-d

United Nations Scientific Committee
on the Effects of Atomic Radiation

1977 report to the General Assembly, with annexes

NOTE
The report of the Committee without its annexes appears as Official Records of the General
Assembly, Thirty-second Session, Supplement No. 40 (A/32/40).
In the text of each annex, Arabic numbers in parentheses are references listed at the end.
The designations employed and the presentation of material in this publication do not imply theexpression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning
the legal status of any country, territory, city or area, or of its authorities, or concerning thedelimitation of its frontiers or boundaries.

UNITED NATIONS PUBLICATION
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Produced by UNIDO, Vienna

ANNEXBNatural sources of radiation

CONTENTSParagraphs

Paragraphs

INTRODUCTION •..••...•••••.•••..

1-6

II.

A.

I. EXTERNAL IRRADIATION •••••....
A.

B.

Cosmic rays • . • . • . . • • • • • • • • •1.
Primary cosmic rays . . . • • • . •(a) Primary galactic cosmic rays(b) Primary solar cosmic rays . •(c) Radiation belts ••••..••
l.
Secondary cosmic rays • . • • • • •3.
Ionization in the atmosphere .••4.
Cosmic-ray neutrons in the atmosphere .••••••••••••••..
5.
Tissue absorbed doses from cosmic
rays . . . • • . . . • • • • • • . • •(a) Ionizing component • . . . • .
(b) Neutron component .•••.
External radation from naturally occurring radionuclides (terrestrial radation)
1.
Source radionuclides . . . . . . • .
2.
Exposure outdoors ...•••••.
(a) Source-exposure relationships(b) Environmental
exposurelevels . . . • . . . . . • • • . .
(c) Variation of the absorbed
dose rate in air with time(d) Estimate of the average exposure level . • . • . . . • . . . •(e) Variability of the exposure(I) Areas with high natural radiation levels • • • • • • • . . • .
3.
Exposure indoors ••.•••.•..
(a) Activity of building materials(b) Source-exposure relationship(c) Estimate of the average in·door ·level of the air absorbed
dose rate in air . • . • • • . •(d) Variability of the absorbed
dose in air . . . . . . . . . . .
4.
T1Ssue absorbed doses from terrestrial radiation • . . • . . • • . . • .

7-77
7-38
8-20
9-15
16-17
18-20
21-25
26-27

B.

28-29
30-38
31-33
34-38

c.
39-77
39-43
44-64
44-45
46-48
49-52
53-55
56-57
58-64
65-73
66
67-71
72
73
74-77

78-20981-93
Cosmogenic radionuclides ••••.•.•
82-84
1.
Tritium . . . • . • . • • . • . • • •85-86
2.
Beryllium-7 ••••...••••••
87-90
3.
Carbon-14 .•••••••.•.•••
91
4.
Sodium-22 ..••••••.•.••
5.
Annual doses from internal irradia92-93
tion by cosmogenic radionuclides
Primordial radionuclides (except radon and its
short-lived decay products) • • • • . • • .
94-151
1.
Potassium-40 • • • • . • • • • • • •95-97
2.
Rubidium-87 • . • • • . . . • . • .
98
3.
Uranium and thorium series . . . .
99· l 51(a) Uranium • • • . . . . • . . • •102-016(b) Thorium . • . . . . . • ... . .
107-110(c) Radium . . • • • . . . • • • .
111-123(d) Long-Jived decay products of
124-151
222Rn • • • • • • • • • • • • •Radon-222, radon·220 and their short152-209
lived decay products .•••. ·..•••.•
152-207
1.
Inhalation . . . . • • . . . • • . • .
153-169(a) Exposure-dose relationship .
170-185(b) Exposure outdoors ••••••
186-204(c) Exposure indoors• ·•••••(d) Recapitulation of tissue ab222
sorbed doses fromRn,
22 0
Rn and their short-lived
205-207
decay products .•.•..••
208-2092.
Ingestion •••....•••.•••

INTERNAL IRRADIATION

Ill. RECAPITULATIONSORBED DOSESOFTISSUE

AB-••••....••.•••••

IV. TECHNOLOGICALLY ENHANCED EXPOSURES TO NATURAL RADIATION ..••
A. Enhanced exposures to cosmic rays
1.
Passengers in aircraft • . . . . . • •2.
Astronauts . . • . . . . . . . . • .
B. Enhanced exposures to naturally occur·
rins radionuclides . . . • • • . • . • . • .
1.
Radiation exposures due to coalfired power plants • . . • • . . . •210-213214-304
218-236
218-234
235-236237-272237-248

35

Paragraphs

Paragraphs

2.

3.
4.

Radiation exposures due to theindustrial use of phosphate products ••••••••.•••••...
(a) Doses arising from the use ofphosphate fertilizers • . . . •(b) Doses arising from the use ofwaste gypsum as a building
material • . . . • . . . . . . .
(c) Other pathways of exposure
Exposure to 2 2 2 Rn in natural gas
and natural-gas products ..••.•
Exposure due to the use ofbuilding
materials
containing
higher-than-average concentrationsof naturally occurring radionuclides . . • • . . . . . . . . . . .

249-261

Appendix. Radiation exposures from consumer
products . . . • • . . • . • . . • • . . . . . . .

254-256

Introduction . . . . • . . . . . • . • . .
1.
Radioluminous timepieces
2.
Other self-luminous devices . • . •3.
Uses of uranium and thorium . . .
4.
Electronic and electrical equipment . . . • • . . . . . . . . . . . .
5. Absorbed doses from disposal of
consumer products as waste •.•.
Conclusions • . • . • . . . . . . . . • . .

257-259260-261262-266

1.
Man has always been exposed to ionizing radiationfrom various natural sources. A distinguishing charac·
teristic of this natural irradiation is that it involves theentire population of the world and that it has been
experienced at a relatively constant rate over a very long
period of time. On the other hand, the exposure tonatural radiation sources varies substantially from place
to place and even locally, for example within one
building.

2.
The assessment of the radiation doses in man fromthe natural sources is of particular importance because
natural irradiation is the largest contributor to thecollective dose of the world population. Furthermore,
the study of the extent of the variation of naturalradiation with location is of practical interest, since it
may influence attitudes towards any additional exposure
caused by man-made sources.

274-304274-276277·29 l
292
293·298299·302
303
304

References

100-114Annex. in chapter IV, discusses situations in which theexposure to natural sources is enhanced as a result oftechnological developments. It is sometimes difficult toseparate normal and technologically enhanced radiation
exposure, since this separation depends on what is
considered to be a normal exposure. However, becauseof current interest, chapter IV considers several examples of what might reasonably be deemed technologicallyenhanced exposures, including those resulting from
irradiation by cosmic rays in aeroplanes, the irradiation
res1:1lting from the phosphate industry, and theirradiation due to the release of naturally occurring
radionuclides from coal-fired power plants.
6.
The exposures from widely used consumer
products are dealt with in an appendix. While theycannot be described as cases of technologically enhanced
exposures to natural sources, they present several
similarities to these exposures, and in many cases theradionuclides involved are naturally occurring.

The various natural radiation sources include:( a)External sources of extraterrestrial origin(cosmic rays) and external sources of terrestrial origin,
i.e., the radioactive nuclides present in the crust of theearth, in building materials and in the air;(b) Internal sources, comprising the naturally
occurring radionuclides which are taken into the humanbody. The concentration of a few radionuclides in thebody, such as naturally occurring 1 4 C and 4 K, arerelatively constant and independent of their concentration in diet or in air, because they are isotopes of
elements with practically constant specific activity,
which are homeostatically controlled in the humanbody. For the majority of the natural radionuclides, on
the other hand. these two conditions do not apply andtheir concentrations in the body vary according to theconcentrations in the environment.

°

4.
As explained in Annex A, the primary data
selected for this document are those that can be used inassessments of absorbed doses in various organs andtissues of the human body. In some instances the data
can be used directly in the calculations of dose; in othercases their use is indirect, constituting the basis for theassumptions used for the calculations.

In addition to the exposures to natural radiation
5.
sources experienced both outdoors and indoors, this

36

273

Page

267-272

Introduction

3.

Summary and conclusions . . . • . . . .

C.

1.

EXTERNAL IRRADIATION
A. COSMIC RAYS

7.
The high-energy radiations that enter the earth's
atmosphere from outer space are known as primarycosmic rays. When they interact with atomic nuclei inthe atmosphere, secondary particles and electromagnetic
radiation are produced, and these are called secondary
cosmic rays.
I. Primary cosmic rays
8.
The origin of the primary cosmic rays is still notcompletely determined. However, it is known that mostof the observed radiation originates in our galaxy. In
addition to the galactic cosmic rays, the sun produces
solar cosmic rays related to solar flares.

(a) Primary galactic cosmic rays
9.
Primary galactic cosmic rays largely cons_ist of
high-energy protons which enter the solar system frominterstellar space, together with 4 He ions in the
proportion of about lU per cent. Much smaller

proportions of heavier particles are also present, together
with electrons, photons and neutrinos. The energy
spectrum of the primary cosmic-ray protons has beenmeasured both in and above the earth's atmosphere bymeans of instruments carried on balloons and spacecraft.
The energy spectrum is peaked around 300 MeV per
particle and is very broad, extending from about 1 to
10 14 MeV. Above about 1000 MeV, the proton flux
density decreases markedly with increasing energy.
Primary cosmic-ray protons with energies above
100 MeV are believed to be essentially of galactic origin,while those with energies below 20 MeV are of solar
origin ( 187).
10. Although all cosmic rays with energies below 10 12
MeV have their origin within the galaxy (59), the detailsof their origin are not yet known. From the elemental
distribution present, it is thought that cosmic-ray nuclei
are synthesized in supernova events, and are subsequently accelerated by undetermined processes, forwhich several theories have been postulated. From theabundance in primary cosmic rays of Fe, Co andNi nuclei, some of which have undergone decay byelectron capture, it is inferred that there is a time lapseof more than one year between nucleosynthesis andacceleration to high energy (59). The average ·'age" ofgalactic cosmic rays reaching the solar system, whichalternatively may be called the escape lifetime from thegalaxy, can be estimated from the abundance of 10 Be
and 36 Cl. The most recent measurements indicate alifetime between 2.5 l 0 6 and 33 I 0 6 y (235).
11. From measurements of the products of thereaction of high-energy cosmic rays with nuclei(spallation products) in meteorites, estimates have been
made of the changes in cosmic-ray flux density withtime. Within a factor of two, the galactic cosmic-ray flux
density has remained constant over the past 109 y (304).
The flux density averaged over the past 400 y is within
10 per cent of that averaged over the past 4 10 5 y,which in turn 1S some 50 per cent higher than that
averaged over the past 109 y. This latter variation may
be due to a cosmic-ray gradient perpendicular to thegalactic plane.
12. Within the solar system, the galactic cosmic-ray
flux density increases with increasing distance from thesun. The radial gradient of the flux density has been
determined from spallation products in meteorites (304)
and more recently by direct measurement on board thePioneer I O and 11 spacecraft (225, 227). For cosmic-ray
particles with energies above 30 MeV per nucleon, theisabout+ 5 per cent per AU
gradient(1 AU= 149.6 10 6 km).
13. Below 10 4 MeV, the primary flux density is
modified by two processes. In the first, it is affected by
the earth's magnetic field, which deflects lower-energy
charged particles back into space. This effect isdependent on the geomagnetic latitude. so that the flux
density of low-energy protons at the top of theatmosphere is greater at the poles than in equatorial
regions. Thus, the ionization produced at a given altitudein the atmosphere, which is a function of the"atmospheric depth". the mass of air above a unit ofarea at that altitude, is also latitude dependent (fig. I).

14. In the second process, the flux density of thegalactic low-energy protons in the upper atmospherevaries with the 11-year solar cycle, the flux density being
at a minimum during times of maximum solar activity
and p~sing through a maximum during the period of
low solar activity. The phenomenon is known as
modulation (89, 313). The modulation of galactic
cosmic rays with the solar cycle has been observed formany years. It has been proposed that it is due to changes in
the flux of magnetic bubbles (large volumes of ionizedgas) of solar origin (256). Solar flares blast open theoverlying solar magnetic field, thus enabling corona
particles access to the interplanetary medium, the large
bubbles so formed moving away from the sun withvelocities of200-1000 km s- 1 •15. During the I I-year solar cycle the density of thesemagnetic bubbles in interplanetary space undergoes acyclical change, reaching a maximum during increased
solar activity and a minimum during the period of thequiet sun. Because galactic cosmic-ray particles withenergies less than 104 MeV are deflected away from theinner solar system by these magnetic irregularities, an
I I-year modulation of the galactic cosmic-ray flux
density is produced at the earth.

(b) Primary solar cosmic rays
16. Solar flares are observed as bright flame-likeprotuberances on the sun's surface which reachmaximum brightness in about 10 min and then slowly
subside (74). They tend to occur more frequently during
periods of sun-spot maximum. Large amounts of energy
in the form of visible, ultraviolet and x-radiation are
emitted, and in the largest flares large quantities ofcharged particles, mainly protons and alpha particles, arealso released. Measurements indicate that most of the
protons have energies in the range 1-40 Me V.
17. Because the solar cosmic rays from solar flares
have relatively low energy, they do not usually causesignificant increases in radiation doses at the earth's
surface. In fact, between 1942 and 1962 only 13 flares
produced observable effects in the lower atmosphere( 150). However, large flares can increase the absorbed
dose index rate in the upper atmosphere by a factor of
about 100 for short periods of time.
( c) Radiation belts
18. There are two radiation belts. often called the Van
Allen belts, situated between 1.2 and 8 earth radii above
the equator. The lower belt extends to latitudes between
30° and 60° north and south (3, 129). The outer belt is
confined more to low-latitude regions. The energetic
particles, mainly protons and electrons, with some alphaparticles in the outer belt, are trapped in these belts by
the earth's magnetic field. They spiral along the lines ofmagnetic force, being reflected back and forth owing to
the increased convergence of the magnetic field towards
the polar regions.
19. The inner radiation belt consists mainly of protons
with energies from several to several· hundred megaelectronvolts, the peak flux density being at about
37

500

..,'E .:i~

v

z

"'1-

z <
g-

400

300

200

100

0

10

ALTITUDE

20

I
30

tm

,o2
ATMOSPHERIC Of PTH

Figure I. Variation of ionization 'with altitude and atmospheric depth at different geomagnetic
btitudes. Based upon the results of Neher (253)

50 MeV, and electrons with a flux density that is fairly
flat over the energy range 100-400 keV. The maximum
proton flux density is about 4 10 4 particles cm - 2 s -i ,and this occurs at a height of about 1.5 earth radii overthe equator (3). In the outer belt, the proton energies
are mainly in the range 0.1-5 Me V, most of the particles
being in the low-energy region. The outer belt also
contains electrons and to a lesser extent alpha particles(3. _129). The flux density in the radiation belts is fairly
co.nstant in time, but does change with the flux densityof primary cosmic rays during the 11-year solar cycle(129).
20. It is believed that the origin of most of the moreenergetic particles in the inner radiation belt is the decayof cosmic-ray albedo neutrons (233). The high-energy
38

primary cosmic-ray protons collide with atoms in the air
to produce neutrons by knock-on {direct) reactions,with energies between 1 and 1000 MeV, or bycompound nuclear reactions that produce evaporation
neutrons with energies of about 8 MeV. Many of theseneutrons escape from the atmosphere either directly, if
their energy is high. or by diffusion, if it is low. Theseescaping n~utrons are called albedo neutrons: they decay
to protons and electrons in an average time of 1000 s,
and since these particles are charged, they will spiralalong the flux lines of the earth's magnetic field. They
are reflected back along the magnetic lines of force inhigh-latitude regions where the magnetic flux lines
converge. If the height where the reflection takes place,termed the image height, is above the atmosphere. theparticles will remain trapped in the earth's magnetic field

(129). The origin of the particles in the outer belt is lesscertain. Since there is an alpha-particle component, it isthought that some of the particles are of solar origin.
2. Secondary cosmic rays
21. When primary cosmic-ray particles enter theatmosphere, those with higher energy undergo nuclear
reactions with nuclei of atoms present in the air.
producing neutrons, protons, pions and kaons. Thosewith lower energy lose energy by causing ionization.
Many of the secondary particles have sufficient energy
to initiate whole sequences of further nuclear reactions
with nitrogen and oxygen nuclei. The initial high-energy
reactions are called spallation reactions and quite avariety of reaction products (cosmogenic nuclides) areformed, such as 3 H. 7 Be, 10 Be, 22 Na and 24 Na.
22. The important initial secondary cosmic-ray particles are high-energy protons, neutrons and pions, manyof which react further with nuclei in the air to form
more secondary particles (100, 277). As this processcontinues. the number of secondary particles builds up;
such a process is called a cascade. The pions decay into
muons or photons, initiating other cascades.
23. The protons and neutrons contribute significantly
to the absorbed dose index rate in the upper
atmosphere. The neutrons lose energy by elastic
collisions, and when thermalized they are captured by
14
N to form 14 C. Because nucleons rapidly lose energy
by ionization and nuclear collisions, the nucleonic flux

density is considerably attenuated in the lower part of
the atmosphere and at sea level accounts for only a few
per cent of the absorbed dose index rate.
24. At lower altitudes in the atmosphere. the major
contribution to the absorbed dose index rate is provided
by the muons produced by the decay of charged pions at
higher altitudes and by the associated collision electrons.
Since muons have only a small cross•section forinteraction with atomic nuclei, have a mean life at restof 2.2 µs before decay into electrons, and move largely
at relativistic velocities, they penetrate quite effectively
into the lower layers of the atmosphere and throughstructural building materials (30 l ). Electrons are also
produced by muon decay. by ionization due to othercharged particles and in electromagnetic cascade
processes. Except in the lower layers of the atmosphere,
electrons are the main contributor to the absorbed doseindex rate.
25. The flux densities of all cosmic-ray particles
undergo variations in time due to modulation over thesolar cycle, the effects of solar flares and changes inatmospheric pressure or temperature. The approximate
amplitude variations expected from these various effects
are shown in table 1. It should be noted that the flux
densities of various secondary cosmic rays at a given
altitude depend primarily on the atmospheric depth (seeparagraph 13). However. for the purposes of radiationdose estimates, atmospheric depth is converted into
altitude (in kilometres) in this report, assuming astandard atmosphere.

TABLE 1. AMPLITUDE AND PERIOD OF THE TIME VARIATION OF COSMIC-RAY FLUX DENSITY

Source of variation

Cosmic.ray
component

Altitudeabove
sea level(km)

Latitude(Nand S)

Relative
amplitude(JOO ti N/N 0lPeriodReference

11 y

253
253
89
313
313

Hours
Hours

74,301
301

0
3.5
0

> 50°
>5()°
>5()°
> 50°
> 50°

25
20

0
0

>5()°
()° .9()°0-400
0-10 OOO

Atmospheric pressure
variations

Muons
Neutrons
Charged particles
Neutrons

00

0° .9()°()° .9()°

< 10
< 15

Days
Days

Atmospheric temperature
variations

Muons

0

<f -90°< 5

1ySolar modulation

Solar flares

Charged particles
Charged particles
Muons
Neutrons
Neutrons

9

5.5

22
16

5

)

54

Source: Reference 249.
aTotal amplitude of variation relative to "normal" or average flux density N 0 •3. Ionization in the atmosphere
26. Many measurements of cosmic-ray ionization at
various altitudes have been reported. The ionization rate
per unit volume in free air is a measure of the flux
density of the total charged-particle component of thecosmic-ray field and is usually expressed as the numberof ion pairs formed per second in each cubic centimetreof air at normal temperature and pressure (NTP) (9, 95.
96, 210. 291, 312). As figure I shows, ionization in theatmosphere becomes increasingly latitude-dependent

with increasing altitude. The ionization also varies overthe solar cycle, being greatest during solar minimum andsmallest during solar maximum (213, 254).
27. For estimating the absorbed dose index rate ataltitudes above sea level, use was made of themeasurements of Neher (254) over Thule, Greenland.
between 1954 and 1959. of Raft et al. (291} made atlatitude 54°N in 1969. and of George (95). who mademeasurements at altitudes of 400 and 1500 km in 1969.
Lowder and Beck (210) also reported ionization
39

measurements in the lower atmosphere up to an altitude
of about 3 km. In its 1972 report, the Committee
discussed inconsistencies in some of the earlier
measurements, particularly the differences between themeasurements of George (96) and those of Lowder andBeck (210) and Shames and Liboff (312). A value forthe ion-pair production rate of 2.14 cm - 3 s -l was usedas the average ionization at sea level. Lowder andO'Brien (213) adopted a value of 2.0-2.2 cm - 3 s- 1 • For
the purposes of computing the absorbed dose index rate.
a value of 2.1 cm- 3 s- 1 will be assumed in this report.

4. Cosmic-ray neutrons in the atmosphere
28. Most of the dose delivered by low-energy neutrons
arise from capture reactions such as (n, -y) and (n, p).
while for high-energy neutrons it comes from knock-on
protons. Since the significant part of the cosmic-ray
neutron energy spectrum extends from 10- 1 to some
10 9 electronvolts, some knowledge of its shape isnecessary to compute the dose from neutrons.
29. As discussed in the 1972 report, a number ofcalculations have been made of the neutron differential
energy spectrum at different altitudes. In general, these
agree with measurements made of neutrons in the range
1-10 MeV at various altitudes. Merker et al. (234) haverecently reported balloon and aircraft measurements ofneutrons in that energy range during the period
1964-1971. These results agree well with the data tl1at
was used to compute neutron doses at higher altitudes in
the 1972 report. Light et al. (201) have carried out
Monte Carlo calculations of the neutron energy
spectrum and normalized their results using theexperimental data of Merker et al. (234). These authors
assessed the neutron production rate averaged over asolar cycle to be 4.0 cm 2 s- 1 •5. Tissue absorbed doses from cosmic rays
30. Traditionally, two quantities that are useful for
estimating dose rates from cosmic rays have beenmeasured, the ionization in air and the ne~1tron flux
density. Since the radiation quality of these twocomponents is different, the absorbed dose index rates
from the ionizing and neutron components will betreated separately. The absorbed dose index rate can beassessed from measured ionization in and above theatmosphere, and from measurements of particle flux
density and energy spectrum. The contribution fromthe neutron component can be calculated from data on
the neutron flux density.

(a) Ionizing component
31. The estimation of the absorbed dose rate in air
from the ionizing component of cosmic rays isstraightforward. Assuming each ion pair requires 33.7 eV
to be produced, the absorbed dose rate for an ionization
rate of 1 cm- 3 s- 1 is 1.50 µrad h- 1 • Using the value forthe ionization rate at sea level of 2.1 cm- 3 s- 1
(para. 27), the absorbed dose rate in air is 3.2 µrad h- 1 •40This value is quantitatively equal to the absorbed doseindex rate at ground level. Using reported values ofionization in the upper atmosphere, absorbed dose index
rates have been computed there in a similar manner andare shown in figure II (347). Kolb and Lauterbach (191)have recently reported measurements in the lower
atmosphere with both an ionization chamber and ascintillation spectrometer. The ionization chamber
results agreed with those reported by Lowder and Beck(210), but the measurements with the scintilla tor wereconsistently higher.
'
32. At sea level about 75 per cent of the ionization isfrom muon collision electrons, 15 per cent from muon
decay electrons and 10 per cent from other electron,
proton and neutron processes (249). As the absorbed
dose index rate is reduced by about 30 per cent by
50 g cm - 2 of material, mostly due to attenuation of theincident electrons, a building may provide substantial
structural shielding.
33. If this structural shielding effect is not taken into
account, the annual absorbed dose in human tissues D isgiven by(see Annex A). where Cc =8.76 mrad µrad- 1 h: q = l:and b 1 is the outdoor absorbed dose index rate. With avalue of b 1 of 3.2 µrad h -i (para. 31 ), the annual
absorbed dose in human tissues from the ionizing
component of cosmic rays at sea level is approximately
28 mrad.

(b) Neutron component
34. The dose rate from the neutron component wasderived in the 1972 report from computed absorbed
dose rates in 30-cm tissue slabs. As indicated in
Annex A, the absorbed-dose index rate is used in thisreport to describe cosmic-ray irradiation conditions.
Hajnal et al. (112) found that the variation of dose ratewith depth, 0-15 cm, for the bilateral incidence ofcosmic-ray neutrons on a 30-cm slab was not very great.
The maximum dose rate (at 1 en'!) was only 6 per centgreater than the average for 0-15 cm. For a 30-cm
sphere, the dose rate would be expected to be- even more
uniform, and so for cosmic-ray neutrons it can beassumed that the absorbed dose index rate is the same as
the average absorbed dose rate computed from the
30-cm slab. The factor to convert neutron flux density
to absorbed dose index rate is 4.93 µrad h- 1 cm 2 s(112).
35. A number of data on the cosmic-ray neutron flux
density at sea level were reported in the 1972 report,
varying from 0.0065 to 0.018 cm - 2 s -i • A neutron flux
density of 0.008 cm -l s -, was adopted for the purposeof estimating doses at high latitudes. Using theconversion factor from the previous paragraph, theabsorbed-dose index rate is 0.04 µrad h -i. This value isin good agreement with tissue absorbed dose rates
calculated by O'Brien and McLaughlin (263).
36. The annual absorbed dose in human tissues at sea
level and at latitudes above 40°, calculated by the

-----0------------~I.

IONIZATION

I

r
I

.

10'~

C

w

:<
X

w
0

1

:!:
w

~

l

0
0
w

"'0a:
en

"'<

10 1

NEUTRONS--- -'=----~-1-- -t-ii--~---x.. ··+..... .,

X

iffli Kolb lion. CNimbers)J~ Kolb hcin1,U.uion)(l 9 0*Ml ltvel- G<to<go (96)
O G«,rge (95)
IONIZATIONNth••• Neher

CJ

J12541\

X Raft (2911• Greenh~ll

0 Greenhill

NEUTRONS

J

(l06)

\

\\

X Haymes 1127)• Boelb 1381
c:, O'Brien (262.2631~ Jenkin$ {1691

10 3

\

\

\
\

10'

\

\

\

\

::J

10•

10•
ALTITUOE

Figure II. Absorbed dose index rates at high geomagnetic latitudes {-50°) from the ionizing and neutron componentsof cosmic rays at different altitudes for 1969 {solar maximum) and 1965 {solar minimum) (347). The ionization
component of the absorbed dose rate at 10- 1 km is inferred from that at ground level

expression given in paragraph 33, is therefore 035 mrad.
In equatorial regions, the annual absorbed dose in
human tissues is about 0.2 mrad (347).

a higher absorbed dose index rate with a much higher
contribution from neutrons in the high-energy region
above 10 MeV. However, there is some question as tothe validity of this spectrum in the high-energy region

37. Although at sea level the neutron absorbed doseindex rate is quite small, it increases rapidly withaltitude, reaching a maximum at altitudes between 10
and 20 km. Measured neutron flux densities at various
altitudes reported in the literature differ in the energy
range they cover, latitude and time in the solar cycle.
These reported values were normalized for these factors,
using a published energy spectrum ( 112) to assess thetotal flux density from the reported values. The
absorbed dose index rates were computed using a factorof 4.93 µrad h -t cm 2 s to convert the neutron flux
density to the absorbed dose index rate, and are shownplotted in figure II versus altitude.

(88).

38. Foelsche et al (88) have recently computed thedose-equivalent rate from cosmic-ray neutrons at highaltitude using a new energy spectrum that does not drop
off so quickly in the high-energy region as that used in
the 1972 report. The use of this new spectrum results in

B. EXTERNAL RADIATION FROM NATURALLYOCCURRING RADIONUCLIDES (TERRESTRIAL

RADIATION)
1. Source radionuclides
39. Radioactive nuclides have always been present in
the natural environment. The decay of naturalradionuclides produces alpha particles. electrons andelectromagnetic radiation. Because the human organs
and tissues in which the doses are calculated for the
purposes of this document are shielded by at least a few
millimetres of tissue, which absorbs practically all of theenergy of the alpha particles and electrons given off by
the natural radionuclides, only the gamma contribution
will be considered here. It is worth noting, however, that41

the skin and, to a lesser extent, the lens of the eye, beingat or near the surface of the body, receive higher doses
than the tissues and organs of primary interest to theCommittee.
40. The natural radionuclides in the environment areof two general classes, the primordial and thecosmogenic. The cosmogenic radionuclides are mainly
produced through interaction of the cosmic rays withtarget atoms in the atmosphere and. to a much lesser

extent, in the earth. The three main cosmogenic
contributors to external exposure at ground level are
7
Be, 22 N.:-. and 24 Na.
41. Among the primordial radionuclides, the main
contributors to external exposure are 4 °K and theradioactive series headed by 2 3 3 U and 2 3 2 Th, which arepresented in tables 2 and 3. Potassium-40, 2 3 3 U and232
Th are long-lived radionuclides that have existed in
the earth's crust throughout its history.

TABLE 2. RADIOACTIVE DECAY PROPERTIES OF THE 238 U SERIES
M4ior radiation m~s (M• VJ and inr.nsitks
Hlsrorical

Nuclide

':;u
1

l

tTh

1

~mPa

99.87%

Half-II/•Uranium I

4.51 10' y

UraniumX 1

24.1 d

0.103
0.193

(21%)
(79%)

0.063
0.093

(3.5%)(4%)

Uranium X,

1.17 min

2.29

(98%)

0.765
1.00)

(0.30%)(0.60%)Uranium Z

6.75 h

0.5'3
1.13

(66%)
(13%)

0.100
0.70
0.90

(50%)
(24%)
(70%)

Uranium II

2.47 10 1 y

Jonium8.0 JO' y

4.15
4.20

6

'l'

(25%)
(75%)

0.13%
1

HPa

1r,u

!

1::Tb

1

l

Radium

URa

!

1

llRn

1

l

~Po

99.98%

1602 y

4.72
4.77

(28%)
(72%)

0.053

(0.2%)

4.62

4.68

(24%)
(76%)

0.068
0.142

(0.6%)(0.07%)

4.60
4.78

(6%)
(95%)

0.186

(4%)

0.510

(0.07%)

0.295
0.352

(36%)

0.609
1.120
1.764

(47%)
(17%)
(17%)

Emanation
Radon (Rn)

3.823 d5.49

(100%)

Radium A

3.05 min

6.00(-100%)

Radium B

26.8 min

0.33 (-0.019%)

0.02%

:~;Pb

L_J.
"l~Bi
99.98%

LJ·
l

0.65
0.71
0.98

Astatine

-2s

6.65
6.70

(6%)
(94%)

Radium C

19.7 min

5.45
5.51

(0.012%)(0.008%)RadiumC

164µs

7.69

(100%)

0.02%

:UPo

RadiumC'

1.3 min

(50%)

(40%)
(6%)

J.0
1.51
3.26

(23%)
(40%)
(19%)

0.799 (0.014%)

1.3
1.9
2.3

(25%)
(56%)
(19%)

0.296
0.795
1.31

(100$)
(21%)

(85%)
(15%)

0.047

(4%)

Radium D

21 y

3.72 (.000002%)

0.016
0.061

lJBi

Radium E

5.01 d

4.65 (.00007%)
4.69 (.00005%)

1.161 (-100%)Radium F

138.4 d

nLJ·

l~~

1

i;Pb

RadiumE"

4.19 minRadium G

StableSource: Reference 288.

5.305

(19%)

(-0.1%)

:l!Pb

1

42

a

name

(100%)(80%)

0.803 (0.00 II%)

1.57) (100%)TABLE 3. RADIOACTIVE DECAY PROPERTIES OF THE•° KAND THE 131 Th SERIES
M,qor rod/4tlon •n•,rles (Me VJ and irtun:ities
Historicalnam•

NucUd~

Hal{-Uf•

/l

"
1.32

1.26 10' y

7(89'Jl\)1.46(l l'Jl\)

89.3%
0
•

c2

StableThorium

1.41 10" yMesothorium 1

5.8 y

0.055 (100$)

Mesothorium II

6.13 h

1.18
1.75
2.09

Radio thorium

1.910 y5.34 (28'Jl\)
5.43 (71'Jl\)

0.084 (I.6'Jl\)
0.214 (0.3'Jl\)

Thorium X

3.64 d5.45 (6'Jl\)
S.68 (94'Jl\)

0.241 (3. 7'Jl\}

Emanation
Thoron (Tn)

55 s

6.29 (IOO'Jl\}o.ss (0.07'Jl\)

Thorium A

0.15 s

6.78 (100%)Thorium B

10.64 hThoriumC

60.6 minThorium C:

Thorium D

6.0S (25'Jl\J6.09 (IO'Jl\}

304 nsThorium C:'

3.95 (24%)
4.01 (76%)(3S'Jl\)
(12$)
(12$)

0.34 (15'Jl\)
0.908 (25'Jl\)
0.96 (20'Jl\)

0.346 (Sl'Jl\}
0.586 (14%)

0.239 (47'Jl\)
0.300 (3.2'Jl\)

I.SS
2.26

(5'Jl\)(55%)

o.04o en>

1.28
1.52
1.80

(25%)
(2l'Jl\)(SO'Jl\)0.511 (23'Jl\)
0.583 (86'Jl\)
0.860 (12'Jl\)
2.614 (100%)0.727 (7'Jl\)
1.620 (l.S'Jl\)

8.78 (IOO'Jl\)

3.10 minStableSource: Reference 2118.

42. The concentration of the primordial radionuclides
in soil is determined by the radioactivity of the sourcerock and by the nature of the processes which had been
involved in the formation of the soil. Table 4 shows
typical natural concentrations in common rocks (249).
In igneous rocks, the concentration of radioactive
nuclides is related to the quantity of silicates, being

highest in acidic rocks and lowest in the ultrabasic rocks.
Igneous rocks generally exhibit higher radioactivity thansedimentary rocks, while metamorphic rocks haveconcentrations typical of the rocks from which they
were derived. However, certain sedimentary rocks,
notably some shales and phosphate rocks, are highly
radioactive (249).

TABLE 4. TYPICAL ACTIVITY CONCENTRATION OF 4 °K, 138 U AND mTh
IN COMMON ROCKS AND ESTIMATED ABSORBED DOSE RATE IN
AIR 1 m ABOVE THE SURF ACE

Typical activity
concentration (pCi g-•)Type of rockIgneous
Acidic (e.g; granite)
Intermediate (e.g. diorite)
Mafic (e.g. basalt)
Ultrabasic (e.g. durite)
Sedimentary
Limestone
Carbonate
Sandstone
Shale

Absorbed dose
rate in air

h-·,

40K

2l•u

1317h

27

1.6
0.62
0.31
0.01

2.2
0.88
0.30
0.66

12
6.2
2.3
2.3

0.75
0.72
0.5
1.2

0.19
0.21
0.3
1.2

2.0
1.7
3.2
7.9

19
6.5
4.0
2.4
10
19

(µrad

Sources: References I, 353.

43

43. The concentration of radionuclides in soil, which
is directly relevant to the outdoor exposure, is that of
the rock from which it is derived, diminished by theleaching action of moving water, diluted by increased
porosity and by added water and organic matter, andaugmented by sorption and precipitation of radionuclides from incoming water (250). ·Jl extensive studyof the mean concentration of the natural radionuclides
in soils of various types in the Soviet Union ( 188) showsthat there is a regular trend for all the naturalradionuclides which partly reflects the extent of
bio-geochemical reworking of the original soil-forming
rocks (table 5). It should be noted. however, that theTABLE S. AVERAGE ACTIVITY CONCENTRATION OF
4°K, 238 U AND 232 Th IN VARIOUS TYPES OF SOIL
AND ABSORBED DOSE RATE IN AIR I m ABOVE
THE SURF ACE
0

Average activity
concentration (pCi g· 1)

Absorbed
doserote in air

Type of soil

•oK

23au

n2 711

SerozemGray-brown
Chestnut
Chernozem
Gray forest
Sodpodzolic
Podzolic
Boggy

18
19
15
11
10
8.1
4.0
2.4

0.85
0.75
0.72
0.58
0.48
0.41
0.24
0.17

1.3
l.l
1.0
0.97
0.72
0.60
0.33
0.17

7.4
6.9
6.0
5.1
4.1
3.4
1.8
1.1

10
3-20

0.7
0.3-1.4

0.7
0.2-1.3

4.6
1.4-9World average
Typical range"(µrad h"')Sources: References 18, 107, 188, 249, 353.
avalues based on data contained in references 18, 107
and 353.

main factor influencing the concentration of the naturalradionuclides in soil is not the soil-forming process but
the corresponding concentration in the soil-forming
rocks. Table 5 also includes an estimate of the averagesoil concentration on a world-wide basis (249), as well as
typical ranges of values reported in the literature (18,107,353).

TABLE 6. ABSORBED DOSE RATE IN AIR 1 m ABOVEGROUND FOR A REPRESENTIVE SOIL CONTAINING
UNIT ACTIVITY CONCENTRATIONS OF 40 K, :, 1 U
AND232Th

0.16
1.58
2.45
Source: Reference 24.
All the decay products of 2 3 • U and 2 ' 2 Th are assumed
to be in radioactive equilibrium with their precursor.
4

their precursors. This assumption, which is reasonable
for rocks. is not strictly valid for soils, since(a) differentiation may result from the soil-forming
process and biological reworking and (b) a fraction of
the radon produced in the soil escapes into the soil air
and diffuses into the atmosphere from the upper soil
layers.
45. The conversion factors of table 6 were used to
calculate the absorbed dose rates in air above the rocks
and soils for which typical concentrations were given intables 4 and 5 (last column). The main contributors to
the absorbed dose rate in air are 2 0 8 TI and 2 2 8 Ac in the
2 32
Th series, while for the 23 8 U series, about 99 percent of the dose rate is due to 214 Pb and 214 Bi. which
are short-lived decay products of 2 2 2 Rn. The gamma
rays that these nuclides emit range in energy up to
2.6 MeV and are partly absorbed in the soil. For atypical natural radiation field, the layer of soil whichmakes the predominant contribution to external
irradiation above the ground is about 30 cm thick(fig. III).
per cent

w 100
I-

<{

a:
a:

UJ

:i

80

Cl)

0
c..
X

UJ

.J
<{

2. Exposure outdoors

Dose rate (µrad h" 1 per pCi g·•)Radionuclidea

60

I-

0

IUJ

(a) Source-exposure relationships

I 40
Iu.

0

44. Methods of calculation of the absorbed dose rate
in air 1 from the radionuclides present in the atmosphereand in the soil are discussed in references 26, 86, 142

z

0

~

20

(.)

<{

a:

and 237. Table 6 presents the absorbed dose rates in air
I m above ground for a representative soil containing
unit activity concentrations of the natural radionuclides,
assumed to be uniformly distributed with depth. The
representative soil is described by its density, 1.6 g cm- 3,
and its constituent concentrations (weight per cent):
SiO:z. 67.5; Ah 03, 13.5; Fe203, 4.5; C02, 4.5; H2o,10.0. The absorbed dose rates in air have been calculatedusing the assumption that all the decay products of
23 8
232
U and
Th are in radioactive equilibrium with

Figure Ill. Calculated relative contribution of naturally
occurring radionuclides to the total exposure rate I m above theground. as a function of soil thickness (24)1
As indicated in Annex A, the absorbed dose rate in air isused in this report to describe environmental exposure situations
resulting from gamma-emitting radionuclides and is unambigu·
ously specified, assuming full equilibrium in air.

46. In recent years, several surveys have been
performed over whole countries and areas for the
purpose of estimating the exposure of the populations of
those countries and areas to natural radiation (table 7).

44

u.

I

0

5

IO

15

20

25

cm

SOIL DEPTH(b) Environmental exposure le~·els

TI

i.
TABLE 7. ESTIMATES OF THE AVERAGE ABSORBED DOSE RATE IN AIR 1 m ABOVE GROUND LEVEL FROM TERRESTRIAL RADIATION
Based on country· and area-wide surveys

Country
or area

Estimated
populationa
Area
in 1975(/0 3 km 1)(IO'J

Austria
German Dern. Rep.

17

10

84
108

Averageabsorbed
dose rate
in air(µrad h. 1)

5.0
9.1

Germany,
Fed. Rep. of
India

62
633

246
3 282

5.9
3.6b

Italy
Japan
Poland

56
110
35

301
370
312

4.lb

Switzerland
United States

7
219

41
7 985

7.4
4.5

Island of Taiwan

12

36

6.0

7.2
5.8

Number ofmeasurements> I OOO
1 005> 20 OOO
35 stations
sampled
1 365
16 stations
sampled
Not indicated25 areas
coveredc
26

Type of survey and instrumentation used

Reference

Ground survey with a Geiger-Millier counter
Ground survey with an ionization chamberand scintillation dosimeters

343

Ground survey with scintillation dosimeters
Analysis of soil samples by gamma spectrometry

189
239

Ground survey with an ionization chamber
Analysis of soil samples by gamma spectrometry
Ground survey with gamma spectrometers

53
374
269

Ground survey with an ionization chamber
Aerial survey with gamma spectrometers

128
261

Analysis of soil samples by gamma spectrometry

362

264

aWith the exception of the island of Taiwan, the population estimates are taken from table A.6.1 of United Nations Population

Studies No. 53 (348).
bcaiculated from the average concentration of 40 K. 231 U (or 226 Ra) and 232 Tb in soil using the conversion factors given in table 6.
c Including approximately 30 per cent of the population.

The results are not altogether coherent as regards thequantity measured, which in practice is the quantity forwhich the measuring device was calibrated. Someauthors report exposure rates, others, absorbed dose
rates in air, and still others, "tissue doses in free air".
Unless the measuring conditions are well specified, thequantities are often ambiguous, and intercomparisons
between different investigations may be difficult.
47. The surveys were conducted using various methods
and types of instrumentation. In the United States ofAmerica, aerial surveys were made in which an array oflarge NaI(Tl) crystals was flown in an aircraft at altitudesof 100-150 m above the terrain (50). This method was
also used in other large countries, such as Canada (349)
and the Union of Soviet Socialist Republics (188), but inthese cases the results have not so far been used toestimate the average dose to the country's population.

48. Ground surveys were conducted in the othercountries listed in table 7. Direct ( or in situ)
measurements were made in Austria. German Democratic Republic, Germany, Federal Republic of, Italy,
Poland and Switzerland, the detectors being Geiger-Miiller
counters in Austria, ionization chambers in the German
Democratic Republic, Italy and Switzerland, gamma
spectrometers in Poland. and scintillation dosimeters
especially developed for the purpose in the Federal
Republic of Germany. In India and Japan and on theisland of Taiwan, soil samples were taken over wide areas
and then analysed by gamma spectrometry in alaboratory.
(c) Variation of the absorbed dose
rate in air with time
49. One common aspect of the surveys is that thevariation with time of the absorbed dose rate in air was
not taken into account. The most significant changes

with time are associated with variations in the amount ofsnow cover and soil moisture and in the atmosphericconcentration of 2 2 2 Rn decay products.
50. Snow cover introduces an effective shielding of
gamma radiation from ground sources; a 20-cm blanket
of typical snow brings about a reduction of about 50 per
cent in the exposure rate (250). As a result, a strong
seasonal pattern in outdoor exposure rates is observed inregions with significant snowfall (218, 270), as shown infigure IV. It may be noted that. for a given thickness ofsnow, the value of the absorbed dose rate in air depends
on whether the snow is accumulating or melting. The
reason is that the soil moisture content is higher during
thawing than during the period of snow accumulation(273). the influence of soil moisture content is
discussed in paragraph 51.
51. Changes in soil moisture content affect soil bulk
density. so that the absorbed dose rate in air above theground decreases with increasing soil moisture content.
For the 238 U series. however, this effect is superimposed on a change of 2 2 2 Rn emanation, which
generally decreases with increasing soil moisture content.
The absorbed dose rate in air from this decay chain istherefore essentially independent of soil moisture, as theshielding effect and the increased source effect roughlycompensate (250). For 4 °K and the 232 Th series, theabsorbed dose rate in air is significantly reduced by soil
moisture. Data reported by Beck et al. (26) show thatthe total external terrestrial annual doses in air in a given
area during dry years generally average about 20 per centmore than those for wet years.
52. As a result of variations in the stability conditionsof the lower atmosphere, the night-time concentrationsof 2 2 2 Rn decay products in the air near the ground areusually a few times higher than those existing during theday (250). Beck (25) has calculated the gamma absorbed
dose rate in air from atmospheric 2 2 2 Rn decay products
45

µR h- 1 Erken
15

snow
cover

10

5

50cm

O..L..~..q..:.._.....o!!~~4-.i----':..l..~4-ii---'f-..i..-'...~-4--i--4....~'+--.a........,~....~oµR h- 1 Torslanda

Total external exposure
Exposure level, summer 1960 and 1961
- · - · - · - · Average exposure from cosmic rays................... Snow cover (scale on the right)

Figure IV. Exposure rates 2.S m above ground and monthly averages of snow cover in Sweden,
1960-1971 (218. 336)

at I m above the ground for four different conditions ofatmospheric stability. The values are 0.05, 0.1, 0.3 andI µrad h -l for strong mixing, normal turbulence, weakmixing, and strong inversion conditions, respectively. It isbelieved that usually the absorbed dose rate in air fromatmospheric 2 2 2 Rn decay products is approximately
0.1-0.2 µrad h- 1 •( d) Estimate of the average exposure level
53. The average absorbed dose rates in air at 1 m
above the ground given in table 7 are, in the case ofFederal Republic of Germany, German Democratic
Republic, Italy, Japan and Switzerland, populationweighted, i.e., the values obtained in the subdivisions of
the country have been weighted according to their
population. In the case of India and Poland, the figures
are the reported or arithmetic averages. while for theisland of Taiwan, the average absorbed dose rate in air
has been calculated from the average concentration of4°K, 238 U and 232 Th in surface soil. Although thesurveys did not take into account the variation ofabsorbed dose rate in air with time, and differed widelyin the type of instrumentation used and in the number
and type of measurements, the average absorbed dose
rates in air obtained fall within the relatively narrow
range of3.6-9.l µrad h- 1 •54. The population-weighted average absorbed dose
rate in air for the surveys listed in table 7 is
4.3 µrad h- 1 • The population involved is about 30 per
cent of that of the world. and the value could beconsidered to be roughly representative of the world
population exposure. The areas covered by the surveys,
however, represent only 2 per cent of the total land areaof the world and all are located in three separate regionsof the northern hemisphere. It is conceivable that therest of the world population might live in areas where46

the absorbed dose rate in air is very different from
4.3 µrad h- 1• However, the result based on the estimateof the world-wide average concentration of primordialradionuclides in soil is 4.6 µrad h -l (table 6) and thus,
in the absence of contradictory evidence, the Committee
believes that a value of 4.5 µrad h -I is a reasonableestimate. on a global basis. of the outdoor averageabsorbed dose rate in air, 1 m above ground. fromterrestrial radiation.
55. As to the cosmogenic nuclide contribution toexternal irradiation, if the concentration of 7 Be, 22 Na
and 24 Na are taken as 7 10-2 • 10-5 and210-s pCi m- 3 • respectively (168. 378). the corresponding absorbed dose rates in air are about 3 1o-6 ,10-s and 6 10-s µrad h- 1 • An estimate can also bemade of the total dose rate from all the otherradionuclides produced by cosmic rays. From theexisting experimental determinations of the ·atmosphericproduction rate for 2 4 Na, the estimated production
rates for some of the short-lived radionuclides, and thecross-sections for the very short-lived radionuclides ofJess than 10-s half-life, it can he calculated (250) that forevery disintegration of 2 4 Na at ground level there arel 0 6 disintegrations of short-lived cosmogenic radionuclides. Assuming an average gamma energy of I Me V
per disintegration, the absorbed dose in air from theshort-lived cosmogenic radionuclides would be of theorder of 0.02 µrad 11- 1 • The contribution of all theradionuclides produced by cosmic rays to the absorbed
dose rate in air is therefore insignificant compared to thecontribution from the primordial nuclides in the ground.
( e) Variability of the exposure
56. The variability of the exposure around the meanvalue can be roughly assessed from data from some ofthe surveys listed in table 7. The surveys in four of theIcountries. each with a population of more than
50 million people, provided the average doses for the
populations of their administrative subdivjsions: the 11
Lander of the Federal Republic of Gennany, the 20
regions of Italy, the 22 districts of Japan. and the 50
states and capital district of the United States. The
populations of those subdivisions range from 0.1 to20 million people.
57. The frequency distribution of the population overabsorbed dose rate in air is presented in figure V for eachof the four countries, and in tigure VI for the four
countries taken together. If the volcanic regions of Lazio
and Campania of Italy are excluded. the combined dataof figure VI are fitted rather well by a Gaussian
distribution, as shown in figure VII. Thus, for the four
countries considered, a large fraction of the population
lives in areas where the population-weighted distributionof the outdoors absorbed dose rate in air is nonnally
distributed, while another fraction, much smaller. lives
in areas outside of the nonnal distribution. The averageabsorbed dose rate in air in the ·'nonnal" areas of the(b) Italy(a) Federal Republic of Germany

50

50

45

45

40

40

35

35

30

30

25

25

20

20

15

15

1-

10

10

a

5

5

...J

<l'.

>
a:
w

z

<l'.
w

z
z

0

0
j::
<l'.

2

3

4

5

6

7

8

0

4

6

7

6

8

9

nn
13

14

16

17

µrad h- 1

...J

::::>
a.
0
a.

(d) United States of Americau..

0(c) Japan

w

50

w

z

45

45

a:
w
a.

40

40

35

35

30

30

25

25

20

20

15

15

10

10

5

5

CJ
<l'.
1-

u

0

2

50

3

4

5

6

7
8
µrad h-l

0

2

3

4

5

6

7
8
µrad h- 1

Figure V. Population-weighted distribution of absorbed dos~ rates in air from terrestrial radiation in four countries

47

ri

-

l

t

I

20

r
I

-

I

15 C

- -

l

10

l
I

I

~

-

-

n

"l

I

10

11

12

13

U.

15

n

IS

t7

18

~ft-lJ

Figure VI. Frequency distribution of outdoor absorbed dose rate in air fromterrestrial radiation. Combined data from the Federal Republic of Germany, Italy,
Japan and the United States. (The isolated bars on the right represent data fromthe Italian regions of Lazio and Campania)

radiation would live where the outdoor absorbed dose
rate in air from the primordial radionucli9es falls
between about 3 and 7 µrad h- 1 • However. it should beborne in mind that these values are themselves averages,
corresponding to population groups of at least 10 5people .

. .
w

<

"'

§

(f) Areas with high natural radiation levels

"iS
z

i"'

58. As indicated above, there are regions in the world
where the outdoor absorbed dose rate in air substantiallyexceeds the range mentioned in paragraph 57. In
addition to the Italian provinces of Lazio and Campania,
such regions are known to exist in Brazil. France, India,
Iran, Madagascar and Nigeria ( 45). The best known
from a dosimetric point of view are those located in
Brazil and India.

90·

isu

..
z
:r

10

~

i

;;

SQ

;;;

:::
"~

:,)

;::
~

~
~
w

10

:!"

~

u

"'r
1,

t,,radh~,,Figure VII. Cumulative frequency distribution of the outdoo1
absorbed dose rate in air from terrestrial radiation. Combined
data from the Federal Republic of Germany, Italy, Japan andthe United States. (The data from the Italian regions of Lazio andCampania have not been included)

four countries is 4.85 µrad h -i, with a standard
deviation of 1.1 µrad h -I. Assuming that the distribution holds on a global basis, 95 per cent of the world
population residing in areas of "normal'' natural
48

59. Deposits of radioactive minerals occur in littoral
formations along the coastal regions of India. Of
particular interest is· a stretch about 250 km long andabout 0.5 km wide on the south-west coast in the statesof Kerala and Tamil Nadu. These deposits are rich inmonazite. which contains principally 2 3 2 Th and its
decay products together with several rare earths; themonazite deposits are admixed with ilmenite, rutile,
sillimanite and zircon. The most concentrated deposits
along the Kerala coast are located on a 55-km strip
populated by about 70 OOO persons. where the thorium
concentration in the monazite ranges from 8.0 to
10.5 per cent by weight, being the highest known in theworld (103). Additional features of this area are that it
has defmable geographical landmarks. with the backwaters sepqrating this strip from the mainland. and it
supports a high density of human population. Further
south, another coastal strip about 2.5 km long in thestate of Tamil Nadu also has high concentrations ofmonazite.
60. In a radiometric survey carried out in the late
1950s, measurements of gamma exposure rates weremade at the main entrance of 200 houses selected at
random in the 55-km strip of Kerala coast describedabove. Values varied widely between houses, demonstrating the rather patchy distribution of monazite along
the coastal strip. On the basis of these measurements, it
was estimated that the average absorbed dose rate in air
from terrestrial radiation in the region was about
130 µrad h -I (103).
61. Two types of high-background regions have beenfound in Brazil: the monazite sand region along theAtlantic coast of the states of Espirito Santo and Rio deJaneiro and the volcanic intrusive anomalies along ageological fracture that extends from the coast throughthe inland state of Minas Gerais (274). Weathering anddecomposition of archeogneisses in the mountain rangethat parallels a long extension of the Brazilian Atlantic
coast produced a natural separation of very insoluble
and hard minerals. such as ilmenite, zirconite andmonazite. Grou~d to fine particles and carried downstream by many rivers emptying into the ocean: theseminerals underwent stratification and were deposited on
fluvial and marine regions (274). The radiation levels inthree towns (Guarapari, Meaipe and Cumuruxatiba) built
over monazite sands along the Atlantic coast weresurveyed in detail by Roser and Cullen (299). Guarapari
is a town of 12 OOO people which receives an influx ofabout 30 OOO vacationers every summer. In that town,
the absorbed dose rates in air were found to range from100 to 200 µrad h- 1 in the streets and up to2000 µrad h- 1 over selected spots on the beach (275,299). Meaipe is a fishing village of about 300 people,
situated 50 km to the south of Guarapari, where theradiation environment is similar: the average absorbed
dose rate in air is about 100 µrad h- 1 with levels up to
1000 µrad h- 1 (274). In Cumuruxatiba, the average levelis 50 µrad h- 1 (299).
62. In the state of Minas Gerais. two volcanic regions
have been intensively studied, Po9os de Caldas andAraxa-Tapira. Near the city of Po9os de Caldas stands ahill where absorbed dose rates in air of up to2800 µrad h- 1 have been reported. However, this hill issmall and uninhabited. The radioactivity of the
Araxa-Tapira region originated from an alkaline
intrusive, the mineralization consisting mostly of apatite.
The radioactive components occur almost exclusively inthe form of pyrochlore, a mineral containing up to
60 per cent niobium oxide, 1.9 per cent thorium oxideand 13 per cent uranium oxide (274). In Araxa-Tapira,absorbed dose rates in air up to 400 µrad h -, have beenmeasured.
63. Information on the tissue absorbed doses in the
populations living in areas of high external terrestrial
radiation in Brazil and India are given in paragraphs 76
and 77.

64.

Quantitative information on the outdoor absorbed
dose rates in air in other areas of high natural radiationlevels is very scarce. In the city of Ramsar, Iran,absorbed dose rates in air ranging from 200 to5000 µrad h -t have been measured within an area of afew square kilometres, characterized by the presence of
22 6
Ra-rich spring water (181). In France, absorbed dose
rates in air of 200 µrad h -I are not uncommon and avery localized value of 10 OOO µrad h- 1 has been
discovered (71).

3. Exposure indoors
65. Knowledge of radiation levels in buildings isimportant in the assessment of population exposure, as
most individuals spend a large proportion of their timeindoors. However, large-scale surveys of indoor exposure
are still relatively few compared to those conducted
outdoors.
(a) Activity of building materials
66. Information on the radioactivity of building
materials is still scarce. Table 8 presents the results ofinvestigations which have been conducted in the Federal
Republic of Germany, Sweden. the United Kingdom ofGreat Britain and Northern Ireland and the USSR. The
range of concentrations found in a given type ofcommonly used building material is very wide, but the
average values obtained in the four countries arereasonably close. Wood and materials used for thermal
insulation, with the exception of the light-weightaggregate used in Sweden, are of low radioactive
content; natural plaster and cement are also relatively
low. while granites, bricks and concrete are in the upper
part of the range.
{b) Source-exposure relationship67. Estimates of indoor exposure could be derived
from the activity concentration of the various building
materials. their dimensions and distribution in thebuilding, the geometrical conditions of irradiation andthe radiation field outdoors, although it would be
extremely difficult to take all those variables irlto properaccount. Furthermore there is not yet sufficient
irlformation available on the activity concentrations of
natural radionuclides in the various building materials.
Therefore, the average absorbed dose rate in air irldoors
has been estimated from the outdoor values using
conversion factors accounting for the type of basic
building material used. These conversion factors are
based mainly on the results of the few surveys that have
involved at least about one hundred dwellings (table 9).
The conversion factors take into account that building
materials act both as sources of radiation andattenuators of outdoor radiation.
68. The importance of the shielding effect of building
materials can be estimated from figure III. If the densityof the soil is assumed to be 1.6 g cm - 3 , a wall thicknessof 50 g cm - 2 absorbs practically all of the radiationfrom outdoors and a thickness of 10 g cm - 2 is sufficient
to absorb half of it. Therefore. the transmission ofradiation through the walls will only play a significant
role in light constructions such as wooden or
prefabricated houses.
69. The shielding effect is clearly seen in wooden
houses. for which the source effect is negligible. Surveys
conducted in Australia (377) and in the United States(202, 211, 376) have shown that the indoor absorbed
dose rate in air on the ground floor of wooden houses isabout 75 per cent of that measured outdoors. One floor
above ground level, the values are lower by a further
10-20 per cent (202, 376). In prefabricated houses made49

TABLE 8. CONCENTRATION OF 4 °K, 2 26 Ra AND 2 32 Th IN BUILDING MATERIALS AND ABSORBED DOSE RATE IN AIR
Average activity concentration(pCl g-'J

..K

226Ra

232n,

Absorbed
dose
rate in air(µrad h-'f

16
20
17

2.6
2.6
1.5
1.4

2.6
3.4
1.0
1.2

26
33
16
16

327
335
194
117

15
19

1.8
1.3

1.7
2.3

19
21

327
335

9
15
14
14

1.5
0.9
2.0
2.0

1.9
0.8
0.9
0.8

17
12
15
15

335
194
194
117

5.2
6.3
6

1.2
1.5
1.2

1.2
1.5

1.2

11
13
8

327
204
194

2
0.6
10
4

<0.5
0.09
0.25
0.6

<0.3
<0.04
0.17
0.2

< 4
< 1
5
4

327
335
194
117

2
7

33
40
28

2.6
3
2.4

2.2
4.5
2.3

30
46
28

327
194
117

20
13

29
18

3.0
2.6

3.4
2.0

35
24

327
194

20
296
3

1
22
22

<0.5
1.3
1.4

<0.5
1.9
0.1

< 5
20
12

327
111
117

so

Natural sand and sand rejects

Germany,
Fed. Rep. of
USSR

7
7.1

< 0.4
0.63

<O.S
0.5

< 6
7

327
194,
195

Wood
Rock and silica wool
Rock and silica wool
Lightweight aggregate

SwedenSwedenUnited Kingdom
Sweden

1
2
2
10

6

0.4

0.4

< 0.4
5

27

3.9

4.3

42

142
335
117
335

Type of building material

Country

BricksGermany,
Fed. Rep. of
SwedenUSSR
United Kingdom

BricksRed bricks
Qay bricks
Concrete
Heavy concrete
Aerated concrete without alum
shale
Heavy concreteLight concrete
Concrete
CementNumber ofsamplesGermany,
Fed. Rep. of
SwedenSwedenUSSR
USSR
United Kingdom
Germany,
Fed. Rep. of
SwedenUSSR

CementCementNatural plaster

Germany,
Fed. Rep. of
SwedenUSSR
United Kingdom

Natural plaster
Plaster
Natural plaster
GraniteGraniteGranite bricks
Pumice stone
Tuff
Limestone and marble
Rock aggregate
Rock aggregate
Gravel and sandGermany,
Fed. Rep. of
USSR
United Kingdom
Germany,
Fed. Rep. of
USSR
Germany,
Fed. Rep. of
SwedenUnited Kingdom

132
21
SS
23
69

15
22
87
16

5
19
8

7
23
4

I
69
34

32

25

negligible

ReferenceaAssuming 4,r-geometry and infinite thickness, and using the conversion factors given in table 6. The values obtained are anindex allowing the comparison between building materials and not an estimate of the doses that would be received in dwellings
constructed with those building materials.

TABLE 9. RESULTS OF SURVEYS OF THE INDOOR ABSORBED DOSE RATE IN AIR DUE TO TERRESTRIAL RADIATIONCountry

GermanDemocratic
Republic

Number of
dwellings

480 in old
buildingsa
187 in newbuildingsa

Germany,
Fed. Rep. ofso> 20 OOO

Type of building

Indooraverageabsorbed
dose
rate in air(µrad h- 1)

Brick (old)Brick (new)Half-timbered (old)Store (old)
Mixed construction (new)Prefabricated (new)

7.2
6.5
7.6
11.2
5.7
5.9

Solid
Frame
Prefabricated (concrete)
Wood

6.8
6.9
4.2
4.2

Populationweighted
averageabsorbed
dose rate
in air(µrad 1r-1J

}

7.4

} 6.8

/ndoontooutdoon
ratio

}

}

Population•weightedindoon-tooutdoon
ratio

Ref·
erence

0.78

264

1.3

192

r
I

j"

Number of
dwellings

Type of building

Indooraverageabsorbed
dose
rate in air(µrad h"')

823
594
609

Wood
Concrete
Brick

7.1
10.5
11.9

Poland37
49
11

Concrete
Prefabricated (fly-ash and slag)
Brick

4.9
6.4
5.7

Swedenb

259
126
365
93
43

Wood (old)Wood (new)Brick (old)Brick (new)Concrete (new)

5.1
4.8
10.6
10.6
12.5

United Kingdom

71
155
103
172

Solid

110
160

Wood
Wood

Country

NorwayUnited States{ ,edunent,zy ,ocl< (D,nde,J

se~entary rock (Edinburgh)
granite (Aberdeen)
granite (Aberdeenshire)

Populationweighted
averageabsorbed
dose rate
in air(µrad h"')Indoorstooutdoors
ratio

Populationweighted
indoors-tooutdoors
Refratio
erence

329
0.73
1.1

271

142
241
142
241
241

7.6
6.8
9.7
9.4

1.07
1.24
0.82
1.17

320

3.9c

0.75
0.70

203
211

0

01d: built before 1945. New: built after 1945.
bTwo surveys have been conducted in Sweden, one in 1956 a:td one in 1976. The buildings surveyed in 1956 are referred to as
old. A large percentage of the buildings surveyed in 1976 are likely to have been built 'after 1956 and are referred to as new.
cMedian value.

out of concrete and in wooden houses it has been
determined in the study conducted in the Federal
Republic of Gennany that absorbed dose rates in air
indoors are lower than outdoors, the average reduction
being 3 per cent for the prefabricated houses and 6 percent for the wooden houses (189).
70. In the other types of houses, outdoor radiation isalmost completely shielded by the walls. This has been
demonstrated in various studies (264, 376) in which it
has been observed that the levels are about the same on
various floors of a given masonry building. Therefore, inthese dwellings. the indoor levels cannot be compared tothose outdoors unless the building materials are of local
origin. If the concentration of radioactive substances in
the ground of a given locality is equal to that in building
materials, the absorbed dose rate in air might be
expected to be somewhat less than twice as large indoors
as outdoors, as a result of the change of source
geometry. However, correction coefficients should beapplied allowing for the presence of windows and doors(195), which makes the ratio much smaller than 2.
Direct determinations of these correction coefficients
have not been reported.
71. An estimate of the average indoors-to-outdoors
dose ratio in masonry buildings may be obtained fromthe extensive country-wide study from the Federal
Republic of Germany, in which nearly 30 OOO
apartments were surveyed. Preliminary infonnation
indicates that the average ratio of the indoors-to-outdoors
absorbed dose rate in air is about 1.3 (192). Assuming
that, on the average, the radioactive content of thebuilding materials is about the same as that of the soils,
roads and pavements around the building, the conversion
factor between the indoor and the outdoor absorbed

dose rates in air for masonry buildings would then be
about 1.3. This figure is in reasonable agreement withthe results of the United Kingdom study (320) but ishigher than those obtained in the German Democratic
Republic (264) and Poland (271). However, each ofthese three surveys involved less than l OOO dwellings,
and the conversion factors derived from their results
might be less representative than that obtained from thecountry-wide study conducted in the Federal Republicof Gennany, where all types of dwellings were included.

(c) Estimate of the average indoor level of theabsorbed dose rate in air
72. Assuming that the proportion of wooden buildings(dwellings, offices, factories, shops, theatres etc.) isabout 20 per cent of the total and taking the average
ratio of the indoor to the outdoor absorbed dose rate in
air to be 0. 7 and 1.3 for wooden and masonry buildings,
respectively, the average indoor absorbed dose rate in air
would be 18 per cent higher than that outdoors.
Therefore, the indoor absorbed dose rate in air, averaged
over the world, is estimated to be about 5.3 µrad h -I.

(d) Variability of the absorbed dose rate in air
73. Indications on the variability of the indoor dose
rates in relation to the average may be derived from thesurvey conducted in the Federal Republic of Germany(189, 192). As in the case of the outdoor absorbed dose
rate in air. the population-weighted distribution seems to
be normal (fig. VIII). The mean value of the indoor
absorbed dose rate in air is 6.7 µrad h -i, and its
standard deviation. 1.0 µrad h -l, while the corresponding values outdoors are 4.9 and 0.5 µrad h -t. The
51

0

"'
<
;!,
....

~

<

"'w

.

ill
0

~
"'

i<

!IO

z"'

o
z

0

~

@

70
"'"'u0z<....,: so

s"
....
le

30

"'uw
~

0

;;
z
;:

0

10

s
2
:,

~
~
~

ffiu

1

(D
@

"'

~

OUldoat abs.orbed doM! rate: ,n 1ir

indoor absorbf'd dow n~ in air

ABSORBED DOSE RATE IN AIR

Figure VIII. Cumulative frequency distribution of the absorbed
dose rate in air measured in the Federal Republic of Germany(189, 192)

outdoor coefficient of variation in the Federal Republicof Germany is about half of the value derived for global
conditions (para. 5 ,'). Assuming that the same relation
applies to the indoor coefficient of variation, it istentatively estimated that 95 per cent of the world
population would be subject to indoor absorbed dose
rates in air ranging from 2 to 9 µrad h - 1 •4. Tissue absorbed doses from terrestrial radiation

74. From the analysis contained in Annex A, theannual gonad absorbed dose D can be derived from theabsorbed dose rate in air Da as
D = (cqDa)outdoors + (cqDa)indoors

where c, the conversion factor from the absorbed dose
rate in air to the gonad annual absorbed dose, is taken as
7 .2 mrad µrad -l h for outdoor exposure and 6.0 mrad
µrad -l h for indoor exposure, and q, the occupancy
factor, is estimated in a later paragraph to be
0.8 indoors, and thus 0.2 outdoors.
75. From
Da = 4.5 µrad h -I
outdoors
and5.3 µrad h -l indoors, it can be estimated that the annual
gonad absorbed dose from external terrestrial radiationis, on average, 32 mrad: 95 per cent of the world
population would receive annual gonad doses in the52

range of 21 to 43 mrad. The doses in other organs ofinterest to the Committee are nearly equal to the gonad
dose. The annual collective dose from terrestrial
radiation, for the present size of the world population, isof the order of 10 8 man rad.
76. Populations living in areas of high externalterrestrial radiation, such as those of Brazil and India,
incur much greater tissue doses. Relevant informatiof!
has been obtained in both countries by means ofthermoluminescent dosimeters distributed to a fractionof the population. Gopal-Ayengar et al. (102. 103)
carried out a .dosimetric survey on the 55-km longcoastal strip described in paragraphs 59 and 60, which
was selected on the basis of high exposure rate, definablegeographical boundaries and high population density.
From results for a sample of 8513 individuals, theaverage annual tissue absorbed dose for the 70 OOO
people residing in the region was estimated at 380 mrad.
It was estimated that about 24 per cent of the people
experienced annual doses in excess of 0.5 rad, about
6 per cent exceeded I rad and about 0.7 per centexceeded 2 rad.
77. On the Brazilian coast (see paragraph 61), Cullen( 63) determined· the average annual tissue dose fromexternal terrestrial irradiation for a group of 317
inhabitants of Guarapari to be 0.55 rad, with a range of
0.09-2.8 rad.

II. INTERNAL IRRADIATION
78. Radioactive nuclides occurring in the biosphere
enter the human body through ingestion and inhalation.
In order to assess the doses from internal exposure in theorgans and tissues of interest to the Committee (lung,gonads, red bone marrow, and endosteal cells), twotypes of information are necessary: (a) the concentration of radionuclides in the organs and tissues
mentioned above and also in neighbouring tissues, suchas bone and yellow marrow, and (b) the dosimetricfactors linking the concentrations to the dose rates. The
following paragraphs deal with the estimation of therelevant dosimetric factors and their application.
79. If a radionuclide emits only one type of~onoenergetic particle per disintegration, the dose rate
D; in an organ or tissue i, can be assessed from theexpression:

D; = "£/Pe(i, j)q
wher~ E is the energy of the particle, q the activity
concentration of the radionuclide in organ or tissue jthat may contribute to dose in tissue i, and '{)£ (i,j) is thedosimetric factor, quantitatively equal to the dose-rate
contribution in tissue i from a unit activity concen·
tration in organ j. In the case of beta decay, the same
expression is valid, provided that there is only one
transition in the decay scheme. The energy E, in thiscase, would be the average energy of the beta particles
emitted in the transition. In the most general case,several types of radiation with several energies are
emitted. The dose rate in organ i becomes

D; = "ik"i:.Efk. E°'i/h,E(i, i)qwhere lk,E is the yield of particles including photons oftype k of energy £ per disintegration, and '{)k,E(i, l)represents that contribution to the dose rate in organ or
tissue i from a unit activity concentration in organ jwhich is due to particles of type k and energy E.
80. The dosimetric factors, symbolized as tp(i.j/-iandj being the target and the source organs, respectively-are
given as a function of energy in figures IX, X, XI and XIL
separately for the three types of radiation (alpha, beta,
gamma) encountered in internal exposure from naturalradionuclides. Four target organs have been considered,namely, the lung. the gonads, the red bone marrow, andthe bone lining cells, which are defined as the cells lying
on endosteal surfaces of bone (mainly trabecular),assumed to form a layer I O µm thick. In the case of thealpha emitters, the dosimetric factors relating theactivity concentration in bone to the dose rates in redbone marrow and in bone lining cells have been
estimated for two types of distribution, (a) distnbution

0.18

throughout the bone matrix and (b) deposition on bone
surfaces. For gamma emitters, two types of distribution
in the human body have been considered; (a) uniform
distribution over the whole body and (b) preferential
distribution in the skeleton. In the latter case, which isthat of the bone seekers, the dosimetric factors havebeen calculated using the assumption that the low
activity present in the soft tissues is distributed over thewhole body and is superimposed over the distribution in
the skeleton. Although most of the dosimetric factors
given here can be used for humans of any age and sex,
they apply strictly to adult man. They have been derived
from published models (147, 318, 319. 321).

A. COSMOGENIC RADIONUCLIDES
81. Very little of the dose from natural background iscontributed by the cosmogenic radionuclides. Of themany nuclides produced by cosmic rays. only 3 H, 7 Be,

RM - red bone tn1trowT- lrabe-cular bone
BLC - bone lining celtsG- gonods
L

-

lung

0.15
op(L,LI
op(RM,RMI

0.1

0.05

-- ----

O.Q2--- --------- --- --·----

op(RM,T.!_.----•

0.01•------ -·--

9

MoV

Figure IX. Dosimetric factors for alpha-emitting radionuclides (mrad y - 1 per pCi kg- 1 )The subscript s denotes that the alpha emitter is assumed to be distributed on the bone surfaces. The
absence of subscript indicates that the alpha emitter is assumed to be uniformly distributed
throughout the whole matrix

53

;~(RM.RMI

/

G
L

-

RM BLC -C
10 10"'"'-

p::,,NIChlungr..:I boftl marra.
bont liming c:a111
boN

co""*'

VJ.I-

yello-borw marrowT-

ntbK\11,r bot9

/ ,.,aLC.SKl

BLC -boM lin"'9 c:tfll

SK

-

RM

-

sk.!•tcm
red bona num,1111

G
L-.......
lung//,;IBLC.CI.;iBLC.RM)--------· -~tB-LC.TI

I
I
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

/

/

/

/

/

/

/

/
,ptRUSK)

I

/,

Ii

0.1

0.2

0.3

O..t

.i

o.s

0.6

0_7

1.0

0.9

0.8

Mt>V

AVEflAGE BETA ENERGY

Figure X. Dosimetric factors for beta-emitting radionuclides(mrad y • 1 per pCi kg·•)

,

"

/

,///""~'G
WB - wtiolil-bodv
RU - red borw marrow
BLC - br:wlt Umno arll1
L- 11.#'11

,

,'

,I

'

Q_

D.1 0.2

0,5

''

''

,''

''

''

'

0,6

1,5

3

PHOTON ENERGY

Figure XII. Dosimetric factors for several tissues for
gamma-emitting radionuclides located in the skeleton (mrady·• per pCi kg·•)

14
C and 22 Na contribute appreciably to the dose. The
production and distribution of these nuclides in theenvironment is presented in table JO.

/

''

1.5

PJotOTON ENERGY

Figure XI. Dosimetric factors for gamma-emitting radionuclides
distributed uniformly over the whole body (mrady·• per pCi kg"')54

0.1 0.2

I. Tritium
82. Tritium. 3 H, is produced naturally in theatmosphere, lithosphere and hydrosphere. The production of man-made 3 H in nuclear explosions andnuclear reactors is discussed in Annexes C and D. The
major source of natural 3 H is the atmosphere, where it
results from the interaction of cosmic-ray protons andneutrons with nitrogen, oxygen, and argon, the main
reaction being 14 N+n-+ 12 C+ 3 H forEn>4.4MeV.
Estimates of the inventory, calculated from publishedvalues of the production rate, range from 17 to 170 MCi(table I I), the most recent estimates being 34 MCi and
28 ± 7 MCi (197, 340). It has been suggested that 3 H
might also be ejected from the sun during solar flares(199) and from stars (83), but the contribution to theinventory from these sources has not been evaluated.
83. About 99 per cent of the 3 H inventory isconverted to HTO and participates in the normal water
cycle. According to the data contained in table l 0, mostof the 3 H inventory, which is taken to be 34 MCi, would
be in the ocellns, as a result of transport by rain and by...v

TABLE

10. DATAON

THE PRODUCTION AND DISTRIBUTION OF
OCCURRING 3 H, 'Be, 1 • C AND 2 2 Na

NATURALLY

'H

'Be

uc

Half-life
Number of atoms produced per unit timeand per unit area of the earth• s surface(cm- 2 s- 1 ) in the:Troposphere
Total atmosphere12.3 y53.6 d5 730 y8.4 10-2
0.25

2.7 10- 2
8.1 10-2

Global inventory (MCi)

34

1

300

0.01

Distribution as a percentage of inventory in the:Stratosphere
Troposphere
Land surface and biosphere
Mixed oceanic layers
Deep ocean
Oceanic sedin1ents

6.8
0.4
27
35
30

60

0.3
1.6
4
2.2
92
0.4

25
1.7
21
44
8

8
20
0.2

2.62 y2.4 10-s
8.6 10-s

10-s

7 10- 2

Activity concentration in surface air (pCi m · 3)b
Activity concentration in continental
surface waters (pCi 1- 1)c

11

1.1
2.3a

,,Na

6-24

Specific activity in terrestrial biosphere(pCi g- 1)d

6.1

Source: Reference 197.
aReference 200.
b Reference 190.
cReferences 52, 178.
dReference 330a.

TABLE 11. PUBLISHED RATES OF PRODUCTION AND
CORRESPONDING INVENTORIES OF NATURAL 'H
Number of atoms
produced per unit
time and per unit
area of the earth's Inventory Year of
surface (cm- 2 s- 1) (MCi)publication

Atmosphere0.10-0.20
0.12
0.14
1.2
1.2
1.06
0.9
0.75
0.6-1.3
0.25-0.35
0.6
0.25
0.20±0.05

distribution of hydrogen in the Reference Man of ICRP
(152), the annual doses from natural 3 H, calculated withthe dosimetric factors given in figure X, are found to beof the order of 1 µrad in each of the four organs andtissues considered by the Committee.

Reference

83

14-28
17
20
170
170
150
130
100
80-18035-150
80
34
28±7

1953
1954
1955
1957
1957
1958
1958
1958
1960
1961
1962
1967
1967

178
52
29
60
27
40
99
367
61
28
197
340

Lithosphere

10-•

0.1

1954

178

Hydrosphere

10-•0.0001

1953

83

direct exchange of water vapour between air andsea water. Once in the ocean, 3 H is dispersed throughmixing processes. Measured concentrations of natural 3 H
in ocean surface water average about 3 pCi 1-1 ( 178).

2. Beryllium-7
85. Mainly because of its short half-life, most of the7
Be inventory is in the atmosphere (table 10). As
exemplified by measurements in the Federal Republic of
Germany (190), the surface-air concentration of 7 Be in
the temperate zones shows a regular seasonal variation
with maximum values of about 100 fCi m - 3 in spring
and minimum values of about 40 fCi m - 3 in lateautumn. Using these concentrations, the annual lungabsorbed dose in adults from inhalation would be about
2 µrad.
86. Reported concentrations in rain range from 2 to
130 pCi 1- 1 with an average value of about 20 pCi 1- 1
(199). In the diet, leafy vegetables have been estimatedto constitute the main source of 7 Be, with a resulting
annual whole-body absorbed dose in adults of 8 µrad(250).
3. Carbon-14

84. The land areas seem to contain about 30 per centof the natural 3 H inventory (table 10). Tritium
concentrations in fresh water are usually higher than insea water. Activity concentrations of continental surface
waters, measured before nuclear explosions began, were
found to be in the range 6-24 pCi i- 1 (178). Assumingthat the specific activity of 3 H in the body is the same asthat in the continental surface waters. and using the

87. Natural 1 4 C is produced in the upper atmosphereby the reaction 14 N(n, p)~ 14 C induced by cosmic-ray
neutrons. The specific activity of biological carbon, as
measured in wood samples grown in the nineteenth
century, was 6.13 ± 0.03 pCi per gram of carbon (341),
corresponding to an atmospheric inventory of 3.8 MCi.
During the present century the specific activity of 14 C
55

in air has decreased due to the diluting effect of releases
into the atmosphere of carbon dioxide from the burningof fossil fuels. By 1954 the specific activity of
atmospheric carbon had been reduced some 2-5 per centdue to this process (I 6). The contributions of 14 C in theenvironment from nuclear explosions and from nuclear
power production are discussed in Annexes C and D.
According to Nydal et al. (260), 14 C activity in thehuman body follows that in the atmosphere with a delayof about 1.4 y.
88. Measurements of the natural 14 C in tree rings andin lake and ocean sediments have shown that 14 C levelsin the atmosphere have remained fairly constant for
many thousands of years, although there is a fluctuatingchange of 10 per cent over a period of JO OOO y (66), in
addition to smaller, more random fluctuations overperiods of th~ order of a hundred years (236). The
long-term fluctuation over a period of 10 OOO y is
attributed to a cyclical change of the dipole strength ofthe earth's magnetic field, which results in a cyclicalchange of the cosmic-ray flux, which in turn changes the
14
C production rate. The causes of the fluctuations overperiods of the order of a hundred years are not known.
Knowledge of the natural production- rate of 14 C
is useful for determining dose commitments from
artificial releases into the environment. Since theCommittee's 1972 report, a new estimate for the 14 C
natural production rate has been reported. Averaged
over the I I-year solar cycle, it is 2.28 atoms cm - 2 s- 1
(201), which is equivalent to an activity production
rate of 0.038 MCi y- 1 and is within the range of values
given
previously (1.6-2.5 atoms
cm - 2 s -l .
or
10.027-0.042 MCi y- ). An independent estimate of the
production rate can be computed from the total
inventory of natural 14 C on the earth. In units ofatmospheric content (which is 6.17 10 1 7 g of 1 2 C), thebiosphere, atmosphere and oceans contain 67 units ofcarbon (16). Noting that the specific activities of 14 C insurface ocean and deep ocean are lower than in theatmosphere by 4 and 17 per cent, respectively (46), theinventory of 14 C in the above reservoirs is 56 units (ofthe atmospheric content of 14 C, which is 3.8 MCi).
From the estimates of Broecker (47) that the slow
movement of carbon from the oceans into sediments
takes place over a time scale of I 00 OOO years, it isinferred that about 8 per cent of the 14 C inventory is in
sediments. The total inventory is therefore estimated to
be 60 units, equivalent to some 230 MCi. This inventory
is in equilibrium with a production rate of natural 14 C
of 0.028 MCi y- 1 • Considering the uncertainties involved in determining both the production rate and also
the total 14 C inventory of the earth, the estimates are in
reasonable agreement, particularly since no account istaken of 14 C entering the humus reservoir.
89.

90. Taking the natural specific activity of 14 C as
6.1 pCi per gram of carbon and using the dosimetricfactors presented in figure X and the concentrations ofcarbon, as well as the masses of organs and tissues in the
Reference Man of ICRP (152), the annual absorbed
doses in man are found to be 1.3 mrad in the whole
body, 0.6 mrad in the lung, 0.5 mrad in the gonads,
2.0 mrad in the bone lining cells and 2.2 mrad in the redbone marrow.
56

4. Sodium-22

91. Even though the production rate and theatmospheric concentration of 22 Na are very small(table 10). the doses in man given in table 12, are higher
than those arising from 3 H and 7 Be because of both themetabolic behaviour of sodium and the decay propertiesof 22 Na.
5. Annual doses from internal irradiationby cosmogenic radionuclides
92. Table 12 summarizes the data given above on theinternal doses from the four cosmogenic radionuclides
considered. It should be mentioned that the annual lungdose received from all the other radionuclides producedby cosmic rays has been estimated to be 10 - 3 mrad
(250).
TABLE 12. ANNUAL DOSE FROM INTERNAL IRRADIATION BY COSMOGENIC 3 H, 7 Be, '• C AND 2 2 Na
Annual dose (mrad)
Radio·
nuclideGonads

Lung

3H
'Be

0.001

,2Na

0.5
0.02

0.001
0.002
0.6
0.02

i•c

Bone
lining
cells

Red
bone
ma"ow

Whole·
body
average

0.001

0.001

0.001
0.008

2.0
0.02

2.2
0.02

1.3

0.02

93. As can be seen from table 12. the major part of
the annual dose from cosmogenic radionuclides isdelivered by 1 4 C. With the present size of the world
population, the annual collective dose is in the range of(2-8) 10 6 man rad for the tissues mentioned in table 12.

B. PRIMORDIAL
RADIONUCLIDES(EXCEPT
RADON AND ITS SHORT-LIVED DECAY PRODUCTS)

94. The primordial radionuclides include those belonging to the 2 3 5 U, 2 3 8 U and 2 3 2 Th series and some othernuclides, among which only 4 °K and 87 Rb are
significant sources of radiation.
1. Potassium40

95. Potassium-40, which is the major naturally
occurring source of internal radiation dose, enters the
body through diet. Being an essential element. potassium
is under close homeostatic control in the body. The dose
rates from 4 K can be calculated from its isotopic
abundance in the biosphere and the concentration ofpotassium in human tissues.

°

96. The mass of potassium contained in the wholebody varies as a function of age and sex. The massconcentration of potassium is highest in adolescentmales and lowest in elderly females, the ratio of the twovalues being about 2. An average value for an adult malewould be about 2 g of potassium per kilogram of bodyweight (10a, 347). According to Kaul et al (l 79), the-rI
mass concentration of potassium in various organs andtissues of interest to the Committee are 0.5 g kg- 1 inbone, 4.4 g kg- 1 in red marrow, 2.2 g kg- 1 in lungs,
2.1 g kg- 1 in testes and 1.35 g kg- 1 in ovaries. The
annual absorbed doses corresponding to these concentrations can be assessed using the dosimetric factors

presented in figures IX to XII, the masses of organs andtissues in the Reference Man of ICRP (152) and theisotopic ratio of 4 °K (0.0118 per cent). The annual
absorbed doses are found to be 27 mrad in red bonemarrow and 15-17 mrad in the lungs, gonads, bone lining
cells and whole body (table 13).

TABLE 13. TISSUE CONCENTRATION AND ANNUAL ABSORBED DOSE DUE TO 4 °K AND 8 7 Rb
Potassium

Organ or tissue
Lung

TestesOvariesBone
Red marrow
Yellow marrow
Bone lining cells
Whole-body
average

Rubidium

Mass con- Activity con- Annual
absorbed
centration cenrrationof element of 4 °K
dose
1
(g kg-')(pCi kg- )(rnrad)
2.1
2.1
1.35
0.5
4.4
0.6

1 700
1 700
1 100
400
3600
500

2

1 600

97. Yamagata (373) studied the variability of the massof potassium in adult man. He found a nonnal
distribution with an average of 136 g and a standard
deviation of 28 g. Using these values, 95 per cent of theadult males would receive annual absorbed doses in thefollowing ranges (mrad): gonads and endosteal cells,
9-21; lung. 10-24; red bone marrow, 16-38.

2. Rubidium-87
98. Very little is known about the behaviour ofrubidium in man's environment. The doses from 8 7 Rb
have been calculated from the mass concentrations ofrubidium in the ICRP Reference Man (152), which are
9.2 µg g- 1 in the lung, 20 µg g- 1 in the testes and26.7 µg g- 1 in the bone. The value for red bone marrow
has been assumed to be equal to the average
concentration in soft tissues, which is 7 .8 µg g- 1 • The
annual absorbed doses obtained range from 0.4 to
0.9 mrad in the organs and tissues of interest to theCommittee (table 13).

3. Uranium and thorium series
99. Uranium-238 and thorium-232 are each the headof a series of more than ten nuclides (tables 2 and 3). In
the same way as in the 1972 report, the 23 8 U and the232
Th series can be classified in the sub series in which
the activity of the precursor to a large degree controls
the activities of the decay products. For the 2 3 8 U series,
the subseries include: (a) 23 8 U, two short-lived nuclides
and 234 U: (b) 226 Ra. which is frequently separated in
the environment from its precursor, 2 3 0 Th, of little
dosimetric significance in natural background, and fromits decay product, 2 2 2 Rn, which is an isotope of a noble
gas; (c) 222 Rn and its short-lived decay products(through 214 Po) a subseries which is important both forexternal radiation because of the energetic gamma rays
emitted through decay of 2 14 Bi, and for internalradiation, and is discussed in section C of this chapter;17
17.Mass conActivity concentration centrationof element of 87 Rb(mg kg- 1)(pCi kg-')
9.2
20

220
480

26.7
7.8
7.8

640
190
190

9.7

230

Annualabsorbeddose(mrad)
0.4
0.8

12
27
6
15
17

0.4
0.3
0.9
0.4

( d) the long-lived 2 2 2 Rn decay products 2 1 0 Pb, 2 1 0 Bi
and 210 Po.
100. The 2 3 2 Th series has also been classified in threesubseries: (a) 232 Th itself; (b) the sequence of 228 Ra,
22 8Ac, 228 Th and 224 Ra; (c) 220 Rn and its decay
products. Because of their similarities, 232 Th and 230 Th
will be discussed together, the sequences headed by
228
Ra and 2 2 6 Ra will be treated in the same sectionand 2 2 0 Rn and its decay product~ will be consideredwith 2 2 2 Rn. The decay chain of 2 3 5 U is not of
dosimetric significance and will not be dealt with here.
101. Since all the long-lived (half-life >l y) radionuclides of the 238 U and 232 Th series are bone seekers.
an important parameter for dose assessment is theaverage activity concentration of those radionuclides inhuman bone. The comparison of the reported
concentrations in the skeleton is complicated since
results are given per unit of various quantities such as
wet. fresh, dry-fat-free, ash or calcium mass and therelationships between these quantities cannot always bereadily assessed. In this report, the conversion factorsthat have been adopted are derived from data publishedby the ICRP (151, 152). The weight of the skeleton ofan adult man is taken to be 10 kg (wet or fresh weight),
including 5 kg of bone (dry or dry-fat-free weight),
which yields 2.7 kg of ash. The total mass of calcium inthe skeleton is 1 kg. Unless otherwise indicated, theactivity concentrations in this document are expressed
per unit mass of dry bone. The following information
has also been used for dose calculations: the 5 kg ofbone comprise 4 kg of compact bone and 1 kg ofcancellous bone; the total bone surface in an adult man
is 10 m 2 with 5 m 2 in compact bone and 5 m 2 incancellous bone (151).
(a) Uranium
102. In this Annex, uranium is assumed to consist of
U in radioactive equilibrium with 234 Th, 234 Pa and234
U, so that I g of uranium contains 0.33 µCi of each238

57

of the four radionuclides. In fact, it is known that adisequilibrium state between 238 U and 234 U is rather
common in nature. The mechanism by which theisotopes 23 8 U and 2 3 4 U can be fractionated in the
ground is the Szilard-Chalmers effect. In the three-step
decay of 238 U to 234 U, the daughter atom (2 34 U) is
displaced from the crystal lattice. The recoil atom 2 3 4 U
is liable to be oxidized to the hexavalent stage andtherefore can be leached into the water phase moreeasily than its parent nuclide 2 3 8 U (56). Depending on
the origin of the water sample, the 234 U to 238 U
activity concentration ratio can vary greatly, and values
ranging from 0.66 up to 9 have been reported (56. 337).
103. In the atmosphere, the main natural source ofuranium are the dust particles resuspended from theearth. Assuming a dust loading of about 100 µg m- 3 insurface air of populated areas, and taking an average
238
U activity concentration in soil of 0.7 pCi g- 1
(table 5). the activity concentrations in air are estimatedto be about 7 10 -s pCi m - 3 • Measured values inground-level air (114, 160, 226) are in good agreementwith this estimate. This average concentration corresponds to a daily iritake by adults through inhalation of
1.4 10 - 3 pCi.
104. The dietary intake of 2 3 8 U has been measured inseveral countries ( 116, 186, 259, 311, 361) and found tolie in the relatively narrow range of 0.3-0.5 pCi d -i inareas of "nonnal" natural radioactivity (table 14). The
activity concentration of 238 U in tap water being
usually less than 0.03 pCi 1- 1 (14, 186). the contri-

TABLE 14. URANIUM-238 IN THE HUMAN DIET AND BODY IN VARIOUS
COUNTRIES
Dietary
intake1Country(pCi d" )Urinary
excretion
1(pCi d" )Activity inskeleton(pCi)

Activity inwhole body Ref(pCi)
erence311

France0.2-0.9

Japan
Kyoto and Sapporo
Okayamaa
Control area

0.50
1.2
0.3

0.03
0.003

United Kingdom

0.40

0.13

186
375
375
21

33

69,
115,

116
United States
New York
ChicagoSan Francisco

0.43
0.46
0.43

USSR

about 0.3

0.05

18

26

361

361
361

186

a Mean of the values observed in two villages located near a uranium mine and its
refinery.

bution of drinking water to the total dietary intake is in
general small. However, it should be mentioned that very
high concentrations of uranium in tap water have beenreported. In the USSR, activity concentrations as high as
70 pCi 1- 1 have been observed (31 ); in Helsinki, Finland,
concentrations of the order of 1OOO pCi 1· 1 have beenmeasured in several wells, the highest concentration
being about 5000 pCil- 1 (176). According to theauthors (176), the very high concentrations of uranium
in the water of those wells are probably caused by small,
localized uranium-rich deposits.
105. There is experimental evidence (332) that thefraction of uranium absorbed in the gastro-intestinal
tract is a few per cent of the amount ingested. As theintake through inhalation is only about 1 fCi d -I, theblood uptake through inhalation is small compared tothat from ingestion. This is confinned by the datacontained in table 14 which show that the daily urinary
excretion. expected to be approximately equal to thedaily uptake (145), exceeds substantially the intake byinhalation.
106. In man. the results of measurements of activity
concentration of 23 8 U in soft tissues range from 0.03 to

58

0.3 pCi kg- 1 , while those in bone are from 4 to
5 pCi kg- 1 (116, 361). From the data contained intable 14 it can be estimated that a daily dietary intake of
0.4 pCi of 2 3 8 U leads to concentrations in soft tissues of
0.2 pCi kg · 1 and to a bone concentration of 4 pCi 1cg- 1
These values have been used to calculate the absorbed
doses (table 15). In bone, uranium has been taken to behomogeneously distributed throughout the volume. Thishas been shown to be approximately true by
neutron-induced autoradiographic studies, althoughhigher concentrations were found on bone surfaces (307,370).
(b) Thorium
107. From a dust loading of I 00 µg m · 3 and a 2 3 2 Th
activity concentration in soil of 0.7 pCi g- 1 (table 5),
the activity intake through inhalation per unit time isabout 1 fCi d -, . There is no direct information on the
dietary activity intake of 2 3 2 Th per unit time but anindirect estimate of about 0.1 pCi d- 1 has been
proposed (250). The contribution of this route to thebody content is probably negligible because of the very
low absorption of thorium through the gastro-intestinal
tract.

TABLE 15. TISSUE ACTIVITY CONCENTRATION Ai'ID ANNUAL ABSORBED DOSE DUE TO
RADIONUCLIDES OF THE 238 U- 23 ' U SUBSERIES
Activity
conce11tratio11 of
131 u. 134 Th.
>kmpa or13•u234771, .. mPa>J<uOrgan or tissue(pCi kg" 1)(a)(/3. 'Y)(/3. 'Y)(a)(a)({3, 'Y)

Lung
TestesOvariesBone
Red marrow
Yellow marrow
Bone lining cells

0.2
0.2
0.2
4
0.2
0.2
0.2

0.02
0.02
0.02

0.00020.00020.0002

0.003
0.003
0.003

0.02
0.02
0:02

0.04
0.04
0.04

0.003
0.003
0.003

0.02

0.0006

0.02

0.03

0.05

0.02

0.12

0.003

0.04

0.14

0.3

0.04

,.. u

Annual absorbed dose (mrad)

108. Measured levels in rib bone show a linear increase
with age (216). The average activity concentration in ash
would be about I fCi g- 1 in adults. which is about 10
times less than the corresponding values for 2 3 8 U.
However, thorium is known to deposit on theendosteum, and the dose rates in this tissue per unit
activity of thorium in bone are much higher than thosefor uranium, because the latter element is distributed
over the total mass of bone. The calculated dose rates tobone tissues from 2 32 Th are shown in table 16.

TABLE 16. TISSUE ACTIVITY CONCENTRATION AND
ANNUAL ABSORBED DOSE DUE TO 2 3 0 Th AND
lllTh

Organ or tissue

Lung
GonadsBone (average)
Trabecular bone
Red marrow
Bone lining cells

Activity
concen·tration230
of
111
or >l>171(pCi kg" 1)

0.5
0.05
0.5

Annualabsorbed dose(mrad}
23077,

very similar, because their activity concentrations in soil
are about equal and their physical half-Jives are verymuch longer than man's life sf.an. The annual absorbed
doses in several tissues from 2 0 Th are given in table 16.

(c) Radium111. Radium has 13 known radioactive isotopes. whose
atomic weights range from 213 to 230 and whoseradioactive half-lives range from 10-3 s to 1600 y. Fromthe point of view of human radiation exposure fromnatural background only 2 2 6 Ra and 2 2 8 Ra, which gives
rise to 224 Ra, are of significance.
112. Inhalation. As in the case of uranium and thorium.
the main natural source of radium in the atmosphere is
the resuspension of soil particles; this corresponds to a
calculated activity intake of about 1 fCi d -i.

232 77,

0.04
0.004

0.04
0.004

0.05
0.8

0.04
0.7

1.3

0.05

Total

109. Pavlovskaya (268) measured the activity concentration of 2 32 Th in soft tissues and found it to be one
fifth to one fourth of that in the skeleton and thus
about one tenth of that in dry bone. Taking the activity
concentration in bone to be 0.5 pCi kg- 1 , the activity
concentration in soft tissues would therefore be about
0.05 pCi kg- 1 • It has been suggested by Wrenn (370), on
the basis of Budinger's measurements (48), that the232
Th concentration could be much higher in lungtissue than in the other soft tissues. Usinf an intake perunit time through inhalation of l fCi d - , a depositionof 25 per cent in the pulmonary region, and a biologicalhalf-life of 4 y, the equilibrium activity concentration inlung tissue would be about 0.5 pCi kg -i • The resulting
annual absorbed dose to soft tissue is presented intable 16.
110. The Committee is not aware of any study dealing
with concentrations of 2 3 0 Th in man. However. it islikely that the 230 Th and the 232 Th levels in man are

113. Ingestion. Food consumption is a much more
important source of radium intake and fractional blood
uptake than inhalation. The average dietary activity
intake per unit time of 2 2 6 Ra in areas of normal
radiation background is of the order of I pCi d -t
( table 17). Typical 22 6 Ra levels in most components ofthe diet range from 0.1 to 5 pCi kg- 1 , but someindividual foods, such as Brazil nuts and Pacific salmon.
contain much larger concentrations of 2 2 6 Ra. Althoughmuch less documented, the dietary activity intake of
228
Ra in areas of normal radiation background seems tobe about the same as that of 2 2 6 Ra (278).
114. The contribution of water to the total intake is in
general small when the drinking-water supplies are drawn
from surface waters. However, 22 6 Ra levels of I to
10 pCil- 1 are not exceptional in well and mineralwaters (5, 176, 296, 316). Available information on theconcentrations of 22 8 Ra in water is limited. bufit seems
that they are of an order of magnitude lower than thecorresponding concentrations of 2 2 6 Ra (14, 176).
115. Two well known populated areas with highconcentrations of thorium and uranium in their soil arelocated along the coast of Kerala in India and in the
Ara...xa-Tapira region in Brazil. The estimated average
daily intakes of 2 2 6 Ra and 2 2 8 Ra of the Indian
population along the Kerala coast are 3 and 160 pCi,
respectively (58, 240). In Brazil. a survey in the59TABLE 17. RADIUM-226 IN THE HUMAN DIET AND DRY BONE INV ARIOUS AREAS
Dietary intake
Area(pCi d" 1)

pCi (gCaJ"'

0.8

1.1

1.1

1.1

Mean activity
concentrationin dry bone"(pCi kg·•,

Bone/dietb
pCi kg-I
perpCi d- 1

Observed
ratio

Ref-

0.030

30
357
357
357
357
311

erenceAreas of normal
external
radiation
background
Argentina
Australia
CanadaChile
Congo
FranceGermany,
Fed. Rep. of
GuatemalaIndia
BombayTarapurIsraelItaly
Japan
SapporoKyoto
PolandEastern
Northern
Southern
Western
Puerto Rico l
Puerto Rico 2
South Africa
Ukrainian SSR
United Kingdom
United States
BostonHoustonIllinois
New England
New York 1
New York 2
San Francisco
Wisconsin

6.6
5.4
3.2
2.2
12

8.2

324
357

7.0
2.7
4.3

0.8
0.5

1.6
1.0

1.4

2.8

0.4
1.0

0.8
2.9

1.6
7.5

0.7

1.3

1.2

1.1

7.7
5.3
6.5
32.6
3.4
2.7
5.9
21
8.1

5.4

0.013

58
177
357
42

4.0
7.5

0.016
0.019

113a
113a

19

1.7

1.7

0.8

0.8

Arithmetic mean

0.9

1.5

Area of high externalradiation
background
Kerala, India

3.3

6.6

7.6
12
20
8.6
7.2
5.4
6.2
6.5

)
4.8

0.013

6.7

0.037

4.2

0.021

7.7

0.039

8.5

6.1

0.024

77

23

0.058

163
113
357
357
245
357,
314
357
357
135
143
85
357
85
222

58

aThe data have been either taken directly from the references or converted in terms of dry boneusing the factors of paragraph IOI.
bThe left-hand column gives the bone-to-diet quotient, the units used being pCi kg-• for theactivity concentration in dry bone and pCi d- 1 for the dietary intake. The right-hand column gives thecorresponding values of the bone-to·diet observed activity ratio, the unit used being pCi per gram of
Ca for both bone and diet.

Araxa-Tapira region showed that, out of a population of1670 people living in and around the radioactive
anomalies of Barreiro and Tapira, only 196 individuals
are ingesting alpha emitters at a level five times or morethan that of a similar group living in Rio de Janeiro.
Their intake of radium per unit time ranged from 10 to
40 pCi d -i of 2 2 6 Ra and from 60 to 240 pCi d- 1 of228
Ra (347).
116. Distribution in man and dose rates. When radium
is taken into the body, its metabolic behaviour is similar
to that of calcium. and an appreciable fraction isdeposited on bone surfaces and in areas of active boneturnover (82). Rowland (300) has shown that. after high60

intakes, approximately half of the initial activity in man
is deposited in "hot spots" and half in the diffuse
component. The initial deposition in hot spots is due
presumably to the fact that these are areas of actively
growing bone where mineralization is occurring. Even in
the case of relatively low-level dietary intake. the same
hot-spot accumulation is thought to occur, but at alower activity level (125). About 70-90 per cent of theradium in the body is contained in bone ( 151 ), theremaining fraction being distributed approximately
uniformly in soft tissues. In the areas of normal
radiation background, the 2 2 6 Ra concentrations in bonerange roughly from 2 to 20 pCi kg· 1 ( table 17), with anarithmetic mean of about 8 pCi kg- 1 • Several studies

121. The concentration of 22 8 Ra in human bone could
be expected to be lower than that of 2 2 6 Ra because of
the shorter half-life of the fonner and the estimatedbiological half-life of radium in the body, which is of theorder of 10 years (151. 363). Thus, the 228 Ra activity
would be limited by its physical half-life to about 30 per
cent of the 22 6 Ra activity. This is consistent with the
ICRP model (151 ), from which a figure of 27 per centcan be derived. In fact, in the few studies dealing withthe detennination in bone of 2 28 Th, which can beassumed to be in radioactive equilibrium with 22 8 Ra,
the average ratio of 22 8 Th to 22 6 Ra in bone ash was
found co vary between 0.25 and 0.5 (143, 215, 324).
Using a value of 0.3, the average 2 2 8 Ra activity in bonewould be 2.4 pCi kg- 1 in areas of normal backgroundradiation. Since no measurement of 2 2 8 Ra in soft tissues
could be found in the literature, the figure of
0.1 pCi kg- 1 derived from the ICRP model (151) is usedin this Annex.

(see, for example, reference 325) have shown that the226
Ra concentration in bone seems to be independentof age.
117. The relationship between the dietary intake andthe skeletal content can be estimated from measurements in countries where both the concentrations inbone and the dietary intake have been published(table 17). The bone-to-diet quotient, expressed inpCi kg- 1 per (pCi d- 1 ), ranges from 4.0 to 8.2 with anaverage of 6.1. The "observed ratio" between theactivity per gram of calcium in the bone and in thediet ranges from 0.013 to 0.039, with an average of
0.024.
118. Another way to estimate the bone-to-diet
relationship is to use the model developed by ICRP on
the metabolism of alkaline earths in adult man (151).
According to that model, a blood uptake of 1 pCi of
22 6 Ra yields a time-integral of the bone activity of
126.3 pCi d, and a time-integral of the whole-body
activity of 143.7 pCi d. Therefore, a continuous blood
uptake of I pCi d- 1 w.ould yield an equilibrium activityof 126 pCi in the skeleton corresponding to an averagebone activity concentration of 25 pCi 1cg- 1 • Since thefractional blood uptake for radium is 0.15-0.20 (125),an intake of about 6 pCi d -i corresponds to a blood
uptake of 1 pCi d -i. The bone-to-diet quotient istherefore calculated to be 4.2 pCi kg- 1 per pCi d -I ,which is in reasonable agreement with the value of 6.1
given in paragraph 117.

122. The dose rates in bone lining cells and bonemarrow presented in tables 18 and 19 have been
calculated using the same assumptions as in the 1972
report: (a) an average retention factor in the skeleton
and in the soft tissues of 0.33 for 2 2 2 Rn and of 1.0 for
2 20
Rn and (b) a uniform concentration of radium andits decay products over the total mass of mineral bone.
In fact, with respect to 2 2 8 Ra and its decay products, it
is known that a fraction of 2 2 8 Th, which is thelong-lived alpha emitter of the radioactive sequence,migrates to the endosteum (330). Furthennore, direct
intake of 2 2 8 Th and 2 2 4 Ra, although contributing to asmall extent to the skeletal activity, leads to depositionof those radionuclides on bone surfaces. Because afraction of the activity of the decay products of 2 2 8 Ra
is surface distributed, the doses from that sequence inbone marrow and in bone lining cells may therefore be
somewhat higher than indicated in table 19.

119. If all the values of the daily dietary intake and of
the activity concentrations in bone shown in table 17 aretaken into account, the averages are 0.9 pCi d -i and8.5 pCi kg- 1 , respectively, corresponding to a bone-todiet quotient of 9 pCi kg- 1 per pCi d- 1 , which issomewhat higher than the two estimates in the previous
paragraphs. The difference may be due to the highconcentrations in bone found in the Congo, Israel,
western Poland, the United States (Houston and Illinois)
and the Ukrainian Soviet Socialist Republic. The 2 2 6 Ra
dietary intake in these regions might be higher than
average. If they are excluded, the bone-to-diet quotient
becomes 6 pCi kg - l per pCi d -I •123. Data on the activity of radium in the skeleton of
the populations living in the high radiation areas of
Brazil and India are very scarce. In Brazil, the mean
226
Ra concentration in the teeth of the population
living in the Araxa-Tapira region has been estimated as
85 fCi per gram of ash, which corresponds to an activity
in the skeleton of about 230 pCi, if it is assumed thatthe concentration in teeth is the same as that in bone. In
India. the analysis of a femur bone yielded a 2 2 6 Ra
concentration per unit mass of ash of 143 fCi g- 1 , whichcorresponds to a skeletal activity of about 400 pCi (58).

120. The fraction of 2 2 6 Ra distn1mted in the soft
tissues will be taken to be 17 per cent, as given in ICRP
Publication 20 (151 ). The average activity of human soft
tissues would thus be 0.13 pCi kg- 1 •TABLE 18. TISSUE ACTIVITY CONCENTRATION AND ANNUAL ABSORBED DOSEDUE TO 12 6 Ra AND ITS SHORT-LIVED DECAY PRODUCTS

Organ or tissue
Lung
GonadsBone
Red marrow
Yellow marrow
Bone lining cells

Activity
concentrationof 226Ra(pCi kg" 1)

Activity
concentrationof thedecay
productsof 226 Ra(pCi kg"')

0.13
0.13
8
0.13
0.13

0.043
0.043
2.6
0.043
0.043

Annual tissue absorbed dose (mrad)
126 Ra

»:Rn

211

(a)

(a}

0.01
0.01

Pb

"•Bi

11•po

(a)

(/J, 'Y)(/J, 'Y)(a)(a)(/J, 'Y)

0.004
0.004

0.005
0.005

0.00030.0004

0.001
0.001

0.006
0.006

0.03
0.03

0.001
0.001

0.03

0.01

0.02

0.003

0.009

0.03

0.09

0.01

0.27

0.11

0.13

0.009

0.02

0.18

0.7

0.03

Po

214

Total

61

228

TABLE 19. ANNUAL TISSUE ABSORBED DOSE

FI

Annual

tu

128

Ra

Ac

l28Th

'"Ra

220

Rn

Organ or tissuea(/3)(/3, 'Y)

(a)

(a)

(a)

Lung
GonadsRed marrow
Bone lining cells

3 10-•
3 10-•
6 10-•

1 10- 3
1 10- 3
8 10-3
1 10-2

1.0 10-2
1.0 10-2
2.5 10-2
1.7 10-l

1.1 10-1
1.1 10-2
2.8 10-2
1.8 10-1

1.2 10-1
1.2 10-2
3.4 10-2
2.1 10-l

2 10-•

aThe activity concentration in the lung, gonads and red marrow is assumed to be 0.1 pCi kg- 1 •The activity concentration in bone is taken to be 4 pCi kg- 1 for cancellous bone and 2 pCi kg-, for(d) Long-lived decay products of 222 Rn.

124. The 210 Pb-210 Bi-210 Po chain is a significant
component of the dose from internal irradiation by
natural alpha emitters. When the three radionuclides are
in radioactive equilibrium, the dose from 210 Po is muchhigher than from 2 1 0 Pb and 2 1 0 Bi, and on this basis
21 0
Po could be considered separately. However, theactivity concentrations of 21 0 Po, in the environment aswell as in man, are usually closely related to those of
21 0
Pb, which is its long-lived precursor and acts as acarrier. For that reason, 210 Po and 21 0 Pb will be dealt
with together. The half-life of 2 1 0 Bi is short comparedto that of 2 1 0 Pb. Therefore, 2 1 0 Bi will almost always be
assumed to be in equilibrium with 2 1 0 Pb in the various
compartments of the environment and of the humanbody.

I • • ••
~

..

...

.

0.5

(i)

Sources and levels in the environment

0.4D.J'----....---....,..---,.---~--~~--~

125. Air. The main source of 2 1 0 Pb and 2 1 0 Po in theatmosphere is 2 2 2 Rn emanation from the ground. The
amount of atmospheric 2 10 Pb produced in this way has
been estimated to be 0.6 MCi y- 1 (164), which would
lead to an equilibrium activity of 2 10 Pb and 2 1 0 Po in
the atmosphere of about 20 MCi if the air concentrations were governed by radioactive decay only.
However, tropospheric aerosols to which these radionuclides are attached are scavenged from the atmospherethrough wash-out and dry deposition with a mean
residence time of about 10 d (91 ). The inventories are
therefore about 20 kCi for 21 0 Pb (164) and 2 kCi for
2 10
Po. The concentrations of these nuclides in surface
air depend mainly on the rate of emanation of 2 2 2 Rnfrom the ground and on the latitudinal distribution ofland and sea areas. Consequently, they are highest in thesubtropical and temperate latitudes of the northernhemisphere. as illustrated in figure XIII for 2 1 0 Pb (295).
In the middle latitudes of the northern hemisphere. theaverage concentrations of 2 1 0 Pb and 2 1 0 Po have been
estimated to be 14 fCi m- 3 (162) and 3.3 fCi m - 3 (267),
respectively. It has been suggested (244) that asignificant source of 2 1 0 Po in surface air could bevegetative transpiration.
126. Rain and drinking water. The global distributionof 2 1 0 Pb and 2 10 Po in rain water follows the same
pattern as that in surface air, being highest in the middle
latitudes (fig. XIV). The annual averages of the
62

90N

60N

JON

0

30S

60S

90S

LATITUOE

Figure XIII. Latitudinal distribution of 2 1 0 Pb in surface air
(295)

~:J
•1

. ..
.

:1

..

..
...
.:...

21
1~

I
o•j
O.S•

D.3'
0.2

90N

60N

30N
LATITUDE.

Figure XIV. Latitudinal distribution of 21 0 Pb in rain water
(295)

,,

IiI ~

fROM 111 Ra AND ITS DECAY PRODUCTS~ e absorbed dose (mrad)
211

y;;Po

Pb

111Bi

Tora/

"'Po

lOl77

(a)

(fJ, 'Y)(a)((J, 'Y)

2 10->
2 10- 1
7 10-J
I 10- 2

6 10- 1
6 10- 118 10- 2
10.8 10- 1

4 10- 3
4 10-1
3 10-'
4 10-•!

(a)(fJ, 'Y)(a)(fJ, 'Y)

1.3 10-:1.3 10- 2

4 10-4
3 10-4
2 10-•
5 10- 3

4 10-•
4 10-•
1.2 10-2
6.5 10-1

8 10-4
8 10-•
1 10-2
1.5 10-2

3.9 10-l
2.4 10- 1

1.0 10-1
1.0 10-•4.3 10- 2
2.1 10- 1

compact bone, yielding an average concentration per unit mass of bone of 2.4 pCi kg-•; the activity
concentration in yellow marrow is assumed to be 0.1 pCi kg- 1 , the same as in other soft tissues.

concentration of 2 1 0 Pb in rain at various locations havebeen found to vary between 0.2 and 7 pCi 1- 1 (295), a
typical value for the continental stations of the middle
northern latitudes being 3 pCi 1- 1 • Reported values ofthe 2 10 Po/21 0 Pb activity concentration ratio in rainwater range from O_l to 0.54 (267). Activity
concentrations in drinking water are usually less than
0.1 pCi 1-1 • However, concentrations in mineral water orin well water may reach the levels observed in rain water.
127. Soil. The activity concentrations of 210 Pb andPo in the top layer of soil are not strictly equal tothose of 22 6 Ra because (a) a fraction of 22 2 Rn diffuses
through soil into the atmosphere and (b) 2 1 0 Pb and
21 0
Po are deposited on the soil surface through dry andwet fallout. Assuming a deposition velocity of
5 10-3 m s- 1 and an atmospheric concentration of
14 fCi m - 3 , the dry deposition of 2 1 0 Pb in the northern
middle latitudes would occur at the rate of
2.2 mCi km- 2 y- 1 , corresponding to an equilibrium
activity in the deposit of 68 mCi km - 2 • With a meanannual precipitation of 800 mm and a concentration inrain or snow of 3 pCi 1-1 , the rate of wet deposition of
21 0
Pb would be 12 mCi km - 2 y- 1 , leading to an
equilibrium value of the deposit of 37 mCi km - 2 •Assuming that the amount de~osited is contained within
the top 20 cm of soil, the 2 1 Pb activity concentrationin that layer, at equilibrium, would be 02 pCi g-1 fromdry deposition and 0.1 pCi g- 1 from wet deposition.
The average activity concentration of 2 2 6 Ra in soil
being about 0.7 pCi g- 1 (table 5), the activity of 2 1 0 Pb
in the top 20 cm of soil is expected to be about 30 per
cent higher than that of 2 2 6 Ra if the fraction of 2 2 2 Rnretained in soil is taken to be 0.9. Measurements of
2 10
Pb and 2 2 6 Ra in the top layers of soil which havebeen conducted in several countries confirm that therelative importance of fallout 2 10 Pb, as assessed above,is reasonably correct. In Massachusetts (United States),
2 10
Pb from fallout was found to migrate to a dej>th o(
40cm(l2l);overthat depth, the average 210 Pb/~ 26 Ra
activity ratio was 1.9. In another sample of soil taken in
Maryland (United States), the migration of 2 1 0 Pb
seemed to extend up to 30 cm, the average 2 1 0 Pb/ 2 2 6 Raover that layer being about 1.2 (4). In New Zealand, theresults of measurements carried out on four types of soil
show that that portion of 2 1 0 Pb which is due to fallout
tends to remain within the top 15 cm of the soil and that
this portion constitutes from 18 to 34 per cent of thetotal 21 0 Pb in this depth ( 17). In Poland, similar
2 10

measurements, limited to a depth of 10 cm, show that ininland areas the excess 2 1 0 Pb is 23 per cent while incoastal areas, where the 2 10 Pb deposition is smaller, theexcess 2 1 0 Pb is only 6 per cent over the top 10 cm of soil(166).
128. Plants. The concentration of 2 10 Pb and 2 10 Po inplants is a function of both direct deposition on theleaves and root uptake from the soil. The relative
importance of these two pathways is controversial.
Francis et al. (90) have studied tobacco and vegetables
under greenhouse and field conditions. They found that
under greenhouse conditions little 2 1 0 Pb or 21 0 Po was
detected in the plants, while under field conditions the
2 10
Pb and 2 1 0 Po levels increased. They concluded thatthe major source of 210 Po in vegetation is from falloutof 210 Pb with decay to 210 Po. A similar conclusion has
been reached by Hansen and Watters (118), who
compared the concentrations obtained in plants grownin control soil and in 2 1 0 Po0 2 -contaminated soil. The
2 10
Po activity concentrations per unit mass of dry
weight measured in the vegetables grown in control soil
ranged from 10 to 100 pCi kg- 1 • On the other hand,studies of tobacco by Tso et aL (344) suggest the sourceof 2 1 0 Po in plants may be root uptake of 2 1 0 Pb.
Tobacco plants exposed to a SOO.fold increase of 2 2 2 Rn
in a greenhouse only exhibited a 2-fold increase in
2 10
Po content. In a study of the transfer of 2 1 0 Pb and
21 0
Po added to soil as nitrate, Tso and Fisenne (345)state that the principal route of entry of 21 0 Pb and21 0
Po in the tobacco plant is probably root absorption.

(ii)

Human intake

129. Inhalation The average concentrations in surface
air given above are 14 fCi m - 3 for 21 0 Pb and3.3 fCi m - 3 for 2 1 0 Po. Assuming that an adult inhales
20 m3 of air daily (152), the intakes of non-smokers are
estimated to be 0.3 pCi d - 1 of 2 1 0 Pb and 0.07 pCi d- 1of 210 Po. Since a cigarette contains about 0.6 pCi of
2 10
Pb and 0.4 pCi of 2 1 0 Po (267) and both nuclides arevolatile at the burning temperature of tobacco, cigarettesmoking will lead to a substantial increase 41 the intakeof 210 Pb and 210 Po through inhalation. About 10 per
cent of the 2 1 0 Pb and 20 per cent of the 2 10 Po
contained in the cigarette will enter the lung with themain smoke stream (267). Therefore, for a personsmoking 20 cigarettes a day, the values of the estimatedintakes are 1.2 pCi for 2 1 0 Pb and 1.6 pCi for 2 1 0 Po.
63

However, it should be pointed out that the conditions of
inhalation while smoking are very different from thosein nonnal respiration.

TABLE 20. COMPARISON OF THE DIETARY INTAKE OF
2 10
Pb AND 2 1 0 Po IN AREAS OF NORMAL AND HIGHINTAKE
Dietary intake

130. Ingestion. For non-smokers, consumption of food210
is usually the most important route by which
Pb and21 0
Po enter the human organism. The dietary intake ispresented in table 20. In cereal products, vegetables andmeat, the typical concentration of 21 0 Pb is2-5 pCi kg- 1 , and the 210 Po/ 210 Pb ratio is in the range
0.5-1.0. The concentration in milk is lower by an orderof magnitude. These products are the main componentsof the diet in the areas of nonnal intake (table 20). In
these areas the values of the intake of 2 1 0 Pb and 2 1 0 Po
lie between I and 10 pCi d- 1 , the contribution ofdrinking water to the intake being only a few per cent. A
value of 3 pCi d- 1 will be taken as representative of theintake of 21 0 Pb and 2 1 0 Po in areas of normal radiation
background. The actual value of the intake in a given
area depends to a certain extent upon the concentrationof these nuclides in surface air and rain water. However,the published values of the dietary intake of 210 Pb andits average concentration in surface air and rain water inthe same regions (table 21) do not seem to be correlated.
131. High concentrations of 21 0 Po are observed in theedible portions of aquatic organisms, for which it is now
well established that the 21 0 Po/ 21 0 Pb activity concen·
tration ratio is greater than I (57). The 210 Po
concentrations in the muscles of fish and in molluscs areapproximately 20 and 500 pCi kg- 1 (267). The intakesof 21 0 Pb and 21 0 Po in populations consuming large(pCi d- 1)

Area

llOpb

21op0

4.6

4.6
3.8
4.1
3.2
1.8

Reference

Areas of normal dietary intake
Argentina
Germany, Federal Republic of
USSR
Rostov
United Kingdoma
United States

1.3

6.2
3.2
1.4

347
347
267
196
347
250,
140

Areas of high dietary intake
High seafood consumption

Japan

347

17

High reindeer and caribou

consumption
CanadaFinland (Inari)
Sweden {Lake Rogen
district)
USSR
Murmansk regionb

8.6

100
69

132
180

72-180
30-70
79

276
267
267,
258

344
60

267
35

3.6·9
44

Yarnalo-Nenetskii National
Area
United States (Alaska)

aThe range of the dietary intake of 2 1 °Pb and 2 1 0 Po in
the United Kingdom is estimated to be 1-10 pCi d- 1 (347).
bThe 2 1 0 Pb dietary intake is based on measurements of
excreta (2 SB).

TABLE 21. ACTIVITY CONCENTRATION OF 210 Pb IN THE ENVIRONMENT, THE HUMAN DIET AND HUMAN BONE ASH

Location
Continental
FinlandGermany, Federal Republic ofIndia, Bombay
PolandUSSR, Rostov
United States
Palmer, Alaska
Los Angeles, California
Chicago, Illinois

Surfaceaira(fCi m- 3)

Rain
water
fpCi r'J

Dietary
intake 1(pCi d- )7 (3-15}
10 (3-38)
18 (5-49)

3.0
3.0

4.6

17

5.2c

6.2

9 (5-16)15 (6-25)
21 (11-76)

0.8
0.8, 3.2
1.3-2.5

1.7
1.5
1.8

Human boneashb 1(fCi g- )Reference

78 C
110 C
321 T
148 T
91 T
134 M

180,295
101,137,295
182,295
161
32
196,295
219,295
219,295

184 T
146 M

105 C
New Orleans, Louisiana
Boston, Massachusetts
New York, New York
IslandJapan
SapporoKyoto
New ZealandUnited Kingdom, England
Puerto Rico
United States
Honolulu, Hawaii

21 (12-35)
14 (10.22)
21 (7-43)

5d

1.8
1.7
1.2

6 (2-13)9 (4-15)

1.4-1.8
2.7
2.2e

3._2

5 (4-7)

1.1

1.6

aThe range of observed values is given within parentheses.
bT = trabecular bone, C = cortical bone, M = mean bone value.
cConcentration measured in Moscow.
dconcentration measured in Melbourne.
eConcentration measured in Nassau.

64}

135,219, 295

200T

219,295
219,295
39,219,295

96 T
218 T
61 M
96 T
118 T

113a
113a
252, 295
134,295
137,295
219,295

......
proportions of seafood are therefore expected to behigher than those of populations with other types ofdiet. This assumption is confirmed by the value of the
21 0
Pb intake in Japan (table 20).

hemisphere. Their main food is the meat of theseanimals, which contains unusually high concentrationsof 2 10 Po because in the winter they graze on lichens
which accumulate 210 Pb and 210 Po.

132. A well documented case of elevated intakes is thatof the tens of thousands of reindeer and caribou eaters
in the arctic and sub-arctic regions of the northern

133. Table 22 presents information on the concentrations of 2 1 0 Pb and 2 1 0 Po in the lichen-reindeer-man
food-chain. Lichens, which do not have a root system,

TABLE 22. MEASUREMENTS OF THE CONCENTRATION OF • 1 0 Pb AND • 1 0 Po IN THE
LICHEN-REINDEER-MAN FOOD-CHAIN

Link in chain and locationof measurement
LichenCanadaFinland, LaplandSweden
USSR, Murmansk
USA, Alaska, Bethel

Comment.r

Reference(pCi kg·• dry weight)
7 300
7 300
6 400

7 900
7 200
9 200
5 800

139
180
276
258
35

5 800

Reindeer or caribou(pCi kg·• fresh weight)
Bone
Finland, 1nari
Sweden
USSR, Murmansk
USA, Alaska, Anaktuvuk

4600
5 800
1500

Pass
Meat
CanadaFinland, LaplandSwedenUSSR
USA, Alaska, Anaktuvuk
Pass

2 OOO
3 700

180
276
258

5 OOO

35

(pCi kg·•)
11
6
18
38

280
160
360
80

139
276
276
293

15

200

138

Man
Bone
Finland, Inari
Sweden(fCi g·• ash)
160
500

160
370

USSR, Nenetskii National
Area

430

220

USA, Alaska

300

220

Levels in teeth
Inferred from bloodconcentration

180
276
258.
267
36

Soft tissues
Blood
FinlandSwedenPlacenta
CanadaFinland6.8

12

Ma 4.7
F 3.3

M 9.4
F 5.0

2.5
1.9

29
36

Concentrations measured
in southern Finns are
2.7 for 210 Pb and 0.7
180
for 110 Po
Corresponding levels in "normal"
populations are about 2 pa 1cg· 1 276
139
Concentrations measured
in southern Finns are
0.8 for 210 Pb and 2.9
for " 0 Po

180

aM =male, F = female.

derive their nutrition prrferentially from the air. As theypresent a high sorption area, live for a long time (as longas 300 y), and eliminate 2 10 Pb very slowly (effective
half-time estimated to be 7 ± 2 y). they concentrate
2 10
Pb and 2 1 0 Po to much higher levels than otherplants. Lichens also accumulate other long-lived naturalradionuclides, such as 22 6 Ra or 2 28 Th (258), but
because of their much lower concentration in surface air
and rain water, the absolute concentrations reached bythose radionuclides in lichens are also much lower.
65

134. As reindeer consume 3-4 kg of lichen per day(276, 292), their daily intake of 210 Pb and 210 Po is of
the order of 10 OOO pCi. The concentrations in reindeerbone and meat presented in table 22 clearly show thedifferent biological behaviour of polonium and lead.
Lead-210 concentrates in the skeleton, where it gives rise
to 110 Po through radioactive decay. Polonium-210
concentrates mainly in the soft tissues, where it is clearlyin excess of its equilibrium value with 2 1 0 Pb. It is worth
mentioning that the 21 0 Po concentration in reindeer
meat varies seasonally by a factor of 4 ( 180), being
lowest in early autumn because of the greater availabilityof forage other than lichens during the warm summer
months.
135. The daily intakes of .2 1 0 Pb and 2 1 0 Po by the
populations living on reindeer or caribou meat are given
in table 20. Most of the estimates were inferred from themeasured concentration in reindeer or caribou meat.
using a daily rate of consumption of 0.2-0.5 kg. The
210
Pb intake is not much higher than that of the
populations of other areas, but the 2 10 Po intake isabout one order of magnitude higher, a typical value
being 100 pCi d- 1 •(iii) Distribution in man and absorbed doses

136. Lead-210, bismuth-210 and polonium-210, being
the last radionuclides of the 2 2 6 Ra decay chain, would
be present in the human body even in the absence of
direct intake. However, under normal conditions, thedecay of 2 2 6 Ra, 2 2 2 Rn and their short-lived products inthe body does not play a major role in the accumulationof 210 Pb and 210 Po in the body {133, 135). Only inoccupational exposure, such as in uranium mining, is therole of the precursors important.
f37. Lead is a bone seeker which is found incorporated
in bone mineral, from where it seems to be eliminatedby the process of Jong-term skeletal remodelling (144,162, 208). About 70 per cent of the body content of210
Pb is found in the skeleton {162). According toHoltzrnan's study {135), in which 128 bone samples
were examined for 210 Pb content, the concentration inmales is higher than in females. In both sexes, the levelin cancellous bone was found to be 70 per cent higher
than in compact bone. No clear correlation could befound in that study between the age of the subject andthe 2 1 0 Pb concentration in bone, but it is worth
mentioning that stable lead concentrations increase withage {167, 308).
138. The 2 10 Pb activity concentrations in bone ash
presented in table 21 show that, in continental areas of
the northern latitudes, a typical value could be
0.15 pCi g- 1 , corresponding to a skeletal content of
400 pCi. In island areas the concentrations in humanbone appear to be somewhat lower than in continental
regions.
139. Assuming that the rate of elimination of 2 1 0 Pb
from bone is described by a single exponential, the total
activity in the skeleton A due to both inhalation andingestion may be estimated from the relationshipA = (Te/0.693) (lmhfinh + ImJing)

66

where I is the daily activity intake (Jinh from inhalationand ling from ingestion), f the fraction of the intake
which is deposited in the skeleton, and Te is theeffective half-life of 2 10 Pb, taken here to be 3300 d(135). In the case of ingestion, assuming a blood uptake
from the gastro-intestinal tract of 0.08 and a fractional
deposition in the skeleton from blood of 0.28, a daily
intake of 3 pCi leads to a bone deposition of
0.067 pCi d -l and to a contribution to the equilibriumskeletal activity of 320 pCi. With respect to inhalation, if
it is assumed that one half of the activity is deposited in
the respiratory tract and that one third of the activity
deposited is absorbed into the blood and the remaining
two thirds are subsequently ingested, a daily intake byinhalation of 0.3 pCi d -l corresponds to a bone
deposition of 0.016 pCi d- 1 and a skeletal content of
76 pCi. The sum of the contributions from inhalationand ingestion to the skeletal content is thus estimated to
be about 400 pCi.
140. Polonium, in contrast to all the other natural alphaemitters, is not a bone seeker but rather accumulates insoft tissues. Therefore. the greatest part of the 210 Po
bone activity arises from the decay of deposited 2 1 0 Pb
(131, 370). Average measured ratios of 210 Po and210
Pb activity concentrations in bone range from 05 to
I.I (35, 135, 180, 1'96, 246). A value of0.8 is assumed
to be representative for the purposes of this report.
Using an average 21 0 Pb activity concentration per unit
mass of ash of 0.15 pCi g- 1 and a 2 10 Po/21 0 Pb ratio of
0.8, the 2 1 0 Po concentration in bone ash would be
0.12 pCi g -l for the populations living in continental
areas in temperate regions of the northern hemisphere.
141. With respect to the soft tissues, 2 1 0 Pb and 2 1 0 Po
are distributed relatively uniformly throughout the
body. From measured concentrations the total amountof 2 1 0 Po in soft tissues has been estimated to be 72 pCi
by Kauranen and Miettinen (180), 160 pCi by Parfenov(267), and 250 pCi by Ladinskaya et al {196), while thecorresponding estimates for 210 Pb were 60, 156, and266 pCi, respectively. Although there is a factor of
more than 3 between the extreme values regarding agiven radionuclide, it is worth noting that in the threestudies the 210 Po/2 1 0 Pb activity ratio is found to beabout 1. Assuming that 70 per cent of the whole-bodycontent of 21 0 Pb is in bone, the representative val·1e of
400 pCi for the 2 1 0 Pb skeletal activity corresponds toan activity of 170 pCi of 2 1 0 Pb and a like amount of2
1 Po in the soft tissues.

°142. Typical concentrations of 21 0 Pb and 210 Po in the
gonads seem to be about 6 pCi kg- 1 {19, 35, 196). In
the lung, the concentrations in non-smokers are around
3 pCi kg- 1 for 210 Po and 6 pCi kg- 1 for 210 Pb (35,139). In red bone marrow, Baratta and Ferri {19)reported 2 1 0 Po concentrations of 26 pCi kg- 1 in men
and 21 pCi kg- 1 in women, but a more recent study byLadinskaya et al. ( 196) found a much lower value of
3.8pCikg- 1 and a 210 Po/210 Pb activity ratio of0.8,
which will be used in this Annex for the purpose of
assessing doses.
143. It is interesting to estimate how much 2 1 0 Po insoft tissues is due to the decay of 2 1 0 Pb in soft tissues,
to the elimination of 2 1 0 Po from bone, and to the direct
dietary intake of 210 Po. Assuming a 2 1 0 Po dietaryintake of 3 pCi d- 1 , a blood uptake of 0.35 (196, 294)
and an effective half-life in the body of 50 d (309), thecontribution to the 2 10 Po inventory in soft tissues fromthe 2 10 Po dietary intake would be abbut 75 pCi. As
inhalation of 2 10 Po, at least for non-smokers, does notlead to a substantial activity in the body, the rest of the
21 0
Po inventory would result from the decay of 2 1 0 Pb.
An average 2 10 Po/2 1 0 Pb ratio of 0.8 in bone yields acontribution of about 30 pCi from the elimination of210
Pb in bone. Finally, the decay of 210 Pb in soft
tissues leads to an amount of 85 pCi if it is assumed thatthe 2 10 Po/2 1 0 Pb ratio at equilibrium in soft tissues, inthe absence of any intake of 2 1 0 Po, is 0.5 ( 162). The
2 10
Po inventory in soft tissues obtained in this way is
190 pCi. Considering the uncertainties attached to thevalues of the parameters used, this result is in good
agreement with the value of 170 pCi given in thepreceding paragraphs.
144. The 2 10 Po activity in man being about 500 pCi(320 pCi in bone and 170 pCi in soft tissues) and thecontribution to that activity due to the 2 1 0 Po dietaryintake being only about 75 pCi, it is clear that the 2 1 0 Po
activity in man depends little on the amount present indiet. It is detennined mainly by the concentration of
21 0
Pb in the body. since approximately 85 per cent of

the 2 1 0 Po body content arises from the decay of 2 1 0 Pb.
This view has also been expressed by Holtzman (136)and by Parfenov (267).
145. Although in most of the soft tissues, thePo/2 10 Pb activity concentration ratio is about 1. itis clearly greater than 1 in a few organs such as the liverand kidney. The excess 2 1 0 Po is probably taken up
directly from food and would be partly attnbutable to ahigher rate of incorporation for 21 0 Po than for 2 1 0 Pb in
those organs (162). It has been suggested (80. 131) thatthe distribution of polonium might be similar to that ofsulphur, which might be replaced by polonium in several
chemical compounds of the body.
210

146. Absorbed doses. The absorbed doses from the
Pb chain depend mainly on the highly energeticalpha particles of 2 1 0 Po, the contribution from the beta
emissions of 2 1 0 Pb and 2 1 0 Bi being at most 30 per centof the dose from 210 Po. For non-smokers, the annual
absorbed doses in the lungs and gonads are about 03
and 0.6 mrad, respectively; those in tissues in bone,
calculated using the dosimetric factors presented infigures IX and X, are found to be 3 mrad for bone lining
cells and 0.7 mrad for the red marrow (table 23). The
annual average whole-body dose is about 0.7 mrad.
210

TABLE 23. ESTIMATED TISSUE CONCENTRATION AND A.'mUAL ABSORBED DOSE DUE TO
21 0
Pb, 110 Bi AND 21 "Po IN AREAS OF NORMAL A.ND HIGH DIETARY INTAKE

Average tissue concentration (pCi kg" 1)
Area andradionuclide

GonadsLung

Cancellous
bone

Red
bone
marrow

6
6
6

6
6
3

100
100
80

5
5

8
8
8

9
9
9

130
130
100

5

15
15
72

15
15
36

250
250
200

12
12
48

Annual tissue absorbed dose (mrad)
Red

Bone
liningcells

GonadsLungbonemarrow

6 10·•
4 10-1
6 10·•

6 10-•
4 10-1
3 10· 1

5 10·•
2 10·•
7 10-18 10·•
4 10· 13

8 10·•
6 10-1
8 10-18 10·•
7 10· 2
9 10-1

6 10-•
3 10·•
9 10·•

1 10·>
6 10·•
4

Areas of normal
dietary intake
Non-smokers
llOpb

110Bi
nopo
Smokers
llOPb

210Bi
11opo

4
6
6

Areas of highdietary intake
Reindeer or
caribou eaters
llOPb

210Bi ·
11opo

147. Differences between smokers and non-smokers.
The additional intake due to smoking leads to increased
concentrations of 2 1 0 Pb and 2 1 0 Po in organs andtissues. As expected, it is in the lung that the increase ismost clearly marked. The concentrations in that organ
exceed on the average the levels found in non-smokers
by factors of about l .5 for 2 1 0 Pb and 3 for 2 1 0 Po (35,131. 267, 289). However. in spite of the fact that thedaily intake from smoking is at least 20 times the natural
intake from atmospheric air, the ratio of the amounts
contained in the lungs of smokers and non-smokers is
relatively small. This strongly suggests that 21 0 Po inhaledduring smoking is rapidly removed from the lungs (267).

1.4 10-> 1.4 10· 3 1.3 10-• 1.9 10·>
1 10· 1 1 10-• 6 10-1
1
7
4
5
10

148. Data on the degree of non-uniformity of 2 1 0 Po in
the individual tissues of the lungs of smokers arecontradictory. One school of thought holds that 21 0 Po
can be concentrated in the bronchial epithelium,
particularly at points of bifurcation (207, 287), whereas
the other considers that the levels in the bronchial
epithelium do not exceed those in the alveolar region( 131. 289). As a result. the estimates of the annual
absorbed dose in the bronchial epithelium as compiled inreference (267), range from 4 to 3000 mrad.
149. The increase due to smoking is less clear in organs
other than lung. Parfenov (267), summarizing the67

relevant published data, shows that on the average theconcentrations in the soft tissues of cigarettesmokers is higher than the corresponding concentrations
in non-smokers by about 30 per cent, but points outthat a number of studies have failed to reveal astatistically significant difference (19, 35,206).

radon and thoron and their daughters outdoors has been
extensively studied since they are also of interest as
tracer elements in meteorological studies. The following
paragraphs summarize the data of interest on levels anddoses and the factors which explain these levels anddoses.

150. An estimate of the increase of the 210 Pb andPo concentration in smokers can be made from theintake and metabolism information presented above. An
additional daily intake of 1.6 pCi of 2 1 0 Po fromsmoking would yield at equilibrium an additional
content of 32 pCi in the soft tissues, which would
increase the average value by about 20 per cent. A more
substantial increase would arise from the additional daily
intake of 1.2 pCi of 21 0 Pb, which would result in an
additional bone content of 300 pCi at equilibrium and in
an excess of 75 per cent above the average value. It
should be pointed out, however, that, under conditionsof steady smoking, a few months are sufficient for
2 10
Po to approach its equilibrium value in the soft
tissues, while tens of years would be required for 2 1 0 Pb.
The full effect of cigarette smoking on the bodycontents of 2 1 0 Pb and 21 0 Po in smokers can thus only
be experienced after a long period of steady smoking.
Shorter periods would cause the excess to lie in therange from 20 to 95 per cent, which is in agreement withthe average value of 30 per cent derived fromexperimental studies and used here to calculate the doses
in smokers (table 23).

(a) Exposure-dose relationship2 1 0 Po

21 0151. Reindeer or caribou eaters. Measurements carriedout on the blood, placenta and bone tissue of
inhabitants of the northern regions who consume
caribou or reindeer meat regularly show levels higher
than those in the populations of the temperate latitudes(table 22). The increase is by a factor of about 2 for
21 0
Pb in all tissues and a factor of about 10 for 2 1 0 Po
in the placenta, which is taken to be representative of all
the soft tissues. On the basis of their own measurements,
Kauranen and Miettinen (180) estimated the factors ofincrease to be 2.5 for 210 Pb and 12 for 210 Po. The useof these values leads to the doses indicated in table 23. It
is interesting to note that the factors are estimated to be
1.6 for 210 Pb and 14 for 210 Po when calculated fromestimated dietary intakes of 6 pCi d -l for 2 1 0 Pb andlOOpCid- 1 for 210 Po, using the values of themetabolism parameter indicated in previous paragraphs.

C. RADON-222, RADON-220 AND THEIRSHORT-LIVED DECAY PRODUCTS

I. Inhalation
152. In the decay chains of 238 U and 232 Th, 222 Rn(radon) and 220 Rn (thoron) are the only isotopes ofnoble gases. This property allows them to emanate fromthe ground and to be present in the atmosphere in muchlarger concentrations than their precursors. Exposure to
the inhaled short-lived decay products of radon andthoron constitutes the main natural irradiation of thevarious parts of the human respiratory tract. The majorpart is normally caused by radon daughters rather thanby thoron daughters, and by indoor exposure. Although
outdoor exposure is normally smaller, the occurrence of68153. Radon and thoron emanate from soil, water,building materials etc. and become dispersed in the air in
the gaseous phase. The decay products, radon andthoron daughters, are produced as free atoms, usually as
positive ioµs since the alpha particles carry electrons
away from the atom during the decay process. These
ions tend to form clusters very rapidly with water,
oxygen or other trace gases. Soon afterwards, in a matterof seconds to minutes, these clusters tend to attach
themselves to aerosol particles. The dimensions of theaerosol particles being much larger than those of theclusters, the aerosols inhaled do not deposit in the same
region of the respiratory tract as the clusters. It is thus
important to make a distinction between the fraction of
the activity of the short-lived decay products of radon
carried by clusters, which is called the unattached' fraction, and the fraction fixed on aerosol particles.
called the attached fraction.
154. The concentration of radon and thoron daughtersin air may be expressed in terms of activity
concentration (unit: pCil- 1 ), or in terms of potentialalpha-energy concentration, which is defined as the totalalpha energy released per unit volume by the short-lived
daughters in their decay (unit: MeV 1- 1 ). A unit which
has been used in mines to describe the radon
decay-product activities in air in terms of potential alphaenergy is the working level (WL). It is defined as any
combination of short-lived radon daughters (through2 14Po) per litre of air that will result in the emission of
I.3 10 5 MeV of alpha energy. An activity concentrationof 100 pCi i- 1 of 2 2 2 Rn, in equilibrium with its
daughters, corresponds to a potential alpha-energy
concentration of 1 WL. The WL unit could tlso be used
for thoron daughters. In this case, 1.3 105 MeV of alphaenergy (1 WL) is released by the thoron daughters inequilibrium with 7.5 pCi of thoron per litre. Table 24
shows the potential alpha-energy concentrations ofradon and thoron daughters (157).
155. Radon and thoron daughters in air are very seldon
in equilibrium with radon and thoron, respectively. The
equilibrium factor F is defined as the ratio of the total
potential alpha energy of the given daughter concentrations to the total potential alpha energy of thedaughters if they are in equilibrium with radon andthoron, respectively.
156. It follows from the definition of the WL that theequilibrium factor F for radon or thoron (Tn) can becalculated as
FRn =a(a)Rnf<Rn); FTn =b(a)TnfITn)

where (a)Rn and (a)Tn are the potential alpha-energy
concentrations, in WL, of Rn daughers and Tn
daughters, respectively; <Rn) is the activity concentration, in pCi 1- 1 • of radon; (fn) is the activity
concentration, in pCi r 1 , of thoron; and a and b are
constants (a= 100 pCi/WL, b = 1.5 pCi/WL).

TABLE 24. POTENTIAL ALPHA ENERGY OF THE SHORT-LIVED DECAY PRODUCTS OF 222 Rn AND »o Rn

Radionuclide

mpo (Ra A)
214

Pb (Ra B)
214
Bi (Ra C)"'Po (Ra C')
216po (Th A)
212

212

Pb(Th B)
Bi(ThC)212

Po (Th C')

Potentialalpha energy (Me VJ

Conversion factor

Radioactive
half-life

Numberof atoms
perpicocurle

Per atomPerpicocurie

3.05 min26.8 min19.7min
1.6 10 4 s
0.158 s10.6 h60.5 min3 10-• s

9.77
85.3
63.l
10-s
0.008442040
194
1.6 10-s

13.68
7.68
7.68
7.68
14.57
7.79
7.79
8.78

134
659
485
7.68 10-•0.123
15 9001 510
1.4 10-•157. If in a given atmosphere radon (or thoron) is notin equilibrium with its daughte·rs and the concentrationof radon ( or thoron) is C, the product CF corresponds toa concentration of radon (or thoron) for which thedaughters in equilibrium would have the same potentialalpha-energy concentration as the actual atmosphere ofinterest. The product CF will be referred to in thisreport as the equilibrium equivalent concentration ofradon (or thoron).

per cent

158. For the purpose of this report, exposure to radonand its daughters is defined as the integral of the activity
concentration in air over the exposure time. The unit,
working level month (WLM), is often used in connection
with radon in mines, and means an exposure during
170 working hours in a radon daughter concentration of
1 WL. One WLM corresponds to a time-integral of theequilibrium equivalent concentration of 1.7 104 pCi h 1- 1
for occupational exposure in mines. For thoron daughters,
I WLM corresponds to an exposure during 170 working
hours in a thoron daughter concentration of 1 WL, whichis equivalent to a time-integral of the equilibrium equivalent concentration of 1.3 103 pCi h 1 - 1 for occupational exposure in mines.

en

WL

Mevr•
pCi/" 1

par•

134
659
485
7.68 10-•0.123
15 9001 510
1.4 10-•0.00103
0.005070.00373
6 10- 1 0
9.5 10-•0.12230.0116
1 10-1:

100

w
N

iii
0

w
u..

80

u

w

0.

2

<(

J:

I-

a:
w

60

..J
..J
<(
~

en
en
w

..J

u
i= 40
a:

<(
0.

u..
0

w

c:,
<(

159. The deposition in the respiratory system of radon
and thoron daughters attached to aerosol particles
depends on, among other things, the size distribution of
the radioactive aerosol, this size distribution being
closely related to the size distribution of the inactive
aerosol present. In both free air and room air this size
distribution is relatively constant. Figure X.V shows the
typical size distribution of the natural aerosols carrying
short-lived radon daughters (146, 242a). When theseaerosols are inhaled, up to 60 per cent of the particles
are deposited in different regions of the respiratory·
system. The attached radon and thoron daughters aremainly deposited in the pulmonary region. The
unattached daughters are deposited in the upper
respiratory tract on account of their high diffusion
coefficient. ·Because of the efficient deposition of
unattached daughters in the respiratory tract, experimentally proved with a model by Chamberlain andDyson (55), the unattached fraction has since been given
great attention. However, the fraction of unattacheddaughters in air is often small and a major proportion(up to 60-70 per cent) of the unattached daughters in
the inhaled air is removed by nasal deposition (93).
160. In indoor air the degree of equilibrium between
radon ( or thoron) and its daughters and the fraction of

I-

2

w
u
a:
w

20

0.

0.010

0.020

0.050

0.100

µm

PARTICLE RADIUS

Figure XV. Size distribution of the natural carriers of 21 • Pb
and 21 4 Bi (149, 242a}unattached daughters are affected by the ventilation rate·(126), by the deposition on walls (371), and byattachment to aerosols. The relative influence of thesefactors has been considered on a theoretical basis by
Jacobi (157). It was found that the fraction of
unattached daughters increases markedly with decreasing
aerosol concentration and decreasing residence time of
the air. Since enhanced ventilation reduces the residence
time of the air and also usually the aerosol
concentration, the effect on the fraction of unattacheddaughters is considerable. However, the net effect ofincreased ventilation is a reduction of dose due to a large
decrease of the potential alpha-energy concentration. In
69daughters, 1.3 per cent. Taking into account thedeposition and translocation rates. the doses in different
regions of the bronchial tree were calculated. With anaerosol size distribution with an activity medianaerodynamic diameter (AMAD) of 0.3 µm, the highest
regional activities were found in the segmental
bronchioles (tertiary bronchi generation 4 of the Weibel
model). The dose-to-exposure quotient was estimatedfor different depths of the airway wall. In basal cell
nuclei at a depth of 22 µm, it was found to be 02 rad(WLMr 1 for a breathing rate of 15 l rnin- 1 , anequilibrium factor F = 1, and 4 per cent of unattached
2 18
Po a toms. However, if these parameters change, so
also does the relationship between the dose and theexposure. For example with F = 0.3 and 4 per centunattached 218 Po, the value is 0.4 rad (WLM)- 1 .

a poorly ventilated room with a low aerosol
concentration, wall deposition of unattached daughters
plays an important role in reducing their concentrationin air.
161. Inhalation of radon and thoron daughters results
in an inhomogeneous internal irradiation of therespiratory tract, with the dose absorbed primarily in the
bronchial region. The factors which influence thedeposition and fate of inhaled activity and the doses,
apart from the physical characteristics of the radioactive
aerosol, are:
Way of breathing, i.e., mouth breathing or nose
breathing and the rate and the depth of respiration
Geometrical parameters of different regions of therespiratory system

164. Corresponding calculations concerning thoron
daughters have been made (124). The highest regional
activities were found in the terminal bronchioles(generation 10 of the Weibel model). For that region,and for an AMAD of 0.15 µm and 2.2 per centunattached 212 Pb, a factor of 0.7 rad (WLM)- 1 may be
calculated from Harley's data (124). The contribution
from the unattached activity is about 20 per cent.

Translocation and clearance of deposited activity
Several models have been used to calculate the resultant
doses in the respiratory system, assuming different
characteristics of the radioactive aerosol, including thefraction of unattached activity.
162. A recent study was made by Harley andPasternack (123), who performed experimental
stopping-power measurements with tissue equivalentmaterial using radon daughters. In the calculation ofdoses it was assumed, on the basis of the experimental
results of Kirichenko et al. (184), that the activity washomogeneously distributed in the mucous layer. Thelung geometry used in the calculations was based on the
Weibel lung model (360), and the fractional retention
was tabulated by applying the Gormley-Kennedy
equations (104).

165. Another recent study of doses from inhaled radon
and thoron daughters has been made by Jacobi (158,159) as a continuation of his studies on thecharacteristics of the inhaled aerosol, activity andpotential alpha-energy of radon and thoron daughters.
He calculated the doses in the trachea-bronchial region(T-B) and in the pulmonary region (P) assuming themasses to be 45 g and 955 g, respectively. The doses
were derived as a function of the unattached fraction f Pof the total potential alpha energy in the inhaled air. The
mean dose from alpha particles is shown in table 25 for abreathing rate of 20 1 min -l.

163. The removal of unattached daughters in the nose
was assumed to be 60 per cent (93) and of the attached

TABLE 25. MEAN DOSE FROM ALPHA PARTICLES IN THE TRACHEO·
BRONCHIAL AND PULMONARY REGIONS AS A FUNCTION OF THE
UNATIACHED FRACTION /p OF THE POTENTIAL ALPHA ENERGYIN AIR
Nose breathing
Dose-to-exposure quotient
Dose totime-integral ofpotential alphaenergy(rad per WLM)

Dose to timeintegral of equilibrium
equivalentconcentration(rad per pCi h r')

0.31 (1 + 6/i)
0.012 (1 + 5.{p)

1.9 10·• (1 + 6 fy)
10-s (1 + 5 Jp}

0.16 (1 - J; )0.087 (1 -10·• (1-J;)
1.6 10·•Tracheobro11clzial region
Radon daughters
Thoran daughters

Pulmonary region
Radon daughters
Theron daughters

166. It was concluded that the mean dose-to-exposure
quotient in the T-B region increases with increasing
ventilation rate and decreases with increasing aerosol
concentration. For the P region the variation is reversed.
As seen in table 25, the mean dose-to-exposure quotient
for thoron daughters is higher in the P region than in the
T-B region with low values of [p. A large fraction of thealpha energy deposited in the T-B region is deposited in
70{p)

u -f!>

the mucous sheet, ciliated cells and goblet cells on the
bronchial epithelium. The dose in the underlying basal
cells. where bronchogenic lung cancer is assumed tooriginate, was derived from different lung models. If thefraction /p of the total potential alpha energy
contributed by unattached radon daughters varied
between 0.02 and 0.1, the factor estimated fromdifferent models covered a range from 0.2 to 10 rad

(WLM)- 1 , assuming nose breathing at
20lmin- 1 •a rate of167. The lung cancer among uranium miners predominantly appearing in the area of the large bronchi(217) presumably originates in the basal cells in thebasement membrane of the upper bronchial epithelium.
It seems reasonable to regard the doses in these cells as
the most relevant in the discussion of the correlation
between dose and effect. However, there is still
incomplete knowledge of the distribution of dose andthe genesis of cancer in the basal cells and it is not yet

considered appropriate to use only the dose in the basal
cells as the basis for the risk assessments. As discussed in
Annex G, most risk assessments are based on the direct
relationship between lung cancer incidence among
uranium miners and exposure as expressed in WLM. In
addition, for purposes of comparison with otherirradiation conditions of the lung, the mean dose in thelung is also calculated in this report.
168. The distribution of the values of the dose-toexposure quotient for radon daughters, derived fromdifferent models is shown in table 26 (171). From theTABLE 26. DOSE-TO-EXPOSURE QUOTIENT FOR RADON DAUGHTERS
Segmental bronchial epithelium

Relative activity concentration
Rn:RaA:RaB:RaC

Exposure conditions

Lung model

Dose-toexposure
quotient(radper WLM)

0.3-µm particles

Weibel (A), 15 1 min· 1

0.2

123

0.3

0.3-µm particles

Weibel (A), 15 1 min- 1

0.4

123

0.6

0.3-µm particles

Landahl

Equl1ibrium
factor F

10: 10: 10: 10
4%free Ra A

10: 6 : 3: 2

Reference

4% free Ra A
10:9:6:4
Noneq uilibrium;
little free Ra A<l

Nonequilibrium;
1-2% free Ra A<l

10: 10: 6: 4

0.6

10: 9: 6: 4

0.6

123
247

Clean airRevised ICRP

0.3-1

158

I h ·• air change;

Findeisen-Landahl,
141 min- 1

1.7

156

0.09-µm particles·

Findeisen-Landahl,
14 1 min· 1

2.7

156

0.3-µm particles

Landahl, 15 1 min·•,mouth breathing

2.0

217

0.09-µm particles,
104 cm·'

10: 10: 10: 10

1.7
0.5-1

8

10:9:6:4
8.5% free Ra A
10 : 9 : 5 : 3.50.6

0.3-µm particles

Nose breathing

l.1

0.5

Adequately ventilatedroom

Weibel, 15 I min· 1,
mouth breathing

1.7-12120

10: 9: 6: 40.6

0.1-µm particles

15 I min· 1

2.2

49

calculations described above, it is believed (159) that in
the case of mining conditions (/p < 0.1) the alpha dosein the basal cell layer of the critical bronchial region liesat the lower end of the range of 0.2-10 rad (WLM)- 1
and that a value of 1 rad (WLM)- 1 could be used in theassessments of dose. One rad per WLM corresponds to
60 µrad per pCi h 1- 1 for occupational exposure inmines. In the case of exposure in houses and outdoor air,taking into account the lower mean breathing rate, theconversion factor would be 45 µrad per pCi h 1- 1 •However, it is recognized that such importantparameters as the size distribution of the aerosols
carrying the short-lived radon daughters, the way ofbreathing and the rate of ventilation might differ fromwhat is found in mining conditions. With regard to themean dose in the lung, from the data in table 25 a meanvalue of 0.2 rad (WLM)- 1 can be derived. correspondiny
to dose-to-exposure quotients of 9 µrad per pCi h 1in houses and outdoor air and 12 µrad per pCi h 1- 1
under occupational conditions.
169. In the case of thoron daughters, the highest doses
occur in the terminal broncholi and the alveolar region.

8

It seems reasonable therefore to estimate only the meanlung dose for the purpose of this report. From the data
in table 25, a value of 0.1 rad (WLM)- 1 can be derived,
corresponding to 60 µrad per pCi h 1- 1 for exposure
outdoors and in houses.

(b) Exposure outdoors(i)Sources170. Radon and thoron in the atmosphere originate
mainly from emanation from the soil. Wilkening et al.
(366) reviewed the results of about a thousandmeasurements of the 2 2 2 Rn emanation rate from soil
and obtained an overall mean value of 0.42 pCi m - 2 s- 1 ,with a range from 6 10- 3 to 1.4 pCi m - 2 s- 1 • Theirworld-wide estimate for the total 2 2 2 Rn emanation ratefrom the land areas of the globe is about 50 Ci s- 1 • The
contribution from the oceans is one to two orders ofmagnitude smaller ( 122, 386), the other souces are
negligibly small. Even though the concentrations of
23 8
U and 2 3 2 Th in the soil are about the same, theemanation rate of thoron in terms of activity is about a71hundred times higher than that of radon because of its
higher decay constant (33, 122).
171. The equilibrium activity of radon in theatmosphere is estimated to be 2.5 107 Ci (3?6), and theaverage surface air concentration, 0.07 pCi 1- 1 (122).
The total inventory of thoron in the atmosphere is muchless because of the short half-life of thoron. How ever, inthe first few metres above ground level, the thoron
concentrations are of the same order of magnitude as
those of radon.
172. The only significant sources of radon and thoron
daughters in the atmosphere are the radon and thoron in
the air. The concentration of the daughter products
depends on the concentration of radon and thoron, theheight above earth and the meteorological conditions.
Because of wash-out effects in connection with
precipitation and deposition, the concentration of radon
daughters is often lower than that of radon and theconcentration of thoron daughters is much lower thanthat of thoron near the ground.

17 5. The concentration of radon and thoron in the air
depend on their emanation rate from the soil,
meteorological factors, geographical factors and theheight of observation. The vertical distribution of radonand its daughters has been studied by several
investigators (10, 34, 44, 183, 198, 238, 364, 365).
Normally, the radon concentration decreases withincreasing altitude, but there are different profiles ofradon concentration at different locations and times.
The reported values are in the range 0.1-0.01 pCil- 1
from about 0.1 km above ground to an altitude of
2-3 km; above this height the concentration is less than
0.01 pCi 1- 1 • The results of measurements of the vertical
distribution of radon in Illinois (United States) are
shown in figure XVI (44). Figure XVII shows a typical
pO

,l
0.2

z
;::

<
z
w
<.>
z

;=

Emanation from the soil

1·•1

0.4

0

(ii)

Variations in air concentration

(iii)

i ·,
~

0.05

0.02

u
>-

..

u

0

0

~~-.
". ~ ........
',·.:"''\' \. ·,...

>;:: 0.01<z

8-3-67t-. ', ·,'\..

0173. The emanation rate of radon is influenced by thecondition of the soil, its porosity, moisture content andtemperature (77, 229, 285). The emanation is reducedby snow cover, increasing atmospheric pressure, andheavy rainfall (193, 229, 338). Light rainfall does notaffect the emanation since it only moistens a thinsurface layer of soil. Diurnal variations of the emanation,
within a factor of 2, may occur with maxima at night
and minima during the afternoon (310). The variations
are influenced by two opposing factors. Temperature
differences in the soil during the night cause convective
flow in the top layer leading to an increased nocturnal
emanation. On the other hand, the greater turbulent
mixing in the atmosphere in daytime enhances thedaytime emanation and the diurnal fluctuations aresmoothed out (229, 310). The seasonal variations of theemanation rate depend on the climatic conditions.
Where there is no snow and temperatures are normally
above O"C all year, only small seasonal variations havebeen found (229), probably because of the relatively
constant moisture content of the deeper soil levels.

·<'·,,.:.:, ·,.

'

l.:~

0.005

<
a:
0.002

0.001

0

5

ALTITUDE

Figure XVI. Variation of radon concentration with altitude
(44)

z

0

i=

<
a:

17 4. Because of the very short radioactive half-life ofthoron (55s), the emanation of thoron is more
dependent on the soil conditions and on meteorologicalfactors than is that of radon. The effective emanating
soil thickness is of the order of a few centimetres. The
emanation decreases rapidly when the moisture increases. The thoron emanation in summer seems to beabout twice that in winter mainly because of higher
moisture in the soil in the winter than in the summer.
When the soil surface is warmer than the air, theemanation of thoron increases because of convection.
This explains the diurnal variations of the emanation ofthoron on dry summer days with maxima at sunset andat night and minima at sunrise and early in the day. The
variations have been found to be within 30 per cent of
the mean. The influence of several other factors on theemanation rate of thoron have been reported in theliterature (75, 108,220,229, 331).

72

I-

z

w

0.1

CJ

z

0

CJ

>-

I-

>
i=
CJ

<

z

0

a: 0.01
0

:i::

I-

HEIGHT

Figure XVII. Vertical profile of thoron in the atmosphere
for wind speeds ranging from 4 to 12 m s· 1 {75)kmvertical profile of thoron below a height of 10 m forwind speeds ranging from 4 to 12 m s- 1 (75). The
vertical distributions of radon and thoron close to theground are also shown in figures XVIII and XIX which

2

0

A -

on sunny days

<:
a:

B

at night

i=
I-

2

UJ
(.)

177. The seasonal variation of radon concentration
depends mainly on the seasonal variation of turbulence.
A maximum value of the radon concentration at groundlevel is reported to occur in the autumn and early
winter, corresponding to a minimum in turbulent
transfer. The minimum occurs in the spring. The local
seasonal variations are normally less than a factor of five.
The concentration of thoron in ground-level air is of thesame order of magnitude as that of radon.

2

2

0

B

(.)

>I>
i=
(.)
<l:

o ... 'o.. __20--0----------A-----------o

0

<l:

a:

0

3

2

m

HEIGHT

Figure XVIII. Vertical distribution of radon concentration
pCi 1- 1
5

z

4

0

i=
<i:

0:

1-

z

w

u

z

3-

A

on sunny days

B -at night

0

u
>-

1-

>

i=

u

<i:

z

0

0:

0

:r

I-

176. The diurnal and seasonal variations of radon andthoron at ground level have been studied by several
investigators (37, 141, 154, 155, 220. 310, 317). Eddy
diffusion is the mechanism by which radon and thoron
and their daughter products are transferred upward fromground level. The diurnal variation of the diffusion
coefficient may be two orders of magnitude (298). The
corresponding diurnal variation of radon is normally less,within one order of magnitude. As a rule, a maximum
occurs towards the end of the night. and a minimum inthe afternoon.

2

~

I

\

178. As the emanation rates of radon and thoron aremuch smaller over sea than over land, the concentrationsof radon and thoron in ground-level air depend on thewind direction and on geographical factors. The
concentration of radon at ground level is of the order of
0.1 pCil -i in continental air, 0.0 l pCil -l in coastal
areas and islands, and of the order of 0.001 pCi 1-1 inoceans and arctic areas (347). In coastal areas, thediurnal variation is increased by the much smaller radon
concentration during the day under sea-breeze conditions than at night with offshore winds. Inland. far awayfrom the coast, there seems to be no correlation between
radon concentration and wind direction (141). On theother hand, air which has passed over land can be
identified thousands of kilometres from the coast at sea,
where the emanation rates are very low (286). The
concentrations of radon and thoron are reported to bevery dependent on wind speed and temperature
stratification (155). This correlation is probably causedby the close connection between wind speed and theintensity of turbulent transfer (141, 155). Maximum
values of the radon and thoron concentrations occur
during light-wind conditions, but the relation between
the concentration of radon and thoron and the windspeed seems to be greatly affected by the stability of theatmosphere ( 146).

'I

I
I

(iv)

'b,

',

A',

\

'0----------~-

0 ~-----.------.------.....----3m
0
2

HEIGHT

Figure XIX. Vertical distribution of thoron concentration

illustrate the influence of turbulent transfer on theradon and thoron profiles. The greater turbulence in thedaytime causes smaller gradients and smaller absolutelevels of radon and thoron than at night. At 1 m andabove, the concentrations of thoron are about the samenight and day.

Levels and doses

179. As discussed in previous paragraphs, there arevariations of the radon and thoron concentrations in air
depending on local conditions. Similar variations arefound for the daughters of radon and thoron, thevariation being enhanced by wash-out and deposition
effects. It is therefore very difficult to estimate
representative values for the concentration of radon andthoron daughters in air, unless long-duration measurements are made. To estimate the resultant doses, it isalso important to know the characteristics of theaerosols inhaled, and also the proportion of time spentout of doors. This proportion varies for different people
depending on season. country, age, habits and type ofwork. For the purpose of this report it will be assumed
that 20 per cent of the time is spent out of doors (4-5 h
per day).
73

180. The equilibrium factor F for radon has been
considered by several authors directly or indirectly. By
comparing the activities of 2 14 Pb and 2 14 Bi and radonin the summer. autumn and winter at a height of 1 m
above the ground. it was concluded that the deviationfrom equilibrium was less during the winter than in theautumn or summer (310). In another study (376) inBoston (United States) the concentrations of 218 Po.
2 14
Pb and 2 1 4 Bi were measured. If 2 1 8 Po is assumed to
be in equilibrium with radon, the values of F vary
between about 0.6 and 0.9 with an average of 0.8.
Measurements in France in March 1970 showed that theratio between 214 Pb and radon varied between about
0.6 and 0.7 at I m above the ground and between 0.8
and 1.0 at 13 m above the ground (41). Measurements
made on the air in the city of New York (United States)from July 1973 through June 1974 gave an averageof
0.1 pCi I -i
(rangeradon
concentration
0.06-0.17 pCi 1-1 ), average radon-to-radon daughters
ratios (2 22 Rn: 218 Po: 214 Pb: 214 Bi) of 1:0.9:0.7:0.7
and an average value of F of 0.7 (84). Measurements atthe same place in June and July 1972 gave an averageof
0.2 pCi 1- 1
(rangeradon
concentration
1
0.10-0.22 pCi r ). average radon-to-radon daughters
ratios of 1:0.8:0.5:0.3 and an average value of F of0.4(range 0.18-0.73) (94). Similar measurements in a ruralatmosphere at Sterling Forest, 80 km north of New
York, in July 1972 gave an average radon concentrationof 0.2 pCi 1- 1 (range 0.16-0.26 pCi 1- 1 ), averageradon-to-radon daughters ratios of 1:0.8:0.5 :0.4. and an
average value of F of 0.42 (rang~ 0.08-0.56) (94). The
lowest value, 0.08, occurred on a rainy day when theradon daughter activity dropped by a factor of almost

10.
18 I. The fraction ~f unattached radon daughters 2 outof doors varies primarily with the concentration and size
distribution of the aerosols in the atmosphere.
Measurements at Sutton, England (United Kingdon)
indicated no consistent difference in the unattachedfraction of 2 18 Po indoors and out of doors (76). It
varied between 0.07 and 0.40 (relative to 2 18 Po). In twoseries of measurements in New York City the averages of
the unattached fraction relative to radon were found tobe 0.04 (range 0.01-0.06) (94) and 0.09 (range
0.05-0.12) (84). The average value for unattached 212 Pb
was 0.02 at an average 2 1 2 Pb concentration of
9 10-4 pCil- 1 (84). In Sterling Forest the unattachedfraction of 218 Po was, on the average, 0.08 relative toradon (range 0.04-0.10). The lowest value. 0.04, wasfound on a rainy day. The average aerosol concentration
was 7.5 10 3 particles cm - 3 compared to L9 10 5particles cm - 3 in New York (94).
182. As the fraction of unattached 218 Po is as a ruleless than 0.1. it is possible to estimate the absorbed
doses in the basal cells of the segmental bronchioles
using a value of 45 µrad per pCi h 1- 1 for the quotient1

1 1

The unattached fraction of• Po is either expressed
relative to the total number of atoms of 2 ' 8 Po measured in theatmosphere ("relative to 1 1 • Po") or to the total number ofatoms of 11 8 Po that would be present at equilibrium with
21 2
Rn ("relative to 111 Rn"). Since the atmospheric activity
concentration of 11 • Po is usually more than 80 per cent of its
equilibrium value with 111 Rn, the difference between the twovalues of the unattached fraction of 1 1 • Po is at most 25 per
cent.

74

between the dose and the time-integral of theequilibrium equivalent concentration of radon(para. 168). The mean radon concentration in continental air is about 0.1 pCi 1- 1 (347). with a mean F of
0.6. Using an occupancy factor of 0.2 for outdoor
exposure, the resulting annual dose in the basal cells is
about 5 mrad, with a range of l-25 mrad for different
persons located in different places.
183. In order to assess the relative importance of thevarious natural radionuclides considered in this Annex,
the doses from the radon decay products in thepulmonary region of the lung, the gonads, the bonemarrow and the bone lining cells also have to be
estimated. With regard to the mean dose in the lung,using a dose-to-exposure quotient of 9 µrad per
pCi h 1-r (para. 168), an annual dose of about 1 mradis calculated. The doses in organs and tissues outside therespiratory system have been evaluated. as in the 1972
report, from the measurements in guinea-pigs (281,282). As the ventilation volume and the weight of blood
are about the same for man and for guinea-pigs when
divided by their respective body weight. the results canbe taken as an estimate of the absorbed doses in man.
They are calculated to be 0.007 mrad in the gonads, and
0.008 mrad in the bone marrow and the bone lining
cells.
184. The thoron daughter concentration in air is mainly
measured as the concentration of 21 2 Pb. In continental
air the measured concentrations of 2 1 2 Pb are on the
average about 0.001 pCi 1- 1 (37, 84. 209). This average
is based on several long-term measurements (months toyears) and the range of the results of thesemeasurements is 0.0001-0.003 pCi 1- 1 • Assuming equilibrium between 2 1 2 Pb and 2 1 2 Bi, a dose-to-exposure
quotient of 60 µrad per pCi h 1- 1 can be used to assess
the annual absorbed dose in the whole lung (para. 169).
Assuming an occupancy factor of 0.2 for outdoor
exposure, the annual dose in the lung is estimated to be
0.1 mrad.
185. More than 90 per cent of the 21 2 Pb atoms
deposited in the bronchial tree are eliminated byswallowing before their decay. Those deposited in thepulmonary region are transferred to the blood with abiological half-life of around I Oh, which means thatabout 50 per cent of the potential decay energy of212
Pb is released outside the lung, whereas thecorresponding figure for 214 Pb is only 4 per cent (347).
The annual doses in tissues outside the respiratory
system, as estimated from experiments on guinea-pigs,
are 2 10-4 mrad in the gonads and 3 10- 3 mrad in bonemarrow and in bone lining cells.

(c) Exposure indoors
186. As the indoor concentrations of thoron daughters
are low compared to those of radon daughters, the mainemphasis in this Annex will be on radon. The main
contribution to radon indoors is from the building
materials. Other sources of significance may be the soil
under the building, natural gas and radon-rich water. The
radon level outdoors may sometimes also be ofsignificance for the radon level indoors. Even if manymeasurements have been made on natural radiation

indoors. most indoor measurements have been concerned with the external irradiation and there are only a
few extensive surveys of radon and radon daughter levels
indoors.

(i)

Sources

J87. Factors influencing radon levels in a room. The
radium content of the building materials constitutes thesource of the emanation of radon. High radon levels may
be found in buildings with high radium content in thebuilding materials (142), and it has been shown thatparticularly low radium contents result in low levels(205).
188. However. it is not possible. on a general basis, tocorrelate the radon levels in a building to the radium
content of the building material, mostly because of thestrong influence of ventilation conditions. Furthermore,variations may occur even with the same building
material, depending on the distance from the groundlevel (342) and whether there is a cellar or not. The
higher radon levels in cellars and lower storeys are
believed to be due to radon emanation from the soil, butthey may also be influenced by the lower ventilation. It
is not unusual for different building materials withdifferent radium contents to be used in houses, for outerwalls, for inner walls and for insulation.
189. The diffusion of radon from the building materials
into a room is influenced by the moisture content of thematerial, its density. whether or not sealants are used

and the nature of the material itself. When the moisture
content in concrete increases by a factor of 2 fromabout 3 to 7 per cent by weight, the radon emanation
may increase by 10 to 20 per cent ( 15). Tilis effect has
also been found with soil samples (230) and it depends
on a decreased adsorption power of the particles in thesoil and concrete. If. however. the moisture content
increases further, the emanation rate decreases. The
temperature effect between 20° and 45°C on theemanation rate from concrete has been found to be
insignificant (15). At temperatures lower than 0°C theemanation of radon is expected to decrease (21). It has
been suggested ( 1 19) that the diurnal variations of radonlevels found in some buildings depend on the higher
temperature during the afternoon. causing higher
emanation rates of radon from the walls than during thenight. A possible dependence of the radon emanation
rate on the atmospheric pressure has also been suggested(I 70).
190. Few data for the rate of emanation from building
materials can be found in the literature. They arepresented as diffusion coefficient (unit: cm 2 s- 1 ). as
emanation rate per unit area (pCi m - 2 s- 1 ) or as
fractional escape (pCi escaped per pCi produced).
However. both the fractional escape and the emanation
per unit area depend on the thickness of the material. As
a rule of thumb the fractional escape is of the order of
1 per cent for building materials in walls and ceilings.
Table 27 shows the estimated emanation rate per unit
activity concentration of 22 6 Ra of different materials
based on data given in the references.

TABLE 27. RADON EMANATION RATES OF VARIOUS MATERL\LSMaterial

Emanarion rare of 222 Rn
per unir activity
concenrration of 226 Ra .
(pCi m- 2 s·' per pCi g·•)Comments

Reference

By-product gypsum

0.01

Internal walls
76 mm thick265

By-product gypsum

0.001

Ceilings
13 mm thick

265
306

Concrete

0.005

10 cm thick

Uranium mill tailings

0.2

10 cm thick

306

Uranium mill tailings

1.6"Infinite" thickness306"Infinite" thickness

33

Soil

0.5

Light concrete

0.02

20 cm thick

195

Heavy concrete

0.01

8 cm thick

195

191. The effect of paints and sealants on the emanation
rate is quite variable. Cement plaster and asphalt coatingon the walls does not reduce the emanation rate ( 15).
However, by heavily coating with epoxy paint theemanation rate can be reduced by a factor of 4.
Furthermore, three layers of oil paint reduce the radon
emanation rate by about an order of magnitude (195).
Several sealants have been tested both in the uranium
industry (297) as well as for buildings incorporating
uranium mill tailings in the construction (64).

192. The most effective factor influencing the radonlevel in houses is the ventilation rate, defined as thefractional change of air per unit time. The equilibriumradon concentration in a room varies with theventilation rate Av ( unit: air changes per hour, h -i)
according to the formula

C = Co + eT/(Xv + X)V
where e is the emanation rate (in pCi m - 2 11- 1 ); T, thearea (in m 2 ) of the emanating surfaces: V. the volume75

(in m 3 ) of the room; >.., the decay constant(0.00755 h -l ): and C0 , radon concentration (inpCi m - 3 ) of the ventilation air ( outdoor air). Changes inthe ventilation of a poorly ventilated room influence theradon level considerably. Conversely, the radon level in aroom in which the ventilation ceases may increase to
100 times an earlier level obtained with an air change
rate of I h- 1 • For example, in a room with V = 30 m 3 ,T = 50 m 2 (walls and ceiling), Xv = 1 h -l, e =0.005 pCi m -z s -i per picocurie of 2 2 6 Ra in each gramof concrete (table 27). and concrete with a 2 2 6 Racontent of 5 pCi g- 1 , the radon activity concentration
will be about 0.15 pCi 1- 1 • If the room is unventilated,
the radon activity concentration increases to about
20 pCil- 1 .
193. The ventilation differs in different types of houses,
depending on age, number of storeys and number ofapartments, and in different parts of a building. It isfrequently found that the basement of a house has Jessventilation than the higher floors and that consequently
the radon levels are higher. The ventilation rate in houses
is different in different countries owing to differences inclimate, heating systems and building standards. Airchange rates of 2-5 h- 1 are not unusual in many
countries (347). However, in countries with cold
climates the ventilation rate may be much less; it has
been found to be in the range 0.1-0.9 h -i in central
Sweden in houses built after 1970 (251 ). Central heating
and good insulation reduce air exchange rates andincrease radon concentrations. In some houses, there isoften only natural draught ventilation, which is Jess
efficient than the forced ventilation found in tallbuildings. In the case of recirculated forced-air heatingor recirculation of ventilation air, only a fraction p offresh air is admitted, and the true air exchange rate will
be reduced to AvP·
194. Diurnal variations of the indoor radon levels may
occur because of variations in the outdoor concentrationand the opening or closing of windows. In measurements
in residential structures in Grand Junction (UnitedStates), diurnal variations of a factor of 2-3 were found(322). Variations occurred even in vacant houses. withmaxima in the afternoon and decreasing levels during thenight, and no correlation was found with either thebarometric pressure or the indoor and outdoor
temperatures. Other long-term measurements of radon
concentrations in a house have shown an increase ofradon level during the night up to levels much greaterthan those outdoors (67). The great effect of closing andopening doors between rooms has also been demonstrated in apartments with natural, as well as forced,
ventilation (333). Opening doors could lead to
reductions in the radon levels by a factor of 5.
195. Temperature, wind direction and wind speed
influence the ventilation rate. It has been shown that amere change in wind direction to a direction at rightangles to the outer wall of a badly ventilated room
reduces the radon level by a factor of 3 (333). In rooms
with open vents the reduction is even greater (73). If theradon levels indoors are of the same order as the levels
outdoors, the variation indoors follow the pattern
outdoors, but the variations are smaller ( 119).
76

196. Levels and doses. For the estimation of doses. use
has to be made of the results of a limited number ofmeasurements. Since large variations may occur, as
already described. it may be very difficult to judge how
representative the results are. It has been suggested(369). as a criterion for determining the radon daughters
concentration, that four to six samples of several weeks'
duration spread throughout the year should be necessary
to provide representative values. Results of radon andradon daughter measurements are shown in table 28.
The measurements by Fisenne, Harley and George (84,94) show the effect of recirculation (high fraction of
unattached Ra A, low value of F) and show that evenwith a low ventilation rate the value of F is fairly low(0.4). The radon activity concentrations in the
Hungarian houses (342) are assumed to be numericallyequal to the 2 1 8 Po activity concentrations (according to
the reference). This results in a rather high value of F.
197. There are no direct measurements reported onradon and radon daughters in houses which give valuesof F higher than 0.5. This value is used in this report forthe purpose of assessing doses in cases in which only theradon values have been given. As indicated inparagraph 168, the quotient of bronchial dose to thetime-integral of the equilibrium equivalent concentrationof radon is taken to be 45 µrad per pCi h 1- 1 , as theunattached fraction is of the order of 0.1 or less. The
occupancy factor is assumed to be 0.8.
198. The difficulty in estimating mean annual bronchialdoses to the population is illustrated by the Hungarianand the Swedish values. As regards the Hungarian data,
the weighted mean dose, taking into account the use ofdifferent types of apartments, differs a great deal fromthe unweighted mean. The weighted mean annual dose is1050 mrad while the unweighted mean annual dose is
700 mrad. Regarding the Swedish data, the mean annual
dose obtained from the levels of radon and radon
daughters measured in the "new buildings" (houses built
after 1970) is 480 mrad, which is twice the result
obtained from the measurements performed in the "oldbuildings" (houses built before 1956). Possible reasonsfor that difference are that, in modem houses, (a) theventilation' rate is lower, (b) more concrete is used, and(c) the activity concentration of 226 Ra in the concrete
is higher (334). Taking into account the proportion of
the ··new buildings", the mean annual dose in thesegmental bronchial epithelium is estimated to be about
320 mrad.
199. The differences between the doses calculated inthis chapter (and in table 29) and those given in thereferences depend on different assumptions concerning
the occupancy factors and the dose-to-exposure
quotients. The arithmetic mean of the annual doses
obtained for the five countries listed in table 29 is about
250 mrad. Since a substantial fraction of the measurements were taken in unventilated buildings, this mean isbelieved to be an overestimate of the average dose.
200. Another estimate can be tentatively derived fromthe information contained in table 28 and theparagraphs above. Assuming that a representative valueof the average 2 22 Rn concentration indoors is 1 pCi 1- 1

TABLE 28. RADON LEVELS IN HOUSES AND WORKING PLACES IN VARIOUS COUNTRIESCountry

Hungary

Number ofbuildings
Type of building
investigateda and material

42
11
252
62
27
158
66
185
30

Poland28

Ground floor, stone, no cellar
Ground floor, stone, with cellar
Ground floor, adobe and other,no cellar
Ground floor, adobe and other,with cellar
Higher floors, other materials

Apartment, concrete

Brick

60

!louse, wood

115

House, brick

109

House, concrete includingalum shale

USSR} Unventilated
for 8 hUnventilatedHouse!louse6

Industrial

4

OfficeRatios(average)
Rn: Ra A:
Ra B: Ra Cc

(5.8)
(2.3)

1 : 1 : 0.8 : 0.8
1 : 1 : 0.8 : 0. 7

(0.8)
(0.8)

4.8
1.8

5.5
1.3

H

(5.3)

1 : I : 0.9 : 0.8

(0.9)

4.6

40.6

II

(3.6)
(1.0)

I : I : 0.8 : 0.8
1 : 1 : 0.9 : 0.9

(0.8)
(0.9)

2.9
0.9

9.5
1.0

H
H

(2.9)
(1.5)
(0.7)

1 : I : 0.8 : 0.8
I : I : 0.9 : 0.8
1 : 1 : 0.8 : 0.8

(0.8)
(0.9)
(0.8)

2.4
1.3
0.6

33.4
7.9
0.8

II
II

(0.7)

1: 1: I

(0.9)

0.7

II

0.44
0.14-2.14
0.35
0.26-l.10
0.19
0.08-0.37

(0.5)

0.22

II

(0.5)

0.18

H

(0.5)

0.10

II

0.41
0.03-1.7
1.08
0.06-8.2

(0.5)

0.21

II

(0.5)

0.54

H

3.13
0.07-16

(0.5)

1.57

II

: 0.9

Unattachedfraction of
Ra A (mea11)d

Equilibrium
factor F

Eq11il/brlum
Proportion
equivalentco11cen tra tionf of dwellersK(per cent)(pCi I"')

Type of
OCCU•

pa11cy 11

Adequate

0.16
0.016-0.3
Inadequate
0.4
0.2-0.7
Poor
0.09
0.005-1.2
Air conditioning 0.17
0.06-0.35

Reference

II

342

II

0.12-4.3
0.19-1.10
0.4
0.3-104.0-8.0

Silicate brickRed brickConcrete
Adobe
Slag

UnitedKingdom-:i-:iUnventilated
for 8 hGronnd floor, brick, no cellar
Ground floor, brick, with cellar
Higher floors, brickHigher floors.
concrete and block panel

Aggregate

Sweden 1

Ventilation

Radon
concentration
mean and rangeb(pCI r'J

)

142

}
(0.5)

(0.08)

II

(0.5)

(0.2)

II

(0.5)

(0.05)(0.5)(0.09)

w
w

271

347

119

-.J

TABLE 28 (co11ti1111ed/00

Type of building
and material

Vc11tih1tion

Rado11co11ce11tratio11
mean and ra11ge b(pCI r'J

Instrument room.
cinder-block walls

Poor
Recirculation

0.2
0.1-0.3

Chemical laboratory

Basement in laboratoryiGood,
filtrationof ventilution air
Low

1

Fifth floor in laboraloryk

7

One-family house, wooden
frame, first floor
One-family house,concrete basement
Apartment, brickN11mberof
b11/ldi11gs
Corm tryi,,,,estigated"

Ratio;,(al'erage)
R11: Ra A:
Ra B: Ra cc

I : 0.5 : 0.3 : 0.2

U11attachedfraction of
Ra A (mean)dEquilibrium
factore F
a11d mea11
range

Eq11/llbrlum
eq11/mlent
Proportion
COiieen tratio11f of dwel/er:sK(per cent)(pCi r'J

Type of
OCCII•

Ref·/JO/IC)'I,

erenceUnited States

New York

·r···
term
mcasure)

I

T"
7
3
4

Office and laboratory,
concrete and cinder block

1 : 0.7: 0.5: 0.3

0.3

0.06

w

0.5

0.05

w

6.0
3.6-7.8

1 : 0.9 : 0.4 : 0.2

0.04(0.3-0.5)

0.4

2.3

w

Normal0.26

1 : 0.9 : 0.4 : 0.2

0.07

0.1

w

2-6 h" 1(0.07)(0.005-0.23)
(0.4)

l : 1

: 0.9: 0.8

0.4
0.2-0.5
(0.9)

0.07

1-1

1: 1

: 0.7

(0.9)

0.4

H

(0.09)(0.01-0.19)(0.05)(0.02-0.1)

1:l

: 0.6

(0.8)

0.07

1-1

l : I

: 0.9: 0.8

(0.9)

0.05

w

1 : 0.9 : 0.6 : 0.4

(0.6)

0.8

H

1 : 0.9 : 0.6 : 0.4

(0.6)

0.7

II

mcasure·ments)

Boston
area

-0.1

0.07
0.02 ( 212 Pb)

1-3 h" 1(0.1-0.94)

5-9 11· 1
6-14 h"1Tennessee

15

I-louses, most of them ofconcrete construction(1.4)(0.13-4.8)

Florida16!louses, most of them ofconcrete construction( 1.3)(0.03-3.6)

84,
94

376

l

347

212
347

aRooms in the case of Jlungary.
bSomc authors have not rnc2sured the Rn concentration. In those cases it is assumed that Rn : Ra A= I I, and the Rn value is given in parentheses.
cRelative to Rn.
dRclativc to Rn, i.e., to the number of Ra A atoms in radiouctive equilibrium with the Rn concentration.
J"F = (A 0 £ 0 )· 1 .r: AtEt, where At is, in turn, the activity concentration (pCi 1· 1 ) of 118 1'0, 214 Pb and 214 Bi; Et is, in turn, the potential alpha energy (McV pCi" 1 ) of 218 Po, 214 l'b and 214 lli (see tublo 24);,=t.
A 0 is the activity concentration of 222 Rn (pCi 1" 1); and E 0 = 1.3 10• MeV.
fcalculatcd as Rn concentration times F.
Kproportion of dwellers in these exposure conditions.

"!-I= home; W=work.Only home values have been used to calculate the doses presented in table 29.
;More recent measurements in Sweden in modern houses with ventilation rates in the range of 0.2-0.9 h"' have shown Rn concentrations ranging from 0.8-19 pCi 1· 1 with F = O.S-0.7 (2S I). The corresponding average equilibrium equivalent concentration is about twice that obtained from the results given in the table, which were published in 195 6.

i Aerosol particle concentration N = (48 ± 8) I 0 4 cm · 3 ; activity median diameter AMO= 0.11 t 0.03.
/cN =(48 :I: 7) 104 cm·• : AMD =0.11 :t: 0.03.

TABLE 29. ESTIMATED Ai'lNUAL INDOORS ABSORBEDDOSE DUE TO RADON DAUGHTERS IN THE
RESPIRATORY SYSTEM IN FIVE OF THE COUNTRIESLISTED IN TABLE 28
Annual indoor absorbed dose (mrad)Country

Hungary
PolandSwedenUnited Kingdom
United States

Segmental bronchial
epithelium

Whole
lung

700
52
320

140
10

65

44

9

130

26

and using an equilibrium factor of 0.5, the annual
absorbed dose in the basal cells of the bronchial
epithelium can be roughly estimated to be about
160 mrad for indoor conditions. The annual dose in thewhole lung would be around 30 mrad, and the annual
doses in the gonads, the bone marrow and the bonelining cells would be of the order of 0.3 mrad.
201. Few data on the concentrations of thoron decay
products in buildings have been published. Harley andPasternack (124) reported average concentrations of
3.6 10- 3 pCi 1- 1 of 212 Pb and of 2.7 10-3 pCil- 1 of
2 12
Bi in a laboratory in New York (United States). In
Salzburg (Austria), Steinhausler et al. (326) found amean 212 Pb concentration of 24 10- 3 pCi 1- 1 , theextreme values being 0.1 10- 3 and 62 10-3 pCi 1- 1 •Taking a typical 2 1 2 Pb concentration to . be
10- 2 pCi 1- 1 and assuming radioactive equilibrium
between 2 1 2 Pb and 2 1 2 Bi, the absorbed dose rate in thebasal cells of the terminal bronchioles is estimated to be
8 µrad h - l , corresponding to an annual dose of around
60 mrad. The annual absorbed dose in the whole lungwould be about 5 mrad. The annual doses in the gonads,
the bone marrow and the bone lining cells would be
0.008. 0.1 and 0.1 mrad, respectively.
202. Future trend of indoor exposures to radon. There
are several factors which will probably influence theexposure to radon indoors. These include: (a) the
development of international and national agreementson limits for 2 2 6 Ra and 2 32 Th ( and 4 K) concentrations in building materials; (b) increasing use ofcentral heating, which will probably have the effect of
decreasing the ventilation of houses; (c) energy economizing programmes. which will involve an increased useof recirculation, resulting in an increased build-up ofradon. However, because of the filtration system, theactivity of the radon daughters might decrease and theunattached fraction might increase so that it is notcertain whether the net effect of the increasing use ofrecirculation will be an increase or a decrease in the lungdoses. In summary. factor (a) will probably lead to lower
indoor exposures to radon. factor (b) to higher
exposures, while the net effect of factor (c) is not clear.
It is therefore difficult to predict the future trend ofindoor exposures to radon.

°

(ii)

Radon in water203. Another source of radon in homes is the use ofradon-rich water. There are many private and communal
wells with radon concentrations in the water far

rexceeding 20 pCi 1 (176, 316). and radon concentration in the water of the order of 1000 pCi 1- 1 is not
unusual. While there are many measurements of radon inwater. there is no information available on the inhalation
exposure resulting from the use of radon-rich water.
Assuming that (a) the radon concentration in water is1000 pCi 1- 1 and is completely released into the air,(b) a normal rate of water consumption in a house withfour persons is about 1000 I per day, and (c) the househas a volume of 230 m3 and is ventilated at a rate ofI h -l , the average concentration of radon from thissource in the air of such a house can be roughly
estimated at 0.2 pCi 1- 1 • Using an equilibrium factor of
0.5 and an occupancy factor of 0.8, the corresponding
annual dose in the bronchial epithelium is about
30 mrad. Further studies on the significance of thisradon source in different countries would be of greatinterest.
204. In certain special areas there may be very highradon concentrations in the water. The highly
radioactive spas at Badgastein (Austria) have been used
for many years as part of a treatment in "thermal
galleries'' with radon inhalation facilities. The radon
concentration of the water varies between 0.5 and120 nCi 1- 1 with a mean value of 40 nCi 1- 1 . The total
amount of radon released into the air in this area by the
daily use of 21 springs has been estimated to be about
200 mCi per day (283). The radon concentrations in the
air are of the order of I pCi 1- 1 in open air and of theorder of 10 pCi 1- 1 in room air. The radon concentration in the air of a thermal gallery is 3000 pCi 1- 1 •The concentration of 212 Pb is about 0.01 pCi 1- 1
indoors and 0.00 I pCi 1- 1 outdoors.
(d) Recapitulation of tissue absorbed doses from 222 Rn,
220
Rn and their short-lived decay products
205. The annual dose arising from inhalation of radon
and thoron decay products can be obtained by adding
the results corresponding to open air and to indoor
conditions (table 30). In fact, since the concentrations
and occupancy factor are much higher in houses thanoutdoors, the outdoor exposure leads to doses which canusually be neglected in comparison with those fromindoor exposure. The main contributions to indoor
exposure appears to be due to the 2 2 6 Ra and 2 3 2 Th
content of building materials. The resulting annual tissue
absorbed doses are estimated in this document to beabout 160 mrad in the segmental bronchioles and30 rnrad in the whole lung from exposure to the 2 2 2 Rn
short-lived decay products, and about 30 mrad in theterminal bronchioles and 4 mrad in the whole lung fromexposure to the 2 2 0 Rn decay products. The doses intissues and organs outside the respiratory system are
expected to be lower by at least an order of magnitude.
206. The contribution to indoor exposure arising fromthe consumption of water has been considered. Fromfragmentary information it seems that the use ofradon-rich water in homes might in some cases
contribute significantly to the absorbed doses.
207. It is very difficult to assess the annual collective
dose due to radon owing to the large diversity of housing

79

TABLE 30. ESTIMATED ANNUAL TISSUE ABSORBED DOSE ARISING FROM INHALATION
OF 2 2 2 Rn AND 2 2 0 Rn SHORT-LIVED DECAY PRODUCTSa,
Equilibrium
equivalentconcentration(pCi r'J

Source of irradiation
222

Annual Tissue absorbed dose (mrad)
Segmental
bronchialepithelium

Lung

GonadsBonemarrow

Bone liningcells

1(0.2-5)0.007(0.001-0.08)

0.008(0.002-0.04)

0.008(0.002-0.04)30(3-300)(0.006-60)

0.2(0.02-2)(5 10" 5.Q.5)

0.3(0.!)3-3)(5 10-s -0.5)

0.3(0.03-3)(5 10- 5 -0.5)

0.001

0.1

2 10·•

0.003

0.003

0.01
(0.001-0.06)

4(0.4-20)

0.008(8 10-• .Q.05)

0.1(0.01-0.6)

0.1(0.01-0.6)

Rn short-lived decay products
Outdoor exposure

0.06

5(1-25)

Indoor exposure
Building materials
Water
220

0.5
(0.05-5)o 0-•.1)

160(20-2 000)
(0.03-300)

Rn decay products
Outdoor exposure
lndoor exposure
Building materials

aThe expected ranges of the concentration or the dose are given within parentheses.

characteristics, materials and building techniques. It
would appear, however, that the order of magnitude of
the annual collective dose to the lung is 10 8 man rad. As
this collective dose is delivered by alpha particles, it can
not be readily compared with the other collective doses
from natural sources.
2. Ingestion
208. Small absorbed doses in human tissues are also
incurred as a result of ingestion of 222 Rn with water.
The presence of 2 2 2 Rn in water has already been
mentioned in paragraph 203, and is due to activity
transfer from soils. Radon-222 concentrations in fresh
water vary from less than I pCi 1· 1 up to the order of
10 6 pCi 1· 1 (346). Levels less than 10 pCi 1· 1 are foundin lakes and rivers, and concentrations in the range
10 2 -10 4 pCi 1·1 have been reported for ground waters;even higher concentrations can be found in deep wells,
and the highest reported values have been observed insome spas.
209. As mentioned in paragraph 203, concentrations of
the prder of 10 3 pCi I• 1 are frequently seen in tap waterfrom ground-water supplies.Assuming a consumption of
0.3 I per day of water containing 10 3 pCi 1· 1 of 22 2 Rn,
the estimated annual absorbed dose in the stomach isabout 2 mrad, while the average dose in the whole body
is lower by a factor of I 00.

III. RECAPITULATION OF TISSUE
ABSORBED DOSES
210. Table 31 summarizes the contribution of natural
sources to the radiation exposure of human populations
living in areas of normal radiation background. The four
tissues considered in table 31 are the gonads, the lung,the bone lining cells and the red bone marrow. In thosetissues. the annual average absorbed dose from natural
sources is estimated to be of the order of 100 mrad. For
80comparison purposes, table 31 includes the estimates forthe gonads, the bone lining cells and the bone marrow
given in the 1972 report. The new estimates of the total
doses are a few per cent lower than the previous ones forthe gonads and the bone lining cells, and a few per centhigher for red bone marrow. The difference is mainly
due to a better knowledge of the terrestrial doses, which
are now estimated to be about 30 per cent lower than
indicated in the 1972 report. The increase of the dose in
the red bone marrow results from a much higher
estimate ofihe contribution from 4 °K than in the 1972
report.
211. As a result of inhalation of 2 2 2 Rn and 22 0 Rn
short-lived decay products, the dose in the entire lung,which has been assessed for the first time by theCommittee, is due primarily to alpha particles and ismore than 30 per cent higher than the doses in the threeother tissues. It is worth mentioning that, in addition to
the doses included in table 31, yearly doses of the orderof 200 mrad are received by the basal epithelial cells of
the tracheo-bronchial tree.
212. The most important components of the total
absorbed dose. in gonads, bone lining cells and red bonemarrow are the ionizing component of the cosmic
radiation, the terrestrial gamma radiation, and 4 °K,
which together amount to 90 per cent or more of thetotal dose. Neglecting the variability of the dose fromcosmic rays and considering only the variability of theannual doses from 4 °K and from terrestrial gamma
radiation given earlier in this Annex, it can be estimatedthat the annual doses from natural sources received by
95 per cent of the population are in the range of
70-92 mrad in the gonads, 77-110 mrad in the bonelining cells, and 67-120 mradin the red bone marrow. In
the lung, an important contribution to the dose arises
from 222 Rn and its short-lived decay products. The
expected range of the annual dose in the lung from
2 22
Rn and its short-lived decay products is fairly large,
extending from 4 to almost 400 mrad (table 30). If thislarge variability were confirmed in large-scale surveys, itwould make the variability of the other contributions to
the lung dose from natural sources unimportant.

TABLE 31. ESTIMATED ANNUAL TISSUE ABSORBED DOSE FROM NATURAL SOURCES IN"NORMAL" AREAS
Compared with the estimates of the 1972 report (in parentheses)

Annual tissue absorbed dose (mrad)
Source of i"adiation

GonadsLung

Bone lining
cells

Red
bone ma"ow

28
0.35
32

(28)
28
0.35 (0.35)
(44)
32

(28)
28
0.35 (0.35)
(44)
32

0.001
0.002
0.6
0.02

0.001 (0.001)

0.001 (0.001)

17
0.4
0.04
0.04
0.03
0.3
30
0.04
0.06
4

External i"adiation
Cosmic rays:
Ionizing component
Neutron component
Terrestrial radiation: ('y)

28
0.35
32

(28)
(0.35)

0.001(0.001)0.5
0.02(0-.7)(44)

Internal illadiation
Cosmogenic radionuclides:

3H (tl)7

Be ('y)••c un"Na (tl+-y)

(0.8)

2.2
0.02

15
0.9
0.3
0.8
0.7
3.4
0.3
0.7
1.1
0.1

(15)
(0.6)
(0.3)

(0.3)
(0.05)

(15)
27
(0.6)
0.4
0.07 (0.06)
0.05
(0.1)
0.1
(0.3)
0.9
(0.08)
0.3
0.04 (0.06)
0.2
0.1(0.05)

86

(92)

92

(89)

8.5

(4.1)

2.1

(1.2)

2.0
0.02

-

(0.7)

Primordial radionuclides:••K (JI+ -y)

(19)
15
(0.3)
0.8
2:1au.234 u (a)(0.03)
0.04
230 Th (a)0.004 i:uRa_2upo (a)(0.02)
0.03
210Pb-21op0 (a+/3)
(0.6)
0.6
(0.07)
mRn· 214 Po (a) inhalation 0.2
232
Th (a)
0.004 na Ra-2••11 (a)(0.03)
0.06
201
220 Rn- 11 (a) inhalation 0.008 (0.003)
87

Rb (P)

Total (rounded)
Fraction of absorbed dosesdelivered by alphaparticles or neutrons (%)- - -(93)- - 110
78

1.2

(1.3)

213. Much higher doses from external radiation arereceived by population groups living at high altitudes orin regions of high natural radioactivity. A number of
population groups are exposed to elevated internal
absorbed doses, such as the caribou or reindeer eaters, or
people living in houses with a low rate of ventilation.
The importance of the contribution of areas of highnatural radiation to the global collective dose cannot yet
be assessed. As a first approximation the global annual
collective dose from natural radiation sources is
estimated to be of the order of 3 108 man rad for the
gonads, bone marrow and bone lining cells, and about
30 per cent higher for the lung.

IV. TECHNOLOGICALLY ENHANCEDEXPOSURES TO NATURAL RADIATION
214. The exposures to natural sources of radiation
discussed in the previous sections are those to whicli
man has always been subjected, namely exposures tocosmic rays at ground level and to naturally occurring
radionuclides in soil, air, water and food. The present
habits of human societies have also been taken into
account, in particular when the doses received indoors
have been estimated. This has been done because thevast majority of the population spends most of its timein buildings, where the radiation environment differs
appreciably from that found outdoors.

31

(0.6)
(1.6)
(0.08)

215. There are other circumstances where man finds
himself in a natural radiation environment to which hewould not be exposed if some kind of technology had
not been developed. Examples of such circumstances aretravelling by air. using natural gas for cooking or heating·purposes, or living in the neighbourhood of a coal-fired
power plant. The resulting exposures have been labelled"technologically enhanced natural radiation" (TENR)
exposures by Gesell and Prichard (97a), who definethem as exposures to truly natural sources of radiation(that is, naturally occurring radionuclides and cosmic
radiation) which would not occur without ( or are
increased by) some technological activity not expressly
designed to produce radiation. This section deals withthese enhanced exposures and presents some assessmentsof the doses arising from such exposures.
216. According to the definition given above, the merefact of being in a building would constitute a TENR
exposure, since both the absorbed dose in air and thetissue absorbed dose from inhalation are on average
higher indoors than outdoors. However, since the indoor
exposures have been abundantly discussed earlier in thisAnnex. the only building materials that will beconsidered in this section are industrial waste products
and raw materials containing relatively high concentrations of natural radionuclides.
217. The exposures from widely used consumer
products containing radionuclides are also dealt with in
the appendix to this Annex. They do not qualify as
81

technologically enhanced exposures for several reasons,the main one being that the radionuclides aredeliberately incorporated into the products. However,these consumer products present enough similarities
with the TENR sources to justify the inclusion of theappendix, particularly because the majority of theradionuclides used are naturally occurring, and most of
the users of the products are not aware that they
constitute a source of radiation.

A. El\1ILWCED EXPOSURES TOCOSMIC RAYS
1. Passengers in aircraft
2 I 8. The number of passenger kilometres flown
annually throughout the world (not L11cluding data from
China) is approaching 10 12 (149a).

Year

Passenger
kilometres( I 012)

1970
1971
1972
1973
1974
1975

0.460
0.494
0.560
0.617
0.654
0.676

The average speed is about 600 km h- 1 , which meansthat a total of about 109 passenger hours are spent
travelling each year. Under average solar conditions, theabsorbed dose index rate at the altitude of subsonicflights is about 0.3 mrad h -l (fig. II). and therefore, theannual collective dose from these flights is about
3.4 105 man rad (with the 1975 data).
219. The prospect of the development of a supersonicaircraft transport (SST) system on a large scale during
the next decade poses the question of the cosmic-ray
absorbed dose index rates to which passengers and crews
will be exposed and of the contribution of this to thecollective dose to the world population. The first
generation of supersonic aircraft flies at altitudes ranging
up to 20 km, compared with at most 12 km for standard
jet aircraft. The absorbed doses in human tissues
received in a particular flight will depend markedly on
the duration of the flight and on the altitude andgeomagnetic latitude of the flight; for example, thedoses will be much higher at latitudes above 50°.
220. When considering dose rates in persons exposed atsuch high altitudes. it is necessary to discuss separately
two contributions. The first of these is due to thegalactic cosmic rays. ever present, which vary inintensity by a factor of about two during the sun's
I I-year solar cycle. Secondly, there may occasionally belarge short-term increases in the radiation as a result ofenergetic solar protons originating from solar flares.
221. Estimates of the absorbed dose index rates fromboth the ionizing and neutron components of galactic
cosmic rays at high latitude and at altitudes of 12 and
20 km can be obtained from figure II. During the timeof solar activity minimum, when cosmic-ray flux
densities are at maximum. the absorbed dose index rates
82

are: at 12 km, 300 µrad h -• from the ionizing
component and 20 µrad 11- 1 from neutrons: at 20 km.
600 µrad 11- 1 from the ionizing component and30 µrad h -l from the neutron component.
222. The estimates of absorbed dose index rates fromthe ionizing component given above probably do notinclude the contribution resulting from local nuclear
interactions of high-energy primary cosmic rays in tissue(called nuclear disintegration stars). A number ofmeasurements of absorbed dose rate in tissue atsupersonic transport altitudes have been reported, someof which include information on absorbed dose rates
from nuclear stars.
223. Some of these measurements have been made with
instruments calibrated in terms of the dose equivalent(expressed in rem), equal to the absorbed dose
multiplied by a mean quality factor. In these cases theabsorbed dose has been inferred from the reported dose
equivalent and quality factor.
224. Fuller and Clarke (92) made measurements fromballoons at 20 km over Fort Churchill, Canada, in July
1964. near solar minimum. Their measurements
correspond to an absorbed dose index rate from theionizing component of 750 µrad h -l. An average quality
factor of 1.5 was calculated for this ionizing component
from a study of tracks recorded in nuclear emulsion
plates. The neutron "rem counter'' indicated adose-equivalent rate from neutrons of 500 µrem h- 1 •O'Brien and McLaughlin (263) concluded that thisneutron dose-equivalent measurement corresponded to asurface dose in a phantom irradiated isotropically fromabove. The dose-equivalent rate for a flux density ofI neutron cm - 2 s- 1 at the surface of a 30 cm slab formonolateral isotropic incidence is 68 µrem h- 1 (112).
The corresponding figure averaged through the 30 cm
slab for bilateral isotropic incidence is 29 µrem h -l. The
500 µrem h- 1 of Fuller and Clarke (92) reduces to
210 µrem 11- 1 for bilateral isotropic incidence averaged
through 30 cm. For the neutron energy spectrum, thequality factor, averaged over 15 cm, is estimated to beabout 6. The absorbed dose rate therefore corresponds
to 35 µrad h -l, in reasonable agreement with figure II.
225. Fuller and Clarke (92) estimated the absorbed
dose rate in tissue from nuclear stars recorded in the
nuclear emulsion plates as 64 µrad h -• {with an average
quality factor of 8.5). These authors were not certain
whether all or part of the dose rate from nuclear stars
was recorded in the ionization chamber measurements ornot. At most, failure to subtract the contribution ofstars from the ionizing component would over-estimate
the absorbed dose in tissue by 10 per cent. The
measurements by Davison (68) at an altitude of 20 km
agree well with those of Fuller and Clarke for all threecomponents (ionizing. neutron and tissue stars) (6, .68).
226. Between 1968 and 1971, measurements weremade at a geomagnetic latitude of 70°N by the UnitedStates Air Force (2). The instrumentation consisted of a
Rossi-type LET spectrometric chamber. a 10-channel
pulse-height analyser and a Geiger counter. The averageabsorbed dose rate at SST altitudes was 450 ± 90 µradh -l . On some of these missions nuclear emulsions were
exposed for some 40 h. Nuclear-track analysis indicateda tissue absorbed dose rate of 580 µrad h -i , with aquality factor of 1.8. In addition, there was acontribution from nuclear stars of 70 µrad h -i, in good
agreement with the measurements of Fuller and Clarke.
227. Measurements made with a BNL dose-equivalentmeter at a number of altitudes near geomagnetic latitude
70°N in 1971 correspond tci absorbed dose index rates
of 603 ± 100 and 288 ± 50 µrad h -i at altitudes of 20
and 12. 7 km, respectively. Absorbed dose index rates
measured with this same instrument at several altitudes
and geomagnetic latitudes are plotted in figure XX (2).
0.4 ·absorbed dose index rates at an altitude of 20 km are
estimated to be about 600 µrad h- 1 from the ionizing
component, 30 µrad h- 1 from neutrons and about
60 µrad h- 1 from nuclear stars. At an altitude of 12 km
they are about 300 µrad h- 1 from the ionizing
component, 20 µrad h- 1 from neutrons and little from
nuclear stars.
230. In an attempt to gain data on absorbed doses
received by passengers of transport aircraft, thermoluminescent dosimeters and films sensitive to ~ and 'Y
radiation were repeatedly sent by airmail between San
Francisco, Washington. Tokyo, Buenos Aires. Rio deJaneiro (356). The doses to a passenger for a round trip,
assessed from the films and TLD devices, are comparedwith the values computed for average solar activity
conditions in table 32. It should be pointed out that theTABLE 32. ESTIMATED COSMIC RAY DOSE TO A PERSONFLYING IN CONVENTIONAL JET AIRCRAFT
Average solar conditions

0.3

Dose per round trip (mrad}
Destination fromSan Francisco

'.c

E
;;;

Experimental assessment(J and "f film

TLD

Calculated a

3.4
3.5
4.1

3.0
3.8
4.4
6.9

3.1
3.3
8.7
6.4

Washington
Tokyo
Buenos Aires
Rio de Janeiro

~

a:
~

0
;; 0.2

5.4

w

"'g

Source: Reference 356.
alncluding neutron contribution.

5l

"'a:
i;s
"'

"

individual experimental results are quite variable. theiraverage for a given route being only a rough estimate ofthe dose to the passenger. The values are in reasonableagreement.

0.1 -231. Wallace (356) used the same computer code to
calculate absorbed doses to passengers for a round trip,
for both subsonic and supersonic transport between
various city pairs. Some of these estimates are shown intable 33. Doses for a round trip in supersonic aircraft are

7km

3km

34

38

42

46

50

54

58

GEOMAGNETIC LATITUDE (deg NJ

Figure XX. Galactic cosmic radiation absorbed dose index rate
at four different altitudes as a function of latitude

TABLE 33. COMPARISON OF CALCULATED COSMIC-RAY
DOSES TO A PERSON FLYING IN SUBSONIC AND
SUPERSONIC AIRCRAFT
Average solar conditions
Subsonic flightat II km

Supersonic flightat 19 km

Route

Dose
per
Flightround
duration trip(h)(mrad)

Doseper
Flightround
duration trip(h)(mrad}

Los Angeles-Paris
Chicago-Paris
New York-Paris
New York-London
Los Angeles-New York
Sydney-Acapulco

11.1
8.3
7.4
7.0
5.2
17.4

3.8
2.8
2.6
2.4
1.9
6.2

228. Foelsche et al. (88) determined galactic cosmic-ray
dose rates in the centre of a body phantom at SST
altitudes from measurements made in balloon flights
over Minnesota (United States; geomagnetic latitude
55°) and over Fort Churchill (Canada; geomagnetic
latitude 69°) from 1965 to 1968. At 20 km altitude theionizing component of the absorbed dose rate was in therange 470-730 µrad h- 1 , the neutron dose-equivalentrate, 320-550 µrem h -i ; and that from nuclear stars,
100-180 µrem h- 1 • Considering that there are considerable changes in dose rates with latitude and altitude andalso that there is some uncertainty about the quality
factor to use in relating dose equivalent to absorbed doseor dose index, all the measured dose rates reported
above are in reasonable agreement with each other andwith the estimates given in paragraph 221 based uponcosmic-ray flux densities.
229. There is general agreement between calculated andmeasured values. At solar minimum and high latitude,

4.8
3.6
3.1
2.9
1.9
4.4

3.7
2.6
2.4
2.2
1.3
2.1

Source: Reference 356.

approximately 70 per cent of those for subsonic speeds.
because of the shorter flying time. However, the dose
rates in supersonic aircraft are about twice as high as insubsonic aircraft. For a round trip across the Atlantic,
the tissue absorbed doses in passengers may be estimatedat about 2 mrad and 3 mrad for an SST and a subsonic83232. Measurements of absorbed dose rates on board theConcorde aircraft have been reported (70, 242c). The
decrease of the absorbed dose index rate as a function of
the geomagnetic latitude, is illustrated in figures XXI
and XXII, which show the results of a continuous

aircraft, respectively, under average solar activity
conditions. Estimates of 4 mrad and 5.6 mrad, respectively, were given in the 1972 report of the Committee
for solar minimum conditions when cosmic-ray intensities are highest (with the exception of solar flares).

17

16

15

14

13

20

' 19

18

PARIS TIME (houril

47 45

49

40

35

30

25

20

15

15

N

N

10

10

0

15

23

20

I

N

s

0

LATITUDE (degrees)700'j 600
.,:;

3

...<w
a:

)(

w

500

0

~

w

~
0
0

400

w

"'a:
5l 300

"'<

200

...·i

Altitude of flighl

E

,g

.;0

.

100

~

.:

i

50

c.
0

<n

c1l
10

Figure:XXI. Recording of the absorbed dose index rate on a flight from Paris to Rio de Janeiro, February 1976
0

2

3

8

6

9

PARIS TIME (houril

23

s

20

15

10

5

0

5

0

N

10

15

15

20

25

30

35

40

45 47

49

LATITUDE (d"9'e.,I

700

.,:;

j

600

.3

...<
w

a:

)(

w

500

0

:!:
w

~
0
0

400

w

CD

a:

0

VI
a,

<

300

200

a

"0a
E

100

so

c.
0
if,

10

Figure XXII. Recording of the absorbed dose index rate on a flight from Rio de Janeiro to Paris, February 197684

recording carried out in February 1976 by Moroni et al.
(242c) during a Paris-Rio de Janeiro-Paris flight. During
the Paris-Rio de Janeiro portion of the flight (fig. XXI),
a plateau at the level of l 00 µrad h -I was observed
between Paris and Nantes when the aircraft was flying at
subsonic speed at an altitude of 7 .2 km. Between Nantes
and Dakar, now at supersonic speed at an altitude of
16 km, the absorbed dose index rate reached
620 µrad h -i at latitude 45°N, then decreased withlatitude down to 300 µrad h- 1 at 25°N. From Dakar to
Rio, in low-latitude regions, the absorbed dose index
rate changed very little. On the return flight, therecording of the absorbed dose index rate (fig. XXII)
shows a few irregularities between Dakar and Paris,
which coincide with the rising of the sun (242c). The
absorbed dose index for the passengers and the crew
during the round trip did not exceed 5 millirad.
233. From dose-rate values given in the 1972 report,
the average absorbed dose index rate from solar
radiation can be estimated to be 4 µrad h -J at I 2 km
and 90 µrad h- 1 at 20 km. The 1972 values had beenobtained by an ICRP working group by averaging theeffects of solar flares over the period 1952-1960 ( 150).
It can be seen that at these altitudes the averagecontribution from this source is small compared withthat from galactic cosmic rays.
234. Although radiation of solar origin does notcontribute significantly to the average absorbed doseindex rate, during an occasional intense solar flareradiation levels at these altitudes may increase by several
orders of magnitude. The absorbed dose index rates atdifferent altitudes have been estimated for the large solar
flare event on 23 February 1956 (7, 12,368). Estimatesof the peak absorbed dose index rates in polar regions at
different altitudes during this flare are shown infigure XXIII ( 12). The radiation at these altitudes fromsolar flares is very latitude-dependent and the absorbed
dose index rates are more than 10 times smaller atlatitudes below 50° ( 110). SST aircraft carry radiation
monitors, and the pilots will move the aircraft to lower
altitudes when the dose rate reaches a prescribed level.
The giant solar flare events last only for about 10 h andoccur a few times in each solar cycle, and therefore are
not likely to add significantly to the collective dose of
the world population.

4.0

2.0

w

~

a::
X

w

a

~

w

~ 1.0

0

8
:

0.8

Sl
~

0.6

0.2

0.1 " - - ' ' - - - - - - - - - - - ~ - - - - - - - - - - - - - - - - 10
20
15
25
km

ALTITUDE

Figure XXIIL Estimated absorbed dose index rate as a function of altitude at high latitudes
during the large solar flare of 23 February 195685

2. Astronauts
SOUTH
POLE
INNER BELT

w

~

OUTER

C:

C

~

~.;R

BELT

(:I

!

INNER BELTOUTER BELTOUTER BELT

l

l J

•

10·

to

C

;;
5 1

~

1400

14:JO

1SOO

1530

1630

UNIVERSAL TIME (MAY 19, 19671

Figure XXIV. Absorbed dose index rate measured by the threetissue-equivalent ionization chambers aboard the OVI-9 satellite
on a polar orbit during a period of no solar activity. Chamber 3
was the most heavily shielded (65, 290)

235. When travelling into space, astronauts are subjected to primru:y cosmic-ray particles. the radiationfrom solar flares, and also the intense radiation present
in the two radiation belts. Savun et al. (303) havereported measurements in the radiation belts in 1971.
Measurements inside a 0.7 g cm - 2 shield indicate thatthe maximum absorbed dose index rate crossing theinner belt was 22 rad h- 1 and crossing the outer belt
belt 5 .4 rad h -I . Dose rates in tissue-equivalent ionization chambers were measured aboard the OVI-9
satellite with different amounts of shielding. Dose index
rates based upon these measurements are shown infigure XXN.
236. Estimated absorbed doses in the chests of theastronauts on five Apollo missions (average for the threeoccupants) based upon dosimeter measurements areshown in table 34 ( 65, 290). A large part of this dose

TABLE 34. ABSORBED DOSE IN THE CHESTS OF ASTRONAUTS ON SPACE MISSIONS
Mission or
mission series

Launch date(Year-month-day)Apollo VII
Apollo VIII
Apollo IX
Apollo X
Apollo XI

1968-08-11
1968-12-21
1969-02-03
1969-05-18
1969-07-16

Vostok 1-6
Voskhad 1, 2
Soyuz 3-9

Duration of
mission (h)Type of orbit

260
147
241
192
195

Earth orbital
Circumlunar
Earth orbital
Circumlunar
Lunar landing

157
150
196
480
179

Earth orbital
Earth orbital
Earth orbital

2-80
30, 7062-234

Dose (mrad)

Sources: References 65, 106a, 290.

was received while the spacecraft was passing throughthe earth's radiation belts. For example, the higher dose
received on the Apollo X mission was largely due to adifferent trajectory through the radiation belts. Analogous data in table 34 from USSR space flights(Vostok, Voskhad and Soyuz series) indicate doses ofcomparable magnitude (106a). In outer space, remotefrom the shielding influence of the earth's magnetic
field, the absorbed dose index rate from solar protons
emitted during solar flares is very high. For example, it
has been estimated that the absorbed dose indices inouter space from the solar proton event of 10 July 1959
were: from protons 360, 170 and 40 rad behindshielding of 1. 2 and 5 g cm - 2 , respectively, and fromalpha particles the corresponding values were 150, 30
and 5 rad, respectively (65).

B. ENHANCED EXPOSURES TO NATURALLYOCCURRING RADIONUCLIDES
I. Radiation exposures due to coal-fired
power plants
237. Burning of coal is one of the sources of enhanced
exposures to natural radionuclides. Large coal-fired
power stations burn pulverized coal, the combustion
products of which, both in gaseous and particulate form,
are discharged into the atmosphere. There is moreparticulate emission during combustion of coal than any
other fuel because of its high ash content (typically,
5-10 per cent) (20, 79). It is estimated that annual world86

coal consumption is approachinf 3 10 9 tonnes (t) (185).
The combustion of about 3 10 t of coal is required to
produce an electrical energy of one megawatt-year (23,
79. 175, 185).
238. Most industrially consumed coal is burned at
central power .plants where the elements entering theboiler in the coal stream are partitioned between abottom-ash (or slag) stream, and a flue-gas stream
containing suspended fly ash and the vapours of volatileelements or compounds. A further partitioning of theflue-gas stream takes place in the particulate emission
control devices (electrostatic precipitators or scrubbers)that efficiently remove larger fly-ash particles but are
Jess efficient for vapours and fmer particles, which arethus discharged into the atmosphere. Ash from theboiler and ash removed by the precipitators are flushedwith water to ash ponds. The disposal of the very large
quantities of ash produced. or their utilization in making
concrete, can also lead to human exposure.
239. Studies relative to the flow of trace elements
through coal-fired power plants (175, 185) indicate thatradium and thorium are at essentially the same
concentration in coal ash, slag, and fly ash while theconcentration of lead increases progressively in fly ash
collected downstream from the burner toward the stack.
The behaviour of uranium seems to be intermediate
between that of lead and that of radium and thorium.
Reported activity concentrations of natural radionuclides in samples of coal, slag and fly ash from several
countries are presented in table 35.

TABLE 35. ACTIVITY CONCENTRATION OF RADIONUCLIDES IN COAL AND COAL RESIDUES(pCi g- 1 )Type of coal or coal residue
and its origin

4oK

23au

llOpb

n6Ra

22•Ra

2287n

232Th

Refenmce

Coal

Australia
Czechoslovakia (brown)
Germany, Fed. Rep. of
Hungary (bituminous)
Poland (bituminous)
Poland (brown)
United States
IllinoisMontana
North Dakota
United States
United States

0.8-1.3
0.11, 0.35
< 0.7
0.04
0.048-0.94
0.90

< 2.5

< 0.6

0.6a
0.3a
0.2a

2.5
0.7
2.2

0.04b

omh
0.02
0.2

0.7
0.014

0.28

23
165
307a
165
165
165
20
20
20
185
175

Coal ash Gaboratory processing)

Australia
Germany, Fed. Rep. ofJapan
CentralSouthern
Northern
United State~ (semibituminous)

4.7-8.3
6.2c
5.8

19

0.10
0.98
0.63

2.6
3.4
19.8
8.16
105.0

3.8

23
172
307a

1.15
0.46
1.45

15.3
2.35
6.79

257
257
257

2.4

2.6

79

1.2b

272
20
185
175

Slag
PolandUnited States
United States
United States

4.3a
4.5a

17.3
26

o.sh

4.9

1.5
0.55

1.0

Fly ashAustralia
Hungary
PolandPolandPoland (bituminous)
Poland Gignite)
United States
United States
United States

22.5
1.5, 2.8

14.0
0.6-151.0
6.4a
0.61, 4.18
0.91

1.1b

4.4, 6.7

0.18. 0.22

10
11

2.6
0.4
3.la

17.3
0.4b

23
204
165
272
166
166
185
175
20

a Assumed equal to activity concentration of 2 1 4 Bi.

b Assumed equal to activity concentration of 2 • • TI.
clncluding activity concentration of 2 2 • Ra.

240. The activity of a given radionuclide discharged
into the atmosphere can be evaluated from the activity
concentration of that radionuclide in fly ash and theflow of fly ash through the stack. On the basis of theresults presented in table 35 it will be assumed that
representative values of activity concentrations in fly ash
are 1 pCig- 1 for 226 Ra, 228 Ra, 228 Th and 232 Th,
5pCig- 1 for 238 U, IOpCi g- 1 for 210 Pb and
15 pCi g- 1 for 4 °K. It will be noted that the activity
concentrations of 4 °K, 226 Ra, 228 Th and 232 Th areabout the same as in average soil, while those of 23 8 U
and 210 Pb are much higher. This results from theenrichment of lead and uranium in fly ash relative to slag
and coal ash.
241. Estimates of the flow of fly ash through the stack
per megawatt-year of electrical energy produced (23,172, 175, 185) range from 0.7 to 30 t. Taking a value of
10 t to be representative, the activities discharged per
megawatt-year produced would amount to 10-s Ci for
226
Ra, 228 Ra, 228 Th and 232 Th, 5 10-5 Ci for 238 U,
4
10- Ci for 21 0 Pb, and 1.5 10-4 Ci for 4 °K.

242. The activity of 2 2 2 Rn released per megawatt-year
has been estimated to be about I 0- 3 Ci on the basis of
the following assumptions: (a) 222 Rn is in radioactive
equilibrium with 22 6 Ra in coal and is discharged in its
entirety when coal is burned. (b) the average activity
concentration of 2 2 6 Ra in coal is 0.3 pCi g- 1 (table 35),
and ( c) the combustion of 3 10 3 t of coal is required to
produce an electrical energy of l MW y.
243. Measurements in environmental samples aroundcoal-fired power plants clearly show the presence ofenhanced concentrations of these nuclides. In air, Martin
et al (221) measured, at a point 6 km downwind of acoal power plant, concentrations of 6 10- 16 Ci m - 3 of
226 Ra. 310- 16 Cim- 3 of 232 Th, and210- 15 Cim- 3
of 2 3 8 U, compared with the "normal" concentrations of
7 10- 17 Ci m- 3 for each of the three radionuclides. In
snow, the 2 2 6 Ra concentrations found by Jaworowski
et al. (164) ranged up to 1.710- 15 Cig- 1 and wererelated to the distance from the power plants. Studies ofa glacier 150 km for an industrial centre revealed a50-fold increase in 2 2 6 Ra concentration over the87

ground-level air concentration of the pollutants released
from such tall stacks increases as a function of distance
up to a few kilometres, reaches a maximum, thendecreases according to a function that can beapproximated by a power law. The fraction of thecollective dose commitments due to the short distances(<10 km), where the stack height has an influence on
the ground-level air concentrations, is small and has been
neglected. The figure of 1.6 1o-s s m - 3 for the average
dilution factor is derived from the value of 5 10-7 s m - 3
at 1 km adopted in Annex D in the case of releases from
nuclear reactors and from assumption (b ). With regard toassumption (c), all of the activity released will bedeposited within a circle of 500 km radius if a value of
8 10- 3 m s- 1 is adopted for the deposition velocity ofaerosols under dry weather conditions.

preceding 80 years (164). In soils of industrial areas, theconcentrations of 226 Ra, uranium and thorium were
found to be higher in the upper 5-cm layer than in the
5-10 cm layer, while this effect was not observed in ruralsoils ( 166).
244. The main pathways through which the populations
living around coal-fired power plants are exposed toenhanced levels of natural radionuclides are inhalationand ingestion of the activity discharged into theatmosphere. The collective dose commitments due toinhalation during the passage of the cloud have been
estimated using the following assumptions:(a) Theaveragedilutionfactoris
1.6 10-s s m - 3 at a distance p 1 = 10 km from the stack:(b) The variation of the concentration as afunction. of the distance p is of the form p-1.s:

246. The collective dose commitment due to inhalation
can be expressed in the form( c) Practically all of the activity is deposited
within a circle of 500 km radius;SC =(d) The human population density 6 is uniform
and equal to 100 km -l around the plant.

!

SOO

IO

p

D (-~ -l.S 6 27ipdp
I P1 J

where D 1 is the dose commitment per MW(e)y at thereference distance p 1 = 10 km. The results for thenatural radionuclides considered are presented intable 36.

245. Assumption (a) takes into account that stacks ofcoal-fired power plants may be as tall as 200 m. The

TABLE 36. ESTIMATES OF COLLECTIVE DOSE COMMITMENT DUE TO ATMOSPHERICRELEASES FROM COAL-FIRED POWER PLANTS(man rad per MW(e) y)
Incomplete collective dose
commitment due tothe activity deposited

Collective dose commitment
arising from inhalation
during the cloud passage b
Radionuclidea

Lung

Bone
ma1'row:»uc
216 Ra3 10·•

210Pb

9 10·•
5 10·•
7 10" 3
9 10·•

2 10" 5
4 10·•
4 10 48 10·•
6 10·•
6 10·•

10· 2

2 10- 3

•nRad
221Th

"

2

n1

Total

2 10 4Boneliningcells

Boneliningcells

Lung

GonadsBonema"ow

5 10·•
7 10-s10-3
1.5 10·•5 1o·•
7 10" 5
2 10· 3l.5 10·•

8.5 10·•2 10·•
2 10- 3
5 10·•

3.6 10· 3
2 10· 3
10-2

10· 2

10·•

10·•

10·•

2 10· 3

2 10· 2

2 10·•

3 10·34 10"

2 10-2

7 10· 5

3 10-s10-3
4 10-•

9 10· 3---3

3 10·'°

aThe collective dose commitments from 4 K have not been estimated; they are expected to bevery small since (a) the activity concentration in fly ash is about the same as in soil, (b) potassium
compounds are very soluble in the lung, and (c) the concentration of potassium in the body ishomeostatically controlled.
bThe collective dose commitments arising from inhalation of 2 2 2 Rn and its short-lived decay
products have been estimated to be about 3 JO · 5 man rad/MW(e) y in the lung and negligible inbone tissues. The collective dose commitments due to all the radionuclides contained in the table arecalculated assuming that all the fly-ash particles are in the respirable range.
curanium-238 is assumed to be in radioactive equilibrium with 2 34 Th, 234 mpa and 234 U.
dThe collective dose commitments due to 2 21 Ra include the contribution of its decay
products, which are assumed to be in radioactive equilibrium with 2 2 8 Ra in the body. When theactivity is deposited on the soil, the doses due to the intake of 2 2 8 1h are small compared to thosefrom 2 2 • Ra. When inhaled, the doses from 2 2 • Th are much higher than those from 2 2 • Ra because of
the long biological half-life of thorium in lung and bone, and because of its deposition on bone
surfaces.
O

247. The incomplete collective dose commitments(Annex A) incurred after deposition can be evaluated bycomparison with the natural soil activity concentrations
and the corresponding tissue dose rates discussed earlier
in this Annex for "normal" levels of natural radionuclides. Making the conservative assumption that thedeposited activity only becomes unavailable to the88vegetation by radioactive decay and that only the upper
20 cm of soil are involved in the uptake of radionuclides
by vegetation. the incomplete collective dose commitdue to deposition
ments per unit energy generated,can be assessed assr.

where A is the activity discharged per unit energy
generated, i>N is the natural tissue dose rate due to theradionuclide under consideration, 6 is the population
density, T is the expected duration of the practice, taken
to be 500 years, S is the thickness of soil involved;
expressed as mass per unit area (assumed to be
3 10 5 g m- 2 ), and CN is the natural concentration of
the nuclide in the soil.

being used to produce other commodities, such as
phosphoric acid (244). Mining and processing phosphateores redistributes 2 3 8 U and its decay products among
the various products, by-products, and wastes of thephosphate industry. The dispersal of the wastes in theenvironment as well as the use of phosphate fertilizers inagriculture and of chemical gypsum as a building
material are possible sources of exposure to the public.

248. The results obtained in this way are presented intable 36. On the basis of these tentative estimates,
210
Pb, 228 Th, and 232 Th appear to be the mostimportant contributors to the collective dose commit·
ments due to atmospheric releases from coal-fired power
plants. Most of the dose is due to alpha radiation.

250. Table 37 presents the results of a survey ofuranium, thorium and radium contents of phosphaterock samples collected from all major phosphateproducing areas of the world (232). The average activity
concentrations obtained range up to 130 pCi g- 1 for
238
U and 2 2 6 Ra, which are generally found to be inradioactive equilibrium, and up to 4.4 pCi g- 1 for
232
Th; The activity concentrations of 2 3 8 U vary widelyfrom area to area but are usually much higher than those.
of 2 3 2 Th, which are comparable to those observed
normally in soil.

2. Radiation exposures due to the industrial useof phosphate products
249. Phosphate deposits usually contain relatively highconcentrations of the naturally occurring radionuclidesof the 2 38 U series. In the United States alone, 130 10 6 t
of phosphate rock were mined in 1973, yielding
38 10 6 t of marketable rock (109). About half of themarketable rock is converted to fertilizer, the other half251. The products and by-products of the phosphateindustry contain various fractions of the uranium,
radium and thorium originally present in the rock,depending on the manufacturing process. In the wet
process, the marketable ore is combined with sulphuric

TABLE 37. ACTIVITY CONCENTRATION OF 2 2 6 Ra, 13 a U, AND 13 2 Th IN PHOSPHATE ROCK

Origin and type of rock

Algeria
Australia
Brazil, apatite
Brazil (Olinda)
Christmas lsland
Cura~oChile and Ecuador islands
Egypt
Guatemala and Mexico
India, China and south-east Asia
Jordan and Turkey
Makatea
MoroccoNauru
Ocean Island
Peru
Poland and USSR, phosphorite
Senegal and other African countries
Seychelles, guano
Spain and other western European countries
Tunisia
USSR, apatite
United States
Arkansas
Florida, land pebble and soft phosphate
Idaho
Montana
North Carolina
OklahomaSouth Carolina
Tennessee, brown rock, blue rock, whiterock and phosphatic limestone
Utah
Wyoming
Venezuela
West Indies

Average activity concentration(pCi g"')Numberofsamples

216Ra

""u

2>2771

12
6
6
4
5
9
9
6
5
5
6
3
5
4
5
14
5
6
4
5
6
5

31
11
I
96
9
5
1
37
12
4
25
32
46
23
32
30
15
37
4
a
14
2

35
10
3
91
9
5
1
41
9
4
16
34
47
22
33
45
17
36
7
2
16
2

1.':
0.5
3.8
4.4
0.2
0.1
0.7
0.7
0.4
0.7
a
0.5
0.9
0.2
0.4
1.0
0.8
1.8
0.2
0.4
2.5
2.5

13
48
5
10
3
5
11

11
54
49
41
18
10
130

10
52
50
38
26
8
130

1.4
1.6
0.9
0.7
1.0
0.8
2.1

38
9
4
4
12

4
50
62
27
3

4

43
61
24
3

0.5
0.8
1.3
1.3
1.5

Source: Reference 232.
aNot detectable.

89acid, and phosphoric acid and gypsum result. This
mixture is called normal superphosphate. By separation,
phosphoric acid is obtained. and gypsum is sent to awaste pile (351 ). Most of the uranium and much of thethorium is transferred to the phosphoric acid during theseparation process. whereas most of the radium remains
with the gypsum by-product. The phosphoric acidobtained can subsequently be used to prepare various
phosphate fertilizers. For example, when combined withammonia. phosphoric acid produces diammonium
phosphate fertilizer, which is expected to have the low
concentrations of 2 2 6 Ra and the high concentrations of238
U characteristic of the phosphoric acid. Triple
superphosphate. which is obtained by combining
phosphoric acid with marketable ore, shows both thehigh concentrations of 22 6 Ra characteristic of thephosphate rock and the high concentrations of 2 3 8 U

characteristic of the phosphoric acid. In the dry furnace
process, the marketable ore is combined with coke andsilica to produce phosphorus and phosphoric acid. Inthat process, almost all of the 2 2 6 Ra activity is retainedby the calcium silicate by-product, with very little
entering the other products (109). Therefore, a large
fraction of the 2 2 6 Ra activity that enters either theelectric furnace plant or the wet-process installation isfound in the by-products slag and gypsum, respectively.
252. The activity concentrations of 226 Ra, 238 U, andTh in various products and by-products of thephosphate industry obtained using ore from the same
origin, namely Florida (United States), are presented intable 38. The variations in the concentrations of 2 2 6 Ra
and 2 3 8 U from one product to another are those
expected from the above discussion.
2 32

TABLE 38. ACTIVITY CONCENTRATION OF 226 Ra, 2 ''U. AND 232 Th IN PHOSPHATE ROCKAND IN PRODUCTS DERIVED FROM IT

Marketable rock produced in Florida (United States)
Production in
the United States in 1973a

Activity concentration(10 6 t)(pCiAmountSampleMarketable rockWet process products
Normal superphosphate
Triple superphosphate
Ammonium phosphate
Phosphoric acid
Gypsum

P 2 0 s content

38

3.1

0.6

3.4
5.3
10.0
23.0

J.6
2.4
5.1

g-•,

22•Ra

2"u

232Th

42

41

0.4

25
21
5.7
0.6
3.3

b

57
63

0.4
0.4

6.1

0.3

Electric furnace process
products

56c

Slag
Source: Reference I 09.

a Florida accounts for 82 per cent of the marketable rock production of the United States.

bThe activity concentration of 2 3 • U in normal ·superphosphate is expected to be equal to thatof 2 2 6 Ra.
cThe > > 6 Ra activity concentration in the input feed ore was 60 pCi g ·•.

253. The use of phosphate fertilizers in agriculture,
resulting in uptake by the food crops of naturalradionuclides from soil. and of chemical gypsum as abuilding material are possible sources of exposure to the
public. Other pathways of exposure include external
irradiation over fertilized fields, in fertilizer storehouses
and in fertilizer production plants, and inhalation ofradon decay products in houses built over land reclaimed
after phosphate mining.

(a) Doses arising from the use of phosphate

fertilizers
254. The world production of phosphate ferilizers was
94 10 6 t in 1972 (205a). The amount of fertilizer usedeach year in agricultural land is about 60 kg of P2 0 5 perhectare {325a).
255 . .Measured activity concentrations of naturally
occurring radionuclides in phosphate fertilizers fromseveral countries are summarized in table 39. For a given
radionuclide and type of fertilizer the concentrations
vary markedly from one country to another, depending
90

probably on the origin of the ore and on the type of
manufacturing process used. Some of the generalfeatures are (a) the concentrations of 232 Tb are always
low; (b) with the exception of the potassium fertilizers,
the concentrations of potassium (and thus 4 °K) are also
generally low; ( c) the concentrations of 22 6 Ra do not
exceed 25 pCi g- 1 ; and (d) 21 0 Pb and 21 0 Po are
generally close to radioactive equilibrium with 2 2 6 Ra.
For the purpose of estimating the doses, it will beassumed that the average activity concentrations of
natural radionuclides in phosphate fertilizers are
15 pCi g- 1 for 2::1su and 10 pCi g- 1 for 226 Ra and foreach of its decay products. The doses from 4 °K andfrom the radionuclides of the 2 3 2 Th series will be
neglected.
256. Taking the example of the United States(table 38). a production of 38 10 6 t of marketable rockyields 11.8 106 t of phosphate fertilizer. Therefore, I t
of marketable rock produces 0.3 t of phosphate fertilizer
containing 5 µCi of 2 3 5 U and 3 µCi of 2 2 6 Ra and eachf its decay products. It is assumed that the total

TABLE 39. ACTIVITY CO~CENTRATION OF NATURALLY OCCURRING RADIONUCLIDES IN PHOSPHATE FERTILIZERS

fpCir'J
Type offertili=er

Country

ApatitePhosphorite dust
"Thomasphosphat"
Phosphate rock, calcined,
soft, partly converted a
Superphosphate
Superphosphate
Normal superphosphate
Triple superphosphate
Triple superphosphate

USSR
USSR
FRG
FRG
FRG
USSR
USA
USA
FRG

Ammonium phosphate
Ammonium phosphate
Nitro phosphate
Nitroammonium phosphate

USSR
USA
USSR
USSR

NPK
NPKC
PKd
NPa

USSR
FRG
FRG
FRG

Enriched concentrate
Phosphate without fluor

USSR
USSR

Hau

226

Ra

llDpb

llDpO

lJl 771•oK

Reference

0.7
10.2

0.8
13.1

< 1.0

0.8
10.6
0.2

1.5
0.7
0.1

2.6
6.2
<0.1

105
105
279

0.7
0.4
1.2

3.1
3.7
3.2

0.4
1.2b

1.4

279
279
105
109
109
279

18.0
14

13.0
14.1
3.1
25
21
6.3

57
21.7

8.0

12
11
25

105
109
105
105

0.4
0.4

2.7
5.7
23

63

4.1

23.6
0.4

25
0.4

0.2
7.2
10
8.5

0.4

0.5

1.4
0.4
0.4
0.8

11.5
0.9

10.6

7.9

0.6

33
140
160

I.I

105
279
279
279

2.0
0.9

105
105

a Assuming a P1 0 5 -to-fertilizer mass concentration ratio of 0.28.
b Assuming that 2 3 2 Th is in radioactive equilibrium with 12 • Th.
c Assuming a P2 0 5 ·to-fertilizer mass concentration ratio of 0.13.
d Assuming a P2 0 5 -to-fertilizer mass concentration ratio of 0.16.

production of phosphate fertilizers is used in agriculture
to improve crops. Assuming, as is done in the section on
coal power plants. that the ploughed layer of soil isabout 20 cm deep. that the availability to plants ofnatural radionuclides is the same whether in fertilizer orin the normal constituents of the soil and is only
reduced by radioactive decay, and that the humanpopulation density is 100 km - 2 , and furthermore
assuming that "the practice of producing phosphate
fertilizers will continue for the order of a century, theincomplete collective dose commitments arising fromthe decision to use I t of marketable rock to produce

phosphate fertilizers can be crudely estimated from thecomparison between the normal concentration ofnatural radionuclides in soil and the resulting doses.
Table 40 shows the results obtained.

(b) Doses arising from the use of waste gypsum
as a building material
257. As shown in table 41. the waste gypsum from thephosphate industry, also called phosphogypsum,
contains concentrations of 2 2 6 Ra of about 25 pCi g- 1 •TABLE 40. INCOMPLETE COLLECTIVE DOSE COMMITMENT PER UNIT MASS OF
MARKETABLE ROCK ARISING FROM THE USE OF PRODUCTS DERIVED FROM IT
Incomplere collective dose commitment
per unit practice (man rad per tonne)
Tracheabronchialtree

Product andtype of i"adiarion

Lung

Gonads

Red
bone
ma"ow

1 10·5
4 10·'
5 10-s

I 10-5
4 10-•
9 10-s

2 10-s
I 10-5
1 10 ...

7 10-s
I 10-•
5 10-•

6. 10-5

1 10...

I 10...

7 10··

1
7 10...

I

1

2 10· 1

7 10 ...

7 10 ...

Phosphate fertilizer

,nu

216Ra

21opb

Total
Phosphogypsum (as building
material)
External irradiation
Inhalation
Total

I
9 10· 1Bonelining
cells

2

91

TABLE 41. ACTIVITY CONCENTRATION OF NATURALLY OCCURRING RADIONUCLIDESIN PHOSPHOGYPSUM
Activity concentration (pCI g- 1J

Numberofsamples••K

Germany, Fed. Rep.of
ApatitePhosphorite
Unknown origin

2
39
7

<1
3
2

United Kingdom

62

Origin of sample

United States

Phosphogypsum can replace natural gypsum in thebuilding industiy and thus be used to make blocks andplasterboard. partition systems and also cement (265).
One tonne of marketable ore produces 0.6 t of gypsum(table 38). The practice of using this waste product has
been considered attractive, since overall building costs
are reduced, natural resources are preserved, andenvironmental pollution is decreased. On the other hand,since phosphogypsum contains a much higher concentration of 2 2 6 Ra than its natural counterpart. its use
increases the radiation doses to the public.
258. O'Riordan et al (265) estimated the doses thatwould be received by the occupants of a residentialbuilding in which 4.2 t of by-product gypsum(considered to be a hlgh, but realistic amount) would
have replaced the established materials. Assuming the226
Ra concentration of phosphogypsum to be
25 pCi g- 1 , they estimated the absorbed dose rate in air
to be 7 µrad h -i . and the radon concentration, using aventilation rate of 1 h- 1 to be 0.2 pCi 1 -•.
259. If it is assumed that all the phosphogypsum
produced by 1 t of marketable ore is used in the building
industiy, that on the average, four persons live in thedwellings so constructed, and that the mean life of thedwelling is 50 y, the collective dose commitments can beevaluated from the estimates provided by O'Riordan etal (265). The results obtained are presented in table 40.
( c) Other pathways of exposure
260. The average addition from phosphate fertilizers
to the soil activity of agricultural areas in the Federal
Republic of Germany during the period 1973-1974, wasestimated to be (nCim- 2 ): 238 U, 9; 226 Ra. 6; 232 Th,
0.3; 40 K, 90 (279). The corresponding absorbed dose
rate in air is about 0.02µradh- 1 (314). Assuming thatthe rate of the addition of activity to the soil has been
constant for the last 80 y. and that there has been no
removal of the added radionuclides by water erosion, theabsorbed dose rate in air would attain a value of about
0.3 µrad h- 1 at the present time. Fertilizer application
therefore results in a small increase of the externalradiation exposure (232, 280). It is worth mentioning,
however, that absorbed dose rates in air of about
50 µrad h- 1 have been measured in fertilizer storehouses
and that similar values are expected in fertilizer
production plants (280).
261. In Florida, much land on which phosphate mining
operations have been completed has been reclaimed and92

Ra232771Ref·
erence

1.5
16
<0.5

<0.5
<0.4
<0.7

327
327
327

3.5

21

0.5

265

5.5

40

0.2

105

•nu

226

some is being developed for residential use. The 2 2 6 Ra
activity concentration in the land fill is about one orderof magnitude hlgher than in ordinaiy soil (214). In apreliminaiy study of buildings on the reclaimed land,
elevated gamma-ray and 2 22 Rn decay-prouuct exposures
were discovered (350).

3. Exposure to 2 2 2 Rn in natural gas andnatural-gas products
262. Natural gas used for kitchen ranges and spaceheaters is a source of radc'l in buildings. The radon
which is produced in the ground diffuses through thegeological fomiations into the natural gas wells. A
summaiy of reported data on radon concentrations innatural gas at production wells is given in table 42.

TABLE 42. RADON CONCENTRATION lN NATURAL GAS
AT THE WELL
Radon concentration
fpCi r' J
Range

Ref·
erence1.5-3.2

352

10-205390-540
4-800

302

Germany, Federal Rep. of

1.0-9.6

352

Netherlands
Slochteren
Other fields

1.1-2.8
3.7-44.7

352

Nigeria
Niger delta

0.9-2.9

352

Location of well

Average

BorneoAmpa field
CanadaAlberta
British Columbia
Ontario.

North Sea
Leman field
Indefatigable field
United States
Colorado, New Mexico
Texas, Kansas, Oklahoma
Texas Panhandle
Colorado
Project Gasbuggy area
California
KansasWyoming
Gulf Coast (Louisiana,
Texas)
California, Louisiana,
Oklahoma, Texas

62
473
169

2.0-3.8
1.8
25
< 100
25.4
15.8

352

0.2-160
5-1 450
10-520
11-45
1-100

171

100
10

5
l-120

98

r--1

I
263. The concentration of radon remaining in the gas
when it reaches the consumer depends on many factors,
including the concentration at the well-head. dilution,gas processing, transmission time, and storage time. The
processing includes fractionation. which mainly separates out methane (the principal constituent), ethane,
propane and heavier hydrocarbons, which are bottled asliquefied gas. This process may remove more than half
the radon content of the natural gas. However, the radon
removed will appear in the liquefied gas sold by retailers
and thus constitute a potential cause of radon exposurein homes. Storage of gas in reservoirs prior toconsumption reduces the radon concentration by decay.
This may lead to seasonal variations depending on the
consumption rate, with maximum concentrations during
winter (22). For liquefied gas, minimum concentration
during winter has been reported because higher
consumption leads to the introduction into the market
of previously stored gas ( 4 7).
264. There are very few data on radon levels caused bynatural gas consumption in homes. Table 43 summarizes the results of measurements made on natural gas

TABLE
43. RADONCONCENTRATIONIN
NATURAL GAS IN THE DISTRIBUTION LINE

Radon concentration(pCi ,-•,

Average

Range

Poland (Warsaw)

8

4-14

United States
ChicagoNew York City
DenverWest coast
Colorado
NevadaNew Mexico
Houston

14.4
1.5
50.5
15
25
8
45
8

2.3-31.3
0.5-3.8
1.2-119
1-100
6.5-43
5.8-10.4
10-53
1.4-14.3

Area

Sources: Poland, 359; United States, 171.

distribution lines in Poland and the United States. In theestimation of the resultant exposure due to radon
daughters in homes supplied with natural gas, thefollowing factors have to be considered: the concentration of radon and radon daughters in the gas, thevolume of gas used, and the volume and ventilation rateof the house. The resultant doses to the bronchial
epithelium have been calculated (22), assuming that theradon concentration in the gas is 20 pCi 1- 1 and that
0.8 m 3 of gas is consumed per day in a kitchen range ina 230-m 3 house with an air change rate of 1 h -l • This
leads to an average radon concentration in the house of
0.0028 pCi 1- 1 • If there are no radon daughters in thereleased gas, the estimated annual absorbed dose to thebasal cells of the bronchial epithelium is 0.6 mrad,assuming an occupancy factm of 0.8 and thedose-to-exposure
quotient
discussedinparagraphs 153-169. With other assumptions, the annual
dose in the bronchial epithelium has been estimated to
be about 1.5 mrad (22). If the radon daughters are in
equilibrium with the radon in the gas, the equilibrium

factor of the radon daughters in the air will be higher. sothat the corresponding doses will be about twice as
great. It should be pointed out, however. that during theuse of the kitchen range the heat build-up and thedepletion of air might lead the user to increase theventilation rate, so that the radon concentration would
drop sharply instead of increasing slightly (352).
265. The doses caused by the gas consumed in spaceheaters have not been calculated specifically because atypical individual could not be defined (171). However,by indirect methods the average individual annual dosein the broncrual epithelium (T-B) was estimated by theauthor to be 5.4 mrad, a value which corresponds to2 mrad if the dosimetric parameters used in this Annex
are applied.
266. The occupation exposure to 2 2 2 Rn and its decay
products in the natural gas industry has been examined(98, 352). External radiation surveys were conducted innine gas processing plants of the United States (98). The
exposure rates obtained at the equipment surfaces
ranged from background to 8 mR h -l • The highest
values were found at the surface of the various productpumps. As the equipment is in low occupancy areas, thetissue absorbed dose rates would be less than
2 mrad h- 1 • The long-lived decay products of 222 Rn
which are likely to be concentrated on the inner surfacesof the pumps do not contrioute to the external absorbed
dose while the pumps remain closed, but if the pumps
are opened for repair or maintenance, an opportunity
exists for inhalation of 2 1 0 Pb and 2 1 0 Po (98).

4. Exposure due to the use of building materials
containing higher-than-average concentrations of
naturally occurring radionuclides
267. As exemplified in table 44, the use of somebuilding materials may lead to elevated indoor radiationlevels. The building materials may be of natural origin,such as pumice stone, (Federal Republic of Germany
and USSR), concrete containing alum shale (Sweden).
and granite wherever it is used. They may also result
from industrial processes. In the non-uranium industries,
the use of phosphogypsum, a waste product of the
manufacture of phosphoric acid, has already been
discussed. Other by-products that were shown to containrelatively high concentrations of naturally occurring
radionuclides were red slime, a waste product ofaluminium mills, and blast furnace slag, a by-product ofiron manufacture (I 92).
268. In its recommendations, the National Commissionof Radiation Protection of the USSR (195) used adosirnetric relationship. If the concentrations of 4 K.
226
Ra and 232 Th, expressed in pCi g- 1 , in building
materials made of industrial wastes satisfy the expression°

the authors ( 195) estimate that the increase of the gonad
absorbed dose indoors over background is less than
150 mrad in a year. They also examined the question of93

TABLE 44. ACTIVITY CONCENTRATION OF NATURALLY OCCURRING RADIONUCLIDESIN BUILDING MATERIALS EXPECTED TO GIVE RISE TO HIGHER-THAN-AVERAGE
EXTERNAL ABSORBED DOSES

Type ofbuilding material

GraniteGranite bricks
GranitePumice stone
Concrete containing
alum shale
Phosphogypsum
From apatite
From phosphorite
Of unknown origin
Phosphogypsum
Phosphogypsum

Country

Numberofsamples

FRG
UK
USSR
FRG

Average activity
concent7arion (pet g- 1 )Absorbed
dose rate
in air'1(µrad h- 1 )Reference

40K

n'Ra

232711

34
7
2
20

33
28
40
29

2.6
2.4
3.0
3.0

2.2
2.3
4.5
3.4

30
28
46
35

327
117
194
327

Sweden

83

23

40.4

2.0

145

335

FRG
FRG
FRG
UK
USA

2
39
7
6

<l
3
2
2

1.5
16
<0.5
21
40

< 0.5
< 0.4
< 0.7
0.5
0.2

<8
54
<6
68
126

r

327
117
105

Red-slime bricks

FRG

23

9

7.6

6.3

58

327

Fly ashFly ashb
Type 1
Type 2Type 3

FRG

28

19

5.7

3.5

42

327

UK
UK
UK

1
1
1

15
15
6

0.2
3.7
1.4

1.0
0.9
1.2

10
20
12

117
117
117

Blast-furnace
slags

USSR

29

6.6

1.8

0.5

10

194

aThe absorbed dose rates in air have been calculated assuming a 471' geometry and an infinite
thickness, and using the conversion factors given in table 6. The values obtained are an index allowing
the comparison between building materials and not an estimate of the doses that would be received indwellings constructed with those building materials.
bMixture of coal clinker, ash and cement.

exposure to 2 2 2 Rn short-lived decay products andestimated that a 2 2 6 Ra activity concentration of
10 pCi g· 1 in a building material would result in an
increase in the concentrations of the 2 2 2 Rn decay
products of less than 0.03 WL.
269. The measurements of activity concentrations of
naturally occurring radionuclides in building materials in
the USSR (195) showed that only a few materials would
cause higher exposures than those quoted above, whilein the Federal Republic of Germany it was found that
12 per cent of the analysed samples would cause suchhigher exposures ( 192).
270. It should be pointed out that the average absorbed
dose rates in air measured in buildings using thesematerials are much lower than what would be expectedfrom the radioactive content of the materials considered,because materials usually less active are also used in thesame buildings. For example, the average absorbed dose
rate derived from measurements carried out in Swedish
houses made of concrete containing alum shale is about
18 µrad h" 1 (241), while the value given in table 44,
calculated from the activity concentrations of radionuclides in that type of concrete, using very pessimistic
assumptions. is 145 µrad h- 1 (335).
271. Use has also been made of waste products of theuranium and radium industry. In the United States,
notably in Grand Junction, Colorado, tailings fromuranium mills were used during the period 1952-1966 as
94fill material under houses and as building materials(348a). Remedial action was deemed necessary by thenational authorities.
272. In the town of Port Hope, Ontario, Canada,another type of problem arose from a plant which had
recovered radium in the 1930s and the 1940s frompitchblende-radium-silver ores (323). In this particularcase, the management of the waste material resulting
from the plant demolition was inadequate and muchcontaminated construction and fill material was used inand around the houses in the town. As in the case ofGrand Junction, remedial action was deemed necessary
by the national authorities.

C. SUMMARY AND CONCLUSIONS
273. This section has dealt with the examples oftechnologically enhanced exposures to natural radiation(TENR) which have been brought to the attention of theCommittee. It should be stressed that it is very likelythat those examples do not present the complete pictureof TENR. From the assessments presented, TENR does
not add significantly to the collective dose on the global
scale but may give rise, in localized areas or for people
exposed under extreme conditions, to appreciable
increases in individual doses from natural radiation. The
present state of knowledge does not allow an accurate
estimate of the collective dose from TENR to be made,and further research is required in this field.

rAppendix
RADIATION EXPOSURES FROM CONSUMERPRODUCTS
Introduction].

274. A wide variety of 9onsumer products containradioactive nuclides that have been deliberately incorporated to satisfy a specific purpose. Table 45 presents alist of such products classified into -six categories,
namelyRadioluminous products
1.
Electronic and electrical devices
2.
3.
Antistatic devices
Gas and aerosol (smoke) detectors
4.
Ceramic, glassware, alloys etc. containing
5.
uranium or thorium
Other devices, including scientific instru6.
ments
TABLE

45. CURRENTLYAVAILABLECONTAINING RADIONUCLIDESPRODUCTS

NuclideProducts

Radioluminous products (continued)(b) Radionuclide contained
in sealed tubes (continued)(7) Exit signs for commercial
buildings(8) Large signs(9) Small exit signs(10) Step markers(11) Mooring buoys and lights(12) Public telephone dials(13) Llght switch markers(14) Bell pushes(15) Miniature light sources'H

Products

Nuclide1. Radioluminous products(a) Radionuclide containedin paint or plastic(1) Timepieces(2) Aircraft instruments(3) Compasses(4) Instrument dials andmarkers(5) Instruments, signs andindicators(6) Thermostat dials andpointers(7) Automobile lock
illuminators(8) Automobile shift
quadrants(9) Bell pushes(10) Speedometers(11) Rims for underwater
watches(12) Fishing lights(13) Spirit levels{ •••pm'H
ll6Ra{ 147Pm
3H
2l6Ra

{ ,H

u'Pm

1-25 mCi
65-200 µCi
0.1-3 µCi
< 10 Ci..; 0.3 Ci..; 20µCi
5-50 mCi
10 µCi'H
63

Ni
141 PmasKr(a) Electronic tubes

0
• co
2l6Ra

asKr

(b) Glow-discharge tubes(c) Voltage-discharge tubes(d) Cold-cathode tubes(e) Fluorescent lamp starters(f) Gas-discharge lamps(high-pressure mercuryvapour lamps)(g) Vacuum tubes(h) Electric lamps(i) Germicidal lamps, sunlamps, lamps for outdoor
and industrial lightingG) Glow lamps

.,,Pm

'H
226Ra

Natural Th

'H

rPm
6
°Co
63Ni

(k) Spark-gap tubes

ll7Cs(1) High-voltage protection'H

25 mCi147Pm

0.75 Ci

3H>H

25 mCi

147Pm
147Pm

devices(m)Low-voltage fuses{147 Pm
3H
3H
•.,Pm

'H

14c

'H

2-15 mCi
2mCi
25 mCi
0.3 mCi
0.1 mCi
0.3 mCi
3-4 mCi
5-25 mCi(a) Llghtning rod

6 nCi
0.8-1.2 wt%
50mg
2g
0.01 mCi
30 µCi
5 µCi
5 µCi
5 µCi
3 µCi
3 µCi

(c) Antistatic brushes

.

}

'H

{ B5Kr(6) Instruments, signs andindicators
{ 'H
'H

85Kr

0.2-0.4 Ci
0.2-0.4 Ci
0.2-2 Ci
0.25 Ci
4 Ci
0.3 Ci
2 Ci
0.25 Ci

0.2-1 mCi
0.06-0.7 mCi'"Ra

10 µCi0.05-0.5 mCi
2-25 µCi{ 21op 0"'Am(d) Antistatic devices containedin precision balances

'H

r~

1 mCi

4. Gas and aerosol (smoke) detectors

Smoke and fire detectors(1) Timepieces

r··Ra
241Am

(b) Antistatic devices contained
in instruments

in sealed tubes(5) Markers

1-104 µCi
1-5 µCi
1 µCi
1-5 µCi
0.15-5 µCi
0.1 µCi
5 µCi
0.01-10 µCi
3 µCi
90 µCi
1 µCi

3. Antistatic devices(b) Radionuclide contained(2) Ordinary compasses(3) Marine compass(4) Marine navigational
instruments

15 Ci
30 Ci
2 Ci
2 Ci
2 Ci
0.5 Ci0.2 CilOmCi
20mCi

2. Electronic and electrical devices

ll?Cs

Activity or
mass perproduct (range
of approximate
values)Activity or
mass perproduct (range
of approximate
values)

2l6Ra
S5Kr

Natural or
depleted U

nsPu

1-100 µCi
0.01-15 µCi
7mCi
7.5 mg
20µCi

5. Ceramic, glassware, alloys etc.
containing uranium or thorium(a) Chinaware(b) Ceramic tableware glaze

Natural U{Natural Th
Natural or
depleted U

10· 2 µCi cm • 2
surface
20 Wt% (glaze)
20 wt% (glaze)

95

TABLE 45 (continued)

NuclideProducts

Activity
mass perproduct (range
of approximate
values}5. Ceramic, glassware, alloys etc.
containing uranium or thorium(continued)(c) Glassware, glass enamel,glass-enamel frit

{ Natural Th
Natural or
depleted U(d) Optical lenses(e) Incandescent gas mantles
Natural Th(f) Magnesium-thorium alloys(g) Products containing rareearths: arc carbons,lighter flints, metallurgicaladditives, precision lenses,
television tubes, electronic
ceramics, microwave{ Natural Th
devices etc.
Natural or
depleted U(h) Welding rods

Natural Th

JO wt%
10wt%<; 30 wt%<: 0.5 g<;4 wt%TABLE 46. TYPES Al\'D QUANTITIES OF LUMINOUS
TIMEPIECES DISTRIBUTED IN THE UNITEDSTATES, 1971-1973(Thousands of units)

Type of timepiece
and activator

1971

1972

1973

Tritium
Domestic
Imported

2 710
5 670

2 330
6 540

1 800
3 600

Promethium
Domestic
Imported

620

negligible
770

900

Wrist-watches
0.25 wt%
0.25 wt%

1-2 wt%

6. Other devices, including

Radium-226

negligible

aocks

scientific instruments(a) Gas chromatographs

278. Table 46 presents the number of luminous
timepieces distributed in the United States in 197 L
1972 and 1973. It is clear from the table that, although
only a few radium watches have been sold in the UnitedStates in recent years. radium continues, in that country,
to be heavily used in clocks. A small survey in Tennessee
showed that, out of a total of 227 clocks reported in 48
households, 35 were luminescent. 17 of which contained
radium (51).

'H{ 6'Ni(b) Static meters(c) Vending-machine coins(d) Bank cheques

24'Am
,•c
14c

250 mCi
12mCi
0.5-50µCi
2µCi
0.01 µCi

Sources: References 81, 359a.

275. The radionuclides and the approximate range ofactivities used are also given in table 45. It must be
pointed out, however. that accurate information on theactivities contained in the consumer products and on thenumber of products manufactured is sometimes difficult
to obtain (355).
276. The purpose of this appendix is to review what
has recently been published in the scientific literatureon the uses of radionuclides in consumer products andon the resulting doses to the public.

Tritium
Domestic
Imported

18
500

10
190

Promethium
Domestic
Imported

1470

negligible
970

I 370

Radium-226

2 800

2 800

2 800

20
240

Source: Reference 242.

279. The activities of 3 H and 14 7 Pm which produce thesame brightness as 1 µCi of 2 2 6 Ra have been estimatedto be 5000 µCi of 3 H and 170 µCi of 14 7 Pm for a newly
manufactured timepiece (148). However, owing toradioactive decay, release of activity and deterioration of
the phosphor, the brightness decreases continuously overthe useful life of the timepiece at a rate that depends
upon the radionuclide used. The activities of 3 H and
14 7
Pm required to produce the same average brightness
as I µCi of 2 2 6 Ra over the useful life of the timepiece,
assumed to be five years, have been estimated as
11 OOO µCi of 3 Hand 390 µCi of 14 7 Pm (242).
(a) Absorbed doses from 2 2 6 Ra-activated timepieces

1. Radioluminous timepieces

277. Radium-226, promethium-147, and tritium havebeen used extensively in the dial-painting industry forthe illumination of timepieces, the radiation emitted bythose radionuclides being converted into light by ascintillator, which is usually zinc sulfide containing small
amounts of copper or silver. From the public healthpoint of view, one of the major disadvantages of radiumis its inherent emission of a great deal of penetratingradiation which is not useful for the production of light
yet irradiates the whole body of the watch wearer.
Radium tends to be replaced by 3 H and 147 Pm, which
are soft beta emitters and thus cause much smaller
external radiaiion doses to the watch users.
96

280. The absorbed doses from 2 2 6 Ra-activated timepieces result mainly from external irradiation. Joyet(173, 174), who made comprehensive measurements ofthe external radiation dose from 2 2 6 Ra-activatedtimepieces, suggested an annual gonad dose of about
60 mrad µCi- 1 for wrist-watches worn continuously.
According to the recommendations issued by a joint
group of experts from the OECD and the IAEA (148),
the total activity of 22 6 Ra should be limited to 0.1 µCi
per wrist-watch. That limit corresponds to a gonad
absorbed dose in a year of 6 mrad.
281. Pocket watches are worn closer to the gonads andthus the dose rate is higher. If it is assumed that thepocket watch is worn 16 h per day at a distance from

r""
I
I
!

the gonads of 0.25 m, the annual dose can be estimatedto be about 80 mrad µCi- 1 if the dose rate for asource-to-target distance of 1 m is taken to be
0.34 µrad h- 1 pCi- 1 (242).
282. The use of 2 26 Ra in pocket watches has not been
permitted in most countries since 1966 (148). Assumingthat in older pocket watches the total activity of 2 2 6 Ra
is 0.1 µCi, the corresponding gonad absorbed dose would
be about 8 mrad in a year.
283. The external radiation dose to the user of a 2 2 6 Ra
activated alarm clock can be estimated in the same way.
Assuming an exposure of 8 h per day at a distance of
2 m and an activity of 0.15 µCi, which is the limit
recommended by the joint group of experts from theOECD and the IAEA (148), the annual gonad dosewould be about 0.1 mrad.
284. The user of a radium-dial timepiece is also exposed
to an inhalation dose from 2 2 2 Rn leaking out of it. As
indicated in the 1972 report, radon emissions fromwatches and clocks vary widely. The radon content
measured after a build-up of 10 h in an air-tight box was
found to range from around 0.1 to 30 nCi per µCi of226
Ra for new, water-tight watches and for loosely
sealed, old watches, respectively (78). Assuming aleakage rate of 1 nCi 11- 1 of 2 2 2 Rn per µCi of 2 2 6 Ra,
the average 22 2 Rn concentration in a 300 m 3 house
ventilated at a rate of 1 h- 1 would be about 3 fCi 1- 1 •corresponding to an annual absorbed dose in the lungs ofthe order of 0.1 mrad.
(b) Absorbed doses from 3 H-activated timepieces
285. The casing of timepieces being at least
50 mg cm - 2 thick, no external dose results fromluminous watches containing tritium, since the beta
particles that are emitted by that radionuclide have amaximum range of 0.6 mg cm - 2 • However, tritiatedwater or tritiated organic molecules evolve slowly fromthe tritium paints leading to intem;u absorbed doses towearers from inhalation and skin absorption.

288. If that result is applied to the results reported by
Fitzsimmons (87) and by Schell et al (305), it would
appear that the watches in these two studies had an
average tritium activity of 10 mCi. This finding is notconsistent with either the observations of Bradley et al.
( 43), whose survey of the storage areas of nine wholesale
importers and two retailers of self-luminous watches in
the New York City area suggested values ranging from 1
to 5.6 mCi per watch, or with the maximum tritium
activity of 7.5 mCi per watch recommended by IAEA
and OECD. It would therefore seem more reasonable toadopt a figure of 0.1 mrad mCi- 1 as a conservative
estimate of the whole-body dose. This value would give a
calculated annual whole-body dose of 0.5 mrad to aperson continuously wearing a 3 H-activated watch
luminized with the average activity of 5 mCi recommended by IAEA and OECD.
(c) Absorbed doses from147

Pm-activatedwrist-watches

289. Since promethium is a rare earth, it does not
evolve from a watch under normal conditions of usage,
so that the risk of external radiation is the only one thathas to be considered. Promethium-147 is a pure beta
emitter. The maximum energy of its beta particles is
224 keV, corresponding to a range of 46 mg cm - 2 • Since
the standards set by the OECD and the IAEA
recommend a minimum thickness of 50 mg cm -2 for thecasing of timepieces, no exposure hazard from beta
radiation should exist. However, a low external radiationdose from bremsstrahlung has to be expected. Moghissi
and Carter (242) estimated that the gonad absorbed dosein a year could be about 5 mrad mCi- 1 • However, more
recent measurements on compasses radioluminized with
14 7
Pm have suggested that a more appropriate figure forthe annual gonad dose from a watch would be about
1 rnrad mCi- 1 (372a). Taking an intermediate value of
3 mrad mCi- 1 would give a calculated annual gonaddose of 0.3 mrad to a person continuously wearing a
14 7
Pm-activated wrist-watch luminized with the average
activity of 0.1 mCi recommended by IAEA and OECD.
(d) Absorbed doses from wrist-watches luminized by3

Hin sealed tubes

3286. The determination of H concentration in the
body water of users of 3 H-painted watches has been
carried out in at least two studies. Fitzsimmons et al.
(87), measuring the 3 H activity in urine of eight persons
wearing 3 H-painted watches, found concentrations
ranging from 0.5 to 11 nCi 1- 1 above background, withan average of 3.2 nCi 1- 1 • The corresponding wholebody absorbed doses in a year range from 0.05 tol.l mrad with an average of 0.3 mrad. Schell and Payne(305). investigating the origin of a relatively high 3 H
concentration in a laboratory, found the source to be an
employee's wrist-watch. The whole-body absorbed dosethat this employee would receive in a year if he wore hiswatch 24 h a day was estimated to about 0.3 mrad.
287. The relationship between the 3 H activity inwatches and the resulting whole-body absorbed dose has
been studied under controlled conditions by Moghissi andCarter (242). The average dose in a year per millicurie oftritium paint was found to be 0.03 rnrad, the range being
0.012-0.044 rnrad.

290. With the advent of liquid-crystal displays, the useof gaseous tritium light sources to illuminate digital
watches is being investigated. The external bremsstrahlung dose rate from a well-designed watch of thistype will be very small; measurements of prototypes
containing 300 mCi of 3 H in the form of several sealed
tubes have shown that external surface dose rates in air
as low as 5 µrad h -l are achievable (372a). There would
be some internal dose to a person breaking one of thesources, but that is unlikely to be a frequent occurrence
as the sources are usually sealed in a metal or glass
capsule with the liquid-crystal display and are notaccessible to the wearer.
(e) Collective dose from radioluminous timepieces

291. Estimates of the collective dose from radioluminous timepieces have been reported for the
population of two countries. For the population of theUnited States, a minimum value of 6100 man rad has
97been proposed for the exposure during the year 1973(242). The population of the United States being about
2 108, the average absorbed dose would be 0.03 mrad ina year. The annual collective dose to the population of
the United Kingdom has been assessed to be about
104 man rad from 2 2 6 Ra luminous watches and about
10 3 man . rad from 3 H luminous watches (339),
correspon.ding to an average absorbed dose of about
0.2 mrad in a year. If it could be extrapolated that thosevalues are representative of the situation in the world's
most populated countries, the collective dose to theworld population would lie in the range from 10 5 to
10 6 man rad in a year.

297. An analysis performed by O'Riordan and Hunt
(266) on 20 porcelain powders under five brand names
showed that 17 of the powders contained uranium. on
the average 0.041 weight per cent, with 2 having about
0.1 per cent. It is estimated in that study that for people
with fluorescent porcelain teeth, the absorbed dose fromexternal irradiation in the basal layer of the oral
epithelium wold be the limiting factor. Assuming a massconcentration of depleted uranium in the porcelain of
0.1 per cent, the absorbed dose in that basal layer. taken
to be at a distance of 30 µm from the interface. wasfound to be of the order of 3 rad in a year .. As the rangesof the alpha particles emitted by the isotopes of uranium
are Jess than 30 µm in soft tissues, most of the absorbed
dose is due to beta radiation.

2. Other self-luminous devices
292. It is known that radioluminous materials are being
used in exit signs, compasses, gun sights, and many otherdevices (see table 45), but there is not enoughinformation available to make a reasonable estimate ofthe doses arising from their use. However, it is likely thatthe resulting collective dose is insignificant in comparison to that from radioluminous timepieces.

298. On the basis of that estimate, the National
Radiological Protection Board has recommended thatthe use of radioactive fluorescers in dental porcelain bediscontinued in the United Kingdom (328). Followingthat decision, the false·teeth industry ·in the UnitedStates has voluntarily agreed to standardize the level ofuse of uranium at 250·300 µg per gram of porcelain(372).

3. Uses of uranium and thorium

4. Electronic and electrical equipment

293. The main uses of uranium in consumer products
are either as a pigment (328) or in applications making
use of its high density. Thorium is used in incandescentmantles and in certain optical lenses.

299. Electronic and electrical equipment may give rise
to radiation exposure if they contain radioactive
substances or if they emit x radiation owing to theacceleration of electrons.

294. The principal hazard from the uses of uranium andthorium under normal conditions is the somatic dosefrom the beta-emitting decay products. In general. doses
received will be small due to substantial attenuation overthe distance between the device and the exposed person.
In particular cases, this may not apply, however. Some
optical lenses containing up to 30 per cent by weight ofuranium or thorium may deliver substantial doses to thelens of the eye (372). The air absorbed dose rate at asurface of a lens which contained 18 per cent thorium
by weight was measured by thermoluminescent dosimetry to be 1 mrad h -r (228).

300. Radioactive materials provide pre-ionization ingases for the purpose of passing an electric current, sothat the equipment reads faster and more reliably. or
displays more constant characteristics (72). Examples ofapplication are starters for tubular fluorescent lamps,
trigger tubes in electrical appliances and excess-voltage
protection devices. In fire alarms and smoke detectors
the radioactive materials are used to provide a sufficient
rate of ionization in gases. The radionuclides mainly
used for that purpose are 3 H, 6 3 Ni, 14 7 Pm, and 2 4 1 Am.
The doses resulting from the normal use of such
equipment can be expected to be very small. It is only inthe event of breakage through accident or disposal thatthe radiation exposure could be significant.

295. Another example which has attracted interest is
the practice of incorporating uranium in the porcelainsused in restorative and prosthetic dentistry. In the
United Kingdom, it is estimated that about one in nine
adults has artificial porcelain teeth (266); in the UnitedStates. that proportion is likely to be even higher (315).
A combination of uranium and cerium compounds isincorporated in the majority of modern porcelains inorder to simulate the fluorescence of natural teeth indaylight and in artificial light. As all the isotopes ofuranium are radioactive, the tissues of the mouth areexposed to ionizing radiation from fluorescent porcelains.
296. In the Federal Republic of Germany and theUnited States, the two countries where most of thedental porcelain seems to be manufactured, the massconcentration of uranium is limited by law. The uranium
content of porcelain powders and artificial teeth should
not exceed 0.1 per cent by weight in the Federal
Republic of Germany and 0.05 per cent in the UnitedStates.
98

301. The absorbed doses from the normal use ofionization-chamber smoke detectors (ICSDs) have been
estimated (242b ). The use of ICSDs is widespread inindustrial, commercial and public buildings, and also, atleast in the United States in private homes. Althoughsome of the ICSDs now on the market contain 2 2 6 Ra.
238
Pu, 85 Kr, and 63 NL the preferred radionuclide
seems to be 2 4 1 Am. During normal use of ICSDs, thedoses to members of the public are virtually limited tothose resulting from external irradiation. Assuming thatin some countries the total number of lCSDs now
installed in industrial, commercial and public buildings
corresponds to one for every hundred members of the
population and that each ICSD contains 60 µCi 2 41 Am,
the consequential average whole·body absorbed dose
received in a year by individuals in those buildings has
been estimated to be about 60 µrad while the per caput
whole·body dose would be about 1 µrad (242b). In
private homes equipped with smoke detectors. therI

average whole-body dose received in a year by theoccupants would be of the order of l µrad if the activityof 2 4 1 Am contained in each smoke detector is taken to
be 1 µCi: assuming that 1 house in 20 is equipped withsuch a smoke detector. the corresponding per caput
whole-body dose would be about 0.05 µrid in a year
{242b).
302. Household colour television receivers are the mostcommon electronic product with the potential of
exposing the general public to x radiation. As indicatedin the 1972 report, several surveys conducted in the
1960s showed that a small proportion of the colour
television sets emitted x radiation in excess of the limit
recommended by the ICRP, that is 0.5 mRh- 1 at 5 cm
from the surface of the television receiver. Since then.
more stringent regulations became effective in the
United States, and more and more solid-state circuitry
has been employed, so that it is likely that the x-ray
emission from recently built colour television receivers is
negligible under conditions of normal operation andproper servicing. The assumption is supported by the
results of measurements recently conducted in theFederal Republic of Germany (192a) and in the islandof Taiwan (358). In the first of these surveys, conductedin I 972, it was found that the average exposure rate
5 cm from the surface of the colour television receivers
was 0.1 mR h- 1 and that the estimated annual gonaddose, under normal viewing conditions, was of the orderof 1 millirad. In the second the exposure rate at thesurface of 28 randomly chosen colour television
receivers was found to vary from 0.001 to
0.076 mR h- 1 under normal working conditions.
,,

5. Absorbed doses from disposal of consumer
producrs as waste
303. Although in many countries the use and eventual
disposal as waste of consumer products containing
relatively high levels of radioactivity are subject to various forms of control. the vast majority of these products
are likely to be disposed of as household refuse. without
control. The normal subsequent disposal of this refuse isby dumping on land or by incineration. Dumping onland will result in the radioactivity being more isolated
from man than when the product containing it was inuse, so that doses from this type of disposal will on the
average be less than from normal use of the product. No
data are available on the likely proportion of theseproducts that might be incinerated. If it is assumed that
10 per cent of the 3 H-radioluminized wrist-watches
distributed in the United States are disposed of in thisway after they have been in use for l Oy and that the
average activity per watch at this time is 2.5 mCi. thenthe disposal would give rise to approximately 1OOO Ci ofairborne tritium distributed more or less uniformly overthe country. Further assuming that this would give rise
to doses of a similar magnitude as those resulting fromairborne tritium discharges from nuclear reactors, i.e., acollective dose per unit activity released of 3 10- 3 man
rad Ci -I (see Annex D), then the annual collective dosewould be about 0.3 man rad. This value is negligible
relative to the collective dose resulting from the wearingof wrist-watches (para. 291 ).

6. Conclusions
304. Many millions of units of various types ofconsumer products containing deliberately incorporated
radionuclides are in everyday use around the world.
Estimates of doses in individuals resulting from the useof such products show .that in all cases these doses are
small. The highest. calculated whole-body doses result
from the wearing of radioluminous watches. which are
the most widespread radioactive consumer product. The
assessment of the global collective dose from thesesources is hampered by wide gaps in the knowledge ofimportant factors such as the activities involved, thenumber of products on the market, and the problems
related to the disposal of those devices. Even for themost common product, watches. the data are not always
available since watches are generally not subject tocontrol. Nevertheless, owing to international recommendations, and national regulations in some countries,
there is a gradual improvement of control. It is likelythat the average annual gc>nad dose due to the use of
consumer products is less than 1 mrad, almost entirely
due to radioluminous timepieces. However, in view ofthe growing number and diversity of consumer products,
it is important to ensure that proper control ismaintained over their use and disposal.

99

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