SOURCES AND EFFECTS
OF IONIZING RADIATION
United Nations Scientific Committee on the Effectsof Atomic Radiation
UNSCEAR 1993 Report to the General Assembly,
with Scientific Annexes

UNITED NATIONSNew York, 1993

NOTE
The report of the Committee without its annexes appears as Official Records of theGeneral Assembly, Forty-eighth Session, Supplement No. 46 (N48/46).
ll1e designation employed and the presentation of material in this publication do not imply
tl1e expression of any opinion whatsoever on the part of tlie Secretariat of the United Nations
concerning the legal status of any country, territory, city or area, or of its authorities, or concerning
tl1e delimitation of its frontiers or boundaries.
The country names used in this document are, in most cases, those tliat were in use at thetime the data were collected or the text prepared. In other cases, however, the names have been
updated, where tliis was possible and appropriate, to reflect political changes.

UNITED NATIONS PUBLICATION
Sales No. E.94.IX.2
ISBN 92-1-142200-0

ANNEX A
Exposures from natural sources of radiation

CONTENTS

Pagc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
I . COSMIC RADIATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
INTRODUCTION

A . COSMIC RAYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
1. Tbe radiation environment . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2. Factors affecting dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3 Exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
B. COSMOGENTC RADTONUCLIDES . . . . . . . . . . . . . . . . . . . . . . . 39
C. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39.

. TERRESTRIAL RADIATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

I1

A . EXTERNALEXPOSURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
1. Outdoors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2 l~idoors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3. Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
B. INTERNAL EXPOSURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
C. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44.

. RADON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

111

A. SOURCES AND MOVEMENT .......................... 45
1. Production in terrestrial materials . . . . . . . . . . . . . . . . . . . . . . 45
2. Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3. Advection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4 . Infil~ation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5 . Transfer from water and natural gas . . . . . . . . . . . . . . . . . . . . 48
6. Entry rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
B. EXPOSURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
1. Indoor concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2. Dosc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
C. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

IV . EXTRACTIVE INDUSTRIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
A. ENERGY PRODUCTION FROM COAL . . . . . . . . . . . . . . . . . . . 55
1 Coal mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2 . Use of coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3. Use of fuel ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.

UNSCMR 1993 UPORT

34

I'agc

B. OTI1ER ENERGY PRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 57

I . Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2. I'cat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7
3. Natural g a s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4. G c o t l ~ c r ~ cncrgy~~al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
C. USE OF PHOSPHATE ROCK . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
1. Pl~osphatcprocessing operations . . . . . . . . . . . . . . . . . . . . . . . 5 8
2. Usc of phosphate fertilizers . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3. Usc of by-products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
D. MINING AND MILLING O F MINERAL SANDS . . . . . . . . . . . . . 60
E. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Tablcs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

INTRODUCTION
Natural ionizing radiation arises in outer space,1.
whcrc cosniic rays arc foniicd, and in and on thecarth, whcrc radionuclidcs norn~allypresent in soil,
air, watcr, food and Ihc body uridcrgo radioactive
dccay. Penetrating radiations and radioactive materials
pervade thc natural cnvironmcnt. The main types ofradiation arc gamma rays, alpha and beta particles,
neutrons and muons. Human exposurc occurs by
irradiation from sourccs outsidc the body (external
exposurc) and upon the dccay of radionuclidcs takcn
into thc body through ingestion and inhalation (intcmal
cxposurc). The assessment of radiatjon doses inhumans from natural sourccs is important because
natural ionizing radiation is the largcst contributor to
Ihc collective cffcctivc dosc rcccived by the world's
population. In this Anncx, the expressions "naturalradiation" and "natural radiation background" arc oflcn
uscd to rcfcr to "natural sourccs of ionizing radiation".
Some of the contributions to thc total cxposurc
2.
from thc natural radiation background are quite
constant in spacc and time and prac~icallyindcpcndentof hurtian practices arid activitics. This is true, forcxamplc, of thc doscs rcccivcd froni the ingestion of
4 0 ~ ,a long-lived radioisotope of an clcnient tihat is
homcostatic;illy controllcd, and also of doscs froni thc
inhalation and ingcstiorl of cos~nogcnicradionuclidcs,
which are rclativcly honiogrl~couslydistributed at thesurface of thc globc.
3.
Other contributions dcpcnd strongly on humanaclivitics and practiccs and arc thcrcforc widely
variable. In par~icular,Ihc doses from indoor inhala-tion of short-lived dccay products of radon gas are
influenced by local gcology and by building dcsign, as
well as by the choice of building materials and ofventilation systcms. Also, concentrations of theshort-lived decay products arc, as a rule, highcr
indoors than outdoors. Therefore, people who rcsidc
somcwhat above the ground surface in apartment
blocks or who mostly stay outdoors in the open air arelikcly to incur far less exposurc to radon than thosc
who occupy single dwellings or who spend most of
their time in enclosed spaces.
4.
Intermediate types of exposurc are thosc that arc
ncithcr widely variable nor rclativcly constant at thesurface of the globc. Examplcs are (a) extcrnal doses
froni cosmic rays, which vary with altitudc and, to amuch lcsser extent, with latitude, and (b) cxtcrnal
doses from radiation of tcrrcstrial origin (that is, theradionuclides present in the crust of thc carlh and inbuilding materials), which arc affcctcd by location andacconimodatio~~.

Doscs frorn the inhalation of radon in dwellings5.
are much grcatcr than thosc from all othcr components
of natural radiation. Thc main causc of high conccn[rations oC radon in dwellirigs is thc influx of thc gas
from the subjaccrit earth; high doscs arc causcd bynlodificd by tllc ~nanncrin
geological circu~nstar~ces
which a dwclling is built and uscd. Since increasing
attention is being dcvotcd worldwide to both theradiological and thc epidcniiological aspccts of this
topic, considerable emphasis is placcd in this Anncx
on cxposure to radon and ils dccay products in air.

ANNEX A: MI'OSURES FROM NATURN, SOURCES 01: KADlK110N

I

1

II

6 . Sincc t l ~ cpublication of thc UNSCEAR 1988
Rcport [Ul], furlllcr illformation on radiatio~lcxposurcs from natural sourccs, especially with regard
to mdon and ils short-livcd dccay products, has
bccomc available. This Annex updatcs thc evaluatio~~of exposures prcscntcd in thc UNSCEAR 1988 Rcport[UI]. The additions and n~odificatior~sprcscnt abroader vicw of avcragc radiation cxposurcs worldwidc and of thc range of lcvcls cxpcric~lccdin particular locatiolls. Thc proccdurcs for cstirnating Lhe tissue
doscs Gom inhalation of radon short-livcd dccay
products arc u ~ ~ d conlinuing
crrevicw and thc Intcrnatiorlal Cornmission on Radiological Protcction(ICRP) has assigned new radiation- and tissucweighting factors to definc thc cffcctivc dosc [I6j.
Dcspitc ~hcscchanges, the overall asscssmcnt of dostfrom natural sources of radiation is similar.

7. Radiation exposurcs Gom extra-terrestrial sources(cosmic rays and cosmo cnic radionuclidcs) and fromtcncstrial sourcw PK, 'Rb and radionuclides of theuranium and thorium series) may be said to form thebasic natural radiation background bccausc of thc rcla-

I.
A.

35

tivc cons[ancy of cxposurc. fllcsc cxposurcs arc discussed in Cllaplcrs I and 11 ill this Anncx. Amoag thc
terrestrial radio~~uclidcs,
tllc radon isolopcs in tllc
ura~liunland tlloriunl dccay scrics play an ilnportarltrolc hcciiusc of UIC n~ag~iiludcof the doscs thcy
dclivcr and bccausc of lhc variability of thosc doscs.
Thc radorl isotopcs arc givcn spccial consideration in
Chaptcr 111. Exposures rclatcd to the extraction andprocessing of carth materials arc considcrcd in Chaptcr
IV, with thc cxceptior~ofthe cxlraction and proccssi~lg
of uranium, which is part of the nuclear fucl cycle andis dcalt with in Annex B, "Exposures from man-madesources of radiation".

8. The exposures asscsscd in this Annex arc thosc
to members of the public. They include thc exposures
outdoors and indoors in normal circumstances both athome and at work. The additional exposures that
pcoplc reccive at work bccausc thcy arc exposed to
man-made radiation sources or to elcvated lcvcls ofnatural radiation caused by their work arc discusscd inAnnex D, "Occupational radiation exposures".

COSMIC RADIATIONCOSMIC RAYS

1. The radiation environment
9.
Space is permeated by ionizing radiation. Thc
radiation consists of various cbargcd particles ofvarious origins and cncrgics. All arc of conccnl inspacc kavcl, and some by creating secondary particles,
lcad to human exposure during air travcl and on carth,with decreasing intensity 6om thc highest altitudes
down to sea level. In this Chapter, emphasis is placcd
on thc cvcryday circumstances of exposure, and brief
rcfcrcncc is made to exposure in space.
10. Radiations in space may be classified according
to origin as wapped particlc radiation, galactic cosmic
radiation or solar particle radiation [ A l , C1, F1,N1,
S11. Trapped radiation consists main1y of clcctronsand protons held in orbits around the earth by ils
niagnctic ficld. Galactic cosniic radiation consisls
mainly of protons with somc hclium and hcavicr ions.
Solar particlc radiation has similar composition. Thcsc
thrcc classes are described in turn.
11. Trapped protons and clcclrons are in two zones
or radiation bclts, onc within and onc outsidc of 2.8
earth radii at tllc equator, with grcatcr intcnsities andencgics in thc outer zone. There are appreciable
temporal variations in intensities; encrgics of clcctrons

rcach scvcral mcgaelcctron~olts(MeV) and encrgics ofprotons reach a few hundred MeV. Trapped protons
arc morc inlportant than clcctrons for manncd missions
in low carth orbit Although particles trapped inradiation bclts can present a radiation ha?ard Tor space
travcllcrs, thcy do not result in any radiation dosc at
ground level.
12. Galactic cosmic rays are created outside thc solar
system: ~Iicyare gcncrally believed to bc produced andaccclcratcd as a consequence of stellar narcs, supcrnova explosions, pulsar acceleration or thc explosionof galactic nuclei [09]. There is, however, nogcncrally accepted theory of their generation andacceleration. Cosmic rays in our galaxy have a mean
residence lime of about 200 million ycars, being
conbined by Lhc magnetic field of interstellar space[ 0 9 ] . Encrgics of the cosnlic-ray particles arc n ~ o s ~ l ybctwccn 10' and 10' MeV, but thcy can rcach muchhighcr values [Sl]. The spcclrum is affcctcd bychanges in the magnetic fields within the solar system,~natcaused by solar activity, with ~ r ~ a x i m uintensity
periods of low activity and vicc versa. Of thc hcavy
ions, called HZE particles (high atomic nurnbcr andcncrgy), that arc components of h e cosmic-ray flux,
iron is the most significant for exposure because of its
relative abundance and high atomic numbcr [ L l ] .
Galactic cosmic rays are also affcctcd by the gcomagnetic field near the earth, which prevents sonlc

36

UNSCEAR 1993 REPORT

particles from reaching the atniosphcre but is progrcssively lcss cflective in doing so from the geomagiictic
equator to the poles. This class of space radiation is
the most significant for exposure on earth and inaircraft.
13. When the primary particlcs from space, mainly
protons, cnlcr the atmosphere, those with high cncrgy
interact with nuclei present in the air (nitrogen,oxygen, argon) to produce neutrons, protons, muons,pions and kaons, in addition to a variety of reaction
products, sonic of the more important of which, fromthe dosimctric point of view, arc 3 ~ 7 , ~ ande **~a.
These high-energy reactions are called spallationrcactions. Many of the secondary particles havesufficient energy to initiate whole sequences of further
nuclear reactions with nuclei present in the air. A
cascade process is the result [12]. The properties ofsome of the more important cosmic-ray particles arelisted in Table 1 [E6, US].

14. The nucleonic components, protons and neutrons,
are mainly produced in the upper layers of theatmosphere. The protons are formed mainly inspallation rcactions, while neutrons are produced bothby spallation reactions and by the so-called
evaporation of neutrons due to low-energy (p,n)
rcactions. Neutrons lose energy by elastic collisions
and, when thermalized, are captured by "N to form"c. Bccause nucleons rapidly lose cncrgy throughionization and nuclear collisions, the nucleonic flux
dcnsity is considerably attenuated in the lower part of
the atmosphcrc and accounts only for a few per centof the dose rate at sea lcvcl [US]. The neutron
spectrum covers a wide cncrgy range in the lower
atmosphcre, from thermal to 100 MeV and more, but
Lhc high-energy neutrons are most significant bccauseof their high fluence to equivalent dose conversion
coefficients.
15. Pions and kaons have short lives and essentiallydecay in the atmosphere before reaching ground level.
The electromagnetic cascade is initiated from photons
produced in the decay of neutral pions. These photons
create electron-positron pairs and Compton electrons,
which in turn produce additional photons bybremsstrahlung and positron-electron annihilation. As
the number of shower particles increases, lheir averageenergy decreases. Finally, the majority of electrons
will drop to energies where collision losses dominate
and [be cascade will die out [I2]. Except in the lower
layers ofthe atmosphcrc, electrons arc main sources ofionization [US]. On the other hand, muons, whichhave a small cross-section for interaction with atomic
nuclei and a mean life of 2.2 ps before decay,
penetrate into the lower layers of the atmosphere andare the main constituent of cosmic rays at sea level[US]. Most muons occur in the energy range
0.2-20 GeV, with a median value of 2 GeV [N2].

16. Solar particlc radiation, as the name i~nplics,
comes fro111the sun. Particles of very low energy are
generated continuously, but tnore energetic particles
are emitted more copiously during magnetic disturbances. Large clnissions associated with narcs, called
solar particle evc~lts,occur occasionally during theactive period of the 11-year sol;~rcycle [HI]. Energies
are usually between 1 and 100 MeV but can be anorder of magnitude higher. Such events arc importantin low earth orbit, but anomalously large solar panicle
events, which occur about once a decade, may be ofvital importance for matined rnissions beyond themagnetosphere. Although the fluence rate of solar
particles over several years exceeds the fluence rate ofgalactic particles, solar particles arc less significant forradiation exposure in the atmosphere, bccause mosthave insufficient energy to penetrate the earth's
magnetic field. The emission of solar particle radiation
follows the 11-year solar cycle, reaching a maximum
during increased solar activity and a minimum during
the period of the quiet sun. Because the less energetic
galactic cosmic-ray particles are deflected away fromthe solar system by the magnetic irregularities
transported by the solar particle radiation, an 11-year
niodulation of the galactic cosmic-ray flux density atthe earth is produced, the cosmic-ray flux dcnsity
being lowest during times of maximum solar activity
and vice versa (Figure I).

2.

Factors affecting dose

17. To estimate human doses from cosmic rays, it isnecessary to consider the effects of altitudc, latitude
and shielding.
(a)

Altitude

18. The absorbed dose rates in air from the directly
ionizing and indirectly ionizing (neutron) componentsof cosmic ray are shown in Figure I as a function ofaltitude at a geomagnetic latitude of 50" N. These
results are based on numerous nieasuremerlts on the
ground and aboard aircraft, which wcrc cotnpilcd in
the UNSCEAR 1977 Report p4]. During periods ofmaximum solar activity, dose rates of the ionizing
component are reduced about 10% at 10 k n ~altitudc
and to a lesser degree at sea level.
19. The dose ratcs from neutrons, the doniinant
indirectly ionizing coniponc~~t,
are much less thanthose due to Ule ionizing component, but they increase
more rapidly with altitudc, peaking at 10-20 km. The
variations during the solar cycle are greater, wiUi
decreases in the dose ratcs of a few tens of pcr cent at
an altitudc of 10 kni during solar maxima and to alesser degree at sea lcvcl.
20. The values of the production rate of cosmic rayions at sea level reported after 1960 for mid- and

,

iI
1
I

.i

g

high-latitudcs show rclativcly good agrccmcnt, witti aclustcr of valucs around 2.1 cmo3sql arid cxtrcmes at
s-I (U31. Sincc 1977, the Committee
1.9 and 2.6
has consistcntiy adoptcd a valuc of 2.1 cm-3 i1
for thepurposcs of computing chc absorbed dosc ratc from thc
directly ionizing compbncnt. Assu~nirtgthat cach ion
pair in moist air rcquircs 33.7 cV to bc produccd, theabsorbcd dosc rate in air is 32 nGy h-I at sca lcvcl at
mid- and high-latitudes. Since thc dose is dclivcrcd
mainly by muons. for which the radiation weighting
factor is unity [I6], this numerical value may also betakcn for d ~ cquivalcnt
cdosc ratc in thc opcn.
21. Thc cosmic-ray ncutron flux density at sea lcvel
is small and difficult to measure, mainly bccause theneutron cncrgy spectrum cxtcnds ovcr a very wide
range, from fractions of eV to tens of GeV. At 50" N
latitudc, the ncutron flux density is about
0.008 em-* s*' at sea lcvcl [H2, H12j. A range of
estimates of equivalent dosc rates from 1.4 to
3.3 nSv h-l were reportcd in the UNSCEAR 1988
Report P I ] for different computational geometries
and exposures. The lowest values arc found for low
latitudcs (24" N) p 2 3 ] , suggesting the presence of a
substantial latitude effect, cvcn at sea lcvel. In thebP7SCEAR 1988 Report, the averagc cffcctivc dose
equivalent ratc was taken to be 2 4 nSv h*'. Changes
to the radiation-weighting factor were rccommcndcd
by the ICRP in 1991 [I6]. Considering the ncutronenergy spcctrum, those changes lead to an increase ofabout 50% of the effcctivc dose rate from ncutrons[H20]. The avcragc effectivc dosc rate from cosmicray ncutrons at sca lcvel is, thcrcforc, estimated to be
3.6 nSv h-l.
(%) Latitude

22 Lowcr-cncrgy chargcd particles arc dcflcctcdback into space by the eaflh's magnctic field. This
cffcct is latitudc-dcpcndcnt, so that a grcatcr flux of
low-cncrgy protons reaches thc top of thc atniosphcrc
at thc poles than in equatorial regions. Thus, theionization produccd in thc atmosphcrc is also latitudcdependcnt. This latitude cffcct increases with altitude;at sea level, the cosmic-ray absorbed dosc ratc fromthe dircctly ionizing componcnt gradually dcclincs to
90% of its high-latitude value bctwccn 40" and thc
gcomagnctic equator [ T l l ] . For example, thecosmic-ray absorbed dosc ratc in air has been found to
be 27-31 nGy h-l at Hong Kong (latitudc 22.3" N)[ T l l ] and 28 nGy h-' at Shcnzcn, China (latitude
22.6" N) [Yl]. Thcsc figurcs are to bc compared to
the value of 32 nGy h-' obscrvcd at high- andmid-latitudes.
I

I
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(c)

Shielding

23. Ordinary buildings such as houses and offices
providc some shiclding against the dircctly ionizing

componcnt of cosniic rays, but data arc still scarcc;
thc magnitude of thc cffcct dcpcnds on the structure
and composition of the buildings. Liniitcd mcasurcmcnts and calculations, suniniarizcd in the UNSCEAR
1988 Report [ U l ] and clscarhcrc [NZ], givc shiclding
factors from 0.96 for sniall woodcn houscs to 0.42 forsubstantial concrctc buildings. Calculations for muonsyicld dosc reductions ranging from 10% to 30%
comparcd to the valuc in a refcrcncc rooni, when thc
parameters affecting cxposurc (size of building,thickness of structural clemcnts, proximity to otherbuildings) are varicd within reason [F2]. Without morc
infomiation on shiclding and on the nature of buildings, the same universal shiclding factor of 0.8 isrctaincd as bcforc [Ul]. It is recognized, howcvcr, thatthcrc may be 25% uncertainty associated with thisvaluc.
24. Information on the shiclding cffect of ordinary
buildings on the ncutrons in cosmic rays is more
limited than for muons, although the broad spectrum
must be affected to some dcgree, with virtually no
attenuation by a shingle roof, for instance, and anorder of magnitude attenuation by a substantial
concrete element [N3]. In this Annex, no account has
been takcn of the shielding effcct of the neutroncomponent.
3.
(a)Exposures

Ground level

25. With the conventional indoor occupancy factorof 0.8, that is, the fraction of time pcrsons arc dccmcd,
on the averagc, to be indoors at honic and at work
[Ul], the annual cffc'ctivc dosc from the dircctly
ionizing componcnt of cosmic rays is estimated to bc
240 pSv at sea Icvcl. Since the shielding cffcct isignored for the ncutron componcnt of cosmic rays, anoccupancy adjustnicnt is not nccdcd. The annual
cffcctivc dosc from the ncutron coniponcnt of cosmic
rays is approximately 3 0 p S v at sea lcvel. Thc
unccrtainty in this estimate is? clearly, appreciable.
26. To estimatc the population-wcighted annual
cffcctive dose from cosmic rays at ground-level,
account needs to be takcn of the variation of thc
cffcctivc dosc ratc with altitude and of the distributionof the world's population with altitude. Analyticalexpressions have been developed for the generalrelationship bctween annual dosc and altitude for both
the directly and indirectly ionizing componcnts [BI 1:

where E, is the cffcctive dose ratc in pSv a-' for thc
directly ionizing componcnt: ~ ~ ( is0 )the reference
valuc at sea levcl, 240 pSv a-l; z is the altitude in km;a, = 0.21; a,= 1.6 km-l; bl = 0.80: PI = 0.45 km-'.

UNSCEAR 1993 REPORT

38wilt) cquation (2) applyi~~gfor z < 2 km and cquation(3) applying for I. > 2 km, wllcrc EN is the cffcctivc
dosc ratc in pSv a-' for thc indircctly ionizing
cornponcnt from ncutrons and ~ ~ ( =0 30) pSv a-l;a, = 1.0 km"; bN = 2.0; and PN = 0.70 km-l. These
cquations may bc applicd to estimate doscs fromcosmic rays at habitable elevations around the world.
They include an allowance for shielding, as describedabovc.

27. The distribution of the world population byaltitude and urbanization has bcen analysed [Bl], withsomc simplifying assumptions. When the foregoing
equations are applicd and the two components
summed, the distribution of collcctive effective dosewith altitudc is obtaincd. Thc annual valuc of the
avcrage cffcctive dosc worldwide is estimated to be
380pSv, with the dircctly ionizing and indirectly
ionizing componcnts contributing 300 pSv and 80 @v,
rcspcctivcly. Thc global valuc of the collective
cffcctivc dosc is about 2 l o 6 man Sv, somc 90% of
which occurs in tlic northcn~hcmisphcrc by virtue ofthc population distribution. Sonicwhat lcss thanonc filth of the collcctive dosc is attributable to China,
whcn account is takcn of both population andelcvation [H13,N221.
28. Since human habitations arc mostly at lower
altitudes, about onc half of the collcctivc dose is
rcccivcd by thc two thirds of thc world population lbat
livcs bclow 0.5 km. Thc onc fifticlh (approximately)of thc population living ahove 3 km receives a
disproportionate one tcnth of thc collcctive dose.
Tablc 2 lists avcragc annual doscs from cosmic rays
with thc scparatc contributions of the dircctly andindirectly ionizing componcnts indicated. In highaltitudc cities thc increasing importance of neutrons
with elcvation is cvidcnt. There is considerable
variability in total dose. Thc annual value in La Paz,for cxamplc, is five timcs the global avcragc. In roundtcmis, annual valucs of the cffcctive dose from cosmic
rays rangc from 270 to 2,000 pSv, with a populationwcightcd mcan of380 pSv.

(h)

Air travel

29. Flight pattern and duration are the principal
determinants of cosmic-ray doscs to aircrcw andpassengers. Modem commercial aircraft have optimum
operating altitudcs ncar 13 km, but flight paths are

assigncd according to usc and safcty rcquircmcnts, andadcquatc data do not sccm to bc available for fligbt
patlcnls [ W l ] . I s t l ~ cUNSCEAR 1988 Report PI 1, a
rcprcscntiitivc opcrating altitudc of 8 km was assunicd,
bccausc of UIC prcdor~iinanccof short-travcl flights,
with an avcragc spccd of 600 krn hml. Altcnlativc
assumptions arc also madc; for cxaniplc, an altitudc of
9 kni and a spccd of 650 km h-I wcrc used for an
asscssnicnt in thc Unitcd Kingdom [H3), and analtitude of 7 km is indicatcd for flights by Unitcd
States carricrs lasting lcss than an hour and 11 km forlongcr flights [09]. Computatiorial codcs havc been
dcvclopcd to allow calculatirig radiation lcvcls
Lbroughout the atmosphcrc (see, e.g. [09]), andadditional mcasurcment expcricnce is being acquired(see, e.g. [N12, R8, S30)). For a given altitude, dosc
ratcs for flights ovcr the poles arc substantially greaterthan those for flights ovcr equatorial rcgions.
30. An international digest of air traffic statistics ispublished routincly [I3]. Data for 1989 show that
1.8 lo1* passenger-kilomctrcs wcrc flown in that year,
which translates into 3 lo9 passcngcr-hours aloft. Withan cffcctivc dosc ratc of 2.8 pSv h-' at 8 km,
calculated using cquations ( I ) and (3), thc collcctive
cffcctive dosc fro111 global air travcl is about
10,000 man SV for thc year. Worldwide, thc annual
value of the pcr caput cffcctivc dosc duc to air travelis, thcrcforc, about 2 @v; in North Amcrica it isaround 10 pSv. Ttlcsc valucs arc small in comparison
to the estimated annual pcr caput cffcctivc dosc at
ground level of 380 pSv.

31. A limited nunibcr of supersonic airplanes opcratc
comnicrcially and cruise at about 15 km. Doscs onboard arc routincly dctcrmincd with monitoring
equipment. Effective dosc-cquivalcnt rates arc
generally around 10 pSv h-', with a maximum around
40pSv h-l [Ul]. In two ycars from July 1987, theovcrall avcrage on six Frcnch airplancs was
12 pSv h-', with nionthly valucs up to 18 @v h-'[Sll]; in 1990, the average was 11 pSv h-' and theannual dosc to aircrcw was about 3 mSv [M16].
During 1990, thc avcragc dosc ratc for about 2.000
flights by British airplancs was 9 pSv h-l, with aV [D4]. Thc equivalentmaximum value of 44 ~ S h-I
dose ratcs so far rcportcd in this paragraph do not take
into account the changcs in thc radiation wcighting
factors for nculrons that wcrc rccommcndcd by ICRP
in 1991 1161. Thc crfcctivc dosc ratcs, estimatcd with
the ncw radiation weighting factors for thc ncutroncomponcnt, arc higbcr than Uic numerical valucs
rcportcd abovc by about 30%. The monitoring
equipment scrvcs to warn of solar narcs so hat the
airplanes can bc brought to lowcr altitudcs. This is avery small sector of the commercial air transportindustry.

II

A N N M A: ~ X P O S U K r sFROM N ~ l l l R h LSOURCES 01: RADIK~oN

13.

COS~IOCISNICKAI)IONUCLII)ES

32. Cosmic rays producc a rangc of radior~uclidcsin
thc ain~osplicrc,biosplicrc and lithosphcrc by a varictyof nuclcar rcactions. Thc four most im lortan1
in terms ol' dosc arc 'H, 7 ~ llC~ and.
radio~~uclides
2 2 ~ a ,and thc most iniportil~~tmechanism of human
exposurc is ingcstion.
33. Thc most significant of thc four radionuclidcs
considcrcd is 14c.The asscssmcnt of its contribution
to thc dosc from natural sources is uscful for thc
derivation of doses fro111 man-made environnrcntal
rcleascs of "c. Thc annual natural production of'k is 1 PBq and the specific activity of "C is230 Bq per kg of carbon, leading to an annual
V
The spatial variability
cffcctivc dose of 12 ~ S [U4].
of thc dose from 1 4 c is not radiologically significa nt.

34. Annual effective doscs to adults from theingcstion of 3H, 7Be and 2 2 ~ ina food and water havebeen dcrivcd frorn estimated average annual intakes[N2, U3, U4], applying standard coefficients for dose
pcr unit intake [I4, NS] and assuming an equilibrium
situation. The annual cffcctive doses obtained for
those tbrce radionuclidcs arc much smaller than thatfor 14c. The annual intakcs and effective doscs for thefour cosmogcnic radionuclidcs arc sun~marizcd in
Tablc 3.

11.

iI

39

C. SUMMARY
35. Cosmic rays, which originate in space, and solar
particlcs cntcr lhc earth's atmosphcrc and bcgin acascadc of sccondary intcractions and dccays. Thc
rcsultlnt ionization is a function of both altitudc andlatitude. Thc iot~izing comporrcnt of cosmic rays
products, on avcragc, an absorbcd dosc ratc in air of
3 2 n G y h-' at sca lcvcl in thc mid-latitudes,
concsponding to an cffcctive dosc rate of 32 nSv h".
Thc neutron coniponcnt of cosmic rays results in ancffcctive dose ratc of 3.6 nSv h-l. Thc intcnsities ofboth components incrcasc with altitude, more s o forthe ncutron componenL
36. Taking into account shielding by buildings forthc ionizing component and the distribution of world
population with altitude, the population-wcightcd
avcragc annual cffcctivc dose from cosmic rays is
380 pSv. The cffcctive dose ratc rcccivcd during acommercial flight is about 3 p S v h-l; the pcr caput
annual cffcctivc dosc for the world population duc to
air travcl is 2 pSv.
37. Exposures to cosmogcnic radionuclides, produccd
by cosnlic ray interactions in the atmosphere, result
primarily from ingcstion and arc rclativcly uniform
throu hout the world. The radionuclidcs include 3 ~'BC, y4C and " ~ a . The annual cffcctive dose frorn"C is 1 2 pSv. Exposure from thc other radionuclidcs
is negligible.

TERRESTRIAL RADIATION

38. Only nuclides with half-lives comparable withthe age of the earth (or dccay products, whose
concentrations are govcrncd by them) cxist in
terrestrial matcrials. In t c m s of dosc, the principal
primordial radionuclidcs arc 4 0 (half-lifc:~
1.28 lo9a), 232Th (half-lifc: 1.41 lo1' a) and '"u (half-life:b
4.47 lo9 a). Of secondary importance arc 6 7 ~ (halflife: 4.7 lo1' a) and 2 3 S ~(half-life: 7.04 10' a). The
thorium and uranium radior~uclidcs hcad scrics of
scvcral radionuclidcs, many of which contribute tohuman cxposurc. Thc dccay scrics hcaded by 2 3 8 and~
L?32Thwcrc illustratcd in thc UNSCEAR 1988 Rc ort[Ul]; the radionuclides in the series hcadcd by AS,,arc less important from a dosimctric point of vicw.
There may be some local departure from secularradioactive equilibrium in thc series becausc ol
physicochcmical proccsscs in the earth, such asleaching and cmanation. The mass ratio of natural
3 5 ~to u'" is about 0.0073 and the activity ratio
0.046. A slight dcgrcc of spontaneous fission occurs in
the uranium scries. Both 4 0 and~ 8 7 ~ undergobbeladccay to stable spccies.

39. Natural radionuclides are also prcsent to varying
dcgrecs in the air, in water, in organic matcrials andin living organisms. Human beings are thcrcforc
exposed to external and internal irradiation by gamma
rays, bcta particlcs and alpha particlcs with a rangc ofcncrgics. The main circumstances of external andinternal cxposurcs arc considered in this Chaptcr.
Scparatc considcration is givcn in Chapter 111 to thc
inhalation of thc radon isotopes in thc uranium andthorium scrics.

A.

EXTERNAL EXI'OSURE
1.

Outdoors

40. Exposure to gamma rays from naturalradionuclides occurs outdoors and indoors. Survcys bydirect measurcmcnts of dose rates havc beenco~rducted during the last fcw dccadcs in many
countries. They are summarized in Tablc 4 andillustratcd in Figurc 11. For thc doscs outdoors thrcc,

40

UNSCMR 1993 REPORT

fifths of the population of tllc world is rcprcscnted.
National avcrages ratigc from 24 to 160 nGy h-l. The
population-weighred average is 5 7 nGy h-l. This islittle diffcrent from the value of 55 nGy h-' estimatedin the UNSCEAR 1988 Report [Ul].
41. In the open, much human exposure occurs overpaved surfaces, but some also occurs over soil; it isdetermined by the activity pcr unit mass of theprincipal radionuclides in the superficial layer. Large
surveys of natural radionuclides in surface soils werecarried out in the United States [MI] and in China[N22]; the results are presented in Table 5. Samples
were taken from fallow land. Variability is quite
marked. Similar mcan values for uranium and radiumarc reported for the United States and China, but themcan values for Lhorium and potassium are somewhat
higher in China than in the United States, and the
distributions are wider.
42. In the UNSCEAR 1988 Report, the average~ 232Tb in soil were taken toconcentrations of 2 3 8 andbe 25 Bq kg-' for each radionuclide. Although it isdifficult to estimate average concentrations for thewide distributions presented in Table 5, it seems that
40 Bq kg-' would be a better estimate of the average
concentration of ='u and 2 3 2 in
~ soil. Data on theconcentrations of naturally occurring radionuclides invarious types of soils in the Nordic countries,
presented in Table 6, are in agreement with therevised estimate.
43. The dose rates per unit activity concentrations ofradionuclides have bcen calculated; for example,
Monte Carlo calculations give the kerma in air for
terrestrial gamma rays [P2, S12]. Since the massenergy transfer and absorption coefficients for air are
not notably diffcrent in the energy range of interest
here, these coefficients may be deemed compatible
with those for absorbed dose rate in air uscd in the
UNSCEAR 1988 Report [ U l , B3]. When these dose
factors, which are included in Table 5 , are applied to
the radionuclide concentrations in soil, the average
dose rates in air are 72 and 5 5 nGy h-' in China andthe United States, respectively. According to Table 4,
the population-weighted average absorbed dose in air
for China was 62 nGy h-' and that for all countries
reporting survey results 5 7 nGy h-'. Since humantiabitations are mostly in areas of sedimentary geology
and since radionuclide concentrations in bedrock andoverburden are similar in such circumstances [W2],the values from Table 5 in the narrower range, 10200 nGy h-', may be considered to be broadly typicalfor the world population. Areas of high activity are
discussed later.
The water content of the soil and snow cover canaffect absorbed dose rates in air. On the whole,44.

increasing water content and snow cover reduce dose,
but these arc second-order phenomena [D3, F3, G2]
when averaged over a year in temperate zones wilh
niodcrate precipitation. In extreme climates with heavy
snow cover, however, the reduction may be as muchas 20% [SS, S351. The addition of phosphate fertilizer,
discussed in Section IV.C, may cause a second-orderincrease in dose rate [P3].
45. Areas of markedly high absorbed dose rates in
air around the world are associated with thoriumbearing and uranium-bearing materials. Mineral sands
containing monazite are prime examples of the former.
Absorbed dose rates in air from gamma rays near
separated monazite may reach 10' nGy h-' dependingon geometry m 6 ] . It is not surprising, therefore, thatdose rates over sands can be remarkable. Two suchareas are well known: on the Arabian Sea coast ofKerala in India, where dose rates in air range from
200 to 4,000 nGy h-I [S6, S7] and on the Atlantic
coast of Espirito Santo in Brazil, where dose rates in
air range from 100 to 4,000 nGy h-' approximately[P4]. Radiation exposures due to mining and millingof mineral sands are discussed in Section 1V.D.
46. Other areas of high background radiation havealso been identified. On the Nile Delta, dose rates in
air arc estimated to range from 20 to 400 nGy h-' [E2and on the Ganges Delta from 260 to 440 nGy h'[M7]. Dose rates in air of up to 12,000 nGy h-' havebeen reported over thorium-bearing carbonatite in anarea near Mornbasa on the coast of Kenya [P6]. An
area of volcanic intrusives in Minas Gerais, Brazil,
with mixed thorium and uranium mineralization, hasdose rates in air roughly from 100 to 3,500 nGy h-'[P17]. Ramsar, on the Cas ian Sea in Iran, has dose
rates up to 30,000 nGy h- because of thorium anduranium deposition by hot springs in travertine [S33].
Many granite areas have elevated natural radiationlevels [M2, WlO]. Localized dose rates in air around
100,000 nGy h-' have been found over uraniferous
rocks in Sweden [S8]. Dose rates associated withuraniferous phosphate deposits are appreciably lower;
on the phosphate lands of Florida, they range from 30
to 100 nGy h-' [N2].

I

P

2.

Indoors

47. During the last decade, several surveys havebcen made of the dose rate in air from terrestrial
gamma rays inside dwellings. The results are includedin Table 4. Over a third of the world population isrepresented. The surveys are not quite as cornplete as
outdoor investigations. National averages range from
20 to 190 nGy h-' with a population-weighted averageof all the data being about 80 nGy h-'. This value issomewhat higher than 70 nGy h-', selected in Ihe

A N N M A: M P O S U R I S FROM NAT'URAL SOURCES 01: JUDIATIONU N S C U R 1988 Report [ U l ] as rcprcsc~~tativcfor
indoor exposure worldwide.

ii

I:
i

i

t

,
1

I

48. In comparing the indoor and outdoor averages.
it is seen that the ovcrall effect of surrounding
building matcrials is to increase the dose ratc
40%-50%. As indicated in Table 4 and illustrated in
Figure III, the ratio of indoor to outdoor dose rates
varics from 0.8 to 2.0. In only two countries, Icelandand the United States. are average absorbed dose rates
indoors judged to be less than outdoors. This ratio issensitive to the structural properties of dwellings(matcrials, thicknesses and dispositions) and is oflimited utility for estimating exposures in particularcases from outdoor data. However, the relatively
narrow range of the indoor-outdoor ratio reflects thefact that building materials arc usually of local origin
and that their radionuclide concentrations are similar
to those in local soil. The building materials act assources of radiation and also as shields against outdoor
radiation. In wooden and lightweight houses, thesource effect is negligible and the walls are an
inefficient shield with respect to the outdoor sourcesof radiation, so that the absorbed dose rate in air could
be expected to be soniewhat lower indoors thanoutdoors. In contrast, in massive houses made ofbrick, concrete or stone, the gamma rays emitted
outdoors are efficiently absorbed by the walls, and theindoor absorbed dose rate depends mainly on theactivity concentrations of natural radionuclides in thebuilding materials. Under these circumstances, theindoor absorbed dose rate is generally highcr as theresult of the change in source geometry, with theindoor-outdoor ratio of absorbed dose ratcs in air
between 1 and 2.
49. There is considerable uncertainty in estimates ofindoor dose ratcs. It is clear that the dose ratcs inmasonry dwellings are appreciably highcr than inwooden ones, as explained in the previous paragraph.
For improved estimates of doses, it would benecessary to have data for representative housing stockaround the world. Data for houses in warm climates
are underrepresented in Table 4; these may beconstructed very differently from houses in cold
climates. It is expected that the percentage of houses
that are largely made of wood and other lightweightmatcrials is greater in warm climates than in cold
climates, so that for the same average absorbed dose
rate in air outdoors, the average absorbed dose ratc in
air indoors would be lower in warm climates than incold climates. This needs to be confirmed bymeasurements. Such an important source of human
exposure should be quantified more extensively.

~

50. The dose ratcs in masonry dwelling aredetermined by the characteristics of the masonrymatcrials: 30 gof masonry, for example,

41

provides 90% of the gamma rays from an infinitely
thick source [N2].If construction materials withclcvatcd concentrations of natural radionuclidcs arc
used, dose ratcs in air indoors will be elevatedaccordingly. Some measurements have k e n madc o f
dosc ratcs in relation to building matcrials.
Measurements in Sweden gavc values of about
230 nGy h - l , on average, in houses with outside walls
madc of lightweight concrete, some of whichcontained uraniferous alum shale (M9, M271.
Measurements in former Czechoslovakia gavc values
approaching 1,000 nGy h-' in houses with outside
walls containing uranifcrous coal slag [T3].
Measurements in a granite region of the United
Kingdom, where some of the houses are made of local
stone, gave 100 nGy h-' [W3]. Estin~atesfor houses
made with mud blocks in Jamaica reach 200 nGy h-l[P18]. It is useful, therefore, to calculate the effect ofusing building materials with different activity
characteristics.
In round terms, the activities per unit mass of
2 2 6 ~ anda *'Th in building materials AK, A
are typically 500, 50 and 5 0 Bq kg ,and A,
respectively [NlO]. If the dose coefficients given in
Table 5 are applied, it is possible to construct anactivity utilization index that facilitates the calculationof dose rates in air from different combinations of thethree radionuclides in building materials. This may
then be weighted for the mass proportion of thebuilding materials in a house. The activity utilizationindex is given by the expression

9'

where CK,CR, and C,, are actual values of theactivities per unit mass ofa& 2 2 6 ~ anda 232Th in thebuilding materials considered (Bq kg-*); fK, fRa andf, arc the fractional contributions to the dose rate in
air from the standard or typical concentrations of tbeseradionuclidcs; and w, is the fractional usage of thebuilding materials in the dwelling with the activity
characteristic. For full utilization of typical masonry,
the activity utilization index is unity by definition andis deemed to imply a dosc ratc of 80 nGy h-l. In
Table 7, illustrative examples are given of the use of
the activity utilization index.

52. To estimate the effect of using atypical matcrials,
it is necessary to determine the fractional utilization bymass, identify the associated dose rate and h e n
subtract the corresponding dosc rate for typicalmasonry. Thus, 0.5 utilization of granite would
increase the dose rate by 70 - 40 = 30 nGy h-' and
0.5 utilization of alum shale would increase it by
390 - 40 = 350 nGy hml. One quarter utilization of

42

UNSCMR I

pliosphogypsum would causc an incrc;~sc of
5 0 nGy h", but a siniilar fraction of natural gypsum
would Icad to a dccrcasc of 15 nGy h-l. Bccausc ofthc simplc irradiation gconictry and roui~dcdparamctcr
v;~lucs,this approacll is olily vcry approxiniatc, but
tl~crcis sonic cxpcrimcnhl colifirmation (E31, and i t
docs dcscribc thc circuriislanccs mcntioncd carlicr.
53. In Kcrala, somc of lhc niorc radioactivc strctchcs
of sand havc conccntr;itions of 40K, 2 2 6 ~ anda 232~hof 100, 1,000 and 7,000 By kgs1, rcspcctivcly [L6],
which would Icad, according to the foregoing
formulation, to 5,000 nGy h*' in dwcllings, since
structures thcrc providc litOc shielding against gamma
rays from thc ground. Mcasurcd dosc rates in air in an
carlicr survcy approachcd 4,000 nGy h-', with anarithmctic mcan around 700 riGy h-I for the
population on thc scgnicnt of the coast wilh thc mostradioactivc sand [S6]. Large-scale surface mining andsubscqucnt refilling with monazitc-frce tailings have,
howcvcr, rcduccd lhc cxtcrnal radiation liclds
substantially, e.g.
at somc locations from
4,000 nGy h-I to 300 nGy h-l, and improvements insocio-economic conditions havc rcsultcd in structuralmodifications of thc liulmcr~ts,which havc rcduccd
indoor extcnial radiation cxposurcs by a factor of 3

[P61.
54. Somc of thc short-livcd decay products of ' ? ' ~ n ,always prcscnt in air, cmil gamma rays. A
scmi-empirical analysis for a single-family housc
yicldcd an absorbcd dosc ratc in air of 0.01 nGy h-I
pcr unit activity conccntration of radon progcny atequilibrium cxprcsscd as Bq n1-3 [MlO]. For
20 Bq m-3, a rcprcscntativc activity concentra~ion
indoors, lhc dosc ratc would bc about 0.2 nGy h-l.
which is rclativcly trivial in rclation to dircct gamma
rays from thc building matcrials and the dose tohunian lungs from alpha particlcs cmittcd by thc olhcr
radon progeny. Anolhcr scmi-empirical cstimatc for
gamma rays from radon progcny outdoors yiclded anincrcment of 0.5% pcr Bq m*3over the flucnce rate ofphotons directly from the carth [ N l l ] . For an cquilibrium cquivalcnt concentration outdoors o f 8 Bq rn3,
h i s implies a dosc ratc incrcment of 2 nGy h-l, lhat
is, a fcw pcr ccnt of the prcvailirig dose rale from thc
carlh. Montc Carlo calculations IF121 substantiale
ihcsc cstimatcs.

55. In thc UNSCEAR 1988 Rcport [Ul], a
coefficicl~t of 0.7 Sv G ~ - ' was uscd to convert
absorbcd dosc in air to cffcctivc dosc cquivalcnt. This
rcfcrs to adults and is bascd on an analysis in the
UNSCEAR 1982 Rcport [U3] of cxpcrimcntal andcalculational data on environmental exposure to

gamma rays. A niorc rcccnt asscssmcnt IP19, S12]
providcs cocfficicats for cxposurc to tcrrcstrial gamma
rays no1 only for adults but also for childrcn andinfants. Rcfcrcncc data arc givcn in Tablc 8. Thc
ovcrall V ~ I I U C is 1101altcrcd apprcciably by weighting
for thc typical radiol~uclidccomposition of soil. nrcsc
rcsults wcrc dcrivcd from Monte Carlo calculations formathcniatical phanlorns, tl~oscfor adults bcing bascd
on ICRP Rcfcrcncc Man 1151 and lhosc for the
youngcr pcrsons on computcd tomographic data for
paticnLs. In round tcmis, thcrcfore, thc corivcrsion
cocficicnt of 0.7 Sv G ~ still- seems~
to bc suitablc for
adults P I ] . Bccausc of thc circumstance of
irradiation, it sccnis unlikely that lhe convcrsion
cocfficicnt to cffcctivc dosc would diffcr apprcciably
from h i s value.
56. The assumption has bccn made in previous
UNSCEAR Reports [ U l , U3, U4] that ihc indoor
occupancy factor is 0.8, implying that 20% of time is
spcnt outdoors, on avcragc, around the world. Thcrc is
no way at prcscnt of validating this assumption, but
the indications are that 0.8 is low for industrializedcountries in tcmpcratc climatcs, whcrc an appreciablefraction of tirnc is spcnt indoors in structures other
Iban the home [N2, W31, and high for agriculturalcountries in warm climatcs, whcrc a substantial
fraction of tirnc is spcnt out of doors even at night[ES]. As niorc infomiation bccorncs available, it may
be possible to refine the cstinialc of the occupancy
factor, but at prcscnt thcrc is no basis for changing theconvcrltional value.
57. W i h valucs for the convcrsion cocfficicnt toeffective dosc (0.7 Sv Gy-') arid the occupancy factor(0.8), it is possiblc to conibinc outdoor (57 nGy h-I)
and indoor (80 nGy h'l) exposures to terrestrial
gamma rays to cstimatc the average effcctive dose.
The arilhmctic annual nican worldwide, wcightcd for
population, is 0.46 mSv, somewhat highcr than thevalue for cosmic rays (0.38 mSv), the olher
component of cxtcrrial cxposurc to natural radiation
sources. For childrcn and infanls, the values arc about
10% and 30% highcr.
58. It is of iritcrcst to prcscnt sonic national
estimates of avcragc annual cffcclivt dosc fromterrestrial gamnia rays. This is done in Table 9. The
underlying assumption in each cast h a t thc cffcctivc
dosc cquivalcnt and h c cffcctivc dosc are numericallyIbc samc for this circumstance. Thc valucs rangc from
0.23 to 0.65 mSv, with a mcdian valuc of 0.40 mSv.
The population-wcightcd value for lhcsc 13 counbies
is 0.45 mSv, in agrccmcnt with Ihc rcsult quotcd in
UIC prcvious paragraph.

59. To coniplctc the consideration of thc cxtcrnal
component of natural background cxposurc, lhe doscs

from cxtcrnal irradiation by cnvironmcnlal bcta
particlcs should bc mcntioncd, although thcsc mainly
affcct thc supcrficial tissucs of the body. Calculations
for soil show illat tlic absorbcd dosc rate in air frorn
bcta particlcs is similar at t l ~ csurfacc of thc ground tothat for gamma rays, but that it drops to 20% of thelattcr a t 1 m above the surfacc 104). Furthcrmorc, thedosc throughout the organs of tbc body gcncrally is
about two ordcrs of magnitude lcss than thc dosc lo
the skin. Similar circumstances exist indoors. The
absorbcd dosc rate from airbornc bcta cmittcrs iscomparablc to that from surface emission indoors andabout an order of magnitude lcss outdoors. If theserclationsliips are applicd to the avcragc valucs for theabsorbcd dosc ratcs from gamma rays outdoors andindoors, the annual absorbcd dosc to the skin fronibcta particles is cstimatcd to be about 0.2 mGy
ovcrall. The contribution to dosc from bcta particles
from the surfaccs of particular matcrials, such as thc
mineral sands in Kcrala, would be much more [S7].

60. Aftcr cosmic rays and terrestrial gamma rays, thethird clement of basic background exposure is thatfrom long-lived natural radionuclidcs in the human
body, which arises from inhalation and ingestion.
Potassium-40 and the uranium and thorium series
radionuclidcs arc trcatcd scparatcly. Radon isconsidcred in Chaptcr 111.
61. Data on a~ in the human body are wellcstablishcd, mainly from dircct measurements ofpersons of various ages [IS, U5] but also from theanalysis of post-mortcm spccimcns [F13]. At the ageof 30 years, approximately thc mcdian forindustrialized countries [Ull],thc body content ofpotassium is about 0.18%, at 10 years about 0.2%, andis assumcd to bc thc samc at 1 ycar, these k i n g thc
averages for thc scxcs. Potassium is undcr homeostatic
control in the body, although lhcrc arc disease statesthat affcct thc level. The isotopic abundance of *K is
1.18 lo4. With an average specific activity of
55 Bq kg-' of body wcight and a roundcd conversion
coeficient of 3 pSv a-' pcr Bq k
[N?],thc annual
cffectivc dosc cquivalcnt from K'
in the body is
165 ,pSv for adults, most of the dosc hcing dclivcrcd
by bcta particlcs. The valuc for children is 185 pSv.
62. Doses from radionuclidcs in thc uranium andthorium scrics, on the othcr hand, rcncct intake to thc
body with dict and air. In prcvious Uh'SCEAR
Rcports [Ul, U3, U4, U5], doses wcrc cstimatcd frommeasured activities in tissues and appropriate
dosimctric cocfficicnts, but intakc data were also
provided. In this Annex, intake data are translated tocommitted effcctive doscs for adults and also forchildrcn and infants, so as to indicate the effect ofintakc with agc. Although Lhc dctcmiination of doscfrom conccntrations in tissuc is morc dircct, t l ~ cdata
on iehkc providc a good secondary indication.
63. A rcfcrcncc food corlsuniption profile isprcscntcd in Tablc 10. Ttiis is bascd on thc normalized
avcragc consurnption rate adoptcd by WHO [W-I],
dcrivcd from the food balance shccts cornpilcd by thc
Food and Agriculture Organization (FAO) [F-l].Thcsc
cstimatcs rcfcr to raw, unprcparcd products with noaccount takcn of losscs in distribution and utilization:
conscqucntly, avcragc valucs arc usually ovcrcstimates. Data on food consumption by age arc usuallyobtaincd from ~~utritionalstudies, but bccausc thc
information is rathcr limitcd, rclative rathcr thanabsolutc valucs arc bcst inferrcd [V2]. In Tablc 10,
therefore, the average valucs [W4] arc adoptcd for
adults, and the consumption ratcs for children andinfants arc takcn to be two thirds and onc third of thc
adult values, except for milk products, which arehigher than unity [V2]. Intakcs of water, both directly
and in bcvcragcs, are bascd on rcfcrcnce ICRP watcr
balance data [IS]. Thc tabulated valucs arc compatible
with othcr assessments [C4, N13, Ul]. Thcrc arc, ofcourse, departures from the rcfcrcnce consumption: theChinese dict, for example, is low in milk, the African
dict in leafy vcgetablcs [W4] and the Indian diet inmeat [ R l l ] . Ccrcal consumption, on the othcr hand, ismuch the same in all typcs of dict. The nominal naturcof the data in Table 10 and the rcsulting uncertainties
in the dose estimates must be stressed. Refcrcncc
ICRP breathing rates [Is] are also givcn in Table 10.
64. The next stcp is to establish rcfcrcnce activity
conccntrations in dietary materials and air. Thc valucs
for food and water in Tablc 11 rcly heavily on data
for northcm tcmpcratc latitudcs [F5, L.5, N2, P5, P20,
S13, S14, S44] and arc compatible with data in the
UNSCEAR 1988 Report [Ul]; fish, for which data arescarce and disparate, includcs a 10% admixture of
invcrtcbrates [CS, J7]. All food valucs arc for wct
weight. Rcfercnce concentrations in air in Tablc 11 arc
from thc samc sourccs [F5, L5, N2, UI] and arc
deemed to apply outdoors and indoors.

65. Information on cffectivc dose pcr unit intakc ofactivity of naturally occurring radionuclides by adults
is givcn in Tablc 12 [I4]; it is based on the biokinetic
modcls of ICRP. It is assumcd in this Anncx that thc
doscs pcr unit activity intake for natural radionuclides
are not age-dcpcndcnt.
66. Avcragc age-wcightcd annual intakes byingestion and associatcd cfrcctive doscs have bccn
estimated using thc fractional distribution of adults,
children and infants of 0.65, 0.3 and 0.05, rcspectively; the results are presentcd in Table 13. Thc intake
values are gencrally similar to thosc in thc UNSCEAR
1988 Repon [Ul], allhough the 'lOpo value is44

UNSCEAR 1993 REPORT

somewhat highcr, mainly bccausc fish and, inparticular, invertebrates wcrc included. The dominantradionuclidcs arc 'lOpb and 'lOpo. There is a scarcity
a '"AC [KlO, V7],of cnviron~ncntaldata for 2 3 1 ~ andbut if they wcrc present to the same degree as 2 3 5 ~ ,the overall cffcctivc dosc would he increased byroximatcly 1%. Along the same line, the intakc ofhas becn assumed to be equal to that of 2)2Th.
In fact, the intakc of *'% should bc greater, becauseof some ingrowth of that radionuclide in foodstuffs
following the dccay of = ' ~ a [ L l l ] ; this ingrowqh,
which is difficult to quantify, would result in an
increase in the overall effective dosc of lcss than 2%.

'klh

67. Table 13 includes analogous information forinhalation. The values are similar to those in the
UNSCEAR 1988 Report [UI]. The dominantradioriuclidc is 'lOpb. It may be noted that smokin 10
cigarettes a day would double the intake of 'PO[N2]. The decay products of 2 3 5 would,~
once more,
add about 1%.

B

68. The doscs from reference annual intakes of thelong-lived series radionuclidcs can be compared to theannual doses re-estimated bom the UNSCEAR 1988
Report [ U l ] with the new TCRP tissue weighting
factors [I6]. For uranium and thorium series
radionuclidcs, the effective doses are 6 2 p S v
committcd from annual intake and 130 $3annuallyfrom average body content. For 'OK the same doscs
are 170 and 180pSv, respectively. The total effective
doses are 230pSv by intake and 3 1 0 p S v by bodycontent. The results are fairly consistent and support
the validity of the intake estimation method. The
advantages of this method ovcr that based on postmortem analyses are that there are more data on
activities in foodstuffs than in human tissues and that
it facilitates the estimation of doses Gom high intakesof activity in unusual circumstances. It is recognized,
however, that there are large uncertaintics in thevalues of the dose coefficients, mainly owing to
urlccrtaintics in the values of the gut absorption
fractions (also called I,) for many radionuclidcs. These
uncertainties may arise for a variety of reasons,
including the chemical nature of the radionuclide
ingested, biological variability in humans andextrapolation from animal data when human data aresparse. It would be desirable to carry out morc postmortem analyscs of tissues to determine naturalradionuclide concentrations, as such analyses would
allow a morc dircct assessment of the absorbed doses.
69. Thevariability of activity conccntratiorls in foods
is clearly shown in Table 14, where selected
information on elevated levels is presented. The
reference values can be exceeded by orders ofmagnitude. In the volcanic area of Minas Gerais,
Brazil [A4, A8, L10, V3] and in the mineral sands

area of Kcrala, India [L6], there is evidence of excess
activity in milk, meat and grain, leafy vegetables, roots .
and fruits. In the granitic area of Guandong, China,
excess activity has bccn reported in foodstufk such as
rice and radisl~cs(Z11. Mention might also be madc offie elevated lcvcls of 2 1 0 ~ oin yerba niatC, a plantused to make a beverage in South America [C15]. For
radiological significance, however, the mostpronounced incrcasc over reference levels occurs in
thc Arctic and sub-Arctic regions, where *lOpb and? l O ~accumulateoin flesh of reindeer and caribou [H7,P7],an important part of the diet of the inhabitants of
those regions. Reindeer and caribou feed on lichens,
which accumulate these radionuclides from theatmosphere. If the annual consumption of reindeer andcaribou meat is taken into account [K3], it is possible
to evaluate the effective dose from this intake.
Assuming the reference intakes for other foods andwater apply, the overall dosc from ingestion isestimated to be about 300 ~ S for
V adults. This is one
example of a community exposed under unusual
circumstanccs.
70. Selected information on elevated levels ofactivity concentrations in potable waters is shown in
Table 15 with values for some bottled mineral waters
and ground watcrs. These elevated levels are to becompared with the reference levels presented inTable 11. As with foods, reference values are
exceeded by orders of niagnitude. Bottled waters in
Brazil i~icludc some from areas of high naturalradiation levels [P8]. The results for France [M19,P5,
P9, R12, R13, R14, S l l ] represent all the principal
sources of mineral waters in that country.
Commercially available waters were widely sampled
in Germany [B12, G4, GS]. The selection of Portuguese watcrs was broadly representative [B6]. An
extensive suntey in Sweden of public and privateawater supplies [K4] yielded high lcvcls of 2 2 6 ~ insome wells with an average of 45 mBq kg-' in watcr
from deep-borcd wclls. In Finland, remarkably highconcentrations have becn discovered in wells drilled in
bedrock throughout the south of the country near
Helsinki [SIS]. If allowance is madc for the extra dosefrom these watcrs with othewisc reference intakes, theoverall value of the committcd effective dose becomes
550 pSv for annual intakes by adults. This is anotherexanlplc of a comnlunity with unusual circumstanccs
of exposure.

C. SUMMARY
71. Natural radio~~uclidcs
of significance in soil, air,water and living or anisms include *K and theisotopes of the UZ'
and 2)2Th decay chains.
Exposures occur by external irradiation and frominternal irradiation following ingestion or inhalation of
the radionuclidcs.

ANNEX A: M P O S U R B FROM NATURAL SOURCES 01' RADIATION

e

1i
i

7 2 Thedosc ratc in air outdoors from terrcstrial gamma rays in normal circurnslanccs is around5 7 nGy h-l. National averages range from 24 to
160 nGy 11.'. Soil and survcy data yicld similar valucs.
Con~riiu~iiticsliving on mincral sands may wcll
bc cxposcd at two orders of magnitude more. The
gamma-ray dosc ratc indoors is cstiniatcd to be
80 11Gy h'l. thc population-wcighlcd mcan ofmeasured values worldwidc, and thc rnngc of reported
national averages is 20-190 nGy h-l, These results arc
in accordancc with valucs infcrrcd froni outdoor
mcasurcments and the conccntrations of radionuclidcs
in building materials. Applying a coefficient of 0.7 Sv
G ~ ' ' to convcrt absorbcd dosc ratc in air to cffectivc
dosc and using an indoor occupancy factor of 0.8, theworld-widc averagc annual effective dose fromexternal exposure to tcrrcstrial radionuclides is0.46 mSv.

45

73. Effcctivc doses resulting frorn inlake of naturalradiorluclidcs in air, food and water may bc
dctcrmincd frorr~measured conccntra~ionsin the bodyor cstiniatcd from conccnlralions in intake matcrials.
Thc worldwidc average committed dosc from annual
intakes is cstirnatcd to be 0.23 mSv, of which
0.17mSv is fromand 0.06niSv fromhVariations
radionuclidcs of the 2 3 8 ~and 2 3 2 ~ scrics.
in cxposurcs occur Gom variations in the l a ~ c rcomponcnt. Communities receiving higher cffcctivc
doses include consumcrs of reindcer meat (avcrageannual cffcctivc dose: 0.3 mSv) and consumers ofdeep well water in some locations (average annual
effcctivc dose: 0.5 mSv). Litllc information cxists on
the variability of dose from the inhalation of
long-lived activity in air, but inhalation is dominatedby radon isotopes and thcir short-lived decay products,
which arc the subject of the ncxt Chapter.

111. RADON
74. Exposure to radon is the most significant elcnicnt
of human irradiation by natural sources. It is distinguished from the other thrce elcmcnts of basic
background bccause exposure varies markedly inordinary circumstances and bccause high exposures
may be avoidcd with comparative ease. The mostimportant mechanism of exposure is the inhalation ofthc short-lived decay products of the princi al isotope,
P')72Rn,with indoor air. conccntrations of 2-2Rn and its
progeny are usually higher in indoor air than in
outdoor air: exceptions arc in tropical areas, where
777---Rn concentrations in well-ventilated dwellings arc
essentially the same as in outdoor air.
75. Thcrc are three natural isotopcs of the radioactive element radon: '19Rn (actinon) in the 1 3 5 ~771
scries; 220Rn thoron) in the 232Th scries; --'Rn(radon) in the 'U series. Because of the low activity
conccntrations o~ and ~the short~ half-lifeuof '19~n,this isotope is not significant for human exposure.
Because of its short half-lifc,
is of conccm only
where the concentration of 233Th is high. Owing to ils
relatively long half-life, '22Rn is thc most significast
isotope, and here is much information on it. Table 16
gives the alpha decay properties of "ORn and ?22Rn
and their short-livcd decay products [B7, M I 11.

'I

76. Radon is a noble gas with slight ability to form
compounds under laboratory conditions IS161. The
density of radon is 9.73 g 1-I at 0" C [WS]. There isvery link radon in air, typically about one atom per
10'' atoms of air indoors, and so it does not stratify.
Its solubility in water at 0' C is 510 cm3 1-I dccreasing to 220 m31-I at 2.5' C and 130 cm3 1-I at 50" C.

A. SOURCES AND hlOVEhiENT
1. Production in terrestrial materials

77. The production of 220Rn and 222Rn in terrestrial
materials dc nds on the activity concentrations ofP" a
2 2 8 ~ aand 2 6 6 ~ present
Indicative values for thcse
radium isotopes in soils may be inferred from Table 5.
Some values for rocks, taken from cxtcnsivc analyses[C13, W6], arc given in Tables 17 and 18. On
average, granitcs are high in radium, basalts are low
and sedimentary and mctamorphoscd rocks haveintermediate values. In the main, the results are fairly
consistent with the soil values, although exceptional
valucs of 2 2 6 ~ doa occur in some dctrital sedimentaryrocks [AS].
78. Earth materials may be envisaged as a porous
matrix through which fluids can move. T o bc Gee todo so, radon must first emanate from thc mincral
subslancc into thc pore space. This is brought about
mainly by the rccoil of radon atoms on formation,with a typical range of 20-70 nm in mincrals, and bymolecular diffusion [T4]. Emanation is thought to be
amplified by the superficial disposition of radon
precursors and thc damage caused by radioactive
dccay. The fraction of radon formcd that enters thepores has variously been called thc emanating powcr,
the ratio, the coefficient and thc fraction. Values of theemanation fraction, as it is callcd here, for various
earth and building materials are given in Table 19.
The results relate to '"h and are supported by otherstudies of soils IB13. M20, M211. Relatively little

I

sirnplc masonry structure is cnvisagcd with a volunlc,
V, of 250 n13 and a surfacc arca, S13,of 450 niZ. Thc
ill lcmpcratc
characlcristics broadly reflect corlstnlctio~~climates. An air cxchangc ratc of 1 h-' is postulated.
T l ~ cratc U of radon cntry from thc building clcmcnls(Bq m-3 h-l) is givcn by the cxprcssion

whcrc JD is dcfincd in equatiorl 6). The resulting
valuc of U is almost 10 Bq ms h-'. Without anlasonry floor, the ratc of cntry by diffusion from barccarth would bc about 37 Bq nlm3h*', this bcing
calculated by substituting thc surfacc arca of thc floor,
SE = 100 m2, for SB and 0.026 Bq nl-' s*' for J D incquation (7). An intact concrete floor 0.2 m thickwould. howcvcr, reduce the ratc of cntry by a factor
of about 14 [C7,U I ] to 2.6 Bq m-' h-', which iscomparable to the contribution from such a floor
element.
86. It should be recognized that floors arc unlikely
to be intact and that holcs and cracks greatly facilitate
the entry of radon. The effect of cracks has bccn
modclled in a mathcmatical sense for a stylized pattcrn
of penetrations through a floor clcmcnt ID6, L8]. Wilhan array of 1 cm widc cracks evcry I m through a
0.2 m thick floor and a diffusion coefficient of5
m2 s'l for the underlying carth, the ratc of cntry
by diffusion is about 20% of that from bare carth[D6], implying 7.5 Bq m 3 h-'. which in turn implies
a flux dcnsity, averaged over the wholc floor, of
0.0052 Bq m-2 sel. In thc reference building, thereforc,
1 % discontinuity in thc floor pcrmits 20% diffusionfrom the carth.

I

3. Advection
47. Attention is now turncd to thc forccd advcction(also frcqucntly callcd convcction) of radon from thecarth into a building. This is causcd by the slighlly
ncgativc prcssurc diffcrcnccs (undcrprcssure) thatusually cxist bctwccn rhc indoor and outdoor
atmosphcrcs. Two rncchanisms arc mainly rcsponsiblc,
wind blowing on thc building and hcating insidc thehuilding [N15]. Other mechanisms, such as changcs inbarometric prcssurc and ncgativc prcssurc causcd hy
mechanical ventilation, may also be significant [N14].

dcpcnds on thc l~cmicabilityof Ilic ground and canvary from scconds for sand to wccks for clay IN141.
89. Hcat also crcatcs a prcssurc drop across thc slicllof t t ~ cbuilding with lllc gradicnt towards thc higher
tcmpcraturc. This phcnorncnon, usually called thc
stack cffcct, also draws air through and undcr thc
shcll. Thc drop is proportional to thc tcrnpcraturc
diffcrc~lccs[F7]:for 20" C,it also amounts to a fcw
pascals. In scvcrc climatcs, howcvcr, it would bc
much morc and in tropical climatcs much Icss. Thc
ovcrall cffcct of both rncchanisms is assumcd to n c a t c
a prcssurc difference, Ap, of about 5 Pa [R4].
90. If a masonry floor is intact, advcction from thc
carth cannot takc placc. The prcscncc of cracks in thc
clcmcnt allows advcction, however. and arnathcmatical modcl has bccn uscd to dctcmiinc theinflux of radon [Dg. As with diffusion through cracks[D6], the finite difference mcthod is used to solve
numerically the steady-statc transport equation foradvcction. Apart from Ap, the parameter of prime
importance is the pcrmcability, k, of the subjacentearth material, which varies in valuc through scvcral
orders of magnitude from a low of 10-l6 m2 for fincclay to a high of loa m2 for coarse gravel [Nl4].
91. Application of the modcl to a floor clement withan array, as before, of 1 cm widc cracks cvcry I m ,yields ratios between thc advcctive and diffusive
influxcs for a rangc of permeabilities [W8].
Theseratios vary from about unity at lower pcrmeabilitics toan ordcr of magnitude greater whcn k is about
10-10 m2 and then dcclinc towards unity again at
highcr pcrmcabilities. Extension of the modcl to a barecarth floor yiclds estimates of influx for lowcr andintcnncdiate pcrmeabilitics, but thc method hrcaks
down at higher permeabilitics. Whcn these results arc
applicd to the modcl building for an underprcssurc of
5 Pa, thcy give the flux dcnsitics in Table 20, which
are avcraged over the wholc area of the floor. Thcy
should be compared to thc diffusive flux dcnsitics of
0.0052 Bq m-' s*' for the crackcd floor and0.026 Bq me2 s-I for the barc carth estimatcd carlicr.
Valucs of the flux density similar to thosc shown inthis Tablc would be obtaincd for similar valucs of the
product kAp within the undcrprcssure rangc 1-10 Pa

ID71.

92 Radon cnlry ratcs by advcction arc calculatcd
88. Wind crcatcs a ncgativc prcssurc drop across lhc
shcll of a building. Thc magnitudc of thc drop is
dctcrmincd by thc configuration of thc building andvaries with the square of thc windspccd; in a lightbrcczc, it may hc a fcw pascals [N14]. Outdoor air isthcrcfore drawn inwards through gaps in thc shcll or
lllrough the suhjaccnt carth with radon cntraincd. The
rapidity with which a pressure drop is transmitted

from cquation (7) by again substituting SE = 100 mZ
for SB and by rcplaci~~g
thc diffusive flux dcnsity by
UIC advcctivc valucs in Table 20. Thc outcome is also
shown in Tablc 20. Entry rates vary from zcro for animpermeable floor element, through 10 Bq ms3 h*' fora cracked floor on carth matcrial of low pcrmcability,
to 274 Bq m-3 h-' for a bare floor of fairly highpcrmcability. The decline in rates at the highcr

pcmicahilities is due to the dcplction of radon in thecarth near thc walls of the building by tllc passage offrcsll air ID7,W8]. If an intcm~cdiatcpcmmcability of
10' 11 m2 for sandy-silty eardl nlatcrial is deemed to be
typical and accordant with Ore diffusion coefficient
adopted earlier, it bccomcs clear from the Table andfrom the earlier paragraphs that advcction is likely todominate over diffusion as a source of radon inbuildillgs under common circumstances.
93. It is possible to cstiniatc an upper value of thecntry rate by advection from Uie earth in a simple
manner if the fraction 4 is known of the air exchange
rate for the building that takes place through the earth.
It is given by the expressionu = +h[(C,, f ~ ) / ~ l(8)where h, is the air exchange rate (1 h-l) and the othersymbols represent the same quantities as before withthe same values. The terms in brackets refer to theradon concentration in equilibrium with radium at
depth in the earth; their conjoint value is about
5 l o 4 Bq m-3. A value of 0.02% for 41 would yield an
cntry rate of 10 Bq m9 h-' for the model building andthus match the contribution by diffusion Gom thebuilding elements. Values of 4 two orders ofmagnitude greater may be realized [S21] for solid
floors on the earth, sometimes called slab on grade.
This simple analysis does not, however, take into
account the depletion of radon near the surface of thecarth.
94. It must be stressed that entry by advection isquite dependent on the configuration of the floor andthat any estimate of an illustrative value is quite
uncertain. Even for Ule simple slab on grade of themodel building, smctural details and the nature of theunderfill make estimating difficult. For suspended
floors, entry is severcly influenced by the degree towhich the living space is dccoupled from the earth.
For buildings w i h basements, the difficulty is
cornpounded by the extensive area of contact between
the structural elemen& and the backfill or earth. Much
still remains to be done to clarify these issucs [GlO,
H15, M22, N16, R4], and it must be realized h a t
reliable cstimates of indoor radon concentrations are
best oblained from measurements of radon in air.

4.

Infiltration

95. Fresh air entcrs a building through open doors,
windows and ventilators and lhrough inadvertent gaps
in the superficial shell. Although che term infiltration
properly refers to thc passage of air through small
openings, it is used here to describe the overall degreeof direct exchange between outdoor and indoor air.

Ou~sidcair brings with it radon, usually at a low
conccntration.
of radon outdoors are detcrmincd
96. Co~~centmtions
by the flux density from the carch and by dispersion in
lhc atmosphere; both are affected by mctcorologicalconditions. There arc pronounced diurnal variations,mainly because of changes in atmospheric stability,and pronou~rcedseasonal variations, mainly bccause ofchanges in patterns of air mass circulation. Water
masses such as lakes and oceans make a negligible
contribution to the atmospheric inventory of radon[N17]. On the basis of exhalation data, NCRP IN21
estimated the average outdoor concentration overcontinents to be 8 Bq m 3 . Hourly measurements over
several years at an inland and a coastal site in the
United States yieldcd average values of 8 and4 Bq m-3 [F8], respectively, but successive quarterly
measurements with integratin devices nationwide at
50 sites gave 15 Bq m'[H16]. Year-longmeasurements with integrating detectors throughout
the United Kingdom gave a population-weighted
average of 4 Bq m 3 [W3]. Integrating devices
dcployed in an urban area of Japan also yielded aycar-long average of about 4 Bq m j , with seasonalvariations from 2.6 to 6.1 Bq m-3 m23]. Summertime
measurements across Canada gave 11 Bq m-3 in theeastern provinces and 56 Bq m'3 in the prairie
provinces, which were particularly dry and where thelevels were reduced by a factor of 5 in the following
summer [Gll]. Protracted measurements in France
showed 60 Bq m'3 in sedimentary regions, withmarked temporal and spatial variations throughout thecountry [R15]. Whereas a tentative estimate of
5 Bq m 3 was made for the population-weighted
parameter worldwide in the UNSCEAR 1988 Report[Ul], thc developing evidence, especially forcontinental as opposed to island air, suggests that it isprobably closer to 10 Bq m-3.
97. With a direct air exchange rate, &, of 1 h-' andan outdoor concentration, X , of 10 Bq m-3, the rate ofentry of radon to the reference building by infiltrationis che product of the two values, 10 Bq m-3 h-l.

5. Transfer from water and natural gas
98. As noted earlier, radon is soluble in water. It
follows that water supplies bring radon indoors andthat some dc-emanation of the water occurs, thus
contributing to the radon entry rate, sometimes to an
appreciable degree. Concentrations of radon in water
vary markedly. Supplies may be ciassiCied broadly as
surface water, groundwater or well water. As shownin Table 21, radon concentrations in these classes
differ by an order of magnitude, and utilization also
varies considerably [N18,05]. Surface waters with thelcast radon but tllc grcatcst variability in conccntration[HS. H(j, NlS] arc uscd ttlc most. Tllc wcigl~trd
avcragc of t11c radon conccntrations for thc rcfcrc~icc
sct of supplics is sorncwl~nta b v c 10,000 Bq 111-~but
not unlikc drc cstimatc for dlc U ~ ~ i t cStatcsdIC8]. IIIllrc UNSCEAR 1988 Rcport [ U l 1, a rcfcrcncc value of
1,000 Bq mJ was adoptcd, but i t was notcd thatcountries such as Finland and Swcdcn had
population-wcightcd avcragcs of ovcr 30.000 Bq m-3[K4,SlS]. Con~prchcnsivcsunrcys of wcll watcr froni
southcrn Finlalid yicldcd a nicdian concc~ltrationof
210,000 Bq mm3 and isolatcd values approaching
50 MBq rn-3 [J8]. It is assurncd in tllis Anncx U~attheworldwide avcragc conccntration of radon in watcr is
10,000 ~q m-3.
99. Radon is slowly rcmovcd froni still watcr bymolccular diffusion, but agitation and hcating cause
watcr to dc-emanate rapidly and transfcr thc gas to thc
indoor air. The transfer factor for buildings, dcfincd as
the ratio of thc conccntrations of radon in water andair, has bcen dctcrmincd both cxperimcntally andanalytically. Values arc distributcd log-normally, but
the avcragc is about loJ. For 10,000 Bq nle3 in water,
Lhis iniplics 1 Bq m'3 in air; for an air cxchange rateof 1 h" this implics a radon cntry ratc of
1 l3q m-3'h-1 to the modcl building.
100. In thc intcrcst of coniplctcncss, natural gas is
mcntioncd as a potcnlial source of radon. It contains
various concentrations of the radioactivc species,
dctcrmincd mainly by the geology of thc gas field andthe dclay in transniission to the user. When it isburncd indoors, the radon is rclcascd. In the
UNSCEAR 1988 Rcport [ U l ] , an cntry ratc of
0.3 Bq m4 h-I to the niodcl building \sfas dccnicd
appropriate. This estimate still seems to rcniain valid.

6.

(a)

Entry rates

Radon

101. Radon cntry ratcs for the modcl building aresummarizcd in Tablc 22, and the relative importanccof thc various sourccs of radon in a tcmpcratc climate
is illustraicd. It will bc recognizcd from thc prcccding
text that thc sclcction of illustrativc valucs is rathcr
arbitrary, sincc i t dcpcnds on thc valucs choscn for theof thcparamctcrs that dctcrnli~lc the sig~~ificancc
various nicchanisms of cntry. Ncvcrthclcss, thc overallcntry ratc is not grcatly at variance with that infcrrcd
from radon mcasurcmcnts in many buildings in
tcmpcratc cli~natcs.With a contribution of ovcr 5096,
mostly from forccd advcction through discontinuitits
in thc floor, radon cntry from the suhjaccnt carthdominates ovcr all othcr sourccs. Diffusion from thebuilding clcnicnts is also impor~ant, as is theinfiltration of outdoor air, but Lhc othcr sourccs are

rclativcly unimportant. Tablc 22 focuscs atrcntion on
thc importancc of advcction in such typicalcircumstanccs; dlc tcxt cltiphasizcs its importancc in
atypical circumstanccs whcrc high radon lcvcls occur
indoors. In tall blocks of dwellings, howcvcr, thc carlh
contribution would virtually disaplxar thc ovcrall entry
ratc would at lcast be halvcd, and UIC pcrccntagcs
would bc altcrcd accordingly.

102. If a building with dimensions similar to those ofthc model but of non-masonry construction iscnvisagcd for a tropical cliniatc, i t is possible tocstilnatc the entry ratc of radon by crudcly adjusting
the data in Tablc 22. Diffusion froni building elemcnts
virtually disappears, but diffusion from the subjaccnt
earth may contributc 37 Bq mJ h-' because board
floors would riot appreciably inipcdc the ingrcss ofradon. Advcctiori from the earth may also disappear
with calm air, balanced tcmpcraturc and highventilation. On rhc other hand, thc contribution frominfiltration would increase twofold, to 20 Bq m 3 h-',with a direct air exchange rate of 2 h-l. The othermechanisms would rcmain unimportant. Overall,therefore, thc cntry ratc of radon under suchconditions should not be much different from that in
Tablc 22, although the individual pcrcentagcs wouldchange.

(b) Thoron
103. There is lcss information on cntry ratcs of tboron
into buildings. Since the precursors of 2 2 0 ~ nand
799---Rn have about equal activities in car& and building
materials (see Tablcs 5, 6, 17 and 18), thc ratcs atwhich the two isotopes arc produccd are also about
equal. It is usually assurned that thc emanation fractionis the same for cach.
104. By definition, the diffusion coeficient is thesamc for both isotopcs, so the diffusive flux dcnsity in
tcrnls of activity is proportional lo thc square root of
the dccay constants (0.0126 s-I for thoron and2.1 1 0 ' ~i1for radon) implying a value 77 times
highcr for thoron. The measured values for thoron.
about 1 Bq m-? s-l from earth materials and0.05 Bq m-? s-l from building matcrials [ D l l , F6,
N19, S19, S36, U3], rcflccl h i s ratio, although thcrc
is considerable variability in tbc value.
105. As Tor advcction, the flux dcnsity should, inprinciple, bc thc same for both isotopcs in matcrials
with the same pcmicability, if all Ule atoms producedarc forccd to thc surface [N19]. Ovcrall, ale ratc of
cntry of thoron into a building with unfinished walls
and floors is likcly to apprcciably exceed that ofradon. However, owing to ils short half-lifc of 55
scconds, only thc superficial layers ofwalls and floors
contributc to thc rate of cntry of thoron into a

U N S C M R 1993 REPORT

50

building, so that covering the floors and walls withplastic materials, tilcs or paint is likely to rcducc the
ratc of entry of thoron by at lcast an order ofmagnitude. This cffcct was indircctly demonstrated inJapan, where indoor nicasurcnicnts generally detectedhigh concentrations of thoron (up to 400 Bq m-3) ncar
unfinished soil walls, but no thoron ncar walls coveredby plastic or by paint [D2].
106. From the rclativeiy few measurements of thoron
outdoors (N19, S23, U3] it would appear that activity
concentrations of thoron at or very ncar the surface ofthe earth exceed those of radon. As altitude increases,
however, the situation reverses because of the disparity
in decay constants. A representative value of
10 Bq rn-3 might be chosen for head height, which isthe same as the value adopted earlier for radon. Wilha direct exchange ratc between outdoor and indoor airof 1 he1, the ratc of entry to the model building byinfiltration is also about 10 Bq mm3h-l.
107. The avcrage rate of entry of thoron to a building
from all mechanisms is crudely estimated in thisAnnex to be siniilar to that of radon, i.e. about
5 0 Bq mJ h-l. This estimate is highly uncertain.

B.

EXTOSURE

1. Indoor collcentrutions
(8)

Radon

108. It is possible to estirnatc the activity
concentration x (Bq m-3) for the modcl building fromthe expression

x = Ul(%

+

Ah)

(9)

where the symbols refer to quantities defincd
prcviously. With U (the radon entry rate) =49 Bq rn-3 h.' (Table 22)= 1 h-l and Ah =0.00756 h-', the value of x is 48.6 Bq
In roundterms, therefore, one would gcnerally e x p e a radon gas
concentrations of about 5 0 Bq m') in masonrybuildings in temperate climatcs and 30 Bq m-3 intropical timber buildings. Witb horon, however, thedecay constant of 45.4 h-l, rather than the air
exchange rate, determines the conccntration: for U =5 0 Bq m-3 h-', x = 1 Bq m-3 of thoron gas. It should
bc noted that the indoor radon and thoron
conccntrations calculated from cquation 9 represent
averages throughout the building. Because of its shorthalf-life, thoron does not bcconle uniformly
distributed. Strong gradients of thoron concentration
have been prcdictcd and observed according to
distance from h e wall [D2, D9, K151. In any case,because of the large uncertainties in the estimation of
the rate of cntry of thoron into buildings, it is notrecommended to use equation 9 to predict thc indoor
lhoron concentration: it is better to rely on direct
measurcmcnts of indoor concentration^, discussed in
Section 1Il.B.l .b.
109. It is now appropriate to compare expectation
with observation. Although most large survcys are ofradon gas concentration, x b , some surveys havc been
conduc~cdof the decay products. The parameter ofintercst in the latter case is the equilibrium equivalentconccntration (EEC) of radon xE and the twoquantities are related through the equ$ibrium factor F,
defincd by the expression.
where X E ~is 0 . 1 0 5 ~ +~ 0 . 5 1 5 ~+~ 0 . 3 8 0 ~ ~Thesymbols x l ,andrepresent the activity'%b and 2 1 4 ~ ithe; constantsconccntrations of'181'o,are the fractional contributions of each decay productto the total potential alpha energy from the decay ofunit activity of the gas [I7]. By analogy, theequilibrium equivalent concentration of thoron is 0.913+ 0.087 x2, where x1 and x2 now represent theactivity concentrations of 2 1 2 ~ band 2 1 2 ~ i .

x-,

x1

110. Many surveys havc been made during the last
decade of radon concentrations in dwellings. An
extensive compilation was included in the UNSCEAR
1988 Report [Ul]; it is updated hcrc by the
infomiation in Table 23. Data arc now available for 35
countries representing almost two thirds of the world
population. The list is not comprehensive: somescattered observations for other countries are omitted,
and summary results for a few countries withadvanced radon prograniincs may. not have been
available. The purpose here is not to record all suchdata, but to select information that is representative of
the various countries. The distribution of the survey
data of Table 23 is illustrated in Figure IV.
111. Whereas early surveys were based on discrctc
sampling of radon decay products, usually called grab
sampling, because it lastcd a maner of minutes,
surveys of substance are now made by sampling radongas for extended periods of time, several days forcharcoal detectors and several months for track etchdetectors. Mass surveys of radon decay products are
not feasible because the equipment and humanresources required to conduct them would be very
costly.
112. A satisfactory national survey might be definedas one in which measurements of adequate quality are
made throughout a year in the living and sleeping
rooms of a stratified sample of at least 1 in 10,000 of
the housing stock. Not many surveys meet thesecriteria. Some are not large enough: many arc made in
the rooms with the highest radon levels: some are

A N N M A: M P O S U W S FROM NAllJRALSOURCES 01: ~ U I I A I I O N

51

biascd to arcas of the country with high radonconccntrations: most do not follow a statistical dcsign.
As a rcsult, any cstimatc of a rcprcscntativc or typicalworld valuc is quite uncertain. Distributions of radonconccntrations arc usually rcportcd as being
log-normal, although dcparturcs arc somctimcs sccn.
Arithmetic mcans arc frcqucntly citcd or may be
calculated from the gconictric mcan and standard
deviation. Extrcme values are often givcn.

to-outdoor radon conccntration from low latitudcs(23" N) to temperate latitudcs (40" N) has been
observed in China [P21]. However, Figurc V, where
the avcragc indoor radon concentrations from Tablc 23
are plottcd against the latitude of the countries or themain population centres, shows a considerable scattcr,
as well as some avcrage indoor radon conccntrations
at high latitudcs that are similar to those at low
latitudcs.

113. Owing to the large populations of China andIndia, the rcsults for these countries wcigh heavily inthc cstimation of a worldwide radon concentration.
Definitive national surveys have not yet bcci~
conducted, but the population-weighted mcan ofsomewhat disparate and developing data for China[ClO, R5, U1, 221 is about 20 Bq m 3 [P21].
Exploratory data for India [S37], pending thecompletion of a national survcy, suggest an arithmetic
mean of 57 Bq ~ n ' with~ , lower values in cities suchas Bombay P I 2 1 and higher values in cities such as
Nagpur [S24] and an equilibrium factor approaching
0.4 [S25]. A national residential radon survey [M24,
0 1 0 , U12] recently completed in the United Statesyielded an arithmetic mcan of 46 Bq m'3, which isconsistent with the outcome of a structured survcy inthe state of New York [ P l l ] .

116. Thc different results of radon concentrations withlatitude may be due to local geology, atmosphericconditions or building design. Local geology andatmospheric conditions may result in outdoor radonlevels that arc high in low latitudcs and low in highlatitudes. For example, the average outdoor radon concentration measured in Bangkok [C23] is 40 Bq mJ,
while that in the United Kingdom is 4 Bq mh3 [W3].
Such a difference alters the indoor-to-outdoor
concentration ratio for most dwellings. Also, thesharply contrasted rainy and dry seasons in tropicalareas may influence the annual avcrage of the indoor
radon concentration in a manner that is not clearly
understood. Finally, the design of traditional subSaharan houses explains the relatively high radon
concentrations in that region [06].

114. Rcsults from scvcral studies in southern Europe
have become available. Generally radon values arelowcr than in northern Europe: for example, only 3 . 2 1of the 244 Spanish dwellings invcstigatcd in Madridand Barcelona cxcecdcd 200 Bq m-3 [GI]; only about
20% were above 100 Bq n1-3 in a Turkish survey of
400 houscs in Istanbul [K14]; and about 5% ofPortugucsc dwcllings had avcrage radon conccntrations
in exccss of 200 Bq m-3 [F14]. Howcvcr, in Italy theuse of natural building materials (tuffs, pozzuolana)
with clcvatcd 2 3 8 ~activity conccntrations ranging up
to 400 Bq kg" can result in elcvatcd indoor radonlcvcls in the arcas conccrncd (arithmetic avcragc:
93 Bq m-3 [B16]). Frcqucntly, scasonal changes arc
sccn to have a pronounced cffcct on indoor radonconccntrations in southcrn climates, with wintcr valucs
up to 80% higher than corresponding summer valucs[B16, GI].

115. Little information is available for large parts ofAfrica and for tropical regions in the Amcricas, Asiaand Oceania. For well-ventilated buildings, indoor andoutdoor radon conccntrations should be essentiallyequal; thus, indoor radon levels should be lower intropical arcas than in temperate arcas if the outdoor
radon concentrations arc similar (M12, S251. The
limited rcsults available for Egypt and Thailand [C23,HI81 show that, for wcll-vcntilatcd buildings intropical areas, indoor radon concentrations areapproximately equal to those measured outdoors;furthermore, a gradual increase in the ratio of indoor-

117. In the UNSCEAR 1988 Report [Ul], a population-weighted value of 40 Bq m-3 was adoptcd for thearithmetic mean worldwide. This value still appears to
be representative. Given the gross uncertainty in thisvalue and the climatic complications, the degree ofagreement with the estimate for the model building isprobably more coincidental than conclusive. It is clearthat additional rcsearch and measurcmcnts are neededin tropical areas in order to estimate more accurately
the worldwide average of indoor radon concentration.
It is hoped that more data from countries at low
latitudcs will become available from a radon survey
programme that is being initiated by IAEA [S22].
118. Because of the trcnd away from tbc measurementof radon decay products, thcre is no new informationof substance on the value of the equilibrium factor F
indoors; it is taken, as before, to be 0.4 [Ul].The
position is much the same for outdoor air; the previous
value of 0.8 is also adoptcd here. In terms of equilibrium cquivalcnt concentration, therefore, tbe worldwide values of the arithmetic mean, populationweighted, are about 16 Bq m-3 indoors and 8 Bq m-3
outdoors.
119. For h e major surveys in tempcratc climates, thevalue of the geometric standard deviation is typically
2.5. This may be somewhat high for tropical climates,
but any adjustment would be arbitrary, and so it isconsidcred to be generally valid. The arithmetic mcanof the radon gas concentration is 40 Bq mJ, and thegcomctric mcan is about 26 Bq
Tbc corrcsponding valucs of thc cquilibriurn cquivalcnt conccntrationarc 16 Bq m-3 indoors (arithmetic mcan) and10 Bq mJ (gcomctric mcan Estimates of lllc 98th
122. Exposurc to radon, thorori and thcir progcny
pcrcc~~tilcsarc 200 Bq In'
for thc radon gas
comcs ~ n a i ~ ~froml y thc inhalation of the dccay
conccntration and 80 Bq I T I - ~ for thc cquilibriuni
products of radon and thoron, which dcposit
cquivalcnt conccntration. It can thus bc suggcstcd that
inhomogcncously within the human respiratory tract
about 2% of dwcllings worldwidc may haveand irradiatc thc bronchial cpithclium. Compared withconccntrations in cxccss of tlicsc valucs. Furtiler, about
0.02% of dwcllings may bc i n cxccss of 800 Bq n ~ - ~ . the lung dosc from inhaled dccay products, thc dosc
contribution from the inhalcd radon (or thoron) gas
Cor~ccntrations far in cxccss of 800 Bq me3 arc,
itself, which is solublc in body fluids arid tissucs, ishowcvcr. frequently rcportcd in thc literature: values
small undcr normal conditions of cxposurc. The twomorc than an ordcr of magnitude grcatcr arc
contributio~ls to the annual cffcctivc dosc arc
somctimcs cncountcrcd, which may rcflcct theconsidcrcd i n turn.
possibility of positivc divcrgcncc from a log-normal
distribution at highcr conccntrations [N20]. Compctcnt
123. Convcrsion coefficients rclating average annual
authorities who havc considcrcd the effccts of humanconccntrations to effcctivc dose eq~i\~alcntwere
cxposure to radon in homcs arc generally agrccd on
prcsentcd in the UNSCEAR 1988 Report [Ul] forthc desirability of taking action at conccntrations
radon and thoron progeny. These wcre based mainly
cxcccding 400 Bq me3 (081; worldwide, a few homcs
on a comprehensive report on lung dosimetry
in a thousand probably cxcccd that lcvcl. Rcmcdial
publisl~cdin 1983 IN211 and ollicr carlicr analyscs [I7,mcasurcs in thosc houses will rcduce thc nurnbcr ofJ3]. Parallel and later developments wcre recognized,
pcrsons exposcd to high doscs from thc inhalation of
however. that pointed to the need for a re-evaluation
radon progeny but it will not change significantly theof the radon dosimetry [J4, N17, V4].
averagc Icvcls.

120. Limited information on tiloron conccntrations has
bccn rcportcd sincc thc publication of thc UNSCEAR
1988 Rc ort [Ul]. A rcprcscntativc valuc of
10 Bq mS was adopted earlier for thoron gas inoutdoor air. Equilibrium cquivalcnt conccntrations ofabout 0.1 Bq mJ havc bccn adoptcd clscwhcrc [N2,
N19, N7-0 ,somcwhat lowcr than thc prcvious valuc of
0.2 Bq m' [Ul]. Estiniatcs of the gas conccntrationindoors point to arourld 3 Bq m-3 [N20, S231, andlimitcd sunlcys of thc equilibrium cquivalcnt
conccntration [C16, D8, G9, M14, M E , N19, P21,
Rl, S9-3, Ti', W3], takcn togcthcr, indicatc about
0.3 Bq m-3, again sonlcwhat lowcr than thc p r ~ \ ~ i o u svaluc of 0.5 Bq m.3 [Ul]. Thcrc is considcrablc
uncertainty in thcsc figurcs, pointing lo a nccd forsyslcmatic mcasurcmcnts.

5(c)Average concentrutions

121. Thc foregoing cstimatcs of thc conccntrations ofradon and thoron in outdoor and indoor air arc
summarized in Table 24. Both the gas and equilibrium
cquivalcnt valucs arc givcn. They arc intcndcd torcprcscnt thc population-wcightcd arithnictic means
worldwidc. hut i l is llcccssary to bear in riii~ld thatconsiderable unccrlainty attachcs to thcni, niainly
because of the gcncral paucity of data for thoron andsomc gcographical bias in the origins of the radon
data. They arc, ncvcrthclcss, robust and round enoughto allow calculating thc radiation doscs from inhalation
for thc gas and dccay products.

124. Dose to lung tissues depends, among othcr
things, on thc fraction f of the total potential alphacncrgy associatcd with t i c mixture of dccay products
not attachcd to the ambicnt acrosol [N21]; as the valucof fp increases, so does the dosc. Values from 0.04 toabout 0.20 havc becn found in scvcral dwellings in the
United Kingdom [JS, S271. A similar range wasdetermined in several Norwegian dwcllings [S28]. Fora Japancsc dwelling, howcvcr, thc range was 0.031 to
0.064, with an arithmetic mcan of 0.043 [K6],rcflccting pcrhaps the diffcrcnt lifestyle [HS].In
Gcrniany, thc arithmetic mcan for many rooms
without additional aerosol sourccs was 0.096, whcrcas
for a fcw with cigarette sniokc it was 0.006 and foroutside air, about 0.02 [R9]. A study in a test dwellingin Germany yicldcd valucs around 0.1, but ranging
below 0.01 as a result of smoking [RlO]. A rcvicw ofthese arid othcr data lcads to a valuc of around 0.1[P16]. Furthcr results rcvcal 0.077 [H21] and 0.20
IS461 for singlc-family dwcllings and 0.086 as anaverage for five dwellings [T13]. Such valucs may becontrastcd with thosc from 0.02 to 0.03. adoptcd
prcviously for dosimctric purposcs 118, N21, Ul]; they
appear to bc about three tinics grcatcr indoors, thc
implication being that the cquivalcnt dosc to thc
bronchial cpid~cliurnmight bc sonicwl~atlargcr thanprcviously cstirnatcd [ J l l 1.

125. Thc ralc of attachment of radon dccay products
to the ambicnt aerosol increases as the acrosol
concentration increases [P12]. Wilh othcr acrosol
conditions constant, therefore, a highcr aerosol

A N N M A: FXPOSURFS FROM NK!

co~~ccntration
Incans a lowcr valuc of f and a lowcr
Pdosc. 111dwellings, thc aerosol conccntration generally
inrre:iscs as t l ~ c infiltration ratc of outside air
dccrcascs, wit11 thc rcsult that t l ~ cvalues of fP anddose also decrcasc. For a givcn conccntration of gas at
a fixcd value of f , thc dosc incrcascs as the value ofthc rcpilibriuni Pactor F incrcascs; tlic valuc of F,
Iiowevcr, incrcascs with tlccrcasing infiltration rate.
The cffccts of fp and F on dosc, with other acrosol
conditions constint, arc thercforc countcrhalanccd.
126. Concurrcnt mcasurcmclits of f and F [JS, P13,P
R9, R10, S Z ] dcnionstrate that values or fP arencgativcly corrclatcd with values of F. Concurrent
mcasurcnicnts of dccay product concentrations,
infil~ration rates and sizc distributions of ambient
acrosols in rooms [V4, V5] and t l ~ cusc of a roommodel [PI41 to cstimatc the valuc of the unattachedfraction also substantiatcd the invcrse relationshipbctwecn fP and F [P16]. Further caiculations of doses
to lung tissues with two rcfcrence dosimetry models
IN211 showed that the gas conccntration was an
adcquatc indicator of effective dose equivalent; aconversion cocfficicnt of around 50 pSv a-'
pcr Bq m'3 of radon gas was dccnicd appropriate[V5]. A similar conclusion had been reached in an
carlier asscssmcnt [J5] and was supported by a later
analysis [Hg]. On the other hand, a more recent
asscssnicnt indicates that the cocfficicnt may bearound 25 pSv a-' pcr Bq m-3 [JlO]. Given the
preponderance of radon gas mcasuremcnts as opposed
to dccay product measurcmcnts in surveys ofdwellings, there is some merit and much convcnicnce
in applying such a conversion cocfficicnt directly tothe rcsults, but unanimity is lacking on thc mostappropriatc valuc to use.
127. The dosimctry of radon and decay products is
undcr revicw to account for Ihc introduction of the
ncw ICRP recommendations 116) and to dcvelop a new
dosimctric model for thc rcspiratory tract [B2].
Dosimctrists arc considcring ncw physical informationon the indoor acrosol, ncw insights into the regional
scnsitivity of thc rcspiratory tract and the new tissuc
weighting factors.
128. For the purposcs of this Anncx, it seems
reasonable to licep the dosc cocfficicnts that wcrc
adopted in Ihc UNSCEAR 1988 Rcport. In that
Rcport, an indoor exposurc to radon at a concentrationof 40 Bq m-3 was estimatcd to corrcspond to anannual effcctivc dose cquivalcnt of 1.0 mSv as a resultof thc irradiation of tissues of the rcspiratory tract by
the radon progcny. This is numerically equivalent toan cffcctive dose coefficient of 25 pSv a-' per Bq m-3
of radon gas for indoor exposurc, assuming an
occupancy factor of 0.8 (7,000 hours spent indoors ina year), or to 3.6 nSv per Bq h m-3 of radon gas.

129. When thc cffcctivc dosc cocfficicnt is cxprcsscd
in tcrrns of cquilibriuni cquivalc~~tconccntraticln (EEC)of radon, the rcsult is siig11LIy diffcrcnt from h a t
adopted in thc UNSCEAR 1988 Rcport, bccausc tlle
EEC of radoti is csti~natcd in Uiis Anricx to bc
16 Bq m-3 instcad of 15 Bq xu3, as in thc carlicr
Rcport, thc radon gas concentrations bcing thc same.
Exprcsscd in tcrms of the EEC of radon, the cffcctivc
dose cocfficicnt is found to bc 3.6 x 40 z 16 = 9 nSv
per Bq h mq3 for EEC of radon instead of 10 nSv per
Bq h m-3, as in the UNSCEAR 1985 Rcport. The
value 9 nSv per Bq h mJ for EEC of radon is also
uscd in this Anncx to estimate cffcctive doses resulting Goni Ihc inhalation of radon progcny outdoors.
130. It is convcnicnt at this point to considcr thc
doses from thc inhalation of radon gas in somewhat
more dctail. Since the gas is soluble in body fluids andtissues, it is transported throughout thc body. Dosesarc dclivcrcd from the dccay of the gas itsclf and theshort-lived dccay products. Equivalent dose ratcs tosome tissues of interest from constant inhalation of thegases at concentrations of 1 Bq m4 arc 1.2 nSv h-' infat, 0.75 nSv h-' in lungs and 0.094 nSv h-' in bonc
marrow from radon and 0.004 nSv h-' in fat,0.58 nSv h-' in lungs and 0.039 nSv h-' in bonemarrow from thoron [J3]. The effcctivc dose ratcs are
0.17 nSv h-' from radon and 0.11 nSv h-' fromthoron. The resulting annual cffcctive doses pcr unit
conccntration in air are 1.5 pSv pcr Bq m 3 of radonand 0.96 @v per Bq m-3 of thoron. Thcsc values aresupported by a more recent asscssmcnt [P15]. The
rclativcly high dosc rate from radon in fatty tissue isduc to h e high solubility of radon. In an carlicr
investigation [HlO], thc distinction was madc bchvccn
fatty and normal marrow; thc ratio of the dosc rates
was about 5. From thesc dose cocfficients it may be
estimated that the equivalent dose to the marrow fromthe worldwidc avcragc valuc of radon and thoron isabout 0.03 mSv a-', an order of magnitude less thanthe cquivalcnt dosc from cosmic rays.
131. The dose coefficients corresponding to thc
inhalation of the thoron progcny arc lakcn to be thc
samc as those adoptcd in thc UNSCEAR 1988 Rcport,
namely 10 nSv pcr Bq h n13 for outdoor exposurc and3 2 nSv per Bq 1 m-3 for indoor exposurc.
132. The effcctivc dose coefficients rclatcd to theinhalation of radon gas, thoron gas, radon progeny andthoron progcny arc summarized in Tablc 24. Annual
effective doses corresponding to the worldwidc
average concentrations are estimated from thosecffcctive dosc coefficients, assuming avcragc
occupancy factors of 0.2 for outdoors and 0.8 forindoors: the results are includcd in Tdble 24. The
average annual effective dose from inhalation of radonand its progeny is estimated to bc 1200pSv, whilc thedose from thoron and its progeny is about 70 pSv.

ANNEX A: MPOSURES FROM NATURAL SOURCES Or: W I A T I O N

inforn~ation has since been published. Collective
effective doscs comniittcd froni almosphcric discharges of radioactive materials arc estimated using
the crudc models dcscribcd in the UNSCEAR 1982
Report [U3].
138. In order to allow their comparison with the doses
from natural radiation background, the annual per
caput effective doscs resulting from the extraction andprocessing of earth materials have been estimated. In
doing so, crude assun~ptionshave bccri r~ladcabout the
dynamics of the dosc rate and ihc duration of thepractice considered. It is emphasized that all estimatcs
of dosc rcsulting from the extraction and processing ofearth materials are fraught with large uncertainties.

A'

PRoDUCT1oN'OAL139. The world production of coal, expressed in coalequivalent for cnergy purposes, was 3.1 x 10'' kg in
1985, the main producers bcing China, the republics of
the Comer Soviet Union and the United States [U13].
A large fraction of the coal extracted from the earth isburned in electric power stations; about 3 x lo9 kg ofcoal is required to produce 1 GW a of electricalenergy. In the UNSCEAR 1982 Report [U3], theCommittee estimated the avcrage concentrations of%.,' 3 8 ~and 232Th in coal to be 50, 20, 20 Bq kg-',
respectively. based on the analysis of coal samples
from 15 countries, and noted that the concentrations
varied by more than two orders of magnitude. The
rcsults of an extensive survey of coal from China,
which produces 20% of the world's total, point lo
conecntrations that are a rcciably higher: 104,36 and30 Bq kg-' for "K, U"'
and 2 3 2 ~ ,rcspectively[P22]. The higher concentrations of naturalradionuclides in coal froni China do not result in
substantial increases in the worldwide averages, which
are little more than educated guesses, but they doallow a better assessment of the doses due to the usesof coal in China. Radiation exposures occur throughout the fucl cycle, which consists of coal mining, theuse of coal and the use of fucl ash.

1. Coal mining
1 4 . Members of the public arc exposed to the radon
present in the exhaust air of coal mines. Since there
are currently no measured data on the emission ofradon from coal mines, the Committee, in the
UNSCEAR 1988 Report [Ul], used two different, very
crude approaches to esdmaling the annual rcleases ofradon from coal mining all over the world; the figuresobtained were 30 and 800 TBq. leading to collective
effective doses per year of practice of 0.5 and
10 man Sv, respeclively. Dividing by the world

55

population of 5.3 109 yields an annual per caput
effcctivc dose of 0.1-2 nSv.
2.

Use of col~l141. Thcrc arc vast diffecrcnccs in the rclativc use ofcoal in various countries. I n the OECD countries,
which account for about one third of Ule world's coalproduction, 68% of the coal produced is burned inelectric power stations, 30% in coke ovens and otherindustrial operations and 2% in dwellings [U13]. In
China, 25% of the coal produced is burned in electric
power stations, 59% in other industries and 16% in
dwellings p23]. Assuming that the usage distributionof coal in China is reprcsc~ltativeof the distribution incountries that are not n~enlbers of the OECD, theaverage worldwide usage of coal is as follows: about
40% is burned in electric power stations, 10% in
dwellings and 50% in other industries. When coal isburnt, the naturally occurring radionuclides arc
redistributed from underground into the biosphere. The
resultant doses from burning coal in power stations
and in dwellings are considered bclow. There is notenough information on the releases of radionuclides
from burning coal in other industries to assess this useof coal.
(a)

Coal-fired power plants

142. Coal is burned in furnaces operating at up to
1,700" C in order to produce electrical energy. In the
combustion process, most of the mineral matter in thecoal is fused into a vitrified ash. A portion of theheavier ash, together with incompletely burned organic
matter, drops to Ihe bottom of the furnace as b o n o ~ n
ash or slag. The lighter fly ash, however, is carriedthrough the boiler, together with the hot flue gases andany volatilized mineral compounds, to Ihe stack,where, depending on the efficiency of emission control
devices, most is collected while the rest (escaping flyasb) is released to tbe atmosphere. Owing mainly tothe elinlination of the organic content of the coal,
there is approximately an order of magnitudeenhancement of the concenlrations from coal to ash.
Consequently, the natural radionuclide concentrationsin ash and slag from coal-fired power stations arc
significantly higher than thc corresponding
concentrations in thc carth's m s t . Arithmetic averagesof the reported concentrations in escapin
fly 240
ash are265 Bq k g ' for "K, 200 Bq kg-' for ' 'u,B
kg-' for 2 - 6 ~ a 930,
B kg-' for 'l0pb, 1,700 Bq kgfor "OPO, 70 Bq kg' for ='Th, 110 Bq kg-' for"% and 130 Bq kg-' for 2 2 8 ~ a([U3], Annex C,
paragraph 11).

3

9143. The amounls of natural radioriuclides discharged
to the atmosphere from a power plant depend on anumber of factors such as the concentrations in coal,

56

UNSCWR 1993 REPORT

the ash contcnt of thc coal, thc tcnipcraturc of
hctwccn bottom ash andconihustion, thc parlilio~~ing
fly as11 and thc cfficicncy of thc cn~ission control
dcvicc. 111 thc UNSCEAR 1988 Rcport ( U l ] , thc
Coniniittcc cstirnalctl tllc :IIII~UIII.S of radioactivc
matcrials discharged lo thc atmosphcrc for typical old
and modcn~plants. Tllc r c s ~ting~ l noniializcd collcctivc
cffcrtivc doscs wcrc G and 0.5 man Sv (GW a)-' fortypical old arid n~odcrnplank, rcspcctivcly. Data from
China indici~tc that bccausc of highcr-than-avcragc
conccntrations of natural radionuclidcs in coal,rclativcly low filtcr cfficic~~cics(90%) and highpopulation dcnsitics around UIC plants, thc nornializcd
collcc~ivccffcctivc doscs arising from atrnosphcricrclcascs of radioactivc matcrials from plants thcrc isapproxirnatcly 50 man Sv (GW a)-' [P22]. Assuming
that, worldwidc, onc third of the clcctrical cncrgy
produced by coal-fircd powcr plants is from modcrn
plants, with anothcr third from old plants and thc
rcmaining third from plants with charactcristics similar
to thosc in China, thc avcragc normalized collective
cffcctivc dosc is 20 man Sv (GW a)-'.
144. According to thc dose asscssmcnt methodology
uscd in thc UNSCEAR 1988 Rcport, about 70% of thecffcctivc dosc resulting from atrnosphcric rclcascs ofnatural radionuclidcs from old plants is due to theinhalation of long-livcd radior~uclidcs as thc cloud
passes. Thc rcmaindcr of thc cffcctivc dose is due to
cxtcrnal irradiation from radionuclidcs dcposited on
thc ground and to the ingcstion of foodstuffs
contaniinatcd by radionuclidcs dcpositcd on the
ground. It is assumcd that thc dcposited activity
becomcs unavailable to thc vcgctation, with a meanlifc of 100 ycars for all thc natural long-livcd
radionuclidcs. On thc wholc, the cffcctive dose perunit release is dclivcrcd at a ratc that decrcases slowly
over a ccntury or so.
145. Assuming lflat (a) 3 1012 kg of coal is produced
in a ycar; (b) 4 0 4 of the coal production is burncd inclcclric powcr stations; and (c) 3 lo9 kg of coal isrcquircd to produce 1 GW a of clcctrical cnergy, theannual elcc~ricalcncrgy produccd by burning coalworldu,idc is 400 G W a. Thc collcctivc cfI-cctive dose
per ycar of practicc is thcrcforc cstimatcd to be
20 man Sv (GW a)-' x 400 GW a = 8,000 man SV.
146. Crudc assumptions arc necessary to derive theannual pcr caput cffcctivc dosc from thc collcctivc
cffcctivc dosc pcr ycar of practicc. If it is assumcd
that similar amounts of radioactivc materials havebccn rclcased into thc atmospl~crcby coal-fired powcr
plants ycar aftcr ycar for thc last ccntury or so, thenthc collcctivc cffcctivc dosc pcr ycar of practicc would
be approxirnatcly equal to the annual collcctive
effective dose. I n fact, coal has bccn used for about a
ccntury to produce electrical cncrgy, but informationis lacking regarding the niagnitudc of thc
cnvironmcntal rclcascs during that tinic. Givcn thc
largc unccrlainty associated with thc cstiniatc of thc
collcc~ivccffcctivc dosc pcr ycar of practicc, it isassumcd in this AIIIICXthat thc annual collcctivc
cffcctivc dosc has thc samc nunicrical valuc as thc
collcctivc cffcctivc dosc pcr ycar of practicc. Thc
annual pcr caput cffcctivc dosc is obtaincd by dividing
thc annual collcctivc cffcctivc dosc (8,000 Inan Sv) by
thc currcnt world population (5.3 lo9); the rcsult isabout 2 pSv.
(b) Domestic use
147. Anothcr significant use of coal is for domcstic
cooking and hcating. No information has becn foundin the litcraturc on thc cnvironmcntal discharges ofnatural radionuclidcs from this source. Thc usc of coalfor cooking or hcating in privatc houscs may,
howcver, bc cstiniatcd to rcsult in high collcctivc
doses since chimncys arc not cquippcd with ash
removal systems and the population dcnsitics aroundsources of cmission arc generally high.
148. Assuming that thc conccntrations in smoke arc
cqual to thosc in coal and that 3 5 % of thc coal isemitted as smoke, the annual worldwidc atrnosphcricreleases caused by thc domcstic burning of coal are
cstimatcd to be 0.7 TBq ofand 0.3 TBq of cachof the radiol~uclidcsof the 2 3 8 ~and 2 3 2 ~ hseries(radon and thoron cxccptcd); these figurcs becomc 20
timcs grcater if it is assumcd that thc conccntrations insmoke are cqual to thosc in ash and that the coalburned has a 5% ash contcnt. Taking thc average
population dcnsitics around thc houses to bc l d km-?
leads to collcctivc cffcctive doscs committed fromycarly worldwidc usc of coal in b e range of 2,00040,000 man Sv. This cstiniatc is highly uncertain, as
it is not supported by any dischargc or environmental
data.
149. It is assumcd that thc annual collcctivc cffcctivc
dosc to thc world's population is in the samc rangc as
thc collcctivc cffcctive dosc pcr ycar of practicc(2,000-40,000 man Sv). It follows that the annual pcr
caput cffcctivc dosc attribu~ablcto thc usc of coal fordomcstic cooking and hcating would bc 0.4-8 fiv.
3.

Use of fuel ash

150. Largc quantities of coal ash (fly ash and bottom
ash combined) are produccd each ycar throughout theworld. I n thc UNSCEAR 1988 Rcport [ U l ] , theCommittee cstirnatcd that about 280 million tonnes ofcoal ash arc produced annually in coal-fired powcr
stations. Coal ash is used in a varicty of applications,the largcst of which is thc nianufaclurc of ccnicnt andconcrcte. It is also uscd as a road stabilizer, as road

A N N M A: EXI'OSIJUFS FROM NATURAI. SOURCES 01: RADIATION

57

fill, in asphalt mix and as fcrtilizcr. Data on thc
various uscs of coal ash in scvcral countrics have bccn
rcportcd [G8]. Ahout 5% of thc total ash production
from coal-buniing powcr stations is uscd for lhc
construction of dwcllings: this rcprcscnts an annual
usagc of 14 niillion ~ouncs.

natural radionuclidcs in thesc matcrials, thc aniountc
rclcascd and thc rcsullanl doscs arc considcrcd in thisScc~ion.

151. Froni thc radiological paint of vicw, thc usc ofcoal ash in building rnatcrials, which may affcct
indoor doscs from cxtcrnal irradiation and thc
inhalation of radon decay products, is the mostsignificant. With rcspcct to cxtcrnal irradiation, thc
Committcc cstinlatcd in thc UNSCEAR 1988 Rcport,on thc basis of mcasurcmcnts madc by Strandcn [S47j,
that thc usc of concrctc containing fly ash forconstructing dwcllings would rcsult in additional
annual cffcctivc doscs of 70 pSv and 30 $3 in
concrctc and woodcn houscs, rcspcctivcly. Taking thc
amount of fly ash concrctc to bc 1.3 tonncs in awooden house and 4 tonncs in a concrctc building andassuming that an avcragc of four pcrsons live in eachhousc and that thc lifctirnc of the housc is 50 years,
thc collcctive cffcctivc dosc arising from cxtcrnal
irradiation attributable to thc annual use of fly ash forconstructing thc dwcllings is cstimatcd to bc about
50,000 man Sv.

155. Oil has a largc numbcr of fucl applications, t l ~ cmost important bcing for road transport vchiclcs, forthe gcncration of clcctrical cncrgy and for dorncstic
hcating. Approximately 3 x 10" kg of crudc
pctrolcum is produccd in thc world annually. In powcr
plants, about 2 x l o 9 kg of oil is nccdcd to producc
1 GW a of clcctrical cncrgy. As thc ash content of oil
is very low, oil-fircd powcr plants arc usually not
cquippcd with cfficicnt ash rcmoval systcms. On thc
basis of limited mcasurcmcnts, Ihc Committcc in thc
UNSCEAR 1988 Rcport cstiniatcd that the amounts ofradioactive matcrials discharged from oil-fircd powcr
plants arc similar to thosc from coal-fired powcr plants
fittcd with efficicnt aerosol control devices; theresulting collcctivc cffcctivc dosc is about 0.5 man Sv(GW a).'. About half of thc cffcctivc dosc resultsfrom inhalation during passagc of the cloud and thc
othcr half from cxtcrnal and intcrnal irradiation Iiom
dcpositcd activity. Assuming that 15% of thc
worldwidc production of c r ~ d cpctrolcum is burncd inclectric powcr plants, thc collcctivc cffcctivc dosc pcr
ycar of practice is about 100 nian Sv. The annual
collcctivc cffcctivc dose is tcntativcly estimated to be
50 man Sv, corresponding to an annual pcr caput
cffcctivc dosc of 10 nSv.

152. The annual collcctivc cffcclivc dosc to theworld's population dcpcnds on thc numbcr of dwellings built with connctc containing coal ash during thc
last 50 ycars. Assuming that thc practice of building
dwcllings with conactc containing coal ash bcgan 25
ycars ago and that 14 nlillion tonnes of coal ash havc
bccn uscd each ycar for that purposc, the annual
collcctive cffcctivc dosc to thc world's populationfrom cxtcrnal irradiation from that sourcc is half thecollcctivc cffcctivc dosc pcr ycar of practicc, or
25.000 man Sv. Thc corrcsponding annual pcr caput
effective dosc is 5 pSv.
153. Thcrc arc conflicting vicws on thc inlpact of theusc of fly ash on thc dosc Gom inhalation of radondccay products. According to sonic investigators, thc
indoor dose should bc highcr in a housc with fly ash
concrctc than in a housc built with ordinary concrctc[B4,S451; according to othcr invcstigalors [S47], theindoor dosc should bc lowcr, while ariothcr groupconcludcd that thcrc should not be any significant
changc [U14, V9]. In this Annex, as in thc UNSCEAR
1988 Rcport, it is assumcd that thc usc of fly ash inbuilding matcrials docs not rcsult in any additional
dosc duc to tbc inhalation of radon dccay products.

B. OTHER ENERGY 1'ROI)IlCTION
154. In addition to the use of coal in powcr plants togcncratc clcctrical encrgy, othcr mincrals, including
oil, pcat and natural gas, as wcll as geothcrmallyhcatcd water, arc also used for this purpose. Thc

1. Oil

2.

I'ent

156. Pcat is burncd to produce cncrgy in scvcral
countrics, notably in Finland and Swcdcn [C14].
Concentrations of natural radionuclidcs in pcat arc
usuatly similar to thosc in coal, but relatively highconccntrations have bccn found to occur. In the
UNSCEAR 1988 Rcport, thc Committcc tcntativcly
estimatcd the normalized collcclivc cffcctive dosc due
to atmospheric rcleases from pcat-fircd powtr plants
to bc 2 man Sv (GW a).'. Sincc no information has
bccn madc availablc to thc Committcc on thc
worldwidc production of elcctrical cncrgy by burningpcat, thc collcctivc cffcctivc dosc pcr ycar of practicehas not bccn cstimatcd.
3. Nuturul gas

157. Likc oil, natural gas has many applications. The
main ones arc domcstic hcating, the gencration ofelectrical cncrgy and as a source of heat in various
industries. The annual worldwidc production of natural
gas is about 1012 m3. Radon concentrations in natural
gas at the wcll may vary widcly around a typical valueof 1 kBq me3. Owing to radioactive dccay during

58

UNSCEARtransfcr and storagc. tlic radon conccntrations at theplant should bc snlallcr; ill thc absence of data.
howcvcr, 110 dccrrasc lias I~ccnassun~cd.Sincc about
2 x lo9 n13 of natural gas nlust l,c burncd to producc
1 GW a of clcctrical cncrgy, thc corrcsporiding radon
cmission is approxirnatcly 2 TBq and Uic normalized
collcctivc cffcctivc dosc is 0.03 nlan Sv (GW a)-'.
Assuming that 15% of thc world production of natural
gas is burncd in clcctric powcr plants, thc collcctivc
effcclivc dosc pcr ycar of practicc is about 3 man Sv.
The annual collcctivc cflcctivc dosc has the same
valuc, lcading to an annual pcr caput cffcctive dose ofabout 1 nSv.

4.

Geothermal energy

158. Gcothcrmal cncrgy is produccd in Iccland, Italy,
Japan, New Zcaland, tbc Russian Federation and theUnitcd States. Gcothcrmal cncrgy makcs use of hot
steam or watcr dcrivcd from high-tcmpcrature rocks
dccp inside the earth. Most of the activity found ingeotbcrn1al fluids is duc to thc uranium decay chain.
Isotopcs of solid clcmcnts may occur in rclcascd watcr
or land-fill, but only radon, which is rclcascd into theatmosphcrc when tbc water or stcam contacts thc air,is considcrcd hcrc. From mcasurcmcnts in Italy and in
the Unitcd Statcs, thc Committcc, in the UNSCEAR
1988 Report, cstimatcd thc avcragc discharge of radon
pcr unit cncrgy gcncratcd to bc 150 TBq (GW a)-' andtbc corresponding collcctivc cffcctivc dose to bc
2 man Sv (GW a)-'. Sincc the annual production ofelectrical energy by gcothcnnal cncrgy is about
1.5 GW a, thc annual worldwide production ofgeothermal cncrgy would yicld an annual collcctivc
effcctive dose of approxirnatcly 3 man Sv and anannual per caput cffcctivc dosc of about 1 nSv.

C. USE OF I'HOSI'HATE ROCK

159. Phosphate rock is the starting material for tbe
production of all phosphate products and is thc main
source of phosphorus for fcrtilizcrs. It can be of
scdimcntary, volcanic or biological origin. The world
production of phosphatc rock was about 130 million
tonnes in 1982, thc main producers being China,
Morocco, tbc formcr Sovict Union and tbe United
Statcs. conccntrations of natural. radionuclidcs inphosphate rock wcrc rcvicwcd in tlic UNSCEAR 1977
and 1982 Rcports [U3, U4j. Concentrations of 232Th
and @I( in phosphate rocks of all types are similar toihosc obscrvcd normallyin soil, whereas
conccntrations of 2 3 8 ~and its decay products tcnd tobe elevated in phosphate deposits of sedimentary~ sedimentary
origin. A typical concentration of 2 3 8 inphosphate deposits is 1,500 Bq kg-'. Uranium-238 andits decay products are gencrally found in close
radioactive equilibrium in phosphate ore.

160. Exposures of mcmbcrs of the public rcsult from
cfflucnt discharges of radionuclidcs of the 2 3 8 ~decay
series into thc environment from ptiosphate rockmining arid proccssing; from Uic use of ptiosphate
fcrtiliiicrs; and from thc use of by-products andwastcs.

1. I'hosphate processing operations
161. Phosptiatc proccssing operations can be dividcd
into thc mining and milling of phosphate ore and thc
manufacture of phosphate products by either the wet
process or the thcrmal proccss. Wet-process plants
produce phosphoric acid, the starting material forammonium phosphate and triple supcrphosphatc
fertilizers: in h a t process, phosphogypsum is produced
as waste or by-product Thermal process plants
produce clemcntal phosphorus, which is in turn usedprimarily for the produc~ionof high-grade phosphoricacid, phosphate-based detergents and organic
chemicals. Waste and by-products of the thermal
process are slag and ferrophosphorus.
162. In thc UNSCEAR 1988 Report [Ul], theCommittee cstimatcd the collcctivc cffcctivc dose fromone ycar of dischargc of radioactive materials into theatmosplierc by phosphatc industrial facilities aroundthe world to bc about 60 mall SV. Maximum annual
individual effective doses wcre estimated to be about
40pSv in tbc vicinity of an elcmental phosphorus
plant in the Ncthcrlands, while cquivalcnt doses in thelungs for individuals near six elemental phosphorus
plants in the Unitcd Statcs wcrc calculated to range
from 0.05 to 6 mSv.
163. Collective effective doses resulting fromdischarges into surface watcrs secm to be more
important than those from atmospheric releases. In the
Netherlands, all phosphogypsum produccd by fertilizer
plants (2 million tonncs per ycar) is dischargcd intoh e Rhinc [K16]; lhcsc annual discharges, whichcontain about 0.4 TBq of 2 3 8 ~ ,2 TBq of
0.7 TBq of 2 1 0 ~ andb 2 TBq of 2 1 0 ~ owcre,
cstimatcd
to result in maximum annual individual cffcctive dosesof 150,uSv and in a collcctivc cffcclive dosc of
170 man Sv per ycar to tbc Dutch population via theingestion of seafood, 'lOpo being thc main contributor
to the dose [K16]. In Spain, about 0.4 million tonncs
per year of phosphogypsurn produccd in a phosphoricacid and fcrtilizer plant is dischargcd into the estuaryof thc Tinto and Odicl rivcrs IC17j; Uic annual
effective dosc to thc critical group is cstimatcd to bc
60 pSv, thc main pathway to man bcing tbc consumption of fish and crustacea [C17]. In France, over
3 million tonnes of phosphogypsun~has been dumped
into the Seine estuary [ P l ] , but tbe corresponding
radiation exposures have not been cstimatcd.

2.

Use of phosphate fertilizers

164. Thc conccntrations of natural radionuclides inphosphate fcrtilizcrs wcrc reviewed in the UNSCEAR
1982 Report. For a givcn radionuclide and type of
fcrtilizcr, the conccntrations vary markedly from one
country to anothcr, depending on the origin of thc
andcorn oncnts. Generally, the conccntrations ofof 2gTb and its decay products are always low, andthc conccntrations of the radionuclides of thc 2 3 8 ~decay series arc 5-50 times higher than in normal soil.
Typical values arc 4,000 and 1,000 Bq per kg P2O5
Lor 2 3 8 ~and 2 2 6 ~ arespectively.
,
The annual worldconsumption of phosphate fertilizers is about
30 million tonnes of P205. The worldwide use ofphosphate fertilizers constitutes one of the mostimportant sources of mobile 2 2 6 ~ ina the environment[JbI.
165. The amounts of fertilizer applicd annually in the
Unitcd States have bcen reported to range from about
30 kg P205 per hectare for barley, wheat and oats toabout 150 kg P2O5 pcr hectare for potatoes andtobacco [N4]. The annual application of phosphatc
fertilizers re rescnts less than 1 % of the normal soil
content of z'U. Assuming an accumulation in the soil
during the past 100 ycars, the mean additional
absorbed dose in air above fertilized fields is about
1 nGy h-l, a small fraction of the normal natural
background from tcrrcstrial sourccs of about
60 nGy h". Small additional doses also occur fromthe ingestion of foodstuffs grown on fcrtilizcd
agricultural land. In the UNSCEAR 1988 Report [Ul],the collective effective dose resulting from theworldwide use of phosphatc fcrtili7ers during one year
was rough1y estirnatcd to bc 10,000 nian Sv. Given tile
long duration of the practice at approximately thesame rate, the numerical value of the annual collective
dose is taken to be the same; the annual per caput
cffcctive dose would be about 2 ,uSv.

I

3.

Use of by-products

166. The main by-products of phosphate industrial
activities are phosphogypsum in wet-process fertilizer
plants and calcium silicate slags in thermal process
plants. Phosphogypsum currcntly has scvenlcommercial applications in the Unitcd Statcs, including(a) as a fertilizer and conditioner for soils wherc
peanuts and a variety of othcr crops are grown: @) asa back-fill and road-base material in roadway andparking lot construction; (c) as an additive to concreteand concrete blocks; (d) in mine reclamation and (e)..
in the recovery of s"lphur [C12]. The amount ofphosphogypsum currently uscd for the above purposesin the United States represents about 5% of the total
amount produced [C12]. In Europe and Japan,
phosphogypsum has bcen used exterrsively in cement,

wallboard and other building materials. Significant
radiation exposures may occur if such by-products arc
uscd in the building industry.
167. Large quantitics of phosphogypsum (about
100 million tonl~cspcr ycar) arc produccd in wctroccss phosphoric acid plank. The concentration of
q26Ra. which dcpcnds on the origin or ihc hosphatc
ore proccsscd, is typically about 900 Bq kg- . Most of
tile pl~osphogypsumis considered waste and is either
storcd in ponds or stacks or discharged into thc
aquatic cnvironmcnt.

P

168. Phosphogypsum is used to some extent in h ebuilding industry as a substitute for natural gypsum inthe manufacture of cement, wallboard and plaster.
O'Riordan ct al. [Ol] cstimated the additional dosesthat would be received by the occupants of aresidential building in which 4.2 tonnes of by-productgypsum would have replaced thc cstablishcd materials.
The additional absorbed dose rate in air from cxtcrnal
irradiation was estimated to be 0.07 pGy h-', while theannual effective dose from inhalation of radon progeny
was assessed at 0.6 mSv. Similar values of the annual
effective dose from inhalation of radon progeny wcrc
estimated by O'Brien el al. [02]. If it is assumed that
5% of the by-product gypsum is used as building
material in dwellings, on average four persons live ineach dwelling, and the mean life of a dwelling is
50 years, the collective cffective doses resulting fromone year of worldwide use of phospho ypsum in thebuilding industry are estirnatcd to be 10 man Sv fromexternal irradiation and 2 lo5 man Sv from h cinhalation of radon progeny. These estimates arehighly uncertain and need to be confirmed bymeasurements in dwellings that have bccn constructedusing known amounts of phosphogypsum.

B

169. The practice of using phosphogypsum in building
matcrials is at lcast 50 ycars old [Fg], but informationis lacking on the amounts that have becn used. If it isassumed that 5% of the currcnt annual production(about 100 million tonncs) has becn used in building
matcrials in each of the last 50 ycars, it is found that60 million houses of the currcnt housing stock,
sheltering about 5% of thc world's population, have
phosphogypsum included in thcir building matcrials.
However, this figure seems to be too high. If it isinstead assumed that 1% of the world's population
livcs in dwellings that include phosphogypsum in theirbuilding matcrials, the annual collective cffective doseis cstimated to be 5 lo4 man Sv. Dividing by theworld's population of 5.3 lo9 yiclds a per caput
annual cfrective dose of about 10 ~ S V .
170. Calcium silicate slag may bc uscd as acomponent of concrete. Mcasurcd conccntrations inslag samples range from 1,300 to 2,200 Bq kg-' of
2 2 6 ~ a[ B l l , M261. Results from an indoor survey
indicate that the gamma absorbed dose rate in air canU N S C U R 1993 REPORT

CObc as high as 0.3pGy h-I above background in
dwellings constructed of concTctc slabs containing
43% hy wcight slag I R l l ] . In a similar survcy carricd
out in Canada, absorbcd dosc ratcs of up to
0.2 pGy 11.' wcrc obtaincd [M26].

I).

MINING AND hfll.I,ING
OF hIINERAI, SANDS

171. Mincral sands, also callcd hcavy mincrals, arc
dcfincd as Ihosc sands that have a spccific gravity
abovc 2.9. They originate froni crodcd inland rocks,
traccs of which wcrc subscqucntly transported bysurfacc watcrs towards the sea, whcrc thcy wcre
depositcd by thc combincd action of wind, waves andsca currents. Thcsc mincral sands nlay occur undcr
watcr, forni part of sca, be part of thc duncs or occur
inland within a fcw tcns of kilomctrcs of the coast[K17]. Countries where rnincral sands are mincd
includc Australia, Bangladcsb, Indonesia, Malaysia,
Thailand and Vict-Nam.
172. Eithcr dry mining or drcdging techniques are
cmploycd in the mining of mincral sands deposits. The
hcavy mincrals are cxtractcd from the ore in two
stagcs. In tile first stage, a hcavy rnincral concentrateis cxtractcd in a wct. gravity separation process. In asccond stage, individual minerals arc scparatcd fromthc hcavy rnincral conccntratc by rncans of dry
clcctrostatic and magnctic tcchniqucs.

173. Thc hcavy mincrals of major commercial
importance are ilmcnite (FeO-TiOz), altcrcd ilmcnite,
callcd icucoxcne (FezO3-TiO?), rutilc (TiO?), zircon(ZrSi04), monazite [a rare carth phosphatc (CcP04
YP04)] and, to a lcsscr cxtcnt, xcnotimc [a yttrium
phos hatc (YF'04)]. Typical conccntrations of 7 3 2 ~andin Australian hcavy rnincral sands, which arc
prcscr~tcd in Tablc 25, are rnuch grcatcr than the\vorldwide avcragc conccntrations in soils and rocks[K17].
174. Hcavy mincrals have numcrous applications. The
titanifcrous mincrals, once thcy have bcen processed
into titanium oxide ViO,), arc uscd as a pigmcnt inpaints, papcr, plastics, cosmetics and ccramics. Rutile
is made into titanium mctal and thcn uscd, forcxaniplc, in aircraft frames and jct cngincs. Zircon,
and thc associated mincrals zirconia and zirconium, is
uscd in Ihc production of ccraniics, refractory, foundry
and abrasivc matcrials, catalysts, paints, fucl cladding
and structural matcrials in nuclear rcactors. Monazite
and xcnotimc rare earth niincrals arc uscd, forcxamplc, in the clcctronics, illumination and glassmaking industries, in the production of magnets,
supcrcor~ductors and ceramics and as chcmical
calalysts and alloying agents in metallurgy lK17j.

175. Infonnation on exposures of membcrs of tllc
public rcsulti~~gfrom thc niining and milling of
mincral sands is cxtrcnicly scarce. In an asscssmcnt ofan Australian p l ; ~ ~ ~ncrnbcrs~t,of the public who
workcd on a propcrty adjaccnt to thc plant sitc wcrc
cstiniatcd to rcccivc a dosc slightly grcatcr than
1 niSv ael, attribulablc mainly to cxtcrnal irradiatio~~from hcavy ~nincralsspillcd on the propcrty [A9].
Away from thc sitc, the main contribution to thc dosc
rcccivcd by mcmbcrs of the public results fiom thc
inhalation of dust from thc plant; the highest doscs
were cstimatcd to bc about 0.25 mSv as' for fivc
persons localcd 1.5-2 km from thc plant [A9].If thc
management of UIC plant is aware of the radiation
impact of mincral sands and takes measures to control
heir emission, Lhc doscs will bc much lower. In a
study of potcntial radiation doscs arising from a
proposcd mincral sand minc and processing plant inAustralia, i t was shown that doscs to the critical group
could bc as low as a fcwr ,uSv a-' [H19].

176. Thc extraction and processing of carth matcrials
expose the gcncral public to additional naturalradiation when thc carth matcrials, or their induslrial
products or by-products, contain above-avcragc
conccntrations of naturally occurring radionuclidcs.
Since vcry little information is available to asscss
thosc additional cxposurcs, the related dosc cstirnatcs
arc highly uncertain.
177. Somc of those carth matcrials (coal, oil, pcatetc.) arc uscd to produce elcctrical cncrgy by nonnuclear nicans. I t is cstimatcd that the production of
1 GW a of clcctrical energy results in collcctivc
effective doscs of 20 man Sv from thc use of coal,
2 man Sv froni UIC use of peal and geothermal watcr
or stcam, 0.5 nlarl Sv from thc use of oil and 0.03
man Sv from thc use of natural gas (Tablc 26). Taking
into account tllc worldwidc production of clcctricalenergy i n coal-fircd powcr plants, tbc corresponding
annual per caput cffcctive dose is about 2pSv. Annual
per caput effective doses fiom other non-nuclcar
rncans of electrical cncrgy production are much lowcr(Table 27).
178. Mineral sands, dcfincd as thosc sands witb a
specific gravity grcatcr than 2.9, usually cxhibit
conccntrations of 2 3 2 ~ hand 2 3 8 ~that arc much
grcatcr than the worldwidc avcrage conccntrations insoils and rocks. Information on cxposures of mcn~bcrsof the public resulting Gom the mining and milling of
mincral san,ds is cxtrcmely scarce; annual effective
doses rcccivcd by critical groups may be about 1 mSv.
Annual per caput cffcctive doscs have not been
estimatcd.

ANNIX I\: F.,,POSURIi!iI'UOM NATURAL SOURCES 01:RADIATION

179. Thc highcst ar111uii1pcr mput cffccti\'c doscs totllc lwl~lic frnm t l ~ c c t r i c
irldustrics arc
csti~n;ltcd to rcsull from tl~cusc of pl~osphalchyproducts by thc h u i l d i ~ ~ i~ldustryg(10 /tSv), thc
do~ncstic usc of coal for cooking and hcating(0.4-8pSv), thc usc of coal ash in building r~latcrials

61(5 /IS\!) and thc usc of pl~ospha~c
fcrtili~crs(2 ~ t S v ) .
Thc i~nnual per caput cffcc.ti~cdosc cstimatcs arc
sun~mari;rcdin Tablc 27. Thc ovcrall annual pcr caput
cffcctivc dosc arising from cllc cxtraction andproccssing of carth matcrials is cstimatcd to be about
20 /tSv.

CONCLUSIONS
1PO. Natural sourccs of ionizing radiation pcrvade
the cnvironmcnt and causc cxposurcs to all humanbcings. Thcrc arc four main componcnts of thcsc
cxposurcs: cosmic rays, tcrrcstrial gamma rays,
ingcstcd or irlhalcd long-lived radionuclidcs andirihalcd radon isotopes. The first thrcc may bc said toform thc basic natural radiation background becausc ofthc rclative constancy of cxposurc. Exposures to radonand its dccay products are much more widely variable.
Radon gas diffuscs from soils and building matcrials
upon thc dccay of tracc Icvcls of radium h a t are
naturally prcscnt. Thc Ic\rcls of radon can build up,
particularly in indoor closcd spaccs.
181. Doscs from natural sourccs of radiation havebccn cvaluatcd for general, worldwide gcographic andgeological conditions that rcsult ia normal doscs andfor urlusual or atypical conditions that rcsult inincrcascd doscs. Thc estimates of dosc arc for adults
or for an agc-wcightcd population if thc doses tochildrcn and infants arc significantly diffcrcnt.
182. The avcragc annual cffcctivc doscs worldwide
for cach of thc four componcnls of natural cxposurc
arc summarized in Tablc 28. For tbc thrcc basic
componcnts, thc annual value is 1 .I mSv. Thc inhalation of radon and thoron prngcny rcsulb in an avcr-

age annual cffcctivc dosc of 1.3 mSv. Thc ovcrall
avcragc annual cffcctivc dosc is found to bc 2.4 mSv.
Small changcs havc bccn madc in thc various
componcnts of the cffcctive dosc; ho\vcvcr, thc
compcnsatory cffcct of thcsc changcs is such that thc
total rcmains the same as in thc UNSCEAR 1988
Rcport.
183. The importance of the inhalation of radon
progcny is apparent from Tablc 28. It is the singlc
most significant mechanism of human cxposurc tonatural radiation in tcrms of both the avcragc dosc andthc spread of doses. In middle and high latitudes, it isalso the most amenable to control by building design,
matcrials sclcction and ventilation: However, in low
latitudcs. little control can be ~xerciscdwhen outdoor
and indoor atnlosphcres are not much different.
184. Radiation exposures resulting from ~ h cxtractioncand processing of carth matcrials have also bccn
considcrcd. Thcsc cxposurcs are rclativcly small in
con~parisonwith thc ovcrall cxposurc Gom natural
sourccs of ionizing radiation. Thc avcrage annual
cffccti\~cdose worldwidc arising from the cxtraction
and processing of earth matcrials is cstimatcd to beabout 20 pSv. Bccausc data rclatcd to those cxposurcs
arc scarcc, this dosc cstirnatc is highly uncertain.

UNSCFAR 1993 REPORT

62

Name

Claw

M a r (Me19

Mcan life (2)Principal nunie of decay

926.2
939.5

Stable1.01 ~dSublc
p + c- + V~

139.6
134.9
493.7
497.7
497.7

255 10"1.78 10.'~
1.23 lod
0.91 lv10
5.7 1 0 . ~r + v,

2 2 10"StablcStableStablec' + u, + vp
StaMc
StableStableStableStableIlndmnaNwlcons

ProtonScutron

Muoru

P~on

(P)
(n)
( ~ 9

(~9

e
l

Lon

6)
(q

Y+Y

r + v,
X + X

I~ptonr
Mwn
Electron
Neutrino

105.6
0.51 1
0
0

Cr9

t.3

( ~ 3
("$

photon^Photon0(1)

Table 2
AVC~H
annual~ C cxposurcs lo cmmic rays

Annual flccriru dose (US)Popularion

A lrirudc(millionr)(4lonlzing

Neutron

Total

1.0
0.3
11.0
17.3
1.2
1.6
7.5

3900

1120
970
690
530
410

2020
1710
11M
820
560

330

900
740
440
290
170
170
110

Sca lcvd

240

30

270

World averagc

300

80

360

Localior:

HI&-rltrtudc cities
L P a r Bdiria
Lhasa, Chrna
W l q Emador
M e u m Gty. Mexico
Nairobi. Kenya
Dolucr. i l ~ t SUICSdTehran Iran

MOO
26 40

2240
16M)
1610
1160

400

90
440

L

-

Tahlc 3A n n u u l intakes by i n ~ c s l i o nor cosrnogcnlc radionucllda and crfcclivc doses In udulls

Hadionurllrle

11-3
Bc-7
C-I4
Sa-22

Inrnk (Bq n-I)

Annual e f i r ~ i wdace (uTvJ

500

0.01
0.03
12
0. IS

I000

2omil
50

'l'nhle 4
Surveys of t t l ~ ~ o r h cdosedrntcs in ttir fmn~terreslriul gamnla mdialionOu~rlmrs
Ccunr~ylarco

Populo~im
Lr 1990

Ycar

(1 8)

SWIW

25.0
16.9
7.6
9.9
9.0
26.5
13.2
1I20

1991
1992
l 980
1987

01

Ngoia

Australia
Austria
13elgurn
Bulgaria
CanadaLXle

China
Taiwan Province

20

Cuba
Denmark
EEYV
Knlandkana
Gnmao h . R c p .
Germany. Fcd.Rcp. d

10.6
5.1
524
5.0
56.1
16.2
61.3
10.0
5.9

GKCC

[long Kcmg
Hungarylccland
India
Indonesia
Ireland
Italy
Japan

10.6
0.25
853
I84
3.7
57.1
I23

Luxcrnhourg
Namibia
Ncthnhnds
NCW7zaland

0.4
1.8
15.0
3.4

1984
1988
1991
1989
1990
1980
1992
1980
1985
1Wl
1978
1990
1990
1992
1987
1982
1986
1986
1980
1972
1980
IWl
1W 1
1Y91
1985

Nlunbaorrne~~~crncftl.r

35 S I I C S a
8 sitcs
1 0 0 0 ~
272 '
3670
33 areas '7 sites8805 I
155 silrs
54 sitcs I
14 sites 8
162 sites
h

5142
2000
24739
724 silcs
27 sites,
76 sites '123 site#
I

2800 i
i

'

284
1365
1127
I2 sites
110
274
1049

'

lndoasAbsorbrd dose role (nGy h-')A~rrogc

Ron~c

70
93
43
43
70
24
60
62
57
42
38
32
65
68
55
53
42
76
160
55
28
55
55
42
57
49

60-80
64-123
20150
13.58
48.96
18-44
30-90
2-34 1

40
I ZO
32

Rorio
indoors
10
o~crdoas

Ycm

Nwnba

of

or
n~cmiwcmcnls

Atwa~e

3367
1900
300
1210

103
71
58
75

57-93

1.11
1.65
1.35
1.07

8605

99

11-418

1.60

S W I ~

1990
1980
1989

1991

Absorbd dose rofc (nGy h-I)
Rnn~e

Ref

10171
(c11. MIlTll
[Dl, S.W]
IV6l
IG2l
IS31
IN221

17-87

[Dl

26-53
17-52
8-93

~481
1x6, S9. 5101
11122 111

10-2504-430
4-350
37-1131M)-230
20.130
11-83
20-1100
47-63<I-1607-500
5-100
66-14480-260
10-60

1987
1991
1983
1985
1977
1978

489
80
5798
1%
29996

1.66

63

'

14-2100
1 .23
1.10
1.27
1.32

80
75
70
70

1992
1987
I982

194
I23

190
84
23

70-29010-200
14-32

1.17
1.53
0.82

1985
1991
1984

223
1500
135

62
86
50

10-140

1.48
1.51
1.02

1991
1985
1988

156
399
716

140
64
20

120-160
30-1(Xl
<I-73

1.17
2.02

I rJl
(.U3. R2j
~ 9 1
lB101
IS41
lL2l
IT121
IN71
[Ell
IS81
IS311
IM4, M81[Q,Cl3l
IN M I
lM23j
IUI
(S32j
[JI. VI]
In31

Oud~ors
Carnf~y'urca

Soruray
McxicoPalaguy
Ph~lippincs
PolandPatugalHanania
Spa~nSudan
SwedenSwiucrland
Ilnitcd KIngdom
Ilnitcd Stntcs
Population -u,cightd a v m g c

f'o/R,lorim
in 1990

Year

Nrunbcr

( 1 4

or
swuy

of
meosurcmenls

4.2
88.6
4.3
62.4
38.4
10.3
24.0
29.2
25.2
8.4
6.6
57.2
249

1977
198611991
I991
IWI
1980
1991
197Y
1991
1Wl
IW19.1989
1W14
1988
1972

234
11121
I

1-K)
352 sites 1
t

2372
1052
k
.-m

k

3 I(K1
2 5 arcar 'Indo~s

A bsorbal dose rnrc (nGy h')

Year

Al w a ~ e

Ranxe

of
swwy

of
mcasurcmenrs

A~wage

73
78
46
56
37
85
81
46
53
56
60
34
46

20- 1200
42-14038-53
31-11815-90
9-226
32-21025-83
26.69041-69 "

l%S

2026

95

8-89
13-1M)

57

Ground survcy uith calcium sulphatc rhcrmolurnincscmt dosimctcrs and a n i o n i ~ a u o nchamber.
Ground survey in p ~ u l a t c darcas with a Gnga-Midlcr muntcr.
Ground surwy with thcrmoluminesccnt dosinctcrs, gamma s p a r o r n u e n and ionizatirn chambers.
Ground survcy uith scintillation dctcctors.
Aerial survey uith a scintillation dctccta.
Ground survcy ~ 4 t hscintillatirn dctcctors and irn~zationchambers.
Ground survcy with ionizatirn chamber and g m n l a tpectromctn.
Ground survcy with t h e r m o l u r n i n ~ n ldosimctcrs.
Ground survey uith cncrgvcompcnsatcd Gcigcr-MGller counters.
Ground survcy with i o n i z a t ~ mchambxs.
Eslimatcd.

Calculated.
m u n b y covcragc.
Rnngc d ccunuy avcrags.

Nwnba

Absorbcd dose rote (nGy h")
Ranre

Rorio
idmrs
ourdoas

1.30

1984
1991

1351
1351

105

1991

1W

68

1975-1978

1298

110

1988
1991

2300
247

42-12037-244R$

10[ S Z SIO][a?]
IF1 11[Dl01[ R I , N91

1.24

IA71

1.48

101, 0 2 1

1.96[MS. M9J

60
37 '

1.76
0.80

(1141
IG3. W3)
IM 18, 031

83

1.44

'
20-460

In1

l Ul

-

Ibl,lc 5
A r l i \ . i t y c o n c e n l r ~ ~ t i o no sf 1111turtiI r t ~ d i o n u c l i d c si n s o i l and u h s o r h c d dose mtcs i n u i r

D m c corfirirnr 'Concrnirn~ion(tlq k8-')I)nvc rarr (nGy h-'J

Hndion~rrlidc
Mcnn

Range

i

Atcon

(nGy h.' pm Hq k~.')Hmxc

Chinn [h'tt]

K-40
Th-27: scrics
KI-238rcrics
R a - 2 6 subxrics

12-2190
1.5-440
1.8-520
Z4-430580 t 20049 :3
40 r 34

37 r 20.01 14
0.623

24
11

0.5-900.9-2700.411

17l.lZ00

72

2-564

I5

4-29
2-61

Taal
C n i ~ c dStaler n t l ]I t 4 [Ul]370

Th-232s c r i u

35

U-36 s c r i u
Ra-'226 s u h K r i a

3540

100-700
4-130
4-140
6-160

0.01 140.623

220.46 1

16

4-74

55

10-30

<

Tdal
Rercrencc IP2 S121.
Area-weighled m n n for China: rrilhmcric mean fa Ihc United Stzlcs.
Dart i r u n n 6 ~ ar u h c r i o .

A c t i v i t y c o n c c n t r t i t i o n s or n a t u r u l r a d i o n u c l i d c s i n various types o f s o i l i n the N o r d i c c o u n t r i c s

[C141

I

1

Acrilaiq conccmarion ( ~ kg.')q

I

I

Tvpc of soil

"K
a

a

~

MaaincSoils cmlaining alum shale

3Zn,

5.25
20-12020.60
100-1000

600-1200
600-13 0900-1-W
600-1000

Sand and sill

I

ah

4-30
25-60
20-60
20-60

Table 7E s t i r n e t c d ahsorhcd dosc rnlcs i n a i r w i t h i n masonry d w c l l i n g

Conccnnorion(flq kK1)

hfarerid

Tjr~calm a s n r y
G r a n ~ ~b lco c k
Coal u h aggcgacc
Alum rhnlc c n n c t e
I'hephogvpsum
Natural gypsum"

Acrh~iqurilbrion

CY

C,

Cn

5M)

I2M

50
90

400

150

770
60
I 50

I1(0

50
80
150
67
20
5

6(10

20

h s u r n ~ n gTull ulillral~ono r the malcrials (u.,,,= I).

rnda

1.0
1.9
24
9.0
3.9
0.25

Abtorbcd d n r c rare in & f aindicarcd /racrimol
mprs 4buildrng mnrrriol ( n Q h-I)
1.0

0.75

0.5

0.3

80
140
180
670
290

60
105
135
500
210
15

40
70

20
35
45
170
70
5

20

90

390
145
10

. Rcfcrcncc[h'101

1n101
11'11
IN10l
IN101
[Nlo]

Tnllle 8
Conversion roctllclcnts rmni 111rkermn b cf'fectlvc d0.w lor tcrrcstrllll gnmn~arays
11'19. SIZ]

Conversion roflcicnr (St, pcr Gy)
H d i n n uclidu

K-40
Ilh.232 scria
U - 3 8rcricr
Overall

Advlu

Childrcn

In/arus

0.74
0.n
0.69
0.n

0.81
0.81
0.78
0.80

0.95
0.92
0.91
0.93

Tehlc 9Nalional cstimelcs or Lhc avcregc annual cffeclive dose lrom lcrrestrial ganlnin rnys
Effccriw dacc ( d v )ComnyBulgaria
Gnr&

R+uvc

0.45
0.23
0.55
0.36
0.49
0.41
0.32
0.48
0.40
0.65
0.35
0.28
0.32

(him

h a r kF~nlandGcrmacy
lapan
Nau-ryspain
SwedenU n i l d Lngdan
United Stales

USSR

Population-weighled w o l d average

[V61
P21
(h'q
[C141
[C141
10, K9, L9]
IA6. FlO]
1~14.
SIO]

(421
v9. SIO]
11131
[h'21

Csl

0.45

Table 10
Rercrcnce annual Inhke of rood and air[IS. W4]
Food conrumprion (kx a-')InrakeAdulrr

ChiLlrcn

InfanuMilk produns
MCPI p o d ~ a s

105Gain poducrs

140
60
170
I5
500

110
35
90
40
110
10
350

120
15
45
20

U y vegctaMu
Roar and fruits
Fish products
Walcr and bcvcngca

50

Arcaihing rruc

M)

5
150

(2a*')

lnrak

I\rr

~drrluChildren

Infanu

Boo0

5500

1400

Tuhic 11
Hclcmncc nclivily mnccnln~tionsor n111urulrudionuclldes in rood and uir

A r f i ~ i r yrmrcnnorion (mRq kK=')
Infokc23bU,ZlfU

h4ilk products

Ledy vegctatrler

1
2
20
20

Roots and frwts
I-irh produds
Water supplies

30
1

Meal produar
Grain products

13077,

LWHn

210pb

210po

Xn

=aRo

LLdn

LIJU

0.5

5
15
80
50

40

60
60
100
30
30
9
' 00

0.3
1
3
15
0.5

5
10
60
40
20

0.3
1
3
15
0.5

0.0s
0.05
1.0
1.0
0.1

5

0.05

0.5

0.05

0.04

2'

10
20
0.5

3

0.1

60

100
30

30

25

100
0.5

200
10

Arfit,ify r m c ~ ~ a l i oCnB q mJ)
Infokck r=9u4u4u

mn,

1

0.5

0.5

zopb

210po

232,-,,

%,

22an

3 5t'

500

50

1

1

1

0.05

Dsrc ro&knr(US" 8 4 ' )Table 12
Committed clTcclivc dose pcr unit activily inlakc or natural radionuclides lor adulls
1141
Inhalorion

lngerrion
RcdionuclLL
Frwriond r r m f e r to Moodhe r o c ~ i i e r f(uSv t9q.l)

C l w of solubilj.

Y
Y
Y

30
30

W

2
2
1

U-38
U-34
Tn-30
Ra-26
Pb-210Po-2100.05
0.05
0.0002
0.2
0.2
0.1

0.025
0.03
0.07
0.2
1
0.2

Tn-232
Ra-228
Th-2280.OOM
O.?
0.000-

0.4
0.3
0.07

W

U-35
Pa-31

0.05
O.M1
0.001

0.03
2
2

Y
W
W

Ac-227

50

D
D

Y

200
1
100

Y

30
200

300

Table 13
Average age-wcighld unnunl i n h k n o l natural radionuclidcs and issociutcd crrcctive d o s olnprIion

hhnlalion

Radionurlidc

Taal

Infnkc (BqJ

Dase (uSSJ

Infnkc (mRq)

Dare (I&.)

0.12
0.15
0.18
3.6
32
11
0.52
3.9
0.09
0.01

6.9
6.9
3.5
3.5
3500
350
6.9
6.9
6.9
0.4

0.21
0.21
0.18
0.01
7.0
0.35
1.4
0.01
0.69
0.01

U-238

4.9

11-2344.9

7h-230Ra-226
Pb-210P0.210Th-232b-228
Th-226
U-235

Z5
19
32
55
1.3
13
1.3
021

52

10

-

UNSCMR 1993 REPORT

68

Tnhlc 14
Elcvalcd values or activity conrcntrntlons or natural radionuclides in roods
L

Arriu'ty conrcnrr~ionin Jrerh ford ( d q kg-')

Food
Cow' milk

CowrhyBrazilaickcn m a t

BrazilIkd

BrazilPork

BrazilRcindccr mot

Sweden

Grulr

India

Corn

BrazilRicemina

Clccn vcgctabl~

India

Carrots

Bradl

R w u and tubers

India

hdts

India

Rodimuclidc
Ra-226
Pb-210Ra-226
Ra-228
Ra-226
Ra-228
Ra-226
Ra-f28
Pb-210Po-210Ra-2267h-228
Ra-226
Pb-210Ra-226
Pb-210Ra-226'Ih-228
Ra-226
Pb-210Ra-226
Th-228
Ra-226
Th-228

RcJ

Rmge

Arirhmcrk meon

3-210
5-60
37-163141-355
30-59
78-111
7-22
93-137400-700

108
45
86
262

[A81
It101

44

It101

1 ~ 4 1

96
13
121
550

It101

Fl

11OOO
174
536
118
144
250
570
1110
1670
41 1
255
1490
21700
296
X90

up to 510
up to 5590

70-229100-222325-2120348-5180
329485218-318477-4780
70-32200
13766859-21900

lUl
P31
1211
[Ul
P31

IL61

IL61

Tnblc 15
Elcvatcd values or activity concentrations or natural radionuclides In pobblc waters or various sources

Activity cmcenharion ( d q I*')
Sowce

Cowhy

Rodimuclide

Refcrcncc
RMKC

Boltled walar

Cirarnd valm

Arirhnuric mcm

G c m n k meon
27
77

BrazilRa.226
Ph-?lo40-13060-190FranceU.238
Ra-226
Th.132up lo 2000
up to 2700

GmnanyU-238
Ra-226
Pb-210Po-2 10el-140~1.1600
3.3-53
0.4-8.9

Indonesia

Ra-226440

P~nugalRa-226
Pb-2 10~3.2185
2.392

Finland

U-38
Ra-736
Pb.210Po-?I0

up to 74000
up to 5300
up to 10200

up to 6300

4200
440
430
220

Su.cdcn

Ra-2262-246045

Yugoslavia

Ra.226

0.5-510

60

60
60
c 40

PI
p5, P9. S l l ][RlZ R13, R14,
MI91

4.4
3
9.0
1.6
22

PI2
G4. GS]

1~311
26.7
18.5

lB61
Is151

13.7

w41
PI11

ANNE3 A: MT'OSIJKES FROM NATURALSOLJRCIS OF RAD~ATION

69

Tuhlc 16
Alphn dcmy propcrtia or OH^ and Z 2 z ~withn shod-lived der~iyproducts
1137. MI11

='~n

Lw~n
Rdionuclide

Brmch ((X)

IldJ-IiJe

E n r r p (.Wc\?

Inremiry (F)I

Rdinnurlidc

dcEnergy ( ~ ~ l c b ' )Inrerj.

m)
Rn-2,O
Po-216l'b.212l3i-21255 a0.15 s10.64 h60.6 minPo-212
n.208

64
36

304 ns3.10 min

6.3
6.76

100
100

P. r
6.05
6.09
8.78

3.824 d3.04 min26.6 min19.7 m n
163.7 ps

Rn-222Po-2 16
Pb.214
Ui.214Po-214

25

10
100

5.49
6.M

100
100

6. r
b. 7
7.69

100

P, r

Table 17
Activity conccntrntions of 226Raand "'RU in various types or rockIW61
Cowcnrmion (Bg kx.')

Type of rock=R.

ExmplcAcid intrusive
Basic cxtrwivc
O ~ & m l sedimentary
Dctrital rc&rnmnry
Mcarnorphoscd i g c o w
Mctamorphosed xdimcntary

GraniteBasaltLimwtmc
Clay. shale. undstmc=Ra.

A r u h m u nuan

Range

Arirhmcric man

78
1I
45

1-370
0.4-41
0.4-340
1-990
1-1800
1660

111
10
60

G ~ s s

60
-50

Schst

37

50

60
49

.

Rmxe

0.4-1030
0.2-36
0.1-540
0.6-1470
0.44200.4-370

Tnble 18
Activity conmntraUons or nntural rndionuclidct in various types of rock in Lhc Nordic munlries[CldI
AcliviIy concnnatbn (Rq kg*')
Hork npc

Samal grarutc
Thonum- =d unn~um-r~chganltcGncissCha~tcSandstme
Lmcstmc
Shalc
Mlddlc Carnb~nnalum shalc
Upper Gmbr~anor Lowcr Ordonclan alum shale"K
600-1800
12W-1800
600.1600
300-1000

300-IMO
30.150MX)-1800
1WO.1800

1000-1R00

3Zn

20-120100-500
20-120
1-20
560
5.20
10-1201204006004500

20-80
40-350
20-80
440
440
1-10
6-60
6-40

6-40

UNSCMR 1993 REPORT

70

Tnt~lc19
Pnramelcrs or cmannlian nntl dirrusion or 2 f 2 ~ nTmm the cat-th and from hullcling rnntednls

MarnialRcpucnrari~rva!uc

N

M

~

Ref.

Fman8tim frmlinn-

0.084 '
0.23 '
0.04
0.15 '
0.08

Rock (sieved)
Soil (various)
Brick (clay)
Concrete (adnrry)
Gypsum (natural)

0.005 0.-10
0.02 0.83
0.02 0.1
0.1 0.4
0.03 4.2

IB61

PSI
IS171
1~171
1~171

Pmrity
0.25
0.15

Lnh
Bulding mtcrials

0.01-0.5
0.01 -0.7[F6. H14.

10.'1.]0.~
10.'1-10.~[F6. 1114.

05. S19]

DiKution rumcicnl [ma I-')
5 I@'
I lfl

61th
Building ma~crialr

05, S 191

Arithmetic mun.
Inferred from rangc.
lnfcncd f r a n rangc and mix.

Teble 20
Flux density lmm the convccllon o l radon and the resultant cntry relcs into the modcl bullding caused by an
undcrprcssum of 5 Pe with vnrying permeability or the subjaccnt e~rrth
F~UX
d-iy

a

Pcrmurbilily (m2)Panrmbildy (m2)

Circururancr

G a c k d Ooor a
Dare earth

Entry rarc (6q mqJK I )( ~ ms2
q 1.')

lo-IJ

,,-I?

lo.r1

I uZ0

lo-@

,,,-I>

J0.12

1 0 - ~ ~ ,,,.Io

0.00710.028

0.0078
0.030

0.014
0.013

0.078
0.19

O.M3
0.065

10
40

11
43

20
62

With an array d 1 nn aactr every 1 m or flar. ValTrend adjustment d published data IW8j.

avnrpd wn u.hdc flax.

112
274

,,-P

62
122

*

ANNEX A: LYPOSURES FROM N A T U M SOURCES OF W l A n O N

71Tnhle 21.4vertlxc radon conccntn~tionsund pcrccnlagc ulill7allon or w n k r supplies[N I R. 051
7

Cnnrcnhafinn (Hq i-))Uri1k01;on(%)

PF of =pply
Unircd Sara

Surfacc w l c r
Ground water
Well uatcr

V d c d hZngdom

Rcfcrcncc wlvc

U d a f Saet

Unirad G;inddorn

Refmcrc rrrlvc

50

66

32
18

34
c 1

60
20

1 I00

loo0

11500
208000

300M)

loo0
loo00

< 1000000

IOOOOO

10

Tahlc 22
Illuslralir~cradon entry mtcs for the modcl masonry bullding in a Lcrnpcrate climate

Sourcc of rodon

Uuilmng clemcnts

Suhjacen~earth
O u l d w air
Walrr supply
Eiuural gas

Mechmism~ n m yrnrc (6q mJ h-I)

Poceruagc

Di [Fusion
Diffusion
Advcclion
Infillralion
Dc-manaticm

10
7.5

21

20

41

10
1

20
2

Consmp6m

0.3

1

49

100

IS

7

All sowccc and mechanisms

'I'nl~le22
K j ~ d o nc o n c c n l r ~ ~ l i o nins dwellings d e L c r n i i n c d ill i n d o o r s t l r v c y s

Counr~l~rca

)'car
of

Duration of aporrrrc

J W , ~

Alpn~aAr~mtina.3 citicx
Australia
Austr~a.Salzhurg
RdgjumCanadaCanada. h'mScdia
Chtnq u v m provinccl
China. Scchuan
Chtna. Shnvhcn
Czcchorlonba
kmark
Emt
finlandirnnccGnrnany (fonnn Fcd. RqmMic)(inmnny. Cht~hus
Gnniany. Saxmy and Thur~ngia
Gornany (fnnnn Fcd. RcpuHic)
Ghttnn. Lepn

(itwccHmg Kmg
lndra
Indonesia
Iran 4 cities
Ireland
Italy
Japan
KuuaitLuxemburg
Ncthnlands
New haland
Snuay
Pakistan
Pdand
Portugal
Spain
Swcdm
Sudm
Suiuerland
S y r ~ a2 areas
llnitcd Kingdom
11~1cSdhta
Ilnicnl Stales. Scw York

1987
I WO
1990
1980
1991
1977.1980
1990
1989
1990
1986
1982
1985
lWl
1982
1988
1984
I 989
1990
lWl
1090

1988
1991
1991
199 1
1988
1987
1991
IW0
1988
1991
1982-1984
1988
IWI
1991
1991
1991
1991
1980-1082
lWO.1991
1991
1990
1991
1W1
1988

Radon rorurnnntion (Aq m."

Numbcr of

Tvpc of sun?
Explora~cry
Prclirninary
National
Local
Salional
Nat~onal
RciondRcljond
RcdonalRcljond
Nat~onal
Nationalh'ationnl
S~llional
Sational
RcdondRc~ondExploratc~y
Rc~nnallirplorr~lr*ylixploratcry
Regional
Exploratcxy
Exploraliny
Explonlcxy
National
National
National
Exploratory
National
National
Na~imaI
National
Explwatny
Preliminary
Sational
Sational
Sational
Sat~tmalNational
Exploratay
National
Hr0onalMcdian vnlws
k r i v c d from radm E C mcasurcrnmtr, using an quilihrium iacior o i 0.4,

60 days
I ycarGrab samples
6 months
G a b samplcs
3 months

G a b ramplo
6 months
1 month
60 days
3 mon~hr
3 monlhs
3 days3 days0 tntrnlhs
6 montlu
3 months
90 days
6 months
1 year
1 yearI ycarI year
1 ycarb nionths
2.5 months
1 year4 months
2 wcclu
3 munths
2.5 months
6 months
3 months
1 ycarI yeardwrllings
sw~qc).ed
50
1M
3413
729
4 9
1313
7 19
3945
1967
69
1?00
4%
329
8150
3006
5970
67
5000
1000
25
73
140
1208
165
121
736
2250
6000
69
2333
1000
717
7500
50
345
4200
1700
512
1-30
1600
77
9 ~ 0 35967
2LU3Arithmetic nuon

32
32
12
48
34
108
24
19
I6
140'
47
9.0
90
62
49
35
270
57

Geomchic m a n
31
8.7
IS
14
20
17
14
29

Geomcrricst&ddoidion,Hurimum vduc
137
127
423
190
4000
1724
5920
378
170
54
2WXl
560
24

2.0
2.1

3.6
3.6
2.2
1.7
2.0
2.2

64
41

4687

40
23
1W
34

I 53
11 5
3100

~

~

3.1
2.7
l .8
2.5
2.4
2.9

80
29
41

42

37
62
23

492
140
2 14
120
3070
1700

29
20
60
30
38
81
86
108
108
71)
20
20
46
42

1.9
1.6

25
26

42

30

37
43
62
56

l I8
94
83
568
2795
15400
3310
3900
3(M)
72
10000
I420

1m1
lLAl
(S40, 5411
l"8l

1L'l
1191

In1
IC101
In51
IT4
[S9. U15]
1K121[C19, (211
IR6. R7l
Is2Ql
1 L91

ml

I L'I

Ik131
lG71

2.2

103
65
24
18
30

101

1-1

350

52
41
57
12
82

Rcj

1.6

3.7

3.1
2.7
2.2

In1

13371
IS311
IS261
IC181
[BIS, B16j
[=I
[MI31
[=I
[H 17,P24.P25]
IR31
IS391
IT101
IBlJl
lFl"1
lOZ 031[ Y 17, S42l
1931
1~381
I071
1~91
[M24, U12]
IP111

ANNEX A: ESI'OSURIS FROM NAIURnl, SOIIKCES 01:RAnl,\llON73'~111)le24
Averi~yemncenlrntions in air or r i ~ d o ntlnd l h o n ~ n ,includitip Lhcir dccny produck, 11nd tinnun1 eITccllvc doses
A

Concmiraiir~n(BY m-')

Locniir~nHdionuclidc

Outdwslndmrs

Radm

I d

C

c

AMW/ rffccriru dose 'c( ~ F Lp* n ~q h m - )6l.71J

Gar

EEC

Cur

EEC

Gar

EEC

10
40

8

16

0.17
0.17

9
9

3.0
48

130
1MO
12M

Tolal (rounded)
Oufdoaslndmrs7horcm

10

0.1

3

0.3

0.11
0.11

10

1.9
23

32

67
73

T d a l (roundcd)*

1.6

W c i g h t d f a cccupancy: 0.2 ouldons. 0.6 indoors.
Thc equilibrium cquivalcnt con:cntratim (EEC) of radon (or thaon) is thc product of the cmccnrra~ionof radon (or thoran) and d thc cquilibriurn f a c t a
ktwcrn radon ( a Ihaon) and i k decay products. lhc valucr d the cquilitriurn factoc have k e n u k c n t o bc 0.8 c u l d m s and 0.4 i n d m f a n d m . T h a o n
EEC cllucs EIC bascd on m c ~ s u r c m m t r .

Tllhlc 25
Typical conccntrulions of "%' h and 2 3 8 ~in hcnvy mincrul sands in Austnrliu[K"I
IrfinrrJ
Orc

llcavy mincral c o n c c n ~ n ~ c
Dmcnitc
Irucoxcnc
RutilcZrrconMmadtcXcnolimc
Avcngc soil znd rock

L127X ccnccnirorion (Rq k f l )= U c m c m a i m (Bq kg-')

60-2DO
10Q).1300
600.6000<IM)~100-400

1000~900<6M-400040

250-bU)~100-YO

2000-3000~

060M00-9M(YIO
160(KlO

1DMO-10000

40

40

Moo0

Tnhle 26
EslimaLa of collcclive c f i c l i v c dosc pcr unil eicclricul cncrpy &!cncrfiLcd hy non-nuclcur sourccs

Normalized c d l r c i i ~ ~rffrcri~rcdate[ m n n SI.(GU'n)-'l0

UNSCWR 1993 REPORT74

Tahlc 27
Eslirnnles or unnunl pcr cupul c.r~y:livedaco resulling from the eXlrncUon nnd ~ I W C M Sor~enrlh~ ~ malerials

I

Sowcc

~ n n w l pa
lr u p w c f f c c f i dose ~ISI,)

Coal
0.0001-0.002

MiningElcclncal energy p r d u c t i m
D a n w t i c usc
Uu d fucl ash

2
0.4-8
5

Othcr nnn-nuclear awrrn d clcrtricol r n r w v p r v d u c t i w ~

0.01
0.001
0.001

011
Natural gas
Gcothcrmal
Explni~slionof phnrphstc rock

0.04

Indulnal operations
Fcr~ilizns
By-products and waslcs

2

I0

Table 28
Avcrngc nnnual clli.ctive dosc Lo adults from nnturnl sources of ionizing radiation

Annual cffccrh,~dose ( d v )C o m p n c M of crpmurc
In mcor of normal backgroundCosmic rays
Cnsmogcnic ndionuclidcs
Tcrrcskial radiation: utcrnal cxposurc
Tcrrcstrial radiation: internal exposure (excluding radon)'Tenatrial radtation: inlcrnal cxposurc f r a n radon and its decay products
Inhalatian d Rn.222
Inhalation d Rn-220
Ingestion of Rn-222
Total

0.38
0.01
0.46
0.3
1.2
0.07
0.035

24

I n mens of dn,ared aposwcc

2.0
0.0 1

4.3
0.6

. I0
0.1
0.1

A N N M A: ['XI'OSURES FROM NATURAL SOIJKCI~SOF WDIATION'OOM- ----

I

Solnr rninirnulll
rninirnul~lSular nlaxirnutll-:,loo0 a

h

2

&

'+'

36

% loo 5lonixing compncnl

8
n
u
m

cZ

0,

2 loNeu~ron compncnl

hLnTUDE (km)Figure 1.
Absorbed dose mlc in nir at 50' gcomegnclic liltiludc imm thc ionizing
itnd nculmn componcnb of cosmic mys ns a function of allilude.
w31

75

1:igui-c 1 1 .
Ahsorhcd dosc r.11cs in air rmnl tcrrestriitl pi1n1111an~dii~lion
nnkcd i~rcordingto lcvcls outdoors.

1:igur-c I l l .
Iblio or indtnlr ur oultlt~c~r
absorh~ddose m k s in ulr from Lermlriill r~~tlii~llon.

ANNFi A: LXI'OSURFS FROM NATURAL SOURCliS 01' KADlAnON

1W .-.

-

..

E

z
i
-

1

0.

Z
C

LL:
C,
Z

.

/o""

'7

z

n

o
lo-

G

C,

l

I

I

0.2 0.5 1

I

2

I I
5

I

I

i

1

I

I

I

I

10

20

30 40 50 60 70
PERCENTAGE

80

90

95

95 99 99.5 99.8

l

l

1

Figure IV.
1)istrihution of s u n c y mcasurcrncnk or radon conccntralions indoon.

Fipurr V.
liiidon mnccnlmlions indoors in relation to It~lltude.
The population-wcighkd avcmge is 40 Rq m-3.

l

l

I

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I)cworrn, J.P., W. SIcgcrs, J . Gillard ct al. Sunpcyof
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ANNEX A: r'N"N'URESFROM N

Fry. R.J.M. and D.S. Nachtwey. Itadiation protection
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Food and Agriculture Organization. FA0 Food
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Gutiirrez. J.. C. Baixeras. B. Robles et al. Indoor
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Gans. I. Nalural radionuclides in mineral waters. Sci.
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Dcutschland. 11411987. Institut fijr Wasscr-. Bodenund Lulthygicne dcs Dundcsgesundhcitsamtcs, Berlin,
1987.

-

Gomcz, J.C., A.A. Olivcira, M.I. Arnaud ct al. Kadonin dwellings in Argentina. p. 391-400 in: Prooxdingsof the International Confcrcnm on lligh Lcvcls 01
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G7 Gcorgiou. E.. K. Ntallcs, M. Molfclas ct al. Radonmcasurcn~cnls in Grccm. p. 387-390 in: Radiation
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G8 Gutt, W. and P.J. Nixon. Usc of waste materials in theconstruction industry. Analysis of the RILEht
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G9 Guo, Q.. M. Shimo. Y. lkcbe et al. The study ofthoron and radon progeny mnccntratiom in dwellings
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GI0 Gadgil. A J . Models of radon entry. Radiat. Prot.
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GI1 Grasty, R.L. Summer outdoor radon variations in
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G6

H2

Ifajnal, F., J.E. McLaughlin. M.S. weinstein et a!.
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82

UNSCEAR 1993 REPORT1113 Ilua. J. and Y. Qingyu. The F~timationof Dose from
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1115 Ilubbard, L.M., N. llagberg and A. Enflo.
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1117 klogeweg. B.. R.F. Bosnjakovic and W.M. Willart.
Radiation aspccts of indoor environments and related
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I118 ilassib, G.M.. M.I. Ilussein. H.A. h e r et al.
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1121 Ilopke, P.K., P. Wasiolek, N. Montassicr et al.
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1.122 I.lusscin, M.I. and F.A. Kawy. lndoor gamma levels insome Egyptian dtics. Atomic Energy Authority, Cairo(1992).
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Inkrnational Civil Aviation Organization. Civil
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International Commission on Radiological Protcction.
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17
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International Cnmmission on Radiological I'rotcction.
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Julius, 1I.W. and R, van Donpn. Radialion doscs totlic population in Ihc Netherlands, due to external
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Jacobi, W. and K. Eisfcld. Dose to tissues and effective dose equivalent by inhalation o i radon-222.
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Jarncs, A.C. A rcconsidcration of cells at risk andother key factors in radon daughter dosimetry. p.
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Jaworowski. J. Sources and the global cycle ofradium. Chapter 2-2, pp. 129-142 in: The
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Jeffries, R.A. and J.B. Twining. Levels ofradionuclides in edible tissucs of organisms from
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Juntuncn, R. Uranium and Radon in Wells Drilled
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