SOURCES AND EFFECTS
OF IONIZING RADIATION
United Nations Scientific Committee on the Effectsof Atomic Radiation
UNSCEAR 2000 Report to the General Assembly,
with Scientific Annexes
VOLUME I: SOURCES

UNITED NATIONSNew York, 2000

NOTE
The report of the Committee without its annexes appears as Official Records of theGeneral Assembly, Fifty-fifth Session, Supplement No. 46 (A/55/46).
The designation employed and the presentation of material in this publication do not
imply the expression of any opinion whatsoever on the part of the Secretariat of the United
Nations concerning the legal status of any country, territory, city or area, or of its authorities,
or concerning the delimitation of its frontiers or boundaries.
The country names used in this document are, in most cases, those that were in use
at the time the data were collected or the text prepared. In other cases, however, the names
have been updated, where this was possible and appropriate, to reflect political changes.

UNITED NATIONS PUBLICATION
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ANNEX B
Exposures from natural radiation sources

CONTENTSPage

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
I.

COSMIC RADIATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. COSMIC RAYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Exposure at ground level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Exposures at aircraft altitudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. COSMOGENIC RADIONUCLIDES . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

84
84
86
87
89

II.

TERRESTRIAL RADIATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
A. EXTERNAL EXPOSURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
1. Outdoors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
2. Indoors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
3. Effective dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
B. INTERNAL EXPOSURES OTHER THAN RADON . . . . . . . . . . . . . . . . . 93
1. Inhalation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
2. Ingestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3. Effective dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
C. RADON AND DECAY PRODUCTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
1. Sources of radon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
2. Concentrations in air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
3. Effective dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

III. ENHANCED EXPOSURES FROM INDUSTRIAL ACTIVITIES . . . . . . . . . . 108
IV. WORLDWIDE AVERAGE EXPOSURE FROM NATURAL SOURCES . . . . . 111
CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

84

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCESINTRODUCTION
1. The exposure of human beings to ionizing radiationfrom natural sources is a continuing and inescapable featureof life on earth. For most individuals, this exposure exceedsthat from all man-made sources combined. There are twomain contributors to natural radiation exposures: high-energy
cosmic ray particles incident on the earth's atmosphere andradioactive nuclides that originated in the earth's crust and arepresent everywhere in the environment, including the humanbody itself. Both external and internal exposures to humans
arise from these sources. These exposures were reviewed inprevious reports of the Committee, the most recent being the
UNSCEAR 1993 Report [U3].
2. In assessing exposures to the natural radiation
background, the Committee has considered the properties ofthe sources and the transport of both radionuclides andradiation in the environment. Estimates have been made oftypical exposures to the world population and the range of thecomponents of such exposures under various environmental
conditions, and note has been taken of the unusually highnatural radiation exposures that occur in some locations. This
information has been combined with relevant dosimetricquantities to estimate the absorbed doses in tissues and theeffective doses from the various sources of exposure.
3. In this Annex, the Committee continues its generalreview of the various components of the natural radiation
background. To broaden the database, an attempt has been
made to gather representative levels of exposure in as many
countries as possible. Many scientists and representatives ofnational institutions have responded to the questionnaire on
natural radiation exposures, UNSCEAR Survey of Natural
Radiation Exposures, which was widely distributed by theCommittee. Respondents to the questionnaire are listed inPart A of the References. The Committee acknowledges withappreciation their useful contributions to its work.
4. The database on natural radiation exposures has become
extensive enough to allow quite detailed analysis. For
example, the distributions of populations within various doseintervals from the different components of exposure can be
examined within and between countries. The processes giving
rise to the exposures can be better described and the time andgeographic variations more accurately evaluated, allowing
some issues to be addressed in greater detail. There remain,
however, some questions that are not yet satisfactorily
resolved. For example, there are difficulties in evaluatingcosmic ray exposures in aircraft because of the complex
neutron and ionizing radiation fields, and the dosimetry of
inhaled radon is complicated by the complexities andvariations of the interacting factors and processes involved.
5.
Many exposures to natural radiation sources are
modified by human practices. In particular, naturalradionuclides are released to the environment in mineralprocessing and uses, such as phosphate fertilizer production
and use and fossil fuel combustion, causing enhanced naturalradiation exposures. In a few cases, for example, by pavingroads or building houses over water, radiation exposures may
be decreased, but these seem to be rather isolated cases. The
general topic of enhanced exposures from natural radiation
sources was considered in detail in the UNSCEAR 1982
Report [U6], and some aspects were further evaluated in the
UNSCEAR 1988 and 1993 Reports [U3, U4]. The topic is
discussed further, with updated information, in Chapter III ofthis Annex. Many persons are also exposed to enhanced
levels of natural radiation at their places of work. Suchworkers include underground miners, some workers involvedin processing of minerals, and aircraft flight crew.
Occupational radiation exposures from both man-made andnatural sources are considered in Annex E, “Occupationalradiation exposures”.
6.
The broad relevance of natural background exposures
to the world population makes the evaluations of thisAnnex particularly pertinent. For most individuals, thenatural background exposures are much more significant
than the exposures caused by man-made sources.
Exceptions that apply to certain individuals are some
exposures caused bymedical radiation procedures, throughmishandling of radiation sources, in accidents allowing
radionuclides to be released to the environment, and atsome workplaces. In all cases, however, the natural
background source forms the baseline upon which all otherexposures are added, and it is a common level against
which other exposures may be compared.

I. COSMIC RADIATION
7. The earth is continually bombarded by high-energy
particles that originate in outer space. These cosmic rays
interact with the nuclei of atmospheric constituents,
producing a cascade of interactions and secondary reaction
products that contribute to cosmic ray exposures that decrease
in intensity with depth in the atmosphere, from aircraft
altitudes to ground level. The cosmic ray interactions also
produce a number of radioactive nuclei known as cosmogenic

radionuclides. Best known of these are 3H and 14C. Exposuresfrom cosmic rays and from cosmogenic radionuclides are
considered in this Chapter.

A. COSMIC RAYS
8.
Galactic cosmic rays incident on the top of theatmosphere consist of a nucleonic component, which inANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

9. It is thought that all but the highest energy cosmic rays
that reach earth originate within the earth’s own galaxy. The
sources and acceleration mechanisms that create cosmic rays
are uncertain, but one possibility recently substantiated bymeasurements from a spacecraft [K16] is that the particles areenergized by shock waves that expand from supernova. The
particles are confined and continuallydeflected bythe galacticmagnetic field. They become isotropic in direction, and theflux is fairly constant in time.
10. Beyond 1015 eV, protons may begin to escape thegalactic confinement. This leaves relatively greater proportions of heavier nuclei particles in the composition of cosmic
rays above this energy level. Protons with energies greaterthan 1019 eV would not be significantly deflected by theintergalactic magnetic field. The fact that protons of such highenergy are also observed to be isotropic and not aligned withthe plane of the galactic disk suggests that they are probablyof extragalactic origin [C7]. Only astrophysical theories cansuggest the origins of these ultra-high-energy cosmic rays.
11. Another component of cosmic rays is generated near
the surface of the sun by magnetic disturbances. Thesesolar particle events are comprised mostly of protons ofenergies generally below 100 MeV and only rarely above
10 GeV (1010 eV). These particles can produce significant
dose rates at high altitudes, but only the most energetic
affect dose rates at ground level. Solar particle events can,in addition, disturb the earth’s magnetic field in such a
way as to change the galactic particle intensity. The events
are of short duration, typically a few hours, and highlyvariable in intensity. They have a negligible impact onlong-term doses to the general population.
12. The most significant long-term solar effect is the 11year cycle in solar activity, which generates a corresponding
cycle in total cosmic radiation intensity. The periodic
variation in solar activity produces a similar variation in thesolar wind. The solar wind is a highly ionized plasma withassociated magnetic field, and it is the varying strength of thisfield that modulates the intensity of galactic cosmic radiation.
At times of maximum solar activity the field is at its highest
and the galactic cosmic radiation intensity is at its lowest.

particles of higher energies can penetrate at lower geomagnetic latitudes. This produces the geomagnetic latitude
effect, with minimum intensities and dose rates at theequator and maximum near the geomagnetic poles.
14. The high-energyparticles incident on the atmosphereinteract with atoms and molecules in the air and generate
a complex set of secondary charged and uncharged
particles, including protons, neutrons, pions and lower-Z
nuclei. The secondary nucleons in turn generate more
nucleons, producing a nucleonic cascade in the atmosphere. Because of their longer mean free path, neutrons
dominate the nucleonic component at lower altitudes. As
a result of the various interactions, the neutron energy
distribution peaks between 50 and 500 MeV; a lower
energy peak, around 1 MeV, is produced by nuclear
deexcitation (evaporation). Both components are importantin dose assessment.
15. The pions generated in nuclear interactions are themain source of the other components of the cosmic radiation field in the atmosphere. The neutral pions decay into
high-energyphotons, which produce high-energyelectrons,
which in turn produce photons etc., thus producing theelectromagnetic, or photon/electron, cascade. Electrons andpositrons dominate the charged particle fluence rate at
middle altitudes. The charged pions decay into muons,
whose long mean free path in the atmosphere makes themthe dominant component of the charged-particle flux at
ground level. They are also accompanied by a small flux ofcollision electrons generated along their path.
16. The changing components of dose rate caused by thesecondary cosmic ray constituents in the atmosphere areillustrated in Figure I. At ground level, the muon component
is the most important contributor to dose; at aircraft altitudes,
neutrons, electrons, positrons, photons, and protons are themost significant components. At higher altitudes, the heavy
nuclei component must also be considered.
CONTRIBUTION TO DOSE EQUIVALENT RATE (%)

aggregate accounts for 98% of the total, and electrons, which
account for the remaining 2%. The nucleonic component isprimarily protons (88%) and alpha particles (11%), with theremainder heavier nuclei [G11]. These primary cosmic
particles have an energy spectrum that extends from 108 eV toover 1020 eV. Below 1015 eV the shape of the energy spectrum
can be represented by a power function of the form E2.7,
where E is expressed in eV. Above that point, known as theknee, the spectrum steepens to a power of 3. The highest
energy thus far measured is 3.2 1020 eV, which was inferredfrom ground measurements of the resulting cascadeinteractions in the atmosphere [O7].

85

80

Muons
Electrons/photons
Protons
Charged pions
Neutrons

70
60
50
40
30
20
10
0
0

5,000

10,00015,00020,000

ALTITUDE (m)13. The magnetic field of the earth partly reduces theintensity of cosmic radiation reaching the top of the atmosphere, the form of the earth’s field being such that only

Figure I. Components of the dose equivalent rate fromcosmic rays in the atmosphere [O4].

86

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

17. The cosmic radiation intensity in the atmosphere has
been measured in increasing detail in recent years. A
complete mapping of the cosmic radiation field and thedetermination of exposure conditions and doses throughout
the atmosphere as a function of time can be based on thesemeasurements with appropriate interpolation or by theapplication of reliable radiation transport codes. Codes
have been developed for this purpose [O1, W3], andtransport codes for accelerator shielding applications havebeen adapted [K18, P17, R19]. Their adequacy has been,
and is currently being, tested against the available
measurements.
18. Since the publication of the UNSCEAR 1993 Report[U3], some new information has been added to the
database on which the exposure of the general population
to cosmic radiation at ground level is based. In particular,
both the low- and high-energy peaks in the neutron energy
distribution are recognized, and instrumentation has beendeveloped that responds to the extended energy range. This
has led to modified estimates of dose from this componentof cosmic radiation. There has been substantial progress inrecent years in the study of the cosmic radiation fields ataircraft altitudes [E1].
1. Exposure at ground level
19. At ground level, the dominant component of thecosmic-ray field is muons with energies mostly between 1
and 20 GeV. These contribute about 80% of the absorbed
dose rate in free air from the directly ionizing radiation;
the remainder comes from electrons produced by themuons or present in the electromagnetic cascade. In theearly literature, these two components of the charged
particle flux were referred to as the “hard” and “soft”
components, respectively, because the electrons are much
more readily absorbed by any shielding. As altitude
increases, the electrons become more important
contributors to the dose rate.
20. Many measurements have been made of the altitude
profile of the charged-particle and photon ionization andthe absorbed dose rate in free air at ground level. A reviewof this information in the UNSCEAR 1988 Report [U4]indicated that a representative value for this dose rate at
sea level is 32 nGy h1. The geomagnetic latitude effect isabout 10%, so that a value of 30 nGy h1 is appropriate for
latitudes below 30-. Considering that a large fraction of
the world population lives at latitudes below 30- (50% in
the northern hemisphere, 85% in the southern hemisphere,
and 54% overall), the population-weighted averageabsorbed dose rate from the directly ionizing and photon
components of cosmic radiation at sea level corresponds to
31 nGy h1, although it is not known to this precision. The
dose rate values may be considered as averages over the
11-year solar activity cycle, with the total range ofvariation about 10%. Since mostly muons are involved, aradiation weighting factor of unity is appropriate [I1],yielding the same values for the effective dose rate, i.e. 31
nSv h1 or 270 µSv a1.

21. It is much more difficult to estimate the neutron
contribution to effective dose rate at sea level. Althoughavailable data on neutron fluences and energy distributions
are sparse, recent measurements and calculations are beginning to provide clarification. Because earlier instrumentation had a low response to high-energy neutrons, which
are an important component of the spectrum, someincreases in the estimates of the fluence rate and effective
dose rate are being suggested. Measurements [R19, S10]
made at the top of the Zugspitze mountain in Germany(altitude 2,963 m, atmospheric depth 718 g cm2) andassociated calculations gave a fluence rate of 0.126 ± 0.01cm2 s1 [S48]. Attenuation with altitude was describedusing the function e0.00721p, where p (g cm2) is theatmospheric depth. From this, a fluence rate at sea level (p= 1,033 g cm2) of 0.0122 ± 0.001 cm2 s1 can be derived.
A value of 0.0133 ± 0.001 cm2 s1 was determined at about
sea level for a geomagnetic latitude of 53-N near Braunschweig in Germany [A15] and a value of 0.0123 cm2 s1at sea level for a geomagnetic latitude of 45-N in
Hampton, Virginia, in the United States [G20]. Earlier
measurement results were 0.008 cm2 s1 [H16, H17].
22. The effective dose rate (resulting from isotropic
incidence) at a fluence rate of 0.013 cm2 s1, obtained byapplying a neutron fluence energy distribution weighting
factor of 200 pSv cm2 (equal to 720 nSv h1 per neutroncm2 s1), is 9 nSv h1 [S48]. The shape of the neutronenergy spectrum at habitable altitudes is considered to berelatively invariant, and therefore the fluence to effective
dose (isotropic) conversion coefficient is expected to begenerally valid. On this basis, the annual effective dose ratefrom neutrons at sea level and at 50- latitude is estimatedto be 80 µSv a1.
23. Birattari et al. [B19], using a remmeter with anextended range, reported a value corresponding to80 µSv a1 (±5%), which is in agreement with the estimate
derived in the preceding paragraph. From a series ofmeasurements by Burgkhardt et al. [B18] and Gaborit et al.
[G16], the sea level effective dose rate from neutrons wasdetermined to be 60 µSv a1, but these results are probably
underestimates, because the instrumentation lacked
response to the high-energy component.
24. Incoming protons that initiate the cosmic ray neutron
field are strongly affected by the earth’s magnetic field,with the effect that the neutron fluence rate in equatorial
regions is less than that in polar regions. Investigators haverecognized the importance of the latitude effect, but it has
not been carefully quantified by reliable measurements.
Florek et al. [F14], quoting results of the Los Alamos
LAHET code system calculation, suggest that theequatorial neutron fluence rate at sea level is one fifth thepolar rate and that the rate at 50- latitude is 80% of thepolar rate. Nakamura et al. [N20], combining measurements made at Tokyo (24-N) with those for higher
latitudes [H16, H17], obtained a narrower range for thepole to equator variation, i.e. the equatorial rate about one
fourth of the polar rate.

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

25. An approximate analysis of the latitude effect forcosmic ray neutrons at sea level is presented in Figure II.
The normalization points are the measurement results ofBirattari et al. [B19] at 50-N (9 nSv h1 = 80 µSv a1) andof Nakamura et al. [N20] at 24-N (4 nSv h1 = 35 µSv a1).
The maximum value is estimated to be roughly 11 nSv h1(9 nSv h1 ÷ 0.8). The resultant curve may be used to infer
the values for 10- latitude bands to be used in deriving a
population-weighted average (Table 1). The world average
effective dose rate at sea level from cosmic ray neutrons
thus determined is 5.5 nSv h1 or 48 µSv a1.

EFFECTIVE DOSE RATE (nSv h -1)

12

10

8

6

Measurements
Birattari et al. [B19]
Nakamura et al. [N20]Calculations
Florek et al. [F14]Fit to measurements

4

2

0
0

10

20

30

40

50

60

70

80

90

GEOMAGNETIC LATITUDE (degrees)

Figure II. Latitude variation in dose rate from cosmic
ray neutrons at sea level.

26. For both the directly ionizing and photon component
and the neutron component of cosmic rays, there is a substantial altitude effect. Bouville and Lowder [B1] used bothmeasurements and calculations to derive expressions of thealtitude dependence of cosmic ray dose rates at habitable locations. These relationships were given in the UNSCEAR 1993
Report [U3] (see also Annex A, “Dose assessment methodologies”). Combining these altitude dependence relationships
with their analysis of the altitude distribution of the world
population, these investigators derived estimates of the
population-weighted average dose rates. For the directly
ionizing and photon component the population-weighted
average dose rate is 1.25 times that at sea level, and forneutrons 2.5 times. Some two thirds of the world population
lives in coastal regions, but because dose rates increase withaltitude, populations at high altitudes contribute proportionately more to the weighted average. The population-weighted
average value corresponds to the dose rate that occurs at
900 m above sea level. The calculations cited by Florek et al.
[F14] and the attenuation factor used in paragraph 21 indicatethat the effective dose rate from neutrons would increase by afactor of 2.1 between sea level and 900 m elevation, in
general agreement with the results of Bouville and Lowder[B1], which were also based on analysis of calculated altitudechanges in the dose rate [O3].
27. From estimates derived above, the latitude- andaltitude-averaged cosmic ray dose rates may be derived.
For the directly ionizing and photon component, the world

87

average effective dose rate is 340 µSv a1 (31 nSv h1 or
270 µSv a1 multiplied by the altitude factor of 1.25); forthe neutron component, the average value is 120 µSv a1(48 µSv a1 multiplied by the altitude factor of 2.5). These
results apply to exposures outdoors.
28. The rather limited data on the shielding effect ofbuildings on cosmic radiation charged particles and photons
were summarized in the UNSCEAR 1988 and 1993 Reports[U3, U4]. Observed shielding factors ranged from close to 1
for minimal vertical shielding, e.g. a small wooden house, to
0.4 for lower storeys of substantial concrete buildings. This isconsistent with the classical ion chamber observations thatdefined the “soft” component. These observations imply thata factor of 0.8 would be appropriate after the radiation has
passed through a substantial ceiling. In any case, values forparticular structures depend on both construction and design,and only broad generalizations can be made. There appears to
be no need to change the representative value of the shielding
factor, 0.8, used in previous reports.
29. In its previous assessments, the Committee did not
apply a shielding factor to the neutron component of cosmic
radiation, because of the uncertain balance between
attenuation and secondary build-up of neutrons passing
through building materials. Although this issue still awaits
evaluation, it seems likelythat 10%20% attenuation could bereasonably expected.
30. From the above considerations, the Committee estimates
the world average effective dose from the directlyionizing andphoton component of cosmic rays to be 280 µSv a1 (applying
the indoor shielding factor of 0.8 and assuming indoor
occupancy to be 80% of time). The corresponding averagevalue for the neutron component (applying the same
adjustment factors) is 100 µSv a1. The component estimateshave been altered slightly from the earlier estimates (300µSv a1 and 80 µSv a1) [U3], but the total of 380 µSv a1
remains unchanged. The average annual dose rates for thehemispheres and the world are summarized in Table 2.
31. The global value of the annual collective effective doseis about 2 106 man Sv. About one half of this dose is received
by the two thirds of the population that lives at altitudes below
0.5 km. The approximately 2% of the population living above
3 km receives a disproportionate 10% of the collective dose.
The average annual effective doses from cosmic rays for somehigh-altitude cities were listed in the UNSCEAR 1993 Report[U3]. Between sea level and 4 km, the neutron contribution to
the cosmic radiation effective dose increases from 8% to 35%of the total. Overall, the range of annual average effective
doses to the world population is 3002,000 µSv, with apopulation-weighted average of 380 µSv.
2. Exposures at aircraft altitudes
32. Aircraft passengers and crew are subject to cosmic
radiation exposure rates much higher than the rates at groundlevel. Total exposure on a given flight depends on theparticular path taken through the atmosphere in terms of

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

altitude (pressure rather than radar altitude) and geomagnetic
latitude, as well as on the speed of the aircraft; that is, it
depends on the duration of exposure at various altitudes andlatitudes. Complicating the situation is the fact that the
exposure associated with any flight path may vary with time.
There are two possible approaches to dose assessment underthese circumstances: (a) area and/or individual monitoring foreach flight and (b) determining the radiation fields as afunction of time and space and calculating the effective dose
for any flight path. Both approaches are being taken, andfurther measurements and results of calculations are
becoming available [E1]33. Duration of exposure is obviously an important factor in
the assessment of doses to passengers and crew. Flight
durations for crew members are expressed as the time
between leaving the terminal before takeoff and returning
after landing. Thus the exposure includes those accrued on the
ground and those accrued at all altitudes up to cruising
altitude. For flights of more than one hour, the exposure rate
at cruising altitude will be the main determinant of dose. The
annual number of hours flown by crew members varies fromindividual to individual and from airline to airline, depending
on policy. The range appears to be 300900 hours per year,with an average of about 500. For the general population, it
can be inferred that there are three groups: non-flyers (0hours), occasional flyers (350 hours, with an average of 10),and frequent flyers, i.e. business flyers, couriers, etc.
(501,200 hours, with an average of 100). The vast majorityof the world's population still falls into the first category.
34. Commercial subsonic aircraft generally have cruising
altitudes of 7 to 12 km. Although many measurements havebeen made in aircraft and balloons at these altitudes, there are
two major problems in using these data to estimate doses.
First, each measurement or set of measurements is carried out
for a particular flight path at a particular time, andgeneralizing such results to other paths and times is not
simple. Secondly, most detectors respond to only certain
components of the total field, and proper calibration of
detector response is generally not simple. In addition,interpreting these data in terms of effective dose requires aknowledge of the overall properties of the complex radiation
fields at these altitudes, and this knowledge is as yet
incomplete. However, the data can be used as benchmarks totest the ability of existing radiation transport codes to provide
reliable information on field properties and effective doses.
Moreover, the data obtained by a number of different detector
systems on many flights in recent years can be interpreted interms of the operational quantity ambient dose equivalent, toan estimated accuracy of about 25% [B16, E1, O9, S46, T12].
35. Estimation of doses to passengers and crew are basedon the route doses that are obtained from measurements or
calculations of the effective dose rate as a function of flightparameters, using, for example, the CARI programme
developed by O’Brien and Friedberg [F12, F13, O3] or acomputer programme based on measurements and calculations, such as the NASA AIR model [W3] andEPCARD [S47].

36. A working group of the European Commission [E1]reviewed measurements of dose equivalent rates at aircraft
altitudes mostly concentrated in the years 19741976, when
there was minimal solar activity, and 1991, during maximum
solar activity. More recent measurement results were
presented at the 1998 Dublin Conference [K19]. The results
clearly indicate the strong dependence of the dose equivalent
rates on altitude, latitude, and the phase of solar activity. The
general pattern of measurements is shown in Figure III. The
report of the working group [E1] noted that the contributionsof the high- and low-LET components are comparable atgeomagnetic latitudes of 50- and that the exposure rate
throughout the aircraft is approximately constant.
10

Solar minimum (1974-1976)
Solar maximum (1991)

9
DOSE EQUIVALENT RATE (µ Sv h-1)

88

o

>50 N

8
7
6
5
4
Equator

3
2
1
0
9

10

11
ALTITUDE (km)12

13Figure III.
Measurement results of cosmic ray
exposure rate at aircraft altitudes [E1].

37. The results of recent measurements and recent
calculations are broadly consistent. For altitudes of 912 km
at temperate latitudes, the effective dose rates are in the range
58 µSv h1, such that for a transatlantic flight from Europe
to North America, the route dose would be 3045 µSv. At
equatorial latitudes, the dose rates are lower and in the rangeof 24 µSv h1.
38. A small proportion of passengers and flight crews
travel at higher altitudes (~18 km) on supersonictransports. Doses on board those flights are routinely
determined from active monitors. Results of thismonitoring were summarized in the UNSCEAR 1993
Report [U3]. Effective dose rates of 1012 µSv h1 werenormallyfound. Recent measurements at these altitudes arein agreement [B24, C29, G21]. One potential problem forhigh-altitude aircraft is the possibly significant dose
contribution from solar particle events. O'Brien et al. [O4]calculated that 13 solar particle events between December
1988 and July 1992 contributed only 2% and 7% of thetotal cosmic-ray equivalent dose at 11 and 18 km altitude,
respectively. However, there is a potential for much moresignificant events such as the highly energetic event of
February 1956. Calculated dose equivalent rates for thisevent at 20 km are of the order of 1 mSv h1 [A2].
However, no events of this magnitude have taken placesince then. It requires both high solar particle flux densities

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

and high energies (1 GeV) for an event to produce highdose rates at aircraft altitudes, and this is a rare occurrence.

B. COSMOGENIC RADIONUCLIDES
39. The interactions of cosmic-ray particles in theatmosphere produce a number of radionuclides, including 3H,
7
Be, 14C, and 22Na. The radioactive half-lives and decay
modes of these and other cosmogenic radionuclides with halflives greater than 1 day are listed in Table 3. Essentially all
nuclear species lighter than the target nuclei (primarily
nitrogen, oxygen and argon) are produced by high-energy
spallation interactions. Production is greatest in the upper
stratosphere, but some energetic cosmic-ray neutrons andprotons survive in the lower atmosphere, producing cosmogenic radionuclides there as well. Production is not only
altitude- but also latitude-dependent and varies as well withthe 11-year solar cycle that modulates cosmic-ray penetration
through the earth's magnetic field.
40. The calculated global average production rates ofcosmogenic radionuclides per unit surface area of the earth89

and the total annual production are listed in Table 4. The
equilibrium global inventory can be derived from the lattervalue (production rate × 1.44 × half-life). These estimates are
somewhat uncertain, as they depend on the validity of thecalculational models. Estimates of the environmental
distribution of cosmogenic radionuclides can be made basedon equilibrium concentrations. The average concentrations in
the troposphere are included in Table 4. Since the production,transfer from stratosphere to troposphere, and deposition
patterns are latitude- and season-dependent, there may be
wide deviations from these average values.
41. Except for 3H, 14C, and 22Na, which are elements withmetabolic roles in the human body, the cosmogenic radionuclides contribute little to radiation doses and are mainlyof relevance as tracers in the atmosphere and in hydrological systems after deposition. The Committee previously
assessed the annual effective doses from cosmogenic radionuclides to be 12 µSv from 14C, 0.15 µSv from 22Na,
0.01 µSv from 3H, and 0.03 µSv from 7Be [U3]. Because of
the importance of 3H and 14C from man-made sources ofradiation, the environmental and dosimetric aspects ofthese radionuclides are reviewed in some detail in
Annex A, “Dose assessment methodologies”.

II. TERRESTRIAL RADIATION
42. Naturally occurring radionuclides of terrestrial origin(also called primordial radionuclides) are present in various
degrees in all media in the environment, including the humanbody itself. Only those radionuclides with half-lives comparable to the age of the earth, and their decay products, exist in
significant quantities in these materials. Irradiation of thehuman body from external sources is mainly by gamma
radiation from radionuclides in the 238U and 232Th series andfrom 40K. These radionuclides are also present in the bodyand
irradiate the various organs with alpha and beta particles, aswell as gamma rays. Some other terrestrial radionuclides,
including those of the 235U series, 87Rb, 138La, 147Sm, and 176Lu,
exist in nature but at such low levels that their contributions
to the dose in humans are small. Physical data for terrestrial
radionuclides are included in Table 3. The external andinternal exposures from these radionuclides are evaluated inthis Chapter.

A. EXTERNAL EXPOSURES
1. Outdoors
43. External exposures outdoors arise from terrestrial
radionuclides present at trace levels in all soils. The specificlevels are related to the types of rock from which the soils
originate. Higher radiation levels are associated with igneousrocks, such as granite, and lower levels with sedimentaryrocks. There are exceptions, however, as some shales andphosphate rocks have relativelyhigh content of radionuclides.
There have been many surveys to determine the backgroundlevels of radionuclides in soils, which can in turn be related tothe absorbed dose rates in air. The latter can easily bemeasured directly, and these results provide an even more
extensive evaluation of the background exposure levels in
different countries. All of these spectrometric measurements
indicate that the three components of the external radiation
field, namely from the gamma-emitting radionuclides in the238
U and 232Th series and 40K, make approximately equal
contributions to the externally incident gamma radiation doseto individuals in typical situations both outdoors and indoors.
44. The radionuclides in the uranium and thorium decay
chains cannot be assumed tobe in radioactive equilibrium. The
isotopes 238U and 234U are in approximate equilibrium, as they
are separated by two much shorter-lived nuclides, 234Th and234
Pa. The decay process itself may, however, allow somedissociation of the decay radionuclide from the source
material, facilitating subsequent environmental transfer. Thus,
234
U may be somewhat deficient relative to 238U in soils andenhanced in rivers and the sea. The radionuclide 226Ra in thischain may have slightly different concentrations than 238U,
because separation may occur between its parent 230Th anduranium and because radium has greater mobility in theenvironment. The decay products of 226Ra include the gaseous
element radon, which diffuses out of the soil, reducing theexposure rate from the 238U series. The radon radionuclide inthis series, 222Rn, has a half-life of only a few days, but it has

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

two longer-lived decay products, 210Pb and 210Po, which areimportant in dose evaluations. For the 232Th series, similar
considerations apply. The radionuclide 228Ra has a sufficiently
long half-life that may allow some separation from its parent,
232
Th. The gaseous element of the chain, 220Rn, has a very shorthalf-life and no long-lived decay products.
45. The results of spectrometric analyses of soil samples
gathered in different countries are listed in Table 5. These are
the in situ concentrations. If the concentrations have beenreported on a dry basis, representative values of soil moistureof 30% by volume and soil density of 1.6 g cm3 have been
assumed. The conversion factor (dry to wet basis) is thus 0.81
(dry weight of 1 cm3: 1.3 g; wet weight of 1 cm3: 1.3 g soil +0.3 g water = 1.6 g; ratio: 1.3 ÷ 1.6 = 0.81).

high; Syria and Albania, where all levels of radionuclides insoil are low; and Ireland, where the outdoor measurements arerather low. The surveys were conducted by various means andwith different numbers of measurements. The representativeness of each survey cannot be judged. The overall results
should be reasonably indicative of the global average.
250

200
POPULATION (millions)

90

150

100

47. Direct measurements of absorbed dose rates in air havebeen carried out in the last few decades in many countries of
the world. The database presented in Table 7 encompasses
70% of the world population. A number of countries havebeen added since the previous evaluation by the Committee[U3], and several values have been revised based on new
information. The population-weighted average is 59 nGy h1,
compared with 57 nGy h1 in the previous assessment [U3].
The average values range from 18 to 93 nGy h1. A typicalrange of variability for measured absorbed dose rates in air isfrom 10 to 200 nGy h1.
48. Of the values reported in Table 7 of the absorbed dose
rate in air outdoors, the lowest are in Cyprus, Iceland, Egypt,
the Netherlands, Brunei, and the United Kingdom, all lessthan 40 nGy h1, and the highest values are in Australia,
Malaysia, and Portugal, all greater than 80 nGy h1.
Exposures inferred from the soil concentration results(Table 5) generally show reasonable agreement with themeasured outdoor absorbed dose rate in air (Table 8). A
discrepancy of 30% or more mayindicate that one or the othersurvey was not representative for the country. Those countries
where there are considerable discrepancies include Luxembourg and Sweden, where the 40K levels in soil are relatively

50

0
0

20

40

60

80

100

120

140

160

180

200

ABSORBED DOSE RATE IN AIR (nGy h-1)

Figure IV. Distribution of population of 25 countries
with respect to the outdoor absorbed dose rate in air
from terrestrial gamma radiation.

49. A few countries have evaluated the distribution of the
population exposed to various ranges of outdoor absorbed dose
rates in air. These data, provided in response to the
UNSCEAR Survey of Natural Radiation Exposures, arepresented in Table 9. The median for the population included(788 million persons in the 25 countries) is in the 5059
nGy h1 range. A relatively large population group in the
Russian Federation is reported to be in the 6069 nGy h1range. Decreasing numbers of people are reported to reside inareas with higher levels of outdoor absorbed dose rate in air.
The distribution of population according to this sample ispresented in Figure IV.
0.30

0.25
FRACTION OF POPULATION

46. The activity concentration of 40K in soil is an order ofmagnitude higher than that of 238U or 232Th. In its firstassessment of representative concentrations of theseradionuclides in soil, in the UNSCEAR 1982 Report [U6], theCommittee suggested the values of 370, 25, and 25 Bq kg1
for 40K, 238U and 232Th, respectively. On the basis of the higher
levels reported for China and the United States, theCommittee revised the values for both 238U and 232Th to40 Bq kg1 in the UNSCEAR 1993 Report [U3]. A more
recently completed country-wide survey in China indicatessomewhat lower values [P1, P16]. These and the results formany more countries are included in Table 5. The medianvalues are 400, 35, and 30 Bq kg1, and the populationweighted values are 420, 33, and 45 Bq kg1 for 40K, 238U, and232
Th, respectively. The results of applying the dosecoefficients relating soil concentrations to absorbed dose rate
in air [I20, S49] to these values are shown in Table 6. The
population-weighted values givean average absorbed dose rate
in air outdoors from terrestrial gamma radiation of60 nGyh1.

0.20

0.15

0.10

0.05

0
-6 -5 -4 -3 -2 -1
0
1
2
3
4
5
6
Intervals of 10 nGy h-1 centered on the average absorbed dose rate in air

Figure V. Standardized distribution of population withrespect to decades about the average absorbed dose
rate in air.

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

50. The total population distribution presented in
Figure IV is obtained by combining the data from 25
countries, each with different average outdoor levels ofabsorbed dose rate in air. The small sample is responsible
for the somewhat uneven distribution. The distributions
within countries follow a more standard pattern. This is
illustrated in Figure V, the data and analysis for which are
in Table 10. The distribution of population for eachcountry is centred about a central decade of dose rate
indicated as 0. In other words, the distributions are aligned
about the central values. Each interval of dose rate
represents a decade of dose rate values (e.g. 5059
nGy h1). The average distribution is derived from the
combined distributions.

51. The standardized distribution is centred about the
average level of outdoor dose; 29% of the population is within
the 10 nGy h1 decade that encompasses the average value(e.g. is within 5059 nGy h1 for average outdoor levels
anywhere in the range 5059 nGy h1). Figure V shows the
distribution to ±6 decades of outdoor absorbed dose rate in air.
The distribution is relatively normal at levels of dose less than
the average, i.e. the population groups are 22% and 14% of
the total at the decades of dose from 10 to 20 nGy h1 below
the average. The distribution falls more sharply for outdoor
levels of dose above the average, i.e. the population groups are
14% and 6% of the total at the next two decades of dose from10 to 20 nGy h1 above the average. The distribution isapproximately log-normal, as shown in Figure VI.

Indoors
Outdoors-1

ABSORBED DOSE RATE IN AIR (nGy h )

10 3

91

10 2

10 1
0.2 0.5 1

2

5

10

20 30 40 50 60 70 80
PERCENTAGE

90

95

98 99 99.5 99.8

Figure VI. Cumulative distribution of population with respect to outdoor and indoor aborbed dose rate in air
from terrestrial gamma radiation.
The data are from independent surveys in different countries (outdoors: Table 9; indoors: Table 12).

52. Although the standardized distribution could be used toindicate the approximate proportions of a population about anaverage exposure level, it would be important to knowwhether there are local features of geology that could lead tounderstandable deviations in the extremes. Extrapolation of
the distribution, which is based on just over 10% of the world
population, to the entire world population would not bejustified, since areas of unusually low or high backgroundlevels are probably not well enough represented in thestandardized distribution.
53. In addition to variations from place to place, theambient background gamma dose rate in air at any specificlocation is not constant in time. It is subject to considerable
fluctuation, in particular from the removal of radon progeny
in air by rainfall, soil moisture and snow cover. Continuous
monitoring records show variations of ±5% from the daily
average level in 30-minute measurement intervals [K1, S6].
Washout and rainout of radon progeny from air may result inthe short-term enhancement, by 50%100%, of the gammaray dose rate in air. The extent of the elevation depends onrain interval [F2] as well as the rainfall amount. The elevatedlevel lasts for several hours and is followed by a depression of
about 5% from the average level, due to shielding fromincreased soil moisture. If there is no further rainfall, thereturn to normal occurs in hours or days as the soil saturation
disappears. Snow cover depresses the background level by
about 1% for each centimetre of snow [F17, H32].
54. There are small areas of markedly high absorbed dose
rates in air throughout the world that are associated withthorium-bearing and uranium-bearing minerals in the soil. In
those areas, absorbed dose rates in air of several hundred
nanograys per hour are not uncommon. The Committee has
noted the existence of these areas in all of its previous
assessments of natural radiation exposures, and a series ofconferences on this topic has helped to bring together theavailable information [C30, S57, V4, W13].
55. Areas of high natural background are listed in Table 11.
There are various causes of these elevated exposure levels.
Some result from monazite sand deposits, which have highlevels of thorium, including Guarapari in Brazil, Yangiang in
China, the states of Kerala and Madras in India, and the Nile
delta in Egypt. Some have volcanic soils such as Mineas
Gerais in Brazil, Niue Island in the Pacific, and parts of Italy.
The central massive in France has granitic and schistic rocks
and sands, and an area in the southwest of that country is one

92

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

of many associated with uranium minerals in soil. The areasof Ramsar and Mahallat in Iran and are caused by 226Ra
deposited from waters flowing from hot springs.
56. It should be noted that exposures in high backgroundareas can vary in time as deposits or beach sands are
replenished by springs and tides. Road construction andurbanization of these areas have led to moderate decreases inthe background levels [S56, V5].

although nearly 50% of the population is in the single decade
just above the mean dose rate for the country. The
distribution in Italy is also wide and approximately bimodal.
The distributions in the Russian Federation, Finland andLithuania are characterized by separate peaks in the
distributions at decades 2 or 3 above the country mean. Thesevarious distributions can no doubt be explained by the types ofbuildings in which the populations live. Data from additional
surveys in other countries will be required to indicate acharacteristic distribution that might be further generalized.

2. Indoors

58. Surveys of absorbed dose rates in air inside dwellings
are not as complete as outdoor surveys. The reported values
are listed in Table 7. About 45% of the world population isrepresented in the data that are currently available. The
population-weighted average is 84 nGy h1 with national
averages ranging from 20 to 200 nGy h1. The lowest values
are in New Zealand, Iceland and the United States, all below
40 nGy h1, which probably reflects the preponderance ofwood-frame houses. The highest values (95115 nGy h1) arein Hungary, Malaysia, China, Albania, Portugal, Australia,
Italy, Spain, Sweden, and Iran, which must reflect wide use ofstone or masonry materials in buildings.
59. The ratios of indoor to outdoor exposure are indicated inTable 7. These are intended not to reflect actual conditions at
specific locations but to give a general, relative idea of thebroad data gathered in different countries. The indoor andoutdoor results may have been derived in separate surveys inlocations not closelycoordinated. The outdoor levels generally
refer to open, undisturbed ground, but sometimes street
locations may have been used. The indoor to outdoor ratios
range from 0.6 to 2.3, with a population-weighted value of
1.4. Thus indoor exposures (absorbed dose rate in air fromterrestrial gamma radiation) are, in general, 40% greater thanoutdoor exposures. Values less than one are determined only
for Thailand, the United States and Iceland, where woodframe construction is common. High values of the ratio (>2)
result from high levels indoors (in Sweden and Hong Kong)
relative to outdoors or from low values outdoors (in the
Netherlands) relative to indoors.
60. The distributions of populations with respect to indoor
exposures have been assessed in several countries. The data
are presented in Table 12. The distributions are more or lesssymmetrical in several countries, e.g. Belgium, Denmark, andRomania. Bulgaria reports a relativelynarrowdistribution: thepopulation falls mostly in the central three decades of dose
rate. By contrast, the distribution in Hungary is very wide,

61. Indoor and outdoor distributions of external
exposures are compared in Figure VII. Only countries forwhich both indoor and outdoor distributions are available(generally the smaller countries of Europe) are included.
The comparison shows the shift to higher exposure rates
indoors and the somewhat broader distribution of
population for the indoor exposure rate. The populationweighted average exposure rates for the countries includedin Figure VII are 58 nGy h1 outdoors and 81 nGy h1indoors, with an indoor/outdoor ratio of 1.4, which is
identical to the population-weighted average for the muchlarger sample of countries in Table 7.
0.30

IndoorOutdoor

0.25
FRACTION OF POPULATION

57. Indoor exposure to gamma rays, mainly determined by
the materials of construction, is inherently greater thanoutdoor exposure if earth materials have been used; the source
geometry changes from half-space to a more surrounding
configuration indoors. When the duration of occupancy istaken into account, indoor exposure becomes even moresignificant. Buildings constructed of wood add little to indoor
exposures, which may then be comparable to outdoor
exposures.

0.20

0.15

0.10

0.05

0
0

20

40
60
80
100 120 140 160
ABSORBED DOSE RATE IN AIR (nGy h-1)

180

200

Figure VII. Comparison of indoor and outdoor exposure
rates for the total population of nine European countries.

3. Effective dose
62. To estimate annual effective doses, account must be
taken of (a) the conversion coefficient from absorbed dose in
air to effective dose and (b) the indoor occupancy factor. The
average numerical values of those parameters vary with theage of the population and the climate at the locationconsidered. In the UNSCEAR 1993 Report [U3], theCommittee used 0.7 Sv Gy1 for the conversion coefficientfrom absorbed dose in air to effective dose received by adults
and 0.8 for the indoor occupancy factor, i.e. the fraction oftime spent indoors and outdoors is 0.8 and 0.2, respectively.
These values are retained in the present analysis. From thedata summarized in this Chapter, the components of theannual effective dose are determined as follows:ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

84 nGy h1 × 8,760 h × 0.8 × 0.7 Sv Gy1 =0.41 mSv
Outdoors: 59 nGy h1 × 8,760 h × 0.2 × 0.7 Sv Gy1 =0.07 mSv
Indoors:

The resulting worldwide average of the annual effective
dose is 0.48 mSv, with the results for individual countries
being generally within the 0.30.6 mSv range. For
children and infants, the values are about 10% and 30%
higher, in direct proportion to an increase in the value ofthe conversion coefficient from absorbed dose in air toeffective dose.

B. INTERNAL EXPOSURESOTHER THAN RADON
63. Internal exposures arise from the intake of terrestrial
radionuclides by inhalation and ingestion. Doses byinhalation result from the presence in air of dust particles
containing radionuclides of the 238U and 232Th decaychains.
The dominant component of inhalation exposure is theshort-lived decay products of radon, which because of theirsignificance are considered separately in Section II.C.
Doses by ingestion are mainly due to 40K and to the 238U
and 232Th series radionuclides present in foods anddrinking water.
64. The dose rate from 40K can be determined directly
and accurately from external measurements of its
concentration in the body. The analysis of the content of
uranium- and thorium-series radionuclides in the bodyrequires more difficult chemical analyses of tissues, andfewer data are available. The analysis of the radionuclide
contents of foods and water, along with bioassay data anda knowledge of the metabolic behaviour of theradionuclides, provides an alternative basis for dose
estimation. The samples are more readily obtained, andthey can reflect widely different locations. With these data,dose estimates for children as well as adults can be derived.
The results of both approaches are presented in
Section II.B.2.
1. Inhalation
65. Inhalation intake of natural radionuclides other thanradon and its decay products makes only a minor
contribution to internal exposure. Broadly representative
breathing rates are listed in Table 13 for infants (1 yearold), children (10 years old), and adults. Results ofmeasurements of the concentrations of uranium- andthorium-series radionuclides in air are listed in Table 14.
These radionuclides are present in air because ofresuspended soil particles; the decay products of radon arepresent because of radon gas in air. A dust loading of
50 µg m3 is generally assumed [U6, U7]. With 238U and232
Th concentrations in the soil of 2550 Bq kg1, theconcentrations in air would be expected to be 12 µBq m3,
and this is generally what is observed.

93

66. It is important to note that the dust loading of air
contains substances other than soil, including considerable
proportions of organic matter and, especially in wintertime,
fly ash from coal burning [K10]. The organic content isdeficient in uranium compared to soil, but fly ash contains
much higher concentrations of uranium. At coastal locations,concentrations of uranium in sea air may be an order ofmagnitude lower than in continental or industrialized areas[K11]. Somewhat higher concentrations were measured
before 1980, as reported, for example, by Stevenson and Pan[S8]. The subsequent reductions may reflect different fuelsupplies.
67. In the UNSCEAR 1993 Report [U3], representativevalues of the concentrations of terrestrial radionuclides in
air were selected. As the database has changed very little,
most of these values, as given in Table 14, are still
considered valid. The highest concentration is for 210Pb.
The concentrations of the other radionuclides are lower byfactors of 10, 500, or 1,000 (see Table 14).
2. Ingestion
68. Ingestion intake of natural radionuclides depends on the
consumption rates of food and water and on the radionuclide
concentrations. The reference food consumption profiles inTable 13 are derived from information on consumption rates
adopted by the World Health Organization (WHO) [W1] andfood balances compiled by the Food and Agriculture
Organization of the United Nations (FAO) [F1]. The values
are best interpreted as average values for adults. Consumption
rates for children and infants are taken to be two thirds andone third, respectively, of these values, except for milk
products, which are consumed in greater amounts by infants
and children [C4]. The water intakes are based on reference
water balance information from the International Commission on Radiological Protection (ICRP) [I4]. Although thetabulated values are in reasonable agreement with otherassessments, there are substantial uncertainties implicit intheir mode of derivation. Moreover, there are large deviations
from this profile in various parts of the world, e.g. lower milk
consumption in Asia and lower leafy vegetable consumptionin Africa [W1].
69. Concentrations of naturally occurring radionuclides infoods vary widely because of the differing background levels,
climate, and agricultural conditions that prevail. There arealso differences in the types of local foods that may be
included in the categories such as vegetables, fruits, or fish. In
the UNSCEAR 1993 Report [U3], reference values wereselected for the concentrations of uranium- and thorium-series
radionuclides in foods. Obviously, these values must bederived from the most widelyavailable and representative data
possible. The database is summarized in Table 15.
70. It is difficult to select reference values from the wide
ranges of concentrations reported for uranium- and thoriumseries radionuclides in foods. An example may be made of210
Po, which is present in relatively high concentrations inseafood. The importance of 210Po to dietary intake has been

94

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

pointed out for countries such as Japan [Y1], the MarshallIslands [N2], Portugal [C1], and South Africa [H1]. A global
review of 210Po in marine food [A3] has suggested that
representative concentrations are 2,400 mBq kg1 in fish,
6,000 mBq kg1 in crustaceans and 15,000 mBq kg1 inmolluscs. Consumption offish and shellfish varies widelyfrom
countrytocountryand between individuals in a single country.
If representative consumption rates are 13 kg a1 of fish and
1 kg a1 each of molluscs and crustaceans, the intake of 210Po
with these foods would be 52 Bq a1. If there are processing or
distribution delays for fish products between catch andconsumption, the activity intake will be reduced owing to theradioactive decay of 210Po. Statistics quoted by Aarkrog et al.
[A3] indicate that 30% of seafood is eaten fresh, 30% frozen,
20% smoked, and 20% canned. For time delays of 0, 1, 2, and12 months, respectively, the weighted mean time delay is 93
days, slightly less than one physical half-life of 210Po.
Application of the correction factor 0.6 suggests an annual
intake of 31 Bq in seafood and a weighted concentra-tion of210
Po in fish products of 2,100 mBq kg1. This result
substantiates the reference value of 2,000 mBq kg1 [U3].
71. Estimates of uranium- and thorium-series radionuclides
in the total diet are presented in Table 16. They are
determined from market-basket evaluations or from duplicate
diet samplings. The values derived by multiplying thereference concentrations in foods and water and the intake
amounts for adults are shown for comparison. The agreementwith presently available data is reasonable.

ANNUAL INTAKE IN DIET (Bq)

10 3

10 2

72. The distributions of the annual intakes in various
countries of uranium- and thorium-series radionuclides areshown in Figure VIII. Each point in the Figure represents theaverage value of the intake for a particular country. If only arange of values has been reported and listed in Table 16, thegeometric mean of the extremes of the range has been taken
as the representative value. The distributions are approximately log-normal for each radionuclide and span an order ofmagnitude. Lead-210 and 210Po have the highest concentrations and similar distributions, and 230Th and 232Th have thelowest concentrations and also similar distributions.
Radium-226 and 238U have intermediate concentrations.
Because drinking water is important for the intake of uranium
and radium radionuclides, it is necessary to ascertain that thissource of ingestion intake is included in the dietary intake
estimates.
73. There are a number of circumstances in which theconcentrations of natural radionuclides in ingested food andwater substantially exceed the reference concentrations or the
more typical range of variation. Examples cited in previous
UNSCEAR Reports include the Arctic food chain and thehigh levels of uranium-series radionuclides in well water.
Since not all components of the diet are affected and becauseof common widespread distributions of foods of manydifferent origins over larger regions, the doses to individuals
in local populations are not usually so markedly elevated. The
circumstances of such exposures should be better described
and the data more systematically evaluated.

Thorium-230
Thorium-232
Uranium-238
Radium-226
Lead-210
Polonium-210

10 1

10 0

10 -1
0.2 0.5 1

2

5

10

20 30 40 50 60 70 80
PERCENTAGE

90

95

98 99 99.5 99.8

Figure VIII. Ranked distribution of annual intakes of uranium and thorium series radionuclides in diet.
Each point represents the average result of measurements made within a country.

3. Effective dose
74. The evaluation of the internal doses from inhalation
is presented in Table 17. Revised dose coefficients takenfrom ICRP [I9] are used. The age-weighted annual
effective dose is 6 µSv from inhalation of uranium- andthorium-series radionuclides in air, which may becompared to the 10 µSv derived in the UNSCEAR 1993
Report [U3].

75. Potassium is more or less uniformly distributed in the
body following intake in foods, and its concentration in the
bodyis under homeostatic control. For adults, the bodycontent
of potassium is about 0.18%, and for children, about 0.2%.
With a natural abundance of 1.17 104 for 40K [F6], a specificactivity of 2.6 108 Bq kg1, and a rounded dose conversion
coefficient of 3 µSv a1 per Bq kg1 [N1], the annual equivalentdoses in tissues from 40K in the body are 165 and 185 µSv a1
for adults and children, respectively. The same values areANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

appropriate for the effective doses, given the more or lessuniform distribution of potassium within the body.
76. The evaluation of the internal doses from ingestion of
uranium- and thorium-series radionuclides is presented inTable 18. The reference values of concentrations in foods areused with the consumption rates for infants, children, andadults. The age-weighted effective dose assumes a fractional
population distribution of 0.05, 0.3, and 0.65, respectively, forinfants, children, and adults. Some revisions have been madeto the dose coefficients since the UNSCEAR 1993 Report[U3]. The revised values of the dose coefficients [I2] give
generally higher estimates of effective dose for theseradionuclides. Much of the dose is due to 210Po, for which thegut uptake value recommended byICRP increased from 0.1 to
0.5. Some of the reference concentrations of 210Pb and 210Po infoods (Table 15) have also been slightly revised. The ageweighted total value is 140 µSv, compared with 52 µSv
derived in the UNSCEAR 1993 Report [U3].
77. The total effective dose from inhalation and ingestion ofterrestrial radionuclides is 310 µSv, of which 170 µSv is from40
K and 140 µSv is from the long-lived radionuclides in theuranium and thorium series. Essentially the same result isobtained for radionuclide concentrations in body tissues.
78. The Committee reviewed the concentrations of naturalradionuclides in tissues in previous assessments, most recently
in the UNSCEAR 1988 Report [U4]. Because of the low
concentrations in tissues of uranium- and thorium-series
radionuclides and variations with age and geographical location, the representative levels remain somewhat uncertain. As
additional studies are published only infrequently, thissituation is unlikelyto change. The database is summarized inTable 19.

CONCENTRATION (mBq kg -1)

10 4

10 3

95

79. Uranium is retained in the body primarily in theskeleton. It has been shown that the concentrations areapproximately similar in various types of bone (vertebrae,rib, femur) [H23]. Fisenne and Welford [F8] reported that,for residents of New York, concentrations of 238U invertebrae increased by a factor of 2 over the range 1473
years and in lungs by a factor of 3 over the same age range.
There were no such variations for liver and kidneys.
Lianqing and Guiyun [L1] found no variation inconcentrations of 238U in bone with age for adult residentsof Beijing, but the concentrations in bone of children were
up to two times greater than the concentrations in adults.
The wide range of concentrations in bone in samples from
Beijing (942,600 mBq kg1 in dry bone) illustrates thegreat variations encountered. The generally higher
concentrations in Beijing are related to a high intake of238
U in the diet and drinking water [L1].
80. An earlier estimate was that 70% of the body content
of 238U was in bone [J9, U6]. This would correspond to
500 mBq in the skeleton (assuming the reference
concentration of 238U in bone to be 100 mBq kg1) and
710 mBq in the body. The average concentration in soft
tissues would then be 3 mBq kg1, although higher
concentrations are measured in the lungs and kidneys.
81. Following intake by ingestion and inhalation, thorium
is mainly deposited on bone surfaces and retained for long
periods. Metabolic modelling assumes that 70% of the bodycontent of thorium is retained in the skeleton [I5]. From thereference concentrations given in Table 19 and assuming thecortical bone mass to be 4 kg and the trabecular bone mass to
be 1 kg, it may be estimated that the body burdens are
210 mBq of 230Th and 70 mBq of 232Th.

Thorium-230
Thorium-232
Uranium-238
Radium-228
Lead-210
Polonium-210
Radium-226

10 2

10 1

10 0
0.2 0.5 1

2

5

10

20 30 40 50 60 70 80
PERCENTAGE

90

95

98 99 99.5 99.8

Figure IX. Ranked distribution of the concentrations of uranium and thorium series radionuclides in bone.
Each point represents the average result of measurements made within a country.

82. The distributions of uranium and thorium concentrations in bone in various countries are shown in Figure IX. The
values are taken from Table 19. Because the distribution is
log-normal within a country, the geometric mean is taken to
be the most representative central value. If only a range ofvalues has been reported, the geometric mean of the extremesis plotted in the Figure. The values for individual countries
are also distributed approximately log-normally and extend
over an order of magnitude, with the variation being caused
primarilyby differences in intake of the radionuclides in foods

96

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

and water. The distributions for 238U and 230Th in bone aresimilar; somewhat lower concentrations are reported for 232Th.
Based on available data, the reference concentrations ofuranium and thorium radionuclides given in Table 19 havebeen revised. These data are limited and must be confirmed as
representative for the countries. The concentrations of 238U insoft tissues reported for the former Soviet Union, for example,
appear to be abnormally high.
83. Data on 226Ra, 210Pb and 210Po in tissues are also
included in Table 19 (the 226Ra data are in summary form).
Radium is retained primarily in bone, and concentrations
have been measured in many countries. In the UNSCEAR
1977 Report [U7], data from 16 countries were reported,which gave an arithmetic mean value of about 300 mBq kg1
in dry bone. With the fraction of 226Ra in the body distributed
in soft tissues taken to be 17% [I3], the average concentration
in soft tissues was inferred to be 4.8 mBq kg1. The population-weighted average of the same data gives somewhat lower
values: 230 mBq kg1 in bone and 3.6 mBq kg1 in soft tissues.
84. On the basis of an extended compilation of data from 26
countries, Fisenne [F15] determined the median value of 226Ra
in bone from a cumulative population frequency plot to be 170
mBq kg1 in bone. This value was quoted in the UNSCEAR
1982 Report [U6] and accepted as a reference value in the
UNSCEAR 1988 and 1993 Reports [U3, U4]. From a further
extended series of measurements in 31 countries that include
over 60% of the world population, Fisenne [F16] more
recently reported a median value of 260 mBq kg1 in bone,inferred from a cumulative frequency plot. The populationweighted averages for these 26 and 31 countries are 230 and
310 mBq kg1, respectively. Several larger countries withrelatively high concentrations in bone have been added to theextended list: Nigeria, 760; Russian Federation, 500; Brazil,
380; and China, 360 mBq kg1. A higher reference value for226
Ra in dry bone in the range 200300 mBq kg1 is thus
suggested.
85. The only recent data on 210Pb and 210Po concentrations
in tissues are those from Japan [T13]. Lead accumulates inbone; by contrast, polonium is distributed mainly to soft
tissues. Both would be present in the body in the absenceof direct intake from decay of 226Ra, but dietary intake is of
most importance in establishing body contents. Early
measurements showed the 210Pb/210Po concentration ratios
to be 0.8 in bone, 0.5 in lungs, and generally 1 in other soft
tissues [U7]. Some enhancement of 210Po in liver andkidneys seems substantiated by the data in Table 19. The
presence of 210Pb and 210Po in tobacco greatly increases theintake of these radionuclides by smokers. The measured
210
Po concentration in the lung parenchyma of smokers isabout 3 times that of non-smokers [C32, H35].
86. The annual effective dose from the reference values ofuraniumand thoriumseries radionuclides in tissue was
evaluated in the UNSCEAR 1988 Report [U4]. The estimate
was adjusted with revised tissue weighting factors in the
UNSCEAR 1993 Report [U3]. The result was 130 µSv. Somechanges have been made in the reference concentrations in thepresent evaluation, and an adjusted value of 120 µSv isobtained. The main contributor to this dose is 210Po. The
details of this evaluation are presented in Table 20. This result
is in close agreement with the estimate of 110 µSv derived
from the dietary consumption of adults and the reference
concentrations in foods and water (Table 18).
87. Further data from direct measurements of radionuclides
in human tissues would be needed to establish more broadly
based estimates of the annual effective dose from internal
radionuclides. Studies involving measurements of both
radionuclide intake and tissue contents in particular
populations would be especially useful to better define thesources and variations in exposures and the magnitudes of theuncertainties in the estimated doses. However, because of thelimited number of samples available and therefore thedifficulties in determining representative concentrations of
natural radionuclides in tissues, it may be necessary to put
more reliance on the more widely based dietaryintake data fordose estimation purposes.

C. RADON AND DECAY PRODUCTS
88. Radon and its short-lived decay products in the atmosphere are the most important contributors to human exposure
from natural sources. While the health risks associated withhigh radon exposures in underground mines have been known
for a long time, relatively little attention was paid toenvironmental radon exposures until the 1970s, when somescientists began to realize that indoor radon exposures could bequite high, in some cases comparable to the exposuresexperienced by many underground miners. Since then, theflood ofinformation on radon continues unabated. Manyof themore recent papers on the subject have appeared in theproceedings of international conferences at Salzburg (1991),
Rimini (1993), Montreal (1995), Prague (1995), Fukuoka(1997), and Athens (1999) [C2, E8, H2, J1, K13, S65], and avaluable synthesis of European research on the subject has
recently been published [E2]. All of this information is
improving the understanding of the environmental processes
that affect radon exposure, but there are still many problems
associated with the accurate assessment ofexposures and doses
to individuals and populations.
89. It is well known that inhalation of the short-lived
decay products of 222Rn, and to a lesser extent the decay
products of 220Rn (thoron), and their subsequent deposition
along the walls of the various airways of the bronchial tree
provide the main pathway for radiation exposure of thelungs. This exposure is mostly produced by the alphaparticles emitted by several of these radionuclides,
although some beta particles and gamma radiation are also
emitted. There is general agreement among scientists that
it is the alpha particle irradiation of the secretory and basal
cells of the upper airways that is responsible for the lungcancer risk seen in miners, although there remains someuncertainty as to exactly which cells are most important forthe subsequent induction of lung cancer. It is this situationthat is central to the problem of dose assessment. The key

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

point is that alpha particles emitted into the walls of the
airways have a short range, tens of micrometers, and there arelarge variations in the density of ionizations and excitations
along and near the tracks. Thus, the damage to the criticaltarget cells of the respiratory tract depends in a sensitive
manner on the source/target geometry. It follows that the dosethat is relevant to risk depends critically on thoseenvironmental factors that affect the probability that the radon
decay products are deposited near the critical target cells after
inhalation, as well as on the overall inhalation rate of these
decay products. In the following paragraphs, the current
concept of radon exposure is described and information on
how various environmental factors influence such exposure issummarized, along with available data on exposure levels
outdoors and indoors. Absorbed doses to the critical cells andeffective doses are then determined by applying the exposureto-dose conversion factors.
90. The radioactive properties of 222Rn and 220Rn and theirrespective short-lived decay products are given in Table 3.
The various half-lives of the radionuclides are very importantin determining the relative contributions of the two series tobronchial dose. The half-life of 222Rn is 3.824 d. It has four
short-lived decay products: 218Po (3.05 min), 214Pb (26.8 min),214
Bi (19.9 min), and 214Po (164 µs). Both polonium isotopes
are alpha-emitters. The relatively short half-life of 220Rn(55.6 s) means that it does not have much time to travel fromits production site to the immediate environment of humanbeings. The relatively long half-life of one of its decay
products, 212Pb (10.6 h), allows this isotope time to deposit on
surfaces or migrate away from its source before producing theimportant alpha-emitter 212Bi (60.6 min). The relative concentrations of the various radionuclides in the two series are alsostrongly affected by dynamic processes, including the attachment of the decay products to aerosol particles and their subsequent deposition on room surfaces or the ground as well as
air movement in general. The fraction of radon progeny in an
ultrafine mode (0.52 nm), not attached to ambient aerosol
particles, is known as the unattached fraction [H5, T16].
91. The evaluation of exposure to radon and the decay
products must thus take account of the actual activity
concentrations of the various alpha-emitting radionuclides inthe two series in the air that is breathed. This consideration,
as well as the fact that it is the total alpha particle energy yet
to be released by, or following, the decay of inhaledradionuclides that is important in determining dose, has led tothe definition of radon exposure rate in terms of potentialalpha energy concentration (PAEC) with unit of J m3 or ofWL (working level). This quantity can be readily calculated
once the activities of the individual radionuclides have been
determined from measurement. In most cases, the individual
activities are not directly measured, so that the exposure rate
must be indirectly determined using assumptions made on
concentration ratios, i.e. equilibrium factors, leading to thedetermination of the equilibrium equivalent concentration.
The essential point here is that environmental factors that
influence concentration ratios in each of the radioactive series
are of great significance for both exposure and dose
assessments.

97

1. Sources of radon(a)Entry into the atmosphere

92. Radon-222 and 220Rn are the gaseous radioactive
products of the decay of the radium isotopes 226Ra and 224Ra,
which are present in all terrestrial materials. Some of theatoms of these radon isotopes are released from the solid
matrix of the material by recoil when the radium decays. For
a radon atom to escape from the mineral grain into the porespace, the decay must occur within the recoil distance of thegrain surface. The range of recoil distance for 222Rn is
2070 nm in common minerals, 100 nm in water, and 63 µm
in air [T2]. Radon atoms entering the pore space are thentransported by diffusion and advection through this space
until they in turn decay or are released into the atmosphere(exhalation). The processes of radon emanation and transport,
particularly in the soil, have been reviewed in several classic
papers by Tanner [T1, T2]. New studies have focused on theeffect of moisture, the dynamics of release or recoil fromminerals, radon behaviour in soils as well as on aspects ofgeology and climate [G22, S50, S59, S60, W9]. Radongeneration and transport in porous materials involve solid,
liquid, and gas phases in the processes of emanation,diffusion, advection, absorption in the liquid phase, andadsorption in the solid phase. Most aspects of these processes
have been characterized individually; however, practicalapplications require a unified theoretical framework thatconsiders the processes simultaneously [N6, R11].
93. The fraction of radon atoms released into rock or soil
pore space from a radium-bearing grain is called theemanation coefficient, the emanation factor or the emanating
power. Factors affecting the emanation coefficient werereviewed by Schumann and Gundersen [S50]. Typicalemanation coefficients for rocks and soils range from 0.05 to
0.7 [N19]. Grain size and shape are two important factors that
control the emanation of radon in soil. They determine howmuch radium is near enough the grain surface to allow radon
to escape into pore spaces. Generally the radon emanation
factor is inversely proportional to grain size. The presence ofradium in increased concentrations in surface coatings of thegrains increases the emanating power relative to that in whichradium is uniformly distributed throughout the grains. The
sorption or co-precipitation of radionuclides with metal oxides[G18] or organic compounds [G17] in grain coatings is one of
the most important processes enhancing the radon emanation
coefficient. A study of granitic esker sand showed a highdegree of radioactive disequilibrium between 226Ra and 238U,
caused by 226Ra adsorbed on the surface of mineral particles[E5]. Microscopic fractures and fissures, called nanopores,
and pits or openings caused by previous radioactive decays
provide additional pathways for radon release. Particularly insand-sized and larger grains, nanopores can increase thespecific surface area of the grain, enhancing emanation by one
or two orders of magnitude.
94. Soil moisture plays an important role in the emanationof radon and its diffusion in soil, for several reasons. Soil
moisture, in the form of a thin film of water surrounding soil

98

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

grains, directly affects radon emanation by capturing theradon recoils from the solid matrix. These captures increase
the likelihood that radon atoms will remain in the pore spaceinstead of crossing the pores and imbedding themselves inadjacent soil grains. Both theoretical estimates [R11] andlaboratory tests show that adsorption on soil grains decreases
rapidly with increasing water content, becoming insignificant
for water contents greater than about 0.30.4 of saturation.
Decreased adsorption increases the emanation factor at low
water contents. Once radon enters the pore space, its partition
between the gas and liquid phases depends on the relative
volume of water in the pore space and on temperature. The
solubility of radon in water decreases with temperature. The
partition coefficient of radon between water and gas, theOstwald coefficient KT, gives the ratio of concentrations ofradon in water and in air [A4, C28, W9]. The value of KT
varies from 0.53 at 0-C to 0.23 at 25-C in water and istypically 0.30 at 15-C. Both partitioning and increased
emanation cause the concentration of radon in the air-filled
pores to be higher under moist conditions than under dry
conditions [A4, W9].
95. The concentration of radon in soil gas, CRn , in theabsence of radon transport is as follows [N19, W9]:
CRn  CRa f ρs C1 (1 C) (m [KT  1]  1)1

(1)

where CRa is the concentration of radium in soil (Bq kg1),
f is the emanation factor, ρs is the density of the soil grains(2700 kg m3), C is the total porosity, including both waterand air phases, m is the fraction of the porosity that iswater-filled (also called the fraction of saturation), and KT
is the partition coefficient for radon between the water andair phases. For dry soil, m is zero and the last term on theright side of the equation can be omitted. A warm, moist
soil (25-C, KT = 0.23, m = 0.95) with typical soil
parameters (CRa = 30 Bq kg1, f = 0.2, C = 0.25) will havea concentration of radon in pore air of 78 kBq m3, whichis 3.7 times higher than for the same soil under cold anddry conditions (0-C, KT = 0.53, m = 0.05, CRn =21 kBq m3) [W9].
96. Radon concentrations in soil within a few meters of thesurface of the ground are clearly important in determining
radon rates of entry into pore spaces and subsequently into theatmosphere. They depend on the distribution andconcentrations of the parent radium radionuclides in the
bedrock and overburden and on the permeability of the soil.
Certain generalizations can be made about the radium
concentrations in bedrocks of various types, but there are verylarge ranges within each type. In general, granites haverelatively high radium contents, sedimentary andmetamorphic rocks intermediate contents, and basalts andmost limestones low contents, although there are many
striking exceptions to this rule. Soils are similarly variable intheir radium content, and generalizations here are even moredifficult. This is due in part to the often complex relationshipbetween the bedrock and its overburden, especially in thosehigher latitude regions that were subject in the past to

glaciation. Radium transfers more readily to vegetation thanthe parent uranium radionuclides, and the emanation fromsoil organic matter is more effective than from soil minerals.
The effective permeabilities of bedrocks and soils are also
highly variable, being related to degree of weathering,
porosity, moisture content, and the presence of cracks or
fissures. This was demonstrated bySchumann and Gundersen[S50] for different soils and climates in the United States. The
regional differences are probablycaused by climate-controlled
differences in soil weathering processes.
97. The key soil-related parameters characterizing radontransport are the radon diffusion coefficient and the soil-air
permeability. The diffusion coefficient relates the gradient of
the radon concentration in air-filled pores to the flux. It can be
determined in many ways, which may cause confusion. The
pore diffusion coefficient De is also called the “interstitial” or“effective” diffusion coefficient. It relates the gradient of theradon concentration in air-filled pores to the flux density
across the air-filled pore area. The “bulk” diffusion coefficient
relates the same gradient to the flux density across thegeometric (bulk) area. The pore volume is divided into airfilled and water-filled parts. An approximate relationshipstates that the bulk diffusion coefficient D is equal to CDe,
where C is the porosity of the soil. Since the radon
concentrations in the air-filled and water-filled parts are not
the same, the parameter C must be replaced by the expression
Ca + KT Cw, which takes into account the partitioning [A4,
N19, R11].
98. Simple models are needed to determine the key
parameters of the diffusion coefficient and the soil-air
permeability for radon transport calculations. Rogers andNielson presented a brief review of such expressions [R12].
They also introduced an updated correlation for the effective
diffusion coefficient, which was based on more than athousand diffusion measurements. The experimental patternof the effective diffusion coefficient De as a function of thevolume fraction of water saturation is given in Figure X. At
low water content, De is a little affected by the water content.
At high water content, the pores become blocked by water andthe diffusion decreases. Typical porosity values for soilmaterials are 0.010.5, with 0.25 representing an averagevalue [U3]. Typical water saturation fractions are 0.10.3 forsand and 0.30.95 for loam, silty clay, or clay[N7]. The rangeof De in soil is typically 107105 m2 s1. For soil with afractional water saturation of 0.2 and a porosity of 0.25, thedata in Figure X yield an effective diffusion constant of 2 106
m2 s1, which is used as the representative value for soil
beneath the reference house (Table 21). In the case of a drysoil(with a total porosity C of 0.25), the corresponding bulk
diffusion coefficient of 5 107 m2 s1 is the product of a soil
porosity of 0.25 and a De of 2 106 m2 s1. This value of thebulk diffusion coefficient corresponds to the representativevalue given in the UNSCEAR 1988 and 1993 Reports [U3,U4]. If the partitioning has been taken into account, e.g. at afraction of saturation m of 0.2 (C = 0.25, Ca = 0.20 and Cw =0.05) and at a temperature of 15-C (KT = 0.3), thecorresponding bulk diffusion coefficient is lower, 4.3 107
m2 s1.

EFFECTIVE DIFFUSION COEFFICIENT (m2 s -1 )ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES
10 -5

101. Under normal circumstances, thoron concentrations
in soil gas would be roughly comparable to or perhaps
somewhat less than the 222Rn concentrations because of thegenerally similar production rates in rocks and soils andtheir similar behaviour in the ground. This has been
observed at two locations in New Jersey, United States[H3]. On the other hand, high thoron entry rates from theground are rarely encountered. Whereas fractures in the
ground and/or bedrock allow 222Rn to be pulled to thesurface from substantial depths (and volumes), the timeframe may be such that most of the thoron present at these
depths decays before reaching the surface.

10 -6

10 -7

10 -8

10 -9

99

Soil porosity 0.2
Soil porosity 0.25
Soil porosity 0.4(b) Entry into buildings

10 -10
0

0.2

0.4

0.6

0.8

1

VOLUME FRACTION OF WATER SATURATION

Figure X. Experimental pattern of the effective diffusion
coefficient of radon for soil of three different porosities asa function of the fraction of saturation [R12].

99. The main mechanism for the entry of radon into theatmosphere is molecular diffusion. An expression to estimate
the diffusive entry rate of radon into the atmosphere wasconsidered in the UNSCEAR 1988 and 1993 Reports [U3,U4]. For a porous mass ofhomogeneous material semi-infinite
in extent, the flux density of radon at the surface of dry soil JD(Bq m2 s1) is given by the expression
JD  CRa λRn f ρs (1 C) L

(2)

where CRa is the activity concentration of 226Ra in earthmaterial (Bq kg1), λRn is the decay constant of 222Rn(2.1 106 s1), f is the emanation fraction for earth material,ρs is the soil grain density (2700 kg m3), and C is theporosity of dry earth material. The diffusion length, L, isequal to (De/λRn)½. With representative values of theseparameters (CRa = 40 Bq kg1, f = 0.2, De = 2 106 m2 s1, C= 0.25), JD is 0.033 Bq m2 s1. Equation (2) is valid only
for dry soil. The presence of water in soil alters thetransport conditions, resulting in a modified equation for
JD. In addition, moisture affects the emanation coefficientand the diffusion coefficient. The estimate of JD,
0.033 Bq m2 s1, is in approximate concordance withmeasured values; however, it is higher than the estimatedmean worldwide flux of 222Rn of 0.016 Bq m2 s1 [W8].
100. Although diffusive entry of radon into the outdoor
atmosphere usuallydominates, there is also some advection
caused by wind and changes in barometric pressure.
Measurements of exhalation rates of radon from soil show
a variability that reflects the variability of radon
concentrations in near-surface pore spaces. Concentrationsof 222Rn in soil gas vary over many orders of magnitude
from place to place and show significant time variations at
any given site. Data have shown that there were prominent
increases in radon concentrations in outdoor air and inground water just before the large earthquake at Kobe,
Japan, in 1995 [I11, Y3].

102. Knowledge of the factors that influence 222Rn entry
rates into structures has considerably improved in recent
years as a result of investigations of the processes involved
and evaluations of simplified model houses [G1, H4, N16,
N19]. In the UNSCEAR 1988 and 1993 Reports [U3, U4],
a model masonry building with a volume of 250 m3,
surface area of 450 m2, and an air exchange rate of 1 h1
was described and calculations carried out to illustrate theeffects of the several mechanisms of radon entry, including
diffusion and advection from the ground and the building
materials, the entry of outdoor air, and 222Rn released fromwater and natural gas. In the following paragraphs thecontributions of these entry mechanisms are reevaluated.
The representative soil and house parameters used in theestimation are given in Table 21.
103. Many studies have shown that when high rates of radon
entry into buildings are found, advection is usually the main
factor [E2, M4]. This advection is driven by the pressure
differential between the building shell and the ground aroundthe foundation, produced by the higher temperatures within
the shell (the "stack" effect), mechanical ventilation, and tosome degree also by wind blowing on the building. The
effectiveness of this pressure differential in pulling in radonladen soil gas through the foundation is critically dependent
on the effective permeabilities of both the building foundationand the adjacent earth. Wind can also cause decreases inradon entry concentrations by its flushing effect on radon insoil surrounding the house [R8]. Under certain conditions,
atmospheric pressure fluctuations can also represent an
important mechanism of radon entry [R13, R14]. Because ofdifferences in the pressure differentials and permeabilities, theadvection contribution varies greatly from structure to
structure, at least in temperate and cold climates. For nonmasonry buildings of similar dimensions in a tropical climate,account must be taken of the usual characteristics andconditions of board floors, calm air, balanced temperatures,and high ventilation (2 h1). The most important contributions
to indoor radon in this case come from outside air anddiffusion from the ground, but the total value is not muchchanged.
104. The effect of anomalous subterranean air flows on
indoor radon concentrations has been observed in the United

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

States in hilly karst terrain [G14, R22] and in Finland on
eskers [A5]. Eskers are long and narrow steep-sided ridges
formed by glacial streams. In the United States, subterranean
networks of cavities and fissures were observed to facilitate
advective transport of radon-bearing air. In eskers the coarse
sand facilitates underground air flows. In both cases
differences between underground and outside air temperatures
and the accompanying differences in air density cause
subterranean air to move between the upper and lower partsof the area. Wind may also strongly affect the soil air andindoor radon concentrations in these areas. These flows
amplify indoor radon levels in winter or summer, dependingon the location of the house. Air flows due to thermal
differences and seasonal patterns of radon concentrations,which are comparable with the observations described above,
have been observed in caves and in mining regions close to
the tunnels and air shafts [C27, L17, S39].
105. Modelling studies have helped in understanding therelevance of factors that influence 222Rn entry rates into
structures. The modelling results were reviewed by Gadgil[G1]. The main entry route into the model house is the gap
between the foundation wall and the floor slab of concrete.
The first analytical studies demonstrated the dominant effectof soil permeability; they also showed that once the gap width
exceeds 0.5 mm, it no longer markedly increases the entryrate[M32, N8]. In later, mainly numerical model studies, theeffect of a subfloor gravel layer, backfill, entry into slab-ongrade houses, and alternative entry routes were modelled [A4,L4, N6, R15, R16]. The gravel layer below the floor slab
greatly increases the radon entry rate. Typically, when theratio of gravel to soil permeability is over 100 and the soil
permeability is less than 109 m2, the aggregate layer increases
the radon entry by a factor of 35 [A4, R15].
106. Permeability strongly affects the convective entry ofradon into houses. The range of soil air permeability values isvery broad, more than eight orders of magnitude, from lessthan 1016 m2 for homogeneous clay to more than 108 m2 forclean gravel. In a house with a slab-on-grade, the gap between
the floor slab and the foundation wall is the most important
entry route for radon-bearing soil air. If the slab is otherwiseradon-tight, high radon entry rates can only occur by meansof advection, and the diffusive entry rate is of minor
importance. For moderate permeabilities (k > 1012 m2), theentry rate is proportional to the permeability and the pressure
difference across the gap. The effect of soil permeability,
calculated for a model house, is illustrated in Figure XI [R15].
Of great importance is the presence of cracks or fractures ofany kind and of any scale in the solid matrix of the material.
These magnify the effects of pressure and temperature
differentials on the convective transport of radon. Fractures in
bedrock formations, cracks in the soil, and similar
inhomogeneities in the materials of the foundation of astructure have been identified as direct causes of high radon
entry rates into many structures exhibiting high indoor radon
concentrations [E2, K14, S3].
107. To estimate the diffusive entry rate from building
materials, the flux density from one side of a building

element, such as wall and floor, must be known. This isgiven by the following expression, presented in the
UNSCEAR 1988 Report [U4]:JD  CRa λRn f ρ L tanh(d/L)(3)

where L is the diffusion length in concrete, given inequation (2), and d is the half-thickness of the slab. The
equation is similar to that related to soil [equation (2)], theonly difference being the introduction of the hyperbolic
term. The parameters of wall materials given in Table 21
and a wall half-thickness of 0.1 m yield an estimate of
0.18 m for the diffusion length in concrete, thecorresponding radon flux JD being 0.0016 Bq m2 s1. Fora floor slab with a half-thickness of 0.05 m and values
given in Table 21, the corresponding diffusion length andradon flux are 0.22 m and 0.0008 Bq m2 s1. Because thediffusion lengths are greater than the half-thickness of thewall and floor, most of the free radon will be exhaled fromthe structures. Consequently, the thickness of the structure
is a dominant factor affecting the radon flux. These flux
densities estimated for building materials are about anorder of magnitude less than the flux density from thesemi-infinitive soil given above.
300
100
RADON ENTRY RATE (Bq s-1 )

100

10

1
No gravel-9
Gravel permeability 1 10 m-2-9Gravel permeability 2 10 m-2
Gravel permeability 5 10-9 m-2-9Gravel permeability 10 10 m-2

0.1

10-12

10 -11

10-10
PERMEABILITY (m 2 )

10-9

10 -8

Figure XI. Advective radon entry rates into a typicalbasement [R15]. Assumes slab-to-wall gap of 3 mm, deep
soil radon concentration of 37 kBq m-3, gravel layer beneathbasement slab of thickness of 15 cm and basement
pressure of 5 Pa with respect to the atmosphere.

108. The rate of radon entry from the building elements in
the reference house, U (Bq m3 h1), is given by theexpression(4)
U  3.6 103 S J / V
B D

where SB is the surface areas of the walls, JD is the flux
density, and V is the volume of the house (m3). The surface
area of radon-emitting walls in the reference house isestimated to be approximately 450 m2. The resulting valueof U is about 10 Bq m3 h1. Similarly, the entry rate from

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

109. Radon flux from concrete samples has been observed
to vary over two orders of magnitude [S40, U3]. This iscaused by differences in the 226Ra content of the material,
its porosity, density, and emanation fraction. Generally,
radon diffusion from the soil through the concrete has been
ignored; however, recent measurements from the UnitedStates show that radon diffusion through concrete can bea significant mechanism for radon entry into dwellings[R17]. Basically, this is because the quality of concrete infloor slabs is not as high as that of industrial concretes.
The porosities are higher, resulting in higher diffusion
constants. The measured effective diffusion coefficients inthe extensive study in the United States ranged from 2 108
to 5 107 m2 s1. These values are consistent with previous
values in the literature; the upper limit of the range is
extended by a factor of about 5. The geometric mean of 1.4
107 m2 s1 is sufficiently high to permit radon diffusion to
be a significant mechanism for indoor radon entry undercommon long-term indoor pressures. The results indicatethat the diffusion constant is also related to the porosity.
The porosity corresponding to the geometric meandiffusion constant was approximately 0.20. When radon
entry into the reference house presented in Table 21 wasestimated, 1 107 m2 s1 was used for the effective diffusion
coefficient of the floor slab. The corresponding estimate of
the effective diffusion coefficient, 7 108 m2 s1, presented
in the UNSCEAR 1993 Report [U3], has been used for wallmaterials.
110. For a slab lying on the ground, the radon flux
transmitted by the slab can be estimated using an empiricalformula, e.g. [U4]. With the parameter values of Table 21, an
estimate of 0.0071 Bq m2 s1 is obtained. This estimate ishigher by a factor of 6 than the estimate presented in the
UNSCEAR 1988 Report [U4], 0.0012 Bq m2 s1, owing todifferences in slab thicknesses, diffusion lengths, and radium
concentrations in the soil. With a floor area of 100 m2 and aflux density, JT, of 0.007 Bq m2 s1 inserted into equation (4),the radon entry rate for the reference house is estimated to be
10 Bq m3 h1 (Table 22). This result is ten times higher than
the radon flux from the slab and is comparable to the flux
from walls of the reference house. This yields further an
indoor radon concentration of 10 Bq m3 when the air
exchange rate is 1 h1. A comparison estimate is available
from Figure XII [A4], which illustrates the entry rate throughboth the slab and the perimeter gap, including the diffusive
and advective components. The parameters used in Figure XII
were approximately those used for the reference house,
Table 21. The diffusive entry through the slab can be
estimated from the entry rate calculated for a permeability of
1013 m2. In this case, the diffusive entry predominates, andadvection through the slab makes a negligible contribution.
Figure XII yields an estimate of 0.97 Bq s1, or 0.0097 Bqm2 s1, from the slab, which is consistent with the estimate
above of 0.007 Bq m2 s1, when the contribution of the
diffusive entry rate from slab material of about 0.002 Bqm2 s1, included in the estimate in Figure XII, is subtracted.
In practice, the cover materials to some extent decrease theradon flux from the floor. In basement houses, diffusion ofradon through concrete block walls may be a significant
source of indoor radon [L21].
50

RADON ENTRY RATE (Bq s-1 )a floor slab with a radon flux density of 0.0008 Bq m2 s1
and a surface area of 100 m2 is 1.2 Bq m3 h1. With an air
exchange rate of 1 h1, the corresponding indoor radon
concentrations in the reference house attributable to thematerials of which the walls and floor slab are built areabout 10 and 1 Bq m3.

101

10
5

Total
1
Slab
Advection through gap

0.5
Gap (3 mm)
0.2
10-14

10-13

10-12
10-11
PERMEABILITY (m )

10-10

10-9

2

Figure XII. Radon entry rates for model masonry house[A4].

111. The diffusive entry rate through the gap between thefloor slab and the foundation wall is next considered. Recent
studies [A4, L4, N6, R15] provide improved data from models
where diffusive transport is coupled with advective flow.
Generally, the increased advective flow through the gaps ofthe floor slab decreases the relative contribution of diffusion.
The upper limit of the diffusive entry rate through the 3 mm
perimeter gap can be estimated roughly using the entry rate at
the permeability of 1013 m2 s1 (Figure XII). For this permeability, diffusive entry is the dominant entry mechanism. The
estimated volumetric entry rate is 4 Bq m3 h1. Thisestimate represents the upper limit for the diffusive entry
rate through the gap and has been used as the representative entry rate for the reference masonry house (Table 22).
112. In the published modelling studies, the estimates of thesoil-air leakage rate for a house with a basement and abasement wall-floor gap length of 40 m (floor slab of 100 m2)
on soil with permeability of 1010 m2 are in the range 0.82
m3 h1 [M32, R15]. In a one-floor house with slab-on-grade
and a pressure difference of 1 Pa, the corresponding estimate
would be 0.20.5 m3 h1. When a flow rate of 0.2 m3 h1 anda leakage air concentration of 25,000 Bq m3 are applied to
the reference house of Table 21, the advective radon entry rateis 20 Bq m3 h1. The leakage air concentration is 40% of the
deep-soil radon concentration for the reference house. The
pressure difference of 1 Pa represents an indoor-outdoor
temperature difference of 20-C in a house with slab-on-grade
and a natural ventilation system. The advective entry rate of
20 Bq m3 h1 represents a permeability of approximately 21011 m2. This estimate has been used as the representativevalue for the reference house (Table 22). In the absence of the

102

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

gravel layer the permeability would have to be higher by afactor of 2 to yield the same entry rate.
113. The estimates of radon entry into a reference masonryhouse derived in the preceding paragraphs are summarized inTable 22. Diffusive and advective radon entry each contributeabout 40%, and the outdoor air contributes about 20%. The
numerical estimates for the various contributions are subject
to uncertainties because of the assumptions made. However,
the results are roughly consistent with measurements made in
actual buildings [H4]. The radon concentration of thereference house is approximately equal to the worldwide
average indoor radon concentration. More specific comparisons are made in Table 23 for typical houses in Finland[A1], where the radon concentrations indoors are higher andthe air exchange rates are lower than assumed for thereference house. The relative contribution of diffusion sources
is lower when the main construction material is wood.
114. Radon dissolved in water may enter indoor air throughde-emanation when the water is used. The water supply
contribution depends on the concentration of radon in thewater used for showering, laundry, etc., and can sometimes beimportant. The concentrations of radon in water may range
over several orders of magnitude, generally being highest in
well water, intermediate in ground water, and lowest in
surface water. Reference values selected in the UNSCEAR
1993 Report [U3] were 100, 10, and 1 kBq m3 and reference
usage was 10%, 30%, and 60%, respectively, for water fromthe three sources. The ratio of concentrations in air and inwater was taken to be 104 [U3]. This value was also
recommended in a national review in the United States ofexperimental and model studyresults [N10]. Thus, an average
concentration of radon in water of 10 kBq m3 implies acontribution of 1 Bq m3 to radon in air; for an air exchange
rate of 1 h1, the radon entry rate is 1 Bq m3 h1 for thereference house (Table 22).
115. Further evaluation of water as a source of radon forindoor air (public water supplies were measured in 100
major cities of China) confirms these results. The range ofradon concentrations in water was 0.04100 kBq m3, withan average value of 8 kBq m3 [R9]. Measurements of the
air-water concentration ratio did, however, showsomewhat
higher values, 270 104 on average, in separate studies[R9]. An analysis of all the existing published data giving
estimates of the transfer coefficient of radon from water toindoor air derived an average value of 1 104 [N10].
116. The results of analysing radon entry rates for thereference house suggest at least the relative contributions of
the processes involved. The main practical result of suchmodelling studies has been to identify strategies to mitigate
the high radon entry rates through the foundation that areusually the cause of high radon exposures [A11, C25, H19,
W4]. These studies have also revealed how complex thesituation is with respect to predicting entry rates forindividual houses or explaining them when they aremeasured. Considering all ofthe factors mentioned above, andespecially the design and quality of construction of anindividual structure, the factors that determine the entry rate
are many, varied, and very site-specific. Successful mitigation
strategies, such as identifying and sealing a limited number ofentry pathways or effectively ventilating the soil immediately
adjacent to the foundation, tend to work because radon entry
into many structures can be fairly readily prevented, or at least
substantially reduced, by redirecting and re-channelling airtransport away from building interiors. Radon concentrations
are typically reduced by about 30%. Other techniques aim at
reducing the building/ground pressure differential that drives
the advection; the radon concentrations are then typicallyreduced by 80%99%. Improvements in ventilation systems
normally change radon concentrations by less than 50%.
117. The processes that may allow thoron to accumulate inindoor air are difficult to assess. Because of thoron’s shorthalf-life, it was once thought that the only mechanisms for
significant thoron entry would be infiltration of outdoor air
and diffusion from building materials. But recent investigations have shown that entry through the foundation can also
be important [L3, S2]. There is an absence of detailed studies
in a sufficiently large sample of buildings to make wide
generalizations. However, given the comparable concentrations of 222Rn and thoron usually found in outdoor air, soil
gas, and building material pore spaces, it is not unexpectedthat indoor air concentrations of the two gases (ground floor
level only) are often roughly comparable.
118. Many of the studies of 222Rn and thoron source terms
have dealt with single-family houses, with or without
basements and crawl spaces. There is less information on
multi-storey buildings, such as apartment houses and officebuildings. The expectation that ground sources would be lessimportant for spaces well above the ground has generally been
supported by lower measured 222Rn and thoron concentrations
in higher storeys [S4], but the ground source contribution
depends on air circulation patterns within the building that areboth time- and building-dependent.
119. Considerable research has been carried out in recent
years to develop methods for defining areas where there is anincreased probability of finding buildings with high radon
entry rates and indoor air concentrations. A number of models
have been developed based on bedrock geology and soil
characteristics that have met with only limited success,undoubtedly because of the complications indicated in thepreceding paragraphs. Recent efforts in Finland [V3], Japan[F18], Sweden [A14], the United Kingdom [M1], and theUnited States [G2, P2] have shown that models thatincorporate measured radon and radiation levels as well as
relevant geological and geophysical parameters are likelyto be
the most effective.
2. Concentrations in air(a)Outdoors

120. Concentrations of radon in the outdoor environment are
affected not only by the magnitude of the exhalation rates in
the general area but also by atmospheric mixing phenomena.

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Solar heating during the daytime tends to induce someturbulence, so that radon is more readily transported upwards
and away from the ground. At night and in the early morning
hours, atmospheric (temperature) inversion conditions areoften found, which tend to trap the radon closer to the ground.
This means outdoor radon concentrations can vary diurnallyby a factor of as much as ten. There are also seasonalvariations related to the effects of precipitation or to changes
in prevailing winds [B23]. These effects must be taken into
account when interpreting the available measurements, manyof which are daytime samples.
121. Recent results of radon measurements outdoors tend to
confirm the estimates of typical outdoor 222Rn and 220Rn
concentrations made in the UNSCEAR 1993 Report of
10 Bq m3 for each [I14]. There is, however, a wide range oflong-term average concentrations of 222Rn, from approximately 1 to more than 100 Bq m3, with the former perhaps
typical of isolated small islands or coastal regions and thelatter typical of sites with high radon exhalation over large
surrounding areas. Although data are sparse for thoron,
considerable variabilityfrom place to place would be expected
because of thoron’s short half-life, which means that theeffective surface source, about 0.1 km2 [S4], is much smaller
than that for 222Rn, emphasizing the effect of local variations
in exhalation rate. Even more important is the fact thatthoron's short half-life results in a very steep vertical gradientin its atmospheric concentration at any location. A few
measurements show that concentrations a few centimeters
above the ground surface and concentrations at a height of
1 m vary by a factor of about 10 [D2, I10, N18]. This gradientwould be expected to vary considerably with atmosphericconditions. Thus, pronounced time variations would be
expected at any height above the ground at any location. Thishas obvious implications for estimating thoron exposure
outdoors and the outdoor air source term for indoor thoron.
122. Direct measurement of the concentrations of all shortlived decay products of 222Rn and 220Rn are difficult andlimited. They are estimated from considerations ofequilibrium (or disequilibrium) between these nuclides andtheir respective decay products. An equilibrium factor F isdefined that permits the exposure to be estimated in terms of
the potential alpha energy concentration (PAEC) from themeasurements of radon gas concentration. This equilibrium
factor is defined as the ratio of the actual PAEC to the PAEC
that would prevail if all the decay products in each series werein equilibrium with the parent radon. However, it is simpler
to evaluate this factor in terms of an equilibrium equivalentradon concentration, Ceq, in the following manner:
F = Ceq/Crn
Ceq = 0.105 C1 + 0.515 C2 + 0.380 C3
Ceq = 0.913 C1 + 0.087 C2(222Rn series)(220Rn series)

where the symbols C1, C2, and C3 are the activity concentrations of the decay progeny, namely 218Po, 214Pb, and 214Bi,
respectively, for the 222Rn series and 212Pb and 212Bi (C1 and
C2) for the thoron series. The constants are the fractional

103

contributions of each decay product to the total potential alphaenergy from the decay of unit activity of the gas. In this way,a measured radon concentration can be converted to an
equilibrium equivalent concentration (EEC) directly proportional to PAEC. This provides a measure of exposure in termsof the product of concentration and time. The EEC can beconverted to the PAEC, when desired, by the relationships
1 Bq m3 = 5.56 106 mJ m3 = 0.27 mWL (222Rn) and1 Bq m3 = 7.6 105 mJ m3 = 3.64 mWL (thoron).
123. Many measurements have been made of 222Rn anddecay product concentrations, allowing estimates to be madeof the magnitude of the equilibrium factor to be estimated interms of both typical values and range. These were discussed
in previous reports of the Committee [U3, U4]. More recent
extensive measurements in Europe [R1, W10], the UnitedStates [W2], Canada [B12], and Japan [H18, K9] indicate
typical outdoor 222Rn equilibrium factors of between 0.5 and0.7. These results suggest that a rounded value of 0.6 may be
more appropriate for the outdoor environment than theprevious estimate of 0.8. There is, of course, a wide range ofvalues from individual measurements, which is understandable given the manyenvironmental factors that influence
the various radionuclide activity ratios, including theexhalation rates and atmospheric stability conditions. The
range of the equilibrium factor for outdoor radon is from 0.2
to 1.0, indicating a degree of uncertainty in the application ofa typical value toderive equilibrium equivalent concentrations.
124. The equilibrium factor approach is more difficult toapply to estimate thoron decay product exposure because,
unlike the 222Rn situation, the concentrations of the gas andthe decay products at any particular location, indoors or
outdoors, may not be closely related. This is primarily due tothe half-lives in the decay series, which produce very different
distributions in the atmosphere of the gas and the decay
products. A very limited amount of data on thoron decay
product concentrations outdoors indicated a typical EEC oftheorder of 0.1 Bq m3 [S4].
(b) Indoors
125. There is a wealth of data available on indoor 222Rn
concentrations, and new information is becoming available
on indoor thoron. Substantial compilations of 222Rn resultsappeared in the UNSCEAR 1988 and 1993 Reports [U3,U4]. These results are supplemented with recent survey
data in Table 24. It is sometimes difficult to evaluate therepresentativeness of results from published reports. New
information will be appearing from many countries inAfrica, Asia, and South America, partly as a result of theCoordinated Research Programme on Radon in theEnvironment, sponsored by the International Atomic
Energy Agency (IAEA). This will provide a better
understanding of how different climates and housing
patterns affect radon exposures. At this stage, it does notappear that the survey results have changed markedly fromthose contained in the UNSCEAR 1993 Report [U3]. In
particular, the values of 40 and 30 Bq m3 for thearithmetic and geometric means of the distribution of

104

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

worldwide indoor 222Rn concentrations, with a geometricstandard deviation of 2.3, still seem reasonable.
126. The geographic (latitudinal) variation in indoor
radon concentration was considered in the UNSCEAR
1993 Report [U3]. Although levels at equatorial latitudes
should reflect higher ventilation rates because of higher
average outdoor temperatures, the general scatter in the
results indicated that many other factors are involved. The
additional data available from the present survey areincluded in Figure XIII.

CONCENTRATION (Bq m -3 )

10 3

10 2

10 1

10 0
0

10

20

30
40
LATITUDE

50

60

70

Figure XIII. Average concentrations of radon indoors
in various countries in which measurements have been
made in relation to latitude.

127. Recent determinations of the equilibrium factor forradon indoors generally confirm the typical value of 0.4
previously assessed by the Committee [U3, U4]. Indoor
measurements show a range from 0.1 to 0.9, but most arewithin 30% of the typical value of 0.4 [H5, R2]. A recent
study [H5] in seven North American houses has shown thatthe equilibrium factor in any building shows a significant
variation with time, typically of a few tens of percent.
Although the measurement of 222Rn gas concentration may
serve as a surrogate for direct measurement of the decay
product concentrations in the determination of exposure, it
is important to recognize that EECs or PAECs estimated inthis manner for particular structures may be in error,
frequently by several tens of percent and, rarely, by asmuch as a factor of 2.
128. Recent research has considerably clarified the situation
with respect to indoor thoron and thoron decay productexposures. Several authors, e.g. [M2, N4, S4], have discussed
the difficulties and uncertainties in measurements of such
exposures and summarized the available data. It is not
surprising, based on considerations discussed in previous
paragraphs, that the limited data show a wide range of values.
This may reflect measurement problems as well as realvariations, since various techniques are used, and there has
been much less international effort devoted to quality
assurance for thoron than for 222Rn. The large uncertainties
are also due to the low concentrations usually encountered.

The concentrations are highly variable in both space and timeand are not closely coupled with the decay product concentrations at a particular location. For example, in a particularroom of a structure, the thoron gas concentration varies
considerably with distance from the walls and floor because of
its short half-life [D1], while the decay products arehomogeneously distributed in the room air. Moreover, thedecay products were produced partly by thoron present hours
earlier, the concentration of which might have been very
different. There is, therefore, no surrogate for decay productmeasurement in the estimation of thoron exposure. Thisconclusion is supported by recent experimental [M2, M27]
and calculational studies [Y2]. Earlier measurement data
indicated that a thoron EEC of about 0.3 Bq m3 is fairly
typical of indoor atmospheres, although regional averages canbe much higher or lower. This value was used in the
UNSCEAR 1993 Report [U3].
129. Although measurements of thoron in indoor air are
limited, most investigations have reported both the radon
and thoron equilibrium equivalent concentrations, so some
generalizations from the derived ratios can be made. Basedon the physical characteristics of radon and thoron andmodel entry rates to buildings, ICRP estimated expectedconcentrations in buildings [I8]. These ranged from 10 to
100 Bq m3 for radon and 2 to 20 Bq m3 for thoron in
typical circumstances (37 Bq m3 for both radon andthoron in outdoor air; concrete and brick building material;a ventilation rate of 0.7 h1). In terms of EEC, theseconcentrations indoors are 250 Bq m3 (mean =15 Bq m3) for radon and 0.042 Bq m3 (mean = 0.5
Bq m3) for thoron. This corresponds to an expected
thoron-radon EEC ratio of 0.03.
130. From regional surveys in the United Kingdom [C26],
the ratio of the PAECs of thoron to radon decay products
ranged from 0.01 to 30. The highest value was obtained
when the ventilation rate in the house was high (2.6 h1)
and the radon concentration was unusually low(2.2 Bq m3). The distribution of values was approximately
log-normal, and most values were between 0.1 and 2. For
the wider survey region in the United Kingdom, including
areas where high indoor radon concentrations occur, thegeometric mean value of the ratio was 0.5. For more
typical regions of the country, i.e. excluding the very
radon-prone areas, the mean ratio was 0.3 [C26].
131. This ratio can also be expressed in terms of the EEC.
The relationship between PAEC and EEC is as follows[I8]: EECRn = 1.81 108 Cp and EECTh = 1.32 107 Cp forradon (222Rn) and thoron (220Rn) decay products,
respectively. The relationships give the EEC with units of
Bq m3 when the potential alpha energy concentration, Cp,
for either radon or thoron is expressed in J m3. The
thoron-radon EEC ratio is thus lower than the PAEC ratio
by a factor of 0.073, so that PAEC ratios of 0.30.5
correspond to EEC ratios of 0.020.04.
132. Available data on thoron EECs are given in Table 25.
These are generally results of a few, short-term measure-ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

ments and are thus far less representative than the resultsfor 222Rn. Because of the short half-life of 220Rn, theconcentration of the gas varied greatly, as mentioned
above, with distance from the soil surface or the structural
material. Since such measurements cannot easily be
standardized, there is little point in presenting data on
concentrations of 220Rn alone. The concentration of thoron
decay products indoors are highest for wood-frame andmud houses, found particularly in Japan [D1, G12] or withthe use of some building materials of volcanic origin, as
found in some Italian regions [B25, S62].
133. The previouslyassumed representative concentrationsof thoron EEC were 0.1 Bq m3 outdoors and 0.3 Bq m3indoors [U3]. These values are at the lower range of values
reported in Table 25, most of which were short-term
measurements, but are in good agreement with the longterm measurements of Harley and Chittaporn [H36]. The
thoron to radon EEC ratio determined in the United
Kingdom (0.02) discussed above times the representative
radon EEC indoors of 16 Bq m3 (40 Bq m3 × 0.4) would
imply a representative value of the concentration of thoron
indoors of 0.3 Bq m3. It thus seems justified to retain theabove concentrations of thoron [U3] as representative.
Further data are needed on the concentrations of thoron in
air in order to provide a reliable estimate of the effective
dose from thoron and its decay products.
134. The exposures and consequent doses from radon thatare of interest in the assessment of health risks are those
integrated over many years. It is well known that there aresubstantial time variations in the exposure rates from thedecay products of both radon nuclides at any location, andeach individual spends time at many locations, bothindoors and outdoors, where exposure rates can be very
different. Much of the published data on indoor 222Rn
concentrations is based on time-integrations of days (e.g.
using charcoal canisters) to 312 months (e.g. using
nuclear track detectors). There have been many studies of
how short-term measurements can be used to estimate
long-term exposures (see, for example, [P2]). One
promising development has been the success of models
based on outdoor temperature variations (effectively asurrogate for the indoor/outdoor temperature difference) in
estimating and tracking the time variations of radon
concentration in a few houses [H6]. Local meteoro-logical
data can then be used to estimate long-term exposure. In
Nordic countries, measurements made indoors in winter,when concentrations are higher because of strong advective
air flows from soil, must be adjusted by a correction factorof 0.8 to estimate the annual mean radon concentrations[A12, M28, N12]. In the United Kingdom, correction
factors of similar magnitude are needed for short-term
measurements in winter and in the opposite direction forsuch measurements in summer to estimate the averageannual concentrations [P11].
135. An important problem in epidemiological radon studies
is to determine the long-term average radon levels that existed
in the homes of the subjects under investigation. It has been

105

proposed tomeasure 210Poactivities resulting from radon decay
on glass surfaces [L2, L19, S52] or in volume traps [O10,S53]. The first technique is based on the deposition of airborneradon decay products onto smooth glass surfaces, followed bytheir subsequent recoil implantation. The second technique isbased on the diffusion of radon throughout the bulk of spongymaterials. The radon decay products are directly deposited
inside the volume traps, where they remain until they are set
free by means of a radiochemical separation procedure. Bothof these techniques are promising [F19, M33].
136. The important distinction between “dwelling exposure
assessment” and “person exposure assessment” was the
subject of a recent experimental study in Austria [S5]. The
six-month exposures of 34 individuals were measured with apersonal radon meter and estimated from the particular
exposure conditions and occupancy times at home, at work,and elsewhere. Results of the two assessments were found todiffer by a factor of up to 3, and the possible reasons for thesedifferences were explored. Judicious placement of monitors in
the dwelling, for example in a bedroom rather than in thecellar, may reduce the differences between the two assessment
approaches [H7].
137. In this Annex, as in previous UNSCEAR reports,
typical exposures and exposure conditions are assessed forboth indoor and outdoor environments, and doses are
estimated from these results and estimated occupancy
factors. This assessment is something like the dwelling
exposure assessment: the basic assumption is that it
reasonably describes typical exposure conditions averaged
over large populations. As the population of interest
becomes smaller, for example, cases and controls in an
epidemiological study, the uncertainties in the assessmentof individual and small group long-term exposures must be
better understood and quantified.
138. In previous UNSCEAR reports, long-term radon
exposures were estimated using indoor and outdoor
occupancy factors of 0.8 and 0.2, respectively. These stillseem to be reasonable estimates for the global population.
However, for smaller population groups and individuals,
the factors may be quite different.

3. Effective dose
139. Estimates of absorbed dose to the critical cells of therespiratory tract per unit 222Rn exposure applicable to thegeneral population can be derived from an analysis of
information on aerosol size distribution, unattached fraction,breathing rate, fractional deposition in the airways, mucous
clearance rate, and location of the target cells in the airways.
Such estimates are model-dependent and necessarilysubject toall of the uncertainties associated with the input data as well as
the assumptions built into the particular calculational model.
140. For both radon-exposed underground miners and those
exposed to other carcinogenic aerosols such as cigarettesmoke, 75% of lung tumours are found in the branchingANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

141. Upon decay of 222Rn gas or in recoil from decay of theparent radionuclide, radon decay products are formed as
small positive ions or neutral atoms approximately 0.5 nm
in diameter. They increase rapidly to 0.55 nm as a resultof clustering on water or other molecules in the air,depending on local conditions. The ultrafine aerosol modeis called the unattached fraction. Most of these small
particles become attached to the local or ambient aerosol,
20500 nm diameter, and this mode is called the attachedfraction. The degree of attachment depends on the ambient
aerosol concentration. In dusty, smoky conditions theunattached fraction will be very low, but in a very clean
environment, such as prevails with air filtration, theunattached fraction can be much higher. Normally, only218
Po is found in the unattached form with lower
concentrations of unattached 214Pb (214Pb/218Po = 1/10).
142. The unattached fraction of radon decay products isexpressed as a fraction of the total potential energy (fpot) [I18].
Other expressions have been used involving ratios of decay
atoms, so care must be taken in interpreting the data. A
central value of the unattached fraction in houses is fpot = 0.05
[H5], but it can vary by a factor of 2 depending on local
sources and air filtration.
143. Aerosol characteristics for the indoor environment havebeen documented by several investigators [B13, H5, N17,
R18, T3, T17]. Although the ambient aerosol size in houses
is about 100 nm on average, the diameter changes with indoor
activities or sources. The use of electric motors, open flames,or electric heaters produces smaller aerosols with diameters of
about 50 nm [T3]. Cigarette smoke produces aerosols about
300 nm in diameter [C23]. There is always a distribution ofsizes present that can be well represented by a log-normal
distribution with a geometric standard deviation of about 2.
144. Breathing rate is an important dosimetric factor because
it controls the volume of air brought into the lungs. It canchange the dose per unit concentration in air by a factor of
about 2, with lower doses derived at lower breathing rates.
The breathing rate varies, of course, with the degree of activityof the individual and is not easily measured. The breathing
rate of an adult male was estimated to be 0.45 m3 h1 resting(8 h per day) and 1.2 m3 h1 in light activity (16 h per day)[I4]. The values for the adult female are 20% less resting and
5% less in light activity. The breathing rates were recently reevaluated [I7], and somewhat lower averages values were
derived, namely 22.2 m3 d1 for the adult male and17.7 m3 d1 for the adult female.

145. The location of target cell nuclei in the bronchial
epithelium has been measured in surgical specimens fromover 100 persons of different sex, smoking history, and age[H8]. The average depth of basal and mucous cells implicatedin carcinogenesis was 27 and 18 µm, respectively.
146. Deposition of aerosols in the bronchial airways has been
investigated with replicate casts from human subjects. The
detailed dimensions of the human bronchial airways were firstreported by Yeh et al. [Y4] and later verified by Gurman et al.
[G15]. Nasal deposition measurements of the unattachedfraction is about 15% greater than oral deposition [C24].
Nasal deposition is approximatelythe same for both cyclic andsteady air flow and for all ages. Deposition in the bronchialregion occurs by diffusion for aerosol diameters less than
200 nm and by impaction for some particles of greater size.
An empirical equation for deposition of aerosols in the upper
bronchial airways was derived by Cohen et al. [C5] frommeasurements using replicate casts. Equations for deposition
by impaction have also been derived [C10, G15, R6, R7].
70

DOSE COEFFICIENT [nGy (Bq h m-3)-1]

airways of the bronchial tree and 15% in the gas exchange
region, or parenchyma [S36]. The dosimetry of inhaled radonand decay products is therefore directed to the cells of thebronchial epithelium. The most important variables affecting
the alpha dose to the nuclei of these cells are the aerosol size
distribution, the unattached fraction, the breathing rate, andthe depth in tissue of the target cell nuclei. Considerable
research has been conducted to determine quantitative valuesof the various biological and physical parameters required forlung dosimetry evaluation.

For unattached fraction of 0.05
Breathing rate
1.2 m h
1.2 m h
0.6 m h0.3 m h

60
50

3

-1

3

-1

3

-1

3

-1

(oral)(nasal)(nasal)(nasal)

40
30
20
10
0
0

200

400

600

800

1000

MEDIAN AEROSOL DIAMETER (nm)For breathing rate 0.6 m3 h-1

50
DOSE COEFFICIENT [nGy (Bq h m-3)-1]

106

Unattached fraction fpot
0.21
0.11
0.05
0.02

40

30

20

10

0
0

200

400

600

800

1000

MEDIAN AEROSOL DIAMETER (nm)Figure XIV. Absorbed dose in bronchial epithelial cells
per unit exposure (EEC) to radon.

147. Utilizing the latest and best available data for thevarious physical and biological parameters, dosimetrists have

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

calculated the absorbed dose per unit time-integrated EEC ofradon in air. The results of Harley et al. [H8] are illustrated in
Figure XIV. Since all particulate exposures contain a
distribution of aerosol diameters rather than a unique ormonodisperse size, it is more relevant to estimate the dose perunit exposure for a given median diameter and a geometricstandard deviation σg. The results in Figure XIV are for
distributions with σg = 2. The variation in dose with several
different breathing rates is shown in the upper portion of
Figure XIV for a specific unattached fraction fpot = 0.05. The
variation of dose with other values of the unattached fraction
for a typical breathing rate (0.6 m3 h1) is shown in the lower
portion of Figure XIV. Similar variations are seen for otherbreathing rates.
148. The dosimetric evaluation of the absorbed dose to basal
cells of the bronchial epithelium per unit exposure gives
values in the range 525 nGy (Bq h m3)1. The central value
is estimated to be 9 nGy (Bq h m3)1 for average indoor
conditions, a breathing rate of 0.6 m3 h1, an aerosol median
diameter of 100150 nm and an unattached fraction of 0.05.
For an apportioned tissue weighting factor of 0.08 for the
bronchial and bronchiolar regions [I7] and the quality factorof 20, the effective dose per unit EEC is 15 nSv (Bq h m3)1.
The dose to the pulmonary region of the lungs is of much lesssignificance.
149. ICRP has developed a more detailed lung model [I7] tocalculate the effective dose for exposure to airborne
radionuclides. It is, nevertheless, still a simplification of actual
respiratory anatomy and physiological behaviour. This model
is not yet recommended for radon and its decay products
because of the discrepancy in results of risk derived from themodel and from epidemiological studies. The difficulties
include the measurement and specification of aerosol
characteristics, including size and unattached fraction. The
model is being used to assess the influence of biological andaerosol parameters and to characterize the uncertainties in
estimates of the human lung dose [B11, Z3].
150. The results of major dosimetric studies of the lungdose from deposited 222Rn decay products are compared inTable 26. Differences in the parameter values are evident,
but consensus is beginning to emerge on the depth of thetarget cells, and the characterization of the airways and thedeposition measurements based on accurate anatomical
representation are greatly improving the dosimetry. Withfurther progress, the derived dosimetric estimates can be
expected to converge.
151. Efforts are being made to use measurement techniques
based on wire screen penetration theory to simulate theparticle collection properties of the nasal and tracheobronchialparts of the respiratory tract [H29]. Several radon progeny
samplers for the direct determination of the lung dose havebeen developed [G19, J11, O2, S54]. Dose coefficients were
derived from experimental data using both approaches [H5,
H28, R21, S54, W2, Y7]. The results for different indoor andoutdoor environments vary from 10 to 50 nSv (Bq h m3)1.
Similar results are obtained in sensitivity studies assessing the107

influence of biological and aerosol parameters on human lungdose [B11, M25, Z3].
152. As an alternative to a dosimetric approach, ICRP has
derived a conversion convention for radon exposures basedon the equality of detriments from epidemiologicaldeterminations. The nominal mortality probability coefficient
for radon for males and females was taken to be 8 105 permJ h m3. This value was determined from occupational
studies of miners. Although the exposure conditions in mines
are different from those in homes, the differences arecompensating, e.g. lower unattached fractions and higher
breathing rates in mines than in homes. This coefficient was
related to the detriment per unit effective dose, chosen to be
5.6 105 per mSv for workers and 7.3 105 per mSv for the
public [I1]. The values of the conversion convention are thus
8 105 ÷ 5.6 105 = 1.43 mSv (mJ h m3)1 (5.06 mSv
WLM1) for workers and 8 105 ÷ 7.3 105 = 1.10 mSv(mJ h m3)1 (3.88 mSv WLM1) for members of the public.
The rounded values adopted by ICRP are 1.4 and 1.1 mSv(mJ h m3)1 (5 and 4 mSv WLM1) at work and at home,respectively [I6]. The latter value corresponds to 6 nSv(Bq h m3)1, which is different by a factor of 2.5 from thecentral value derived using the dosimetric approach. This is
not a big discrepancy, considering the complex physical andbiological issues involved.
153. The range of dose conversion factors for radon, derived
from epidemiological studies [I6] and physical dosimetry,varies from 6 to 15 nSv (Bq h m3)1. The previous value
applied in the UNSCEAR 1993 Report was 9 nSv(Bq h m3)1. Updated and additional epidemiological studiesof 11 underground mining cohorts [C33], performed
subsequently to the calculation made in [I6], suggests anincreased radon risk per unit exposure. Therefore an increasein the epidemiologically based dose conversion convention is
anticipated. The domestic epidemiological radon studies do
not yet have sufficient precision to provide numerical risk
estimates that could be used in an epidemiological doseconversion convention. Given the present range of values ofthe dose conversion factor, the established value of 9 nSv(Bq h m3)1, used in past UNSCEAR calculations [U3, U4],
is still considered appropriate for average effective dose
calculations. For the representative concentrations of radon
selected in Section II.C.2, equilibrium factors of 0.4 indoors
and 0.6 outdoors, occupancy, and the dose coefficient as given
above, the following annual effective doses are derived:
40 Bq m3 × 0.4 × 7,000 h × 9 nSv (Bq h m3)1= 1.0 mSv
Outdoors: 10 Bq m3 × 0.6 × 1,760 h × 9 nSv (Bq h m3)1= 0.095 mSv
Indoors:154. Less work has been done to derive the dose coefficientfor thoron. The values used in the UNSCEAR 1993 Report[U3] were 10 nSv (Bq h m3)1 for exposures outdoors and
32 nSv (Bq h m3)1 indoors. Applying the new lung model[I7] results in significantly higher values. There are no
epidemiological data for lung cancer risk following thoron
exposure from which to derive a conversion convention for

108

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

thoron decayproducts similar to that for radon decayproducts.
The value of 40 nSv (Bq h m3)1 for equilibrium equivalentconcentrations of thoron, derived in Annex A, “Doseassessment methodologies”, seems appropriate for evaluating
exposures both indoors and outdoors.
155. The concentration of 220Rn is about 10 Bq m3
outdoors and approximately the same indoors. However, it
is not possible to use the concentration of the gas in dose
evalua-tion, since the concentration is strongly dependent
on the distance from the source. Starting with the assumed
represen-tative equilibrium equivalent concentrations, as
discussed above, the annual effective dose may be derived
as follows:
Indoors: 0.3 Bq m3 (EEC) × 7,000 h × 40 nSv (Bq h m3)1= 0.084 mSv
Outdoors: 0.1 Bq m3 (EEC) × 1,760 h × 40 nSv (Bq h m3)1= 0.007 mSv
The average annual effective dose from thoron decay
products is thus estimated to be 0.09 mSv.
156. For completeness, the contributions to effective dosefrom two relatively minor pathways of exposure to radon
and thoron can be added, namely dissolution of the gases
in blood with distribution throughout the body and thepresence of radon in tap water. The dose coefficients forradon and thoron dissolved in blood following inhalation
intake are those used in the UNSCEAR 1993 Report [U3].
The dose estimate for radon is40 Bq m3 × 7,000 h × 0.17 nSv (Bq h m3)1= 0.048 mSv
Outdoors: 10 Bq m3 × 1,760 h × 0.17 nSv (Bq h m3)1= 0.003 mSv
For thoron, it isIndoors:
10 Bq m3 × 7,000 h × 0.11 nSv (Bq h m3)1= 0.008 mSv
Outdoors: 10 Bq m3 × 1,760 h × 0.11 nSv (Bq h m3)1= 0.002 mSv.

radon released to air when water is used. The concentrationof radon in water and the release to air were discussed
earlier. Although the calculated result is shown below, thisis not a separate contribution to the effective dose, since theradon source from water usage would have been includedin the measured indoor radon concentrations. The
parameters for the inhalation pathway were presented inparagraph 114: concentration in water of 10 kBq m3, airwater concentration ratio of 104, indoor occupancy of
7,000 hours per year. The inhalation dose coefficient
applied is that for the gas. The ingestion of tap water was
estimated in the UNSCEAR 1993 Report [U3] to be 100,
75, and 50 l a1 by infants, children, and adults. Assuming
the proportion of these groups in the population to be 0.05,
0.3, and 0.65, the weighted estimate of consumption is
60 l a1. A conservative estimate of the ingestion dosecoefficient has recently been evaluated [N10]. The
estimated exposures from radon in water are therefore
Inhalation: 10 kBq m3 × 104 × 7,000 h × 0.4 ×= 0.025 mSv
× 9 nSv (Bq h m3)1
Ingestion:
10 kBq m3 × 60 l a1 × 103 m3 l1 ×= 0.002 mSv.
× 3.5 nSv Bq1158. The total annual effective dose from radon is thus
1.1 mSv from inhalation of 222Rn and its decay productspresent in air from all sources, 0.05 from radon gas
dissolved in blood, and 0.002 from radon gas in ingested
tap water (total = 1.15 mSv). The estimates for thoron are
0.09 from inhalation of 220Rn and its decay products and0.01 from thoron gas dissolved in blood (total = 0.10 mSv).

Indoors:157. Radon in tap water may lead to exposures from theingestion of drinking water and from the inhalation of

159. Considering the range of radon exposures determinedfrom survey data and the generally log-normal distributionof such exposures in particular areas, one would expect tofind many large populations around the world (~106
individuals) whose average exposures differ from theabove-estimated global averages by a factor of more than2, and many smaller populations (~104 individuals) whose
average exposures differ by a factor of more than 10. Thus
the estimates of the global averages are significant
primarily because they define the normal radon and thoron
exposures and typical effective doses.

III. ENHANCED EXPOSURES FROM INDUSTRIAL ACTIVITIES
160. There are a number of circumstances in whichmaterials containing natural radionuclides are recovered,processed, used, or brought into position such that radiation
exposures result. This human intervention causes extra orenhanced exposures. Although any indoor exposure frombuilding materials surrounding the body would fall in thiscategory, such an exposure is considered a normal componentof the natural radiation background. The exposures generally
included in the category of enhanced exposures are thosearising from the mineral processing industries and from fossil
fuel combustion.

161. TheCommitteegenerallyreviewsenhancedexposuresin its
evaluations of natural radiation sources, as in the latest
assessment in the UNSCEAR 1993 Report [U3]. The
contribution to the total exposure is usually rather minimal. The
UNSCEAR 1982 Report [U6] provided more detailed review ofenhanced exposures from natural sources, referringtothem at thattime as technologically modified exposures. There are also some
practices that lead to diminished exposures such as paving roads
and using building materials of low radioactive content. These
alterations in exposures are usuallyof less significance than thosethat cause enhanced exposures.

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

162. In general, the topic of enhanced exposures isreceiving greater attention with several meetings devoted
to this subject having recently taken place and several
publications issued, e.g. [B26, E6, E7, K20, K21, M34].
Since the Committee has not yet undertaken a wider reviewof this subject, the reader is referred to the topical
publications and proceedings for updated information.
163. In this Chapter, exposures of the general public arisingfrom emissions of naturally occurring radionuclides to theenvironment from industrial activities are reviewed. Industry
uses many different raw materials that contain naturally
occurring radioactive materials, sometime abbreviated
NORM. These raw materials are mined, transported, andprocessed for further use. The consequent emissions ofradionuclides to air and water lead to the eventual exposure ofhumans. The main industries are identified below, along withthe raw materials and by-products or wastes they generate.
The radionuclide content of these raw materials and wastes issummarized in Table 27.
164. Phosphate processing. This industry may be subdivided into (a) wet processing, (b) thermal processing, and(c) fertilizer production. The primaryproduct is phosphoricacid. In the thermal process, the product may bephosphorus or, using nitric acid, phosphoric acid.
Phosphoric acid is used in the manufacture of fertilizers. In
the wet phosphate processing industry, phosphogypsum is
produced as a by-product. The thermal process (using
cokes and silica) produces a slag (CaSiO2) as a waste
product.
165. Metal ore processing. Important metal ores are
cassiterite or tinstone (tin), tantalite, columbite,
fergusonite, koppite, samarskite, and pyrochlore (niobium,iron, manganese, and others). Most of the metals are
separated using charcoal or coke. Furnace slag from theprocessing is often used in cement production. Another byproduct, tar coal, is used to produce electrode pitch,creosote oil, carbolineum, soot oil, and road tar mix.
166. Uranium mining. There are several locations that
contain the residues of former uranium mining operations,for example, in eastern Germany [B29, E9, R23]. The
procedures to deal with the landfills, waste rock and slag
piles and the radiological consequences are being
evaluated.
167. Zircon sands. Important zirconium minerals arezircon (ZrSiO4) and baddeleyite (ZrO2). Sorting
discriminates these minerals from other heavy minerals or
simple silica. The processing involves procedures such as
sieving, washing, drying, and grinding. These processes do
not produce any specific waste products.
168. Titanium pigment production. Titanium pigments
include titanium dioxide (TiO2) and synthetic rutile.
Processing waste products include large quantities ofcokes, ore and SiO2 particles, and filter cake (classified as
chemical waste).

109

169. Fossil fuels. For electric power production the mostimportant fossil fuels are coal, natural gas, and oil. Largeamounts of fly ash and bottom ash result from coal
combustion. Gypsum is recovered if a desulphurization
installation is present.
170. Oil and gas extraction. The large volumes of
production water needed for the extraction of oil and gas may
contain natural radionuclides, mainly 226Ra and its decay
products. Scalings may form as a result of precipitation at theoil/water interface, or radon decay products (especially 210Pb
and 210Po) may be deposited in the installations.
171. Building materials. Materials used by the building
industry that maybe of radiological significance include marl,blast furnace slag, fly ash, Portland clinker, and anhydrate (inthe cement industry) and clay (in the ceramics industry). In
the cement industry, some silex is produced as a waste
product.
172. Thorium compounds. Thorium is used mainly as anadditive in other products, such as welding electrodes, gas
mantles, and special alloys and is retrieved from monazite,
thorite, or thorianite. The activity content of the compounds
is present mainly in the primary product, metallic thorium.
173. Scrap metal industry. Scrap metal such as tubing,valves, and heat exchangers from various process industries
may contain scales with enhanced levels of naturalradionuclides. The particular radionuclides and theirconcentrations would depend on the origin of the scrap. Since
objects from nuclear industries and the uncontrolled releasesof radioactive sources may add to this material, which may berecycled, the scrap-metal industry is a source of variable andheterogenous releases of radionuclides into the environment.
174. Emissions. The natural radionuclides present in the
raw materials or wastes of these industries are those of the238
U and 232Th series. Releases are mainly to air or water,
although landfills after dredging or wastes disposed onland may also provide pathways of exposure.
175. Emissions of radionuclides to air and water from theseindustries are listed in Table 28. The throughput of ore or raw
material is for a typical installation. One of the mainradionuclides released to air is 222Rn. It is released by thephosphate and cement industries, gas and oil extraction, gasfired power production, and, generally, industries that burnnatural gas. For example, in the phosphate industry, enhanced
radon concentrations between 35 and 780 Bq m3 have been
observed, depending on the working area and season [V6].
Important sources of 210Pb to air are the elementary
phosphorus and iron and steel production industries. Cement
production gives rise to much of the 210Po released. Brick andtile installations may also be of importance because they areso numerous.
176. A special problem is imposed by the storage of uraniumcontaining minerals in museums [V6]. In a museum inBrussels, where radium- and uranium-containing minerals

110

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

from Katanga were stored, concentrations of radon of about
1015 kBq m3were found in spite of enhanced ventilation.
Besides radon emissions, high levels of gamma radiation werealso observed in the vicinity of the storage rooms. In the houseof the museum caretaker who lived nearby, gamma levels of
56 µSv h1 were found. After shielding of the minerals, theradiation level was reduced to 12 µSv h1.
177. The radionuclides released to the atmosphere by large
thermal processes such as those used by elementary
phosphorus production, iron and steel production, and thecement industry, are dispersed over great distances. Smaller
thermal processes, such as the brick and tile industry, are also
sources of airborne releases. For other mineral processing
industries, dusty conditions during handling and shipment ofores are the main reason for the releases of radionuclides toair. In those circumstances, the rather coarse particles are
generally released mainly to the immediate surroundings ofthe plant.
178. The largest releases of radionuclides to water are
from the phosphate processing, followed by oil and gas
production and primary iron and steel production. As an
example, two phosphoric acid plants in the Netherlands are
responsible for some 90% of all discharges of 210Pb and210
Po to water [L18]. These two plants release about
0.60.8 TBq of 226Ra per year [L24], which is comparable
to the estimated annual release of 226Ra with process water
into the North Sea by the offshore oil production industry
in the United Kingdom, Norway, the Netherlands, andDenmark [L25]. Annual releases into rivers of 226Ra and of228
Ra present in diluted brines from single Upper Silesiancoal mines may be as high as 20 and 30 GBq, respectively,
resulting in locally enhanced concentrations in bottom
sediments [L26, S63].
179. The large amounts of gypsum slurry discharged inphosphoric acid production may be released into the sea as is
the case in the Netherlands, but industrial wastes are
sometimes also stored on land or in large landfills.
Radionuclides released to water in, for example, discharges
from oil and gas extraction offshore are generally diluted by
the large volumes of water involved. Onshore process water isoften pumped back into the oilfield. The treatment of
production waters before they are released may significantly
reduce the radionuclide concentration [L26].
180. Enhanced levels of radionuclides in the environment
can come from the processing and use of scrap andrecycled metals [B28, L22]. Although in general extensive
measures are taken to ensure the continuous quality of thescrap and the new metal that is manufactured from it,enhanced radiation levels are sometimes found. The
number of reports on such incidents is growing, partly
because of increased awareness of the problem and partly
because more measurements are being made. The
enhanced exposures may arise from lost radium radiation
sources or from naturally occurring radionuclides in pipes
with scale containing enhanced concentrations [T15].
Similar problems arise from man-made sources, forexample, 22Na, 54Mn [W15], 60Co [C31], 137Cs [B27, J12] or
Ir, leading to contaminated scrap and recycled metals.
The levels vary greatly, and the consequences depend on
specific local circumstances.

192

181. Exposures. Both external and internal exposures
may result from naturally occurring radionuclides released
by industrial activities. In general, installations are locatedaway from residential areas, and because external radiationlevels decrease with distance from the plant, local residents
are not significantly exposed. The workers, however, may
receive low doses in connection with ore stock piles orwaste deposits. Estimated and measured doses are in therange 0.1300 µSv a1 from direct exposures, with thehigher values for locations near mineral-sands-handlingindustries. The maximum effective doses are summarizedin Table 29.
182. Radionuclides dispersed in air may contribute toexternal irradiation while airborne and after deposition.
The contributions to total dose appear to be negligible.
Inhalation and ingestion are the pathways that contributeto internal exposure. Inhalation contributes to exposure
only in the vicinity of the plant, particularly with mineralsands-processing plants. Doses depend on distance andcould be up to 50 µSv a1 for office workers in a building
just outside the plant site [L18].
183. Because most food products consumed by individuals
are produced in large agricultural regions, possible dose fromingestion of radionuclides are small. For a typical situation, asmall population in the vicinity of an elementary phosphorus
plant, the calculated dose would be of the order 100 µSv a1[L18]. More generally, the estimated doses would be 110
µSv a1. Ingestion doses that could result from discharges ofwastes to water are negligible compared to those by the otherpathways.
184. In the United Kingdom, the doses from sintering plantsof the steel industry to critical groups of the population were
calculated to be between about 1.5 and 18 µSv a1. The
highest dose was attributed to a sinter site with relatively low
stacks. Inhalation contributed less than 22%, with the main
exposure route being the ingestion of food. The annual
collective dose calculated for the population (to a distance of
3,000 km) was estimated to be between about 2.9 and 5.5 man
Sv [H33].
185. Penfold et al. [P10] made a pilot study of theradiological impact of coal-fired stations in the United
Kingdom. Various pathways of exposure were considered.
The highest dose rate for a critical group (about 250 µSva1) came from the use of fly ash in building materials.
Other pathways caused dose rates for critical groups
between 0.07 and 55 µSv a1.
186. The radiation exposure of critical groups of the
population surrounding a site with a wood-chip-burningoven was determined in a Swedish study [H34]. The
maximum individual dose rate was found to be 2.4 nSv a1.

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

187. Annual per caput effective doses from processindustries documented in the UNSCEAR 1993 Report
ranged from 1 nSv to 20 µSv and for critical groups up to
about 1 mSv. Those mentioned above and other more
recent data are for very specific situations or criticalgroups. On the whole, however, they are in agreement withthe earlier estimates, and they support the conclusions of
the UNSCEAR 1993 Report [U3].
188. Summary. The industrial activities enhancing
exposure from natural sources involve large volumes ofraw materials containing natural radionuclides. Discharges
from industrial plants to air and water and the use of by-

111

products and waste materials may be the main contributors toenhanced exposure of the general public. For typicalindustries and releases, exposures occur primarily in close
proximityto the plants. A complete review is made difficult by
the diversityof industries involved and the local circumstances
associated with the exposures. Estimated maximum exposures
are greatest for phosphoric acid production and the mineralsands-processing industries. Although exposure rates of theorder of 100 µSv a1 could be received by a few local
residents, levels of 110 µSv a1 would be more common.
These exposure rates constitute a negligible component of thetotal annual effective dose from all natural sources ofradiation.

IV. WORLDWIDE AVERAGE EXPOSURE FROM NATURAL SOURCES

190. In a few countries the proportion of the population at
various levels of total exposures has been assessed. These
data are included in Table 30, and the combined
distribution is shown in Figure XV. The average annual
exposure for this distribution is 2.0 mSv. The distribution
rises in a few dose intervals to the peak exposure and thentails off to decreasing population at doses 2 to 3 times theaverage. To smooth the distribution somewhat, most
exposure intervals have been subdivided. The generalshape of the distribution is probably fairly relevant.
Although populations living in areas of high backgroundexposures are not well represented in this particular
distribution, they would not be expected to be a prominent
feature, in part because not all components of their
exposure are enhanced at the same time and because there
is a relatively small proportion of the population of mostcountries with significantly elevated exposures.
191. Average worldwide exposure determined by adding
the various components is summarized in Table 31. Thechanges from the earlier assessment of the Committee [U3]are also indicated. There are only rather minor changes forthe exposure components. The worldwide average annual
exposure to natural radiation sources remains 2.4 mSv.
Neither the magnitude nor the precision of this estimate
should be overemphasized. As indicated in Figure XV,
based on the sample population of Table 30, a broad
distribution of exposures would be expected in any large
population.
0.3

0.25
FRACTION OF POPULATION

189. The components of exposure caused by naturalradiation sources have been reassessed in this Annex basedon new information and data from measurements and on
further analysis of the processes involved. These exposurecomponents can now be added to provide an estimate of thetotal average exposure. It must first be stated that the
average exposure probably does not pertain to any one
individual, since there are wide distributions of exposuresfrom each source and the exposures combine in various
ways at each location, depending on the specificconcentrations of radionuclides in the environment and in
the body, the latitude and altitude of the location, andmany other factors.

0.2

0.15

0.1

0.05

0
0

1

2

3

4

5

6

7

8

9

10

TOTAL ANNUAL EFFECTIVE DOSE (mSv)

Figure XV. Distribution of population of fifteen
countries with respect to total annual effective dose.

192. The normal ranges of exposures to the various
components of natural radiation are indicated in Table 31.
This accounts for common variations in exposures but
excludes those individuals at the extreme ends of the
distributions. On this basis, worldwide annual exposures tonatural radiation sources would generally be expected to bein the range 110 mSv, with 2.4 mSv being the present
estimate of the central value.

112

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCESCONCLUSIONS
193. Since exposures to natural radiation sources are moresignificant for the world's population than most exposures to
man-made sources, the natural background baseline warrants
evaluation in some detail. Efforts should continue to broaden
the database used for determining both representative values
and extremes in exposures and to improve dosimetric
procedures.
194. Because of the wide variations in natural backgroundexposures even within relatively small regions, more efforts
will be required to determine the detailed distributions of
populations within dose intervals for the various components
of exposure. Initial, still limited evaluations of distributions ofexternal exposures outdoors and indoors and of the total
exposure have been presented in this Annex. Theseevaluations seem to reveal patterns that would be expected tobe generally valid for other countries and for the world
population as a whole. The analysis of distributions will
provide an improved basis for deriving worldwide average
exposures and their normal and extreme variations.
195. The main uncertainties in the assessment of dose fromnatural radiation sources arise less from the limited number ofmeasurements than from the complications of the dosimetricconsiderations. The situation with respect to radon decay
products is well known, but similar problems exist for cosmic
radiation and ingested radionuclides. For cosmic radiation,
more information is needed on exposures to neutrons at all
altitudes and latitudes, especially high-energy neutrons andhigh-Z nuclei at aircraft altitudes, along with critical data or
improved models to allow a reasonable estimation of effective
doses from these components of the radiation field. For
ingested radionuclides, good dosimetric models are available,
but the problem is to estimate representative intake amountsof the radionuclides and associate them with relatively fewer
determinations of concentrations in tissues of the body.
196. There are many circumstances in which individuals
receive enhanced exposures to natural radiation. Living insidebuildings is considered normal in this regard, and flying in
airplanes usually involves an insignificant proportion of mostpeople’s time. In the past, the Committee has reviewed theexposures caused from the release of natural radionuclides inmineral processing industries, the use of phosphate fertilizers,
and the combustion of fossil fuels. These enhanced exposures
are usually quite insignificant compared with the normal
background exposure from natural sources. This conclusion isstill valid, based on a brief review of new information in thisAnnex.
197. The evaluations in this Annex of exposures fromnatural radiation sources indicate that the average annual
effective dose to the world population is approximately
2.4 mSv, which is the same as the previous estimate of theCommittee [U3]. The value of the estimated average
exposure should not be taken to be too precise, since broad
averaging is involved. For individuals, annual exposures
ranging from 1 mSv to two or three times the world
average are frequently encountered. It is estimated thatabout 65% of individuals have exposures between 1 and3 mSv, about 25% of the population have exposures lessthan 1 mSv, and 10% have exposures greater than 3 mSv.
Although the database continues to expand andcharacterization of the distributions of populations withrespect to the various components of natural backgroundradiation is being improved, the generally assessed
exposure levels to which the broad spectrum of the world
population is exposed seem reasonably well substantiated.

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

113

Table 1
Latitude distribution of cosmic ray dose rates outdoors at sea level
Effective dose rate (nSv h-1)

Population in latitude band (%)
Latitude (degrees)
Northern hemisphere

Southern hemisphere

Directly ionizing component a

Neutron component b

0
0
0.4
13.7
15.5
20.4
32.7
11.0
6.3

0
0
0
0.5
0.9
13.0
14.9
16.7
54.0

32
32
32
32
32
32
30
30
30

11
11
10.9
10.0
7.8
5.3
4.0
3.7
3.6

100

100

31.0
30.3
30.9

5.6
4.0
5.5

80!90
70!80
60!70
50!60
40!50
30!40
20!30
10!20
0!10
Total
Population-weighted average
Northern hemisphere
Southern hemisphere
World cabcAverage measurement results.
From fit to measurements of Figure II.
Population distribution: northern hemisphere 0.89; southern hemisphere 0.11.

Table 2
Population-weighted average cosmic ray dose rates
Effective dose rate (µSv a-1)
Directly ionizing component

Conditions

Outdoors, at sea level
Outdoors, altitude adjusted a
Altitude, shielding,occupancy adjusted bab

Neutron component

Total

North

South

World

North

South

World

World

272
339

265
332

270
340

49
124

35
87

48
120

320
460

285

279

280

104

73

100

380

Altitude-weighting factors applied to sea level values: directly ionizing component 1.25; neutron component 2.5.
Building shielding factor 0.8; indoor occupancy factor 0.8.

114

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 3
Physical data for radionuclides of natural origin[F6]
Element

IsotopeHalf-life

Decay mode

Cosmogenic radionuclides
Hydrogen
Beryllium

3

H
Be
Be
14
C
22
Na
26
Al
32
Si
32
P
33
P
35
S
36
Cl
37
Ar
39
Ar
81
Kr
7

10

CarbonSodiumAluminium
SiliconPhosphorus
Sulphur
Chlorine
Argon
Krypton12.33 a53.29 d1.51 106 a
5730 a2.602 a7.4 105 a
172 a
14.26 d25.34 d87.51 d3.01 105 a
35.04 d269 a2.29 105 abeta (100%)
EC a (100%)beta (100%)beta (100%)
EC (100%)
EC (100%)
beta (100%)beta (100%)beta (100%)beta (100%)EC(1.9%), beta (98.1%)
EC (100%)
beta (100%)
EC (100%)

Terrestrial radionuclides
Potassium
Rubidium
Lanthanum
Samarium
Lutecium

40

K
Rb
138
La
147
Sm
176
Lu

1.28 109 a4.75 1010 a
1.05 1011 a
1.06 1011 a
3.73 1010 abeta (89.3%), EC (10.7%)
beta (100%)beta (33.6%), EC (66.4%)
alpha (100%)beta (100%)

238

U
Th
234m
Pa
234
U
230
Th
226
Ra
222
Rn
218
Po
214
Pb
214
Bi
214
Po
210
Pb
210
Bi
210
Po
206
Pb

4.47 109 a
24.10 d1.17 m2.45 105 a
7.54 104 a
1600 a3.824 d3.05 m26.8 m19.9 m164 µs22.3 a5.013 d138.4 dstablealpha (100%)beta (100%)beta (99.8%), IT b
alpha (100%)alpha (100%)alpha (100%)alpha (100%)alpha (99.98%), beta (0.02%)
beta (100%)alpha (0.02), beta (99.98%)
alpha (100%)beta (100%)beta (100%)alpha (100%)

232

Th
Ra
228
Ac
228
Th
224
Ra
220
Rn
216
Po
212
Pb
212
Bi
212
Po
208
Tl
208
Pb

1.405 1010 a
5.75 a6.15 h
1.912 a3.66 d55.6 s0.145 s10.64 h60.55 m0.299 µs
3.053 mstablealpha (100%)beta (100%)beta (100%)alpha (100%alpha (100%)alpha (100%)alpha (100%)beta (100%)alpha (36%), beta (64%)
alpha (100%)beta (100%)235

7.038 108 a
25.52 h32760 a21.77 a18.72 d21.8 m
11.44 d3.96 s
1.781 ms
36.1 m2.14 m4.77 mstablealpha (100%)beta (100%)alpha (100%)alpha (1.4%), beta 98.6%)
alpha (100%)beta (100%)alpha (100%)alpha (100%)alpha (100%)beta (100%)alpha (99.7%), beta 0.3%)
beta (100%)

87

238

U series:
UraniumThorium
Protactinium
UraniumThorium
RadiumRadon
Polonium
Lead
BismuthPolonium
Lead
BismuthPolonium
Lead

234

232

Th series:
Thorium
RadiumActinium
Thorium
RadiumRadon
Polonium
Lead
BismuthPolonium
Thalium
Lead

228

235

U series:
UraniumThorium
Protactinium
Actinium
Thorium
Francium
RadiumRadon
Polonium
Lead
BismuthThalium
Leadab

Electron capture.
Internal transition.

U
Th
231
Pa
227
Ac
227
Th
223
Fr
223
Ra
219
Rn
215
Po
211
Pb
211
Bi
207
Tl
207
Pb
231

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

115

Table 4
Production rates and concentrations of cosmogenic radionuclides in the atmosphere
Production rate
Radionuclide
Per unit area a(atoms m-2 s-1)

Annual amount c(PBq a-1)

2 500
810
450
25 000
0.86
1.4
1.6
8.1
6.8
14
11
8.3
56
0.01

72
1 960
0.000064
1.54
0.12
0.000001
0.0008773
35
210.000013
31
0.074
1.7 108

3

H
Be
10
Be
14
C
22
Na
26
Al
32
Si
32
P
33
P
35
S
36
Cl
37
Ar
39
Ar
81
Kr
7

a
b
c

Globalinventory(PBq )

Fractionalamountin troposphere aConcentrationintroposphere b(mBq m-3)

0.004
0.11
0.0023
0.016
0.017
7.7 108
0.00011
0.24
0.16
0.08
6 108
0.37
0.83
0.82

1.4
12.5
0.15
56.3
0.0021
1.5 108
0.000025
0.27
0.15
0.16
9.3 108
0.43
6.5
0.0012

1 275
413
230
12 750
0.44
0.71
0.82
4.1
3.5
7.1
5.6
4.2
28.6
0.005

References [L5, L6].
Assumes tropospheric volume of 3.62275 1018 m3; inferred from [L5].
Assumes surface area of world = 5.1005 1014 m2 [L14].

Table 5Natural radionuclide content in soil
Data not referenced are from UNSCEAR Survey of Natural Radiation Exposures
Concentration in soil (Bq kg1)
Region / country

Populationin 1996
(106)

40

238

K

226

U

232

Ra

Th

Mean

Range

Mean

Range

Mean

Range

Mean

Range

AfricaAlgeria
Egypt

28.78
63.27

370
320

66!1 150
29!650

30
37

2!110
6!120

50
17

5!180
5!64

25
18

2!140
2!96

North America
Costa Rica
United States [M7]

3.50
269.4

140
370

6!380
100!700

46
35

11!130
4!140

46
40

11!130
8!160

11
35

1!42
4!130

South America
Argentina

35.22

650

540!750

East Asia
Bangladesh
China [P16, Z5]– Hong Kong SAR [W12]IndiaJapan [M5]
Kazakstan
Korea, Rep. of
Malaysia
Thailand

120.1
1232
6.19
944.6
125.4
16.82
45.31
20.58
58.70

350
440
530
400
310
300
670
310
230

130!610
9!1 800
80!1 100
38!760
15!990
100!1 200
17!1 500
170!430
7!712

33
84
29
29
37

2!690
25!130
7!81
2!59
12!120

34
32
59
29
33
35

21!43
2!440
20!110
7!81
6!98
12!120

41
95
64
28
60

1!360
16!200
14!160
2!88
10!220

66
114

49!86
3!370

67
48

38!94
11!78

82
51

63!110
7!120

West Asia
Armenia
Iran (Islamic Rep. of)
Syrian Arab Republic

3.64
69.98
14.57

360
640
270

310!420
250!980
87!780

46

20!78

23

10!64

51
28
20

32!77
8!55
13!32

30
22
20

29!60
5!42
10!32

116

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 5 (continued)
Concentration in soil (Bq kg1)
Region / country

Populationin 1996
(106)

40

238

K

Mean

Range

North Europe
Denmark [N5]
Estonia
Lithuania
NorwaySweden

5.24
1.47
3.73
4.35
8.82

460
510
600
850
780

240!610
140!1 120
350!850

West Europe
Belgium
Germany
Ireland [M6]
Luxembourg
Netherlands [K2]
Switzerland
United Kingdom [B2]

10.16
81.92
3.55
0.41
15.58
7.22
58.14

380

70!90040!1 340
40!80080!1 800
120!730
40!1 000
0!3 200

East Europe
Bulgaria
Hungary
Poland [J7]Romania [I12]
Russian Federation
Slovakia

8.47
10.05
38.60
22.66
148.1
5.35

400
370
410
490
520
520

South Europe
Albania
Croatia
CyprusGreecePortugalSlovenia
Spain

3.40
4.50
0.76
10.49
9.81
1.92
39.67

560!1 150

350
620

Mean

226

U
Range

3!30

16
50

11!330
8!120

Range

Mean

Range

17
35

9!29
6!310

8!30
5!59
9!46

50
42

12!170

19
27
25
45
42

26

14!94

5!50
5!200
10!200
6!52
6!63
10!900

27

30
28
21
38
30
38

7!160
12!45
4!77
11!75
2!79
12!80

24
45

4!160
12!65

21
51
35
33

1!190
22!100
2!90
2!210

30

11!64

40

5!53
10!150
2!330

40!80079!570110!970
250!1 100
100!1 400
200!1 380

40
29
26
32
19
32

8!190
12!66
5!120
8!60
0!67
15!130

45
33
26
32
27
32

12!210
14!76
5!120
8!60
1!76
12!120

360
490
140
360
840
370
470

15!1 150
140!710
0!670
12!1 570
220!1 230
15!1 410
25!1 650

23
110

6!96
83!180

25
49

1!240
26!82

54
17
25
44
41
32

21!77
0!120
1!240
8!65
2!210
6!250

Median400

140!850

35

16!11035

17!60

Population!weighted average

420

33

Th

Mean

60
35
23
40
37

370

37

232

Ra

32

5!50
7!134
3!60
7!70
8!77
4!70
1!180

26
50
25

45

Table 6External exposure rates calculated from various concentrations of terrestrial radionuclides in soil
Concentration in soil (Bq kg-1)
Radionuclide
40
K
U series232
Th series
228

Total
a

Values from Table 5.

Medianvalue aPopulation-weighted
value a

400
35
30

420
33
45

Dose coefficient[I20, S49]
(nGy h-1 per Bq kg-1)

0.04170.462
0.604

Absorbed dose rate in air (nGy h-1)
Medianvalue

Population-weighted
value

17
16
18

18
15
27

51

60

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

117

Table 7External exposure rates from terrestrial gamma radiation
Data not referenced are from UNSCEAR Survey of Natural Radiation Exposures
Absorbed dose rate in air (nGy h1)
Region / country

Populationin 1996(106)

Outdoors

Ratio
indoors to
outdoors

Indoors

Average

Range

AfricaAlgeria [B4]Egypt [H9, I13]
Namibia [S12]
Sudan

28.78
63.27
1.58
27.29

70
32

20!133
8!93

53

26!690

North America
Canada [G3, T14]
Cuba [S13]
Mexico [C8]United States [M8, O5]

29.68
11.02
92.72
269.4

63
42
78
47

43!101
26!53
42!140
14!118South America
Chile [S14]Paraguay

14.42
4.96

51
46

21!83
38!53

East Asia
Brunei [L20]
China [N3]
– Taiwan Province [C11]– Hong Kong SAR [W12]India [N11]
Indonesia
Japan [A7, A8]
Kazakstan
Korea, Rep. of
Malaysia
Philippines [D3]Thailand

0.30
1232
20
6.19
944.6
200.45
125.4
16.82
45.31
20.58
69.28
58.70

33
62
57
87
56
55
53
63
79
92
56
77

3!70
2!340
17!87
51!120
20!1 100
47!63
21!77
10!250
18!200
55!130
31!120
2!100

West Asia
Iran (Islamic Rep. of )Syrian Arab Republic

69.98
14.57

71
59

North Europe
Denmark [N5, S15]
Estonia
Finland [A9]Iceland [E4]
Lithuania
Norway [S16, S17]
Sweden [M9]

5.24
1.47
5.13
0.27
3.73
4.35
8.82

West Europe
Austria [T5]
Belgium [D4, S18]
France [M10, R3]
Germany [B5, W11]
Ireland [M11, M12]
Luxembourg
Netherlands [J2, V1]
Switzerland
United Kingdom [G4, W5]

AverageRange
14!2 100

38

12!1600.8

61

25!105

1.2

99

11!420

1.6

200

140!270

2.3

53
70

21!77
20!100

1.0
1.1

96

65!130

1.0

48

2!22

0.6

36!130
52!67

115

70!165

1.6

52
59
71
28
58
73
56

35!70
14!23045!13911!83
36!85
20!1 200
40!50054

19!260

1.0

73
23
85
79
110

22!184
14!32
34!19520!1 250
20!2 000

1.0
0.8
1.5
1.1
2.0

8.11
10.16
58.33
81.92
3.55
0.41
15.58
7.22
58.14

43
43
68
50
42
49
32
45
34

20!150
13!80
10!250
4!350
1!180
14!73
10!60
15!120
8!89

60
75
70
62

32!90

1.4
1.1
1.4
1.5

East Europe
Bulgaria [V2]
Hungary [N14, N15]
Poland [B10, M3]
Romania [I12]
Russian Federation
Slovakia

8.47
10.05
38.60
22.66
148.1
5.35

70
61
45
59
65
67

South Europe
Albania
CyprusGreece

3.40
0.76
10.49

71
18
56

13!290
10!140

64
62
60

30!100
20!200

2.0
1.4
1.8

48!96
15!130
18!97
21!122
12!102
24!154

75
95
67
83
74
79

57!93
11!23628!16730!170
24!14736!180

1.1
1.6
1.5
1.4
1.1
1.2

20!350
9!52
30!109100

20!300

1.4

67

36!131

1.2

118

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 7 (continued)
Absorbed dose rate in air (nGy h1)
Region / country

Populationin 1996(106)

Outdoors

Ratio
indoors to
outdoors

Indoors

Average

Range

Average

Range

3!228
4!230
4!147
40!120

105
101
75
110

0!700
4!280
40!25057!180

103
20

1!73

75

20!200South Europe
Italy [B6, C12]
Portugal [A10]
Slovenia
Spain [Q1, Q2]

57.23
9.81
1.92
39.67

74
84
56
76

Oceania
Australia [C13, L7]
New Zealand [R4]

18.06
3.6

93

Median57

Population-weighted average

59

18!93

1.4
1.2
1.3
1.4

1.1
1.3 (0.6!2.3)

84

1.4

Table 8Outdoor absorbed dose rates in air inferred from concentrations of radionuclides in soil compared withdirect measurements
Absorbed dose rate in air (nGy h-1)
Country
Luxembourg
IrelandSwedenIndia
China (Hong Kong SAR)
NorwayUnited States
Switzerland
Kazakstan
Belgium
Portugal
Malaysia
Egypt
Slovenia
Romania
China
PolandEstonia
Slovakia
Japan
Lithuania
ThailandRussian Federation
Bulgaria
Hungary
Algeria
Iran (Islamic Rep. of)
Denmark
Spain
GreeceAlbania
Syrian Arab Republic

From soil concentrations

From direct measurements

Ratio soil/measurements

72
58
77
69
107
86
55
49
65
44
86
93
32
56
58
58
42
54
60
45
48
62
52
56
48
54
53
39
54
39
40
33

49
42
56
56
87
73
47
45
63
43
84
92
32
56
59
62
45
59
67
53
58
77
65
70
61
70
71
52
76
56
71
59

1.5
1.4
1.4
1.2
1.2
1.2
1.2
1.1
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6

13 535
0.017

Cumulative total
Cumulative fraction

59 6380.08

46 103
0.059

444

333

13 535
0.017

50

22

479
2 915
295

13
5 484
631
12 000

2 200
8 600

0

Total
Fraction of total

South Europe
Albania
GreecePortugal
Spain

163
150

East Europe
Bulgaria
Hungary
PolandRomania
Russian Federation
Slovakia

450

300
700
125
29
3 459
60
6 000

166 8080.21

107 170
0.14

50
1 160
1 814
1 115

836
12 014
1 407
460
192

2 400
10 000
275
52
2 353
1 131
30 000275 405
0.35

108 597
0.14

100
5 605
606
5 490

186
1 071
12 268
4 177
7 150
721

2 600
20 900
5 300
230
2 976
3 983
6 000

967

138

West Europe
Belgium
Germany
Italy
Luxembourg
Netherlands
Switzerland
United Kingdom

2 200
149

250
5

1 260

20 561
4 097

40-49
nGy h-1

2 100
25

6

26 4639 605

30-39
nGy h-1

North Europe
Denmark
Estonia
FinlandLithuania

9 619
3 096

20-29
nGy h-1

3 580

1 760

< 20
nGy h-1

416 687
0.53

141 282
0.18

100
1 067
1 325
5 082

392
1 316
7 163
6 447
22 8001 364

2 500
28 00028 075
82
1 262
584

600
314
913
414

4 896

23 382
2 220
984

50-59
nGy h-1

623 760
0.79

207 073
0.26

500
1 250
653
10 129

5 212
3 488
2 637
5 130
84 470
1 292

200
9 600
8 575
4
47
74

50
367
1 131
1 381

29 40039 546
1 724
213

60-69
nGy h-1

666 1190.85

42 359
0.054

2 000
572
313
2 903

1 239
1 163
622
3 904
5 730
868

161

20
1 500
1 975

592
2 606
553

4 810

5 193
4 421
1 214

70-79
nGy h-1

710 8410.90

44 722
0.057

300
147
582
1 977

234
765
213
726
17 800
498

74

800
150

9
172
276

13 080

4 421
2 498

80-89
nGy h-1

740 935
0.94

30 094
0.038

200
225
417
2 447

1 614
367
136
568
5 330
243

64

700
3 100

325

3 660

2 211
8 487

90-99
nGy h-1

Population (103) residing in areas with various levels of outdoor absorbed dose rate in air

West Asia
Iran (Islamic Rep. of)

East Asia
Japan
Korea
Malaysia

Region / country

Table 9Distribution of population with respect to the outdoor absorbed dose rate in air from terrestrial gamma radiation

783 6390.995

42 704
0.054

100
231
2 352
8 152

45
3 910
85

530

98

300
6 400

3 200

11 053
6 248

100-199nGy h-1

787 5830.9999

3 944
0.005

594

50

3 300

200-299nGy h-1

787 6501.000

670.00009

50

17

>300
nGy h-1

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES
119

a
b

5.2
1.5
5.1
3.7

10.2
81.1
57.3
0.4
15.6
6.9
54.0

8.9
10.2
38.1
22.7
148.1
5.3

3.5
10.3
9.4
37.3

North Europe
Denmark
Estonia
FinlandLithuania

West Europe
Belgium
Germany
Italy
Luxembourg
Netherlands
Switzerland
United Kingdom

East Europe
Bulgaria
Hungary
PolandRomania
Russian Fed.
Slovakia

South Europe
Albania
GreecePortugal
Spain

71
56
84
76

70
61
45
59
65
67

43
50
74
43
32
45
34

52
59
71
61

71

53
79
92

Averageoutdoordose rate(nGy h-1)

2.3
0.003

0.05

0.002

0.04

-6

5.6
0.007

0.19

0.01

0.003

0.02

0.004

0.07

-5

17.5
0.022

0.06
0.03

0.01

0.004

0.05

0.01
0.005

0.003

0.065

0.22
0.05

-4

39.8
0.051

0.14
0.15

0.03

0.02
0.08
0.004
0.01
0.003
0.04

0.009

0.03
0.12
0.09
0.07

0.04

0.02

0.02

0.08
0.09
0.01

-3

108
0.14

0.03
0.11
0.07
0.14

0.04
0.11
0.08
0.06
0.05
0.14

0.22
0.12
0.49
0.03
0.22
0.09
0.11

0.05
0.10
0.18
0.26

0.08

0.21
0.05
0.06

-2

171
0.22

0.14
0.55
0.03
0.27

0.59
0.13
0.32
0.18
0.15
0.26

0.23
0.25
0.15
0.13
0.35
0.16
0.22

0.40
0.21
0.22
0.11

0.46

0.16
0.04
0.13

-1

232
0.29

0.57
0.10
0.06
0.08

0.14
0.34
0.32
0.28
0.57
0.24

0.25
0.34
0.03
0.56
0.15
0.58
0.56

0.42
0.25
0.51
0.37

0.08

0.19
0.10
0.43

0

111
0.14

0.09
0.12
0.04
0.05

0.03
0.11
0.19
0.23
0.04
0.16

0.24
0.12
0.003
0.20
0.19
0.09
0.11

0.12
0.40
0.03
0.15

0.20

0.32
0.10
0.32

1

50.8
0.064

0.06
0.06
0.25
0.07

0.18
0.08
0.07
0.17
0.12
0.09

0.02
0.02
0.05
0.01
0.08
0.01

0.01
0.006
0.06
0.07

0.057

0.04
0.05

2

38.0
0.048

0.03
0.01
0.06
0.22

9.8
0.012

0.01
0.02

0.05
0.006
0.03
0.03
0.02

0.01

0.003
0.02

0.04
0.02
0.03
0.04
0.05

0.01
0.06

4

0.002
0.01
0.11

0.05

0.25

3

Fraction of population with respect to decades of outdoor absorbed dose rate in air a
5

0.53
0.0007

0.01
0.02

0.004
0.002

0.009

The average outdoor absorbed dose rate in air in the country is placed in the decade 0; e.g. for 52 nGy h-1 average, would indicate decade 0 is the dose interval 50-59 nGy h-1, decade -1 is 40-49 nGy h-1, etc.
Total distributed population within ranges indicated is 787.3 106.

787.7 b63.9

West Asia
Iran (Islamic Rep.)

Total population (106)
Fraction of total

124.8
44.6
19.6

(106)

Base
population

East Asia
Japan
Korea
Malaysia

Region / country

Table 10Distribution of population with respect to the average outdoor absorbed dose rate in air from terrestrial gamma radiation

0.12
0.0001

0.002

0.01

6

120
ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCESANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

121

Table 11
Areas of high natural radiation background

Country

BrazilArea

Characteristics of area

Approximate
population

Guarapari

Monazite sands; coastal areas

73 000

Mineas Gerais and Goias
Pocos de Caldas Araxá

Volcanic intrusives

350

80 000Ref.

90!170 (streets)
90!90 000 (beaches)110!1 300
340 average
2 800 average[A17, P4]

370 average[W14]

20!400[E3][P4, V5]

[V5]

China

Yangjiang
Quangdong

Monazite particles

Egypt

Nile delta

Monazite sands

FranceCentral region
Southwest

Granitic, schistous, sandstone area
Uranium minerals

7 000 000

20!400
10!10 000

[J3]
[D10]

India

Kerala and Madras

Monazite sands, coastal areas
200 km long, 0.5 km wide

100 000

200!4 000
1 800 average
260!440[S19, S20]

Ganges deltaaAbsorbed dose
rate in air a(nGy h1)[M13]

Iran (Islamic
Rep. of)RamsarMahallat

Spring waters

2 000

70!17 000
800!4 000

[S21]
[S58]

Italy

Lazio
Campania
Orvieto town
South Toscana

Volcanic soil

5 100 000
5 600 000
21 000-100 000

180 average
200 average
560 average
150!200

[C12]
[C12]
[C20]
[B21]

Niue Island

Pacific

Volcanic soil

4 500

1 100 maximum[M14]

Switzerland

Tessin, Alps, Jura

Gneiss, verucano, 226Ra in karst soils

300 000

100!200[S51]

Includes cosmic and terrestrial radiation.

1 045
0.003

1 045
0.003

Total
Fraction of total

Cumulative total
Cumulative fraction

4 485
0.014

3 440
0.011

2 175

18 5940.058

14 109
0.044

329
4 225

800

South Europe
Greece
Italy
Spain

460

306
23
7 670

581

245

300
633
23

30-39
nGy h-1

East Europe
Bulgaria
Hungary
Romania
Russian Federation

80
144

20-29
nGy h-1

600< 20
nGy h-1

West Europe
Belgium

North Europe
Denmark
FinlandLithuania

Region / country

49 9050.16

31 311
0.10

900
5 400

245
272
20 970

2 000

600
779
145

40-49
nGy h-1

88 576
0.28

38 671
0.12

5 536
4 400
1 115

270
357
1 498
21 020

2 500

1 100
636
239

50-59
nGy h-1

134 927
0.42

46 350
0.15

1 043
3 975
5 490

3 362
696
2 293
24 660

2 500

1 300
398
633

60-69
nGy h-1

167 8310.53

32 904
0.10

1 135
4 850
1 285

2 370
696
5 538
12 810

2 000

1 000
474
746

70-79
nGy h-1

203 5370.64

35 707
0.11

417
8 500
8 908

2 572
903
7 038
4 860

620

600
491
798

80-89
nGy h-1

260 851
0.82

57 313
0.18

293
6 800
4 015

201
1 150
5 176
38 670

200
470
338

90-99
nGy h-1

Population (103) residing in areas with various levels of indoor absorbed dose rate in air

Table 12Distribution of population with respect to the indoor absorbed dose rate in air from terrestrial gamma radiation

310 755
0.97

49 905
0.16

603
8 875
15 584

102
4 988
794
16 980

50
1 122
807

100-199nGy h-1

315 781
0.99

5 026
0.016

4 025
906

17
68

10

200-299nGy h-1

319 047
1.000

3 266
0.010

3 250

16

>300
nGy h-1

122
ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCESANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

123

Table 13
Reference annual intake of air, food, and water[I7, W1]
Breathing rate (m3 a1)
IntakeAir

Infants (1 year)

Children (10 years)

Adults

1 900

5 600

7 300

Food consumption rate (kg a1)
IntakeInfants

Children

Adults

120
15
45
20
60
5
150

110
35
90
40
110
10
350

105
50
140
60
170
15
500

Milk products
Meat products
Grain products
Leafy vegetables
Roots and fruits
Fish products
Water and beverages

Table 14
Concentrations of uranium and thorium series radionuclides in air
Concentration (µBq m3)

Region / country

Ref.
238

230

226

0.9!5

0.6

0.6

100-1 000

10-40

0.4

0.3!1.7

0.3!1.7

1.2!3.3

12-80

0.2!0.9

0.02!0.06
1!18

0.02!0.07

28!2 250
410

0.8!32<40!710200-2 0001

0.5

1 (0.5) a

500

U

North America
United States
EuropeGermany
Netherlands
NorwayPolandSwitzerland
Reference value
a

Th

Ra

Revised value; previous value [U3] in parentheses.

210

Pb

210

Po

232

Th

228

Ra

228

Th

1.0

235

U

0.04

<0.3-1.5[H31, K4, K10]
[N21]
[K4]
[K5]
[S51]

0.01!0.0750

0.5 (1)a1[F3, L8, M15,
P5, W6]

1

0.05

[U3]

124

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 15
Concentrations of uranium and thorium series radionuclides in foods and drinking water

Region /country

Concentration (mBq kg1)
Ref.
238

U

230

Th

226

Ra

210

210

Pb

Po

232

Th

228

Ra

228

Th

235

U

Milk products
North America
United States

0.7[F3, M16]

Asia
China
India
Japan

13
17
0.55

0.4

Reference value

2.6

1.2

0.1!4.9
1

11

6

16

0.27

13
15

12

Europe
Italy
Germany
PolandRomania
U.K.

5.7

0.5

1.2

21

0.6

0.29

3!19
2!130

5!280

2!80

10
0.9!44<0.4!200

18
11!15
35!88

16
13!140
20!2201.2

15 (60)

0.3

5

0.05

15 (40)a[M17][B3, J4,
M18][P3, P7][B20,R20]
[B2]

56
5

0.3

[Z1]
[D6, K6]
[S22]

0.05

Meat products
North America
United States
Asia
China
India
Japan
EuropeGermany

0.8!2.3

0.5!3

0.3!2

20

18

10

41

140

13

36

1!20

30!2201001 000

37-4 000

11!19
2!30
2.6!74

98!10515!1940-3 700

99!102
38!11062-67 000

0.5!3.6

15

80

60

1

PolandRomania
U.K.

1.6!5.6

Reference value2

0.7!3.0

4.9
2

120
440

4.3

120

0.02

[F3,M16]

0.5

[Z1]
[K6]
[S22]

2.3

[B3,
G5,M18][P3, P7][B20,R20]
[B2]

22!93
10

1

0.05

Grain products
North America
United States

3!23

Asia
China
India
Japan

9.8
7.4!67
1.2

EuropeGermany
PolandRomania
U.K.

20!400
4.7!11
6.1!85
6.2!35

Reference value

20

0.9!10

7!100

33!81

17

34

0.1!2.8
42
15!12014

1.4!1710

0.11.3[F3,M16]

0.5

1.2

[Z1]
[D6, K6][S22][B3, G5][P3, P7][B20,R20][B2]

13

20-2 900
80!11030!90
0.7-5 200

40-4 000
110!160
49!59
56!120

37!1 900
90!140
20!36027!260

2.0!21
1.6!331280

50 (100)

60 (100)3

38

180-230060

31

Leafy vegetables
North America
United States
Asia
China
India

24

16
61!72

20

56

41

75

360

18

430
320

23

220

1.2

[F3,M16]

0.7[Z1][D6, K6]

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

125

Table 15 (continued)

Region /country
EuropeGermany
Italy
PolandU.K.
Reference value

Concentration (mBq kg1)
Ref.
238

U

230

Th

6!2 200

226

Ra

14!15
9.8!400

6!9
80!380

6!1 150
27!44
37!43
2.2!170

20

20

50

210

Pb

210

232

Po

Th

4!4 100

4!7 400

43!51
16-3 300

40!67
37-3 300

4!7

80 (30)100 (30)

15

228

Ra

228

Th

235

U
[B3,
G5,M18][D9][P3, P7]
[B2]

40

15

1

Root vegetables and fruits
North America
United States

0.9!7.7

Asia
China
India
Japan
EuropeGermany
Italy
PolandRomania
U.K.
Reference value

0.2!1.1

7!47

8!150

0.08!1.4

13
0.4!7726

63

27

10-2 900

5!9 400
14!25
11!2159!190
9.0!4120-4 900

22!5 200

24!93
19!44
18!76

28!210
12!1400.7!7.1
0.4!2.13030 (25)40 (30)0.5

29
16!14011

0.9!106!120
6

0.7!7.5

3

0.5

4.7

110

0.1

[F3,M16]

0.6[Z1][D6, K6]
[S22]

2.3

[B3,
G5,M18][D9][P3, P7][B20,R20]
[B2]

22

20

0.5

0.1

Fish products
North America
United States

Asia
China

13-1 900

1.2!2912EuropeFranceGermany
PolandPortugal
U.K.

2.5

Reference value

30

10

30!59

14-1 800

150-55 000

1.2!30

39

3 500

4 900

1.3

37
100-7 400
28!43

20-4 400
81!93

50-5 200

8.5-2 100

180-4 800

60-53 000

100

200

2 000

320

3 100-3 800
80-120 000

0.4-90[F3, M16,
S23]

0.5

[Z1]

[P6]
[G5,M18]
[P7]
[C14]
[B2]

56!70010100Drinking waterNorth America
United States

0.3!77

Asia
China
India

0.1!700
0.09!1.5

0.2!1200.5!
150 000
4.4!930
0.4!600

10!
49 000
7!700
1!1 800

EuropeFinlandFranceGermanya

Italy
PolandRomania
Switzerland
Spain
U.K.

0.5!130
7.3
0.4!370!1 000
3.7!4.4

Reference value

1

0.1

1.4

0.1

0.4!1.8

0.1!1.5

0.05

0!0.5

0.04

0.04!120.2!
21 0000.2!7 600

0.2!200

0.1!200

1.6
7!44

0.5
7!44

0.06
0.04!9.3

5

0.05

0.2!1200
1.7!4.5
0.7!21
0!1500<20-4 000
0!180

40!2000.5

10Revised value with previous value [U3] (if different) in parentheses.

[C15, F3,
H11, M20]

[N3]
[D6]

18-570[A16,S11]

0!4.2

0!200

0.5

0!50

0.05

0.04

[D8, P6][B3, G5,
G6][S55][P3, P7][B20,R20]
[S51]
[S24]
[B2]

126

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 16
Annual intake of uranium and thorium series radionuclides in diet
Region / country

Annual intake (Bq)
Ref.
238

U

North America
Puerto Rico
United States

5.5!6.2230

Th

2.2!3.7

South America
Argentina
Brazil

57
2.9

Japan

3.2!6.6

Reference value a
a

210

9.1
10!24

16!23

Ra

Pb

9.5
40

Asia
China
India

EuropeBelgium
Bulgaria
Czech Rep.
FranceGermany
Italy
Netherlands
PolandRomania
Russian Fed.
U.K.

226

0.6

3.4

6.4
5.8
16
4.4

2.1

5.7

3.0

Po

22

232

Th

1.1!2.2

Ra

13!16

228

Th

235

U

[H13]
[B8, F3, F5, H12,
L9, M23, M24, P8,
S31, S33, W6]

7.3!8.0[B7, U8][L10, P9]40
75!11046

68!130
20

9.3
3.3

9!15

73!80

220

0.6!0.8

40
14!19
40
11!19
27
19!20
19

228

18

12!32
8.8

16

4.4
11

210

66
47

2.6

[S28]
[K8]
[T6]
[G7, S32, U8][F4, G8, M22]
[C17, D9, M21]
[S28]
[P3, P7][I12][D7, L12][C18, H14, H15,
S29, S30]

22!28
18
62
40

40
44
51
40!55
28!44

1.2
2.2

11!16

45
57
55!84
16!30

22

30

58

1.7

2.2

17

17

2.2

15

3.0

Intake by adults; consumption rates from Table 13 and reference concentrations in foods and water from Table 15.

[L16,Y5,Y6, Z1][C16, D5, L11,
S41]
[K7, N13, S22,
S27, S42, S45]

0.2

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

127

Table 17
Annual effective dose from inhalation of uranium and thorium series radionuclides

Radionuclide
238

U
U
Th
226
Ra
210
Pb
210
Po
232
Th
228
Ra
228
Th
235
U
234

230

Effective dose coefficient [I9] (µSv Bq1)

Concentrationin air(µBq m3)

Infants

Children

AdultsInfants

Children

AdultsAgeweighted

9.4
11
35
11
3.7
11
50
10
130
10

4
4.8
16
4.9
1.5
4.6
26
4.6
55
4.3

2.9
3.5
14
3.5
1.1
3.3
25
2.6
40
3.1

0.018
0.021
0.033
0.021
3.5
1.0
0.048
0.019
0.25
0.001

0.022
0.027
0.045
0.027
4.2
1.3
0.073
0.026
0.31
0.001

0.021
0.026
0.051
0.026
4.0
1.2
0.091
0.019
0.29
0.001

0.021
0.026
0.048
0.026
4.0
1.2
0.084
0.021
0.29
0.001

5.0

6.0

5.8

5.8

1
1
0.5
1
500
50
0.5
1
1
0.05

Total
a
b

Committed effective dose a , b (µSv)

Assumed breathing rates: infants 1,900 m3 a1, children 5,600 m3 a1, adults 7,300 m3 a1.
Committed effective dose from the annual intake. Age distribution for weighted values: infants 0.05, children 0.3, adults 0.65.

Table 18
Annual intake and effective dose from ingestion of uranium and thorium series radionuclides
Activity intake a(Bq)

Radionuclide

238

U
U
230
Th
226
Ra
210
Pb
210
Po
232
Th
228
Ra
228
Th
235
U
234

Total
a
b

Committed effective dose b(µSv)

Effective dose coefficient [I2, I21](µSv Bq1)

Infants

Children

AdultsInfants

Children

AdultsInfants

Children

AdultsAgeweighted

1.9
1.9
1.0
7.8
11
21
0.6
5.5
1.0
0.1

3.8
3.8
2.0
15
21
39
1.1
10
2.0
0.2

5.7
5.7
3.0
22
30
58
1.7
15
3.0
0.2

0.12
0.13
0.41
0.96
3.6
8.8
0.45
5.7
0.37
0.13

0.068
0.074
0.24
0.80
1.9
2.6
0.29
3.9
0.15
0.071

0.045
0.049
0.21
0.28
0.69
1.2
0.23
0.69
0.072
0.047

0.23
0.25
0.42
7.5
40
180
0.26
31
0.38
0.011

0.26
0.28
0.48
12
40
100
0.32
40
0.30
0.012

0.25
0.28
0.64
6.3
21
70
0.38
11
0.22
0.012

0.25
0.28
0.58
8.0
28
85
0.36
21
0.25
0.011

260

200

110

140

Consumption rates from Table 13 and concentrations in foods and water (reference values) from Table 15.
Committed effective dose from the annual intake. Age distribution for weighted values: infants 0.05, children 0.3, adults 0.65.

128

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 19
Uranium and thorium series radionuclides in human tissues
Concentration (mBq kg1)
Ref.

Region / country
Lung

Liver

KidneyMuscle andother tissues

Bone

a

238

U

AfricaNigeria
North America
CanadaUnited States

6.2!15

1.5!4.1

340

[F9]

120
11!52

[F9]
[F8, S44]

130!150[F9]5.3410 (94!2 600)
140
17!59
110

[L1]
[G13]
[I17]
[F10]

2.4

10
150
2.7

[H20]
[H15]
[P14]

81!95

74!120[D7, F10, M31]

23

[F10]

4.8!12South America
BrazilEast Asia
China
India
Japan
Nepal

21

EuropeAustria
United Kingdom
Yugoslavia
Russian Federation

27
4.2

3.0

62
3.1
67!84

72!14066!68

Oceania
Australia
Median value
Range

21
(6!84)

3(2!140)

Reference value

20 (15) b

3

27(4!68)

5(2!95)

100(3!410)30 (5)5 (2)100 (50)

230

Th

AfricaNigeria
North America
CanadaUnited States

110

[F11]

41
45!130[F11][H23, I15, S1]

120 (58!220)
24

[C3]
[H22]

12!31

6

6!11

29
19

12

1

1.4

Median value
Range

19
(12!29)9(6!12)

5(1!11)

1

76(24!120)

Reference value

20

9 (7)

5 (10)

1 (0.3)20!70 cEast Asia
China
Japan

226

Ra

16 countries d
31 countries e

3.6
4.1

3.6
4.1

3.6
4.1

3.6
4.1

230
260

Reference value

4.1 (2.7)

4.1 (2.7)

4.1 (2.7)

4.1 (2.7)

260 (170)[F15, U7]
[F16]

210

Pb

EuropeFinland
Russian Federation

240

90
450

170
270

30
140!270

2 400
5 000

[K17]
[L12]

East Asia
Japan

240

560

430

30!230

2 600

[T13]

North America
United States

230

340

160

140

[B22]

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

129

Table 19 (continued)
Concentration (mBq kg1)
Ref.

Region / country
Lung

Liver

KidneyMuscle andother tissues

Bone aMedian value
Range

240
(230!240)

400(90!560)

220(160!430)

110(30!270)

2 600(2 400!5 000)

Reference value

200

400 (200)200

100 (200)

3 000

210

Po

EuropeFinland
Russian Federation
United Kingdom

330
200

510
970
630

490
760
640

110
110!220
120

2 200
2 400
2 200

[K17]
[L12]
[H10]

East Asia
Japan

370

1 700

1 200

40!310

2 600

[T13]

North America
United States

190

410!540

420

130!220

2 900[B22, H30]

Median value
Range

270
(190!370)

630(410!970)

640(420!1 200)

120
(40!310)

2 400(2 200!2 900)

Reference value

200 (100)600 (200)

600 (200)

100 (200)

2 400

232

Th

AfricaNigeria
North America
CanadaUnited States

East Asia
China
India
Japan
EuropeUnited Kingdom
Yugoslavia

9.3!32

2.2!3.0

1.9!4.1

38
24
22

3.6
2.1

6.8
1.0

2.2
0.8

22

86

[F11]

15
21!35

[F11]
[H23, I15, L15,
S1, W7]68 (34!140)
8
11

[C3]
[J8, S41]
[H22]

62
50

[H21]
[P14]

Median value
Range

22
(9!53)

3
(2!4)

3
(1!7)

1
(1!2)

38
(8!86)

Reference value

20

3 (2)

3

1 (0.15)

6!24 c228

Ra

AfricaNigeria

a
b
c
d
e

320

[F11]

23
39!230[F11][I15, S1]

290 (140!570)
100

[C3]
[H22]

North America
CanadaUnited States

9!10

2.6!3.3

2.6!3.3

East Asia
China
Japan

41
19

3.9

1.3

1.5

Median value
Range

19
(9!41)

3
(3!4)

2
(1!3)

2

100
(23!320)

Reference value

20 (15)3 (5)2 (10)

2 (0.5)100 (50)

Assumes 5 kg dry bone yields 2.7 kg ash per skeleton.
Revised reference value with previous value [U4] (if different) in parentheses.
First value given is for cortical bone and the second value for trabecular bone.
Representing 30% of the world population.
Representing 66% of the world population.

130

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 20
Dose rates to adults from ingestion of uranium and thorium radionuclides estimated from reference
concentrations in tissues
Concentration (mBq kg-1)
Tissue238/234

U

Bone
Lung
KidneyLiverOther a

100
20
30
3
5

230

226

30 b
20
5
9
1

260
4.1
4.1
4.1
4.1

Th

210

Ra

Pb/Po

2 400 c
200
600
600
100

232

Th

228/224

9.6b
20
3
3
1

100
20
2
3
2

Ra

Absorbed dose rate per unit concentration (µGy a-1 per mBq kg-1) [U4]238/234

230

226

0.046
0.085
0.008

0.024
1.9
0.005

0.063
0.18
0.022

U

Soft tissues
Bone marrow
Bone lining cells e

Th

Ra d

210

Pb/Po

232

0.027
0.046
0.005

0.020
1.1
0.003

0.16
0.70
0.056

232

228/224Th

228/224Ra

Effective dose rate (µSv a-1)
238/234

230

226

7

6

7

U

Body fTh

Total fIntake g

a
b
c
d
e
f
g

Pb/Po

Th

Ra

80

4

18

91

0.4

11

120
0.5

Total g

210

Ra

0.6

6
110

Includes gonads, breast, red bone marrow, and thyroid.
Assumes 4 kg cortical and 1 kg trabecular bone in 5 kg skeleton.
Concentration of 210Po.
Includes dose from 222Rn and its short-lived decay products; retention factor of one third.
Referred to concentration in bone; cells located 10 µm from bone surface [H23].
Estimated from reference concentrations in body.
Estimated from intake of radionuclides in foods and water for adults (see Table 18).

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

131

Table 21
Parameters of the model masonry house
Parameter

Notation

Value

Dimensions and relevant parameters
250 m3
100 m240 m
3 mm
450 m21 h1VolumeSurface area of floor
Length of floor to wall gap
Width of floor to wall gap
Total surface area including internal walls, furniture, etc.
Air exchange rate
Subsoil
Activity concentration of 226Ra
Emanation fraction
Porosity
Fraction of water saturation
Effective diffusion coefficient
Bulk diffusion coefficient
Soil density
Permeability

CRa
f
ε

m
De
D
ρ

k

a

Aggregate layer thickness
Aggregate layer permeability a

50 Bq kg-1
0.2
0.25
0.2
2.0 106 m2 s-1
5.0 107 m2 s-1
1 600 kg m-3
2 1011 m2
0.15 m
5 109 m2

Building elements, wall and floor
Thickness of floor
Thickness of walls and ceiling
Activity concentration of 226Ra
Emanation fraction
Porosity of wall
Porosity of floor
Effective diffusion coefficient of wall
Effective diffusion coefficient of floor
Densitya

The other specifications of the aggregate layer are similar to the subsoil specifications.

CRa
f
ε

De
ρ

0.1 m
0.2 m
50 Bq kg-1
0.1
0.15
0.20
7 108 m2 s-1
1 107 m2 s-1
1 600 kg m-3

132

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 22
Representative radon entry rates of the model masonry house
Radon entry rate (Bq m-3 h-1)

Source of radon
Building materials
Subjacent earth

Outdoor air
Water supply
Natural gas

10
1
10
4
20
10
1
0.3

Diffusion, walls and ceiling
Diffusion, floor slab
Diffusion through the slab
Diffusion through gaps
Advection
Infiltration
De-emanation
Consumption

Total

56

Table 23
Representative radon entry rates in low-rise residential houses in Finland compared to the model masonryhouse
Radon entry rate (Bq m-3 h-1) a
Source of radon
Building elements
Walls and ceiling
Floor slab
Subjacent earth
Through gaps
Through slab
Outdoor air
Water supply
Natural gas
Total
a
b
c
d

Mechanism

Diffusion
Diffusion
Diffusion
Advection
Diffusion
Infiltration
De-emanation
Consumption

Wooden house b

Masonry house c

Model masonry house d2 (3)16 (18)10 (18)1 (2)60 (86)
4 (6)
3(4)
1 (1)

66 (73)
4 (4)
3 (3)
1 (1)

4(7)
20 (35)10 (18)10 (18)1 (2)0.3 (!)

70 (100)

90 (100)

56 (100)

Percentage in parentheses.
Radon concentration indoors 140 Bq m-3; air exchange rate 0.5 h-1 [A1].
Radon concentration indoors 180 Bq m-3; air exchange rate 0.5 h-1 [A1].
Radon concentration indoors 56 Bq m-3; air exchange rate 1.0 h-1 [U3].

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

133

Table 24
Radon concentrations in dwellings determined in indoor surveys
Data not referenced are from UNSCEAR Survey of Natural Radiation Exposures

RegionCountry

Populationin 1996(106)

Radon concentration (Bq m-3)
Arithmetic
mean

Geometricmean

Maximum
value

Geometric
standard
deviation

AfricaAlgeria
Egypt
Ghana

28.78
63.27
17.83

30
9

North America

CanadaUnited States

29.68
269.4

34
46

14
25

1 720

3.6
3.1

[L13]
[M26, U14]South America

Argentina
Chile
Paraguay

35.22
14.42
4.96

37
25
28

26

211
86
51

2.2

[G9]
[S14]

East Asia

China– Hong Kong SAR
India
Indonesia
Japan
Kazakstan
Malaysia
PakistanThailand

1232
6.19
944.6
200.45
125.4
16.82
20.58
140.0
58.7

24
41
57
12
16
10
14
30
23

20

380
140
210
120
310
6 000
20
83
480

2.2
2.2

[Z2]
[T8]
[S37]

1.8

[F20, S61]

Armenia
Iran (Islamic Rep. of)
Kuwait
Syria

3.64
69.98
1.69
14.57

104
82
14
44

216
3 070
120
520

1.3

Denmark
Estonia
FinlandLithuania
NorwaySweden

5.24
1.47
5.13
3.73
4.35
8.82

53
120
120
55
73
108

29
92
84
22
40
56

600
1 390
20 000
1 860
50 00085 0002.2

Austria
Belgium
FranceGermany
Ireland
Luxembourg
Netherlands
Switzerland
United Kingdom

8.11
10.16
58.33
81.92
3.55
0.41
15.58
7.22
58.14

110
23
70
20

15
38
41
40
37
70
18
50

190
12 000
4 690>10 000
1 700
2 500
380
10 000
10 000Bulgaria
Czech RepublicHungary
PolandRomania
Slovakia

8.47
10.25
10.05
38.60
22.66
5.35

22
140
107
41
45
87

82
32

250
20 000
1 990
432
1 025
3 750

Albania
Croatia
CyprusGreece
Italy
PortugalSlovenia
Spain

3.40
4.50
0.76
10.49
57.23
9.81
1.92
39.67

120
35
7
73
75
62
87
86

105
32
7
52
57
45
60
42

270
92
78
490
1 040
2 700
1 330
15 4002.0

Australia
New Zealand

18.06
3.60

11
20

8
18

420
90

2.1

46
39

37
30

480
1 200

2.2
2.3

West Asia

North Europe

West Europe

Eastern Europe

South Europe

Oceania

MedianPopulation-weighted average

48
62
50

140
24
340

Ref.

42
13

16

6

[C19]
[K12]
[O6]

[T9]
1.2

[S38]
[B15]
[O8]

2.1

[S15, U15]
[P15]
[A13, C21]

[S25]
[S34, S35]
2.0
2.7
1.9

[R5]
[C22]

2.0
1.6

2.7
2.0

2.6
2.0
2.2
2.2
3.7

[N22, P10]
[S26]
[W5]

[T7]
[N14]
[B10]
[I12]

[C6]
[G10]
[B9]
[F7]
[K15]

[L7]
[R4]

134

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 25
Thoron concentrations in outdoor and indoor air

Region / country
or territory
North America
United States

East Asia
China
Hong Kong SAR
Japan

Equilibrium equivalent concentration a (Bq m3)
Indoors

0.09 (0.03!0.3)

0.5 (0.03!4.7)
0.2 (0.1!0.3)

0.4
0.3 (0.1!0.5)

0.5 (0.3!1.8)

0.8
0.8 (0.4!1.2)
0.6 (0.4!0.9) b
0.5 (0.1!1.0) b
0.2 (0.1!0.6) b
3.2 (1.0!6.0) c
2.7 (0.2!8.2) c
1.7 (0.3!5.3) c
0.7 (0.04!2.1) d
1.5 (1.4!1.6) d
1.1 (0.4!2.5)

Outdoors

0.05
0.04

Indoors

0.04

[T11]
[H36]

0.07
0.06
0.1

[P12]
[T10]
[G12, G23]
[Y8]
[Z6]
[G12, G23]
[Y8]
[Z6]
[Y8]
[G23]

0.03
0.4
0.2

0.08

0.08

e

North Europe
NorwaySweden0.7 (0.07!1.1)
0.3 (0.1!0.6)

0.04
0.01

[S43]
[M29]

West Europe
FranceUnited Kingdom

0.8 (0.6!13.3)
0.3 (0.07!1.1)

0.03
0.02

[R10]
[C26]

0.05
0.04

[P13]
[I16]
[I12, M30]

0.09 (0.02!0.24)[Z4]

0.11 (0.01!0.38)[B14, S7, S9][K3]

Central Europe
Germany
Rep. of Moldova
Romania0.2
0.3 (0.1!0.6)

East Europe
Russian Federation
South Europe
Italy
Slovenia
Range
a
b
c
d
e

Rn/ 222Rn EEC ratio
Ref.

Outdoors

0.09 (0.03!0.12)
Malaysia220

0.5 (0.1!1.0)
1.0 (0.1!6.4)
1.1 (0.1!6.4)

0.04
0.05

1.1!7.1

0.12 (0.05!0.37)
0.09!0.5

12 (0.5!76)
0.013
0.2!12Range in parentheses.
Concrete dwellings.
Wood frame and mud dwellings.
New materials, e.g. mortar wallboard.
Response to UNSCEAR Survey of Natural Radiation Exposures.

0.01!0.08

0.01!0.5

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

135

Table 26
Principal dosimetric assessments of lung dose from deposited radon decay products
Parameter values
InvestigatorYeara

Unattachedfraction

Breathingrate(m3 h1)

Target region

Model type

Dose factor a[nGy(Bq h m-3)-1]

1956

Chamberlain,
Dyson [C9]

0.09

1.2

Average in 45 µm
epithelium

Cast of trachea and bronchi

11

1959

ICRP [I19]

0.1

1.2

Mean TB region

Deposition retention assumptions

6.7

1964

Jacobi [J10]0.25

Basal cells (30 µm)

Findeisen/Landahl 6-region anatomical
model

24

1964

Altshuler et al.
[A6]

0.085

Basal cells (22 µm)

Findeisen/Landahl 6-region anatomical
model

32

1967

Haque, Collinson
[H24]

0.35

Basal cells (30 µm)

Weibel dichotomous airway model

71

1972

Harley,Pasternack [H25]

0.04

0.9

Basal cells (22µm)

Weibel dichotomous airway model

5.7

1980

Jacobi, Eisfeld
[J5]

0.1

1.2

Mean epithelium

Weibel dichotomous airway model,
correction for upper airway turbulent
diffusion [M19]

8.9

1980

James et al. [J6]

0.1

1.2

Mean epithelium

Yeh-Shum anatomical model [Y4]

14

1982

Harley,Pasternack [H26]

0.07

1.1

Basal cells (22 µm)

Weibel dichotomous airway model,
correction for upper airway turbulent
diffusion [M19]

6.4

1982

Hoffman [H27]

0.2

0.9

Mean epithelium

Weibel dichotomous airway model,
correction for upper airway turbulent
diffusion [M19]]

11

1991

National ResearchCouncil [N17]

0.16

1.2

Basal cells (35!50 µm)

Yeh-Shum anatomical model [Y4],correction for upper airway turbulent
diffusion

21

1996

Harley et al. [H8]

0.1

1.2

Basal cells (27 µm)

Nikiforov et al. [N9] anatomical model,
airway deposition from empirical datafrom human airway casts

9

1998

Marsh, Birchall
[M25]

0.08

0.8

Bronchial cells
Basal (35!50 µm)
Secretary(10!40 µm)
Bronchiolar cells
Secretary(4!12 µm)

ICRP lung model [I7]0.9

Per unit 222Rn concentration (EEC). WLM converted to Bq h m-3 with 0.27 10-3 WL (Bq m-3)-1 and 170 h per working month.

8.5
19

14

136

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 27
Typical concentrations of radionuclides in raw and produced materials and in wastes of the mineralprocessing industry

Material

Typical concentration in ore / raw material(kBq kg-1)
238

232

U-series

Typical concentration in product or tailings / wastes(kBq kg-1)
238

Th-series

U-series

232

Th-series

Phosphate industry
Phosphate

Artificial fertilizer

0.2!1.5
1.5 (Florida ore)
0.03 (Kovdor ore)
0.11 (Palfos ore)
0.3!3
0.2!1 (226Ra and 210Pb)
2.2 (TSP)

0.02 (Florida ore)

0.008!0.04

0.9!1.3 a
100 (210Po)
600 (210Pb) in calcinate
1 (Phosphorus slag)

0.02 (Phosphorus slag)

0.005 (TSP)

Rare earths, thorium compounds
6!40

Monazite450 b

4% (by weight)
8!300

3000 b

Oil and gas extraction
Natural gas
Oil0.34 kBq m-3 (222Rn)(Scale)1!1 000 (scale)8!42 kBq m-3 (production
water)
Metal ores

Iron ore

Cassiterite
Pyrochlore

1
6!10

0.3
7!80

0.1!0.3 (coal tar)
0.15 (blast furnace slag)/ zinc-rich filtercake
1 (slag)

0.15 (blast furnace slag)
4 (slag)

Coal tar treatment
Coal tar

0.1!0.3 (210Po and 210Pb)

0.2!0.6 (electrode pitch)

Cokes and electric power production
Coal

0.01!0.025

0.01!0.025

0.02!0.04 (cokes)
0.1!0.3 (coal tar)
0.2 (fly and bottom ash)
0.4 (fly dust)

0.2 (fly dust)

0.05!0.11 (cement)
0.02 (silex)

0.03!0.1 (cement)
0.003 (silex)

Cement industry
Marl

0.022

0.003

SchistPortland clinker

0.04
0.08

0.056
0.05
Mineral sands handling

Zirconium sandBauxiteIlmenite
Rutile0.2!740.4!0.6
2.3 (1.5 : 238U)
3.8

0.4!40
0.3!0.4
1.2
0.56

RutileTitanium pigment production
Ilmenite
Titanium oreabc

2.3 (1.5 : U)
0.07!9Phosphogypsum, Central Florida ore.
Ra in sulphate precipitate.
226
Ra precipitate.
226

238

1.2
0.07!9400 c0.15 (VBM)
2.3 (filtercake)0.03 (water)

up to 1 500 (scale)
0.13 (VBM)
2.6 (filtercake)0.01 (water)

ab

Zirconium.
106 m3 a-1.

Elementary phosphorus– Transport
Phosphoric acidFertilizer plant– Transport
Iron and steel production– Transport
Coal tar treatment
Coal-fired power plant (600 MW e)– Transport
Cokes production– Transport
Cement industry
Ceramics
Mineral sands handling
Titanium-pigment
Gas-fired power plant (400 MW e)
Oil extraction
Gas extraction

2 000
3 200
183 a
50
600 b
3 500
72 000 b

885

120
1 350

7 500

700
375

570

Ore
throughput(kt a-1)

0.16
0.004
0.013
0.001
0.2
0.03
0.97
0.001
0.12
0.001

0.08
0.004
0.009
0.001
0.05

0.01
0.11
0.004
0.013
0.001
0.2
0.03
0.73
0.001

0.01

0.02

0.0001

0.02
0.01

0.06
0.09

Ra

226

0.001
0.002

Th

228

0.06
0.07

U

238

Rn

34
0.004
13
0.001
157
0.03
0.73
6.2
230
540
500

563
0.03
820
221
0.02
180
0.01

222

Pb

66
0.06
0.08
0.044
0.02
55
0.01
0
0.4
0.004
0.012
0.002
0.2
0.09
0.73
0.001

210

Releases to atmosphere (GBq a-1)-

Industry
Po

490
0.06
0.14
0.034
0.02
90
0.01
0
0.8
0.004
0.07
0.001
78
0.3
0.73
0.001

210

-

Table 28
Release of radionuclides from typical installations of mineral processing industries
[L18]

K

0.27
0.012
0.032
0.004
0.4
0.14

0.01

0.001

0.004
0.008

40

0.18
336
0.07
0.03
0.011
0.004
0.088
0.002
-

U

238

Th

0.002
8
0.0004
0.03
0.011
0.003
0.011
0.003
217
2.7

228

Rn
0.18
0.07
0.03
0.011
0.004
0.066
0.002
174
32

0.18
737
0.07
0.03
0.011
0.004
0.066
0.002
174
32

222

Ra

226

K
0.013
79
0.002
0.04
0.036
0.011
166
0.18
997
0.057
0.06
8
0.04
0.011
0.032
0.004
0.066
0.002
174
32
24
0.18
654
0.054
0.07
0.51
0.04
0.011
0.024
0.005
0.066
0.003
174
32

40

Po

210

Pb

210

Releases to water (GBq a-1)

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES
137

138

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 29
Maximum effective doses from natural radionuclides released from typical installations or operations of themineral processing industry[L18]
Maximum effective dose rate (µSv a-1)
Industry
External irradiation
Elementary phosphorus production
Phosphoric acid production
Fertilizer production
Primary iron and steel production
Coal tar processing
Cokes production
Coal-fired power plantGas-fired power plant
Oil and gas extraction
Cement production
Ceramic industry plant
Mineral sands handling
Titanium pigment productionab

Air dispersion pathways

Water dispersion pathways

2

<0.4
2
15
3

130
8
20
8
4
4
12
<0.4
2a
5
<0.4
60
<0.4

Inhalation dose (radon) due to land fill with harbour sludge below a residential area.
Rather uncertain value.

-2 000 b
<0.4
<0.4
<0.4
<0.4
<0.4
<0.4
<0.4 b
<0.4
<0.4
<0.4
<0.4

4

!

320
1

80 941

50
150
3 650

174 258
0.39

174 258
0.39

South Europe
Albania
Italy
Portugal

Total
Fraction of total

Cumulative total
Cumulative fraction

280
14 023

West Europe
Belgium
Netherlands

560

223
1 680

North Europe
Denmark
FinlandLithuania

East Europe
Bulgaria
Hungary
Romania
Russian Federation

60 211
12 490< 1.5
mSv a-1

East Asia
China (Hong Kong SAR)Japan
Malaysia

Region / country

306 058
0.69

131 800
0.30

200
15 125
2 076

990
2 101
4 653
32 000

3 300
779

800
1 376
854

1 130
63 306
4 240

1.5-1.99
mSv a-1

386 5290.88

80 4710.18

2 500
25 800
1 994

6 051
3 325
8 717
20 027

4 500
701

2 800
2 039
770

4 370
1 247

2.0-2.99
mSv a-1

414 220
0.94

27 691
0.063

300
7 825
792

1 836
1 683
5 312
6 642

1400
39

900
687
275

770

3.0-3.99
mSv a-1

427 762
0.97

13 542
0.031

300
4 175
770

1 010
2 951
3 067

440
39

400
310
80

160

4.0-4.99
mSv a-1

433 553
0.982

5 791
0.013

100
2 175
113

633
567
1 685

150

200
154
14

46

5.0-5.99
mSv a-1

436 819
0.989

3 266
0.007

50
1 025
39

388
500
1 029

70

50
87
28

11

6.0-6.99
mSv a-1

Population (103) with various levels of total exposure

Table 30
Distribution of population with respect to total exposure to natural sources

438 339
0.993

1 520
0.003

439 142
0.995

803
0.002

150

465

675

500

102

14

30
37
5

5

8.0-8.99
mSv a-1

184

30

30
82
19

5

7.0-7.99
mSv a-1

439 747
0.996

605
0.001

150

333

61

7

20
29
5

9.0-9.99
mSv a-1

441 508
1.0

1 761
0.004

200

1 236

153

29

20
123

>10
mSv a-1

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES
139

140

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

Table 31
Average worldwide exposure to natural radiation sources
Annual effective dose (mSv)
Source of exposure
Average
Cosmic radiation
Directly ionizing and photon component
Neutron component
Cosmogenic radionuclides
Total cosmic and cosmogenic
External terrestrial radiation
Outdoors
Indoors0.28 (0.30) a
0.10 (0.08)
0.01 (0.01)
0.39

0.3!1.0 b

0.07 (0.07)
0.41 (0.39)

Total external terrestrial radiation
Inhalation exposure
Uranium and thorium series
Radon (222Rn)
Thoron (220Rn)

0.48

0.3!0.6 c

0.006 (0.01)
1.15 (1.2)
0.10 (0.07)

Total inhalation exposure
Ingestion exposure
40
K
Uranium and thorium series

1.26

0.2!10 d

0.17 (0.17)
0.12 (0.06)
Total ingestion exposure

Total
a
b
c
d
e

Typical range

Result of previous assessment [U3] in parentheses.
Range from sea level to high ground elevation.
Depending on radionuclide composition of soil and building materials.
Depending on indoor accumulation of radon gas.
Depending on radionuclide composition of foods and drinking water.

0.29

0.2!0.8 e

2.4

1!10

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

References
PART A

Responses to UNSCEAR Survey of Exposures from natural radiation sourcesCountry

Respondent

Albania

R. Kushe. Institute of Nuclear Physics, Tirana
S. Bushati. Department of Radiometry, Center of Geophysical and Geochemical Exploration, Tirana

AlgeriaS. Djeffal. Centre de Radioprotection et de Sûreté, Alger

Argentina

A. Curti. Nuclear Regulatory Authority, Buenos Aires

ArmeniaA. Martirosyan and A. Avetisyan. Armenian Nuclear Regulatory Authority, Yerevan

Bangladesh

K. Obaidul Awal and F. Karin Mia. Bangladesh Atomic Energy Commission, Dhaka

Belgium

H. Vanmarcke. Nuclear Research Centre, SCK-CEN, Mol

Bulgaria

G. Vassilev. National Centre of Radiobiology and Radiation Protection, Sofia

CanadaS. Vlahovich. Radiation Protection Bureau, Health and Welfare Canada, Ontario

Chile

E. Stuardo. Comisión Chilena de Energía Nuclear, Santiago

Costa Rica

P. Mora. University of Costa Rica, Nuclear Physics Laboratory, Costa Rica

Croatia, Republic of

G. Marovi and S. Grgi. Institute for Medical Research and Occupational Health, Ministry of Health, Zagreb

CyprusS. Christofides. Medical Physics Department, Nicosia General Hospital, Nicosia

Denmark

K. Ulbak. National Institute of Radiation Hygiene, Brønshøj
A. Aarkrog, A. Damkjaer and S.P. Nielsen. Environmental Science and Technology Department, Risø National
Laboratory, Roskilde

Egypt

N.M. Ibrahiem. Central Laboratory for Environmental Radiation Measurements, Intercomparison and Training,
Atomic Energy Authority, Cairo

Estonia

E. Realo. University of Tartu, Institute of Physics, Tartu

Finland

H. Arvela. Radiation and Nuclear Safety Authority, STUK, Helsinki

Germany

A. Bayer, E. Ettenhuber and W. Burkart. Bundesamt für Strahlenschutz, Oberschleissheim

GreeceC. Papastefanou. Aristotle University of Thessaloniki, Nuclear Physics Department, Thessaloniki

Hong Kong

M.Y. Tso. The University of Hong Kong, Radioisotope Unit, Pokfulam Road

Hungary

L.B. Sztanyik and I. Nikl. Frédéric Joliot-Curie, National Research Institute for Radiobiology and Radiohygiene,
Budapest

India

U.C. Mishra and K.S.V. Nambi. Bhabha Atomic Research Centre, Environmental Assessment Division, Mumbai

Indonesia

S. Soekarno. National Atomic Energy Agency, Jakarta

Iran, Islamic Republic of

M. Sohrabi. National Radiation Protection Department, Atomic Energy Organization of Iran, Tehran

Italy

S. Risica, F. Bochicchio and C. Nuccetelli. National Institute of Health, Physics Laboratory, Rome
S. Piermattei, Environmental Protection Agency (ANPA), RomeJapan

Y. Sasaki, K. Fujitaka, Y. Hirao. National Institute of Radiological Sciences, Chiba-shi

Kazakstan, Republic ofT. Zhantikin and A.V. Galkin. Atomic Energy Agency of the Republic of Kazakstan, Almaty

Korea, Republic of

S-D. Sa and D.M. Lee. Ministry of Science and Technology. Korea Institute of Nuclear Safety, Taejon

Lithuania

A. Mastauskas and G. Morkãnas. Radiation Protection Centre, Ministry of Health, Vilnius

141

142

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCESCountry

Respondent

Luxembourg

M. Feider. Division de la Radioprotection, Direction de la Santé, Luxembourg-Belair

Macedonia, Republic of

M. Drakalski and D. Nedelkovski. Institute of Public Health, Ministry of Science, Skopje

Malaysia

M. Omar and I. Sulaiman. Malaysian Institute for Nuclear Technology Research (MINT), Kajang

MonacoA. Veglia. Service de l’Environnement, Monaco

The Netherlands

R.O. Blaauboer. Laboratory of Radiation Research, National Institute of Public Health and the Environment,
Bilthoven

New Zealand

A.C. McEwan. National Radiation Laboratory, Christchurch

NorwayT. Strand. Norwegian Radiation Protection Authority, Østerås

Paraguay

J.C. Cabello. Comisión Nacional de Energía Atomica, San Lorenzo

PolandJ. Henschke. Central Laboratory for Radiological Protection, Warsaw

PortugalA. Ortins de Bettencourt and E.M. Amaral. Direcção-Geral do Ambiente, Departamento de Protecção e SegurançaRadiológica, Sacavem

Romania

O. Iacob. Institute of Public Health, Iasi

Russian Federation

M.N. Savkin. Institute of Biophysics, State Research Center, Moscow

Slovak Republic

D. Viktory. State Health Institute of the Slovak Republic, Department of Radiation Protection, Bratislava

Slovenia

M. Kriñman. Slovenian Nuclear Safety Administration, Ljubljana

Spain

D. Cancio. Centro de Investigaciones Energéticas, Medioambientales y Tecnologicas (CIEMAT), Madrid
J. Luis Butragueño and C. Martínez Ten. Consejo de Seguridad Nuclear, Madrid

Sudan

O.I. Elamin. National Council for Research, Khartoum

SwedenG. Åkerblom and L. Mjönes. Swedish Radiation Protection Institute, Stockholm
H. Mellander. National Institute for Radiation Protection, Stockholm

Switzerland

C. Murith and H. Völkle. Swiss Federal Office of Public Health, Fribourg

Syrian Arab Republic

I. Othman. Atomic Energy Commission, Damascus

Tanzania

F.P. Banzi. National Radiation Commission, Environmental Monitoring Section, Arusha

Thailand

K. Bhadrakom. Office of Atomic Energy for Peace, Bangkok

United Kingdom

J.S. Hughes. National Radiological Protection Board, Didcot

ANNEX B: EXPOSURES FROM NATURAL RADIATION SOURCES

143

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A2

A3

A4
A5

A6

A7

A8

A9

A10

A11

A12

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A16
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I14

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I17

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I21

J1

J2

J3

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J5

J6

J7
J8

J9
J10

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Q1

Q2

Q3
R1

R2

R3

R4
R5

R6

R7

R8

R9

R10

R11

R12

R13

R14

R15

R16

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