## External Dose Estimates from Global Fallout

##  

External Radiation Exposure to the Population of the Continental U.S.
from High Yield Weapons Tests Conducted by the U.S., U.K. and U.S.S.R.
between 1952 and 1963

Harold L. Beck

Report to the National Cancer Institute in fulfillment of

P.O. #263-MQ-003539

March 15, 2000

**Abstract**

This report provides estimates of the external radiation exposure and
whole body effective dose received by residents of the continental U.S.
during the period 1953-2000 from nuclear weapons tests. Doses were
calculated for tests carried out in the Pacific by the U.S. and U.K. and
by the U.S.S.R. at various sites in the former Soviet Union during the
years 1952-62. Estimates are given on a county by county basis for each
month from 1953-1972.

The average population dose from the fallout from all of these tests was
about 0.7 mSv, about equivalent to 2-3 years of external radiation
exposure from natural background. In contrast to the fallout from tests
at the Nevada Test site, the variation in exposure across the country
from "global" fallout was relatively small, reflecting primarily
variations in annual rainfall. Precipitation was the main mechanism for
the deposition of fallout from these mostly high-yield thermonuclear
tests that injected most of their debris into the stratosphere. Thus
residents of counties in the eastern and Midwestern U.S. that received
above average rainfall were impacted more than residents of the more
arid Southwestern states. Since the states downwind from the NTS that
were impacted most by the NTS fallout are in general more arid than the
eastern U.S., the areas most impacted by NTS fallout were in general
least impacted by "global" fallout.

In contrast to fallout from the NTS where most of the exposure was due
to the short-lived radionuclides (primarily I-Te-132 and Ba-La-140),
Zr-Nb-95 was the major contributor to external dose from "global"
fallout during the years of testing. The total dose through 2000 was
dominated by the long-lived Cs-137. Cs-137 present in soil continues to
result in a small radiation exposure to the public even at the present
time. As was the case for NTS fallout, the most exposed individuals were
outdoor workers, the least exposed, persons who spent most of their time
indoors in heavily constructed buildings.

The deposition of all radionuclides that contribute significantly to
external exposure, as well as a few that contributed significantly
(Sr-89, Sr-90) to internal radiation exposure via the ingestion pathway,
were calculated on a county by county and test by test basis. The
general pattern of deposition is discussed. In general the
population-weighted total deposition of long-lived radionuclides such as
Sr-90 and Cs-137 was about a factor of about 10-15 greater than that
from NTS fallout. However, the population-weighted deposition of
short-lived isotopes such as I-131 was generally much less than from NTS
fallout.

**Introduction**

In response to a request by Congress to the CDC and NCI to investigate
the impact on the U.S. population from weapons tests, the NCI contracted
with the author of this report to:

1.  Prepare crude estimates of the doses *[from external
    irradiation]{.underline}* received by the American people as a
    result of the above-ground tests carried out in the 1950s and early
    1960s *[by the U.S. in the Pacific and by the USSR in Kazakhstan and
    on Arctic Islands]{.underline}*. These dose estimates would be:

-   based on a review of the readily available open literature and
    information. It is not expected that sophisticated computer models
    should be developed or used for this purpose nor that a formal
    uncertainty analysis be carried out;

-   averaged over states or groups of states of the continental U.S.,
    with indications on how the high-risk populations would be
    identified. However, if feasible, primary dose estimates should be
    made on a county-by-county basis, and averaged only for presentation
    purposes;

-   calculated separately for the most important radionuclides produced
    in these nuclear weapons tests with respect to external irradiation
    of the U.S. population. Those would include, but would not be
    limited to Cs-137, Zr-Nb-95, Mn-54, Sb-125, and Ba-La-140;

-   provided in terms of average whole-body dose for gamma irradiation.
    The dose to the skin for beta irradiation should also be indicated,
    however, since this dose is expected to be small compared to the
    gamma dose, it is not expected that detailed beta dose calculations
    will be made for each geographical area and month/year of fallout;
    calculated by year of fallout and summed over all tests, with a
    comparison to the results previously obtained for the NTS tests. If
    feasible, calculations should be carried out by month of fallout.

2.  Provide an electronic database with the deposition densities and
    estimated doses of the important fallout radionuclides, by month of
    fallout and geographical area (county, state or group of states).
    From the point of view of external irradiation, the important
    radionuclides include those listed above. In addition, the
    deposition densities of Sr-90, Sr-89, I-131, Fe-55, and Pu-239
    should be estimated, as they are important from the point of view of
    internal irradiation.

3.  Indicate whether it would be feasible to improve the dose and
    deposition density estimates provided in this assessment. If so,
    discuss briefly how it could be done and estimate the level of
    effort, in terms of man-months, that would be needed.

This report along with an associated electronic database is presented in
fulfillment of the above scope of work.

In a previous report (Beck, 1999), this author estimated the external
exposure of the population of the continental U.S. from Nevada Weapons
Tests. The mostly low-yield (\<100 kT) weapons tests conducted at the
NTS injected almost all of their debris into the troposphere where it
was deposited mostly within the continental U.S.A. (Beck, 1999). In
contrast, the mostly high-yield (thermonuclear tests with yields greater
than 1 MT accounted for over 90% of the fission products produced) tests
carried out by the U.S., UK and USSR in the Pacific and at various sites
in the USSR injected most of their debris into the stratosphere
(UNSCEAR, 1982,1993). The total fission yield of these tests was about
150 MT (see Table 1) compared to about 1 MT for NTS tests. However,
because of the long residence times for the transfer of air between the
stratosphere and troposphere (on the order of 1 year), the fallout from
these high yield tests was relatively depleted of short-lived
radionuclides. Thus the total deposition in the continental U.S.A. of
short-lived radionuclides such as I-131 was considerably lower than that
from NTS tests.

The debris from these high-yield tests was dispersed throughout the
atmosphere resulting in "global" fallout as opposed to the local and
regional fallout from the NTS tests. This resulted in even the
deposition of long-lived radionuclides such as Cs-137 and Sr-90 in the
continental U.S. being only about 10-15 times that from NTS fallout. The
deposition from this "global" fallout was also much more evenly
distributed across the U.S. than the fallout from NTS tests. Thus even
the deposition density for I-131 may have been comparable to the
deposition of I-131 from NTS tests at some sites in the eastern U.S.
with high average annual precipitation. Unfortunately, however, in this
preliminary study, it was not feasible to estimate the deposition of
I-131 from "global" fallout in any particular county with a reasonable
degree of confidence.

While much of the fallout from NTS tests, particularly in areas close to
the NTS, was dry deposition, most of the debris from this "global"
fallout was deposited by precipitation scavenging of debris which had
reentered the troposphere from the stratosphere or was originally
injected into the high troposphere. Thus the deposition of fallout at
any site tended to reflect whether or not, and how frequently, rain
occurred at that site, particularly during the months of peak
atmospheric fission product concentrations. While separate estimates
were made for each NTS test, the estimates in the present report cannot
easily be attributed to any particular test due to the frequency of the
tests and the difference in the mechanism of fallout deposition. During
the periods of testing, tests were often held on a daily basis and
sometimes multiple tests occurred on the same day at separate sites.
Fig.1 shows the estimated FY on a monthly basis and illustrates that the
debris was released over a few relatively intense intervals of testing,
primarily in 1954, 1956, 1958 and 1961-62. Since most of the debris from
these tests was injected into the stratosphere, the activity in
stratospheric air at any time generally represented a complex mixture of
contributions from a large number of tests. Since most if not all of the
subsequent fallout was from this stratospheric reservoir, it is
impossible to attribute the deposition at any particular time to a
particular test. However, one can assume that the relative contribution
of USSR tests to the total U.S. fallout is roughly proportional to the
relative fission yield of Soviet versus U.S. and UK tests. About 84 MT
of the total estimated fission yield of 150 MT is estimated to be from
tests carried out in the USSR (see Table 1).

A huge body of literature exists regarding fallout from nuclear weapons
tests. However, the only widespread continuous monitoring of fallout
deposition were the global networks of gummed-film samplers and later
precipitation collectors (stainless-steel pots and ion exchange columns)
operated by the USAEC's Health and Safety Laboratory (HASL) and the
network of air sampling stations along the 80^th^ meridian operated
prior to 1963 by the Naval Research Laboratory and after 1963 by HASL
(Harley, 1976; Lockhart et al., 1965). The Public Health Service
monitored radioactivity in milk at a number of U.S. cities beginning in
1958 and also total beta activity in air and precipitation at a number
of sites in the U.S. beginning in 1957 (Rad. Health Data, 1958-; PHS,
1958-). A large amount of other scattered sources of data are available
in reports by investigators at National Labs, Universities and State and
Local Agencies. The HASL, in conjunction with the USDA, also carried out
extensive soil sample surveys in 1956, 1958 and 1964-66 (Alexander et
al., 1961; Meyer et al., 1968; Hardy et al., 1968). These soil data
provide estimates of the geographical variation in the cumulative
deposition estimates of long-lived radionuclides such as Cs-137 and
Sr-90. The HASL also carried out nationwide surveys of external exposure
rate levels in 1962-64, using in situ gamma-ray spectrometry to identify
the contribution of fallout to the total exposure rate in air (Beck et
al., 1964,1966; Lowder et al., 1964). These exposure rate measurements
also provide confirmation of the exposure and dose estimates in this
report.

The basic starting point for the estimates in this report were the
monthly Sr-90 deposition density measurements reported by the HASL for
about 30 sites across the U.S. (HASL, 1958-72, USERDA, 1977}. These data
were supplemented by scattered data from the literature (Collins and
Hallden, 1958; Collins et al., 1961; Kuroda et al., 1965). The
deposition of Sr-90 (and for some sites also Sr-89) was measured by
collecting precipitation using steel pots and/or ion exchange columns.
Figure 2 shows the location of HASL monitoring sites in operation in
1962. The number of monitoring sites varied from year to year with the
maximum number in operation during 1962-1965. Except for one or two
sites (i.e. New York City) continuous measurements were not carried out
extensively prior to 1958. Thus little or no data exist for years prior
to 1958. The HASL did monitor total beta deposition at about 50 sites
from 1952 through 1960 using gummed film (see Beck, 1999, Beck et al.,
1990). However, only the data for years of NTS testing has been
reevaluated and thus these data were unavailable for use in this
analysis.

Monthly deposition densities were estimated for the radionuclides listed
in Table 2. The expected production rates of each radionuclide per MT
fission are also listed based on estimates of the fission yield from
thermonuclear tests (UNSCEAR, 1993) and reported estimates of
radionuclide production relative to Sr-90 for selected Pacific tests
(Hicks, 1984). Because of the delay in transfer of debris from the
stratosphere to the troposphere discussed above, the relative fission
yields shown in Table 1 and production ratios shown in Table 2 are not
necessarily reflective of the relative deposition density of particular
radionuclides or the variation in deposition with time. However, the
deposition of nuclides with similar half-life can be expected to track
reasonably well. Note that with the agreement of the contracting
officer, detailed estimates have not been made in this preliminary
report for a few of the radionuclides listed in the scope of work (e.g.,
Fe-55, Pu-239). Pu deposition was generally proportional to Sr-90
deposition (UNSCEAR, 1993) and as a first approximation can be estimated
from the reported Sr-90 estimates. Fe-55, an activation product, is a
minor contributor to ingestion dose and does not contribute to external
dose. Because the production of Fe-55 from any particular test may have
varied considerably, it was decided not to attempt to estimate Fe-55
deposition for this preliminary feasibility study.

The patterns of total deposition for some of the longer-lived nuclides
are discussed in this report and the total deposition of various
radionuclides is compared to that from the fallout from the NTS
previously reported by this author (Beck, 1999). The general validity of
the deposition density estimates and dose estimates are indicated by
comparisons with measurements of Sr-90 in soil samples and in situ
gamma-ray measurements of exposure rate that were made during the peak
fallout years (1963-65).

All calculations for this report were carried out separately for each
county in the Continental U.S. using a relatively crude model. Fallout
in Hawaii and Alaska has not been considered in this study. Estimates
were made of deposition density for each nuclide contributing
significantly to the external exposure for the years 1953-72, as well as
for Sr-90, which is a major contributor to internal exposure. These
deposition density estimates and the resultant external exposure
estimates for each nuclide are included in the electronic database that
accompanies this report. A portion of this database containing the
estimated deposition density on a monthly and county by county basis for
Sr-90 and Cs-137 was provided to NCI earlier in partial fulfillment of
this contract. The database containing these deposition density
estimates will be used by the NCI to estimate internal radiation doses
due to ingestion of contaminated food.

The monthly results for individual nuclides were summed to provide
annual and total estimates of deposition density and doses for each
county as well as population weighted estimates for the continental U.S.
Besides the total free-in-air exposure rate from gamma emitters,
estimates were also made of the annual whole-body effective dose. The
beta-ray dose to the skin from radionuclides in the surface soil is also
discussed and the radionuclides that contributed most to both gamma and
beta-ray exposures were identified.

The results presented in this report are not intended to be definitive
estimates of the geographical and temporal variations in "global"
fallout across the U.S. They are preliminary estimates intended to
demonstrate the feasibility of making such estimates given sufficient
data and the resources to develop more sophisticated models than the
crude models used here. The present results are believed to reasonably
indicate the overall geographical and temporal variations in fallout,
particularly for the years of greatest fallout (1961-65). However, the
specific county estimates or estimates for years prior to 1958 and for
any particular month and county at any time may be quite uncertain and
should be used with discretion. This is particularly true for the
short-lived radionuclides for which little or no actual data was
available upon which to base estimates. Possible improvements in the
methodology are discussed later in this report, as are additional data
requirements. Recommendations are made on how to improve the estimates
in this preliminary feasibility study and to estimate the uncertainty in
the individual monthly or annual dose estimates for residents of any
particular county.

The next section of this report describes in detail the methodology used
to calculate exposure and deposition densities.

+-----------------------------------------------------------------------+
| [Table 1: Estimated Fission Yields\*- MT]{.underline}                 |
|                                                                       |
| \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  |
+-----------------------------------------------------------------------+

> [Year US, UK USSR]{.underline}
>
> 1952 6.0 0
>
> 1953 0 0.04
>
> 1954 31 0.1
>
> 1955 0.0 1
>
> 1956 8.6 1
>
> 1957 1.5 2.4
>
> 1958 18.5 8.5
>
> 1959 0 0
>
> 1960 0 0
>
> 1961 0 18
>
> 1962 53 19

  -----------------------------------------------------------------------

  -----------------------------------------------------------------------

\*Total yields were reported in DOE (1994) and VNIEF (1996). Because the
fission yield of individual tests are still classified, assumptions were
made to estimate the values of the fission yields. For purposes of
providing values for Table 1, all tests smaller than 0.1 Mt total yield
were assumed to be due only to fission. For tests in the range 0.5-5 Mt,
fission yields averaging about 50% have been assumed here. For tests in
the range 0.1-0.5 MT, a fission yield of 67% was assumed. There were 17
tests in the range 5-25 Mt. With no other indications available, fission
yields of 33% were assumed for those tests. However, the fission yields
of the U.S. tests were arbitrarily adjusted to agree with the reported
total fission yields for the years 1952, 1954 and 1958 (USDOE, 1999).
Note: tests carried out at the NTS are not included in Table 1.

Table 2: Radionuclides for which deposition densities and external
exposures were calculated

###### Nuclide Half life (parent), d FY(%) (a) PBq/MT {#nuclide-half-life-parent-d-fy-a-pbqmt .unnumbered}

Mn-54 313 activation product b)

Sr-89 51 3.2 (c) 731

Sr-90,Y-90\* 28.6 y 3.5 3.9

Zr-95, 64 5.1 922

Nb-95 35 0 0 (d)

Ru-103, Rh103m\* 39 5.2 1540

Ru-106, Rh-106\* 372 2.4 76.4

Sb-125 2.73 y 0.4 4.66 (e)

I-131 8 2.9 4200

Cs-137 30.14 y 5.6 5.9

Ba-140, La-140\* 13 5.2 4730

Ce-141 33 4.6 1640

Ce-144, Pr-144\* 285 4.7 191

-   In equilibrium with parent

a)  Fission yields from UNSCEAR, 1993.

b)  approx. 15.9 PBq/MT fusion (UNSCEAR, 1993)

c)  Based on reported ratio to Sr-90 for US Pacific tests (Hicks, 1984).

d)  Nb-95 is a decay product of Zr-95. The deposition of Nb-95 will
    depend on the age of the fallout as will the amount of Nb-95 present
    in soil at any time.

e)  Some additional Sb-125 (as well as Sb-124) was also produced by
    activation of Sb-123 in some of the very high yield tests carried
    out by the USSR in 1962 (UNSCEAR, 1993).

**Methodology**

#### [General]{.underline} {#general .unnumbered}

The basic model used to estimate the deposition of various fallout
radionuclides from the "global" fallout produced by the generally high
yield tests described in the introduction was as follows.

a)  The average precipitation for each month for each county of the
    continental U.S. was estimated from U.S. Weather Service records.

b)  Based on available deposition data and soil analysis results, a
    crude model was developed to describe the geographical variation in
    Sr-90 deposition density per unit precipitation as a function of
    latitude and longitude. This geographical variation was assumed to
    be independent of time.

c)  The deposition density of Sr-90 per unit precipitation (specific
    activity) in the NE U.S. for each month from 1952 through 1971 was
    estimated from available monitoring data. The deposition for other
    areas of the U.S. was then estimated from the model described in b)
    and the measured monthly precipitation.

d)  The ratio of the deposition of each nuclide listed in Table 2 to the
    deposition of Sr-90 for each month for the period 1953-1972 was
    estimated using actual data if data were available. If no data were
    available for a particular period for a particular radionuclide, an
    atmospheric model was used to estimate the ratio of the deposition
    density of that nuclide that of a nuclide of similar half-life for
    which data was available. For the purposes of this preliminary
    feasibility study, the deposition-density ratios of one nuclide to
    another were assumed to be independent of location.

e)  The monthly deposition density of each radionuclide was then
    calculated by multiplying its estimated ratio to Sr-90 for that
    month by the estimated Sr-90 deposition density for that month to
    obtain an estimate of the nuclide deposition density.

f)  The cumulative amount of each radionuclide present in the soil in
    each county was calculated from the estimated monthly depositions
    and nuclide half-life, correcting for decay during the month of
    deposition and decay from one month to another as well as ingrowth
    of daughter activity (e.g., Nb-95 from Zr-95).

g)  The exposure rate in air and dose to a typically-exposed adult
    produced by each radionuclide present in the soil was calculated
    from its cumulative deposition density using conversion factors from
    (Beck, 1980). The dose contributions from each radionuclide were
    summed to estimate the total monthly dose, the annual dose from
    external radiation and the total dose for an individual resident in
    the same county throughout the period 1953-2000. Population doses
    (per capita doses) were also calculated by weighting the individual
    county estimates by the county population during the time of
    testing.

h)  An electronic data base with the estimated deposition densities of
    Sr-90 by month and county, the estimated isotopic ratios by month,
    the estimated external doses to a typically exposed individual for
    each county, month and radionuclide was prepared.

In the following paragraphs, each of the steps above is described in
more detail.

#### [Precipitation estimates]{.underline} {#precipitation-estimates .unnumbered}

Monthly precipitation has been measured at over 8000 U.S. Weather
Service cooperative monitoring sites and data is available for most
sites beginning in about 1900. This data is available on the world wide
web (<http://www.ncdc.noaa.gov/ol/climate/online/coop-precip.html)>. Not
all sites were in operation at all times and even for sites in operation
continuously, data was often missing for some or all months during a
given year. Since there are about 3,000 counties in the continental
U.S., the average number of monitoring sites per county was about 3.
However, some counties had a large number of sites (10 or more) while
precipitation was not measured at all in other counties.

For this preliminary feasibility study a single estimate of monthly
precipitation was obtained for each county for each month from 1953-1972
by averaging the available reported monthly data for each site in
operation during that month. If no data were available for a county for
any particular month the value for the nearest county was used (the
nearest county was defined as the smallest distance between county
centroids).

The crude estimates of monthly precipitation thus obtained are subject
to a certain level of bias. First, for many counties, particularly large
counties with large variation in topography, there were large variations
in monthly precipitation from one monitoring site to another as shown in
Table 3. Thus the average for that county may not be representative of
the precipitation in the areas where most of the population reside
(e.g., Seattle or Salt Lake City). Furthermore, the average
precipitation may be much less than the maximum in the county. As will
be discussed later, the exposure to individuals living in these higher
precipitation regions may be considerably higher than the average
exposure estimated for the county. Also, the substitution of missing
values with values for the nearest county may not be the most
appropriate for areas of the country with rapidly varying topology.
Suggestions for improving the estimates of precipitation are discussed
later in this report.

The estimates of average precipitation for each county used for the
calculations in this report are contained in the electronic database
accompanying this report.

##### [Table 3: Variation of monthly precipitation within selected counties during Dec., 1962]{.underline} {#table-3-variation-of-monthly-precipitation-within-selected-counties-during-dec.-1962 .unnumbered}

[Clallam County, WA]{.underline} [King County, WA]{.underline} [Salt
Lake County, UT]{.underline}

[Site]{.underline} [(cm)]{.underline} [Site]{.underline}
([cm)]{.underline} [Site]{.underline} [(cm)]{.underline}

Clallam Bay 32 Cedar Lake 25 Alta 4.0

Elwha 22 Grotto 34 City Creek 1.1

Forks 48 Landburg 19 Cottonwd. W. 0.8

Lake Suther. 23 Mod Mt. Dam 17 Gorfield 0.15

Neah Bay 45 Palmer 34 Midvale 0.4

Port Angelos 9 Scenic 27 Mt. Dell Dam 1.4

Suppho 34 Seattle 10 Salt Lake 0.23

Sequim 4 SeTac AP 13 SLC AP 0.71

Tatoosh Is. 33 Snaqual. Falls 15 Silver Lake 3.2

Snaqual. Pass 34 Univ. Utah 0.8

#####  {#section-1 .unnumbered}

##### [Variation in specific activity of Sr-90 with latitude and longitude]{.underline} {#variation-in-specific-activity-of-sr-90-with-latitude-and-longitude .unnumbered}

Previous studies have demonstrated that the deposition of Sr-90 or
Cs-137 from "global" fallout was generally proportional to the amount of
precipitation over any particular localized area (Krey and Beck, 1981;
Beck and Krey, 1983; Collins and Hallden, 1958; Martell, 1959; Alexander
et al., 1961; Hardy et al.,1962, 1968). However, the slope of the
regression (Bq per cm of rain) was known to vary significantly with both
latitude and longitude across the continental U.S. Fig 3 from Alexander
et al., (1964) shows the variation of cumulative Sr-90 deposition with
latitude at sites with the same average annual precipitation in the
central U.S. as determined from soil sampling at various times as shown.
There is a clear variation with latitude with a maximum in the 35-40
degree latitude band. The deposition at low latitudes is less than the
maximum by about a factor of two. Furthermore, based on the different
sampling times, the variation with latitude did not appear to vary
significantly over time.

A similar variation with longitude is illustrated by Fig 4. Here the
cumulative activity per cm of rain for cumulative Sr-90 measured in soil
samples at sites in the latitude band 35-45 degrees is shown. Data from
the cumulative deposition of Sr-90 from 1958-65 as measured in
deposition in the HASL pot and column sites are also plotted. These data
indicate a clear trend of a relatively constant specific activity in the
eastern U.S. and then a steep increase as one approaches the mountainous
area of western Colorado, Utah and Wyoming. The specific activity
reaches a peak of about a factor of two at approximately the longitude
of Salt Lake City but drops precipitously to less than northeastern U.S.
levels as one reaches the West Coast. The result of this increase in
specific activity is that sites such as Salt Lake City, where the
average annual rainfall is about ½ that of New York City, received about
the same total Sr-90 deposition as New York City. The exact reason for
apparent steep gradient with longitude is not known but may be due to a
combination of factors including the relatively high latitudes and
increased thunderstorm activity during the months of peak stratosphere
to troposphere air transfer (Hardy et al., 1968).

As described below, the results shown in Figures 3 and 4 were used to
create a crude time-independent model of the variation of Sr-90 specific
activity as a function of latitude and longitude that was used to
estimate Sr-90 deposition density for each county of the continental
U.S.

##### [Specific activity of Sr-90 at NE U.S. sites]{.underline} {#specific-activity-of-sr-90-at-ne-u.s.-sites .unnumbered}

As discussed earlier, monitoring of fallout deposition was carried out
at only a limited number of sites in the U.S., mostly in the late 1950's
and 1960's. Many of these monitoring sites were in the northeastern U.S.
(Fig 2). Thus it was decided to use the average of the measured data for
sites in the latitude band 38-45 degrees and longitude band 70-85
degrees as the benchmark for estimating the specific activity in other
regions of the continental U.S. This choice was made for several
reasons. First, as shown in Fig 4, the variation in specific activity in
this longitude band was relatively constant. Second, for years beginning
in 1958 and for several months in 1956, data were available for at least
2-3 or more sites that could be used to obtain a reasonable estimate of
the mean for the region. Finally, for periods prior to 1956, data are
available only for NYC.

The benchmark specific activity values thus obtained are shown in Fig 5
for the years through 1965. It should be noted that there were often
large variations in measured monthly values at sites relatively near to
each other (e.g., New York City and Westwood, NJ) as well as occasional
large differences in duplicate samples taken at the same site. This
suggests that significant measurement errors were possible in either the
Sr-90 measurement or the local precipitation measurement that was
reported by the HASL. Thus in calculating the average specific activity
for any particular month, the author's judgment was used to discard
apparent anomalous measurements in order to obtain a set of specific
activity measurements that were consistent with the time of year and
previous and subsequent months data. The data from other sites in the
U.S., along with Figures 3 and 4, was also used to identify clearly
anomalous data. Note that the monthly variations in specific activity do
not track the fission yields shown in Fig 1. This reflects the fact that
most of the fallout in the U.S. was from debris injected into the
stratosphere resulting in a relatively long delay between its creation
and subsequent deposition. Note also the annual spring peaks in
deposition that reflect the greater transfer of debris from the
stratosphere to the troposphere during the late winter and early spring
(Bennett, 1978; UNSCEAR, 1982).

Prior to 1954, there were no reported measurements of Sr-90 from which
to make specific activity measurements. However, soil sample data were
available for a few sites in the eastern U.S. These provided a crude
estimate of the total deposition of Sr-90 from "global" fallout up to
1954. Almost all of this deposition was assumed to have occurred in
1953, primarily as a result of the high-yield U.S. tests carried out in
the Pacific in late 1952. The monthly variation in specific activity
during the year was assumed to be the same as that measured in NYC
during 1954.

For each month from 1953 through 1972, an estimate of the baseline
specific activity of Sr-90 in precipitation was thus obtained for use in
estimating the specific activity in other regions of the country as
described in the next section. These specific activity estimates are
contained in the electronic database supplied with this report. The
section later in this report on possible improvements to the crude
estimates in this report discusses improvements that might be made in
these estimates.

[Deposition density of Sr-90 in the continental U.S.A.]{.underline}

In order to estimate the deposition density of Sr-90 in each county of
the continental U.S.A. a monthly basis a number of assumptions have been
made.

First, it was assumed that the deposition in any particular county was
proportional to the precipitation that occurred in that county during
that month. Since the specific activity has been shown to vary
significantly with latitude and longitude, it was thus necessary to
develop a model describing this variation. Because of the sparse
available data, it was not feasible to develop a detailed continuously
varying model of the variation with latitude and longitude for this
preliminary feasibility study. Thus a relatively crude model consistent
with the data shown on Fig 3 and 4 was adopted. The Continental U.S. was
divided into 25 latitude-longitude quadrangles and the average specific
activity for each quadrangle relative to the default specific activity
discussed in the previous section was estimated from the data shown in
Figs 3 and 4. These default specific activities are given in Table 4.
For this study, it is assumed that the variation was independent of
time. This may not be strictly true, as discussed later in the section
on possible methodology improvements, particularly for months of testing
when some of the fallout may have been from debris injected into the
troposphere instead of the stratosphere.

[Table 4 :Sr/cm:default ratios (relative to NE U.S. baseline
values)]{.underline}

[Lat]{.underline} \\ lon:(degrees): [60-90]{.underline}
[90-100]{.underline} [100-110]{.underline} [110-120]{.underline}
[\>120]{.underline}

25-30 0.45 0.45 0.6 0.5 0.5

30-35 0.6 0.65 1.2 1.0 0.7

35-40 0.8 0.9 1.5 2.0 0.8

45-45 1.0 1.1 1.6 1.9 0.6

45-50 0.8 0.85 0.9 1.0 0.5

Because the variation with longitude and latitude is not uniform,
counties near the boundary of quadrangles where the default specific
activity estimates differ significantly will have larger uncertainties
in Sr-90 deposition estimates than counties in sections of the U.S.
where the gradations from quad to quad are smaller. Clearly, as
discussed later, a more sophisticated model might be developed,
particularly if additional data can be located to better define the
actual variations with latitude and longitude and with time. However, it
is likely that the variations in precipitation within a county discussed
earlier are a larger contributor to the total uncertainty in deposition
in these areas than the crude estimates of geographical variation in
specific activity.

Finally, the present model does not account for dry fallout. For most
areas of the U.S. dry fallout was probably less than 10% of the total
deposition. However, for any particular month where the precipitation
was very low the dry deposition may have been more significant. The
impact of not accounting for dry deposition is most significant for the
more arid regions of the U.S. Thus, as discussed in the section on
possible improvements, the estimates for fallout for those areas are
likely underestimated in this report. It should be noted, however, that
even, accounting for more dry fallout in such counties, the total
fallout in these counties would still have been relatively low compared
to counties with even average amounts of precipitation.

The deposition density of Sr-90 was thus estimated for each county for
each month from 1953-1972 by multiplying the average precipitation for
that county for that month by the benchmark specific activity and the
assumed relative specific activity for that particular
latitude-longitude band. The resultant deposition density estimates for
each county and month are provided in the electronic database
accompanying this report.[^1]

Although the model used to estimate the Sr-90 deposition is fairly
crude, a comparison with the available data for a number of sites where
sufficient data is available indicates that the agreement is fairly
good. This is true even on a monthly basis when one considers the
measurement errors and variations in monthly precipitation within a
given county. Figures 6a-6f compare the model estimates of Sr-90
deposition for six different cities in various parts of the U.S. with
the actual measured Sr-90 in rain. Although there are sometimes large
differences for a particular month, the overall agreement is quite good.
Keep in mind that the model results are based on the average
precipitation for the entire county while the measurement results are
for a single location.

For this preliminary study, any NTS Sr-90 deposition density in
precipitation at the northeastern benchmark sites was not subtracted. As
shown in Beck (1999), the deposition density of Sr-90 in the N.E. U.S.A.
was fairly low compared to areas closer to the NTS and to "global"
fallout. Thus the resultant slight bias in the estimates of "global"
fallout for months of NTS testing based on using uncorrected benchmark
data did not have any significant impact on the annual or total
estimates of "global" fallout.

In addition to the comparisons shown in Figs. 6a-6f, the annual
depositions for the years 1958-65 predicted by the model were compared
to those at the measured sites for about 30 measurement sites with a
significant amount of measured data. On average, the agreement in annual
Sr-90 deposition was better than 10% although for some sites, there
were differences in the calculated and measured total deposition density
estimates of as much as 50% for some years.

An additional test of the validity of the model estimates can be
obtained by comparing the calculated cumulative Sr-90 deposition density
for a given county with the results of soil samples taken at a site in
that county. Comparisons with soil samples from 1964-66 are shown in
Table 5. As seen, the model estimates of cumulative Sr-90 deposition
agree reasonably well with the soil data. The largest differences occur
in counties in mountainous regions of the country. The average
precipitation for these counties may not be representative of the
rainfall at the measurement site. In addition, the soil samples include
both "global" and NTS fallout while the model estimates exclude most of
the NTS fallout. Thus one would expect the soil data to be somewhat
higher than the model estimates for areas immediately downwind of the
NTS. There are also large differences for counties in very arid locales
where the model's neglect of dry fallout resulted in a significant
underestimate in Sr-90 deposition density. Additional soil data are
available beginning in 1953 and further comparisons, subtracting the
contributions from NTS fallout, might be useful for refining the
deposition model.

The comparisons discussed above suggest that the model estimates of
total Sr-90 deposition density for any given year and over a longer
period are probably quite reasonable although estimates for any
particular month may be quite uncertain. Possible improvements are
discussed later in this report.

[Table 5: Comparison of Model Sr-90 Cumulative Deposition Density
Estimates with Soil Sample Measurements]{.underline}

[Site]{.underline} [Soil Sample Date]{.underline} [Cumulative Deposition
Density (Bq.m2)]{.underline}

[Soil Sample]{.underline} [Model]{.underline}

Clallam County, WA 9/64 1150-4200 (6 sites) 2290

9/65 1300-6440 2440

Puyallup, WA 9/64 2110 1850

9/65 2180 2110

Mandan, ND 10/64 3000 1440

Bozeman, MT 9/64 2780 1630

Orono, ME 6/64 2110 2410

7/65 2180 2480

St. Paul. MN 10/64 2740 1890

Corvalis, OR 9/64 1630 1920

9/65 1920 2070

Burlington, VT 6/64 1960 2440

7/65 2220 2590

Rapid City, SD 9/64 3590 3150

9/65 3590 3480

Boise, ID 9/64 2150 1630

9/65 2550 1810

Ithaca, NY 9/64 2040 2440

10/65 2110 2590

Amherst, MA 6/64 2000 2660

7/65 2330 2890

S. Wellflect, MA 6/64 2780 2920

7/65 2890 3030

Logan, UT 9/64 1520 2590

9/65 1810 2740

Des Moines. IO 9/64 2780 2960

8/65 3030 3180

Kingston, RI 6/64 2780 3030

7/65 3330 3180

Brigham City, UT 9/64 3440 2370

9/65 3370 2550

New York City 12/64 2590 2590

Salt lake City, UT 9/64 3740 3260

9/65 3850 3550

Heber, UT 9/64 2330 2740

9/65 2550 2960

Rosemont, NB 9/64 2890 2370

9/65 3110 2850

Columbus, OH 8/64 2890 2180

8/65 2960 2370

Derby, CO 9/64 2180 1700

9/65 2290 1920

Healdsburg, CA 9/64 1920 2070

9/65 1920 2220

Cedar City, UT 9/64 1260 1330

9/65 1410 1550

Norfolk, VA 2/64 2110 2220

2/65 2740 2290

2/66 2810 2370

Tulsa, OK 10/64 1850 2330

Florence, SC 2/65 2890 2220

3/66 2810 2220

Los Angeles, CA 9/64 810 1000

9/65 850 1110

Atlanta, GA 2/64 2000 2510

3/65 2740 2590

3/66 2110 2660

El Centro, CA 9/64 570 110

9/65 670 110

Newton, MS 3/65 1890 2260

Tifton, GA 3/65 2000 2290

Jacksonville, FL 2/65 2260 2370

3/66 2150 2520

New Orleans, LA 3/65 2260 2520

3/66 1890 2630

Ft. Lauderdale, FL 2/65 1850 2070

3/66 2370 2070

Soil data from Meyer et al., 1968.

[Ratios of deposition to Sr-90, Sr-89]{.underline}

The previous sections discussed the estimates of Sr-90 deposition
density. Only two radionuclides were monitored fairly continuously for
global fallout, Sr-90 and for fewer sites and times, Sr-89. The reason
for this was that Sr-90 at that time was considered to be the most
significant health hazard from "global" fallout due to its incorporation
in bone via ingestion of contaminated foodstuffs and its long physical
and biological half life. Thus other radionuclides were monitored
infrequently and only at a few sites in the U.S. Because short-lived
nuclides such as Zr-Nb-95 and others listed in Table 2 contributed
significantly to external exposure rates, it is necessary to estimate
the deposition density of these nuclides as well in order to estimate
the exposure of the U.S. population to external gamma radiation.

Because of the sparseness of actual data, a critical assumption was
required for this preliminary study, i.e., that the ratios of the
various radionuclide deposition densities for any given month did not
vary significantly across the U.S. Considering that most of the fallout
deposited in the continental U.S. was from debris originally injected
into the stratosphere where it had time to mix and equilibrate, this
assumption is probably reasonable for the nuclides with half-lives
greater than about a month. However, it may not be reasonable for
nuclides with shorter half-lives for several reasons. First, some
significant fraction of the fallout during months of testing,
particularly for tests held at latitudes comparable to the U.S., may be
from debris injected into the troposphere. The fallout would then vary
across the U.S. because of decay in transit as the debris traversed the
country. If debris from the stratosphere was transferred preferentially
to the troposphere at specific longitudes, as indicated by Figure 4,
again one might expect a variation with longitude in deposition. Debris
injected into the troposphere tends to remain in a band close to the
latitude of injection. However, some of the debris injected into the
troposphere from U.S. tests in the Pacific at low latitudes might have
diffused to higher latitudes and impacted the southern latitudes of the
U.S. more than the more northerly latitudes. Unfortunately, except for
Sr-89 with a half-life of 50 d, there is insufficient data upon which to
base a geographical variation in deposition for these nuclides. In
general, the Sr-89 to Sr-90 ratios do not indicate any significant
geographical variation. Measurements of short-lived nuclides have been
reported in precipitation and in air at only a few scattered sites
across the U.S. and only during years after 1957.

Scattered data on individual nuclide activities in precipitation samples
are available for Pittsburgh, Westwood, NJ, Houston TX (HASL, 1958-72,
USAEC, 1958), New York City (Collins et al., 1961) and Fayetteville AK
(Kuroda et al., 1965). There is also some data on short-lived and
long-lived radionuclides in air for Miami and Sterling, VA (Lockhart et
al., 1965), Richland, WA (Perkins et al., 1965), and Argonne, IL
(Gustafson et al., 1965). Data for Ce-144 are also available from
England for 1955 and 1956 (Stewart et al., 1957). Although these data do
indicate a possible geographical variation during some of the months of
testing, the data are often inconsistent and ambiguous. Further study is
required along with a search for additional data in order to develop a
credible model for the variation with location for these radionuclides.
Thus, the deposition density estimates for nuclides shorted than about 1
month are highly uncertain and should be used with discretion.

Because of the sparseness of available data, even for Sr-89, a global
circulation model developed by Bennett (1978) was used as an aid in
estimating ratios of radionuclide deposition. This model was developed
to describe atmospheric dispersion and deposition of radioactive debris
produced in atmospheric nuclear testing (Bennett, 1978; UNSCEAR, 1982).
The atmosphere is divided into a number of equatorial and polar regions
from 0 to 30 and 30 to 90 degrees latitude, respectively. The
troposphere height is variable with latitude and season, but for
modeling purposes it is assumed to be at an average of 9 km altitude in
the polar region and 17 km in the equatorial region. The lower
stratosphere is assumed to extend to 17 km or 24 km in the two regions
and the upper stratosphere to 50 km in both regions. The model requires
certain assumptions regarding the fraction of fission products injected
into the stratosphere versus the troposphere from each test. It also
requires information on the yield and height of burst and estimates of
the residence time and transfer rates of air from various regions of the
stratosphere to other regions, from the stratosphere to the troposphere,
and from the troposphere to deposition. Apportionment of debris to
various compartments in the atmosphere is based on the reported
stabilization heights of cloud formation following the explosion.
Empirical values derived from a number of observations are used
(Bennett, 1980, UNSCEAR 1982). The model tends to predict the temporal
variation of Sr-90 deposition quite well (UNSCEAR, 1982). However, the
estimates of the deposition of the shorter-lived nuclides are much more
uncertain due to uncertainties in the exact fission yields for any
particular test and the fractions of activity injected into the
stratosphere versus the troposphere. The latter estimates are much more
important for the short-lived nuclides than for the longer-lived
nuclides.

Although the model is not able to accurately predict the actual
deposition density of a particular short-lived nuclide, it served as a
useful guide to the expected ratio of depositions for nuclides of about
the same half life. Thus, for example, for periods when no measurements
of Zr-95 were reported anywhere in the U.S., but measurements of Sr-89
were available, the model estimates of the ratio of Zr-95 to Sr-89 as a
function of time were used to estimate the Zr-95/Sr-90 deposition
density ratio from the average measured Sr-89/Sr-90 ratio. Similarly,
where Ce-144 data were available, but not Ru-106 data, the model
deposition-density ratios of Ru-106/Ce-144 and the measured ratios of
Ce-144/Sr-90 were used to estimate the Ru-106/Sr-90 ratio. A similar
procedure was used to estimate I-131 deposition density from the sparse
Ba-140 measurements. Ratios of Nb-95 to Zr-95 were estimated based on
the estimated age of the Zr-95 being deposited and the relative
half-lives of Zr-95 and Nb-95[^2]. Since the half lives of Cs-137 and
Sr-90 are similar (Table 2), the ratios of deposition were assumed to be
equal to the production ratio for this report.[^3] For periods where no
data were available for a particular radionuclide the author made rough
estimates using the production ratios shown in Table 2, and the model
calculations as a guide. In all cases, where actual credible data was
available, the actual data was used.

Again, the author's judgement was used to evaluate available data and
thus the final estimates of the isotopic ratios presented in Appendix 1
of this report are a synthesis if the available data, the model
predictions, and the author's professional judgement. Recommendations
for estimating the uncertainty in and improving the estimates of
isotopic ratios are discussed later in this report. The estimated ratios
of Zr-95 to Sr-90 deposition density versus time are shown in Figure 7.
Note that the ratio approaches the ratio of production rates given in
Table 2 during the fall of 1961. This is expected since the
stratospheric reservoir of Sr-90 was relatively depleted due to the
moratorium on atmospheric testing from 1959 through most of 1961. At
other times, the large inventory of Sr-90 in the stratosphere from
earlier tests reduces the ratio below the production ratio even during
months of heavy testing.

#### [Deposition densities of radionuclides contributing to external radiation exposure]{.underline} {#deposition-densities-of-radionuclides-contributing-to-external-radiation-exposure .unnumbered}

The deposition density of each of the radionuclides listed in Table 2
was thus estimated for each county and month by multiplying the
estimated Sr-90 deposition density for that county and month by the
monthly isotopic ratio estimates in given in Appendix 1. The estimates
for the more important contributors to external dose, Zr-Nb-95 and
Cs-137 are probably quite reasonable since Zr-95 was measured in
precipitation or air at several sites in 1958 and 1961-62 and Sr-89 was
measured at a relatively large number of sites (HASL, 1958-72).
Furthermore, the model Sr-89/Zr-95 ratios agree reasonably well with the
measurements for periods where both were measured simultaneously,
supporting the use of the model ratios at other times. Similarly, the
estimates for Ce-144 and Ru-106 are also considered reasonably valid.
The deposition of Cs-137 as estimated from the production ratios is in
reasonable agreement with available data. Ru-103 was not generally
measured but Ce-141 measurements were occasionally reported. The use of
the model and available Ce-141 data to infer Ru-103 deposition is
probably reasonably valid. The most uncertain estimates are for Ba-140
and I-131, both for reasons discussed above regarding geographical
variations and due to the sparseness of available data. No actual data
on I-131 deposition density was available for this report and thus I-131
deposition densities were estimated from available Ba-140 data.
Scattered Ba-140 measurements in precipitation are available for
Pittsburgh, Westwood, NJ, Houston, Richmond, CA, and Fayetteville,
Arkansas at various times and a rough ratio to Sr-89 could be inferred
from these measurements that was consistent with the ratio suggested by
the Bennett model.

#### [External radiation exposure]{.underline} {#external-radiation-exposure .unnumbered}

For the author's previous report on external exposure from NTS fallout,
conversion factors from Beck (1980) were used to convert cumulative
deposition density[^4] to exposure rate in air assuming the
radioactivity was distributed in the soil with a relaxation length of
about 0.1 cm for the first 20 days. From 20 d to 200 d, a relaxation
length of 1 cm was used, while for times greater than 200 days, a
relaxation length of 3 cm was used. This report uses a similar model,
multiplying the deposition on the ground less than 1 month by the
conversion factor corresponding to a relaxation length of 0.1 cm. A
relaxation length of 1 cm is used for the activity remaining in the soil
that was deposited within the period 1-6 months while a relaxation
length of 3 cm was used to calculate the exposure rate from the activity
that had been present for greater than 6 months. The corresponding
deposition-density to exposure conversion factor for each of these
relaxation lengths is from Beck (1980). Since the penetration into the
soil would be slower in more arid regions, maintaining the 0.1-cm
relaxation length for the first 30 d provides a slightly conservative
estimate of the exposure for sites with greater precipitation. Table 6
illustrates the dependence of the exposure rate in air on the various
relaxation lengths. Note that the exposure rate is reduced by about 1/3
as the activity penetrates to a relaxation length of 1 cm and about ½ as
the activity penetrates to a relaxation length of 3 cm from 0.1 cm. This
accentuates the importance of the first few weeks after deposition with
respect to total external radiation exposure to an even greater degree
than previous calculations based only on radionuclide decay. For a
discussion of available data on nuclide penetration with depth on the
soil see Beck (1999).

Table 6: Exposure rate (R/h per mCi/km^2^) versus relaxation length for
selected fission [products (Beck, 1980)]{.underline}

[Nuclide]{.underline} [Relaxation length (cm)]{.underline}

[0.1]{.underline} [1]{.underline} [3]{.underline}

Zr-95 1.20E-02 7.94E-03 5.63E-03

Nb-95 1.24E-02 8.20E-03 5.82E-03

Mn-54 1.34E-02 8.82E-03 6.28E-03

Ba-La-140 3.57E-02 2.44E-02 1.71E-02

Sb-125 6.91E-03 4.61E-03 3.17E-03

Ru-103 7.85E-03 5.25E-03 3.58E-03

Rh-106 3.37E-03 2.25E-03 1.56E-03

I-131 6.32E-03 4.34E-03 2.89E-03

Cs-137 9.29E-03 6.15E-03 4.32E-03

Ce-141 1.09E-03 7.25E-04 4.92E-04

Ce-Pr-144 7.04E-04 4.80E-04 3.37E-04

#### [Whole-body effective dose]{.underline} {#whole-body-effective-dose .unnumbered}

In order to calculate the whole body dose from the free-in-air exposure
data, one must first convert exposure to dose in air by multiplying by a
factor of 0.875 rad/R. Then, to convert to dose in tissue and account
for shielding by the body, one must convert from rads in air to rem (or
in S.I. units, Gy to Sv). In this report, as was the case for NTS
fallout (Beck, 1999, we chose to follow the ICRP guidelines (ICRP, 1991)
and estimate the effective whole body dose that weights the effects on
various organs in a proscribed manner. The UNSCEAR (1993) recommends a
factor of 0.75 ± 0.05 to convert from Gy to Sv for adults. This is
similar to average values recommended by the ICRP and others (NCRP,
1999). This factor of course varies with the energy of the radiation and
the orientation with respect to radiation incidence (NCRP, 1999,
Eckerman and Ryman, 1993), However, a value of 0.75 is a reasonable
average for fission products (NCRP, 1999). The net conversion from
exposure in air to effective dose is thus about 0.875 \* 0.75 = 0.66 for
adults. Calculations using computer phantoms have indicated that the
effective dose to young children is about 30% higher (NCRP, 1999).

Thus the dose to adults exposed outdoors is about 2/3 the outdoor
exposure. However, most people spend most of their time indoors and thus
their exposure is reduced greatly due to attenuation of the radiation by
building materials. The amount of shielding (i.e. the shielding factor)
will depend on the type of structure. In general, based on a review of
the available literature, it is estimated that heavily constructed
buildings made of brick or concrete will provide a shielding factor of
about 0.2 ± 20% (1 s,d,) while lightly constructed buildings will
provide a shielding factor of about 0.4. ±20% (NCRP, 1999). These
estimates are fairly conservative and allow for a small amount of
radioactivity that may be tracked into the home from contamination of
shoes, etc. Assuming that on average most persons spend about 80% of
their time indoors (UNSCEAR, 1993; NCRP, 1999) with an average shielding
factor of 0.3, their whole body effective dose would be 0.66 \* (0.2 +
0.8 \* 0.3) = 0.29 x Outdoor exposure. However, the UNSCEAR estimated
that persons who work outdoor spend on average only 40% of their time
indoors and the most exposed outdoor worker spends only about 30% of
his/her time indoors. The NRC (1977) made a similar estimate of 40% of
time spent indoors for the maximum exposed individual. Assuming only 30%
indoors in a lightly shielded structure for the maximum exposed outdoor
worker, the dose to the most exposed individuals would be

0.66 \* (0.7 + 0.3 \* 0.4) = 0.54 x Outdoor exposure or almost twice
that of the average exposure. Conversely, the UNSCEAR (1993) estimated
indoor workers spend only about 10% of their time outdoors while other
estimates indicate some individuals spend even less time outdoors.
Assuming 5% as a reasonable estimate for the least exposed individual
living in a well shielded house and/or working in a well-shielded
building, the minimum exposed individual would receive a dose of about
0.66 \* (0.05 + 0.95 \* 0.2) = 0.16 x outdoor exposure, or about ½ that
of the average dose.

Thus the actual dose to any individual can range by about a factor of
four depending on the amount of time spent outdoors and the type of
structure the individual lives and works in. The dose to children could
be about 30% higher than that for adults for the same fraction of time
outdoors. In this report, all calculations of dose are based on the
average exposure given above and estimates for any individual should be
adjusted up or down based on the above discussion.

As discussed previously, the dose in a particularly individual in some
counties may be considerably higher than estimated in this report. This
is due to the use of an average precipitation for the county.
Conversely, the use of the average precipitation for the county may have
resulted in the estimated dose for most of the population being somewhat
overestimated if most of the population resides at lower altitude, lower
precipitation regions of the county. It should also be noted that the
rate of penetration of radionuclides into the soil will also vary from
site to site depending on the amount of rainfall and type of soil. Thus
the relaxation lengths used for estimating the free-in-air exposure
rates may also not correctly reflect the actual depth distribution at
any particular locale and thus the dose to any particular individual.

[Beta-ray skin dose]{.underline}

All of the exposures and doses discussed above refer to exposure to
gamma radiation from the fission products deposited onto the ground.
However almost all of the gamma emitting radionuclides also emit beta
rays and a number of fission products emit beta rays but no gamma rays.
Because of their low penetrating power, beta rays are attenuated rapidly
in soil and even in air and thus contribute little to whole body
radiation exposure (Eckerman and Ryman, 1993; NCRP, 1999). However, beta
rays can contribute to the dose to skin, particularly in the days
immediately following fallout before the activity has penetrated more
deeply into the soil. Because the beta radiation is so sensitive to the
actual depth distribution in the soil, only a very crude estimate can be
made of the dose.

Besides the beta radiation itself, the beta rays produce a small amount
of gamma radiation via bremsstrahlung (Eckerman and Ryman, 1993). This
gamma radiation, although only a small fraction of the energy of the
beta ray itself, can produce a small whole body exposure and add to skin
dose. Furthermore, it is generally the only way a beta emitter can
irradiate body organs other than the skin. The calculation of doses from
beta radiation from fission products in the soil was discussed in the
previous report by this author on NTS fallout exposure rates. Because of
the fact that most of the short-lived beta ray emitters decayed prior to
the deposition of "global" fallout, the relative impact of beta
radiation compared to gamma radiation is expected to be have been even
more minor than was estimated for NTS fallout.

**Discussion of Results**

##### [Fallout deposition]{.underline} {#fallout-deposition .unnumbered}

The total deposition density of Cs-137 from "global" fallout through
1972 is shown in Figure 8. The total deposition Density of Zr-95+Nb-95
is shown in Fig. 9. The small differences in geographical variations for
Cs-137 as compared to Zr-Nb-95 reflect the fact that Zr-Nb-95 was
deposited only during and within a few months after testing while
Cs-137, due to its long half-life and long stratospheric-residence time,
was deposited essentially continuously. Thus areas with more frequent
precipitation during periods of testing received relatively higher
Zr-Nb-95 (as well as other short-lived radionuclides) deposition. Figs.
10 and 11 illustrate the variation with time of the annual
population-weighted deposition density of Cs-137 and Zr-95,
respectively. Also shown for Cs-137 is the cumulative deposition
density. The latter illustrates the gradual build-up of activity in the
soil that occurs for the longer-lived radionuclides. This buildup
results in a gradually increasing exposure rate with time as shown
later. Fig. 10 indicates that the deposition of Zr-95 in 1954 was less
than that in 1958 and much less than the relative fission yields shown
in Table 1. This is not exactly unexpected, however, since all of the
tests conducted in 1954 were surface shots compared to only about 2/3 of
the yield in 1958 being from surface shots in 1958 and ¾ in 1956 (USDOE,
1994). Surface shots would result in a much larger proportion of the
debris being deposited locally and regionally as opposed to globally.

Table 7 gives the calculated total deposition (1953-1972) of each
radionuclide and the population-weighted deposition density, and
compares these with the estimates for NTS fallout from Beck (1999) and
estimates for the Northern Hemisphere from UNSCEAR (1993).

As can be seen from Table 7, the deposition density of long-lived
radionuclides from "global" fallout is about a factor of 10-15 greater
than that from NTS fallout. However, the total deposition of short-lived
nuclides such as I-131 was much less for "global" fallout than for NTS
fallout. The "global" to NTS fallout ratios of population-weighted
deposition density differ from the total deposition ratios reflecting
the more uniform deposition of "global" fallout across the country. As
shown in Beck (1999), the deposition of NTS fallout generally declined
as the distance from NTS increased. The higher relative proportion of
"global" fallout in the more populous (and higher rainfall) eastern U.S.
resulted in a relatively higher per capita exposure from "global"
fallout for the same total continental U.S. deposition.

[Table 7: Total deposition and population-weighted mean deposition
density of selected]{.underline} [radionuclides for NTS fallout and
"global" fallout. Bq/m^2^]{.underline}

[Nuclide]{.underline} [Total Deposition]{.underline} [Population
weighted Deposition density]{.underline} (10^15^ Bq) (kBq / m^2^)

[NTS "Global NTS Global (this study) "global"\*\*]{.underline}

Cs-137 2.3 28 0.26 4.4 5.2

Sr-90 1.8 19 0.11 2.9 3.2

Zr-95 218 313 25 50 38

Nb-95 0 400 0 65 64

Ru-103 426 212 46 35 28

Ba-140 1390 290 144 46 23

Ce-141 500 223 54 37 21

Ce-144 40 302 4.6 47 48

Ru-106 24 157 2.6 24 24

Sr-89 333 170 36 28 20

I-131 1484 112 192 18 19

Pu-239+240 0.13 \~0.4 \~0.015 \~0.06 0.06

\*\* for 40-50 degree latitude band (UNSCEAR, 1993)

The deposition of course varied from year to year. The annual per capita
deposition density for each nuclide for "global" fallout is shown in
Table 8. Because of the delay that resulted due to the injection of
debris into the stratosphere, the deposition of long-lived nuclides
continued for many years after the cessation of testing.

[Table 8: Annual per capita deposition density for "global" fallout.
Bq/m^2^]{.underline}

  -------------------- ----- ---------------------- ------- --------------------- ------- --------------------- ------ ---------------------- ------ ---------------------- ------ --------------------- ------- ---------------------- ------ ---------------------- ------- ---------------------- ----- ---------------------- ------ --------------------- ------ --------------------- ----- --------------------- --
                                                                                                                                                                                                                                                                                                                                                                                                                        

                                                                                                                                                                                                                                                                                                                                                                                                                        

  [Year]{.underline}         [Cs-137]{.underline}           [Zr-95]{.underline}           [Nb-95]{.underline}          [Ru-103]{.underline}          [Ru-106]{.underline}          [I-131]{.underline}           [Ba-140]{.underline}          [Ce-141]{.underline}           [Ce-144]{.underline}         [Sb-125]{.underline}          [Mn-54]{.underline}          [Sr-89]{.underline}         [Sr-90]{.underline}   

  1953                 55                           920                           1549                          740                           475                           210                          614                            737                           671                            39                           40                           895                          37                          

  1954                 96                           2424                          2458                          3077                          873                           1408                         4273                           2540                          1095                           67                           58                           1815                         64                          

  1955                 191                          296                           390                           129                           1218                          47                           153                            144                           1261                           117                          58                           308                          127                         

  1956                 181                          3738                          4510                          3503                          935                           2241                         5606                           3313                          1367                           106                          132                          2103                         121                         

  1957                 138                          3890                          6978                          2760                          922                           2120                         5323                           3712                          1737                           84                           128                          2139                         92                          

  1958                 269                          5401                          6026                          7442                          2243                          3977                         10477                          8337                          4209                           184                          348                          3851                         180                         

  1959                 379                          6685                          12933                         3171                          2416                          5                            166                            2870                          4585                           246                          514                          3060                         252                         

  1960                 95                           0                             0                             0                             250                           0                            0                              0                             374                            48                           55                           0                            64                          

  1961                 115                          4265                          3257                          2870                          598                           1463                         4247                           4028                          1284                           77                           104                          2279                         77                          

  1962                 549                          13813                         14253                         5307                          4524                          6009                         15020                          7327                          10245                          560                          2125                         6852                         366                         

  1963                 921                          8920                          12477                         6216                          5958                          62                           308                            3901                          12954                          910                          2197                         4526                         614                         

  1964                 647                          108                           227                           5                             2660                          0                            0                              0                             5007                           505                          818                          0                            431                         

  1965                 288                          0                             0                             0                             818                           0                            0                              0                             1151                           184                          201                          0                            192                         

  1966                 109                          0                             0                             0                             220                           0                            0                              0                             314                            62                           52                           0                            73                          

  1967                 57                           0                             0                             0                             82                            0                            0                              0                             118                            29                           18                           0                            38                          

  1968                 58                           0                             0                             0                             59                            0                            0                              0                             86                             26                           12                           0                            39                          

  1969                 54                           0                             0                             0                             39                            0                            0                              0                             58                             22                           8                            0                            36                          

  1970                 67                           0                             0                             0                             34                            0                            0                              0                             51                             24                           6                            0                            45                          

  1971                 57                           0                             0                             0                             21                            0                            0                              0                             31                             18                           4                            0                            38                          

  1972                 23                           0                             0                             0                             6                             0                            0                              0                             0                              7                            1                            0                            15                          
  -------------------- ----- ---------------------- ------- --------------------- ------- --------------------- ------ ---------------------- ------ ---------------------- ------ --------------------- ------- ---------------------- ------ ---------------------- ------- ---------------------- ----- ---------------------- ------ --------------------- ------ --------------------- ----- --------------------- --

[Exposure and dose]{.underline}

The geographical distribution of total whole-body effective dose from
all "global" fallout through 1972 for a typically exposed individual
(80% indoors, 0.3 shielding factor) is shown in Figure 12. As can be
seen, the variation across the continental U.S. is relatively small,
about a factor of four for most counties, reflecting primarily
variations in precipitation. The specific mean doses for each county for
each month, year, and total are included in the database that
accompanies this report. The interested reader can estimate his/her
exposure and dose by multiplying by the appropriate indoor/outdoor and
shielding factor correction factor as discussed in the previous section.
The distribution of doses for 1962 is shown in Fig. 13 to illustrate the
variation during a period of heavy testing when short-lived
radionuclides contributed most of the exposure.

The relative impact as a function of time was investigated by
calculating the population exposure for each county (the product of the
average exposure for a given county multiplied by its population) and
then summing over all counties. The annual population exposure versus
year of exposure is given in Table 9. The per capita dose (population
exposure divided by total population) is also shown. The corresponding
estimates for NTS fallout from Beck (1999) are also shown for
comparison.

From Table 9, one sees that the total and per capita population dose
from external radiation through 2000 was about 50% higher than that from
NTS fallout. The per capita dose to an average-exposed individual was
0.73 mSv. The UNSCEAR, 1993 estimate a population-weighted dose from
"global" fallout in the latitude band 40-50 degrees to be about 1 mSv.
Considering the variations in fallout with latitude discussed earlier in
this report, the present doses estimate and the UNSCEAR estimate agree
well. The highest annual per capita doses occurred in 1962 and 1963 and
are comparable to the annual per capita doses from NTS fallout in 1952,
1953, 1955 and 1957. In fact the total population dose from "global"
fallout through 1972 was comparable to that from the NTS for the same
period.

Table 9: Population dose and per capita dose to typically-exposed
individuals versus year of exposure

#######  {#section-2 .unnumbered}

####### [Year "Global" Fallout NTS Fallout \*]{.underline}  {#year-global-fallout-nts-fallout .unnumbered}

[Pop. dose Per cap. dose Pop. dose Per cap. dose]{.underline}

([10^3^person-Sv)]{.underline} ([mSv)]{.underline}
([10^3^person-Sv)]{.underline} ([mSv)]{.underline}

1951 6.5 0.039

1952 15 0.093

1953 7.7 0.007 19 0.12

1954\* 2.8 0.017 0.2 0.001

1955 1.0 0.006 12 0.072

1956\* 4.1 0.025 0.1 0.001

1957 4.9 0.030 20 0.12

1958\* 6.8 0.042 0.8 0.005

1959 7.7 0.047 -

1960 1.6 0.010 -

1961 3.3 0.020

1962 14.5 0.089 4.7 0.029

1963 12.6 0.077

1964 5.9 0.036

1965 3.7 0.023

1966 2.8 0.019

1967 2.4 0.015

1968 2.3 0.014

1969 2.1 0.013

1970 2.0 0.012

1971 1.8 0.011

1972 1.8 0.011

1973-2000 34.4 0.211 0.45 (1963-2000)

Total 119 0.73 80 0.49

\*From Beck (1999). Based on 1960 population of 1.63 x 10^8^

A large number of fission products are produced in a nuclear explosion.
However, only a relatively few account for most of the external
exposure. Table 10 shows the largest contributors to total integrated
exposure (% of total integrated exposure from nuclide and decay
products). The global fallout percentages vary only slightly with
location but vary significantly from year to year as shown in Figure 14.
Figure 15 shows the per capita dose that resulted from each radionuclide
as a function of time. The short-lived radionuclides have been grouped.
As can be seen, during periods of testing the shorter-lived isotopes
contribute relatively more to the dose while for years with no testing
the longer-lived radionuclides are dominant. In contrast to the doses
from NTS fallout, very short-lived radionuclides such as Te-I-132 and
I-131 were insignificant contributors to exposure rates while Zr-Nb-95
accounted for a large portion of the exposure. For NTS fallout, Zr-Nb-95
was significant only at large distances from the NTS (Beck, 1999). Most
of the cumulative dose from "global" fallout was due to Zr-Nb-95 and the
longer-lived nuclides. Cs-137 and Zr-Nb-95 accounted for about 70% of
the cumulative population exposure (see Table 9). In contrast, Cs-137
contributed only a small amount of (about 2%) of the integral dose from
NTS fallout (Beck, 1999).

[Table 10: Percentage of total integral exposure contributed by various
fission products]{.underline}

[Global Fallout (1953-2000) NTS\*]{.underline}

[Nuclide (%) (%)]{.underline}

Te-I-132 \<1 20-30

Ba-La-140 7 20-50

I-133 \<\<1 \<1-10

Np-239 \<\<1 3-6

Zr-Nb-95 26 5-20

Zr-Nb-97, 97m \<\<1 \<1-6

I-135 \<\<1 \<1-5

Ru-103 3 3-10

I-131 \<1 3-4

Cs-137 45 1-3

Ru-106 6 \<\<1

Sb-125 4 \<\<1

Ce-Pr-144 2 \<\<1

Mn-54 6 0

Ce-141 \<1 \<1

\*Depends on distance from NTS (see Beck, 1999)

Since, as discussed earlier, the estimates in this report are based on a
relatively crude model(s) and there are large uncertainties,
particularly, in the ratios of deposition for the short-lived
radionuclides. The average monthly exposure rates calculated for various
counties across the U.S. agreed quite well with actual measurements of
fallout exposure rates made at sites in those counties using in situ
gamma ray spectrometry, at least during 1962 and 1963 when the "global"
fallout exposure rates were the highest. These comparisons are shown in
Table 11. Since again the model results are an average for the entire
county and the entire month of sampling while the measurements are
instantaneous point measurements at a single location, the agreement is
quite satisfying and lends confidence that the estimates for other
periods of high fallout are also reasonably valid. Even though most of
the exposure rate is due to Zr-95-Nb-95 and Cs-137, one can assume that
the contributions to dose from other nuclides have not been drastically
under- or over-estimated.

#####   {#section-3 .unnumbered}

##### [Table 11: Comparison of Measured Fallout Exposure Rates with Model Estimates]{.underline} {#table-11-comparison-of-measured-fallout-exposure-rates-with-model-estimates .unnumbered}

[Location]{.underline} [Date]{.underline} [Measurement
(R/h)\*]{.underline} [Model estimate (R/h)\*]{.underline}

Butte, MT 9/27/62 2.3 1.2

Missoula, MT 9/27/62 1.6 1.6

Ellensburg, WA 9/29/62 0.5 1.4

Seattle, WA 9/29/62 2.2 1.8

Clallam City, WA 10/1-2/62 2.0 (avg. of 5 sites) 1.8

Corvalis, OR 10/3/62 1.0 2.3

Crater Lk, OR 10/4/62 2.9 1.9

Richmond, CA 10/5/62 0.7 0.5

10/12/63 1.4 1.2

Felton, CA 10/6/62 1.1 0.9

Santa Cruz, CA 10/6/62 1.0 0.9

Sunnyvale, CA 10/6/62 0.7 0.7

10/12/63 0.4 1.4

Reno, NV 10/7/63 1.0 2.4

Winnemucca, NV 10/8/62 1.2 0.9

Elko, NV 10/8/62 1.8 2.2

10/8/63 2.5 2.6

Wendover, UT 10/8/62 1.9 2.2

Salt Flats nr. Wend. 10/9/62 3.1 2.2

10/16/63 1.7 1.8

Rawlins, WY 10/10/63 1.6 1.5

Laramie, WY 10/10/62 4.1 2.5

10/8/63 3.6 1.8

Ft. Collins, CO 10/10/62 2.1 2.6

Denver, CO 10/10/62 1.6 (avg. of 5 sites) 2.2

10/19/63 1.0 (avg. of 6 sites) 1.8

Colo. Springs, CO 10/11/62 2.7 (avg. of 2 sites) 2.3

10/20/63 1.6 (avg. of 4 sites) 2.2

La Junta, CO 10/11/62 2.0 1.7

Dodge City, KS 10/12/62 3.1 2.4

10/21/63 2.2 1.8

Wichita, KS 10/12/62 3.6 3.5

Kansas City, MO 10/13/62 4.1 3.6

Hannibal, MO 10/13/62 4.1 4.5

Springfield, IL 10/14/63 3.8 2.3

Franklin Pk., IL 10/22/63 2.5 2.5

Argonne Lab 10/15/62 2.5 2.8

10/3/63 3.1 (2 sites) 2.8

Somerset, PA 10/16/62 3.6 3.6

10/1/63 6.8 2.3

[Location]{.underline} [Date]{.underline} [Measurement
(R/h)\*]{.underline} [Model estimate (R/h)\*]{.underline}

Carlisle, PA 4/5/63 4.4 3.8

10/1/63 1.9 1.8

Decatur, AL 4/7/63 6.0 6.0

Memphis, TN 4/8/63 5.0 5.3

Little Rock, AR 4/9/63 6.6 3.9

Houston, TX 4/10/63 5.6 1.8

Galveston, TX 4/10/63 0.5 1.2

Lake Chas., LA 4/14/63 5.2 3.1

Bay Minette, LA 4/13/63 4.6 3.2

Macon, GA 4/16/63 4.3 4.4

Aiken, SC 4/17/63 6.6 4.7

US25&SC19, SC 4/17/63 4.2 (5 sites) 4.7

Nr. Warrenton, NC 4/18/63 4.1 3.8

Madison, WI 9/22/62 2.6 3.0

Spring Valley, MN 9/22/62 2.6 3.8

10/3/63 2.4 3.4

Sioux Falls, SD 9/23/62 5.1 (2 sites0 4.0

10/5/63 3.6 2.6

Chamberlain, SD 9/23/62 4.6 4.2

10/6/63 3.6 2.9

Murdo, SD 9/24/62 3.6 5.0

10/6/63 3.7 3.0

Rapid City, SD 9/24/62 3.8 (2 sites) 5.3

10/17/63 2.8 3.8

Spearfish, SD 9/24/62 3.7 6.6

Sundance, WY 9/25/62 2.3 5.2

10/7/63 2.7 3.1

Moorecroft, WY 9/25/62 2.3 5.2

10/7/63 2.7 3.1

Pelham, NY 8/63 3-5 (multiple measurements) 3.9

\*Measurement results from Beck et al, (1963, 1966).

The model results are the average for the county and for the month of
sampling. The measurement results are for a specific date and place(s).
Measurement error was on the order of 0.2-0.4 R/hr. Thus the lack of
agreement for any individual measurement-model pair could just reflect
changes in deposition density during the month, the site precipitation
not being representative of the county average, or the site itself not
being representative of the general area.

The doses discussed above are from gamma irradiation. As discussed in
Beck (1999), the ICRU (1997) estimated the beta skin dose rate from a
plane source of fission products to be about 8-16 times the total
effective dose. In Beck (1999), the ratio of dose rates for a 0.1-cm
relaxation length for early arrival times was estimated to be about 3-5.
The age (arrival time) of "global" fallout compared to NTS fallout was
very long and most of the dose was delivered over a long period of time
during which the longer-lived radionuclides penetrated further into the
soil. It can thus be assumed that the beta skin dose from "global"
fallout was even less significant than that estimated for NTS fallout.
This is particularly true since most of the global fallout was deposited
during rain and the assumption of a 0.1-cm relaxation length for the
first 30 days is thus probably conservative. Only a relatively few
longer-lived nuclides emitting higher energy beta rays such as Y-90, the
daughter of Sr-90, contribute significantly to the dose.

The actual impact of beta exposure is of course even less than estimated
by the ICRU. The average individual would be exposed to beta radiation
only for the 20% of time spent outdoors, resulting in an actual beta
skin dose to gamma whole body dose ratio of about 0.2-0.4. Furthermore,
since the radio-sensitivity of the skin is generally accepted to be much
lower than for other organs, even the beta dose to the most exposed
individuals who spend up to 70% of their time outdoors can be considered
insignificant compared to their whole-body gamma exposure.

One source of beta radiation exposure that might be significant for
"global" fallout in some cases is contamination to the skin from
children playing in contaminated soil, both from soil adhering to the
skin as well as due to a closer proximity to the source. The dose to a
child playing on the ground would probably be about a factor of two
higher than that to a standing adult due to the closer proximity to the
source plane. However, this would still probably not constitute a
significant exposure. A more significant exposure route would likely be
direct ingestion of soil (NCRP, 1999).

**Recommendations for Future Work and for Improving the Preliminary
Estimates of This Feasibility Study**

As is evident from the discussions above, the models used to estimate
exposure rates and deposition densities are quite crude and monthly and
individual county estimates may have large uncertainties particularly
estimates for short-lived radionuclides such as I-131. Comparisons with
soil sample analyses and in situ gamma spectrometric estimates of
exposure rates suggest that the overall geographical distribution of
external dose to the U.S. population, and the per capita or population
dose, are probably quite reasonable. The per capita dose is also
consistent with previous estimates made for residents of the mid
latitudes of the Northern Hemisphere by the UNSCEAR (1993). Because most
of the external dose was delivered after 1956, at least some data was
available for the more important contributors to dose upon which to base
the estimates.

However, the analysis carried out for this preliminary study suggests
that considerable improvement could be made. This might allow more
accurate estimates of deposition densities and doses for particular
months to be made, particularly for years prior to 1958, as well as more
accurate predictions of the geographical variation for any particular
time. For example, by weighting the various precipitation measurements
in a given county by the population one might be able to calculate a
population-weighted Sr-90 deposition density that in turn would allow a
better estimate of the dose to a typical resident of that county than
the present estimate. An analysis of the gummed-film data for the years
prior to 1958, in a manner similar to that carried out for NTS fallout,
might also allow better estimates of deposition as a function of
location for years prior to 1958. A further assessment of the variations
in precipitation within counties might identify some populations that
were exposed to much higher doses than presently estimated ("hotspots").
Areas with large amounts of thunderstorm activity during months of
testing could be identified since this was believed to be one mechanism
that resulted in high fallout of short-lived radionuclides such as
I-131.

By assigning reasonable estimates of uncertainty and variability to
critical parameters for each of the steps used in this preliminary
study, one could estimate a confidence limit for the estimated monthly
doses for each county in a manner similar to that provided by NCI
(1997). Without such a systematic analysis it is difficult to assess the
validity of any particular county's monthly dose estimate.

In addition to estimating the uncertainties in the various deposition
and exposure estimates, the estimates themselves might be improved if
additional data can be located, particularly data on the ratios of the
deposition of the various nuclides as a function of location in the U.S.
Additional data could also be used to develop a more sophisticated,
higher resolution, model of the distribution of Sr-90 specific activity
with latitude and longitude. This might be accomplished using a
technique such as kriging to provide estimates of specific activity that
vary smoothly across the country. A more sophisticated model would also
attempt to account for the impact of "dry" deposition at arid locations.
A thorough review and assessment of the vast amount of other scattered
sources of data might also allow the estimates of isotopic ratios for
particular months to be improved. It may also allow improvements to the
atmospheric model, which would then allow one to more confidently
utilize the model for periods with no data. Because the current effort
was limited in scope and resources, only a small subset of the vast
literature could be evaluated and utilized.

I-131 may have been a significant contributor to ingestion dose. The
present preliminary results suggest I-131 deposition was comparable to
that from the NTS in many areas of the country. However, due to the lack
of actual data, a much more comprehensive effort will be necessary to
provide estimates of I-131 deposition density and associated uncertainty
comparable to those estimated for NTS fallout. This effort would include
development of a model for the likely geographical variation in the
deposition of short-lived radionuclides across the U.S.

The estimates in this report do not include the impact from tests
conducted after 1963 by China and France. The atmospheric tests by China
in particular, although the total fission yield was only about 20 MT,
were conducted at mid latitudes in the Northern Hemisphere and did
result in additional exposures to the continental U.S. population during
the 1970s and early 1980s.

A number of minor contributors to external exposure were not considered
in this preliminary assessment. Small quantities of Co-60, an activation
product, were measured in fallout at some sites during 1962-63, as were
small quantities of Sb-124 and Cs-134. Small quantities of radioactive
tracers were also released during tests in 1958 (W-185) and 1962
(Rh-102). None of these nuclides are believed to have contributed
significantly to population doses. Also not considered in this study was
the deposition of a few radionuclides that may contribute in a minor way
to ingestion exposure such as Fe-55, Pu-239+240, Pu-241, Am-241 and
Tc-99.

An additional possibility for further study would be to also estimate
the doses to the populations of Alaska and Hawaii. These states were not
included in the present analysis since they represent special unique
situations: Hawaii due to its proximity to the Pacific weapons testing
area and Alaska due to its proximity to Soviet testing sites.

The scope of work for this project requested an estimate of the time
(resources) that would be required for each of the suggested
improvements discussed above. It is difficult to make such an estimate
at the present time. It should be noted that the NCI project to estimate
the exposure of the U.S. population from I-131 required a large number
of person-years of effort. An effort at least as comprehensive would be
required to provide estimates of equal quality for "global" fallout
along with credible estimates of uncertainty. A thorough search for
additional data might require the assessment of data provided in a large
subset of the thousands of publications and reports that have been
published on aspects of "global" fallout. Development of more
sophisticated models and assignment of realistic uncertainty estimates
would be dependent on such on assessment of all retrievable data. A
critical question that must be answered first is how fine a spatial and
temporal resolution is desired. The present study indicates that a
temporal resolution on the order of a month is reasonable and feasible
but that for some counties, the spatial variation across the county may
be very large and difficult to quantity.

**Summary and Conclusions**

Fallout from atmospheric tests resulted in a per capita external
radiation exposure of about 0.7 mSv to the population of the U.S.
through the year 2000, about 1½ times that incurred from NTS fallout.
However, residents in the states immediately downwind from the NTS
received much higher than average exposures from NTS fallout while the
exposures in the western and northwestern U.S. and some areas of the
Midwest and SE were much less than the average. The doses from "global"
fallout were more uniformly distributed across the U.S. with differences
from place to place reflecting differences in average precipitation.

Annual per capita doses from "global" fallout were comparable to annual
doses from NTS fallout during the years of testing. However, most of the
exposure from the NTS tests occurred with the first 3 weeks of each test
and was due to relatively short-lived radionuclides. In contrast, the
exposure from "global" fallout occurred over a much greater span of time
and was primarily from Zr-Nb-95 and a few long-lived radionuclides. Thus
the dose rate was more uniform with time. Almost the entire whole-body
effective dose to the population was from gamma rays emitted by fission
products deposited on the ground. The actual dose received by any
individual depended on the fraction of time he/she spent outdoors and
the degree of shielding provided by his/her dwelling. The most exposed
individuals at any particular location would have been outdoor workers
or others who spent most of their day outdoors. The locations with the
highest dose rates were those areas with high average annual
precipitation. Beta radiation from fission products in the surface soil
did result in additional dose to the skin when outdoors. However, this
contribution was not large enough to be considered an important
component of total fallout radiation and for "global" fallout was
probably even less significant than it was for NTS fallout exposure. The
only significant possible impact might have been for children who played
in the soil for significant intervals of time.

The deposition of fission products contributed to internal radiation
exposure via ingestion as well as external exposure. The deposition
densities of several nuclides that could contribute significantly to
ingestion doses were calculated for this study although the internal
doses via ingestion will be treated in a separate report.

Comparisons with soil sample data and exposure rate measurements at a
large number of sites in the U.S. during 1963-65 indicate that the model
predictions reliably represent the overall pattern of total fallout and
resultant population doses. Due to the sparseness of data prior to 1956,
estimates of deposition and doses for 1953-56 are more uncertain than
for years where fallout was monitored more extensively. However, the
contribution to the total population dose from fallout in those years
was relatively small.

This report has demonstrated that it is feasible to grossly estimate the
external exposure of the population of the U.S. as a function of
location and time. However, the monthly estimates for any particular
county are probably quite uncertain and the exposure rate probably
varied significantly from place to place within a county, particularly
for counties with large variations in topography. If more precise
estimates of exposure are required for particular times and places, a
more exhaustive study will be required. Such a study would need to carry
out an intensive investigation to locate and evaluate additional
measurement data, particularly for the shorter-lived radionuclides. A
more sophisticated model would need to be developed those accounts for
variations in the specific activity of Sr-90 deposition with latitude
and longitude and accounts for any variations in this quantity with
time. Geographic variations in isotopic ratios need to be investigated
in greater detail, especially for the shorter-lived radionuclides such
as I-131 that likely contributed significantly to ingestion doses to
children. Variations in precipitation across a given county will also
need to be considered in much more detail in order to obtain a better
estimate of dose rates to an individual living in any particular county.
Finally, uncertainty estimates need to be incorporated into the various
components of the dose assessment model used here in order to allow
reasonable estimates to be made of the relative uncertainties in the
estimates as a function of location and time.

The database annex to this report, in the form of Excel spreadsheet
files, gives the calculated deposition densities of all the
radionuclides considered for each test for each county of the U.S. The
whole-body effective dose to a typically exposed adult for each month is
also tabulated for each county. By accessing the data for their
particular county of residence for any given year(s), and applying the
appropriate correction factor to adjust the tabulated doses for the
actual fraction of time spent outdoors, the interested reader can
estimate his/her whole body dose for any particular time interval and
location.

**List of Figures**

Figure 1: Estimated fission yield of tests conducted by the U.S., U.K.
and U.S.S.R. for each month from 1952 through 1962.

Figure 2: HASL and NRL Precipitation and Air Sampling Sites in 1962.

Figure 3: Variation of Sr-90 deposition density per unit precipitation
with latitude. Cumulative deposition of Sr-90 along a constant
precipitation transect.

Figure 4: Variation of Sr-90 Deposition Density per cm of rain with
longitude. The ordinate values for the deposition data have been
normalized to those for the soil data since the soil data represent
cumulate deposition at the time of sampling.

Figure 5: Specific activity of Sr-90 in precipitation (deposition
density per cm of rain) for N.E. U.S. baseline sites for each month from
1953-1965.

Figure 6a-6f. Comparisons of monthly model estimates of Sr-90 deposition
density with measurements for selected cities. The model estimate is the
average for the entire county in which the measurement site is located.

Figure 7: Estimated deposition density ratio of Zr-95 to Sr-90 for each
month from 1953-1965.

Figure 8: Total Cs-137 deposited from 1953-72 in each county.

Figure 9: Total deposition of Zr-95+Nb-95 from 1953-1965 for each
county.

Figure 10: Annual population-weighted deposition density of Cs-137 and
cumulative activity in soil at the end of each year.

Figure 11: Annual population-weighted deposition density of Zr-95.

Figure 12: Dose received by typically exposed adults for each county
during 1962.

Figure 13: Fraction (%) of total annual population dose from each
radionuclide; 1953-1972.

Figure 14: Monthly variations in Per Capita Dose from specific
radionuclides. The short-lived radionuclides (I-131, Ba-La-140, Ru-103,
and Ce-141) are grouped together.

![](media/image1.wmf){width="7.9006944444444445in"
height="4.497916666666667in"}

> Figure 1: Estimated fission yield of tests conducted by the U.S., U.K.
> and U.S.S.R. for each month from 1952 through 1962.

![](media/image2.png){width="8.10625in" height="5.604861111111111in"}

> Figure 2: HASL and NRL Precipitation and Air Sampling Sites in 1962.

![](media/image3.png)

![](media/image4.wmf)

> Figure 4: Variation of Sr-90 Deposition Density per cm of rain with
> longitude. The ordinate values for the deposition data have been
> normalized to those for the soil data since the soil data represent
> cumulate deposition at the time of sampling.

.

![](media/image5.wmf){width="8.268055555555556in" height="5.5in"}

Figure 5: Specific activity of Sr-90 in precipitation (deposition
density per cm of rain) for N.E. U.S. baseline sites for each month from
1953-1965.

![](media/image6.wmf){width="6.67007874015748in"
height="2.7263779527559056in"}![](media/image7.wmf){width="6.698425196850394in"
height="2.745275590551181in"}![](media/image8.wmf){width="6.688976377952756in"
height="2.7263779527559056in"}Figure 6a-6f. Comparisons of monthly model
estimates of Sr-90 deposition density with measurements for selected
cities. The model estimate is the average for the entire county in which
the measurement site is located.

![](media/image9.wmf){width="7.2in"
height="2.8598425196850394in"}![](media/image10.wmf){width="7.2in"
height="2.9in"}![](media/image11.wmf){width="7.200787401574803in"
height="2.87992125984252in"}.

![](media/image12.wmf){width="7.601388888888889in"
height="5.059027777777778in"}

Figure 7: Estimated deposition density ratio of Zr-95 to Sr-90 for each
month from 1953-1965.

Figure 8: Total Cs-137 deposited from 1953-72 in each county.

![](media/image13.png){width="8.461023622047245in"
height="5.75in"}![](media/image14.png){width="2.2255905511811025in"
height="1.0881889763779529in"}

Figure 9: Total deposition of Zr-95+Nb-95 from 1953-1965 for each
county.

![](media/image15.png){width="8.5in"
height="5.8in"}![](media/image16.png){width="2.3173228346456693in"
height="1.0279527559055117in"}.

![](media/image17.wmf){width="7.740277777777778in"
height="5.8805555555555555in"}

> Figure 10: Annual population-weighted deposition density of Cs-137 and
> cumulative activity in soil at the end of each year.

![](media/image18.wmf){width="7.959027777777778in"
height="4.886111111111111in"}

Figure 11: Annual population-weighted deposition density of Zr-95.

.

> Figure 12: Dose received by typically exposed adults for each county
> during 1962.

![](media/image19.png){width="8.4in"
height="5.195669291338582in"}![](media/image20.png){width="0.9783464566929134in"
height="0.99251968503937in"}

![](media/image21.wmf){width="7.9006944444444445in"
height="4.897222222222222in"}

> Figure 13: Fraction (%) of total annual population dose from each
> radionuclide; 1953-1972.
>
> ![](media/image22.wmf){width="9.125694444444445in"
> height="6.080555555555556in"}Figure 14: Monthly variations in Per
> Capita Dose from specific radionuclides. The short-lived radionuclides
> (I-131, Ba-La-140, Ru-103, and Ce-141) are grouped together.

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**Appendix 1: Nuclide Ratios Used in This Preliminary Assessment**

  --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  [Month]{.underline}   [95/90]{.underline}   [103/90]{.underline}   [106/90]{.underline}   [125/90]{.underline}   [131/90]{.underline}   [140/90]{.underline}   [141/90]{.underline}   [144/90]{.underline}   [54/90]{.underline}   [Nb/Zr]{.underline}
  --------------------- --------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- ---------------------- --------------------- ---------------------
                                                                                                                                                                                                                                     

  Jan-53                77.08                 76.33                  17.09                  1.14                   2.56                   31.03                  68.45                  28.00                  2.18                  0.90

  2                     47.69                 42.94                  16.19                  1.12                   0.14                   5.11                   29.80                  23.00                  1.73                  1.20

  3                     33.54                 31.61                  15.66                  1.10                   0.00                   0.00                   19.37                  20.00                  1.39                  1.50

  4                     23.00                 12.58                  15.13                  1.09                   0.00                   0.00                   10.00                  19.00                  1.12                  1.60

  5                     15.00                 5.99                   13.64                  1.08                   0.00                   0.00                   6.00                   18.00                  0.93                  1.80

  6                     10.00                 2.31                   10.94                  1.08                   0.00                   0.00                   3.00                   17.00                  0.73                  1.90

  7                     7.00                  1.69                   10.07                  1.06                   0.00                   0.00                   2.00                   15.00                  0.72                  1.90

  8                     36.65                 34.31                  8.93                   1.04                   40.13                  83.03                  40.40                  13.00                  1.33                  2.00

  9                     54.51                 51.84                  13.50                  1.04                   43.64                  116.39                 70.46                  22.00                  1.23                  2.10

  10                    30.20                 23.45                  12.24                  1.01                   3.47                   20.19                  28.90                  18.00                  1.06                  2.10

  11                    13.88                 13.94                  10.83                  0.97                   0.14                   2.26                   15.00                  14.00                  0.94                  2.10

  12                    5.59                  8.78                   9.67                   0.94                   0.01                   0.21                   8.00                   11.00                  0.84                  2.10

  Jan-54                2.40                  5.54                   8.60                   0.91                   0.00                   0.02                   4.00                   9.00                   0.77                  2.10

  2                     1.29                  3.62                   8.99                   0.89                   0.00                   0.00                   2.00                   9.00                   0.72                  2.10

  3                     32.00                 62.01                  11.67                  0.98                   52.12                  146.42                 46.12                  13.00                  0.87                  0.50

  4                     58.00                 92.87                  14.18                  1.06                   50.69                  158.86                 75.84                  18.00                  0.93                  0.70

  5                     73.00                 102.77                 15.88                  1.10                   68.87                  186.57                 93.41                  22.00                  1.25                  0.70

  6                     59.00                 74.14                  15.58                  1.10                   12.01                  63.15                  60.24                  21.00                  1.18                  0.90

  7                     41.00                 43.47                  14.85                  1.08                   0.82                   11.81                  29.83                  19.00                  1.03                  1.20

  8                     28.00                 25.16                  13.97                  1.06                   0.05                   2.11                   14.55                  17.00                  0.90                  1.50

  9                     28.00                 24.12                  13.63                  1.05                   16.60                  35.28                  22.48                  17.00                  0.76                  1.60

  10                    23.00                 18.06                  13.00                  1.04                   6.63                   19.77                  17.08                  16.00                  0.68                  1.80

  11                    15.00                 10.65                  12.90                  1.02                   3.44                   9.72                   8.20                   15.00                  0.64                  1.90

  12                    9.00                  4.39                   11.78                  1.00                   0.00                   0.00                   2.38                   13.00                  0.61                  1.90

  Jan-55                6.00                  2.58                   11.24                  0.98                   0.00                   0.00                   1.00                   12.00                  0.57                  2.00

  2                     4.00                  1.41                   10.52                  0.96                   0.00                   0.00                   0.64                   11.00                  0.54                  2.10

  3                     2.00                  0.41                   10.63                  0.95                   0.00                   0.00                   0.30                   11.00                  0.49                  2.10

  4                     0.00                  0.00                   9.79                   0.93                   0.00                   0.00                   0.00                   10.00                  0.46                  2.20

  5                     0.00                  0.00                   9.91                   0.92                   0.00                   0.00                   0.00                   10.00                  0.43                  2.20

  6                     0.00                  0.00                   9.09                   0.90                   0.00                   0.00                   0.00                   9.00                   0.40                  2.20

  7                     0.00                  0.00                   8.26                   0.88                   0.00                   0.00                   0.00                   8.00                   0.38                  2.20

  8                     0.00                  0.00                   8.37                   0.87                   0.00                   0.00                   0.00                   8.00                   0.36                  2.20

  9                     0.00                  0.00                   7.49                   0.85                   0.00                   0.00                   0.00                   7.00                   0.34                  2.20

  10                    0.00                  0.79                   6.55                   0.83                   0.31                   1.00                   0.53                   6.00                   0.32                  2.20

  11                    25.00                 4.02                   9.32                   0.90                   5.86                   13.00                  6.16                   15.00                  0.68                  0.50

  12                    42.00                 37.01                  8.89                   0.88                   14.12                  56.00                  52.50                  14.00                  0.77                  0.90

  Jan-56                18.00                 13.34                  8.14                   0.85                   0.87                   8.00                   17.20                  12.00                  0.75                  1.20

  2                     32.00                 19.41                  7.08                   0.83                   0.17                   4.00                   22.57                  10.00                  0.70                  1.50

  3                     50.00                 29.90                  11.27                  0.82                   10.54                  23.00                  27.34                  16.00                  0.72                  1.60

  4                     25.00                 13.14                  8.49                   0.81                   2.10                   7.00                   10.32                  12.00                  0.71                  1.80

  5                     14.00                 14.77                  6.13                   0.82                   23.04                  47.00                  16.64                  9.00                   0.87                  0.50

  6                     11.00                 15.54                  3.93                   0.89                   18.42                  43.00                  15.06                  6.00                   1.38                  0.70

  7                     38.00                 65.95                  8.75                   0.99                   70.94                  171.00                 52.12                  12.00                  1.49                  0.70

  8                     24.00                 35.51                  6.61                   0.98                   11.47                  45.00                  25.89                  9.00                   1.45                  0.90

  9                     87.00                 96.78                  7.48                   0.98                   66.07                  167.00                 103.44                 12.00                  1.40                  0.90

  10                    61.00                 54.72                  7.52                   0.96                   6.18                   35.00                  53.10                  12.00                  1.48                  1.00

  11                    48.00                 37.19                  8.78                   0.94                   17.21                  40.00                  37.84                  14.00                  1.62                  1.20

  12                    37.00                 29.27                  12.47                  0.94                   20.69                  52.00                  36.61                  21.00                  1.66                  1.50

  Jan-57                40.00                 27.04                  8.44                   0.92                   8.49                   28.00                  31.88                  14.00                  1.60                  1.60

  2                     43.00                 23.91                  13.70                  0.90                   3.01                   13.00                  25.32                  22.00                  1.54                  1.80

  3                     32.00                 18.00                  9.35                   0.89                   11.40                  26.00                  20.96                  15.00                  1.47                  1.90

  4                     27.00                 20.57                  11.89                  0.91                   31.29                  68.00                  36.67                  23.00                  1.39                  1.90

  5                     47.00                 18.33                  8.63                   0.89                   11.50                  44.00                  33.00                  17.00                  1.39                  2.00

  6                     35.00                 11.05                  8.58                   0.87                   4.16                   10.00                  17.00                  16.00                  1.27                  2.10

  7                     25.00                 6.13                   10.67                  0.90                   0.85                   2.00                   9.00                   21.00                  1.03                  2.10

  8                     87.00                 56.57                  10.56                  0.90                   85.03                  195.00                 80.00                  21.00                  1.08                  2.20

  9                     82.00                 141.01                 12.00                  0.96                   102.38                 243.00                 170.00                 23.00                  1.10                  2.20

  10                    73.00                 75.83                  9.11                   0.97                   47.28                  141.00                 95.00                  18.00                  1.14                  0.60

  11                    32.00                 28.36                  9.60                   1.01                   27.00                  66.00                  40.00                  21.00                  2.12                  0.60

  12                    38.00                 27.03                  9.23                   0.97                   4.76                   25.00                  35.00                  20.00                  2.13                  0.80

  Jan-58                37.00                 36.39                  9.50                   0.93                   1.10                   7.00                   42.00                  20.00                  1.95                  0.90

  2                     30.00                 15.38                  10.08                  0.91                   16.01                  30.00                  19.00                  21.00                  1.85                  1.20

  3                     34.00                 32.04                  9.76                   0.99                   32.48                  78.00                  47.00                  22.00                  2.08                  1.00

  4                     38.00                 30.93                  11.15                  0.98                   6.66                   25.00                  42.00                  25.00                  2.17                  1.00

  5                     20.00                 15.82                  11.17                  1.01                   23.95                  54.00                  16.00                  22.00                  2.11                  1.00

  6                     16.00                 24.36                  13.53                  1.04                   22.08                  53.00                  20.00                  23.00                  1.80                  1.00

  7                     18.00                 49.59                  14.13                  1.07                   28.33                  70.00                  36.00                  21.00                  1.59                  1.00

  8                     17.00                 44.24                  14.97                  1.06                   5.97                   20.00                  31.00                  22.00                  1.58                  1.00

  9                     78.00                 55.23                  11.71                  1.06                   50.12                  118.00                 66.00                  21.00                  2.14                  1.00

  10                    82.00                 64.11                  15.48                  1.08                   69.12                  160.00                 90.00                  32.00                  2.00                  1.20

  11                    27.00                 109.30                 10.66                  1.09                   18.96                  65.00                  150.00                 23.00                  2.13                  1.50

  12                    27.00                 60.40                  14.80                  1.06                   3.59                   33.00                  74.00                  31.00                  2.30                  1.60

  Jan-59                70.00                 44.16                  11.85                  1.03                   0.28                   7.00                   48.00                  24.00                  2.31                  1.80

  2                     50.00                 23.72                  14.19                  1.01                   0.03                   2.00                   23.00                  28.00                  2.23                  1.90

  3                     35.00                 16.01                  9.00                   0.99                   0.00                   0.00                   14.00                  22.00                  2.18                  1.90

  4                     22.00                 11.43                  9.00                   0.98                   0.00                   0.00                   9.00                   13.00                  2.09                  2.00

  5                     15.00                 2.83                   10.00                  0.96                   0.00                   0.00                   2.00                   19.00                  1.97                  2.10

  6                     10.00                 3.16                   9.56                   0.94                   0.00                   0.00                   2.00                   18.00                  1.85                  2.10

  7                     7.00                  1.76                   8.06                   0.93                   0.00                   0.00                   1.00                   15.00                  1.75                  2.20

  8                     5.00                  1.97                   5.99                   0.91                   0.00                   0.00                   1.00                   11.00                  1.64                  2.20

  9                     4.00                  0.00                   6.12                   0.89                   0.00                   0.00                   0.00                   11.00                  1.54                  2.20

  10                    3.00                  0.00                   4.58                   0.87                   0.00                   0.00                   0.00                   8.00                   1.43                  2.20

  11                    2.00                  0.00                   4.71                   0.86                   0.00                   0.00                   0.00                   8.00                   1.33                  2.20

  12                    1.00                  0.00                   3.05                   0.84                   0.00                   0.00                   0.00                   5.00                   1.22                  2.20

  Jan-60                0.00                  0.00                   5.65                   0.82                   0.00                   0.00                   0.00                   9.00                   1.13                  2.20

  2                     0.00                  0.00                   5.25                   0.82                   0.00                   0.00                   0.00                   8.00                   1.02                  2.20

  3                     0.00                  0.00                   4.62                   0.80                   0.00                   0.00                   0.00                   7.00                   0.97                  2.20

  4                     0.00                  0.00                   3.96                   0.78                   0.00                   0.00                   0.00                   6.00                   0.93                  2.20

  5                     0.00                  0.00                   4.01                   0.76                   0.00                   0.00                   0.00                   6.00                   0.88                  2.20

  6                     0.00                  0.00                   3.39                   0.75                   0.00                   0.00                   0.00                   5.00                   0.83                  2.20

  7                     0.00                  0.00                   3.43                   0.74                   0.00                   0.00                   0.00                   5.00                   0.78                  2.20

  8                     0.00                  0.00                   2.78                   0.72                   0.00                   0.00                   0.00                   4.00                   0.74                  2.20

  9                     0.00                  0.00                   2.83                   0.71                   0.00                   0.00                   0.00                   4.00                   0.69                  2.20

  10                    0.00                  0.00                   2.89                   0.69                   0.00                   0.00                   0.00                   4.00                   0.65                  2.20

  11                    0.00                  0.00                   2.21                   0.68                   0.00                   0.00                   0.00                   3.00                   0.60                  2.20

  12                    0.00                  0.00                   3.01                   0.67                   0.00                   0.00                   0.00                   4.00                   0.56                  2.20

  Jan-61                0.00                  0.00                   3.07                   0.65                   0.00                   0.00                   0.00                   4.00                   0.52                  2.20

  2                     0.00                  0.00                   3.12                   0.64                   0.00                   0.00                   0.00                   4.00                   0.49                  2.20

  3                     0.00                  0.00                   2.37                   0.63                   0.00                   0.00                   0.00                   3.00                   0.46                  2.20

  4                     0.00                  0.00                   2.40                   0.62                   0.00                   0.00                   0.00                   3.00                   0.44                  2.20

  5                     0.00                  0.00                   2.44                   0.61                   0.00                   0.00                   0.00                   3.00                   0.41                  2.20

  6                     0.00                  0.00                   3.30                   0.60                   0.00                   0.00                   0.00                   4.00                   0.38                  2.20

  7                     0.00                  0.00                   4.19                   0.58                   0.00                   0.00                   0.00                   5.00                   0.36                  2.20

  8                     0.00                  0.00                   4.00                   0.57                   0.00                   0.00                   0.00                   4.10                   0.34                  2.20

  9                     132.00                138.55                 10.00                  0.97                   240.03                 500.00                 215.00                 25.00                  1.25                  0.50

  10                    175.00                188.93                 14.00                  1.60                   96.10                  250.00                 280.00                 33.00                  1.89                  0.70

  11                    150.00                76.09                  13.00                  1.60                   46.45                  120.00                 110.00                 32.00                  2.30                  0.70

  12                    110.00                73.83                  17.00                  1.60                   11.16                  75.00                  95.00                  40.00                  3.29                  0.90

  Jan-62                80.00                 31.00                  12.00                  1.40                   0.62                   12.00                  32.00                  35.00                  4.46                  1.20

  2                     55.00                 31.45                  13.00                  1.50                   0.07                   4.00                   32.00                  29.00                  5.36                  1.50

  3                     50.00                 7.68                   13.00                  1.50                   0.01                   1.00                   7.00                   37.00                  6.67                  1.60

  4                     20.00                 2.90                   13.00                  1.60                   11.88                  22.00                  3.00                   28.00                  7.25                  1.80

  5                     40.00                 5.49                   13.00                  1.60                   24.78                  56.00                  8.00                   31.00                  6.55                  0.70

  6                     30.00                 9.61                   12.00                  1.70                   17.32                  41.00                  14.00                  26.00                  6.18                  0.90

  7                     15.00                 2.82                   13.00                  1.50                   12.21                  32.00                  4.00                   22.00                  5.86                  1.00

  8                     20.00                 3.68                   11.00                  1.50                   8.92                   24.00                  5.00                   21.00                  5.87                  0.70

  9                     30.00                 14.39                  11.00                  1.60                   7.49                   22.00                  20.00                  26.00                  5.43                  0.70

  10                    45.00                 27.00                  11.00                  1.40                   43.78                  100.00                 66.00                  28.00                  4.59                  0.70

  11                    60.00                 50.00                  11.00                  1.30                   58.53                  156.00                 73.00                  30.00                  3.91                  0.70

  12                    70.00                 45.00                  12.00                  1.50                   23.91                  72.00                  61.00                  32.00                  3.93                  0.70

  Jan-63                40.00                 62.00                  11.00                  1.40                   1.99                   7.00                   34.00                  30.00                  3.87                  0.70

  2                     30.00                 41.00                  12.00                  2.40                   0.22                   2.00                   22.00                  30.00                  3.89                  0.90

  3                     25.00                 18.00                  13.00                  1.40                   0.04                   1.00                   9.00                   27.00                  3.98                  1.20

  4                     20.00                 9.89                   11.00                  1.20                   0.00                   0.00                   8.96                   24.00                  3.92                  1.50

  5                     15.00                 5.92                   9.00                   1.40                   0.00                   0.00                   4.84                   22.00                  3.77                  1.60

  6                     11.00                 3.53                   8.00                   1.60                   0.00                   0.00                   2.60                   20.00                  3.60                  1.80

  7                     8.00                  2.60                   10.00                  1.50                   0.00                   0.00                   1.72                   19.00                  3.44                  1.90

  8                     6.00                  1.40                   9.00                   1.50                   0.00                   0.00                   0.83                   15.00                  3.29                  1.90

  9                     5.00                  0.62                   8.00                   1.70                   0.00                   0.00                   0.33                   16.00                  3.11                  2.00

  10                    4.00                  0.30                   8.00                   1.30                   0.00                   0.00                   0.00                   13.00                  2.92                  2.10

  11                    3.00                  0.15                   6.00                   1.10                   0.00                   0.00                   0.00                   13.00                  2.74                  2.10

  12                    2.00                  0.08                   6.00                   1.30                   0.00                   0.00                   0.00                   14.00                  2.55                  2.10

  Jan-64                2.00                  0.05                   7.00                   1.27                   0.00                   0.00                   0.00                   16.00                  2.36                  2.10

  2                     1.00                  0.03                   6.00                   1.25                   0.00                   0.00                   0.00                   14.00                  2.21                  2.10

  3                     0.00                  0.02                   7.00                   1.22                   0.00                   0.00                   0.00                   13.00                  2.11                  

  4                     0.00                  0.01                   7.00                   1.19                   0.00                   0.00                   0.00                   12.00                  2.00                  

  5                     0.00                  0.00                   6.00                   1.17                   0.00                   0.00                   0.00                   11.00                  1.89                  

  6                     0.00                  0.00                   6.00                   1.15                   0.00                   0.00                   0.00                   11.00                  1.77                  

  7                     0.00                  0.00                   6.00                   1.12                   0.00                   0.00                   0.00                   10.00                  1.67                  

  8                     0.00                  0.00                   5.00                   1.10                   0.00                   0.00                   0.00                   9.00                   1.58                  

  9                     0.00                  0.00                   5.00                   1.08                   0.00                   0.00                   0.00                   9.00                   1.48                  

  10                    0.00                  0.00                   5.00                   1.05                   0.00                   0.00                   0.00                   8.00                   1.37                  

  11                    0.00                  0.00                   5.00                   1.03                   0.00                   0.00                   0.00                   7.00                   1.28                  

  12                                                                 5.00                   1.00                                                                                        7.00                   1.25                  

  Jan-65                                                             4.73                   1.01                                                                                        6.63                   1.20                  

  2                                                                  4.72                   0.98                                                                                        6.63                   1.17                  

  3                                                                  4.47                   0.99                                                                                        6.28                   1.12                  

  4                                                                  4.46                   0.96                                                                                        6.28                   1.10                  

  5                                                                  4.23                   0.97                                                                                        5.94                   1.05                  

  6                                                                  4.22                   0.94                                                                                        5.94                   1.03                  

  7                                                                  3.99                   0.95                                                                                        5.63                   0.98                  

  8                                                                  3.99                   0.93                                                                                        5.63                   0.96                  

  9                                                                  3.77                   0.94                                                                                        5.33                   0.92                  

  10                                                                 3.77                   0.91                                                                                        5.33                   0.90                  

  11                                                                 3.57                   0.92                                                                                        5.04                   0.86                  

  12                                                                 3.56                   0.89                                                                                        5.04                   0.84                  

  Jan-66                                                             3.37                   0.90                                                                                        4.78                   0.81                  

  2                                                                  3.36                   0.87                                                                                        4.78                   0.79                  

  3                                                                  3.18                   0.88                                                                                        4.52                   0.76                  

  4                                                                  3.18                   0.86                                                                                        4.52                   0.74                  

  5                                                                  3.01                   0.87                                                                                        4.28                   0.71                  

  6                                                                  3.00                   0.84                                                                                        4.28                   0.69                  

  7                                                                  2.84                   0.85                                                                                        4.06                   0.66                  

  8                                                                  2.84                   0.83                                                                                        4.06                   0.65                  

  9                                                                  2.69                   0.84                                                                                        3.84                   0.62                  

  10                                                                 2.68                   0.81                                                                                        3.84                   0.61                  

  11                                                                 2.54                   0.82                                                                                        3.64                   0.58                  

  12                                                                 2.53                   0.80                                                                                        3.64                   0.57                  

  Jan-67                                                             2.40                   0.80                                                                                        3.44                   0.55                  

  2                                                                  2.39                   0.78                                                                                        3.44                   0.54                  

  3                                                                  2.27                   0.79                                                                                        3.26                   0.51                  

  4                                                                  2.26                   0.77                                                                                        3.26                   0.50                  

  5                                                                  2.14                   0.77                                                                                        3.09                   0.48                  

  6                                                                  2.14                   0.75                                                                                        3.09                   0.47                  

  7                                                                  2.02                   0.76                                                                                        2.92                   0.45                  

  8                                                                  2.02                   0.74                                                                                        2.92                   0.44                  

  9                                                                  1.91                   0.75                                                                                        2.77                   0.42                  

  10                                                                 1.91                   0.72                                                                                        2.77                   0.41                  

  11                                                                 1.81                   0.73                                                                                        2.62                   0.39                  

  12                                                                 1.80                   0.71                                                                                        2.62                   0.39                  

  Jan-68                                                             1.71                   0.72                                                                                        2.48                   0.37                  

  2                                                                  1.70                   0.70                                                                                        2.48                   0.36                  

  3                                                                  1.61                   0.70                                                                                        2.35                   0.35                  

  4                                                                  1.61                   0.68                                                                                        2.35                   0.34                  

  5                                                                  1.53                   0.69                                                                                        2.22                   0.32                  

  6                                                                  1.52                   0.67                                                                                        2.22                   0.32                  

  7                                                                  1.44                   0.68                                                                                        2.11                   0.30                  

  8                                                                  1.44                   0.66                                                                                        2.11                   0.30                  

  9                                                                  1.36                   0.66                                                                                        1.99                   0.28                  

  10                                                                 1.36                   0.64                                                                                        1.99                   0.28                  

  11                                                                 1.29                   0.65                                                                                        1.89                   0.27                  

  12                                                                 1.28                   0.63                                                                                        1.89                   0.26                  

  Jan-69                                                             1.22                   0.64                                                                                        1.79                   0.25                  

  2                                                                  1.21                   0.62                                                                                        1.79                   0.24                  

  3                                                                  1.15                   0.63                                                                                        1.69                   0.23                  

  4                                                                  1.15                   0.61                                                                                        1.69                   0.23                  

  5                                                                  1.09                   0.62                                                                                        1.60                   0.22                  

  6                                                                  1.08                   0.60                                                                                        1.60                   0.21                  

  7                                                                  1.03                   0.60                                                                                        1.52                   0.21                  

  8                                                                  1.02                   0.59                                                                                        1.52                   0.20                  

  9                                                                  0.97                   0.59                                                                                        1.44                   0.19                  

  10                                                                 0.97                   0.57                                                                                        1.44                   0.19                  

  11                                                                 0.92                   0.58                                                                                        1.36                   0.18                  

  12                                                                 0.91                   0.56                                                                                        1.36                   0.18                  

  Jan-70                                                             0.87                   0.57                                                                                        1.29                   0.17                  

  2                                                                  0.86                   0.55                                                                                        1.29                   0.17                  

  3                                                                  0.82                   0.56                                                                                        1.22                   0.16                  

  4                                                                  0.82                   0.54                                                                                        1.22                   0.15                  

  5                                                                  0.77                   0.55                                                                                        1.16                   0.15                  

  6                                                                  0.77                   0.53                                                                                        1.16                   0.15                  

  7                                                                  0.73                   0.54                                                                                        1.09                   0.14                  

  8                                                                  0.73                   0.52                                                                                        1.09                   0.14                  

  9                                                                  0.69                   0.53                                                                                        1.04                   0.13                  

  10                                                                 0.69                   0.51                                                                                        1.04                   0.13                  

  11                                                                 0.65                   0.52                                                                                        0.98                   0.12                  

  12                                                                 0.65                   0.50                                                                                        0.98                   0.12                  

  Jan-71                                                             0.62                   0.51                                                                                        0.93                   0.11                  

  2                                                                  0.62                   0.49                                                                                        0.93                   0.11                  

  3                                                                  0.58                   0.50                                                                                        0.88                   0.11                  

  4                                                                  0.58                   0.48                                                                                        0.88                   0.10                  

  5                                                                  0.55                   0.49                                                                                        0.83                   0.10                  

  6                                                                  0.55                   0.47                                                                                        0.83                   0.10                  

  7                                                                  0.52                   0.48                                                                                        0.79                   0.09                  

  8                                                                  0.52                   0.47                                                                                        0.79                   0.09                  

  9                                                                  0.49                   0.47                                                                                        0.75                   0.09                  

  10                                                                 0.49                   0.46                                                                                        0.75                   0.09                  

  11                                                                 0.46                   0.46                                                                                        0.71                   0.08                  

  12                                                                 0.46                   0.45                                                                                        0.71                   0.08                  

  Jan-72                                                             0.44                   0.45                                                                                        0.67                   0.08                  

  2                                                                  0.44                   0.44                                                                                        0.67                   0.08                  

  3                                                                  0.41                   0.44                                                                                        0.63                   0.07                  

  4                                                                  0.41                   0.43                                                                                        0.63                   0.07                  

  5                                                                  0.39                   0.44                                                                                        0.60                   0.07                  

  6                                                                  0.39                   0.42                                                                                        0.60                   0.07                  

  7                                                                  0.37                   0.43                                                                                        0.57                   0.06                  

  8                                                                  0.37                   0.42                                                                                        0.57                   0.06                  

  9                                                                  0.35                   0.42                                                                                        0.54                   0.06                  

  10                                                                 0.35                   0.41                                                                                        0.54                   0.06                  

  11                                                                 0.33                   0.41                                                                                        0.51                   0.06                  

  12                                                                 0.33                   0.40                                                                                        0.51                   0.05                  
  --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

**Appendix 2: Classified Data That Could be of Use in Assessing Fallout
Impact on U.S. Population**

The ability to estimate fallout deposition from NTS shots was made
possible by the calculations of Hicks based on cloud measurements of the
relative production of the various fission products from each test. The
composition of debris is very dependent on the spectrum of neutrons
produced in the device and the composition of the fuel. Similar data for
test carried out by the U.S. and U.K. in the Pacific as well as for
tests carried out in the Soviet Union would be useful for making
comparable estimates of fallout deposition for tests carried out outside
the U.S. Such data, if available, is classified.

Also classified is the fraction of the total yield of individual shots
that resulted from fission versus fusion. Again, this information is
needed to make reasonable estimates of deposition and resultant doses
from tests held outside the U.S. The atmospheric model developed by
Bennett (1980) described in this report requires estimates of the
fission yield to estimate the amount of debris injected into various
compartments of the atmosphere. This model in turn is useful for
estimating nuclide deposition ratios as described in this report.

[^1]: Note that even for counties where an actual measurement exists at
    one or more sites for a particular month, the model estimates appear
    in the database. A subsequent analysis might decide to substitute
    measured values if available.

[^2]: Nb-95 is not produced during fission but grows in as Zr-95 decays.
    The ratio of Zr-95 to Nb-95 at any time thus depends on the time
    since the Zr-95 was produced. Nb-95 reaches about 97 % of secular
    equilibrium (Nb/Zr=2.2) in about 12 months.

[^3]: Since the half life of Cs-137 is actually slightly greater than
    that of Sr-90, this ratio probably increased very slightly with time
    since injection of debris into the stratosphere. Thus the total
    Cs-137 deposition may have been very slightly underestimated.

[^4]: Again the ingrowth of Nb-95 from the decay of deposited Zr-95 was
    accounted for in the calculation of the cumulative deposition
    density of Nb-95. The buildup of Nb-95 activity relative to Zr-95 at
    any time is given by Nb = Zr \* 2.17 \* (1- exp (-0.00914 \* t ))
    where t is in d.