IONIZING RADIATION:
SOURCES AND BIOLOGICALEFFECTS
United Nations Scientific Committee
on the Effects of Atomic Radiation
1982 Report to the General Assembly, with annexes

UNITED NATIONSNew York, 1982

NOTE
The report of the Committee without its annexes appears as Official Records of the General Assembly, Thirtyseventh Session, Supplement No. 45 (A/37/45).
The designations employed and the presentation of material in this publication do not imply the expression of
any opinion whatsoever on the part oft he Secretariat of the United Nations concerning the legal status of any country,
territory. city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries.

UNITED NATIONS PUBLICATION
Sales No. E.82.IX.806300PANNEXB

Exposures to natural radiation sources

CONTENTSParagraphs

Paragraphs

II. INTERNAL IRRADIATION ......... .

34-84

Cosmogenic radionuclides ......... .
1.
Tritium .................... .
2.
Beryllium-7 ................ .
Carbon-14 ................. .
3.
4.
Sodium-22 ................. .
Primordial radionuclides .......... .
1.
Potassium-40 ............... .
2.
Rubidium-87 ............... .
3.
Uranium-238 series .......... .
4.
Thorium-232 series .......... .

35-42
36-37
38
39-41
42
43-84
44-45
46
47-73
74-84

14-33
14-16
17-27
28-31

III. RECAPITULATION ................ .

85-88

32-33

References .............................. .

Page
103

INTRODUCTION ....................... .
I. EXTERNAL IRRADIATION ......... .

2-33

Cosmic rays ..................... .
Primary cosmic rays ......... .
I.
Secondary cosmic rays ....... .
2.
Absorbed dose indexes from3.
cosmic rays ................ .
4.
Annual effective dose equivalents from cosmic rays ....... .
External radiation from naturallyoccurring radionuclides (terrestrial
radiation) ...................... .
1.
Source radionuclides ........ .
2.
Exposure outdoors .......... .
3.
Exposure indoors ........... .
4.
Annual effective dose equival:nt:5 from gamma terrestrial
radiation .................. .

2-13
3-6
7-8

A.

B.

9-11

A.

B.

12-13

Introduction
1. The assessment of the radiation doses from natural
sources in humans is of particular importance because
natural radiation is the largest contributor to thecollective dose of the world population. The naturalradiation sources are classified into:(a) External sources of extraterrestrial origin (cosmicrays) and of terrestrial origin, i.e., the radioactive
nuclides present in the crust of the earth, inbuilding materials and in the air;(b) Internal sources, compnsmg the naturallyoccurring radionuclides which are taken into thehuman body.
This Annex is to a large extent a summary of Annex Bof the 1977 report of the Committee [Ul]. Modifications have been made only for those components of thenatural radiation environment for which knowledge has
substantially improved since 1977. The doses due to theradon isotopes and to their short-lived decay products
are briefly reviewed; a detailed treatment of the sourcesof exposure to th_ose radionuclides and of the corresponding doses is provided in Annex D.

I.

EXTERNAL IRRADIATIONA.

COSMIC RAYS

2. The high-energy radiation that enters the earth's
atmosphere from outer space is known as primarycosmic rays. When these interact with atomic nuclei inthe atmosphere, secondary particles and electromagnetic radiation are produced which are called
secondary cosmic rays.

1. Primary cosmic rays
3. Most of the primary cosmic rays originate outsideof the solar system. In addition, there are also solar
cosmic rays related to solar flares.
(a)Primary galactic cosmic rays

4. Primary galactic cosmic rays consist largely ofhigh-energy protons which enter the solar system from83

interstellar space, together with 4He ions in the
proportion of about 10% and much smaller proportionsof heavier particles. and of electrons, photons andneutrinos. The primary nux density is affected by theearth's magnetic field, which denects low-energy
charged particles back into space. This effect isdependent on the geomagnetic latitude, so that the nux

density of low-energy protons at the top of the atmosphere is greater at the poles than in equatorial regions.
Thus, as shown in Figure I, the ion density production
rate at a given altitude in the atmosphere (which is afunction of the "atmospheric depth" i.e., of the mass of
air above a unit of area at that altitude) is latitudedependent.

M.TlTlJO(

...

,0

...

ATMOSPHERIC OEPTH

Figure I. Variation of Ion density production rate with altitude
end atmospheric depth at different geomagnetic latitudes.
Based upon the results of Neher [N1l5. The nuence rate of the galactic low-energy protons
in the upper atmosphere varies with time according to
the 11-year solar cycle. This is known as modulation.
The nuence rate is at a minimum during times ofmaximum solar activity and passes through a maximum
during the period of low solar activity.

(b)

Primary solar cosmic rays

6. During the solar nares. large numbers of charged
particles, mainly protons and alpha particles, arereleased. However. these particles have relatively low
energies and do not usually cause significant increases
in radiation doses at the earth's surface.
2.

Secondary cosmic rays

7. When primary cosmic-ray particles enter the atmosphere, those with higher energy undergo nuclear
reactions (spallation reactions) with nuclei of atoms
present in the air, producing neutrons, protons, pions,and kaons, and quite a variety of reaction products
84(cosmogenic nuclides) such as 3H, 'Be, toBe, 22Na, and:4Na. The high-energy protons, neutrons and pions thus
formed react further with nuclei in the air to form moresecondary particles [G 1, Pl ]. Such a process is called acascade. The pions decay into muons or photons,
initiating other cascades.
8. The protons and neutrons contribute significantly
to the absorbed dose index rate 1 in the upper atmosphere. The neutrons lose energy by elastic collisions,and when thermalized they are captured by 14N to form
14C. Because nucleons rapidly lose energy by ionizationand nuclear collisions, the nucleonic nuence rate isconsiderably attenuated in the lower part of the atmosphere and accounts for only a few per cent of theabsorbed dose index rate from cosmic rays at sea level.
The major contribution here is provided by the muons
produced by the decay of charged pions at higher
altitude and by the electrons that result from ionization,from muon decay and from cascade processes.
1
The absorbed dose index rate is the maximum absorbed
dose rate that would occur in a 30-cm diameter tissue equi~alent sphere located with its centre at the point of interest.

3.

with a cluster of values around 2.1 cm-3 s-1 andextremes at 1.9 and 2.6 cm-3 s-1 [G2, G3, Hl, Kl, Ll,01, 02, Sl, Yl]. Here. as in Annex B of the 1977 report[Ul], a value of2.1 cm-3 s-1 will be used for the purposesof computing the absorbed dose index rate. Assuming
each ion pair in moist air requires 33.7 eV to be
produced, the absorbed dose rate in air is 3.2 10-S Gy
h-1. This value is taken to be numerically equal to theabsorbed dose index rate. About 75% of the dose isfrom muon collision electrons, 15% from muon decay
electrons, and 10% from other processes [N2]. If theshielding effect by building structures is not taken into
account, the annual absorbed dose index is found to be
2.8 1Q--4 Gy at ground level. Using reported values ofion density production rate in the upper atmosphere.
absorbed dose index rates have been computed there ina similar manner and are shown in Figure II [Ul].

Absorbed dose indexes from cosmic rays

9. The doses from direclly ionizing components ofcosmic rays and from neutrons will be examined separately.

(a)

Ionizing compo11e11t

10. The ion production rate per unit volume in free air
is a measure of the nuence rate of the total chargedparticle component of the cosmic-ray field and isusually expressed as the number of ions formed per
second in each cubic centimetre of air at normal
temperature and pressure (STP). The values of thecosmic ray ion density production rate at sea level
reported after 1960 show a relatively good agreement.

ALTITUDE 1km)

100

10

0.1

------------c-----+SOLAR MINIMUMIONIZING COMPONENT.. Kolb (ion. CNmbe,s) !K2)
" Kolb hc1-r.till1tion)[K2}• GfO<go (G2J

IONIZING COMPONENTo George lGSJ
0 Nt'h~r

INJJ• N,hef(NJJ

x Raft.-r

(RI)

10-•

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w
0

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SOLAR MINIMUM: ... ,,,NEUTRON COMPONENT

/;

I
110·'

V,

0

0

~

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"'0:
5!

I

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6 .knkint (JI)

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,:_, Gre-r-nh1II JG6J

/
I

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SOLAR MAXIMU~' ..... _

/
I

l

~

I

I

_ __,,_~-~~~-'---~-~~--'-'-----~.....J.-~--~~.....c: 10·'
0.1

10

100

AlTITUDE (kml

Figure II. Absorbed dose Index rates at high geomagnetic latitudes (50°) from the Ionizing andneutron components of cosmic rays at different altitudes for 1969 (solar maximum) and 1965 (solar
minimum). The Ionizing component of the absorbed dose Index rate at 0.1 km Is Interred from that at
ground level(b)

Ne111ron component

11. As in Annex B of the 1977 report of UNSCEAR, aneutron fluence rate of 8 1Q-3 cm-2 s-1 at sea level isadopted for the purpose of estimating doses at high latitudes. Using a conversion factor from neutron nuence
rate to absorbed dose index rate of 5 1Q-8 Gy h-1 cm2 s[H3], the absorbed dose index rate would be 4 10-10
Gy h-1, yielding an annual absorbed dose index of
3.5 1Q-6 Gy at ground level. The neutron absorbed doseindex rate increases rapidly with altitude, reaching amaximum at altitudes between 10 and 20 km(Figure II).

4.

Annual effecth·e dose equivalents from cosmic rays

12. For both the ionizing and the neutron component,
the absorbed dose index is assumed to represent sufficiently well the absorbed dose in all organs and tissuesof the body. Using a value of one for the quality factorof the ionizing radiation. the annual effective dose
equivalent is thus found to be 280 µSv at ground level.
13. For the neutron component a quality factor of 6 isadopted, as in Annex B of the 1977 report of theCommittee [Ul ], on the basis of computations of thedose equivalent and of the absorbed dose by Hajnal et8515. The main primordial radionuclides are 4°K. B7Rb,
and the elements of the two radioactive series headed
by mu and 232Th, which are presented in Figures lll
and IV and have existed in the earth's crust throughout
its history. Other radionuclides, such as those present in
the 235U decay series, have been neglected as they
contribute very little to the total dose from natural
background.

al. [H3] for isotropic bilateral incidence on a slab
averaged to a depth of 15 cm. The annual effective dose
equivalent for the neutron component is thus estimatedto be 21 µSv at ground level.

B.

EXTERNAL RADIATION FROM NATURALLY-OCCURRING RADIONUCLIDES (TERRESTRIAL RADIATION)

1.

16. lt should be mentioned that 238U is not only thehead of a radioactive decay series but also gives rise to
many radioactive nuclides by spontaneous fission. The
inventory of the long-lived fission products in theearth's crust is rather large, but the average activity
concentrations in soil are extremely small and theresulting doses trivial. Taking 90Sr as an example,
the inventory in the earth's crust is estimated to be
5 1 Q16 Bq [S2]: its activity concentration in soil would be
2 1Q-6 Qq kg-I, yielding an annual dose in red bonemarrow of the order of 10-11 Gy.

Source radionuclides

14. The natural radionuclides in the environment areof two general classes, the cosmogenic and theprimordial. The cosmogenic radionuclides (3H, 7De,
14C, 22Na, 24Na, etc.), which are mainly produced
through interaction of the cosmic rays with target atoms
in the atmosphere, do not contribute significantly to theexternal gamma radiation doses at ground level.

(I

234mp•(1.17 mini

234Th
(24.1 di

a

r
2148,

214p 0210p 011.6410·',)l138.4dla

U9.7mcnl

2108,

r

206Pb

210Pb
(22.Jol

214Pb
C26.BminJa15.01 di(uablrl

Figure Ill. Uranlum-23B decay series. Redlonuclldes produced In less than one per centof the transformations of the parent nuclide are not shown [LB]
232Th
1.41 10'°•.----, r228~(6.13 hi

212p0
3.04 10·1 ,

a
212Pb

21281

a 3611.

208Pb(ttablel

110.64h)2118.ri
IJ.05mml

Figure IV. Thorlum-232 decay series [LB]86(l

I00.6minl

I
I

2.

19. Intercomparisons between the above surveys are
difficult as they were conducted using different
methods and types of instrumentation. The results arealso not altogether coherent as regards the quantity
measured. Often in the same survey significant differences were shown when several types of instrumentation were used [N6]. Despite these difficulties.
country-averaged absorbed dose rates in air fall within
the relatively narrow range of 3.7 to 9.4 10-8 Gy h-1,
with a population-weighted average of 4.9 10-s Gy h-1.
The population involved represents about 30% of thatof the world, while the corresponding area covered isabout 10% of the total land surface. The populationweighted value of 4.9 10-S Gy h-1 is in relatively good
agreement with the estimate of 4.5 I 0-S Gy h-1 derived
by the Committee in Annex B of the 1977 report [Ul]for the global average of the absorbed dose rate in air,
1 m above ground, from gamma terrestrial radiation. A
rounde~ value of 5 l o-s Gy h-1 will be adopted in thisAnnex.

Exposure outdoors

17. The concentration of radionuclides in soil, which
is directly relevant to the outdoor exposure, is largely
determined by the activity concentration in the sourcerock. Igneous rocks generally exhibit higher activity
concentrations than sedimentary rocks, while metamorphic rocks have concentrations typical of the rocks
from which they were derived. However, certain
sedimentary rocks, notably some shales and phosphaterocks, arc highly active [N2]. The average activity
concentrations of 40K,
and 232Th in soil and thecorresponding absorbed dose rates in air 1 m above theground surface, calculated on the assumption that all
decay products of 23SU and 232Th are in radioactive
equilibrium with their precursors, are given in Table 1.
The average outdoor terrestrial absorbed dose rate in
air from gamma radiation would be 4.4 lQ-8 Gy h-1, andthe relative contributions of 40K, 238U and 232Th about
35%, 25% and 40%, respectively.

mu

18. Several surveys have been performed over wholecountries and areas for the purpose of estimating theexposure of the relevant populations to outdoor
external gamma radiation. Since the publication of the
1977 report of the Committee [Ul], results have beenreported from Denmark, France, Ireland, Japan,
Norway, Poland and Romania: they are summarized inTable 2.·20.

The variability of the exposure around the meanvalues can be roughly assessed from the detailed results
relative to the administrative subdivisions of France,
the Federal Republic of Germany, Italy, Japan and theUnited States. Figure V presents the populationweighted frequency distribution of the outdoor
absorbed dose rate in air from terrestrial radiation
obtained from the combined data of the five countries.

40

30

20

10

-1n.--i-o L..._,---+---+---+--+--I--J--I---F-F~--.---1-~-~.
6

9

10

11

12

13

14

16

16

17

10·• Gy h.,

ABSORBED DOSE RATE IN AIR

Figure V. Frequency distribution of outdoor ebeorbed dose rate In air from terreetrlal radiation.
Combined data from France [MB], the Federal Republic of Germany [CB], Italy [C2], Japan [A3]and the United States [07)87From Figure V. it is seen that a large fraction of the
population lives in areas where the populationweighted distribution of the outdoor absorbed dose rate
in air is normally distributed, while another fraction,much smaller, lives in areas outside of the normal
distribution. The average absorbed dose rate in air inthe "normal" areas of the live countries is 5.2 1o-s Gyh-1, with a standard deviation of approximately 1 10-S
Gy h-1. Assuming that the distribution holds on a global
basis, 95% of the world population residing in areas of"normal" natural radiation would live where theoutdoor absorbed dose rate in air from the primordialradionuclides falls between about 3 and 7 10-S Gy h-1.
However, it should be borne in mind that these values
are themselves averages, corresponding to populationgroups of at least 105 people.
21. As shown in Figure V, there are regions in theworld where the outdoor terrestrial radiation substantially exceeds the normal range of variation. In addition
to the Italian provinces of Lazio and Campania, suchregions are known to exist in Brazil, France, India,
Iran, Madagascar and Nigeria [83]. The best known
from a dosimetric point of view are those located in
Brazil and India.
22. Deposits of radioactive minerals rich in monazite
occur in littoral formations along the coastal regions ofIndia. Of particular interest is a stretch about 250 kmlong and about 0.5 km wide on the south-west coast in
the states of Kerala and Tamil Nadu. 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% by weight, being the highest known in theworld [G7]. Gopal-Ayengar et al. [G7, GS] carried out adosimetric survey using thermo-luminescent dosimeters
distributed to 8513 individuals of the population of that
55 km strip. Assuming an homogeneous whole-body
irradiation. the average absorbed dose rate for the
70 OOO people residing in the region can be estimatedat 4.3 10-7 Gy h-1; about 24% of the people would
experience average absorbed dose rates in excess of
5.7 10-1 Gy h-1, about 6% would exceed lfr-6 Gy h- 1
and about 0.7% would exceed 2.3 10"6 Gy h-1. As thethermoluminescent dosimeters were worn on a 24-hourbasis, these results represent an average (outdoors plus
indoors) absorbed dose rate from terrestrial radiation.
23. 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 [P2].
24. Along the Atlantic coast, the radiation levels inthree towns (Guarapari, Meaipe and Cumuruxatiba)
built over monazite sands were surveyed in detail byRoser and Cullen [R3]. Guarapari is a community of
12 OOO people which receives an influx of about 30 OOO
vacationers every summer. In that town, the absorbed
dose rates in air were found to range from 1fr-6 to 2 1fr-6
Gy h-1 in the streets and up to 2 10-s Gy h-1 overselected spots on the beach [P3, R3]. Cullen [Cl] bymeans of thermoluminescent dosimeters distributed to
317 inhabitants of Guarapari determined the averageabsorbed dose rate from external terrestrial irradiation(indoors plus outdoors) to be 6.3 J0-7 Gy h-1, with arange of 1 J0-7 to 3.2 JQ-6 Gy h-1.

88

25. Meaipe is a fishing village of about 3000 people.
situated 50 km to the South of Guarapari, where theradiation environment is similar: the outdoor averageabsorbed dose rate in air is about lQ-6 Gy h-1 with levels
up to 10-5 Gy h-1 [P2]. In Cumuruxatiba, the averagelevel is 5 10-7 Gy h-1 [R3].
26. In the state of Minas Gerais, two volcanic regions
have been intensively studied, Po~os de Caldas andAraxa-Tapira. There is a hill near the city of Po~osde Caldas where absorbed dose rates in air of up to
2.8 10-5 Gy h-1 have been reported. However, this hill issmall and uninhabited. In Araxa-Tapira, absorbed dose
rates in air up to 4 1fr-6 Gy h-1 have been measured.
27. Quantitative information on the outdoor absorbed
dose rates in air in other areas of high natural radiationlevels is very limited. It is worth noting that in the cityof Ramsar, Iran, absorbed dose rates in air ranging
from 7 10-7 to 5 J0-5 Gy h-1 have been measured within
an area of a few square kilometres, characterized by thepresence of 226Ra-rich spring water [K3].
3.

Exposure indoors

28. Knowledge of radiation levels in buildings isimportant in the assessment of population exposure, as
most individuals spend a large portion of their timeindoors. Table 3 summarizes the results obtained in the
few large scale surveys of indoor exposure that havebeen reported. As the number of country-wide indoor
surveys is relatively small compared to those conducted
outdoors, the average absorbed dose rate in air indoors
has been estimated from the outdoor value using an
indoors to outdoors ratio.
29. The relationship between the indoor and theoutdoor absorbed dose rates depends essentially on thetype of building material used and on its origin. The
building materials act as sources of radiation and also
as attenuators of outdoor radiation. In wooden andprefabricated houses the source effect is negligible andthe walls are an inefficient shield with respect to the
outdoor sources of radiation, so that the absorbed dose
rate is generally lower indoors than outdoors. The
indoors to outdoors ratios presented in Table 3 range
from 0.7 to 1.0 for wooden and prefabricated houses.
30. In massive houses made of bricks, concrete orstone, the gamma rays emitted outdoors are efficiently
absorbed by the walls and the indoor absorbed dose
rate depends mainly on the activity concentrations of
natural radionuclides in the building materials. If they
are of local origin, as is frequently the case, it may
generally be assumed that the concentrations of naturalradionuclides in the building materials are equal tothose in the soil or the pavement surrounding thedwelling. Under these circumstances. ii may be
expected that the value of the indoors to outdoors ratioof the absorbed dose rates in air lies between I and 2, as
the result of the change in source geometry and of thepresence of doors and windows.
3 l. Calculations taking into account the thickness andthe dimensions of the walls yielded ratios of 1.35 fortypical brick dwellings and 1.48 for concrete buildings[Kl 1], which are in good agreement with the results
obtained in the extensive survey conducted in theFederal Republic of Germany [02] and also with thelarge number of data from Norway [S6, S7] and Austria[T2]. In order lo obtain a representative value of theindoor absorbed dose rate in air, the indoor to outdoor

ratios should be weighted according to the relative
number of dwellings made of wood, brick or concrete.
Jn Annex B of its 1977 report [U1], the Committee
estimated the overall ratio to be about 1.2, which figureis also adopted in this Annex. This figure, combinedwith an average outdoor absorbed dose rate in air of
5 1~ Gy h-1, yields an indoor absorbed dose rate inair, averaged over the world, of 6 10-s Gy h-1. It is
recognized that this figure is lower than the populationweighted average absorbed dose rates in air reported
for a few countries (Table 3). It is felt however thatthese countries being all located in the northern part ofEurope are not representative of the world-widesituation. More information would be required in orderto provide a better estimate.

4.

the most abundant stable isotope of the element. As
discussed in Annex A. the conversion from the activity
concentrations in tissues to the absorbed dose rates isbased on ICRP models [Il].
A.

COSMOGENIC RADIONUCLIDES

35. Very little of the dose from natural background iscontributed by the cosmogenic radionuclides. Of themany nuclides produced by cosmic rays, only 3H, 7Be,
J4C and 22Na contribute appreciably to the dose. The
production and distribution of these nuclides in theenvironment is presented in Table 4, while Tables 5 and6 show the resulting annual tissue doses in man.

Annual effective dose equivalents from gamma
terrestrial radiation

32. The most appropriate average value of thequotient of effective dose equivalent rate to absorbed
dose rate in air appears now to be 0.7 for environmental exposures to gamma rays of moderate energy(see Annex A. paragraph 27). This value applies equally
to males and females, and to the indoor and outdoor
environments. Taking the outdoor occupancy factor tobe 0.2, the annual effective dose equivalent fromoutdoor terrestrial gamma radiation is found to be
5 10- 8 (Gy h- 1) x 0.7 (Sv Gy-1) x 8760 {h a-1) x

x 0.2 = 6.1 10- 5 Sv.
As to indoor exposure, using an occupancy factor of
0.8, the annual effective dose equivalent would be
6 10- 8 (Gy h- 1) x 0.7 (Sv Gy- 1) x 8760 (h a- 1) xx 0.8 = 2.9 10-4 Sv.
33. The total (outdoors plus indoors) annual effective
dose equivalent from terrestrial radiation, averaged
over the world's population, would thus lie between
3 10-5 and 4 104 Sv. For the purpose of this report a
representative value of 3.5 104 Sv has been adopted.
From information contained in Annex B of the 1977
report of UNSCEAR [Ul], 95% of the world population
would thus receive annual effective dose equivalents in
the range from about 2 104 to 5 104 Sv. In addition to
the gamma radiation, the beta rays emitted by thenaturally-occurring radionuclides contained in the soil
and air contribute to a small extent to the effective dose
equivalent from terrestrial radiation. According toO'Brien [05]. the annual effective dose equivalent
resulting from beta radiation would be about 7 lQ-6 Sv.
The radon and thoron decay products present in air
contribute also to the total effective dose equivalentfrom external gamma radiation to a small extent [82,
05].

II.

INTERNAL IRRADIATION

34. Radioactive nuclides occurring in the biosphere
enter the human body through ingestion and inhalation. The absorbed doses from internal exposure inlungs, gonads, red bone marrow, bone lining cells andother tissues will be estimated as well as the effective
dose equivalent. For all radionuclides considered, 7Be
and 22Na excepted, the absorbed doses are derived
from measurements of the concentrations, in bodyorgans or tissues. of the radionuclide concerned or of

1.

Tritium

36. The major source of natural tritium is the atmosphere, where it is formed mainly from the interaction ofcosmic-ray neutrons with nitrogen and oxygen. About
99% of the 3H inventory, which is taken to be 1.3 101s
Bq is converted to tritiated water (HTO) and participates in the normal water cycle. Activity concentrationsof surface waters, measured before nuclear explosions
began, were found to be in the range 200-900 Bq m-3
for continental waters and about 100 Bq m-3 for ocean
waters [K5]. In this report, the average activity concentration of natural tritium in continental surface waters
is taken to be 400 Bq m-3. Tritium enters food crops in
the form of HTO and is partly incorporated into
organic matter. Therefore, tritium in the diet can be in
the form of HTO and of organic compounds. As theenvironment has been contaminated with artificial
tritium since the early 1950s, there is no direct
measurement of the natural tritium concentration inhuman tissues and the doses from natural tritium haveto be estimated on the basis of indirect evidence.
37. In this Annex, as in Annex B of the 1977 report of
UNSCEAR [Ul], the absorbed dose rates due to natural
tritium have been estimated by assuming that the
specific activities of 3H in body tissues are the same as
those in the continental surface waters before nuclear
explosions began; the annual absorbed doses obtainedin that way are of the order of 10-B Gy in all tissues{Table 5).
2.

Beryllium-7

38. Environmental concentrations of 7Be in thetemperate zones are about 3000 µBq m-3 in surface air[K9] and 700 Bq m-3 in rainwater [A2]. The main
pathway to man would be the ingestion of leafy
vegetables, resulting in an annual intake of about 50 Bq[N4]. The tissue absorbed doses calculated using ICRP
dosimetry [I 1] are found to be 12 µGy in the walls of thelower large intestine and somewhat lower in the othertissues (Table 6). The annual effective dose equivalentwould be about 3 µSv.
3.

Carbon-14

39. Natural 14c is produced in the upper atmosphereby the reaction 14N(n,p)l4C induced by slow cosmic-ray
neutrons. The specific activity in biological carbon, as
measured in wood samples of trees grown in theni!:)eteenth century, \Vas 227 ± 1 Bq kg-I of carbon {T1 ],corresponding to an atmospheric inventory of 140 PBq.
89

During the present century the specilic activity of 14C in
air has decreased due to the diluting effect of releases
into the atmosphere of carbon dioxide from the burningof fossil fuels: this is known as the Suess effect [S3].
40. In its 1977 report [Ul]. UNSCEAR estimated theworld's inventory of natural 14C to be about 60 times
the amount found in the atmosphere, leading to a valueof approximately 8500 PI3q, corresponding to a
production rate of 1 PBq a-1.
41. Taking the natural specific activity of 14C in the
body to be 227 Bq kg-I of carbon, and using the concentrations of carbon in body tissues indicated by JCRP
for the Reference Man [12], the annual absorbed doses
in tissue are found to be in the range from 5 to 24 µGy(Table 5). The annual effective dose equivalent would
be 12 µSv. This value is in agreement with the ligure
derived from ICRP (11]. assuming an annual intake of
93 kg of carbon [12].

age of 20 and more gradually later on [A4, 12]. Actually
the variation with age and sex of the concentration ofpotassium in the total body renects the amount ofrelatively potassium-free adipose tissue which is present
with the "lean body mass'' in the total body at different
ages (12). Similar results were found by Oberhausen[08] in the Federal Republic of Germany in a study
involving 12 OOO subjects. The relationship between themass of potassium in the total body and the age wasfound to be linear for boys and girls under 12 [S10].
With respect to adults, Andrasi and Beleznay [A 1], frommeasurements on about 600 subjects derived thefollowing linear relationships between the quotient of
the mass of potassium in the body C. in g kg-1. for thewhole body and the age A, in years:
C = 2.34 - 0.0110 A for males andC = 1.99 - 0.0 I09 A for females.

2.
4.

42. The annual absorbed doses from 22Na have been
calculated on the basis of an annual intake by ingestionof 50 Bq [N4] and using ICRP dosimetry [11). The
annual absorbed doses in tissues are in the range of 0.1
to 0.3 µGy (Table 6), corresponding to an annual
effective dose equivalent of about 0.2 µSv. Even though
the production rate and the atmospheric concentrationof 22Na are very small (Table 4), the estimated annual
absorbed doses arising from the incorporation of thatradionuclide (Table 6) are higher than those due to 3H(Table 5) because of the metabolic behaviour of sodium
and of the decay properties of 22Na.
B.

PRIMORDIAL RADIONUCLIDES

43. The primordial radionuclides include thosebelonging to the mu. mu and 232Th series and someother nuclides, among which only 40K and 87Rb are
signilicant sources of radiation.

1.

Potassium-40

44. Potassium is an essential element, and is underclose homeostatic control in the body. The average
mass concentration for an adult male is about 2 g ofpotassium per kg of body weight [Al, K10]. The
isotopic ratio of 40K is 1.18 1Q-4 and the average activity
concentration of 40K in the body is about 60 Bq kg-1.
The distribution of potassium in various tissues andorgans of the body [K 10] and the corresponding
absorbed dose rates are presented in Table 7. The
highest annual absorbed dose (270 µGy) is received in
the red bone marrow. The annual effective dose equivalent is estimated to be 180 µSv.
45. The variation of the mass of potassium in the total
body with age and sex has been investigated by several
groups. In the United States during the period
1956-1961, total body potassium was determined inabout 3000 subjects who ranged from less than one year
to 79 years of age [A4, 12]. The results of this study showthat the concentrations of potassium in the total bodyincrease from birth to about 10 years for girls and 18
years for boys, when they reach estimated averagevalues of about 2.1 and 2.3 g kg-I, respectively; theconcentrations then decrease rather sharply until the90

Rubidium-87

Sodium-22

46. Very little is known about the behaviour ofrubidium in man's environment. From the massconcentrations of rubidium in the ICRP Reference
Man [12], the average ~ n t r a t i o n of 87Rb in
the body would be <!J Bq kg~able 7 presents theassumed distribution 01rubidium in the body and theresulting absorbed dose rates from 87Rb. Bone lining
cells receive the highest annual dose (14 µGy). The
annual effective dose equivalent is estimated to beabout 6 µSv.
3.

Uranium-238 series

47. Uranium-238 is the head of a series of 15 principal
nuclides (Figure Ill). In its 1972 and 1977 reports [U1,U2]. the Committee has classilied the mu series insubseries in which the activity of the precursor controls
to a large degree the activities of the decay products.
The 238U series has been divided into: (1) mu - 234U;(2) 230Th; (3) 226Ra; (4) 222Rn - 214Po, which is
discussed in detail in Annex D; (5) 210Pb - 210Po. For
each subseries, the intakes by inhalation and byingestion as well as the concentrations in bone and insoft tissues will be estimated. The conversion from theactivity concentrations in bone and in soft tissues to theabsorbed doses is based on the models described in
ICRP Publication 30 (11].

(a)

Uranium-238 subseries (238U, 234Th, 234mPa, 234U)

48.

In this Annex, uranium is assumed to consist of

mu in radioactive equilibrium with 234Th, 234Pa and234U. so that 1 kg of uranium contains 12 MBq of eachof the four radionuclides. The contribution of 23SU and
its decay products to the total dose from natural
background has been neglected.
49. 1n the atmosphere, the main natural source ofuranium has been assumed to be the resuspension ofdust particles from the earth. Assuming a dust loadingof about 50 µg m-3 in surface air of populated areas,
and taking an average 238U activity concentration insoil of 25 Bq kg-1 (Table I), the activity concentration in
ground level air is estimated to be about 1.2 µBq m-3.
Measurements of the activity concentration in groundlevel air, as for example in Munich (Federal Republicof Germany) conlirm the validity of the assumption

[J4]. The corresponding annual intake by adults throughinhalation is approximately 0.01 Bq (Table 8).
50. The annual dietary intake of 238U has been foundto be about 5 llq in areas of "normal" natural activity[Ul] and the contribution of drinking water is generally
negligible in comparison. However, it should be
mentioned that very high concentrations of uranium in
tap water have been reported. In France [R4. RSJ and in
the USSR [86], activity concentrations as high as 1.0
and 2.6 kBq m-3, respectively, have been observed. Jn
Helsinki, Finland. activity concentrations of the orderof 100 kBq m-3 have been measured in several wells, thehighest concentration being about 200 kBq m-3 [K 7].
According to the authors [K 7], the very high concentrations of uranium in the water of those wells areprobably caused by small, localized uranium-rich
deposits.
51. Measured values of the activity concentrations of
23SU in bone of adults who have lived in areas with"normal" dietary levels are in the range of 100 to 200
mBq kg-1, yielding an activity in bone of about 0.7 Bq[J4. Ul]. In soft tissues, the activity concentrations of
238U cover a much broader range. The measured values
lie between I and 10 mBq kg-I for most of the soft
tissues and between 10 and 80 mBq kg-I for kidneys[J4]. Assuming that the distribution of the activity in the
body is 70% in bone and 30% in soft tissue [J4], and thatthe levels in kidney are 10 times higher than those inother soft tissues. the average activity concentrations
are found to be about 150 mBq kg-1 in bone, 50 mBq
kg-I in kidneys and 5 mBq kg-1 in the other soft tissues.
The resulting annual absorbed doses vary from 2 10-s
Gy in lung to 3 1()-6 Gy in bone lining cells (Table 9).

(b)

Thorium-230

52. The activity intake of 230Th through inhalation,
estimated in the same way as for 238U, is about 0.01 Bq
a-1. There is no information on the dietary intake of
230To. However. the activity ingested is probably anegligible contribution to the body content of 230Th
because of the very low absorption of thorium throughthe gastro-intestinal tract.
53. Thorium is a bone seeker which has a longresidence time in the skeleton and is assumed to remainon the bone surfaces [11]. The distribution of 2JOTh in
human tissues has been investigated by Wrenn and his
collaborators [S9, Wl, W4]. In samples of two
population groups living in Colorado and in
Washington, D.C., the highest concentrations were in
general measured in the lymph nodes, followed bybone. lung. kidneys, liver and spleen. The mass of bone
being much greater than that of the lymph nodes, mostof the thorium body content was found in the skeleton(about 70%). As thorium has a long residence time inthe skeleton. the concentration of 230Th in boneincreases continuously with age for a constant rate ofintake. On the basis of the available measurements [S9,Wl, W4], it seems that a typical activity of230Th in bone
is 140 mBq. resulting in activity concentrations ofapproximately 20 mBq kg-1 in cortical bone and 70
mBq kg-I in trabecular bone. This is on the assumptionthat the deposit of thorium is proportional to the bone
area. In soft tissues, representative values of the activity
concentrations could be 300 mBq kg-I in lymph nodes.
20 mBq kg-1 in lungs. 10 mBq kg-1 in kidneys, 7 mBq
kg-I in liver and 0.3 mBq kg-I in the other soft tissues.

The corresponding annual absorbed doses arepresented in Table 10. The annual effective dose equivalent is estimated to be about 7µSv.
(c)Radium-226

54. For inhalation, as in the case of uranium andthorium, the main natural source of radium in the air at
ground level is assumed to be the resuspension of soil
particles: this corresponds to a calculated activity
intake of about 0.01 Bq a-1.

55.

Food is a much more important source of radium
for intake and blood uptake than is inhalation. The
average annual dietary intake of 226Ra in areas ofnormal radiation background is about 15 Bq (seeAnnex B in the UNSCEAR 1977 report [Ul]). The
contribution of drinking water is generally small when
the drinking water supplies are drawn from surface
waters. However, activity concentrations of 0.1 Bq 1-1
are not exceptional in well and mineral waters [K 12.
K13, M7. P7. R4, R5]. In France. for example, anactivity concentration of 2.7 Bq 1-1 has been measured
in a spring used as drinking water [R4, R5]. The
population groups drinking exclusively those waters are
expected to derive most of their 226Ra intake from thewater.
56. Two well-known populated areas with highconcentrations of uranium in their soil are locatedalong the coast of Kerala in India and in the AraxaTapira region in Brazil. The estimated average annual
intake of 226Ra of the Indian population along theKerala coast is 40 Bq [C3, Ml]. In Brazil, a survey in the
Araxa-Tapira region showed that, out of a populationof 1670 people living in and around the radioactive
anomalies of Barreiro and Tapira, only 196 individuals
ingested alpha emitters at a level 5 times or more thanthat of a similar group living in Rio de Janeiro. The
annual 226Ra intake of those individuals ranged from
140 to 540 Bq [P4].
57. When radium is taken into the body, its metabolic
behaviour is similar to that of calcium. and an appreciable fraction is deposited in bone [E2]. About 70-90%
of the radium in the body is contained in bone [13]. theremaining fraction being distributed approximately
uniformly in soft tissues. Fisenne et al. [Fl] havesummarized the available data from 26 countries on
measured activity concentrations of 226Ra in humanbone. The 26 countries sampled have 1.4 109 persons
and thus represent about 30% of the world population.
The population-weighted distribution was found tohave a median of 850 mBq per kg of calcium (corresponding to 170 m Bq per kg of bone and to 850 mBq in
the skeleton) and a geometric standard deviation of 1.6.
If the fraction of 226Ra distributed in the soft tissues istaken to be 17%, as given in ICRP publication 20 [I3],the average activity concentration in human soft tissues
is found to be 2.7 mBq kg-I.
58. The annual absorbed doses in tissues have been
calculated using the same assumptions as in Annex B of
the 1977 report, namely, that an average retention
factor of 0.33 applies to 22:Rn in the skeleton and also,
conservatively, in soft tissues; and that the concentration of radium and its decay products is uniform
over the tot.ii mass of mineral bone. The results arepresented in Table 11. The annual effective dose equivalent resulting from 226Ra intake in "normal" areas isfound to be about 7 µSv.
9159. Data on the activity of radium in the skeleton ofpeople living in the high radiation areas of Brazil andIndia arc very scarce. In Brazil, the mean 226Ra concentration in the teeth of the population living in the
Araxa-Tapira region has been estimated as approximately 3 Bq kg- 1 of ash, which corresponds to an
acti\'ity in the skeleton of about 8 Uq, assuming that theconcentration in teeth is the same as that in bone. In
India, the analysis of a femur yielded a 226Ra concentration per unit mass of ash of 5 Bq kg-1, which corresponds to a skeletal activity of about 15 Bq [C3].

(d)Radon-222, and its short-lived decay products(218Po, 214Pb, 214Bi, and 214Po)

60. Man is exposed to 212Rn (radon) and to its shortlived decay products mainly by inhalation. Mean
annual values of radon concentration in outdoor air
vary between 0.1 and 10 Bq m-3. Over land, areasonable estimate of the average concentration at
ground level is 3 Bq m-3; taking the equilibrium factor
to be 0.6. the average equilibrium equivalent concentration of radon in outdoor air at ground level isestimated to be 1.8 Bq m-3.
61. In temperate latitudes, the average equilibrium
equivalent concentration of radon in air is several times
higher indoors than outdoors. The mean values of theindoor equilibrium equivalent radon concentrations indifferent countries cover the range from 5 to 25 Bq m-3,
with the exception of Sweden, where the average valueis 60 Bq m-3. For the total population in the temperateregions of the world, 15 Bq m-3 seems to be an appropriate mean indoor equilibrium equivalent concentration.
62. Using the dose conversion coefficients derived in
Annex D. the annual effective dose equivalents corresponding to the average equilibrium equivalent concentrations of radon outdoors and indoors in temperate
latitudes are estimated to be 0.92 mSv from indoor
exposure and about 0.06 mSv from outdoor exposure,giving a total of about 1 mSv for inhaled 222Rn
daughters.
63. For equatorial regions no measurements areavailable. Because of the different domestic conditions,the indoor level of radon daughters in this region might
be considerably lower than in temperate regions. For
large population groups this level will be comparablewith the normal outdoor level, leading to an annual
effective dose equivalent of about 0.2 mSv. Taking into
account that about two thirds of the total world
population is living in temperate regions, a global meanvalue of about 0.8 mSv per year-averaged over all age
groups-from inhaled 221Rn daughters should be
expected.
64. Table 12 summarizes the estimated equilibrium
equivalent concentrations of 222Rn and the corresponding annual effective dose equivalents. A detailed
treatment of the exposures to 222Rn and its daughters isprovided in Annex D.

(e)Long-lived decay products of 222Rn(210Pb, 2JOBi, and 2JOPo)

65. For inhalation, the main source of 21opb and 21opo
in the atmosphere is 222Rn emanation from the ground.
In the mid-latitudes of the northern hemisphere, the92average concentration of 21opb in surface air has been
estimated to be 0.5 mBq m-3 (J2]. The 21opo/210Pb
activity ratio in ground level air being about 0.2 [J3], theactivity concentration of 2JOPo is about 0.1 mBq m-3.
Assuming that the atmospheric concentrations are thesame indoors and outdoors, the annual intakes of nonsmokers would thus be 4 Bq of 210Pb and O.~ Bq of
210Po. Cigarette smoking will lead to an increase in theintake of 210Pb and 2JOPo through inhalation [PS].
66. Consumption of food is usually the mostimportant route by which 210Pb and 2l0Po enter thehuman organism. For the areas of normal intake, avalue of 40 Bq was taken in Annex B of the 1977 report[Ul] as representative of the annual intake of 21opb and210ro. Recent estimates for the populations of India
and of Italy are in good agreement with that figure [C7,
L7]. It should be noted however that lower values are
consistently obtained for the populations of the UnitedStates [H9, H 1OJ. High concentrations of 21opo are
observed in the edible portions of aquatic organisms,
for which it is well established that the 210Po/210pb
activity concentration ratio is greater than 1 [C4]. The
21opo concentrations in the muscles of fish and inmolluscs are approximately 0.7 and 20 Bq kg-I. The
intakes of 21opb and 21opo in populations consuming
large proportions of seafood are therefore expected tobe higher than those of populations with other types of.
diet.
67. A well-documented case of elevated intake is thatof the tens of thousands of individuals living on
reindeer or caribou meat in the arctic and sub-arctic
regions of the northern hemisphere [HlO, P8]. Theirmain food is the meat of these animals, which contains
unusually high concentrations of 2JOPo because in thewinter they graze on lichens which accumulate 210Pb
and 2IOPo. The annual intakes of 21opb and 210ro by the
populations living on reindeer or caribou meat areabout 140 Bq for 210Pb and about 1400 Bq for 210Po.
Another documented case of elevated intake relates toan uranium-rich area of Western Australia, where theannual intake of 21opb from the carcasses of local sheep
and kangaroos is about 100 Bq and from the offal
about 300 to 3000 Bq [W5].
68. In view of the short half-life of 210Bi (5 d), theactivity intakes of that radionuclide can be assumed tobe the same as those of 210Pb. Precise values are of nointerest for the purpose of this Annex as 210Bi can beassumed to be in radioactive equilibrium with 21opb inthe body tissues so that the absorbed doses from 210Bi
mainly arise from the intake of 210pb and not from theintake of 210Bi itself.
69. Concerning distribution in man, lead is a boneseeker which is found incorporated in bone mineral,from where it seems to be eliminated by long-termskeletal remodelling [H6. L6]. About 70% of the bodycontent of 21opb is found in the skeleton [J2). In continental areas of the northern latitudes, a typical activity
concentration of 21opb in bone would be 3 Bq kg-I [Ul].
The skeletal activity would thus be 15 Bq and theactivity in soft tissues would be 6.4 Bq distributed
relatively uniformly throughout the body (Table 13).
70. Polonium, in contrast to all the other naturalalpha emitters, is not a bone seeker but is rather distributed in soft tissues after intake. Therefore, the greatest
part of the 2JOPo bone activity arises from the decay ofdeposited 2JOPb [H7, W2]. Average measured ratios of210po and 21opb activity concentrations in bone range

from 0.5 to 1.1 (87, H4, KS, LS, M2]. A value of 0.8 isassumed to be representative for the purposes of thisAnnex. The 2JOPo concentration in bone would thus beabout 2.4 Bq kg-I for the populations living in continental areas in temperate regions of the northern hemisphere.
71. In soft tissues, the activity of 21opo is about thesame as that of :IOPb. Typical concentrations of 21opb
and 210ro in the gonads are about 0.2 Bq kg-1 [87, LS,88). In lungs the concentrations in non-smokers arearound 0.1 Bq kg-I for 210Po and 0.2 Bq kg-I for 210pb[B7, H5]. In red bone marrow, Ladinskaya et al. [L5]measured a 21opb concentration of 0.14 Bq kg-I and a210po;21opb activity ratio of 0.8. Although in most of
the soft tissues the 210po;21opb activity concentration
ratio is about 1, it is dearly greater than 1 in a few
organs such as the liver and kidney. The excess 210Po is
probably taken up directly from food and would be
partly attributable to a higher rate of incorporation for
21opo than for 21opb in those organs (J2]. The additional
intake due to smoking leads to increased concentrations of 210Pb and 21opo in organs and tissues. As
expected, it is in the lung that the increases are mostclearly marked. The concentrations in that organ
exceed on the average the levels found in non-smokers
by factors of about 1.5 for 21opb and 3 for 210Po (87, H7,
HlO, PS, R2]. The figures given in Table 13 correspondto non-smokers.
I

72. With respect to the arctic and sub-arctic populations, measurements carried out on the blood, placentaand bone tissues of inhabitants of the northern regions
who consume reindeer or caribou meat regularly showlevels higher than those in the populations of thetemperate latitudes. The increase is by a factor of 2 to 3
for 210Pb in all tissues and for 21opo in bone tissues andby a factor of about 10 for 21opo in soft tissues [H10,K8, P8].
73. The absorbed doses from the 21opb subseries
depend mainly on the highly energetic alpha particlesof 21oro. as the contribution from the beta emissions of
210Pb and 210Bi amounts to about 10% of the total.
Table 13 presents the estimated annual absorbed doses
from 210Pb. 210Bi and 210Po for non-smokers in areas ofnormal dietary intake. The annual effective dose equivalent arising from the total intake of 21orb, 21osi and
210Po would be about 130 ~tSv. The corresponding
figure for the populations living on reindeer or caribou
meat would be about 10 times higher.
4.

Thorium-232 series

74. Thorium-232 is the head of a series of 12 nuclides(Figure IV). The 232Th and the 238U series present
strong similarities: they include isotopes of the sameelements (radium. radon, lead, bismuth, polonium) andcontain a large proportion of a-emitters. The maindifference between the two series is that 232Th is the
only very long-lived radionuclide in its chain.
75. The 232Th series has been divided into threesubseries: (a} 232Th itself; (b) 228Ra - 224Ra; (c} 220Rn- ::oBPb. which is discussed in detail in Annex D. The
three subseries will be considered in turn.

(a)

Thorium-232

76. The activity concentration of 232Th in soil isestimated to be on average the same as that of 23NU and

its decay product BOTh (25 Bq kg-1, see Table I). Since
the main natural source of 232Th in air at ground level isassumed to be the resuspension of soil particles, theannual activity intake of 232Th through inhalation,
estimated in the same way as for 238U and 230Th, is also
about 0.01 Bq. As in the case of 230Th. the contributionof the ingestion pathway to the body content of 232Th
can be probably neglected because of the very low
absorption of thorium through the gastro-intestinal
tract.
77. The distribution of 232Th in human tissues was
mainly investigated by Wrenn and his collaborators[S9, W1. W4] in their studies on the comparison of
uranium. thorium and plutonium in man. In
comparison with 230Th, the activity concentrations of
232Th were found to be lower by a factor of about 10.
On the basis of those measurements, the body content
of 232Th would be about 80 mBq, 60% of which is in theskeleton. The activity concentrations adopted in thisAnnex are presented in Table 14, along with theresulting annual absorbed doses. The annual effective
dose equivalent is calculated to be about 3 µSv.

{b)

Radium-228 subseries (228Ra, 228Ac, 228Tb, 224Ra)

78. Radium is much more available to plants and toanimals than 232Th so that the activity concentrations of228Ra in man are mostly due to the dietary intake of
228Ra itself and not to the decay of 232Th in the body.
Radium-228 can thus be considered to be the head of asubseries in which 228Th (1.9 a) and 224Ra (3.6 d), as
alpha emitters, are the most important contributors to
the dose.
79. The annual activity intake arising from inhalationof resuspended soil particles is estimated to be about
0.01 Bq, as for all precursors of radon isotopes (Table
8). However, food consumption is a much more
important source of 228Ra intake than inhalation. In
areas of normal radiation background the annual
intake is about 15 Bq (Table 8).
80. In the high-background area along the Kerala
coast in India, the estimated average annual intake of
228Ra is about 2000 Bq [Ml) whereas a survey
conducted in the Araxa-Tapira region of Brazil showedthat about 200 individuals ingested 228Ra at a rate of
between 700 and 3000 Bq a-I [U1].
81. Radium and thorium are bone seekers. In
Annex B of its 1977 report [Ul], the Committee
estimated the average 228Ra activity concentrations inbone and in soft tissues to be 90 mBq kg-I and 4 mBq
kg-1, respectively, in areas of normal backgroundradiation. With respect to 228Tb, Wrenn and Singh (S9,W4] showed that approximately 80% of the bodycontent (about 300 mBq) is in bone. The values of theactivity concentrations adopted in this Annex are
shown in Table 15; they are mainly based on themeasurements of Wrenn and Singh [S9, W4).
82. The annual absorbed doses in tissues have been
calculated using the same assumptions as in Annex U of
the 1977 report [Ul). namely. that complete retention in
the body of the 220Rn activity arises from decay of:24 Ra; and that the concentrations of 228Ra and its
decay products over the total mass of bone is uniform.
The results are presented in Table 15. The corre-93

sponding annual effective dose equivalent for thesuhseries is found to be about 13 ~1Sv.

(c)Radon-220 and its decay products (2l<1 Po, 212Pb,
212fli, mp 0 , 2osTI)

83. As is the case with 222Rn, inhalation is the major
pathway through which man is exposed to 220Rn(thoron) and to its short-lived decay products. A
detailed treatment of the sources of exposure to 220Rn isprovided in Annex D. In outdoor air, the equilibrium
equivalent concentration of 220Rn is about 0.2 I3q m-3.
With respect to indoor air, very few measurements of
220Rn daughters have been reported, if compared withthe available information on 222Rn daughters. However,the simultaneous measurements of 222Rn and 220Rn
daughters in houses in the Federal Republic of
Germany and in the United Kingdom indicate a ratio
of about 20 between equilibrium equivalent 222Rn
concentration and the equilibrium equivalent 220Rn
concentration. Applying this factor it can be concluded
that the mean value of the indoor equilibrium equivalent 220Rn concentration in different countries should
be in the range 0.2-1.2 Bq m-3. For the total populationin temperate regions of the world a mean value ofabout 0.7 Bq m-3 should be expected. Taking into
account the dose conversion coefficients for 220Rn
daughters given in Annex D, the annual effective dose
equivalents corresponding to the average equilibrium
equivalent concentrations of radon indoors andoutdoors in temperate latitudes are estimated to be
0.20 mSv from indoor exposure and about 0.02 mSv
from outdoor exposure, giving a total of 0.22 mSv forinhaled 220Rn daughters.
84. For equatorial regions no measurements areavailable. Because of the different domestic conditions.
the indoor levels of 220Rn daughters might be considerably lower than in temperate regions. For large
population groups this level will be comparable with
the normal outdoor equilibrium equivalent concentration. leading to an annual effective dose equivalent
in equatorial regions of 0.08 mSv from inhalation of
220Rn daughters. Taking into account that about two
thirds of the total world population is living intemperate regions, a global mean value of the annual
effective dose equivalent of about 0.17 mSv frominhalation of 220Rn daughters should be expected.
Table 16 summarizes the estimated average equilibrium
equivalent concentrations of 220Rn and the corresponding annual effective dose equivalents.

94

Ill.

RECAPITULATION

85. Table 17 summarizes the contributions of natural
sources to the radiation exposure of human populations
living in areas of normal radiation background. The
exposures refer to adult persons and arc expressed interms of effective dose equivalent in order to facilitate
the comparison of the various sources of radiation. The
effective dose equivalent from all internal sources is
estimated to be about twice that from external irradiation. Among the various contributors to the internal
irradiation, the short-lived decay products of 222Rn are
by far the most important as they are responsible forabout 60% of the effective dose equivalent from internal
emitters. Then follow, by decreasing order of importance, 4 0K (13%), the short-lived decay products of
220Rn ( 13%). and 2t0pb.2rnro (8%). With regard to
external irradiation. the effective dose equivalent fromcosmic rays is slightly lower than that from terrestrial
radiation.
86. Significantly higher doses from external radiation
are received by population groups living at highaltitudes or in regions of high natural radioactivity. A
number of population groups are exposed to elevatedinternal absorbed doses, such as the people living inhouses with a low rate of ventilation or the caribou andreindeer eaters. The importance of the contribution ofareas of high natural radiation to the global effective
collective dose equivalent cannot yet be assessed. As afirst approximation the global annual collective
effective dose equivalent from natural radiation sources
is estimated to be of the order of 107 man Sv.
87. From Table 17 a median annual effective dose
equivalent of about 2 mSv from natural sources in areasof normal background results. This average value refers
to the adult part of the population. For children thevalues of the annual effective dose equivalent, particularly for inhaled radon daughters. are higher than for
adults. Estimates yield a mean annual effective dose
equivalent from natural sources of about 3 mSv forchildren in the O to 10-year age group.
88. The available data. particularly on the relevant
contributions from radon daughters and terrestrial
gamma radiation, indicate that on a global scale the
distribution function of the natural radiation exposure
can be approximated in its central part by a normal or
log-normal distribution. With this assumption astandard deviation of about 0.3 to 0.6 mSv can be
estimated.

T a tJ l e

Average activity concentration of potassium-40, uranium-230 and thoriurn-238
in soil and absorbed dose rate in air Im above the ground surface
Radionuclideor
decay series

40K
238u
232Th

Dose rate perunit act iv i ty
concentration
in soil(10-lO Gy t1i 1
per Bq kg )
0.43
4.27
6.62

Averageconcentration
in soil a/

Absorhed dose
rate in air a/(Bq kg-l)(10- 8 Gy h-l)

370 ( 100- 700)
25 ( 10- 50)
25 ( 7- 50)

1.6 (0.4-3.0)
1.1 (0.4-2.1)
1. 7 (0.5-3.3)

a/ The typical range is given within brackets.

T a b l e2

Estimates of the average absorbed dose rate in air 1 m above ground level(based on country- and area-wide surveys)
Averageabsorbed
dose rate
in airand range a/(10- 8 Gyh-T)

Number ofmeasurements

Period ofsurveyAustria

4.3 (0.2-15)> 10001970-1974

Denmark

3.8 (I. 7-5.2)

France8.1 (0.9-29}

Gennan Dern.Rep.

9.4 (2.4-27)

Country or area/

Gennany, Fed.Rep.5.3 (0.4-35)
ofIndia
4.2 (norma 1
areas)
Ireland4.2 (0-18)
Italy

5.7 (0.7-50)

Japan

4.9 {0.5-10)

Norway7.3 (2-110)

Poland3.7 (1.5-9)

Romania

8.1 (3.2-21)

Switzerland

8.7

United States

4.6 (l .3-10)

Other Asia

6.9

Type of survey
and instrumentation used

Ref.

Ground survey in populated areas [T2]with a Gei ger-11Uller counter1978
14 sites
Ground survey with an ionization '.N5)
chamber and a gamma spectrometer
865
1978
Ground survey with thermolumi{M3,nescent dosimeters (preliminaryMS]
results)
1965-1966 Ground survey with an ionization IOI]
1005
chamber24739
1973-1974 Ground survey with scintillation :cs,
detectors
02]
1965-1972 Analysis of soil samples by
35 sites[M4]
garmta spectrometry
264
1978
Ground survey with an ionization [MS]chamber1365
not indicated Ground survey with an ionization :A3)
chamber1127
196 7-1977 Ground survey with an ionization [A3)chamber and scintillation detectors
234
1976
Ground survey with an ionization [S6]chamber placed in a car
352 sites
1975-1978 Ground survey with thermol1.1111i[N6]nescent dosimeters2372
not indicated Analysis of soil samples by[TJJ
gamma spectrometry
not indicated1962
Ground survey with an ionization [HI]chamber
25 areas
1958-1963 Aerial survey with scintillation ro7J
covered b/
detectors
26 1969
Analysis of soil samples by[W3]
garmta spectrometrya/ The range is given within brackets.
&1 Inhabited by approximately 30 % of the country's population.

95

T a b l e

3

Results of surveys of indoor absorbed dose rate in air due to gamma terrestrial radiation

Indooraverageabsorbed
dose rate
in airCountry

Period of Number ofsurveydwellings

Type of building

Austria

1975-1978

Brick
10.8
Concrete
8.1
Wood
7.5
Natural stone
10.9
Various types
8.8
Various types
9.9
Various types
Solid
7.0
Frame
7.1
Prefabricated
4.0
Wood
4.5
Brick
11.9
Concrete
10.5
Wood
7.1
Red BrickConcrete
Building material containing
blast furnace slag
Brick
9.2
Concrete
11.6
Aerated concrete
17.2
Wood
5.3
Sol id: sedimentary rock
7.6
- Dundee
6.8- Edinburgh
granite
9.7- Aberdeen- Aberdeenshire
9.4
Wood3,9 2_/
Wood

France ( 1)(2)German Dern.Rep.
Germany, Fed.Rep.
of

1978
1977-1979
1965-1966
1973-1974

Norway1963+ 1976

1900

946
1020
667
29996

2026

Poland1978

49

Sweden1977

1189

United Kingdom

United States ( 1)
(2)
2_/

1959

1971
1962

501

110
160

ropulationPopulationIndoors to weighted
weighted
averageoutdoors indoors toabsorbed
ratio
outdoors
ratiodose rate
in air

7. 1

Ref.

1.65

(12]

0.78

(M3]
[89]
[01]

1.36

[D2]

1.12

[S6,
S7]

1.09
1.11
7.4
1.37
1.34
0.94
1.02
1.60
1.42
0.95
1.2
1.1

7.0

9,5

[N6]

1.8
9.6

[M6]
(58]

1.07
1.24
0.82
1.17
0.75
0.70

[L2]
(L3]

Median value.
4
3 7Be, 14c. and 22Na
Data on naturally-occurring H,
Ta b l e('-

Radionuclide
Ref.

Item
3H
Ha lf-1 ife
12.3 aNumbers of atoms produced perunit time and per unit 2~e2 1ofthe earth's surface (m s )Troposphere
840
Total atmosphere
2500
Global inventory (PBq)
1300
Distribution as a percentage
of inventory
Stratosphere
6.8
Troposphere
0.4
Land surface and biosphere
27
Mixed oceanic layers
35
Deep ocean
30
Oceanic sediments
Activity concentra~!on insurface air (uBq m )Activity concentration inconti~~ntal surface waters(Bq m )
200-900
Specific activitt 1in terrestrial
biosphere (Bq kg )

96

7Be

14c

22Na

53.6 d5730 a2.62 a

[LBJ

270
810
37

11000
16000-25000
8500

0.24
0.86
0.4

[L4]
fl4,Ul][L4,Ul)

60

0.3
1.6

25

8

4

20
0.2

2.2
92
0.4

21
44
8

[L4)
rL4]
[L4 J
[L4]
[L4]
fL4]

0.3

[K9]

11

3000

1. 7

rB5,K5)230'S3]---=--

Table5

Estimated tissue concentrations and annual absorbed doses
from 3H and 14 c
CarbonHy d r o g e nO,·gan or tissue

GonadsLungs
Red bone marrow
Bone lining cells
Thyroid
Other tissues

Massconcentrationof element(g kg-I)

Activity
concent 3ationof H(llq kg-I)

f,nnua 1
absorbed
dose (µGy)

100
99
100

0.4
0.4
0.4

100
105

0.4
0.4

0.01
0.01
0.01
0.01
0.01
0.01

11ass
Activity
concentration concen ~ationof elementof 1 C(g kg-I)(llq kg-I)

e

100
410

20
23
93

105
230

24
52

89

T a b l e

Annualabsorbed
dose (µGy)

e
5.0
5.7
24
22
5.9
13

6

Absorbed doses in tissues
from internal irradiation by Be and 22 t:aAnnual absorbed dose (µGy)
Organ or tissue

GonadsBreastLungs
Red bone marrow
Bone lining cells
Thyroid
Stomach wa 11
SI wa 11
Ull wa 11
LLI wal 1
Remainder

7Be

22ua

y

e,+,y

5.7

0.14
0.13
0.12
0.22
0.27
0.12
0.14
0.15

1.2

5.4
7.3
12

Table

0.15
0.10

7

Average tissue concentrations in adult males and annual absorbed doses
from 4°K and 87 Rb
Po t a s s i um
Tissue or organ

Gonads (Testes)
Lungs
Red bone marrow
Bone lining cells
Thyroid
Other tissues

11ass
concentrationof e 1ement(g kg-I)

Activity
concen 5ationof K(Bq kg-l)

4

2.1
2.1
4.4

64
64
130

I. I

33
61

2.0

Rubidium
Annualabsorbed
dose (µGy)

e- ,Y
180
180
270
140
100
170

Mass
concentrationof element(mg kg-l)

Activity
concen 8~a ti onof Rb(Bq kg-l)

Annualabsorbed
dose (µGy)

20
9.2
7.8

18
8.1
7.0

6.0
7 .8

5.3
7.0

10.0
4.5
7.0
14.0
3.0
4.0

e

97

Ta b l e

8

Intakes in normal areas of 238u, 232Th
ana tlie1r oecax eroauds
Annua 1 intake (Bq}

SourceInhalation

Ingestion

0.01
0.01
0.01
0.01
0.01
0.01

5

238u series
23Bu
234Th
234
23la
u
230Th
226
210Ra
21lb
Po
232 Th series
232Th
22~
228 a
22~~

5
5
5

0.8

15
40
40

0.01
0.01
0.01
0.01

15
15
15

4

Ta b l e

9

Avera e activit

concentrations in tissues and annual absorbed doses
resu ting rom rnterna irra iation
by radionuclides from the uranium-238 subseries

Organ or tissue

GonadsBreastLungs
Cortical bone
Trabecular bone
Red bone r:iarrow
Bone lining cells
Thyroid
Kidneys
Other tissues

Activity
concentrationof 238 u a/(mBq kg-T)
5
5
5
150
150
5

.A.nnual absorbed doses (10

Gy)

238[)

234Th

234mPa

234u

0.

13,Y

13,Y

a

1.1

0.02
0.02
0.02

0.2
0.2
0.2

1.2
1.2
1.2

0.11
0.34
0.02
0.15
0.02

1.4
4,3
0.2
2.1
0.2

2.4
20
1. 2
12
1.2

I. I

1.1
2.1
17

5
50

11

5

1.1

1.1

2 34m
a/ 238and 234 U are assumed to be in radioactive equilibrium with23 ~h,in all Pa,
organs and tissues.

Tab 1 e10

Average activitX concentrations in tissues and annual absorbed doses
resulting from internal irradiation by thorium-230

Organ or tissue

Activity
concentration(mBq kg-l)

Annua 1 absorbed
doses(lD- 7 Gy)aGonadsBreastLungs
Cortical bone
Trabecu la r bone
Red bone marrow
Bone lining cells
Thyroid
Kidneys
Other tissues

98

0.3
0.3
20
20
70
0. 3
0.3
10
0.3

0.07
0.07
4.7
5.6
74
0.07
2.4
0.07

T a b 1e

11

Average activitx concentrations in tissues and annual absorbed doses
result in from 1nterna 1 irrailiat1on 6 railium-226
an its s ort- 1 ve ecax ero uctsa7

Organ or tissue

Activity
concentration(mllq kg- 1)
226Ra

Gonads2.7
llreas t
2.7
Lungs
2.7
Cortical bone
170
Trabecul ar bone 170
Red bone marrow
2.7
Bone lining cells
Thyroid
2.7
Other tissues
2.7

Annual absorbed doses (10226Ra222R 11

a

a

o. 7
0.7
0. 7

0.3
0.3
0.3

2.0
22
0.7
o. 7

222R~/
0.9
0.9
0.9
60
60
0.9
0.9
0.9

Gy)

218ro 214Pb

214Bi

2141'0

a

p,y

p,y

a.

0.3
0.3
0.3

0.01
0.01
0.01

0.03
0.03
0.03

0.4
0.4
0.4

0.8

0.9

9. I

9.9
'0.3
0.3

0.2
0.7
0.01
O.Oi

0.6
1.1
I. 7
13
0.03 0.4
0.03 0.4

0.3
0.3

a/

Includes doses resulting from the formation of radon-222 and its
short-1 ived decay products in t'le body by decay of radium-226 but
does not take into account the joses arising from inhalation ofradon-222 and its daughters.
b/ 218 Po, 214 Pb, 214 Bi, and 214 Po are assumed to be in radioactive
equilibrium with radon-222 in all organs and tissues.

T a b 1e

12

Estimated e uilibrium e uivalent concentration of radon-222
an annua e ect ve ose equiva ents ar1s ng rom 1n a at1on

OUTDOOR EXPOSURE
Equilibrium equivalent-3
concentration(Bq m_~)
Range of mean annual values (Sq m -')Average annual effective
dose equivalent(mSv)
Range of mean annual values (mSv)
I NOOOR EXPOSURE
Equilibrium equivalentconcentration
Range of mean values
in various countries
Average annual effective
dose equivalent
Range of mean values
in various countries

Populations intemperate regions

Global population

1.8
0.1-101.8
0.1-100.06
0.003-0.3

0.06
0.003-0.06(Bq m- 3 )15(Bq m- 3 )

5-60

(mSv)

0.92

(mSv)

0.3-3.7

Tota 1 average annua 1
effective dose equivalent (mSv)

1.0

0.7

0.8

99

Tab l e

13

Estimated avera e activit concentrations of 210 rb, 210 si, and 210p 0
in t ssues o non-smo ers n areas of norma
eta ry nta e,
and corresponding annual absorbed doses

Organ or tissue

GonadsBreastLungs
Cortical bone
Trabecular bone
Red bone marrow
Bone lining cells
Thyroid
Other tissues
Annual effective
dose equivalent(µSv)

Lead-210

Bismuth-210

Polonium-210

Activity
Annualconcenabsorbed
tration dose (µGy)(Bq kg-l)
13

Activity
Annualconcenabsorbed
trati on dose (pGy)(Bq kg-I)'3

Activity
Annualabsorbed
concentra t ion
dose (µGy)(Bq kg-l)
a

0.2
0.2
0.2
3
3
0.14
0.2
0.2

0.04
0.04
0.04
0.17
0.44
0.04
0.04

0.4
0.4
0.4

0.2
0.2
0.2
3
3
0.14

0.2
0.2
0.1
2.4
2.4
0.11

I. 7
4.2
0.4
0.4

0.2
0.2

0.2
0.2

0.7

0.07

Tab 1 e

5.4
5.4
2.7
5.1
36
5.4
5.4

130

14

Average activit~ concentrations in tissues and annual absorbed doses
resulting from internal irradiation by thorium-232

Organ or tissue

Activity
Annual absorbed
concentration
doses( I0- 7 Gy)(mBq kg- 1 )aGonadsBreastLungs
Cortical bone
Trabecu 1a r bone
Red bone marrow
Bone lining cells
Thyroid
Kidneys
Liver
Other tissues

100

0.15
0.15
20

0.03
0.03
4.0

6

24
0.15
0.15
3
2
0.15

1. 7

20
0.03
0.6
0.4
0.03

Ta b 1e

15

Average activitX concentrations in tissues and annual absorbed doses
resulti n from internal 1rraaiation D raa,um-228 ana ,ts aeca
roaucts~

Organ or tissue

Annual absorbed doses {10-S Gy)

Activity
concentration(mBq kg-i)

228Ra

228Ra~/228ThE_/

13

13, y

u

0.03
0.03
0.03

1.1
1.1
1.1

0.14
0.30
0.03
0.03
0.03
0.03

4.1
10
1.1
1.1
I. 1
1.1

Gonads4
Breast4
Lungs
4
Cortical bone50
Trabecular bonesoRed bone marrow
4
Bone lining cells
Thyroid4
Kidneys4
Liver4
Other tissue
4

0.5
0.5
15
50
50
0.5
0.5
10
5
0.5

220Rn

216r 0

212Pb

2129;

212p 0

2osn

a.

a

a.

(3,y

a.,13 'y

Cl

13, y

'..4
1.4

1.4
1.4

I. 7

41

1. 7

0.05
0.05

43

1.6
1.6
48

51

1.4

5.9

6.2
78

87

7.4
93
1. 7
34
17
I. 7

1.1
2.3
3.4 290.05 0.5
0.9
11
0.5
5.4
0.05 0.5

228Ac 228Th 224Ra

74
1.4

1.4

27

29
14
1.4

14

1.4

6.9

:i1 ·6
16
1.6

0.5
0.5
16

1.4
1.4

43
6.2
77

1.4
28
14
1.4

0.07
0.07
2.0
1.6
5.5
0.07
1. 3
0.7
0.07

a/

Includes doses resulting from the formation of radon-220 and its decay products in the body bydecay of radiurn-224 but does not take into account the doses arising from inhalation of radon-220
and its daughters.
~/ Actinium-228 is assumed to be in radioactive equilibrium with radium-228.
224c/
Ra, 220Rn, 216 Po, 212 Pb, and 212 Bi are assumed to be in radioactive equilibrium with thorium-228;
owing to the decay characteristics of bismuth-212, the activity concentrations of polonium-212 andof thallium-208 are 64 % and 36 % of those of bismuth-212, respectively.

T a b l e

16

Estimated e uilibrium e uivalent concentration of radon-220
an annual e ect1ve dose egu,va ents ar,s ng from in a at,on
Populations intemperate regions

Global population

OUTDOOR EXPOSURE
Equilibrium equivalentconcentration
Annual effective
dose equivalent(Bq m- 3 ;

0.2

0.2

(mSv)

0.02

0.02

INDOOR EXPOSURE
Equilibrium equivalentconcentration
Annual effective
dose equivalent(Bq m- 3 }

0.7

(mSv)

0.20

0.15

Total annual
effective dose equivalent (mSv)

0.22

0.17

101

Tab 1 e

17

Estimated er ea ut annual effective dose e uivalents
rom na ura sources ,n areas o norma
ac groun
Annual effective dose equivalent (µSv)
Source of irradiation

External
irradiation

lnterna lirradiation

Total

COSMIC RAYS-

Ionizing component
tleutron component

280
21

280
21

COSMDGEtHC RADIDNUCLJDES

15

15

180

300

6

6

PR lt10RD !AL RAD IDIIUCLIDES

40K
87Rb
238 u series

238u-,.2 34u
230Th
226Ra
222R 0 ...214p 0
21 OPb-+ 210p 0
2 32 Th series
232Th
228Ra...224Ra
220Rn...208rl
TOTAL (rounded)

102

l
l

120

10

90

7
7

800
130
3

140

13
170

650

1340

l
l

!044

326
2000

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B1

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B8

B9

Cl

C2

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C7

CB

D2

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