RP/SID72-
NATURAL RADIATION EXPOSURE
IN THE UNITED STATES
S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Programs
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The mention of commercial products or their use in connection with
material reported herein is not to be construed us either an actual or
implied endorsement by t!>p Environmental Protection Agency.
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NATURAL RADIATION EXPOSURE
IN THE UNITED STATES
Donald T. Oakley
June li>7-2
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Program*
Surveillance and Insertion Division
Washington, D.C. '20460
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FOREWORD
The Office of Radiation Programs of the Environmental Protection Agency carries
out a national program designed to evaluate population exposure to ionizing and non-
ionizing radiation and to promote development of controls necessary to protect public
health and safety.
Within the Office of Radiation Programs, the Surveillance and Inspection Division
conducts programs relating to sources and levels of environmental radioactivity and the
resulting population radiation dose. Reports of the findings are published in the monthly
publication Radiation Data and Reports, appropriate scientific journals, and Division
technical reports.
The technical reports of the Surveillance and Inspection Division allow comprehen-
sive publication of the results of intramural and contract projects and, as in the case of
the present report, of studies supported by the Division. The reports are distributed to
State and local radiological health agencies, Office of Radiation Programs technical and
advisory committees, universities, libraries and information services, industry, hospitals,
laboratories, and other interested groups and individuals. They are also included in the
collections of the Library of Congress and the National Technical Information Service.
Readers of these reports are encouraged to inform the Office of Radiation Programs
of any omissions or errors. Comments or requests for further information are also invited.
W. D. Rowe
Deputy Assistant Administrator
for Radiation Programs
in
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ACKNOWLEDGMENTS
My deepest gratitude is extended to my thesis advisors: Bade W. Moeller, principal
advisor, Abraham S. Goldin, and Robert B. Reed, members of the faculty of the
Harvard School of Public Health. Special thanks are due Dr. Moeller for his patient guid-
ance which led to the thesis topic and for his attention to my problems and progress
throughout the preparation of the thesis. I am especially grateful to Dr. Reed for his
numerous suggestions for improving the interpretation and presentation of the data.
and to Dr. Goldin for his thorough review of my work "and for his wise counsel that
helped me to steer clear of contradictions and other pitfalls. Above all, I am apprecia-
tive of the many instances of kindness and wit which accompanied suggestions from all
three advisors. Although not an advisor, Jacob Shapiro contributed substantially to my
understanding of natural radiation exposure through his teaching at the School of Public
Health, and I gratefully acknowledge his help.
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CONTENTS
Chapter pa£,<,
FOREWORD iii
ACKNOWLEDGMENTS v
LIST OF FIGURES ix
LIST OF TABLES xi
ABSTRACT xiii
r
1. INTRODUCTION 1
1.1. General 1
1/2. Estimates of natural radiation exposure 1
1.3. Sources of natural radiation exposure 2
1.4. Methology 3
COSMIC RADIATION
2.1. Introduction
2.1.1. Galactic- radiation
2.1.2. Solar radiation ...
2.2. Cosmic ray variation
2.2.1. Time variations
2.2.2. Latitude variation 7
2.2.3. Altitude variation S
2.3. Cosmic ray measurements 9
2.3.1. Ionizing component 9
2.3.2. Neutron component 10
2.4. Population distribution '. 11
3. TERRESTRIAL RADIATION EXPOSURE 13
3.1. Sources 13
3.2. Variations in terrestrial radiation 17
3.2.1. Radon daughter products 17
3.2.2. Moisture and snow cover 1?
3.3. Measurements 19
3.3.1. Ground surveys 19
3.3.2. Dose equivalent rate due to fallout 21
3.3.3. Aerial surveys 22
VII
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Chapter Page
4. NATURAL RADIATION EXPOSURE OF THE U.S. POPULATION 33
4.1. External sources 33
4.2. Attenuation of external sources 33
4.2.1. Housing 35
4.2.2. Biological shielding 35
4.3. Internal sources 36
4.4. Dose equivalent to the gonads and bone marrow 36
4.5. Discussion 37
SUMMARY 41
REFERENCES 4.3
APPENDICES 47
Appendix A. Calculation of average dose equivalents due to terrestrial and
cosmic radiation 49
Appendix B. Effect of building materials on exposure 65
Appendix C. Calculation of 2o- error of total dose equivalent 67
vm
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LIST OF FIGURES
Figure Pazp
1 Formation of cosmic ray secondary products f,
2 Cosmic ray ground level measurements during a 3+ flare Yakutsk, F.S.S.R., 51° geo-
magnetic latitude f>
3 Variation of cosmic radiation with latitude 7
4: Cosmic ray dose equivalent rate variation with altitude *
5 Summary of sea-level ionization cine to cosmic radiation 9
t
6 Cosmic ray dose equivalent vs. elevation 10
7 Population distribution, 1960 11
8 Dose equivalent from cosmic radiation 12
9 Ionization vs. date and local time (PST) on offshore drilling platform near Hunting-
ton Beach, Calif !•*
10 Decrease in gamma radiation with depth of snow cover at three different densities
11 Dose equivalent rate due to fallout in the United States, 1958-1971
12 Aerial radiological measuring surveys -?>
13 Dose equivalent rates in ARMS areas -26
14 Dose equivalent from terrestrial sources based on population-weighted ARMS data .... 30
15 Dose equivalent from terrestrial sources in Coastal and non-Coastal Plain region? 31
16 Population distribution vs. dose equivalent from terrestrial and cosmic radiation :U
17 Cumulative distribution of population vs. dose equivalent from terrestrial and cosmic
radiation ;^>
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LIST OF TABLES
Table Pasf.
1 Estimates of dose equivalent due to terrestrial and cosmic radiation in several countries 2
2 Summary of sea-level ionization due to cosmic radiation at U.S. latitudes 9
3 Cosmic ray neutron dose equivalent at sea level 10
4 Cosmic radiation dose equivalent at sea level 10
5 Distribution of the U.S. population vs. elevation (1960) 11
6a Uranium-238 decay chain—uranium series {4n + 2) 14
6b Thorium-232 decay chain—thorium series (4n) 15
7 Gamma-ray energy released by 1 gram of rock (lithosphere) 15
8 Types of bedrock in the contiguous United States 16
9 Radionuclide content and dose equivalent rates from common rocks and soil 16
10 Ground surveys of background radiation in the United States 20
11 Dose equivalent measurements in 24 States 21
12 Population in ARMS areas 24
13 Dose equivalent rates in areas on or straddling the Coastal Plain 2!>
14 Dose equivalent rate from terrestrial sources based on population-weighted ARMS data ?s2
15 Dose equivalent outdoors from terrestrial and cosmic radiation 34
16 Ratio of indoor to outdoor dose equivalent 35
17 Gonadal dose equivalent to the U.S. population from natural radiation 37
18 Estimate of errors in determining the gonadal equivalent 3S
A-l Calculation of average dose equivalents due to terrestrial and cosmic radiation by
State urbanized and nonurbanized areas j°
A-2 Total calculation of average dose equivalents due to terrestrial and cosmic radiation by
States 60
A-3 Program to calculate average dose equivalents from terrestrial and cosmic radiation .... 61
C-l Evaluation of partial derivatives in error calculation 6>
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ABSTRACT
The exposure of man to natural radiation sources in the United States has been esti-
mated by considering the distribution of the population with respect to certain factors,
principally geology and elevation, which influence exposure to terrestrial and cosmic
radiation. Data obtained by aerial surveys in the United States have been used to calculate
an average dose equivalent (DE) estimate of 40 mrem/yr. to the population. The results
also indicate three distinct areas of terrestrial radioactivity in the United States—(1)
the Coastal Plain, which consists of all or portions of States from Texas to New Jersey
(23 mrem/yr.); (2) a portion of the Colorado Front Range (90 mrem/yr.): and (3) the
rest of the United States, i.e., portions of the United States not included in "1" or "2"
(46 mrem/yr.).
Since elevation is the primary determinant of cosmic ray DE in the United States,
the population distribution with respect to elevation was determined. The average pop-
ulation elevation of the United States was determined to be approximately 700 feet, and
the average cosmic ray DE was estimated to be 44 mrem/yr.
To arrive at an estimate of the gonadal DE, the influence of housing, biological shield-
ing, and the DE contribution from internal emitters was also considered. The first two
factors serve to attenuate man's gonadal DE due to terrestrial radiation by about the same
amount that is contributed by internal emitters. The average gonadal DE to the U.S.
population was calculated to be 88 mrem/yr.
sin
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NATURAL RADIATION EXPOSURE
IN THE UNITED STATES '
D
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Safety Laboratory, U.S. Atomic Energy Com-
mission (AEC) (Beck et al., 1964ab; 1966ab).
The second category of measurements has resulted
from special studies, which have been conducted
primarily for the purpose of estimating back-
ground radiation exposure to the population.
Examples of this work include studies in New
England by Segall (1963) and Lowder and
Condon (1965), and measurements in 24 States
by Levin et al. (1968). The third category con-
sists of aerial surveys which have been performed
by AEC and its contractors around nuclear in-
stallations within the United States.
In several other countries, surveys have been
performed on a countrywide basis for the pur-
pose of estimating the population exposure to
natural radiation (table 1). The investigators
have employed different techniques and instru-
mentation so that a direct comparison cannot be
made. However, even if we consider these factors
and the differing emphasis on measurements
(open field vs. paved areas, indoors vs. out-
doors), there is reasonable agreement among the
estimates.
Measurements obtained in the United States
will be presented in the following chapters, and it
will be soon that they are similar to measurements
obtained in other countries (table 1). It should
be noted that the measurements by Hultqvist
(1956), Herbst (1964), and Ohlsen (1969) were
made with either ion chambers or portable scin-
tillation detectors, and therefore the measure-
ments include the contribution of nuclear weapons
fallout to the total DE. The measurements by
Herbst, which were made during 1957 to 1959 and
in 1961, respectively, are probably most in error
on this account, since fallout contributed as much
as 30 percent to the total external DE rate during
thc.se. periods.
1.3. Sources of Natural Radiation
Exposure
Exposure to external natural radiation sources
occurs through cosmic radiation and radioactive
elements in the earth's crust and in building ma-
terials. An additional increment of external expo-
sure, which accounts for less than 5 percent of the
total, is due to the presence of radioactive decay
products of radon and thoron in the atmosphere.
The natural radiation environment has been
relatively constant since at least the beginning of
the Neolithic Age (10,000 B.C.) and probably for
much longer. The most recent reversal of the
earth's magnetic field occurred 700,000 years ago,
and at that time the cosmic ray intensity may
have increased by 10 percent in equatorial regions
of the earth for approximately 1,000 years
(Black, 1967). With the exception of short-term
variations in cosmic ray intensity, there is noth-
ing in the literature to indicate the occurrence of
significant changes in natural radiation sources
since the most recent magnetic field reversal.
Although the intensity of natural radiation
sources has remained constant in recent times,
man's living habits have changed in such a way
Table 1. Estimates of dose equivalent due to terrestrial and cosmic radiation in several countries
Reference
Hultqvist, 1956
Herbst, 1964
Yamagata and Iwashi-
ma, 1967
Ohlsen, 1969
Weng and Huang, 1970
Country
Sweden
Switzerland
Japan
E. Germany
Taiwan
Dose equivalent (mean)
(mrem/yr.)
77 wood dwellings
130 brick
197 concrete
122
87
91
112
Remarks
Measurements at centers of rooms in 086 apartments, 677
houses (all indoors); authors values of ion pairs/
cm-'-sec. converted to mrein/j'rt, assuming 1 ion pair/
cm'-si'c. = 1.
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as to influence liis exposure. Populations have
tended to migrate from coastal to inland areas,
thus increasing their elevation and exposure to
cosmic radiation. At the same time, the outdoor
agrarian society has largely been replaced by in-
door work and life in urban centers. Man's expo-
sure has thus been increased in some instances
because of the natural radioactivity of building
materials; in other instances, buildings attenuate
exposure to the outdoor terrestrial sources, result-
ing in lower exposure.
Although this dissertation is primarily con-
cerned with external radiation sources, it is im-
portant to note that additional increments of I)E
result from ingestion and inhalation of natural
radionuclides. Potassium-40 is the principal con-
tributor of internal DE: other significant internal
emitters are radium-226 and -228 and their
daughter products, carbon-l-t and radon-222
(UNSCEAR, 1962). Gonadal exposure to ex-
ternal radiation is about five times greater than
that from internal sources, and the ratio is simi-
lar for exposure to the bone marrow. With regard
to natural internal radioactivity, Cherry et al.
(1970) have recently shown that man has rela-
tively low concentrations as compared to other
mammals, fish, and birds. In fact, in a comparison
of total alpha activity in the bones of 18 different
mammals, only the pig ranked lower than man.
From their analysis of herbivore bones and ma-
rine livers, Cherry et al. predict DE in excess of
1,000 mrem/yr. to these organs, of which 90 per-
cent or more is due to internal alpha emitters.
The retention of inhaled radioactive daughter
products of radon and thoron is the primary
source of lung DE to the general population. Al-
though the inhalation of radon daughters has
been given special attention in the case of ura-
nium miners (Federal Radiation Council, 1967),
exposure to occupants of residential dwelling
can also be significant. Hultqvist (1956) calcu-
lated a potential average lung dose of 205 mrem/
yr. to occupants of unventilated wood dwellings
and 1,780 millirem/yr. to occupants of unventi-
lated concrete buildings. More recently, Veates
et al. (1971) have found that first-floor occupants
of frame dwellings may receive a lung DE of 150
inrad/yr. from alpha emitters. If a quality factor
of 10 is assumed, then the DE is 1,500 mrem/yr.
1.4. Methodology
One of the primary objectives of this .-tudy was
to estimate the external natural radiation expo-
sure to the population of the United Stute-. To
do so, existing data on terrestrial and cosmic
radiation measurements were conMdt-red in Hjrht
of population distribution and living habit,-..
Many measurements made for other purposes con-
tribute information on man's exposure to radia-
tion from natural sources. For example, much
of the existing data on cosmic radiation exposure
has resulted from interest in high-energy panicle
reactions or from studies of cosmic ray variation.
External exposure to terrestrial radiation
sources may be estimated by direct measurement
or calculated from chemical assays of natural
emitters in soil. Ground analyses and soil analyses,
however, have not been sufficiently extensive to
make an overall estimate of exposure in the
United States. For this reason, the estimate of
exposure due to terrestrial sources in this study
relies principally on data from aerial surreys.
The aerial surveys, which were previously men-
tioned, have been made over areas across the
United States and all together cover land areas
occupied by approximately 30 percent of the U.S.
population.
A combined estimate of the total cosmic ray
and terrestrial DE was then made in this study
cm the basis of what is known concerning the di>-
tribution of the population by elevation, geology,
and living habits.
Units of radioactivity have perplexed practic-
ing health physicists and those recommending
units since the discovery of ionizing radiation. As
a result, it is common to find units of roentgens,
rads, and rems used to describe the same thing in
radiation protection literature. Fortunately, the
three entities are approximately equal in the case
of ionizing radiation from external natural back-
ground sources, and therefore the unit of DE,
the rem, is used throughout for the sake of uni-
formity. A full description of dosimetric terms
may be found in Comber (1969} and the recom-
mendations of the International Commission on
Radiation Units and Measurements (ICRU)
(W71).
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CHAPTER 2. COSMIC RADIATION
2.1. Introduction
Cosmic radiation is composed primarily of ga-
lactic radiation and a varying component of solar
radiation. Galactic radiation originates outside of
our own solar system, and, as the name implies,
solar radiation results from phenomena on the
sun.
2.1.1. Galactic radiation
The primary component of galactic radiation,
as it impinges on the earth's atmosphere, is esti-
mated to be 75 to 89 percent protons, 10 to 18
percent helium nuclei, and 1 to 7 percent nuclei
with Z ^=3 (UNSCEAR, 1966; Neher, 1967). The
energy range is thought to extend beyond 1019 eV,
and the average energy flux arriving at the top of
the atmosphere is 2 x 103 MeV/cmz-sec. (Korff,
1964). In addition to heavy particulate radiation,
electrons and x rays have also been detected in
primary cosmic radiation.
Primary cosmic ray interactions with the at-
mosphere result in an ionizing component of
cosmic radiation in the lower atmosphere, pri-
marily muons and electrons, and a minor neutron
component. The process of formation is shown
schematically in figure 1. Of most significance to
population exposure is the formation of muons,
which are generally assumed to account for ap-
proximately 70 percent of the cosmic ray dose at
sea level (Lowder and Beck, 1966).
2.1.2. Solar radiation
Particulate solar radiation is comprised almost
entirely of bursts of protons and helium nuclei
with energies ranging up to several GeV. The
proton bursts, or flares, follow approximately 6
percent of the observed sunspots, and about 3 per
cent of all flares belong to class 3 (the largest)
(Langham, 1967). As will be discussed later, the
relatively low energy of the solar particles pre-
cludes their secondary radiations from reaching
the earth's surface in all but the largest flares.
2.2. Cosmic Ray Variation
The factors which contribute to cosmic radia-
tion variations are extensively reviewed in books
by Rossi (1964), Sandstrom (1965), and Haya-
kawa (1969). A brief summary of the present
knowledge of cosmic ray variations is presented
here in order to justify the dose estimation pro-
cedures which follow. In addition, knowledge of
the many variations which exist is helpful in
understanding rather large differences in the
reported measurements.
2.2.L Time variations
The temporal variation of cosmic radiation has
been observed for approximately 35 years, com-
mencing with the work of Forbush (1938). At
that time, Forbush reported the effect of the "sea-
sonal wave" on cosmic ray magnitude and specu-
lated upon the possibility of the influence of the
solar cycle on cosmic ray intensity. Research thus
far indicates that most variations in ground-level
cosmic ray intensity are attributable to solar influ-
ence on the interplanetary magnetic field (For-
bush, 1954, 1958; Kuzmin and Skrtpin, 1966a;
Pal, 1967). In general, where variations are
attributed to solar influence, the ionization inten-
sity on earth is inversely correlated with st»lar
activity.
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PRIMARY COSMIC RAY NUCLEI
INTERACTION VUTH ATOMS -N
UPPER ATMOSPHERE
T= 2.6x10 " SECS.
7=2<10-'«SECS
i 10 SECS.
NUCLEON CASCADES
SPAILATION PRODUCTS
NEUTRONS
ANTI-NUCL60NS
TJ PIONS
|/ MUONS
J) NEUTRINOS
y G.'.MMA RAYS
P ELECTRONS
Figure 1. Formation of cosmic ray secondary products
Variations in cosmic radiation have been ob-
served to occur in cycles of 11 years, 1 year, -11
days, and 1 day. and Xeher (It'll) has recently
reviewed the evidence for a cycle which persists
for several 11-year periods. As a result of these
variations, the intensity of sea-level ionization at
a given location may vary by approximately 10
percent. Based on the consideration of cosmic
ray-induced radionuclides on the earth and in
meteorites, Hayaka-wa (1969) asserts that average
cosmic ray levels have remained relatively con-
stant for at least 108 years. Maximum levels prob-
ably existed during the reversals of the magnetic
field, the most recent of which occurred 700,000
years ago, when an increase of 10 percent may
have occurred (Black, 1967).
Solar flares occur more frequently during the
solar maximum period of the 11-year cycle, and
therefore flares are also considered here as a tem-
poral variation. Although the hazards to space
travelers during this period are potentially great
(Upton, 1966; Langham, 1967; Haffner, 1967),
the magnetic field of the earth and the shielding
properties of the atmosphere result in little per-
turbation of the sea-level intensity during a flare.
According to Haffner (1967), eleven "3 + "
solar flares (the largest) occurred during the
1958 to 1961 period of maximum solar activity.
The ground effect of a 3+ flare is shown in fig-
ure 2. Although other flares have had a more pro-
nounced temporary effect on neutron levels, the
lack of significant influence on the ion chamber
measurement is typical. Following an initial rise
in neutron and muon counting rates, the levels
are observed to decrease below the preflare values.
1.04 -
14 16 18
MAY 1959
Figure 2. Cosmic ray ground level measurements dur-
ing a 3+ flare, Yakutsk, U.S.S.R., 51° geomagnetic
latitude (Kuzmin and Skripin, 1966b)
6
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The phenomenon is known as the Forbush de-
crease, and is due to the fact that flares are fol-
lowed by magnetic disturbances which reduce the
low energy galactic radiation component.
2.2.2. Latitude variation
Of the factors which influence cosmic ray ioni-
zation at the earth's surface, the latitude effect
was the first to be well described. This effect re-
sults from the earth's geomagnetic field, which
approximates a dipole located 215 miles from the
earth's center with the poles at 79° X., 69° W.
(northwest Greenland) and 76° S., 121° E. (Ant-
arctica) (UNSCEAR, 1966; Pal, 1967). The mag-
netic field serves to cut off incident low energy
cosmic particles, and the screening effect is larger
in the lower latitudes in both betntspherfes,
Millikan et al. (1936a), through a worldwide
survey, observed the cosmic ray variation at sea
level due to the latitude effect: his results are
summarized in figure 3. As shown in this figure.
the ionizing component of cosmic radiation varies
by about 2 percent throughout contiguous U.S.
latitudes, which range from 36° to aS° X. geo-
magnetic. Extensive reviews of later work have
been presented by Lowder and Solon (1956),
Hultqvist (1956). and UXSCEAR (1962, 1966).
More recent work (Raft et al., 1970: George.
1970) indicated a slight decrease in cosmic ray
ionization commencing around 50° geomagnetic
latitude (a line through Washington, D.C., and
LINES OF EQUAL COSMIC-RAY INTENSITY
AT SEA LEVEL ( RELATIVE VALUES )
30
60
90 120 150 180 150 120 90 60 30 0
Figure 3. Variation of cosmic radiation with latitude (Millikan et al.. 1936a)
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central Oregon). However, it still appears that
the influence of latitude on cosmic radiation ex-
posure within the United States is negligible in
terms of population exposure.
Neutron flux varies by approximately 30 per-
cent between the poles and the equator and by
15 percent within the range of latitudes covered
by United States (UNSCEAR, 1966). However,
since neutrons account for a small fraction of the
total cosmic ray exposure, the variation of DE
with latitude in the United States is insignificant.
Furthermore, in a comparison of cosmic ray meas-
urements in section 2.3, it will be seen that uncer-
tainties in the various measurements tend to
obscure all variations except the increase of expo-
sure with elevation, and, for purposes of dose
estimation in the present study, the latitude
variation in the United States will be neglected.
£2.3. Altitude variation
The atmosphere attenuates the cosmic ray flux;
the attenuation of the secondary particles is
varied so the relative DE contribution from dif-
ferent particles changes as the atmospheric depth
increases. As a general view of cosmic ray DE
variation with altitude, a summary of O'Brien
and McLaughlin's (1970) calculations is pre-
sented in figure 4. In their work, O'Brien and
McLaughlin have shown that the calculated
values agree well with measured ionization values
throughout most of the atmosphere.
The ionizing component of cosmic radiation
in the lower atmosphere has been measured by
workers at the California Institute of Technol-
ogy (Bowen et al., 1934; Millikan et al., 1936b;
and George, 1970) and the AEG Health and
Safety Laboratory (Solon et al., 1960; Lowder
and Beck, 1966; and Raft et al., 1970). The ioniza-
tion profiles (ionization vs. elevation) up to 15,000
feet as obtained by each investigator" have ap-
proximately the same shape, the primary differ-
ence being in the absolute values. The profile
determined by Lowder and Beck (1966) is repre-
sentative of the existing information and is used
to obtain the DE variation with elevation.
The neutron contribution to the cosmic radia-
tion DE is approximately 15 percent of the total
and will be discussed further in the next section.
Neutron density in the atmosphere varies expo-
10'
i
-TOTAL
,'" ELECTRONS
/..-•*''' ^---- PROTONS
.* ..*" -*•**
•NEUTRONS
-' ^ .
// / ^
4 6 8
ALTITUDE -10* FEET
Figure 4. Cosmic ray dose equivalent rate variation
with altitude (O'Brien and McLaughlin, 1970)
nentially with pressure with an e-folding thick-
ness of 165 g/cm2, or a half thickness of 114 g/
cm2 (Patterson et al., 1959; Miles, 1964). The
constant slope in the lower atmosphere indicates
that the neutron spectrum does not change over
the same range, and therefore in this report the
neutron DE is assumed to vary as the neutron
density.
Closely related to altitude variation is the vari-
ation of cosmic radiation with barometric pres-
sure at a fixed elevation; Shamos and Liboff
(1966), in addition to their own work, have re-
viewed the findings in 21 investigations concerned
with this effect. The "hard component" (primar-
ily muons) varies by about 0.17%/torr, and the
"soft component" has been estimated to vary by
about 0.93%/torr. The overall variation is 0.3 to
0.4%/torr. For purposes of long-term estimation,
8
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the variation is not important. However, since
the barometric pressure may vary by about 3
percent from day to day, it represents a potential
source of error in correcting and comparing
different measurements.
2.3. Cosmic Ray Measurements
2.3.1. Ionizing component
The measurement of the ionizing component of
cosmic radiation is generally expressed as ion
pairs/cm3-sec. (commonly expressed as "I"), and
corrected to the sea-level value at T60 torr and
0° C., although not all authors mention a temper-
ature and pressure correction. One I corresponds
to a value of 1.65 /xrem/hr. This ratio has been
used to convert all measurements to the same
units.
Summarized in figure 5 and table 2 are meas-
urements of the sea-level intensity that have been
made by various investigators over a period of
40 years. As can be seen, there has been a con-
siderable spread in the reported values, which is
remarkable even in view of the natural variations
that have been cited. Even the most recent meas-
urements which have been reported differ by 30
Table 2. Summary of sea-level ionization due to cos-
mic radiation at UJS. latitudes
Reference
Hultqvist (1956)
Solon et al (I960)
Kastner «>t al {1963)
Sharaos and Liboff (1966)
Ohlsen (1!I69)
George (1970)
O'Brien and McLaugblln (1970)
Yeates (1970)
Average of post-1950 vaiuea
lonlzaUou
(Ion pairs/
ca?-sK.i
•2.06
252
2 78
2 IS
2 10
2 18
2.60
220
2.*9
2.22
244
1 Average of 12 values from previous investigations.
to 40 percent. Shamos and Liboff (1966), Lowdcr
and Beck (1966), and George (1970) have at-
tempted to explain the differences through ion
chamber construction, calibration, alpha contami-
nation of the measuring chamber, and radon
daughters in the atmosphere (the latter two fac-
tors may contribute up to 15 to 20 percent of the
measured cosmic ray dose). However, differences
still remain, and, in view of the numerous cor-
rections which must be made to compare measure-
ments at different locations, it appears that the
s
3
*:
an !
YflU OF MEASUREMENT
Figure 5. Summary of sea-level ionization due to cosmic radiation
-------
differences will not be resolved soon. For the pur-
pose of DE estimation in the present work, a
value of -2A4: I has been assumed for the average
cosmic ray ionization at sea level in the United
States. This is the average of eight reported
values since 1960 and is equi valent to 4.0 /irem/hr.,
or 35.3 mrem/yr. The value used in this study,
35.3 mrem/yr.., compares reasonably well with the
most recent reported UXSCEAR (1966) value of
28 mrem/yr.
2.3.2. Neutron component
Several factors have contributed to relatively
poorer knowledge of the neutron DE rate at sea
level as compared to the ionizing DE rate. First,
the neutron flux in the atmosphere is more sen-
sitive to the time, latitude, and altitude variations
which have been described. Since the neutron DB
rate has been measured over a rel at i vely shorter
time and by fewer investigators, the intercom-
parison of different work is complicated by the
greater natural variations. In addition, incon-
sistencies exist in reporting results so that it is
common to find data reported either in dose or
DE units.
UXSCEAR (1966) reviewed the neutron meas-
urements through 1965 and, based upon a re-
ported range of 0.3 to 1.1 mrad/yr., concluded that
0.7 mrad/yr. should be taken as the typical sea-
level value at middle latitudes. The International
Commission on Radiological Protection (ICRP)
(Upton, 1966), in reviewing cosmic radiation
hazards to supersonic jet passengers and crew, has
assumed a sea-level value of 4.3 X 10"2 prad/hr.
(0.38 mrad/yr.) and a quality factor of 8, which
corresponds to 3.0 mrem/yr. Watt (196T) has
calculated a value of 6.8 mrem/yr. O'Brien and
MVLaughlin (1970), in addition to reviewing the
discrepancies which presently exist in the neutron
data, have calculated a value of ~0.33 mrem/yr.
A quality factor of 3 may also be inferred from
their data. A summary of the preceding informa-
tion is presented in table 3. For the purpose of
close estimation in the present study, the recom-
mendations of UXSCEAR (1966) and Upton et
al. (1966) have been followed by using the values
of 0.7 mrad/yr. and QF = 8, respectively.
The cosmic radiation dose rates to be used in
Table 3. Cosmic ray neutron dose equivalent at sea level
Reference
t'NSCEAR (1966)
Upton et al (1966)
Watt (1967) _
O'Brien and McLaughlln (1970)
Hajnal et al. (1971)
Dose equlraleut
(mrem/yr.)
• 5.6
•30
6.8
033
3.3
5 6
• Based on dose values presented by UNSCBAK (1966) and
QF = 8.
this study are summarized in table 4. Based upon
the adopted sea-level values and ionization pro-
file of Lowder and Beck (1966), the DE rates at
altitudes up to 15,000 feet have been plotted in
figure 6. Estimates of cosmic radiation DE at
Table 4. Cosmic radiation dose equivalent at sea level
Source
Ionizing component —
Neutrons ,
Total
/trem/hr.
4.0
0.64
4.6
mrem/yr.
35.3
5.6
40.9
10'
10'
NEUTRON COMPONENT
NOTES:
@ IONIZING COMPONENT DETERMINED BY (.EAST SQUARES FIT TO
PROFILE OF LOVOER AND BECK HtM). AND NORUALtZED TO SEA
LEVEL VALUE OF J It I. OR 35.3 »REMS rEAR iSEE TABLE 11.
® NEUTRON COMPONENT J I -REM! TEAR . EX» I ^^^ I
1033 »» Mi' = 3IA LEVEL PRESSURE OF
U.S. STANDAttO AfMOSPKERE
o, = PRESSURE AI ELEVATION "a"
( I 10
ELEVATION • THOUSANDS OF FEET
Figure 6. Cosmic ray dose equivalent vs. elevation
10
-------
different elevations were made using data from
this figure.
2.4. Population Distribution
The poptilation of the United States was dis-
tributed in 1960 as shown in figure 7, which is
adapted from the U.S. Census Bureau (1963).
Through use of the population distribution map
and a U.S. Geological Survey topographic map
{Gannett, 1916), the population of the United
States was found to be distributed by elevation
as presented in table 5. The mean populated ele-
vation of each State was computed by averaging
the population of urbanized areas, for which an
approximate elevation was available (Rand Mc-
Nally, 1971; Gannett, 1906), and the population
Table 5. Distribution of the U.S. population vs. elevation
(1960)
Elevation Interval
(103 feet)
0-05
051
1 2
2—4
4 6
6-8
8-10
->10
Total
Population
86 629 494
63 007 720
19 746 062
5 298 236
3 938 663
618 000
71,000
14,000
179 3°3 175
Cumulative percent
48 3
83 4
94 5
97 4
99 6
99 9
100.0
100.0
of the nonurbanized areas. The mean elevation
of the nonurbanized population was computed
by weighting the population in each elevation
segment by the segment midpoint. Thus, the mean
populated elevation (feet) of the nonurbanized
area of state =
ONE DOT EQUALS 10,000 PERSONS
OUTSIDE URBANIZED AREAS
Figure 7. Population distribution, 1960
LI
-------
/No. living at\ / No. living at \
\ 0 to 500 feetj "*" \ 500 to 1,000 feet/
Nonurbanized population of State
X 750 ...
Three exceptions to this procedure were re-
quired. First, the population of Hawaii was as-
sumed to be distributed 95 percent in the 0 to
500-foot interval and 5 percent in the 500 to
1,000-foot interval, since the scale of the U.S.
Census Bureau map did not justify a comparison
with topographic data. Secondly, several low-
lying States on the Atlantic and Gulf Coasts have
mean elevations less than 250 feet based on geog-
raphy alone. In these States, which are Delaware,
Florida, Louisiana, and Rhode Island, Gannett's
(1894) estimates of mean elevations were used
(60, 100, 100, 200 feet, respectively) for the non-
urbanized population. Thirdly, it becomes neces-
sary later in this report to divide certain States
into Coastal Plain and non-Coastal Plain regions.
The Coastal Plain regions (to be specified later)
are also low-lying areas and have been assigned
mean elevations based on a comparison of popu-
lation distribution and topographic data for the
respective regions.
The estimates of mean populated elevations
have been used in conjunction with values ob-
tained from figure 6 in order to estimate the
cosmic ray DE in the United States, and this
information is summarized in figure 8. As can be
seen, the DE is relatively uniform in the eastern
half of the country but increases in areas of
higher elevation in the west. The populations of
Alaska and Hawaii, which are not shown, were
also calculated as receiving between 40 and 50
mrem/yr.
It is interesting to note that a small area
on the east side of the Rocky Mountains, in the
vicinity of Leadville, Colorado, includes all of the
populated communities in the United States
which are at elevations greater than 10,000 feet.
These communities are between 10,000'and 10,500
feet; this elevation corresponds to a cosmic ray
DE of 160 mrem/yr., or approximately four times
the sea-level DE. Additional calculations are
presented in chapter 4, where the contribution
from terrestrial and other sources will also be
discussed.
Figure 8. Dose equivalent from cosmic radiation (mrem/yr.)
12
-------
CHAPTER 3. TERRESTRIAL RADIATION EXPOSURE
In the preceding chapter, the factors which
affect exposure to cosmic radiation have been
discussed. In this chapter, the same approach will
be taken to discuss man's exposure to natural ter-
restrial sources of radiation.
3.1. Sources
Naturally occurring radionuclides contribute
significantly to man's external exposure. In most
of the United States, the magnitude of terrestrial
radiation exposure is relatively uniform and is
similar to that due to cosmic radiation. As far as
is known, there are no terrestrial areas in the
United States which yield DE rates comparable
to the high radiation levels 10 to 100 times greater
than "normal") which have been observed in
other parts of the world, notably a few popu-
lated areas of Brazil and India (UNSCEAR,
1962).
The nuclides which contribute to man's natural
exposure have been extensively reviewed else-
where (Lowder and Solon, 1956; UNSCEAR,
1962). From the standpoint of man's exposure,
only potassium-40 and the radioactive decay
chains of uranium-238 and thorium-232 are
significant. In addition to these nuclides, Lowder
and Solon (1956) summarized physical data for
21 nuclides which exist or are hypothesized to
exist; however, long half-lives and low abun-
dances account for their insignificant DE to man.
The presence of cosmic ray neutrons insures that
capture reactions do occur in soil at the earth's
surface and in the atmosphere, thus resulting in
the probable occurrence of many additional radio-
active nuclides. The production of carbon-14 and
tritium are two well-known examples of this
process; however, the DE due to cosmic ray-
induced nuclides is insignificant.
Potassium-40 occurs as one of three potassium
isotopes. The two most abundant isotopes, potas-
sium-39 (93.1 percent) and potassium-41 (6.9
percent), are stable, whereas potassium-40 (0.0118
percent) decays with a half life of 1.25 X 10"
years. A 1.46 MeV gamma ray is emitted in 11
percent of the disintegrations, and this gamma
ray is the source of terrestrial DE from the
nuclide.
Thorium-232 and uranium-238 decay chains
are shown in tables 6a and 6b. Uranium-235 is
the parent element of a third decay chain: how-
ever, as can be seen from table 7, the energy re-
leased from radioactive decay from this chain
is insignificant in comparison to the uranium-238
and thorium-232 chains. Although the nuclide
composition of the rock in table 7 differs slightly
from estimates which will be presented later, it
is clear that uranium-238, thorium-232, and
potassium-40 may be assumed to account for
practically all of man's terrestrial radiation
exposure.
As in the case of cosmic radiation, terrestrial
sources have been studied primarily for purposes
other than interest in population exposure to
background radiation. For example, measure-
ments made early in this century were concerned
with geologic dating and heat seneration due to
radioactive decay. Since the 1940's, however, most
of the literature concerning uranium and thorium
has resulted from an economic interest in the two
elements. Within the past 15 years, additional
data have been reported which relate directly to
man's exposure to terrestrial sources.
-------
Table 6a. Uranium-238 decay chain—uranium series (4n + 2)*
(Courtesy Radiological Health Handbook, Revised January 1970)
Nu,.! ids
"1°
1
1
•j.'Th
234pa">
99 87" OU
--' Ll
1
1
's'STh
1
. J
2||Rn
J||Po
1
?A
99.987. 0.027.
I
^Pfa
2XeAt
i
3JjBi
99.987. 0.027.
P0
SJ<
1
210DK
ejPb
-J
Tl
-1007. .000137.
\
30
1
ag|Pb
.1
Historical
name
Uranium 1
Uranium X;
Uranium Xg
Uranium Z
Uranium II
Ionium
Radium
Emanation
Radon (Rn)
Radium A
Radium B
Astatine
Radium C
Radium C'
Radium C"
Radium D
Radium E
Radium F
Radium E"
Radium G
Half-life
•«.51xl09y
24. Id
1.17m
6.75h
2.47>lOEv
8.0 «104y
1602y
3.823d
3.05m
26.8m
-2s
19.7m
164..
1.3m
21y
5. Old
138. 4d
a. 19m
Stable
Major radiation energies (KeV)
*
4.15 (255)
4.20 (757.)
—
4.72 (28%)
4.77 (727.)
4.62 (24',)
4.68 (765.)
4.60 (6?,)
4.78 (957.)
5.49 (1007.)
6.00 (-1007.)
6.65 (6'-.)
6.70 (947.)
5.45 (0.0127.)
5.51 (0.0087.)
7.69 (100%)
...
J.72 (.000002%)
4.65 (.00007%)
4.69 (.00005%)
5.305 (100%)
...
...
3
0.103 (215.)
0.193 (795)
2.29 (98%)
0.53 (665.)
1.13 (13%)
...
0.33 (-0.019%)
0.65 (50?)
0.71 (40")
0.98 (65)
? (-0.17.)
1.0 (237.)
1.51 (40%)
3.26 (19%)
—
1.3 (25%)
1.9 (56%)
2.3 (197.)
0.016 (85%)
0.061 (157.)
1.161 (-1007.)
...
1.571 (1007.)
___
Y
O.Oiici (3.5"/)
0.093c (4")
0.765 (0.307.)
1.001 (0.607.)
0.100 (50%)
0.70 (24',)
0.90 (70%)
0.053 (0.27.)
0.068 (0.6%)
0.142 (0.07%)
0.186 (47.)
0.510 (0.077.)
—
0.295 (197.)
0.352 (367.)
...
0.609 (47%)
1.120 (17%)
1.764 (177.)
0.799 (0.014%)
0.296 (80%)
0.795 (1007.)
1.31 (21%)
0.047 (4%)
...
0.803(0.0011%)
1
T /
~~*
*Thls expression describes the DUBS number of any member In this series, where « is an Integer.
Example: agSPb <4n + 2)......4(51) +2-206
tlntertsitiea refer Co percentage of disintegrations of the nuclide itself, not to original parent of series.
*Coaplex energy peak which would be incompletely resolved by instruments of moderately low resolving power such as sciotillators.
Data taken from; Table of Isotopes and USNRDL-TR-802.
-------
Table 6b. Thorium-232 decay chain—thorium series (4n)*
(Courtesy Radiological Health Handbook, Revised January 1970)
Nuclide
8!?Th
«:R.
,*
)
6.29 (1007.)
6.78 (1007.)
6.05 (25%)
6.09 (107.)
8.78 (1007.)
•-
...
0.055 (100X)
1.18 (357.)
1.75 (12')
2.09 (12*)
---
*
0.346 (8i:>
0.586 (14')
1.55 (57.)
2.26 (557-)
1.28 (257.)
1.52 (21%)
1.80 (507.)
v
...
...
0.34ci <"155!)
0.908 C25*,)
0.96c C20"'.)
0.034 (1.6'j
0.214 (0.3'.)
0.241 (3.77,)
0.55 (0.07')
0.239 <4r,)
0.300 (3.2'-)
0.040 (2°.,)
0.727 (7^)
1.620 (l.S'.)
0.511 (23')
0.583 (86')
0.860 (12'.)
2.t>14 (100')
*This expression describes the mass number of any member in this series, where n is an integer.
Example: ""in (4n) 4(58) - 232
tlntensities refer to percentage of disintegrations of the nucllde Itself, not to original parent of series.
^Complex energy peak which would be Incompletely resolved by Instruments of moderately low resolving power such as >vintillac.T
Data tJkcn from: Ledcrer, C. M., Hollander, J. H-, and Ferlman, I., Table of Isotopes (6th ed.; New York: John Wiley & Sons,
Inc., 1967) and Hogan, 0. B., Zlgman, P. E., and Mackin, J. L., »eta Spectra (USNRDL-TR-802 [Washington, D.C.
U.S. Atomic Energy Commission, 1964]).
Table 7. Gamma-ray energy released by 1 gram of rock
(litkosphere) Kogan et al. (1971)
Isotope
TTranium-238 (In equilibrium with
Uranlum-235 (In equilibrium with
decay products)
Thortum-232 (in equilibrium with
Average
concentration,
percent
2.98X10-*
0.02 X1(H
11.4 X10-*
3.0
Energy
(MeV/
sec.XlOJ)
6.82
0.153
8.78
11.4
.27
Gentry et al. (1959) and Grahn and Kratch-
man (1963), in investigations of fetal malforma-
tion, estimated population exposure from data
on local geology and uranium reserves, but made
no measurements. Segall (1963) conducted a later
study concerned with health effects of background
radiation, and, in support of the study, Billings
(1961) prepared a radioactivity map (uisorad
map") of Vermont, Xew Hampshire, and Maine,
based upon chemical analysis of bedrock. At
15
-------
about, this time, portable multichannel gamma-
ray spectrometers were developed, and these
instruments allowed field determinations of
the amounts of potassium-40, uranium-238, and
thorium-2.'5'2 present in the soil. Data reported by
Beck et al. (1964a, 1964b, 1966a) are representa-
tive of this technique.
Extensive literature reviews exist concerning
the distribution and abundance of the naturally
occurring radioactive elements in the earth's crust
(Adams et al., 1959; Peterman, 1963; Clark et al.,
1966; Finch, 1967; Over-street, 1967; Wedepohl,
1969). The purpose of the following text is not
to duplicate this information, but rather to pre-
sent sufficient data from these sources to permit
an understanding of variations which exist in
measurements of background radiation.
The earth's crust is composed of igneous, meta-
morphic, and sedimentary rocks; the first two
classifications account for approximately 90 per-
cent of the mass of the crust. Sedimentary rocks
accumulate at the top of the crust, however, and
thus Jackson (1964) estimates that sedimentary
rocks cover about 75 percent of the earth's land
area.
Based on an analysis of the geology map, U.S.
Geological Survey (1971), sedimentary rocks
cover approximately 85 percent of the contiguous
U.S. land area, and are distributed by geologic
age as shown in table 8. Sedimentary rocks may
be classified as shale, sandstone, or limestone,
which have a relative abundance in the ratio of
3:1:1. Since the metamorphic and igneous rocks
of table 8 are concentrated in sparsely inhabited
mountainous areas, it can be assumed that the
U.S. population lives almost entirely over rocks
of sedimentary origin.
Table 8. Types of bedrock in the contiguous
United States
Geologic period
Quaternary
Upper Tertiary
Lower Tertiary
Cretaceous
Jurassic and Triassic
Upper Paleozoic
Mid Paleozoic
Lower Paleozoic
Younger Precambri an .
Old Precambrian
Quarternary and
Tertiary
Lower Tertiary, Meso-
zole. Paleozoic
Total
Type
Sedimentary
Metamorpblc and
igneous
Volcanic — Igneous
Intrusive — Igneous
Percent of
land area
6.5
13.8
9.6
17.9
3.4
19.3
5.4
5.9
3.3
85.1
4.4
7.7
2.8
100.0
Table 9 presents the average amounts of ura-
nium, thorium, and potassium-40 in common rocks,
soil, and the earth's upper crust. It can be seen
from the crustal average that potassium-40 and
the thorium-232 decay chain each contribute ap-
proximately 40 percent of the dose rate at three
feet above the ground, and the uranium-238 decay
chain contributes approximately 20 percent of the
total. The uranium-238 decay chain includes the
gas radon-222, which can diffuse through the soil
and into the atmosphere. The diffusion reduces the
equilibrium concentration of radon-222 daughters
in the soil, thereby reducing the DE contribution
from the uranium-238 series by as much as 50
percent (Beck and de Planque, 1968). The
thorium-232 decay chain also includes a gas,
Table 9. Radionuclide content and dose equivalent rates from common rocks and soil
Rock
Igneous *
Basic
Silicic (granite)
Sedimentary »
Shale
Sandstone
Limestone
Upper ernatjil mrorngp c
TJ.B. snrfldal average a _
ppm
09
47
3.7
.45
2.2
28
1.8
Uranium
(mrem/yr.) •
62
269
21.2
2.6
12.6
16.0
10.3
ppm
27
200
12.0
1.7
1.7
10
9.0
Thorium
(mrem/yr.) •
73
53 8
323
4.6
4.6
26.9
24.2
ppm
12
50
32
11
0.32
2.4
1.8
Potansluin-40
(mrem/yr.) •
14 7
61 3
392
135
3.9
294
21.8
Total
(mrem/yr.) •
27.2
1420
927
207
21.1
72.3
56.3
• mrem/yr./ppm.: uranium, 5.73; thorium, 2.69; potassium-4O, 12.3; Beck and de Planque (1968).
•Clark et al. (1966).
' Uranium and thorium averages from Pbalr and Gottfried (1964) ; potassium from Heler and Billings (1969).
< Lewder et al. (1064).
16
-------
radon-220; however, the short half-life of radon-
220 (54.5 sec.) prevents a significant loss of gas
(and daughter products) to the atmosphere.
In addition to the gamma rays from terrestrial
sources, which are the basis for the DE values
in table 9, alpha and beta particle emissions also
occur. The alpha particles may be assumed to be
absorbed in the soil, and it is generally assumed
that the beta rays may also be neglected. Beck
et al. (1966a) have completed the most recent
and thorough study of terrestrial beta-ray
sources. In measurements conducted 40 to 180 cm
above the ground surface, they found beta rays
were attenuated with a half thickness of 150
mg/cm2. At one meter above the ground, gamma
rays and cosmic rays produced 7 ion pair/cm3-
sec.(I) in air and beta rays produced 13 I. Al-
though these authors concluded that the gonads
and bone marrow received a small and negligible
DE from beta rays, it is conceivable that this
source could present a significant exposure for
persons in special circumstances, e.g., individuals
who live on earthen floors. In summary, present
evidence suggests that the beta-ray DE due to
terrestrial sources may be neglected; however,
extensive supporting evidence is lacking.
Table 9 is intended to present a general idea of
the DE rate from various rocks, but practical
limitations prevent the use of these data for esti-
mating population exposure. Phair and Gottfried
(1964) have outlined some of the pitfalls in esti-
mating average elemental contents of various
rocks. For example, they recommend that the
number of analyses of a rock type should be pro-
portional to the abundance of the rock in nature.
In practice, however, rare rocks tend to be over-
analyzed in relation to the common types and
thereby contribute a disproportionate share to
the overall mean. In addition, surficial events,
such as mixing of rocks with organic matter,
glaciation, and the simultaneous occurrence of
several rock types, make population exposure
from a single rock type or rock derivative un-
likely. For these reasons, elemental analyses of
rocks are not adequate for making estimates of
population exposure, but are helpful in under-
standing variations which exist in DE rate
measurements.
Table 9 shows that the averages for surficial
measurements are slightly less than for the upper
crust. This is as expected, since the surficial data
are based upon in situ spectromctric inf-asure-
ments and reflect the factors whifh have already
been discussed. Mixing and weathering processes
at the soil/atmosphere interface serve to reduce
the amount of variation that one would expect
based upon bedrock analyses. Lowder and Con-
don (1965), for example, found that although
bedrock radioactivity and above-jrround DE
rates could be correlated, the L>E rate above
ground increased only slightly for a several-fold
increase in bedrock radioactivity.
3.2. Variations in Terrestrial Radiation
As one miglit expect from section 3.1, the pri-
mary determinant of the terrestrial radiation
level in a given location is the soil concentration
of natural radionuclides. However, the radiation
level above the ground will vary because of the
presence of soil moisture and the amount of radon
daughters present in the atmosphere. The two fac-
tors are related but will be discussed separately.
The resulting variations in terrestrial radia-
tion exposure will be cyclical and can markedly
affect the observations from day to day. As with
the variations in cosmic radiation, an understand-
ing of the sources of variation in terrestrial
sources is helpful in explaining differences in
reported measurements.
3.2.L Radon daughter products
Eadon-222, Ti/2 = 3.8 days, occurs in the ura-
nium-238 decay chain, and radon-220, Ti/z = 54.5
sec., in the thorium-232 decay chain. Because of
the shorter half-life of radon-220, there is less
opportunity for diffusion from the ground, and
thus airborne concentrations of radon-'2'J2 are
generally two orders of magnitude greater than
those of radon-220 (Gold et al., 1964).
Under most conditions radon daughters in the
atmosphere contribute a few tenths of a jirem/hr.
to the DE rate (Beck et al., 1964b). Low baro-
metric pressure, atmospheric temperature inver-
sions, little wind, and low soil moisture result in
increased radon emanation from the ground and
high air concentrations of radon daughters (Ciold
et al., 1964; Kraner et al., 1964). Gold et al.
-------
(1964), in a o-year study of atmospheric radon
levels, reported an average radon-2^-2 concentra-
tion of 0.26 pCi /liter, with maximum concentra-
tions (0.8 pCi/liter) occurring during the fall
months. These concentrations correspond to 0.4
and 1.3 jirem/hr., assuming the conversion factor
of Hultqvist (1956).3 In developing this factor,
Hultqvist assumed the radon-222 was in equilib-
rium with its daughters. In fact, however, the
daughter concentrations are generally 50 to 100
percent of the values that could be estimated
from the radon-222 concentration (Gold et al.,
1964; Harley, 1953), so that a value of 0.3 jirem/
hr. is probably a reasonable estimate of the aver-
age external DE due to radon daughters. This
estimate is supported by the spectrometric meas-
urements by Beck et al. (1966a), who reported
gamma DE rates at several locations to be be-
tween 0.1 to 0.5 /trem/hr. due to radon daughters.
There are other reports of outdoor radon levels
averaging 10 percent of the estimate cited here
(see Lowder and Solon, 1956; and Hultqvist,
1956), but the estimate by Gold et al. (196-4) is
assumed to be more correct because of the longer
period of observation.
George (1970) has provided what may be an
example of a relatively high DE rate due to
radon and its daughters. In an effort to isolate
his cosmic ray detection instruments from terres-
trial sources, he moved to an offshore drilling plat-
form 3.6 km west of Los Angeles. By so doing,
he was able to observe increases in the ionization
which coincided with the offshore winds (fig-
ure 9). The difference in high and low readings
was approximately 0.6 ion pairs/cm3-sec., or 1.0
/irem/hr. Since the usual temperature inversion of
the Los Angeles basin results in little vertical
mixing, this value is probably close to the upper
limit of the external DE from radon and its
daughters. It should be noted that radon levels
over oceans are approximately one one-hundredth
of land values (Hess and Parkinson, 1953), and
thus there was probably an insignificant radon
contribution from the ocean to the measurement.
The probable range of external DE due to
radon daughters, therefore, is 0 to 1 /irem/hr., and
3.3
3.2
3.1
3.0
2.9
2.8
2.7
2.6
2.5
UNION OIL DRILLING PLATFORM
8.8 LITER IONIZATION CHAMBER
]LAT. 33°40'N, LONG. 118° 5' W
ALTITUDE=.~100 FT..
APRIL 23-27.1968
I
6 12 18 6 1218 6 12 18 6 12 18 6 12 18
APRIL 23 APRIL 24 APRIL 25 APRIL 26 APRIL 27
'Ion pairs/cm'-sec. = 0.97 X radon-222 concentration
pCi/liter; 1 ion pair/cm'-sec. = 1.65 prem/hr.
Figure 9. Ionization vs. date and local time (PST) on
offshore drilling platform near Huntington Beach,
Calif., (George, 1970)
the average is about 0.3 /*rem/hr. Under these
circumstances, the contribution of radon daugh-
ters to the total terrestrial plus cosmic DE rate
at most locations will be less than 10 percent, and
usually less than 5 percent of the total.
3.2.2. Moisture and snow cover
It has already been mentioned that soil mois-
ture retards the diffusion of radon into the
atmosphere and thus reduces exposure to the
airborne daughter products; in most soils, the
amount of water varies from 5 to 25 percent on
a weight basis (Jackson, 1964). Beck et al.
(1966a) found that the potassium-40 DE rate
decreases by about 30 percent when the soil water
content increases from 0 to 30 percent, because
of the increased shielding provided by the water;
however, soil moisture acts in two conflicting
ways on the terrestrial DE rate. The first has al-
ready been mentioned, e.g., the gamma-ray at-
tenuation of the natural emitters. Conflicting with
this is the reduced radon migration to the surface
and accumulation of radon daughters in the
ground. The daughters of radon account for more
than 95 percent of the gamma ray energy from
the uranium-238 series (Kogan et al., 1971), so
that their presence in the ground increases the
exposure from this series. The net effect is for
soil moisture to decrease the potassium-40 and
thorium-232 rates and to increase or leave un-
changed the uranium-238 series DE rate (Beck
et al., 1966a).
18
-------
In a comparison of spectrometeric measure-
ments obtained in Denver, Beck et al. (1966a)
observed that the measurements obtained in dry
years (1962 and 1963) were 15 to 25 percent less
than in a wet year (1965). This indicates that
the gamma ray attenuation by the soil water was
more than offset by accompanying soil retention
of radon daughter products. Therefore, one
would expect variations of this magnitude
throughout the country where periodic drought
and rainy periods occur. Once again, this empha-
sizes the difficulty in interpreting spot measure-
ments and using such measurements for long-term
exposure estimates.
The effect of snow cover on the dose rate
from terrestrial sources was calculated by Sievert
and Hultqvist (1952) (figure 10). The calculated
values agree well with measurements reported
in the same reference and with more recent
measurements by Magi et al. (1970). Concur-
rently obtained snow cover and background
radiation measurements are virtually nonexist-
ent. This fact illustrates a bias which might
exist in practically all measurements of back-
ground radiation. They are obtained in fair
20 40 60 80
DEPTH OF SNOW IN cm
Figure 10. Decrease in gamma radiation with depth
of snow cover at three different densities (Sievert and
Hultqvist, 1952)
weather when personnel and equipment stress is
at a minimum, and therefore the ntf-a.-urements
may not reflect the seasonal variations of back-
ground due to ground moisture and snow cover.
It is possible, however, to estimate the impor-
tance of snow cover on long-term exposure from
the data of Magi et al. (1970). Based on summer
measurements alone, they estimated the yearly
DE from natural radiation to be 78 mrem/yr.
at Idre, Sweden, whereas year-round measure-
ments resulted in a 10 percent lower e-timato. 70
mrem/yr. They attributed this difference to the
attenuation of terrestrial sources by snow cover.
The average snow cover at this location is 15
inches and persists for approximately ISQ days/
yr. (Pershagen, 1969). Natural radiation meas-
urements in three other Swedish cities, located in
regions of less snowfall, showed no variation
from summer to winter.
Although the effect of snow cover on measure-
ments can be substantial, the overall influence on
population exposure is assumed to be negligible
in the United States. In most populated area?.
there is relatively little snowfall, and it does not
remain for long periods of time. In addition to
these factors, the propensity for indoor urban
living, and rapid removal of snow in most popu-
lated areas in the United States, tend to reduce
the significance of snow buildup as an attenuator
of terrestrial gamma sources.
In addition to the variation in the source term
(terrestrial gamma-ray sources), there are also
other factors which affect the exposure of man to
natural radiation. Examples of such factors are
man's choice of home—elevation, geology, and
building material. In addition, shielding provided
by the body attenuates the dose to internal or-
gans. These factors will be discussed in chapter 4.
3.3. Measurements
3.3.1. Ground surveys
A summary of ground surveys of natural ter-
restrial radiation in the United States is pre-
sented in table 10. Lowder and Solon (1956) re-
viewed several isolated background measurements
made prior to that time, but the more extensive
measurements have been reported since 1956. The
19
-------
Table 10. Ground surveys of background radiation in the United States
Reference
Solon, 1960
Stephens et al..
Iii61
Beck et al.. lf>64a.
l»r,4b, li>66a,
lOGOb
Somali and Reed.
1»G4
Lowder and Condon,
1965
Wollenberg et al.,
1969
Levin et al., 1963
Golden, J., 1968
Yeates et al., 1970
Llndeken et al..
1971
Location
38 U.S. towns and
cities
30 locations near
Sun Francisco
Approx. 210 loca-
tions in lio States
New Hampshire,
Vermont
New Hampshire,
Vermont
30 locations near
San Francisco
(same as Ste-
phens et al..
1961)
1102 towns In 24
States
Florida — vicinity of
phosphate beds
Boston, Mass.
Livermore. Calif..
Inside 110 lionn
-------
and an ion chamber reading at each location.
The spectral data were especially important for
interpreting measurements obtained in the first
half of the l!)GO's, when work by Beck et al. \\ :i~.
accomplished. In addition to allowing for an
estimation of the contribution of potassium-40,
thorium--2:5^, and uranium-^iS to the total terres-
trial DE, the contribution of nuclear weapons
fallout to the total 1)E could be estimated with
the spectrometer data. The significance <>f fallout
will be discussed later in tins >ection.
Several investigators have used portable scin-
tillation detectors for measuring natural back-
ground. These small, hand-held instruments allow
the user to make several measurements in the
time it would take to obtain ion chamber and
spectrum measurements at one location. Unfor-
tunately sodium iodide (Xal) detectors, the scin-
tillating medium, do not detect cosmic radiation
as efficiently as gamma radiation. In using a 3-
by 5-inch detector with a high energy cutoff of
3.4 MeV, Beck et al. (1964b) found that the sea-
level cosmic ray contribution to the energy spec-
trum was equivalent to a gamma-ray DK of (>.-_!
jirem/hr. instead of the expected value of approx-
imately 3.7 /irem/hr. In a similar study using
several energy bands with a 4- by 4-inch detector,
Beck et al. (1966a) observed a gamma-ray re-
sponse of less than 0.5 /irem/hr. up to (!.()()» feet.
This figure is based on the response of several
energy bands of less than 3.4 MeV, but it is also
indicative of the lack of detector response to cos-
mic rays. Another limitation on the use of port-
able scintillators is the strong directional depend-
ence of the detector (see Ohlsen, 1969). However,
this limitation can be overcome by maintaining
the same detector orientation during calibration
and measurements.
Notwithstanding the limitations which have
been discussed, it seems desirable to report in
more detail the scintillometer measurements by
Levin et al. (1968), since they greatly outnumber
all other U.S. measurements combined. Levin does
not report the averages for the states in which
measurements were obtained, ostensibly because
of the fact that measured sites were not neces-
sarily representative of the entire State. How-
ever, the averages have been computed from his
reported data and are presented in table 11. As
Table 11. Dose equivalent measurements in 21 State1-,
adapted from Levin et al. (1968;
State
C 1 r- 1«
Mlrhlpm
ConniK'ticut
Florida
Illinois
Maine
Massachusetts -
North <'nrolina_
N«-\v Hampshire.
New Jersey
New York
Oh Jo
Pennsylvania
Khode Island
South Carolina.
Virginia '
Total
NumbiT of
mc;i-urt-mpnts
T'JO
2 :(."i4
1.014
41
b~'.i
31ft
4!I4
4SH
62
301
M
3-j<;
"C3
1!I2
1'Hl
4
53
.->!
1H7
34
15
1.->1
ft ci"f,
T<>*.vn«
jl
24
i
"in
07
^7
*>•»
~|S
'17
11
ti'i
4s
in
4
SO
•>o
3
43
m-'-rr./J"
117
7f,
-1
»
fc-
•"*
90
f>
79
71
44
70
( —
• Mean.
Extreme values : Enst of
orinm. Colo., I'-'S mrem/yr.
Faoil. Fla., ."n mrem/.vr. . F<-
can be seen from table 11. the means vary by a-
much as a factor of two—from 6.7<"> /irem/hr. (W
mivm'yr.) in Florida to 13.32 /irem/hr. (117
mrem yr.) in Colorado.
The response to oo3) were made in the field.
it is likely that the reported value- are repre-
sentative of the terrestrial, fallout, and cosmic
radiation. Levin's observation was that "the read-
ings were within 4 percent of the ionization
chamber readings O."i percent of the time.'
3.3.2. Dose equivalent rate due to fallout
The presence of fission products on the ground
from nuclear weapons testing complicate? the
interpretation of terrestrial DE rate measure-
ments obtained during the late 19.10's and the
early and middle lOfiO's. Unless spectrometric
measurements are made, the DE contribution
from fallout cannot be accurately assessed. 1h\~
could be a source of varying error, since fallout
contributed a DE of a magnitude similar to that
from terrestrial sources in 1!V>2 to 19t'". whereas
more recent measurements show the DE rate
from fallout to be approximately 5 to lo percent
-------
of the natural terrestrial DE rate (McLaughlin,
1970).
An estimate of the external DE rate due to
fallout is presented in figure 11. The figure is
based upon estimates and measurements in the
United States; the two solid lines define a range
in which most measurements would be expected
to fall, and the dashed line represents the best
estimate for making a fallout correction to non-
spectrometric dose measurements.
u 1.0
o
HIGHEST
ANDIOWEST
ESTIMATES
VALUE USED
FOR CORRECTION
64 EC
YEAR
Figure 11. Dose equivalent rate due to fallout in the
United States, 1958-1971
For purposes of making corrections, it would
be desirable to know the local and countrywide
variations in fallout dose rate. It has been shown,
for example, that variations in fallout deposition
are closely related to precipitation and, as a re-
sult, wet areas (i.e., areas of higher precipitation)
receive more fallout than dry areas (Straub et al.,
1964). Unfortunately, existing data are not suffi-
ciently detailed to justify making more than one
estimate of the DE rate contributed by fallout
at a given time in the United States.
Fallout measurements by Beck (1966a) sug-
gest more uniformity in fallout DE rates across
tlve United States than would be expected from
rainfall patterns. For example, measurements in
relatively "dry' States (Wyoming, Nevada,
Utah) varied between 0.6 to 1.5 ^rem/hr. in 1965,
and at approximately the same time measure-
ments in "wet" States (Louisiana, South Caro-
lina, North Carolina) varied between 0.7 and 1.3
/*rem/hr. However, too few measurements are
reported to allow a conclusion as to how the
fallout DE rate varied across the country.
Three different procedures were used in de-
veloping figure 11. These are as follows:
1958 to 1962: The range of values was obtained
froirTTNSCEAR (1964), figure 32. The correc-
tion values are 54 percent of the maximum value.
This correction is based on a composite of 67
measurements in the United States between 1962
to 1965 (Beck et al., 1964a, 1966a).
1962 to 196IK The range of values and the
averages are based on the same measurements by
Becket al. (1964a, 1966a).
1966 to present: The 1965 values of Beck et al.
(1966a) show that 25 percent of the fallout dose
rate was due to ruthenium-106 and manganese-54
and 75 percent was due to cesium-137. The post-
1965 values are based on the assumption that the
25 percent portion decayed with the half-life of
1 year and the To percent portion decayed with a
half-life of 28 years. The resulting range of
values is consistent with fallout measurements
in the northern hemisphere (UNSCEAR, 1966),
in San Francisco (Wollenberg et al., 1969), and
in the eastern United States (McLaughlin, 1970)
during this time. Some fresh fission products have
been added in this interval as a result of French
and Chinese weapons tests, but their contribution
to the total is negligible.
3.3.3. Aerial surveys
The U.S. Atomic Energy Commission has spon-
sored nationwide aerial surveys of radioactivity
in the vicinity of nuclear facilities. During 1958
to 1963, Aerial Radiological Measurement Sur-
veys (ARMS) were conducted (by the U.S.
22
-------
Geological Survey and E.G.&G., Inc.) over ap-
proximately 25 areas which are shown in figure
12. A few additional areas have been surveyed
but are not included in this analysis because of
their relatively small size and sparse population.
In the course of reviewing available sources
of information on natural radiation sources, it
was found that none of the published ARMS data
had been used for estimating population expo-
sure. As a first step in determining if the data
would be useful for this purpose, the population
of each survey area (table 12) was estimated
from U.S. Census Bureau Map G.E. 50, No. 1,
1963. It was found that approximately 30 percent
of the U.S. population (1960 census) resided in
the survey areas, and thus it was concluded that
the ARMS data would be potentially useful for
making exposure .estimates.
Details of the purpose and procedures of th--
ARMS surveys are presented in the reports listed
in table 12 (or see Guillou, 1964); however, -i
brief description is presented here in order to
introduce the measurements. The standard ARMS
survey covered an area of 10,000 square miles
encompassing a nuclear facility, although there
is some variation in areas covered depending on
the site location in relation to mountains and
oceans. The surveys were intended to provide in-
formation on radiation levels in the vicinity of
nuclear installations, so that future releases of
radioactive material to the environment from the
facilities could be detected. This naturally raises
ARMS I, U.S. GEOLOGICAL SURVEY
ARMS H,EGiG, INC
Figure 12. Aerial radiological measuring surveys
-------
Table 12. Population in ARMS areas
Reference
Bates (1962) -
Bates (lOOGn) -
Bates (l!M>6b)
Buok-i (1!)62)
Books (I960)
Flint nnd Pitkln 63a>
Gulllou <1903b) — -
Guillou (1963C) -
Gulllou et al (1963)
Guillou (1965)
Gulllou (1966a)
Guillou (1966b) - - - -
Gulllou (1966c)
Gulllou (1966d)
MncKallor (1962)
MarKallor (1965) ~
NcUM'ht'l (1966) - -
Popenoe (1964) -
Popenoe (1966a)
Popenoe (IflOGb) -
Schmidt (1962a)
Schmidt (1962b)
Total
Area (figure 10)
Oak Ridge. Tenn.
Idaho Falls, Idaho (NETS)
Pittsburgh, Pa.
Columbus, Ohio
Los Angeles, Calif.
San Francisco, Calif.
Chicago, 111.
Camden, N.J.— Philadelphia Pa
Norfolk, Va.
Galveston, Tex.
Las Vegas, Nev.
Santa Barbara, Calif. (Arguello)
Parr, S.C.
Orlando, Fla.
Cincinnati, Ohio
Albuquerque, N.Mex.
Atlanta. Ga. (GNL)
Gnome-Carlsbad, N.Mex.
Washington, D.C. (Ft. Belvolr)
Minneapolis. Minn. (Elk River)
NPW England (North)
Now England (South)
Denver, Colo. (Rocky Flats)
Augusta, Ga. (Savannah)
RlchJand, Wash. (Hanford)
Population
00 feet in the
aircraft to DE rate at 3 feet above ground was
not performed in the ARMS reports. A conver-
sion factor of 1 ftrem/hr. at 3 feet from 25 cps
at 500 feet (for cesium-137, 0.662 MeV gamma
ray) is reported in many of the ARMS reports
and is based on the work of Davis and Reinhardt
(1962). It should be noted that the monoenergetic
emission of cesium-lH7 is probably not repre-
sentative of the wide spectrum of energies ob-
served in radiation from natural radionuclides.
A low energy component from scattered radia-
tion is especially prominent with these nuclides.
In addition, the conversion factor obtained by
Davis and Reinhardt is based on flights over dis-
tributed point sources on the surface of the
ground rather than over a uniform volume source
24
-------
such as natural terrestrial radioactivity. Thus, it
does not appear valid to use this conversion (25
cps = 1 /trem/hr.) for terrestrial DE rates due
to natural background radiation. In addition, un-
published experimental work by K. Larsen (Uni-
versity of California at Los Angeles) is quoted
in the ASMS reports in relation to the contri-
bution from fallout. Larsen is quoted by Popenoe
(1966a) as stating that "... a count rate of
approximately 77,000 cps measured at 500 feet
above the ground by Geological Survey equip-
ment over an infinite fallout source is equivalent
to 1 mR/hr. measured at three feet above the
ground . . ," or 77 cps = 1 jirem/hr. This
value was used in conjunction with figure 11 in
order to correct the ARMS data, for fallout con-
tribution. Fourteen areas had fallout corrections
of less than 1 /irem/hr., whereas the fallout DE
rate in 11 areas was greater than 1 /irem/hr.
Ground measurements were compared with
aerial data from several locations in order to
arrive at a conversion for natural emitters.
There are four separate determinations of this
conversion:
1. MacKallor (1962), based on a comparison of
ground survey and aerial measurements, found
a conversion of 47 cps (500 feet) = 1 jarem/hr.
at 3 feet. However, the ground and air meas-
urements were taken li/fc years apart, during
which time the dose contribution to fallout
changed by 1.6 /irem/hr. When this difference
is accounted for, the conversion is 76 cps =
1 /trem/hr.
2. Levin et al. (1968) reported an average DE
rate of 8.5 /trem/hr. in Little Falls, Minn. (76
measurements); the ARMS data map (Neu-
schel, 1970) for this location presents an aver-
age of 275 cps. To compare the two,' 0.9
/arem/hr. (fallout in summer of 1965 from
figure 11) and 43 prem/hr. (ionizing compo-
nent of cosmic radiation) were subtracted from
the ground value; the fallout value from figure
11 in the summer of 1961 was 0.8
or 0.3 X 77 = 23 cps. Thus,
et al. (1968) and Neuschel (1970) for Falcon
Heights, Minn. In this case, the conversion was
325-23 _ 90 cps
8.6- (0.9+4.3) ~ 1 prem/hr.
4. A total of 16 terrestrial measurements, cor-
rected for fallout (Beck et al., 196ia, 1966a),
were obtained in Denver, Colo., in 1962, 1963,
and 1965. The average DE rate was 11.6
/trem/hr. The ARMS map for this area gives
a value of 850 cps in the vicinity of Denver,
and the fallout contribution during the ARMS
study was 0.37 /irem/hr., or 28 cps. The con-
version value is thus
850-28 _ 71 cps
275-23
76 cps
8.5-(0.9+4.3) 1 /*rem/hr.
3. A similar comparison was made from Levin
11.6
Based on the comparison of aerial and ground
data, a factor of 78 cps at 500 feet = 1 /irem/hr.
at 3 feet was assumed for converting the aerial
data to dose values at the 3-foot level. In apply-
ing this factor to the data of all ARMS areas,
it is assumed that the source spectra do not
change significantly across the United States,
i.e., the relative contributions of potassium-40,
uranium-238, and thorium-232 do not change dras-
tically. This assumption is supported by the
countrywide spectrometric surveys of Beck et al.
(1964ab, 1966a). In addition, the utility of aerial
survey data has been enhanced by the demon-
stration that the DE rates from potassium-40,
uranium-238, and thorium-232 show almost ex-
actly the same variation with height (Beck and
La Planque, 1968).
The procedure in analyzing the aerial data may
then be summarized as follows :
counts/sec, at 500 ft. minus fallout correction
78 cps//irem/hr.
= j*rem/hr. at 3 ft.
The data were then grouped in 2 /»rem/hr. inter-
vals in order to arrive at figures 13, which pre-
sent the percent of each ARMS area vs. DE
rate. The average DE rates of the ARMS areas
varied from 1.51 prem/hr. in the Orlando, Fla.
area to 10.23 /xrem/hr. in the Rocky Flats-Denver,
Colo., area.
-------
40
20
0
40
20
_i
1 °
g SO
ce
cvj
•<
«c 40
u.
o
a»
20
0
40
20
0
*
60
40
r 20
N. NEW ENGLAND (»)
.
I I I I 1
1 '
S. N
_H , H
-
" 1
CAMUhN / PI
..h.
- I
0
*
NORFOLK, VA. (e)
L_^
40 1-
1 — . — V 1
20
EW ENGLAND (b) ^
£
UJ g
Z
UJ
= 40
• Ol
S
OS
fe 20
0
80
1ILADELPHIA (c)
60
i i }
40
FORT BELVOiR / D.C. (d)
20
,ii.l
=3 1 1 0
,
, PARR.S.C. (f)
."""H- -^_
•
1
CAPE KENNEDY • ORLANDO, FLA. (h)
II ^ | 1 1 f i
0 2 4 6 8 10 12 14 16
/JREM/HR.
02 4 6 8 10 12 14 16
V REM HR.
Figure 13. Dose equivalent rates in ARMS areas
(mean denoted by arrow)
26
-------
40
20
0
40
20
0
60
| 40
a
20
0
80
60
40
20
GEORGIA NUCLEAR LAB.
-ATLANTA, GA. (i)
OAK RIDGE, TENN. 0)
PITTSBURGH, PA. (k)
COLUMBUS, OHIO (1)
0 2 48 8 10 12 14 IS 18
40 r
20
60 r
40
20
Of
a.
40 r
o
-l «' 20
CINCINNATI, OHIO in
i I
CHICAGO. ILL- in)
-
,
1
1
MINNEAPOLIS, MINN (o)
1 i i i
GALVESTON, TEX. (p)
i i i
02 4 6 8 10 12 14 16
' HR.
Figure 13. Dose equivalent rates in ARMS areas—Continued
(mean denoted by arrow)
-------
20
40 -
20 •
40 r
20 -
40 r
— ft
ROCKY FLATS -
DENVER, COLO, (q)
ALBUQUERQUE, N M. ID
-
1
t
CARLSBAD (GNOME), N.M. (s)
-
1
1 1
NRTS - IDAHO FALLS, IDAHO (I)
1 1 , i , , •
g
HANFORD • RtCHLAND, WASH (v)
SAN FRANCISCO, CALIF, (w)
ARGUELLO- SANTA BARBARA. CALIF. (1)
20
40
-JLA
LAS VEGAS, NEV. (u)
LOS ANGELES, CALIF, (y)
0 24 6 6 10 12 14 16 18 20 22 24
V REM / HR.
0 2 4 6 8 10 12 14 16
fJ REM / HR.
Figure 13. Dose equivalent rates in ARMS areas—Continued
(mean denoted by arrow)
28
-------
Each histogram covers between 98 to 100 per-
cent of the respective ARMS area with the excep-
tion of Las Vegas, which covers 95.2 percent of
the area. The totals do not add up to 100 percent
in each case since the count rate data for 1 to
2 percent of some areas were presented in very
broad contours (i.e., 1,200 to 4,000 cps) relative
to the rest of the map data. In general, the
omitted portions covered unpopulated areas such
as mountainous terrain. The highest count rate
found in the ARMS data occurred in the Las
Vegas area (Guillou et al., 1963) and the Albu-
querque area (Guillou, 1966d), where a maximum
of 4,000 cps was observed (50 /trem/hr.). In both
cases the locations were unpopulated; the Albu-
querque area maximum occurred in the vicinity
of a uranium mine.
The original ARMS data are grouped in count
intervals which commence at zero cps, and this is
reflected in the histograms, which in most in-
stances commence at a zero DE rate. Therefore,
it should be noted that the zero DE rate repre-
sents the lower limit of the ARMS reporting
method rather than an actual estimate of DE
rate. The mean DE of each area was computed
by assuming that the midpoint of each DE inter-
val (1, 3, 5, etc.) was representative of the DE
for the respective interval, and the means are
designated by arrows on figure 13.
By weighting the individual distributions of
figure 13 by the population of each area, a sum-
mary histogram was obtained (figure 14), of
which the mean is 5.0 /irem/hr., or 44 mrem/yr.
As shown in table 11, the overall mean of 9,026
measurements by Levin et al. (1968) is 77
mrem/yr. If the ionizing component of cosmic
radiation is assumed to account for 36 mrem/yr.,
then the terrestrial DE is 41 mrem/yr., which
compares well with the mean obtained from the
ARMS data. A summary of 210 ground survey
measurements (Beck, 1966b) also is presented in
figure 14, and, as can be seen, the mean is ap-
proximately 40 percent higher than the value
derived from the ARMS data. The locations of
Beck's (1966b) measurements are not given;
however, the measurements are a summary of
data reported in Beck et al. (1964ab, 1966a). The
latter references include 16 measurements (rang-
ing from 7.1 to 15.2 ^rem/hr.) in the relatively
high background area of Denver and measure-
ments over unpopulated granitic outcrop-- in
North Carolina; this could explain the hipher
overall mean.
Three distinct areas of terrestrial radiation are
evident from an analysis of the ARMS data.
First, the Coastal Plain, bordering the Atlantic
Ocean and the Gulf of Mexico, has a terrestrial
radiation level of approximately half the U.S.
average. This is partially evident from the mean
exposure of three areas lying entirely on the
plain: Norfolk (3.09 /irem/hr.), Orlando (1.51
/irem/hr.) and Galveston (2.26 prem/hr.). The
Coastal Plain includes marine deposits of Qua-
ternary, Tertiary and Late Cretaceous age (Xeu-
schel, 1966;* Schmidt, 1967a) and is shown in
figure 12.
Neuschel and Schmidt observed in their re-
spective reports of ARMS surveys (Washington,
D.C., and the AEC's Savannah River plant) that
the portion of the area on the Coastal Plain was
considerably less radioactive than the rest of the
area. In order to quantitate this observation, the
radiation levels of four areas which straddle
the Coastal Plain were studied in more detail.
Table 13 summarizes the DE rates of the total
and partial Coastal Plain area. It is interesting to
note that the average radiation level in the non-
Coastal Plain portion of the mixed areas is simi-
lar to the U.S. average.
Table 13. Dose equivalent rates in areas on or straddling
the Coastal Plain
Area
Washington. D.C.-Fott Belvoir —
Norfolk _
Savannah River
Galveston
Average
Mean dose equivalent rates
daemfla.}
Coastal
Plain
1.9
3.2
3.1
2.9
3.5
1.5
2.3
2.6
Non-
Coastal
Plain
4.9
5.0
4.0
5.S
4.9
Entire
area
2.7
4.1
3.1
3.8
3.9
1.5
2.3
3.1
In order to compare the Coastal Plain and non-
Coastal Plain regions graphically (excluding the
Denver ARMS data), the ARMS data for each
region were population-weighted in the sam?
-------
40
< 30
oc
LU
UJ
a.
CM
20
10
0 2
1
SUMMARY: ARMS MEASUREMENTS
x = 4.98/u REM/HR.
= 43.7 mREM/YR.
6 8 10 12 14 16 18 20
/I REM / HR.
40
30
QC
10
SUMMARY: 210 HASL MEASUREMENTS
(BECK, 1966 b)
x = 6.97 MREM /HR.
= 61 mREM'/YR.
0 2 4 6 8 10 12 14 16 18 20
AIREM/HR.
Figure 14. Dose equivalent from terrestrial sources based on population-weighted
ARMS data
30
-------
manner that was used to obtain figure 14, and the
resulting distributions are presented in figure
15. As can be seen, the DE in approximately 80
percent of the Coastal Plain area is less than 4
/»rem/hr. (35 mrem/yr.), whereas most of the
non-Coastal Plain (64 percent) lies in the range
4 to 8 f*rem/hr. (35 to 70 mrem/yr.).
COASTAL PLAIN
X =22.8 mREM / YR.
NON-COASTAL PLAIN
« = 4S.AnREII / YR.
0 2 4 C B 10 12
DOSE EQUIVALENT - IIREM / HR.
Figure 15. Dose equivalent from terrestrial sources
in Coastal and non-Coastal Plain regions
The areas of table 13 are all on the Atlantic
Coastal Plain except Galveston, and therefore it
is assumed with less certainty that the Gulf
Coastal Plain follows the pattern of lower radio-
activity that was observed in the Atlantic Coastal
Plain. The natural radioactivity of Gulf and
Atlantic beach sands has been shown to be rela-
tively uniform (Mahdavi, 1964); yet this fact
can probably not be related to the radioactivity
of the entire Coastal Plain since Mahdavi's sam-
ples were taken on and near the beaches. Signifi-
cant uranium ore deposits exist in the Tertiary
portion of the Coastal Plain of south Texas
(Finch, 1967), and the deposits may be reflected
in increased radiation levels over the region of
the deposits. There are no reported measurements
in the region, which is sparsely populated, and
there are no other significant deposits in the en-
tire Coastal Plain. Recognizing the limitations on
data from the Gulf Coastal Pkin, it will be
assumed that the Gulf and Atlantic Coastal
Plains follow the same pattern of producing low
terrestrial radiation exposures. This assumption
is based primarily upon the fact that both areas
have similar geology, i.e., marine sediments de-
posited since the late Cretaceous age.
The second region of the United States, which
stands apart from the rest, is the Denver region
of Colorado. Based on the ARMS data analysis,
the mean terrestrial DE rate for the Denver area
is 10.2 /irem/hr. This is approximately 40 per<»nt
higher than the next highest value of 7.3 /trem/
hr. (Albuquerque area) and twice the average
of all the ARMS areas. Phair and Gottfried
(1964) found that levels of uranium and tho-
rium were twice the normal crustal concentra-
tions over a 7,000 square mile area along the
Colorado Front Range. Furthermore, they ob-
served that the Front Range was the only large
area in the United States in which the uranium
and thorium concentrations in bedrock were con-
sistently above average. Much of the Denver sur-
vey area is over alluvia derived from the Front
Range, and the aerial data and the previously
mentioned ground data (Beck et al., 1964a,
1966a) corroborate the measurements of Phair
and Gottfried (1964), There is no evidence to
suggest that other areas of higher terrestrial
radiation and comparable size to the Front Range
exist in the United States.
Levin et al. (1968) obtained ground readings
in 11 Colorado towns, none of which were in the
Denver ARMS area. They found terrestrial +
cosmic -f fallout DE rates of 11.6 to 14.6
/irem/hr.; the average of all Colorado measure-
ments was 13.3 /*rem/hr. If cosmic radiation
and fallout (1966) are assumed to result in 7.3
/irem/hr., then the average terrestrial DE in
Colorado outside the ARMS area is about 6.0
/irem/hr., which is similar to the values ob-
tained in many of the ARMS areas. It is
not suggested that natural background levels
vary according to political units. The fact is,
31
-------
however, that Xe\v Mexico, Colorado, Utah, and
Wyoming are the principal uranium ore-bearing
States (Finch, 1967), and it is not surprising that
areas on alluvia derived from ore-rich regions
would have higher background radiation levels.
If the Coastal Plain and Colorado may be con-
sidered as the location of low and high values of
terrestrial radiation, than the balance of the
United States represents a vast Middle America,
radiologically speaking. A summary of ARMS-
derived DE rates due to terrestrial sources is
presented in table 14, and these estimates will be
used in chapter -i to compute the total DE due
to natural radiation.
Table 14. Dose equivalent rate from terrestrial sources
based on population-weighted ARMS data
Area
Coastal Plain
Non-Coastal Plain (excluding
Average - -
Population
covered by
ARMS (1900)
6 750 772
46 781 330
1 073 624
Dose
equivalent
(mrem/yr. )
22.8
45 6
89 7
43.7
32
-------
CHAPTER 4. NATURAL RADIATION EXPOSURE OF THE U.S.
POPULATION
In the preceding chapters, two major natural
contributors to population DE have been consid-
ered. These are (a) cosmic radiation and (b)
terrestrial radiation. In order to calculate an
average and range of external DE in the United
States, it is necessary to consider the influence
of population distribution on exposure from each
of these two sources. Initial calculations are di-
rected to the determination of external radiation
DE from these two sources outdoors, and these
estimates will then be modified in this chapter
to consider the influence of housing construction
and man's biological shielding on DE to the
gonads and bone marrow.
4.1. External Sources
The calculation of DE from external sources
has been performed by considering the popula-
tion to be located in either urbanized or non-
urbanized areas; an urbanized area, as described
by the U.S. Census Bureau, is a city (including
suburbs) which has a total population of more
than 50,000. As of the 1960 census, there were 213
urbanized areas in the United States, som'e of
which overlap adjoining States. The nonurban-
ized areas of the 50 States are treated as addi-
tional segments. Thirteen of the 50 States lie
partially on the Coastal Plain as shown in figure
12. Each of these States contains two nonurban-
ized segments corresponding to the Coastal Plain
and non-Coastal Plain portions, and thus there
are 50 + 13 — 63 nonurbanized segments. The
total number of areas is 310, 247 of which are
urbanized and 63 of which are nonurbanized.
Urbanized and nonurbanized areas were se-
lected as the basis for the model because they
provide the potential for updating exposure esti-
mates in the future as new census data become
available. As a secondary reason, manmade
sources of 'radiation are concentrated around
urban areas (hospital use of x rays and radio-
nuclides and nuclear power reactors), and this
model may facilitate the computation of total
natural and manmade radiation exposure.
For each population segment, the cosmic ray
(ionizing and neutron components), terrestrial,
and total external radiation DE rates have been
calculated. The cosmic ray DE rates due to ioniz-
ing and neutron radiation were calculated based
on the elevation of each segment and the data
presented in figure 6. The terrestrial DE rates
for each population segment were assigned on the
basis of general estimates from table 14, except
in the case of those urbanized areas (49) which
lie within the boundaries of ARMS areas. These
areas have been assigned a DE which was ob-
tained by converting the measured count rate in
the same manner as discussed in Chapter 3.
The results of the computations for each area
are shown in appendix A, tables A-l and A-2,
and a summary of DE estimates is presented in
table 15. The data in the table are presented In
two different ways, urbanized vs. nonurbanized
areas and Coastal Plain vs. non-Coastal Plain.
First, the mean and ranges of data for urbanized
areas and nonurbanized areas are given. The most
significant difference in the two groups is the
average and range of elevations; urbanized areas
range in elevation from 5 feet (New Orleans.
La.) to 5,980 feet (Colorado Springs, Colo.),
vrhereas the nonurbanized population lives in
areas ranging up to 10,500 feet (Leadville, Colo.,
and vicinity). The terrestrial DE ranges from
33
-------
Table 15. Dose equivalent outdoors from terrestrial and cosmic radiation (1960 census)
Nonuruanized areas
Coastal Plain
IS sinmimrv
Population
(>.-i,S48.4S7
83,474,688
32,140.217
147.1*2,!i.->8
1T1I.32S.715
Populated eleva-
tion (feet)
Mean
4S1
965
170
824
707
Range
5 !i 980
0-10,500
0-400
0-10,500
0-10.500
Cosmic ray DB
(mrem/yr.)
Mean
43
4o
41
44
44
Range
40-83
40-160
40-42
40-160
40-160
Terrestrial DE •
< mrem/yr. )
Mean
41
40
24
44
40
Bangc
0-120
0-120
0-90
0-120
0-120
Total external
DE •> (mrem/yr.)
Mean
83
85
65
88
84
Range
40 -200
40-300
40-130
40-300
4O-300
Inte-
grated
DE (10«
man-rem)
8.0
7.1
2.1
13.0
15.1
• Lower and upper limits correspond to values presented In figure 15.
'Totals are based npim the combination of cosmic ray and t«rn»*trlnl DE. The UE's for the nonurbanlzed and non-Coastal Plain
areas, and the total Vnlted States, have been rounded off to 300 mrcm/yr.
approximately 10 mrem/jT. (12 mrem/yr. in
Orlando, Fla.) to 92 mrem/yr. (Denver, Colo.).
At present, there is no reason to indicate that
the populations of urbanized and nonurbanized
areas have different exposures to terrestrial
sources. A similar conclusion was reported by
Segal 1 and Eeed (1964), who found no difference
in DE to residents of urban and rural regions in
New Hampshire and Vermont. The total DE due
to external sources is also practically the same
for both areas, and the difference in integrated
exposure (man-rem) is due to the difference in
population of each group.
It is interesting to note from table A-l that
the lowest cosmic and terrestrial DE estimates
both occur in areas on the Coastal Plain, and the
highest values of each occur in Colorado. For this
reason the results have also been divided into the
Coastal Plain and non-Coastal Plain regions;
Denver has been placed in the latter category in
this classification. As can be seen, there is a large
difference in the ranges of cosmic and terrestrial
DE in both regions. Although the mean of cosmic
radiation DE is approximately the same in both
regions, it can be seen that the range of DE in the
non-Coastal Plain (40 to 160 mrem/yr.) is much
greater than the range in the Coastal Plain (40
to 42 mrem/yr.). In contrast to this, the mean
terrestrial DE of the non-Coastal Plain region is
nearly twice that of the Coastal Plain. This is as
expected, since the terrestrial DE estimates are
based on the results of the ARMS surveys which
were summarized in the previous chapter. As a
result of the difference in terrestrial DE, there
is considerable difference in the total DE of the
two regions. The differences in total DE, in addi-
tion to the fact that the Coastal Plain holds only
18 percent of the population, are reflected in the
larger integrated DE (man-rem) of the non-
Coastal Plain population.
Summary data for the entire United States are
presented in the last line of table 15. As can be
seen, the average DE of the population due to
terrestrial and cosmic ray sources is 84 mrem/yr.;
this value will be used to calculate the gonadal
DE in section 4.4. The distribution of the popu-
lation vs. external radiation levels is presented
in figure 16. In order to determine the overall
distribution of population DE in figure 16, the
terrestrial DE in each population segment was
assumed to be distributed as shown in figure 15,
except for those segments in ARMS areas for
which the terrestrial DE could be directly esti-
mated. In other words, those population segments
in table A-l for which a general estimate of ter-
restrial DE is given (22.8 or 45.6 mrem/yr.)
n
0 20 10 SO 80 100 120 140 ISO 180
DOSE EQUIVALENT «REM TEAR
Figure 16. Population distribution vs. dose equivalent
from terrestrial and cosmic radiation
-------
were assumed to have a variation in terrestrial
DE as shown in figure 15. A cumulative distribu-
tion of population vs. DE is presented in figure
17. As can be seen, virtually the entire population
receives less than 1TO mrem/yr.
II
0 20 « W JO ICO 120 1« 160 ISO
DOSE EQUIVALENT mREH YEAR
Figure 17. Cumulative distribution of population vs.
dose equivalent from terrestrial and cosmic rediation
The distribution in figure 16 should be re-
garded as an approximation of the population
distribution vs. external DE since the distribu-
tion is based upon aerial surveys of terrestrial
DE rather than on estimates of population DE
within the survey areas. It should also be noted
that the distribution is based on the two quite
different distributions of terrestrial DE in the
Coastal and non-Coastal Plain regions, as shown
in figure 15. The contribution of the Coastal
Plain distribution of terrestrial DE, which is
skewed strongly to the right, is muted in figure
16 since only 18 percent of the population resides
in the Coastal Plain.
4.2. Attenuation of External Sources
The estimate of man's DE which was presented
in section 4.1 is that due to natural external radi-
ation sources and is based on outdoor measure-
ments. In this section, the effect on the DE of
housing construction materials, biological shield-
ing and the contribution of internal emitters,
principally potassium-40, will be discussed.
4.2.1. Housing
Inasmuch as man spends most of his time in-
doors, the nature of construction materials will
influence his exposure to natural sources. In gen-
eral, the interiors of stone houses have the highest
exposure rates; brick and frame houses have the
next highest. The amount of time spent indoors
will, of course, determine the importance of con-
struction materials as a source. Estimates of both
factors, time and -the amount of natural radio-
activity in building materials, are based on rela-
tively little data, and probably represent the
greatest uncertainty in estimating man's exposure
to natural sources.
A summary of indoor measurements is pre-
sented in table 16. As can be seen, exposures in
Table 16. Ratio of indoor to outdoor dose equivalent
Country and reference
United States:
Solon et al. (1960)
United States :
Lowder and Condon (1965) —
East Germany :
Ohlsen (1969) - -
Poland :
Pensko et al (1969)
United States :
Yeates et al. (1970)
United States :
Ilndeken et al. (1972)
Building material
(outer vails)
Frame, brick, and stone apart-
ments and nouses
Mostly wood frame
(half-frame
Pre-1945 ^ stone
(brick
fbrick
Post-1945 •{prefabricated
[mixed
All buildings
Concrete and brick
Frame
Brick
Steel and concrete
Mostly wood frame (96%)
Ratio of Indoor/outdoor
DB (%)
Approx. 80-100
70
78
106
81
72
68
66
82
102
82
96
87-106
78
Bemarks
17 dwellings
160 single homes
667 Indoor measurements
Single homes and apartments
732 measurements In 97 new
apartments
5 single homes. 1st floor
1 apartment. 2nd Boor
4 office buildings
110 single homes
35
-------
frame dwellings are 70 to 80 percent of outdoor
values. In masonry buildings the percentage is
somewhat higher (80 to 106 percent), which indi-
cates that the DE from nuclides in the building
material partially offsets the attenuation of out-
door terrestrial sources. It is interesting to note
that, the second-floor measurements by Yeates et
al. (1970) in single family frame houses aver-
aged 84 percent of the first-floor measurements.
In a multistory building of masonry construction,
however, there is no apparent variation of the
DE with height in the building (Ohlsen, r.»7<>;
Pensko et al., 1969). The comprehensive measure-
ments by Ohlsen indicate that buildings of more
recent construction (since 1945) tend to have
lower indoor DE rates than older buildings,
at least in the German Democratic Eepublic
(DDR). Although buildings of "mixed" con-
struction materials may include a number of
variations, the low inside DE ratio for this type
of construction possibly reflects the increased use
of glass, plastics, steel, aluminum, and other ma-
terials containing relatively little natural radio-
activity.
In order to determine what effect building con-
struction might have on natural exposures, it is
necessary to make assumptions on how people
spend their time in various activities. A basic
approach to this problem has been taken in ap-
pendix B, in which it is estimated that indoor
living habits of the United States result in the
population receiving 80 percent of the out-
door DE.
4.2.2. Biological shielding
The estimates of DE in section 4.1 are for
tissue with no self-shielding. Since the gonadal
DE and bone marrow DE are often used for dose-
risk assessment, it is necessary to determine the
effect of buildup and attenuation of radiation in
the overlying tissue. The most widely quoted ref-
erence on this subject, UXSCEAR, (190-2), recom-
mends a screening factor of 0.6 for gonadal and
bone marrow dose rates from terrestrial radiation.
This factor was partly based on the work of
Spiers (19.10), who found that terrestrial gamma
radiation was reduced by factors of 0.5-2 to ().,">!)
depending on the body orientation. In males, the
screening factor varied from 0.67 to 0.7-2. In both
sexes, the least attenuation (i.e., highest screen-
ing factor) occurred in the standing position,
the greatest attenuation was provided in a hori-
zontal position, and intermediate attenuation oc-
curred in a sitting position.
More recent work by Bennett (1970) indicates
that the gonadal screening factor, averaged over
both sexes, is 0.82, and a personal communication
from Bennett indicated that he believes the bone
marrow screening factor also to be closer to 0.8.
In addition to discussing limitations of earlier
work, Bennett also has inferred similar screen-
ing factors from work by Jones (1966) and Clif-
ford and Facey (1970). Based on these data, it
is assumed that in the present work a screening
factor of 0.8 describes the biological shielding of
the gonads and bone marrow by overlying tis-
sue. The shielding factor is assumed to apply to
the terrestrial component of background radia-
tion and not to cosmic radiation, which is more
penetrating. This is the same approach used by
UXSCEAR (1962, 1966).
4.3. Internal Sources
This study is devoted primarily to natural ex-
ternal sources of radiation, which have been dis-
cussed in the preceding sections; however, in
order to arrive at an overall estimate of whole
body exposure, the contribution of internal nat-
ural emitters also must be considered.
The average potassium content of the body is
about 0.2 percent. On the basis of g K/kg body
weight, males show higher values past the age
of puberty, but this is related to the difference
in fat content of the body since fat contains rela-
tively little potassium (Anderson and Langham,
19,")S). Females have more fatty tissue than males
and therefore have a lower ratio of g K/kg body
weight. Ninety percent of the tissue DE from
potassium-40 is due to /3 particles (range = 2
mm in tissue); the remaining 10 percent is due to
gamma rays (Rundo, l!)f>0). Therefore, the tissue
DE is largely determined by the potassium-40
concentrations within the tissue in question.
Gonadal concentrations of potassium in the
I'.S. population are 0.2 percent and 0.14 percent
for males and females, respectively (Tipton and
Cook, 1963); these concentrations correspond to
36
-------
DE rates of 19 and 13 mrem/yr., assuming the
conversion factor calculated by Rundo (1960).
For the purpose of estimating gonadal DE. an
average of these two values, 16 mrem/yr., will be
assumed. Other internally deposited natural
nuclides, principally rubidium-87, carbon-14,
radium-226, radium-228, polonium-216, and
radon-222, are assumed to result in DE rates to
the gonads and bone marrow of 2 mrem/yr.
(UNSCEAR, 1966). These estimates will be pre-
sented in section 4.4, in which the overall esti-
mate of population DE is made.
4.4. Dose Equivalent to the Gonads
and Bone Marrow
Table 17 presents a summary of gonadal DE to
the U.S. population. The estimates for cosmic and
terrestrial exposure are based upon the results
of section 4.1, and the terrestrial DE contribution
Table 17. Gonadal dose equivalent to the U.S. popula-
tion from natural radiation
Source
External
Terrestrial
Bousing factor = 0.80 (section 4.2.1)
Screening factor = 0.80 (section 4.2.2)
Internal
Other nuclides —
Total
Dose equivalent
(mrcm/yr.)
26
44
16
2
88
has been reduced by the housing and gonadal
screening factors of section 4.2. As can be seen,
the estimate of DE to the gonads from natural
radiation sources is 88 mrem/yr. Since all mem-
bers of the population are exposed to background
radiation, the gonadal DE is also equivalent to
the genetically significant DE. It should be noted
that the reduction of terrestrial radiation con-
tribution to gonadal DE is 14 mrem/yr. due to
biological and housing attenuation. However, this
reduction is offset by the contribution of internal
emitters (18 mrem/yr.). With this in mind, it
can be seen that figures 16 and 17 are also reason-
able approximations of the population distribu-
tion vs. gonadal DE.
Estimates of DE to the bone marrow from in-
ternally deposited nuclides are 15 mrem/yr. be-
cause of potassium-40 and 2 mrem/ yr. because of
the other nuclides mentioned in section 4.4.3
(UXSCEAR, 1966). As has been di.-x-ussed, the
same biological screening factor is assumed for
bone marrow as for gonads, so that the bone
marrow DE from terrestrial and cosmic sources
is the same as that presented in table 17, or 70
mrem/yr. Thus, the total bone marrow DE from
natural sources is 87 mrem/yr.
The estimate of gonadal DE in table 17 is con-
siderably lower than the UXSCEAR (1962)
worldwide estimate of 125 mrem/yr.. which i<
often cited in the United States as the "base-
line" radiation level against which manmade
radiation sources are compared. If the relative
importance of manmade sources is evaluated by
comparing the magnitude of manmade and nat-
ural radiation DE, as is often done, then it follows
that manmade radiation sources must be con-
sidered as a more significant portion of man's
total exposure to ionizing radiation.
4.5. Discussion
The estimates of DE in the present work are
based upon measurements and census and housing
data from many different sources. For this rea-
son it is not possible to calculate the variance of
the end result in the conventional manner. It is
possible, however, to discuss the uncertainties
which affect the separate components of the over-
all totals and, based on the uncertainties, to esti-
mate the accuracy of the several important
factors. These contributing errors are taken to
represent in each case a sample at the 95 percent
probability level drawn from a normal popula-
tion of observations.
Cosmic radiation accounts for approximately
40 to 70 percent of the external radiation DE to
the U.S. population. The ionizing and neutron
components contribute about 85 and 15 percent,
respectively, of the cosmic ray DE. The estimate
of the sea-level ionization values, from which the
DE estimates are derived, is probably within 10
percent of the true value; however, the sea-level
neutron value may be in error by as much as 50
percent. As a result, the cosmic ray DE at a
-------
specified elevation is probably within 12 percent
of the true value.
At this point it is appropriate to discuss the
uncertainties present in the determination of the
terrestrial DE, which is based upon the aerial data
conversion values discussed in section 3.3.3. In
this regard, there are three observations to be
made on the conversion determination. First,
three of the four individiial conversion determi-
nations (1., 2., and 3.) in section 3.3.3. required
a cosmic ray correction. The relationship is such
that, for example, a 10 percent decrease in the
cosmic ray DE will result in approximately a 7
percent increase in the terrestrial DE estimate,
so that the net effect of a change in the cosmic
ray DE on the overall DE estimate is small.
Secondly, it should be noted that the fallout
correction value does not have a significant
influence on the final conversion factor. For ex-
ample, if the fallout correction in conversions
"1, 2, and 3'' in section 3.3.3. were increased by
100 percent (3.2, 1.8, 1.8, respectively) the aver-
age terrestrial DE decreases by 20 percent (from
40 to 32 mrem/yr.), and the overall DE decreases
by approximately 10 percent (from 84 to 7(i
mrem/yr.). It should be noted that a 100 percent
decrease in the present fallout estimates will have
a smaller effect—approximately a 10 percent in-
crease in the terrestrial DE and 5 percent increase
in the overall DE.
Thirdly, since the terrestrial and cosmic ray
DE are approximately the same, an arbitrary
change in the conversion value (with no change
in cosmic ray DE) will have a smaller impact on
the combined estimate. For example, a 10 percent
change in the conversion value (and terrestrial
DE) will result in a 5 percent change in the
overall DE.
The average terrestrial DE estimated for the
entire United States is probably within 20 per-
cent of the true value. Support for this belief
rests primarily on the similarity in AKMS esti-
mates of ground DE rates and the spectrometric
data-DE estimates by Beck (1966b). The accu-
racy of DE estimates for individual ARMS
areas and urbanized areas within ARMS areas is
strongly influenced by the accuracy of the weap-
ons fallout DE during the time of each survey.
During much of the 1961 to 1963 period, for
example, the DE from weapons-testing fallout
was 50 percent or more of the natural terrestrial
DE. As a result the DE estimates for the ARMS
areas are probably within 30 percent of the true
value. Most of the locations in appendix A were
assigned terrestrial DE values based on location
—either Coastal Plain or non-Coastal Plain.
These estimates may be in error by 50 percent.
The estimate of the contribution of internal
emitters to gonadal and bone marrow DE is
probably within 30 percent of the true value.
The estimate in this work is slightly lower than
the commonly quoted USSCEAR (19<>2) esti-
mate of 25 mrem/yr., and this is due to the use
of more recent and complete data for the potas-
sium-40 contribution to the total.
The biological shielding factor used in this
work is believed to be within 10 percent of the
true value, based upon the similarity of recent
estimates (Bennett, 1970). As has already been
mentioned, the other major modifying influence
on the natural radiation source term is the con-
tribution and attenuation by housing. Even with
the uncertainties present in the development of
the housing factor, it seems unlikely that this
factor is in error by more than 20 percent. The
amount of time spent outdoors is based on little
more than a guess; however, if this proportion
were 0.25 instead of 0.05, the housing factor
would only increase to 0.84, or by 5 percent.
A summary of the error estimates is presented
in table 18, and as can be seen the gonadal DE
is 88 ± 11 mrem/yr. The error of the bone mar-
row DE also may be assumed to be the same.
The error calculation tends to impart an unin-
tended sense of precision to the overall estimate.
Therefore, one may wish to say that the estimate
Table 18. Estimate of errors in determining the gonadal
dose equivalent (appendix C)
Parameter
Terrestrial DE » _
Housing factor _„-.
Cosmic DE
Internal emitters
Gonadal DE
Value
40
0.8
8
44
18
88
2
-------
of the average gonadal and bone marrow DE is
approximately 90 mrem/yr.
In summary, the average DE from terrestrial
radiation (unattenuated by housing or biological
shielding) and cosmic radiation to the U.S. pop-
ulation is 84 mrem/yr. There are three distinct
areas of different population DE—the Coastal
Plain, non-Coastal Plain (excluding Denver),
and Denver vicinity. Eighteen percent of the
population lives in the Coastal Plain, where the
mean DE is 65 mrem/yr., and 82 percent lives in
non-Coastal Plain regions where the mean DE is
88 mrem/yr. The Denver area, which has approx-
imately 0.5 percent of the population, receives
165 mrem/yr. Population DE in the United
States probably varies by a factor of 7.5, from
approximately 40 to 300 inrem/yr.
In view of the uncertainties which affect the
development of natural radiation exposure esti-
mates, one may question the improvement of the
results over earlier estimates and the usefulness
of the results. The use of the ARMS data has
provided a basis for directly estimating the nat-
ural exposure of approximately 30 percent of the
U.S. population, which is a considerably larger
sample than can be associated with previous
ground surveys. In addition, the same data indi-
cate the existence of three distinct areas of ter-
restrial radiation in the United States. Through
the determination of the U.S. population distri-
bution vs. elevation, it is now possible to cite
State-to-State differences in cosmic ray DE.
The present data may be used as a guide to the
average U.S. background radiation exposure and
as reasonable estimates of background exposure
in the areas for which ARMS data exist. Caution
is advised when using the total DE estimates
for locations in which general terrestrial DE
values have been assigned, although the total DE
estimates for these locations are of value in assess-
ing the relative contribution of cosmic ray DE.
The DE estimation procedure outlined in appen-
dix A may be refined as more specific data be-
come available on natural radiation DE rates in
various sections of the country. Similarly, infor-
mation concerning living habits may easily be
factored into the computation, and the author
would be grateful for any information which
could be used for updating and improving the
present DE estimates.
39
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SUMMARY
Natural background constitutes the greatest
source of ionizing radiation to the world's popu-
lation today. This exposure is by no means uni-
form for all individuals, but varies because of a
number of influencing factors. Such factors in-
clude altitude, geological features, and living
habits. The resulting variations in exposures
often exceed those from manmade sources which
generally receive considerably more attention. For
example, although no detailed overall study of
the subject has been made, published data indi-
cate that the genetically significant dose equiva-
lent (DE) from natural background in the
United States ranges from 80 to 200 mrem/yr.
A survey conducted by the U.S. Public; Health
Service in 1964 indicated that the comparable
dose from medical x radiation was only 55
mrem/yr. Other sources, such as nuclear reactors,
fallout from atmospheric weapons tests, etc., ac-
count for a DE less than 5 mrem/yr.
The purposes of this study of natural radiation
exposure in the United States were to better esti-
mate population dose from radiation of natural
origin, to investigate the DE variations that
occur, and to examine the parameters that influ-
ence both the levels and the variations so that the
relative importance of manmade exposures can
be better evaluated. In undertaking these tasks,
it was recognized that external exposure to ter-
restrial radiation sources, a primary component
of natural background exposure, can be estimated
by direct measurements or calculated on the basis
of knowledge of chemical assays of natural emit-
ters in the soil. Direct measurements and soil
analyses, however, have not been sufficiently
extensive to provide adequate data to make an
overall estimate of the population DE in the
United States. For these reasons, alternate meth-
ods were sought and an answer was found in the
series of ARMS conducted over major areas of
the United States under sponsorship of the AEC
A second major component of natural back-
ground exposure to the population is cosrnl-
radiation. The DE from this source was com-
puted on the basis of knowledge of the distribu-
tion of population with elevation. The third, and
last, major component of population dose from
natural background, that is, exposure from natu-
rally occurring radionuclides deposited within the
body, was calculated on the basis of published
information. Once data were available for the DE
from each of the three major components of nat-
ural background, a combined estimate of the total
cosmic and terrestrial DE was made taking into
account what is known concerning the distribu-
tion of population by elevation, geology, and
living habits. These data were then combined
with those for internal exposure to yield a final
estimate of total population dose from natural
sources.
The primary problem in using the information
resulting from the ARMS surveys was in con-
verting the count rate data taken at altitude into
DE rate data at ground level. In addition, there
was the necessity in certain cases of subtracting
the contribution of weapons testing fallout from
the ARMS readings. Suitable corrections for this
latter factor were made, and a conversion factor
for the ARMS data was determined by correlat-
ing the measurements at a number of jioints with
readings made at 3 feet above ground level. The
mean terrestrial DE, obtained on the basis of -2.">
areas surveyed under the ARMS program and
weighted for the population of each area, was
computed to be 44 mrem/yr. This value compared
well with results from limited ground survt-y-
41
-------
within the United State?, which are summarized
in the text.
On the basis of an analysis of the ARMS data,
it appears that the United States can be divided
into three distinct terrestrial radiation zones, or
areas. One is the Atlantic and Gulf Coastal Plain,
which includes all or portions of all States bor-
dering the Atlantic Ocean and Gulf of Mexico
from Texas to Xew Jersey. For this area, the
mean terrestrial DE was -22.8 mrem/yr. The sec-
ond area is a portion of the Colorado Front
Range, on the eastern slope of the Rocky Moun-
tains, which yielded a mean terrestrial I)E rate
of 89.7 mrem/yr. This is somewhat as expected
since this area (approximately 7,000 square
miles) has crustal concentrations of natural
radionuclides which have been shown to be ap-
proximately twice the U.S. average. The DE in
the rest of the United States, that is, excluding
the Coastal Plain and the Colorado Range, was
calculated to be 45.6 mrem/yr. When the distri-
bution of the population in the three zones was
considered, the mean terrestrial DE in the United
States was calculated to be 40 mrem/yr.
A detailed analysis of the distribution of pop-
ulation with elevation showed that 83 percent of
the people in the United States live in areas with
an elevation of less than 1,000 feet. Populated
areas, however, occur up to 10,500 feet. At sea
level, the ionizing and neutron components of
cosmic radiation result in DE of 35 and 6
mrem/yr. for a total of 41 mrem/yr. The DE
increases to 44 mrem/yr. at 1,000 feet and ranges
up to 162 mrem/yr. at 10,500 feet. On this basis,
the DE from cosmic radiation for various popu-
lation groups in the United States varies by a
factor of 4. Overall, the calculations revealed that
the average DE from this source in the United
States was 44 mrcm/yr.
Combining the DE from terrestrial and cosmic
radiation, the average DE to the U.S. population
from natural external radiation was computed to
be. 84 mrem/yr. per person. Based on the 1960
census, this results in an integrated DE of 15.1
million man-rem/yr. The range in DE in the
United States is 40 to 300 mrem/yr.; however,
almost the entire population receives less than
170 mrem/yr.
For the purpose of determining the DE to the
gonads and bone marrow, the influence of hous-
ing, biological shielding, and internal emitters
was also considered. A "housing factor" was
computed to take into account the attenuation of
terrestrial radiation due to building materials.
This factor included allowances for the major
types of building materials in use in the United
States and for the percentage of total time spent
indoors by the population. Also included in the
calculations was the attenuation of terrestrial
radiation by body tissues. On the basis of these
considerations, the ratio of indoor to outdoor DE
from terrestrial sources was calculated to be 0.8;
coincidentally the biological "screening factor"
was estimated to be 0.8. Allowing for these factors
and a DE from internally deposited radionu-
clides of 18 mrem/yr. to the gonads and 17
mrem/yr. to the bone marrow, the total gonadal
and bone marrow DE for the U.S. population
were calculated to be 88 and 87 mrem/yr.,
respectively.
It is to be noted that the gonadal DE as calcu-
lated in this study is considerably lower than the
UXSCEAR worldwide estimate of 125 mrem/yr.,
which is often cited in the United States as the
"baseline'7 radiation level against which manmade
radiation sources are compared. If the results of
this study are true, it is quite probable that cer-
tain manmade sources, particularly medical x ra-
diation, will now be given greater importance in
terms of their overall contribution to the popu-
lation's total dose.
42
-------
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U.S. Census Bureau ( 1969) : Statistical Abstract of the
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U.S. Department of Housing and Urban Development
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U.S. Geological Survey (1970) : Geology, a map in the
I! .8. Xational Atlas. U.S. Geological Survey, Washing-
ton, D.C.
U.S. Public Health Service (1969) : Population dose from
-------
X rays, U.S. 1064, Publication Xo. 2001. Superintendent
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U.S. Public Hewitt! Service (1970): Radiological Health
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1>.C. 20402.
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UNSCEAR (1964) : Report of the United Nations Scien-
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114*.
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46
-------
APPENDICES
-------
APPENDIX A
Calculation of Average Dose Equivalents
due to Terrestrial and Cosmic Radiation *
Table A-l. Calculation of average dose equivalents due to
terrestrial and cosmic radiation by State urban-
ized and unurbanized areas
Table A-2. Total calculation of average dose equivalents
due to terrestrial and cosmic radiation by States
Table A-3. Program to calculate average dose equivalents
from terrestrial and cosmic radiation
4 Some of the values in the following tables are presented in tenths of
mrem/yr. This was done in order to avoid rounding off errors, and one
should not assume that the data are known to the accuracy indicated by
the numbers.
-------
Table A-l. Calculation of average dose equivalents due to terrestrial and cosmic radiation by State urbanized and nonurbanized areas
1
IPCATIPN
,
I960
P1PUI ATMN
,
FFF*
4
rn$>iic SATIATION r>F
"•N MAGLAT MRFMS/yo
CEG NP 5 6
7-5*6
p
)S7.,
10=1 >»•>! H.O.T1
Tfpp on«F FO mMl r«7 TF Mj'i-ofM
NFHT MN mTAl
IIRHINC.HAM AI
COLUHBUS M -CA
GAPSnFN AI
HUNTSVILLf. 4L
MONTGOMFRY AI
TIJSCALOnSl 41
ALABAMA Nll-rP
ALABAMA NJ-NCP
ALABAMA
ALASKA Nil
ALASKA
PHOENIX A/
TUCSCN AZ
ARIZONA NU
A">1 ZCNA
FORT S^ITH 4"
LITTLF ROCK AR
TFXARKANA AR-TX
ARKANSAS NII-C"
ARKANSAS NIJ-MCP
ARKANSAS
571110
27610
51944
26813°
7611 5
1020000
1066019
3266740
726167
226167
552041
5'76B5
1 309 1 61
59770
18'OIT
20371
1010000
511106
1716777
<-00
616
15
750
1*6
498
750
750
7390
V6R
7191
450
136
?no
If 1«
649
44
43
44
45
41
43
42
44
43
61
61
41
40
42
4?
45
43
45
44
5.9
S.I
5.1
5". 9
6.1
-.1
5.9
5.9
7.1
9.5
1 1.4
9 . ?
6.2
4.0
5.9
6.5
36.4
35.7
16.5
15. 1
15.5
15.6
35.7
37.1
36.?
35.7
35.7
42.1
4*. 7
41.9
36.1
35.8
35.8
35 . 6
39.6
36.1
42.1
41.7
47. 7
43.0
40. 9
41 .1
41 .5
41.6
41.°
47. 5
41.6
41.6
44.8
51 .7
57.5
51.1
47.1
41.0
41.9
41.5
47.7
41.1
4 5 . t-.
7?."
45.6
72.1
77. S
'.S.*.
14.9
45.fr
41.6
45.6
45.6
45.6
45.6
41. h
77.1
77.8
45.6
10.1
OP .4
18. 1
18. 6
63.7
64.1
^4. 1
64.4
19. 5
T7. 4
»7.2
17.2
90.4
'.7.?
1-11.1
96.7
P7.9
(• 4. 7
64. 7
64.1
11. 1
73.4
'"!m
fc 014
17090
Q1«.A
*'?05
*>*17'
T17P74
I"'?1!
10726
77|36
"Til
1 7^970
5251
1111
^4 906
HUM
RAKEPSFIFL1 CA
FRESNO CA
LOS ANCELFS r A
PDMCNA CA
SACRAMFNTH CA
S P.F.RNAROINO CA
SAN DlFT.n CA
S FRANCISCO CA
SAN JCSF CA
STA BARBARA TA
STOCKTON CA
CALIFORNIA Nil
CALIFORNIA
cniORAon SPC, rn
DENVER en
PUEBLO en
COLORADO Nil
CniORAOO
2*^44
*tp6547
177511
2430663
602005
3771221
15717704
1002?0
803624
103136
1751947
?94
287
P50
75
1049
4?
65
42
13
P91
391
"so
4690
5555
5407
42
43
41
41
45
41
40
44
44
41
44
43
43
48
48
47
48
4ft
6. I
6.0
6.1
5.6
7.1
5.7
5.7
5.7
S.6
6.0
6.1
IS. 5
17.0
15.1
1 7.9
17.4
36. 0
35. «
15.8
37.0
35.1
37.6
15.4
15.4
15.4
15.4
35.3
37.1
36.0
63.1
57.9
54.0
59.8
51. «
47.1
41 .8
41. 7
41. H
41.0
44.6
41 .0
41.1
41.1
41.0
40.9
44.0
42.2
82.6
74.9
69. 1
77. fl
76.2
45.6
45.6
31 .9
45.6
45.6
45.6
75.9
45.6
45.6
36.4
45.6
R9.7
45.6
45.6
65. P.
P 7. 7
P7.4
RQ.4
86.6
90.2
R6. 6
68. 7
6B.7
76.9
86.5
19.6
78.6
1 28.2
164.6
IU.7
123.4
142.0
11646
16677
i°120
14071
7?420
166905
41106
5594
12251
17 3H10
12144
132245
11854
92171
249066
-------
tnVltr BAIIATIOM Of
i=7«-9
TrT\L rXT
"»%££" i"
^'flPITMM -T
So"-"""1/7
l^wn rr"""1
TNM Ml
rr«m
"FL'WAOF M'l-rP
"K««A»F
WASH nr
HASH pr.
FT LA»n rL
iuSi^i11" rL
»rNSArnL«Li=l
TAMPA FL
W PAH nci'h ei
nrPiriA
IL'ANY 01
AUANTt f,A
CMATTA fit-TS
Mgr^N CA
r.FnpiitA HII-CP
Crn«r,jA s l-Nrp
r-FORr.H
M"M1l.MU MI
HAHMI
— 3s<"»'. pi
qo Q4/. 700
l<.fQ,QO 3"5
" \k\i-tt, ' 'mn
.'5"'34 Jft9
?7o^4 ''n
446'0? ](,<:
7«'3'3'S^ 1SQ
Tft^OSS JSQ
319051 10
3^2^69 70
3S?705 10
7OOt""% TO
179049 l^
30170(1 | *V
I14IM T>^
16<1*(<(7 70
10^0^00 'SO
3*43116 6RO
3MT-6 ,.
*7
53
53
53
51
S3
st
53
S3
51
M
50
50
„
37
39
38
3D
3ft'
38
47
44
44
45
43
43
43
47
43
21
21
S*.7
5.1
5.7
5.7
sil
4'.l
5.1
s.a
S.7
5.7
S.I
S.I
5.6
5.6
5.6
S.7
5.6
5.6
5.6
5.7
5.7
5. ft
7.1
S.«
6.5
si5
7.0
6.A
S.I
35.'
35.3
35.5
35.6
3S.3
35.4
35.3
35.7
35.9
35.6
35.4
35.4
35. S
35. S
35,'
35.3
35.3
35.4.
35.3
35.3
35.3
35.'
35.4
35.4
35.6
37.4
35. S
34.6
35.7
35.1
35.'
35.7
37, S
36.7
35.3
35.5
40.9
41.0
41.3
41.5
44.0
41.0
41.1
41.0
41.6
41.9
41.4
41.3
41.1
*I.Z
41.3
41.3
40.1
40.9
40. <)
41.1
40.9
40.9
40.9
40."
41.?
41.0
41.4 "
44.7
41 .3
43.1
41.7
41.9
40.1
41.4
44. S
43.3
40."
41.1)
41.3
"8.8
41.4
*?.?
«0.3
Tfi.O
40.0
64.4
«s!t
51.1
77.1
?o.» -
3B .4
"5.4
72.0
":5
11 .4
72. 8
"i°
27. •
72.3
47.1
45.6
77. R
72. A
45.6
'0.9
4?.6
4«,6
90, T
14.5
113.1
iu.n
•1.1
P7.S
02.5
77.5
72.0
76.7
7fr,7
63.7
43.7
6'. 7
K2, 7
•S3.T
63.7
43.7
63.7
*4, p
63.4
,
64.7
14.1
PR. 7
f4.S
63.7
-.0.1
12.2
•7.'.
P6.9
36544
31 43 «
4901
10»9S
913'
755*
17SO9
HI '49
'34503
20433
U'.°7
3M25
S3616
51414
7031S
23751
54337
I OS90
*16l
19235
11016
1'.57!3
3)3399
3741
«3'3
l in*
14?9
7315
10»31
1 36O06
3?4I30
'4597
SS003
-------
CO
Table A-l. Calculation of average dose equivalents due to terrestrial and cosmic radiation by State urbanized and nonurbanized
areaa—Continued
1
LOCATION
I04HC NU
IDAHO
2
1960
POPIII ATI1N
667191
667191
5 , 4
ELEVATION MAGLAT
FFFT CFG NO
3*59 51
3650 51
COSMIC RADIATION OE
M&FMS/YR
5 &
NEUT ION
1?.3 48.1
17.3 48.1
7* 54 6
TOTAL
60.4
60.4
8
TERR DOSE EQ
45.6
45.6
9-7«fl 10-(2X9|X.001
TOTAL
106
106
EXT OE
.0
.0
MAN-REM
70751
70751
AURORA ti
CHAMPAIGN IL
CHICAGO IL
DAVENPORT Il-IA
OECATUR IL
OUBUQUE IL-IA
JOLIET IL
PEORIA IL
ROCK FORD IL
ST LOUIS IL-M1
SPRlNGFIELn IL
ILLINOIS NU
ILLINOIS
CHICAGO IN-!L
EVANSVILLF IN
FT WAYNE IN
INDIANAPOLIS IN
LOUJSV'LE IN-KY
HUNCIE IN
SO REND 11 -MI
TERRA HAUTE IN
INDIANA Ntl
INDIANA
CECAR RAPins IA
DAVENPORT IA-IL
DES HO INF S I A
OUBUQUE IA-U
1MAHA 1A-NE
SOUIX CTY IA-NE
WATERLOO IA
IOWA NU
IOWA
ST JOSEPH KS-KO
TOPEKA «S
WICHITA KS
KANSAS NU
8S522
7K014
5480767
12M58
("9516
2082
1165D5
181M'
1716BI
J76791)
111401
316?203
10081H9
478446
1 436SO
179571
639140
7?396
77S04
198514
1141 5
?79USZ
4662496
105118
101018
241115
5716S
60547
89990
102827
1999557
2757537
1191
119500
292138
1 493687
636
740
595
500
682
645
545
470
715
470
610
738
641
595
790
710
450
«50
710
495
779
729
730
590
805
645
1040
1110
850
1125
1040
850
910
1290
1570
52
50
52
51
50
52
50
51
52
48
50
52
52
52
52
50
49
51
52
50
50
50
52
51
51
52
51
52
52
52
52
48
49
48
47
48
6.5
6.6
6.4
6.4
6.5
6.5
6.3
is. 2
6.6
6.?
6.4
6.6
6.5
6.4
A.I
6.7
6.6
6.2
6.9
6.6
6.3
6.7
6.6
6.6
6.4
6.7
6.5
7.1
7.2
6.8
7.2
7.1
6.6
6.8
6.9
7.5
7.9
36.5
36.7
36.4
36.4
36.6
36.5
36.3
36.1
36.7
36.1
36.4
?6.7
36.5
36.4
35.9
36.9
36.7
36.1
37.3
36.7
36.2
36.8
36.7
36.7
36.4
36.9
36.5
37.5
37.7
37. 0
37.8
?7.6
36.8
37.0
37.2
38.3
39.2
43.0
43.4
42.8
42.8
43.1
43.0
42.6
42.3
43,3
42.3
42.9
43.3
43.0
42.8
4^.1
43. A
43.2
4?. 3
44.2
43.2
42.4
43.5
43.3
43.3
42.8
43.6
43.0
44.6
44.9
43. 8
45.0
44.6
43.4
43.8
44.1
45.6
47.1
38.6
45.6
38.6
45.6
45.6
45.6
44.3
45.6"
45.6
45.6
45.6
45.*.
41 .7
38.6
45 .6
45.6
45 .6
4S.6
45.6
45.6
45.6
44.9
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
81.6
89.0
81.4
88.4
B8.7
88.6
86.9
87.9
R8.9
17. 0
98.5
"8.9
84.7
81.4
P7. 7
89.2
88. P
87.9
89.8
P8.8
"8.0
89.1
88.2
88.9
86.4
")9.2
88.6
90.7
90.5
89.4
90.6
90.2
89.0
89.4
89.7
91.4
92.7
6975
6940
446088
11150
7943
184
10133
15956
15255
24299
9854
299059
853836
38986
12593
16010
56797
6362
6961
17633
7167
248721
411232
9347
8928
21511
5082
5462
8146
9193
181135
248803
24215
106
10723
26687
138512
KANSAS
"JT78611 T395-
46TT
~4776~
91.9
-------
1
2
3
4
COSMIC RADIATION OE
LOCATION 1">60 ELEVATION MAGLAT MREMSfYB
POPULATION FEET DEC NO 5 6
CINTI KY-OH
HUNT KY-WV-OH
LEX INGTON KY
LQUISV'LE KY-IN
KENTUCKY NU-CP
KENTUCKY NU-NCP
KENTUCKY
BATON ROUGE LA
LAKE CHARLES LA
MONROE LA
NEW ORLEANS LA
SHREVEPORT LA
LOUISIANA NU-CP
LOUISIANA
179489
48091
111940
534263
1TOOOO
1994373
301815*1
1934H5
80115
80546
845237
206581
1 8". 0056
3257022
550
565
055
450
340
934
788
57
20
P2
5
204
100
77
50
49
48
49
47
48
48
40
40
42
40
42
41
41
NEUT
A. 3
6.4
6.9
6.2
A.O
6.9
A. 7
5.7
5.6
1.7
5.6
5.9
5.7
5,7
I3N
36.3
36.3
37.3
36. I
35.9
37.2
36.9
35.4
35.3
35.4
35.1
35.6
35.4
35.4
7-5*6
TOTAL
42. A
42.7
44.2
42 ,_3
41.9
44.2
43. A
41.1
40.9
41.1
40.9
41.5
41.2
41.1
8
TER» POSE 50
MREMS/YR.
30.?
4-J.6
45. h
45.6
?2 .fl
45.6
43.4
?2.8
22.8
?2.R
22.8
72.8
?2.8
22.8
9:7*8
10-12X9IX.001
TOTAL FXT OE MAN-REM
MREMS/YR
72.8
B8.3
89.8
87.9
S4. 7
89.8
87.0
43.9
63.7
63.9
63.7
64.3
«4.0
63.9
13073
4246
1005T
4*950
1 1 000
179996
264320
12354
5681
5148
53850
13407
117709
201149
LEWISTON ME
PORTLAND ME
MAINE NU
MAINE
BALTIMORE MO
WASH CCIMOI
MARYLAND NU-tP
MARYLAND NU-NCP
MARYLAND
BOSTON MA
BROCKTON MA
FALL RIV MA-RI
FITCH-LEO MA
LAW-HAVER MA-NH
LOWELL HA
NEW BEDFORD MA
PITTSFIELD MA
PRO'DENCE MA-RI
SPRNGFLD MA-CT
WORCESTER MA
MASS NU
MASS
ANN ARBOR MI
BAY CITY Ml
DETROIT MI
FLlNV MI
45751
111701
792311
969265
1418948
578«80
470000
632761
3100689
2413236
111315
1177*7
72347
165233
118547
126657
62306
43381
418313
225446
I 27*010
5148578
115282
72763
3537709
2*7>86
200
25
3«5
139
20
150
100
558
16A
27
no
40
440
65
100
15
1015
80
85
475
492
190
§18-,^
iff-
600
715
56
55
56
56
51
50
50
51
51
54
54
53
54
54
54
53
54
53
54
54
54
54
53
54
53
53
5.9
5.6
6.1
6.0
5.6
5.8
5.7
6.3
5.8
5.6
5.8
5.7
6.2
5.7
5.7
5,6
7.0
5.7
5.T
6.2
6.3
5.9
6.B
6.4
6.*
6.6
35.6
35.3
36.0
35.9
35.3
35.5
35.4
36.3
35.6
35.3
35.5
35.3
36.1
35.4
35.4
35.3
37.5
35.4
35.4
36.1
16.2
35.6
37.1
16.4
J6.4
36. T
41.5
41.0
42.1
41.9
40.9
41.3
41.2
42.7
41.4
41.0
41.3
41.0
42.2
41.1
4t.l
40.9
44.5
41.1
41.1
42.4
'4i.4
41.5
*».9
42 IS
42.8
43.3
45.6
45.6
45.6
45.6
27.4
35.4
22.8
45.6
31.9
45.6
45.6
45. A
45.6
45.6
45.6
45.6
27.9
41.9
40.0
53.1
4.5.6
45.2
45.6
45.6
43.6
45.6
87. 1
86.6
87.7
87.?
68.3
76. 7
f>4.0
88.3
73.3
86.6
06.9
86.6
87.8
86.7
86.8
86.5
72.4
83.0
81.1
95.5
88. 0
86.7
89.5
88.4
88.4
8B.9
5681
9669
69477
84827
96985
444] 6
30066
55849
227316
208910
9668
10201
6355
14321
10286
10960
4511
3601
33937
215Z2
UMU
446418
10320
H-*iz
312796
24683
-------
w Table A-l. Calculation of average dose equivalents due to terrestrial and cosmic radiation by State urbanized and nnnurbani/.cd
areas—Continued
1
2
LOCATION 1<>60
POPULATION
GRn RAPIDS MI
JACKSON M|
KALAMAZOO Ml
LANSING MI
MUSKEGCN HI
SAGINAW HI
SO REND MI-IN
MICHIGAN NU
MICHIGAN
DULL'TH MN-WI
FAPG HOOP MN-NO
MlNN-ST PAUL «N
MINNESOTA NU
MINNESOTA
294230
71*1?
115*50
169325
OS350
129215
2 04 19
29?4044
7823194
110826
25054
1377143
1910841
3413B64
3
4
COSMIC RADIATION OE
ELFVATIflN MAGLAT MREMS/YH
FEET DEC NO 5 6
610
940
Ti1*
H30
*25
•<95
710
S17
701
6i n
900
*15
1403
in*
53
53
?3
53
53
54
52
54
54
56
56
55
54
54
NEUT
6.4
>>.9
h.6
6.7
A. 4
6.4
6.6
6.7
6.6
6.4
>>.9
b.7
7.6
7,2
ION
3*. 4
37.3
36. n
31.0
36. 5
36.4
36.7
36.9
36.7
36.4
37.2
36.9
38. A
37.9
7=5+6
TQTAI
4?.o
44.2
43.4
43.7
42.9
42.8
43.7
43.7
43.2
42.0
44.0
43.7
46.3
45.1
P
9=7+9
10=1 2X91 X.001
TFPH nnsE Ft) riTAi EXT OF MAN-OEM
MREMS/YR MREHS/YR
45.6
45. *
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
31.2
45.6
39.8
IS.I
89. 8
89.0
R9. 3
88.5
88.4
88.8
89.3
8fl,8
88.5
89.6
'4.1
91,9
14,9
26026
4411
10205
15124
0440
11422
1814
261012
694776
9803
2245
103087
174680
289815
JACKSCN MS
•MSS'IPPI NU-CP
MISSISSIPPI
KANSAS CY MQ-KS
ST JOSEPH MP-KS
ST LOUIS in- i i
SPRINGFIELD MO
MISSOURI NU-CP
MISSOURI NU-NCP
MISSOURI
147480
20)0661
2178141
6*0026
79096
1391398
97?24
150000
1952169
4319813
294
267
269
750
850
470
1300
350
881
719
42
43
43
48
49
48
47
47
48
48
6.0
6.0
6.0
6.6
6.8
6.2
7.5
6.1
6.3
6.6
35.8
35.7
35.7
36. S
37.0
36. 1
38.3
35.9
37.1
36.7
41. 8
41.7
41,7
43.4
43.8
42. 3
45.8
41.9
43.9
43.3
22.8
2?. 8
22.8
45.6
45.6
45,6
45.6
22.8
45.6
44.8
64.6
64.5
64.5
89,0
89.4
87.9
91.4
64.7
89.5
88.1
9521
13091 8
140438
57760
7152
122369
8886
9711
174773
380651
BILLINGS MT
GRFAT FALIS MT
MONTANA NU
MONTANA
LINCCIN NF
OMAHA NE-IA
SIOUX CY NE-IA
NEBRASKA NU
NEBRASKA
LAS VEGAS NV
NEVADA NU
NEVADA
6071?
57629
556426
674^67"
136220
329334
7200
938576
1411310
89427
125662
2*5278
3120
3*30
3521
3469
1150
1040
1110
1604
1426
2030
4565
3754
54
55
54
54
50
51
52
50
50
43
45
45
1 1.0
11.5
12.0
11.8
7.2
7.1
7.2
8.0
7,7
8.8
14.8
12.8
45.5
46.5
47.4
47. 2
37.9
37. 5
37.7
39.3
38.8
40.9
53.2
49,2
56.5
58.0
59.4
59.0
45.1
44.6
44.9
47.3
46.5
49.6
68.0
62.1
45.6
45. 6
45.6
45.6
45.6
45.6
45.6
45.6
45.6
19.9
45.6
45.6
37.5
102.1
103.6
105.0
104.6
90.7
90.2
90.5
92.9
92. 1
69.5
1 13.0
113.6
99.*
6199
5970
58423
70592
12355
29709
652
87199
129915
6216
7930
14272
28*1 8
-------
I
1960
3 4
ELEVATION MAGLAT
COSMIC RADIATION Of
MRFMS/YR
5 6 7^5*6
10=I2X9|X.OOI
LOCATION
POPULATION FEET
PEG NO
TERR OOSF FO
HREMS/YR
TnTAl EKT OF
MREMS/YR
NAN-HEM
LAM HAVER NH-HA
MANCHESTER NH
NEW HAMP NU
N HAMPSHIRE
ATLANTIC CY NJ
NEW YORK NJ-NY
PH1LAOEL NJ-PA
TRENTON >)J-1>A
WILMINRTN NJ-OF
N JEfcSFY «IIJ-CP
N JE»SFY NU-NCP
NEW JEOSFY
ALBUQUfOUE NM
NEW MEXICO NU
NEW MFXICO
ALBANY NY
B1NGHAMPTON NY
RUFFAin NY
NEW YORK NY
ROCHESTER NY
SYRACUSC NY
UTICA RQMF NY
NEW YORK NU
NEW YORK
ASHEVtLLE NC
CHARLOTTF NC
DURHAM NC
HIGH POINT NC
GREENSBORO NC
RALEIGH NC
WTNSTCN SAL NC
N CAROL NU-CP
N CAROL NU-NfP
FARC MOOR ND-MN
N DAKOTA NU
892
91698
514331
60*921
124902
3878897
531995
226561
17320
44000O
857096
6066782
241216
709807
951021
455<.*7
1581*1
1 054370
10236030
493402
11?2W
1 P7779
3863849
16782104
6859?
209551
84642
66543
123 334
93931
128176
1410000
2371386
4556155
47676
584770
632446
65
175
712
630
10
30
45
35
115
200
?««
81
4<)58
5254
1179
'0
865
5"5
50
515
400
415
544
217
2216
721
414
940
841
361
860
100
1204
900
re'B'7
1628
54
54
55
55
51
52
52
52
52
52
52
52
43
43
43
?4
53
54
52
54
54
54
53
53
46
46
47
47
47
47
47
47
*7
4T '
56
56
$6
5.7
5.8
6.6
6.5
5.6
5.6
5.7
5.6
5.8
5.9
6.0
5.7
16.0
16.9
16.7
^.6
6.8
6.4
5.6
6.3
6.1
6.2
6.3
5.9
«.l
6.6
h.l
6.9
6.8
6.1
6.8
5.7
7.3
6.?
6.8
8.1
8.0
35.4
35.6
36.7
36.5
35.3
35.3
35.4
35.3
15.5
35.6
35.8
35.4
55.7
57.7
57.2
35.3
37.1
36.4
35.3
36.2
36.0
36.0
36.3
35.7
'41. 6'
36.7
36.0
17.3
37. 0
35.9
37.1
35.4
18.0
vo
37.2
19.6
39.4
41. 1
41.4
4?, 2
41.0
40.9
41.0
41.0
41.0
41.3
41.5
41. P
41.1
71. h
74.6
73.8
40.9
43.9
42.8
41.0
47.5
42.1
42.2
42.6
41 .6
50.7
43.1
42.2
44.2
43. 8
42.0
43.8
41.2
45.3
43.8
44. O
47.7
4?. 5
45.6
45.6
45.6
45.6
22.8
45.6
47.5
41 .9
16.2
?2.8
45.6
43.5
69.5
45.6
51 .7
25.1
45.6
45.6
45.6
45.6
45.6
45.6
45.6
45.0
45.6
45.6
45.6
45.6
45.6
45.6
45.6
22.8
45.6
3*7?
45.6
45.6
45.6
86.7
87.0
88.8
88.6
63.7
86.6
58.5
82.9
77.5
64.1
«7.4
84.6
141.1
120.2
125.5
66.0
89.5
88. 4
86.6
8B.1
87.7
87. 8
88.2
86.6
" 46.3
88.9
87.8
89.8
89.4
87.6
89.4
64.0
90.9
82.4
89.6
93. >
9T7T
77
7977
45696
53750
7959
115821
46206
18780
1142
282T6
74875
513259
'4047
85315
1 19362
nos?
14147
93166
886199
41472
29231
16479
140816
1451613
6605
18625
?4?8
S974
11 02 1
8227
11464
90198
21-56T4
• • iTrju
4272
;4$Ri
5TTOTT
-------
en Table A-l. Calculation of average dose equivalents due to terrestrial and cosmic radiation by State urbanized and nonurbanized
areas—Continued
I
IOC»T
ION
f
I960
POPULATION
1
ei FVATIHN
FFFT
4
OEG NO
fnSMlC PAD1ATION DC
KOFMWYR
5 6
7»5»6
8
TFBP 0"Sf EO
9»7»1
TOTAL FXT
MRFMSS
Of
f
10>(2X9I X.
1AN-PEM
001
AXRCN OH
CANTCN 1M
CINCINNATI 1H
CLEVFUNP OH
COLU*8US OH
OAYTCN DH
HAMH TIN 1H
HUNT OH-KY-WV
LIMA CM
LO»-FLY»IA PH
SPRINGFIFin nH
STFUBENVL riH-NV
TOlfftO OH
HHFFLING OH-HV
OH 1C Nil
(IHln
FT SMITH PK-AG
LAKTC* IK
TIILSA OK
OKi/kHonMlulNrP
1KLAHCHA
FUGFKE OR
HRFGHN NIJ
ORFfiCN
AllFN-RFT* PA
E»IF PA
HARRfSRUPR °A
J1HNSTOWN PA
LANCASTER PA
PHIIAOEL PA-NJ
READING PA
5rP ANTON PA
TRFNTON PA-NJ
YORK PA
PFNN N'l
458251 1077
213574 1060
114079 5*0
1 7R4991 6RO
616741 7RO
501664 7S7
19771 605
67961 PRO
4731* 715
418211 5R7
11471 650
4014«i'l 799
9706197 717
M941 1109
29897? 744
70001 450
1466171 15J?
712R784 1M4
9S616 4??
604729 77
106R772 1063
176P697 69]
25601S 755
R1O51 URO
177411 685
96474 1185
3111213 ?45
1 P04400 760
160297 265
210676 725
15838 35
100R7? 370
47637H1 750
11
5?
"I
50
50
49
51
52
5 1
51
52
51
'2
52
52
45
43
45
44
45
45
51
5?
51
51
52
52
53
52
52
52
52
5^2
52
53
52
53
51
52
7.0
7.1
6'.5
6.*6
6.4
I'.l
7,0
6 '.5
6.7
6.6
7.2
7,1
6.6
7.8
7.5
5.7
7.1
6.6
5.9
7.1
6.5
6.1
7.3
6.1
5.7
6.6
5.9
6.6
5.6
6.5
6.1
6.6
.17.5
37.4
16. 1
16.6
36."
36. •
16.4
36.3
37, 1
16.4
37. 4
16.7
36.4
36.5
17.0
36.9
16,4
16. 1
37.7
3R. 0
16. R
36.1
39.0
38.4
J5.4
37.6
36.8
35.7
38.0
36.6
35.9
38. 0
15.9
35.4
36. A
35.7
36.7
35.3
36,5
35.9
36. A
44, 6
44.7
47.6
41.1
43.4
42. R
42.7
43.9
47.8
44, 1
43.1
47. S
41.0
41.1
43.6
41.4
42.1
44.9
45.4
41.4
42,3
46. R
45.9
41.1
44.7
43.1
41.6
45.2
41.1
42. 0
45.3
42.0
41.0
43.4
41.7
43.3
41.0
43.0
42.0
41.4
45. f
4S.6
10.?
45.6
M.*
41.9
45.6
45.6
47 .*
4«,6
45.6
60. «
45. <•
68.9
40. P
45.6
41.9
45.6
45.6
45 .6
45.6
45.6
44.9
45 .6
45,6
45.6
45.6
4e,6
4*. 6
45.6
4* ,6
45.6
45.6
42.5
52.0
45.6
45.6
41.9
45.6
45.6
27.8
90.7
72.
88.
15.
R8,4
8R.3
91,4
18.4
103.8
1R.4
111.9
14.6
19.2
87.1
87.0
90.5
9],O
19.0
65.1
12.4
90. R
17. e
86,7
90.3
88,9
«7.2
90. R
88.7
90.9
87.6
13.5
95.4
87.3
88,9
82.9
88.6
87.6
66.2
41312
19285
5929?
158366
52679
47803
7940
?198
5756
12616
8109
4909
3R731
3746
11519
358068
147149
164
5607
39040
76595
4555
115547
211508
9399
52433
96476
1 571O8
27331
7545
15745
1 8150
8766
8217
260008
172202
13988
187Z8
1313
20719
8837
315337
4TTT
TSTT
-------
COSMIC fiAOIATlON Dt
9.7*8
10-1?XS|X.001
l**60 EiEViTtnN MAGLAT HRFMS/Y
PQ!>UiaT10N PEPT DEC NO S 6
HKFHS/Yft
FAIL «IV ol-MA
PRO'OENCF 91-NA
RHODE 10 Nil
OHPOE IP
AUGUST* SC-G4
CHARLESTON $<•
CdLUHBIA SC
GREENVHIF SC
S CAB 01 NII-CP
S CAROL NU-NCP
S CAHOUN*
SIOUX CV Sn-lA
MODI FALLS SO
S OAKCTA Nil
S DAKOTA
CHATTA TN-GA
KNOXVULF TN
KPMPMIS TN
NASHMILLf TN
TFNN NU-NCC
TENNESSEE
ABILFNF TX
ANARIUO T*
AUSTIN TX
8EAUNCNT TX
CORPUS CHITS TX
•3ALLAS T«
FT KORTH TX
MARLINGEN TK
HOUSTON TX
LARIOO TX
LUB60CK TX
MIDLAND TX
ODESSA TX
PORT ARTHUR TX
SAN ANJElA Tl
SAN ANTONIO TX
T»LER TX
UACO TX
6164
616161
737161
'HO^HB
12D2D
160113
162601
1Z61S7
1)10000
1110165
'.^83?5
*5
**
«5
45
52
S3
S3
53
*5
46
45
46
46
46
46
42
44
39
40
37
42
40
42
39
36
39
37
42
41
41
40
41
38
42
4l
5.7
5.7
5.9
5.7
5.8
5.6
5.9
6.9
5.7
6.5
fc.Z
7.2
7.6
8.7
H.6
6.5
6.8
6.0
6.2
6.0
7.0
6.6
8.2
12.1
6.3
5.6
"• o
6.3
12.6
£.5
5.6
5.6
5.7
6.2
11.3
10.)
10.?
5.6
1.4
6.6
6.0
6.3
6.2
35.3
35.4
35.6
35.5
35.5
35.3
35.7
37.3
35.4
36. «,
36.1
37.7
38.6
40.7
40.5
36.6
37.1
35.7
36.1
35.5
37.5
36.8
39.8
48.2
36.3
35.3
5?.}
36.2
48.7
36.6
35.3
35.3
35.4
36.0
46.1
43.9
44.4
35.3
*6.J
36.6
35.8
36.3
U.6
41.0
41.1
41.5
41.2
41.3
40.9
41.6
44.3
41.2
43.1
42.3
44.9
46.3
49.3
49.0
43.1
44.0
41.7
42.1
41.8
44.5
43.4
48.0
60.6
42.6
41.0
41.6
42.5
61.2
43.1
40.9
41.0
*!.&
42.2
?T.l
54.2
54.9
40.9
48.6
43.2
»!.•»
42.6
4}.i
45.6
41.9
45.6
42.9
42.8
?2.8
68.3
?2.9
72. S
45.6
36.6
45.6
45. A
*5.6
45.6
45.6
60.0
??.8
45.6
72.8
45.6
39.4
45.6
4!.6
?2.8
22.8
??.»
22.8
*5.6
45.6
19.7
22.8
ICT
22.8
w.g
45.6
45.6
22.8
4J.6
22.8
zz.a
22.8
».S
06.6
R3.0
87. 1
84.2
14.1
63.7
109.9
67.1
64.0
*8.T
78.9
90.5
91.9
9*. 9
94.6
88. 7
104.0
64.5
87.9
64. A
90.1
12.8
93.6
106.2
- 65.4
63.8
6 J.I
65.3
ne.H
88. 7
60.6
63.8
60.7
65.0
101.0
99. 8
100.5
63.7
»*.?'
66. 0
64.7
69.4
45. fl
534
51150
20648
7?332
1079
10202
17877
8512
516L6
98521
1 8ROQ7
67
6116
58201
64383
1 A396
17958
35118
30470
34225
161208
295375
85~M
14649
1Z746
7599
inn
60879
ZV60Q
44579
71 56
3933
69229
3942
13M1
6314
8*73
7*18
«49
42371
-------
Table A-l. Calculation of average dose equivalents due to terrestrial and cosmic radiation by State urbanized and nonurbani/cd
areas—Continued
1
2
LOCATION I960
POPULATION
WICHMA FAll TX
TEXAS NU-C"
TEXAS NU-NCP
TEXAS
OGDEN UT
PROVO UT
SALT LAKF CY UT
UTAH NU
UTAH
VERMONT NU
VERMCNT
IYNCHBURG VA
NEWPORT NEWS VA
ROANOKE VA
RICHNQNO VA
WASH CCIVAI
VIRGINIA Nlt-CP
VIRGINIA NU-NCP
VIRGINIA
PORTLAND MA-OR
SEATTLE 'WA
SPOKANE WA
TACOHA WA
WASHINGTON NU
WASHINGTON
CHARLESTON WV
HUNT WV-KY-OH
STEUBENVL WV-OH
WHEELING WV-OM
WEST VA NU
WEST VA
102104
1040000
1336T?4
9579^77
1219?T
60795
348661
359244
190627
389811
3898<)1
59319
201874
124752
333438
465487
560000
1707254
3966949
46956
864109
2Z6938
214930
I 500281
2853214
169500
92744
34298
65430
1498399
1160421
3
4
EIFVATION MAGLAT
FEET DEC NO
946
250
73R8
863
4300
4549
4260
5028
4595
590
590
648
20
12
948
150
150
100
1214
609
77
125
1180
250
577
455
601
565
715
650
1421
1263
43
39
41
41
COSMIC RAnl&TION PF
MBF^S/YP
5 6
NF1IT ION
6.9 37.'
5.9 35.7
9.4 42.3
7.0 37.6
49 14.0 51.6
48
48
48
4.7 53.1
3.9 51.4
6.2 56. 1
48 14.9 53.5
55
55
49
48
48
48
49
50
49
49
49
52
54
55
53
54
54
49
49
51
51
50
50
6.4 36.4
6.4 36.4
*.5 36.5
5.6 35.3
5.6 35.3
6.9 37.3
5.8 35.5
5.8 35.5
S.7 35.4
7.3 38.1
6.5 36.6
5.7 35.4
5.1 35.5
7.3 36.0
5.9 35.7
6.4 36.4
6.2 36.2
6.4 36.4
6.4 36.3
6.6 36.7
6.5 36.5
7.7 38.7
7.4 38.3
R
9 = 7.1
10M2X9IX.001
TEPB DOSE FO TOTAL EXT DF MAN-RFM
7=5.6 HPEMS/YR M«CMS/YR
TOTAL
44.2
41.6
51.7
44. 6
65.6
67. R
65.3
72. 3
61.4
42.8
42.8
43.0
40.9
4O. 9
44.2
41.3
41.3
41.2
45.4
43.1
41. 1
41.2
45.7
41.6
42. 7
42*4
42.8
42.7
43.3
43.0
46.4
45.7
45.6
22. 1
45.6
29 .0
45.6
45.6
45.6
45.6
45.6
45.6
45.6
19.5
19.5
45.6
72.8
35.4
45.6
34.6
45.6
45.6
45,6
45.6
45 .6
45.6
45.6
45.6
60.5
68.9
45.6
46.7
64.4
97. 3
T3.6
111.7
113.4
110.9
1 17.9
114.0
18.4
18.4
18.6
60.4
60.4
19.1
64.1
76.7
64.0
91.0
77.7
86.7
86.1
90. P
87.2
18. ?
18.0
18.4
ft R. 3
103.8
111.9
92.0
02.4
9169
105821
130019
705323
13564
6196
42366
101494
34458
34458
5256
12626
30687
11204
21378
35710
35823
155352
308035
4071
75041
20615
18746
132523
250996
14987
8188
3559
7328
137879
171191
OULUTH WI-MN
" GRFEN SAY WI
KENOSHA WI
HAD1SON WI
MILWAUKEE wl
33937
97162
7Z852
157814
1 I 49^97
610
590
610
860
610
56
55
53
53
53
6.4 36.4
6.4 36.4
6.8 37.1
6.4 36.4
42.9
42.8
43.1
42.9
45.6
45.6
45.6
45.6
45.6
88.5
88.4
88.5
89.4
88.5
3002
1587
6444
14115
101773
-------
FIFV^TION HAGUT
FEET CEGNCl
COSMIC KADI&TIONOE
MRFHS/rR
5 6 7-5*6
TEPH OnSF f=0
MBFMS/Yg
10M ?X9I K.001
IHCAMUN
flTiL EXT De
HRfMS/YR
RALINE W!
WISCONSIN NU
2344153
968
5*
T.O
36.5
37.3
8487
44.3
45.A
WISCONSIN
3951T77
832
6.4
37.0
43.7
So75~
UVDPINU NU
"TJOT5S
^0046
5T5
HO
T57*
5T7T
6T7T
4S.IS
41614
4S.A
41614
-------
Table A-2. Total calculation of average dose equivalents due to terrestrial and cosmic radiation by States
COSMIC RADIATION DE
9«7»8
10=( 2X91 x. 001
STATF
I960 ELEVATICN MAGLAT
pnPIIIATinfl FEET DFft NO
•4PEMS/YR
5 h
TERR DOSE FO TOTAL EXT OE MAN-HEM
ALAPAMA
ALASKA
ARlfCNA
ARKANSAS
CALIFORNIA
CPLCPADO
crNN
DELAWARE
WASH nc
FLORIDA
GEORG
-------
Table A-3. Program to calculate average dose equivalents from terrestrial and cosmic radiation
ISN OOP?
IMPLICIT RFAL«fl (A-H.i-7)
ISN 0003
1! MANSION PT>n50t ,STAPnP(5l l.
I,TO<4I, A TO( '50 t , AC [M 3Sn|
?»Tnnso(sn , SANP<5i i.sc
,L&T(<; n , INTFPV(4P| ,
ISN 0004
ISN 0005
DATA IWRITC,IHnLn,IS*ITCH,J/4*0/, INTF9V/4i «o.o, 51 *o.n,M«o.n,c
ISN 0007
ISN OOC"
on 10 1=1,0
11=1*6-5
ISN 000«
ISN 0010
I?=T*6
ISN 0012
ISN nnn
c,0 17 1=9, Ih
ISN oo?* K=i*in
ISN 00?7 W=N-<»
ISN 007R
ISN 00?<»
ISN 00*0
ISN 0031
ISN 003?
ISN 0033
ISN 0035
ISN 0037
ISN 003"
ISN 0040
ISN 0041
ISN 004?
ISN 0043
ISN 0044
ISN 0045
ISN 004IS
17 CTNTINtlF
j=m
9F ADI":, 9061 (4LOC( Ii Jl ,1=1 ,4) ,ISTATc,oop(j),ELEV,GLAT,ITO,TO(4l
IF ( ISTATE.NF. IH
Ft MF(VN=ELMEAN»FLFV*'>nPU
f inNl=I.OO».030»CL».0?5*FL*El-.0038*EL**3».0304S3*EI **4-. 0000 156*
flCN? - ?.44*CI1N1
ISN 004K
ISN 0040
TIHN3 = I.'.^'CIIN?
CICN4 = H.7(,f,*r ION3
ISN 0050
CNIIT4= S.fr^EXPf (1033.-1033.*(.<'?146n-6*EL**4»q.30'*070- H«Et
61
-------
Table A-3. Program to calculate average dose equivalents from terrestrial and cosmic radiation—Continued
ISN OO^l
ISN P05*
ISN OPS?
ISN OOS4
ISN OPS';
ISN 00*7
ISN POSO
I SN 00*10
ISN P061
ISN DOS?
ISN 006?
ISN 0164
ISN 00«>S
ISN 006*
ISN 0067
ISN 006"
ISN C070
ISN 0071
ISN 007?
ISN 0071
ISN 0074
ISN 007-5
ISN 007A
ISN 0077
ISN 007ft
ISN 0070
ISN OORO
ISN 0081
ISN P01">
ISN 008?
ISN OOB4
ISN TP15
ISM pr>R>,
ISN OOP7
ISN OOP"
ISN OOOn
ISN 0001
ISN 00«2
ISN 00b
rni;HP = CI ON?*rNim
msYP « 8. 7«iC>*rnsHR
Ic( ITn.PQ. 1 K.1 Tn 120
^(ITn.PQ.?ir,n TH i?0
\t (OEO-f I60,5o!s0
*0 fTNTINUF
INTE»V(N)=INTFI>V(NI+POPII
cosYR«=&cnsYRS»rosYR*pnPl(
TonsnM= ion sow* inns n*pnpi)
ATOI JMTOPSO
Arnt JMCCSYR
SPCM( i STATE I = S"FM( 1ST AT E)*nED*DnPU
STAPOPt I ST»TFl=STAPOPlISTATei+PnPU
P?LFVUSTATFI = PFLFV(ISTATF) »POPU*ELFV
PnnNtMlTtTFE! = »CmN^'TST*TlJtpOPU*[nN4
^nFO(ISTATF) = SOEDJ ISTATF )»PEn*PnPU
PTOOSPtl STATF)-PTDOST(ISTATE)*PnPlJ*TOnsn
IANP = ANP*.001 + .">
IFIE =FLCV*.1;
\ , IE 0, IANP
r,n Tn ?n
ISMTCH=I
!HOLD=ISTATE
r,n Tn ?o
|F(STAPTP( II.OT.O. IPO^U^STAPOPII 1
1 pnp - o
IFLF-PFl EV( 1 ) ^POPU* .5
CNUT4=PCNUT4( I I/POPU
r ION4=Pf !ON4( I 1/PHPU
rnsYR=scnsYR( i I/POPU
TOOSO=PTOOSn( I ) /PHPU
OFO=SOEniI I/PTPJ
I»NR=S4NH( I»«.001».S
62
-------
Table A-3. Program to calculate average dose equivalents from terrestrial and cosmic radiation—Continued
ISN 0108
ISN 0109
ISN 0110
ISN 0111
ISN 0112
ISN 0113
ISN 0114
ISN 0116
ISN 0117
ISN 0119
ISN 0120
ISN 0121
ISN 012?
ISN 0123
ISN 0124
ISN 0125
ISN 0126
ISN 0127
ISN 0128
ISN 0179
ISM 0110
ISN 0131
ISN 013?
WITE«*.900,IST.TFfI.HI.H.1.3I.IPnP.IELE.L4Tlll.fN,,T*.C!«l* f«YR
i TOOSO.OFD, I&NR ' *
IHOLO-IST4TF
on TO 30
00 tOO 1=1,51
POPU-1.050
I»OP = 0
IFtST&PTPUl.TF.O.) IPOPUI
170 CONTINUE
GO TO A5
130 DO 220 H=81,154
-------
Table A-3. Program to calculate average dose equivalents from terrestrial and cosmic radiation—Continued
ISN 0162
M = AHID1L t+EOSYR
ISN 0163
ISN 016*
210
ISN 016S
ISN 016*
IHNK-I I 210.200,200
?00
ISN 0167
ISN 0168
?10 CONTINUE
INTERV(NI = I NTERV(NI»IPERCTIHI«POPU1
ISN 016<>
ISN 0170
ISN 0171
TO
11X,!!<.//! ;
001 FORMAT UHl,inX,46HO I ST« IRIITIPN OF POPULATION VS. OOSF EQUIVALENT,
ISN 017?
1//A?X.7?HTQT4L HE
? FORMAT(40X,IA.2H -
I960
POPULATION//!
ISN 0173
ISN 017*
ISN 0175
ISN 0176
ISN 0177
ISN 0178
QOJ FORMATI1H1,20X,22HTOT»1 POPULATION =
.F12.0I
qn<> FORMAT
i, 121 1
90* FORMAT (3FS.1,3F».? I
90S FORMAT < BA<,, A3,i2.Fs.o,F6.o,F4.o,i l,F6.K
qp7 FORHATI1H1, 1RX.1H1.I2X, 1H2, 10X,1H1,'»X,1H4,'IX, iqHCOSMlC RADIATION 0
,1'5X,RHLOCATION,7X,
OOSF FQ
EXT DE MAN-REM,/,1H ,? 7X, 1 OHPQPUl AT I ON , 3X ,
X . *HDFG
H ,S6X,
ISN 017Q
OQB FORM AT (1H ,llXtlA4,A3,2X,16,2X,15,Sx,17,»X,3(F'i.l.2X),ftX,F6.1texf
ISN OHO
I Tft.T^'JX,! 10)
OQQ F"RmTX .
. 1 3X t
,OX,
60
•'TOTAL FXT OF MAN-RFM,/,1H ,2 7X, 1 OHPOPUL AT HN 1 3X .4HFEET, AX , *HPEG
,lH ,56X,
S 4HNEUT.3X, 3HIPN,4X,SHTnTALi/J
Q10 FQRMAT(1-I , 1 2X .""A* ,4 X . T B , ?X , I % 5X ,
X , 3 I FS. 1 , ?X I , 6X , F6 . 1 , 8X , F6. 1
ISN 01"»2
FORMAT(lHl,4?X,2qHSUMHARy DATA-FXT FBNA.L DOSF FQ, / / , 3 1 x. 27HMF AN POP
IUIATED HEAN r.nsMir,^x,??HMFAN TERR oe TOTAL DE,3x,i3HTPTAi
2FHt/.?lx,?8HELEVATION-LI.S.
ISN 0181
,10X,8HMREMS/YR)
FnRMATtlH0.3SX.FS.l,10X,F6.1j,jX,F6.1,7X,F8.1,2X.Il?l
ISN f>l»4
ISN 0185
ISN 01«6
FND
-------
APPENDIX B
Effect of Building Materials on Exposure
The following assumptions are made in esti-
mating the effect of indoor living on DE:
1. From table 16, it can be seen that the ratio of
the indoor to outdoor DE for wood frame
houses ranges from 70 percent (Lowder and
Condon, 1965) to 82 percent (Yeates et al.,
1970).
Similar ratios for homes of masonry construc-
tion range from about 72 percent (Ohlsen,
1969) to 106 percent (Ohlsen, 1969, and Yeates
et al, 1970). Based on an analysis of these
data, it has been assumed for purposes of this
study that the inside to outside BE for frame
houses is 70 percent and for masonry houses is
100 percent.
2. Seventy-five percent of the U.S. population is
assumed to live in one-family homes, based
upon U.S. Census Bureau (1960) estimates that
76.3 percent of all housing units are single
homes and that the mean number of occupants
per household does not vary significantly ac-
cording to single or multihousing unit status.
During 1964 to 1968, data collected by the Fed-
eral Housing Administration (FHA) on financ-
ing new and existing homes (U.S. Department
of Housing and Urban Development, 1969)
• showed that the proportion of frame houses
sold in the United States ranged from 75.0 per-
cent to 92.2 percent. Although FHA-financed
sales account for only a minority of home
sales, they represent the only data available on
housing construction. On the basis of these
data, it has been estimated for purposes of this
study that 80 percent of the single homes in
the nation are of frame construction. Masonry
construction is assumed to account for the bal-
ance of single homes. It should be noted that
the FHA designation of frame houses refers
to the method of roof support, and approxi-
mately one-third of all frame homes have some
brick or stone facing. The other 25 percent of
the U.S. population is assumed to be divided
equally between living-in-frame and masonry
dwellings.
3. Sixty-eight percent of the U.S. population
(U.S. Census Bureau (1969) for 1966) is as-
sumed to be engaged in away-from-home activ-
ity (school and work) for 40 hours/week, or
24 percent of the time. This time is assumed
to be spent in buildings which are 50 percent
frame and 50 percent masonry. The remaining
32 percent of the population is assumed to be
at home.
4. Ninety-five percent of an individual's time is
assumed to be spent indoors. This value is
based on a survey by Robinson and Converse
(1966), in which they summarize the ways (27
different categories) in which people spend
their time. Only two categories can be clearly
identified as outdoor activities (gardening and
walking) and these account for 0.1 hours/day.
Leisure activities account for 2.1 hours/day;
50 percent of this time is assumed to be out-
doors, making a total of 1.2 hours/day (5 per-
cent). Commuting time and nonwork trips aro
assumed to be indoor activities for die purpose
65
-------
of this study. Automobiles provide an attenua-
tion of 0.77 (indoor/outdoor terrestrial DE)
^ Solon et al.. IJHiO), which is similar to that of
dwellings. Other modes of transportation are
also as>umed to similarly reduce the terrestrial
DE. An error may be introduced by assuming
that all work is done indoors. We must keep in
mind that many kinds of work are ''outdoor"
occupations. On the other hand, much of the
work in outdoor occupations, such as police and
fire duty, transportation, and construction, take
place under cover.
Based on these assumptions, it is possible to
estimate a "housing factor," which is, the average
factor by which indoor living reduces man's ex-
posure to natural sources. The expression for
determining the housing factor (HF) is as
follows:
Home population
HF = ph[(hAti) + (hJSmt,)]
Scbool and labor
population at home
ftA) + (ICS.
School and labor
population at work
Outside
exposure
+ (Pi + Pi) to
(B-l)
where
ph = proportion of population at home
(0.32),
h{ = proportion of population living in
frame dwellings [(0.75 X 0.8) +
(0.25 X 0.5) = 0.73],
Sf = frame attenuation (0.70),
ti = proportion of time spent indoors
(0.95),
hm = proportion of population living in ma-
sonry dwellings (1 - hf = 0.27),
Sm = masonry attenuation (1.0),
PI = proportion of population working or
attending school (0.68),
dh = proportion of time spent by workers
and students at home (1 — du. = 0.76),
Wf = proportion of workers and students in
frame dwellings (0.50),
d*. = proportion of time spent at work
(0.24),
Wm= proportion of workers and students in
masonry dwellings (1 — YT, = O.."»0),
and
t0 = proportion of time spent outdoors (1 —
t, = 0.05).
The housing factor is found to be 0.80, when the
above values are substituted in eq. (B-l).
66
-------
APPENDIX C
Calculation of 2o- Error of Total Dose Equivalent
For the purpose of calculating an estimate of
the errors associated with the overall DE esti-
mate, the method suggested by Kline and McClin-
tock (1953) has been used. The overall DE is
calculated by \
DE =
+ X
5,
(C-l)
where
X,
X2
xs
X,
X5
terrestrial DE,
housing factor,
gonadal screening factor,
cosmic ray DE, and
internal emitter DE.
The estimate of the ±2E = 10.7mrem/yr.
It is interesting to note the relative contribu-
tions to the error variance of the overall estimate:
Parameter
Xi — terrestrial DE
X« — housing factor
X3 — gonadal screening factor
X« — cosmic ray DE
Xs — internal emitter DE
Relative
contribution
1
5
4
For further improvement in the total error, it
would appear most useful to improve estimates
of X,, Xi, X2, and X5, in that order. Relatively
little would be gained in accuracy by improv-
ing X».
Table C-l. Evaluation of partial derivatives in error
calculation
Parameter
Partial derivative
. AXi
= 32AXi
Xi
x<
XB
ABB =
dDE
ADS =
AX.
4X»
6T
-------
THE ABSTRACT CARDS accompanying this report are de-
signed to facilitate information retrieval. They provide suggested
key words, bibliographic information, and an abstract. The key
word concept of reference material filing is readily adaptable to a
variety of filing systems ranging from manual-visual to electronic
data processing. The cards are furnished in triplicate to allow
for flexibility in their use.
U.S. GOVERNMENT PRINTING OFFICE: 1972 O — 465-83S
68
-------
NATURAL RADIATION EXPOSURE IN THE UNITED STATES, (ORP/SID
72-1) by Donald T. Oakley; June 1072; SID, ORP, EPA
ABSTRACT: The exposure of man to natural radiation sources in the United
States has been estimated by considering the distribution of the population
with respect to certain factors, principally geology and elevation, which influ-
ence exposure to terrestrial and cosmic radiation. Data obtained by aerial
surreys in the United States have been used to calculate an average dose
equivalent (DE) estimate of 40 mrem/yr. to the population. The results also
indicate three distinct areas of terrestrial radioactivity in the United States—
(1) the Coastal Plain, which consists of all or portions of States from Texas
to New Jersey (23 mrem/yr.) ; (2) a portion of the Colorado Front Range
(90 mrem/yr.); and <3) the rest of the United States, i.e., portions of the
United States not included in "1" or "2" (46 mrem/yr.).
Since elevation is the primary determinant of cosmic ray DE in the United
States, the population distribution with respect to elevation was determined.
The average population elevation of the United States was determined to be
approximately 700 feet, and the average cosmic ray DE was estimated to
be 44 mrem/yr.
(over)
NATURAL RADIATION EXPOSURE IN THE UNITED STATES, (ORP/SID
72-1) by Donald T. Oakley; June 1972; SID, ORP, EPA
ABSTRACT: The exposure of man to natural radiation sources in the United
States has been estimated by considering the distribution of the population
with respect to certain factors, principally geology and elevation, which influ-
ence exposure to terrestrial and cosmic radiation. Data obtained by aerial
surveys in the United States have been used to calculate an. average dose
equivalent (BE) estimate of 40 mrem/yr. to the population. The results also
indicate three distinct areas of terrestrial radioactivity in the United States—
(1) the Coastal Plain, which consists of all or portions of States from Texas
to New Jersey (23 mrem/yr.); (2) a portion of the Colorado Front Range
(90 mrem/yr.) ; and (3) the rest of the United States, te., portions of the
United States not included in "1" or "2" (46 mrem/yr.).
Since elevation is the primary determinant of cosmic ray DE in the United
States, the population distribution with respect to elevation was determined.
The average population elevation of the United States was determined to be
approximately 700 feet, and the average cosmic ray DE was estimated to
be 44 mrem/yr.
(over)
NATURAL RADIATION EXPOSURE IN THE UNITED STATES, (ORP/SID
72-1) by Donald T. Oakley; June 1972; SID, ORP, EPA
ABSTRACT: The exposure of man to natural radiation sources in the United
States has been estimated by considering the distribution of the population
with respect to certain factors, principally geology and elevation, which influ-
ence exposure to terrestrial and cosmic radiation. Data obtained by aerial
surveys in the United States have been used to calculate an average dose
equivalent (DE) estimate of 40 mrem/yr. to the population. The results also
indicate three distinct areas of terrestrial radioactivity in the United States—
(1) the Coastal Plain, which consists of all or portions of States from Texas
to New Jersey (23 mrem/yr.) ; (2) a portion of the Colorado Front Range
(90 mrem/yr.); and (3) the rest of the United States, i-e.. portions of the
United States not included in "1" or "2" (46 mrem/yr.).
Since elevation is the primary determinant of cosmic ray DE is the United
States, the population distribution with respect to elevation was determined.
The average population elevation of the United States was determined to be
approximately 700 feet, and the average cosmic ray DE was estimated to
be 44 mrem/yr.
(over)
-------
To arrive at an estimate of the gonadal DE, the influence of housing, bio-
logical shielding, and the DE contribution from internal emitters was also
considered. The first two factors serve to attenuate man's gonadal DE due to
terrestrial radiation by about the same amount that is contributed by internal
emitters. The average gonadal DE to the U.S. population was calculated to
be 88 mrem/yr.
KEY WORDS: Cosmic radiation; dose equivalent; natural radiation; population
exposure; surveillance; terrestrial radiation; United States.
To arrive at an estimate of the gonadal DE, the influence of housing, bio-
logical shielding, and the DE contribution from internal emitters was also
considered. The first two factors serve to attenuate man's gonadal DE due to
terrestrial radiation by about the same amount that is contributed by internal
emitters. The average gonadal DE to the U.S. population was calculated to
be 88 mrem/yr.
KEY WORDS: Cosmic radiation; dose equivalent; natural radiation; population
exposure; surveillance; terrestrial radiation; United States.
To arrive at an estimate of the gonadal DE, the influence of housing, bio-
logical shielding, and the DE contribution from internal emitters was also
considered. The first two factors serve to attenuate man's gonadal DE due to
terrestrial radiation by about the same amount that is contributed by internal
emitters. The average gonadal DE to the U.S. population was calculated to
be 88 mrem/yr.
KEY WORDS: Cosmic radiation; dose equivalent; natural radiation; population
exposure; surveillance; terrestrial radiation; United States.
------- |