, Investigated.

Trinitywould appear in the light of the previousdiscussionto

be as suitablea place as any to hold future atomic bomb tests. It has

the virtues of proximityto Los Alamos and existingcamp factlitlesas

well as the requtreddistancesfrom populatedareas, although the latter

po$.ntshould be re-investigated. In additton,the weather history of

Trinity is reasonablywell known because of its proxfmityto the Alamogordo

air base as well as the studiesmade in connectionwfth the first bomb

test. The behaviouragainst ~ratertngis also familiar because of past

experience.

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It should be emphasized,however~ that further studiesshould be

made along the lines indicatedin this report before any reliableanswer

can be given to the question of whether an atomic bomb can be safely

explodedon continental.U@ited States.

.,.

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