Health Physics

The estimates of deposition density of '*’Cs in this

work are our best estimates inferred from all available
monitoring data, muchofit historical and available only

in the gray literature, e.g., government laboratory reports
and internal memoranda from laboratories. As discussed,
in a previous assessmentof radiation dose to residents of
the Marshall Islands from regional fallout by the National Cancer Institute (DCEG 2004), emphasis was

August 2010, Volume 99, Number 2

and to make crude estimates of the ground deposition

of '*’Cs on anyatoll after anytest.

These data as well as the models used to estimate
deposition density are described in detail in the following
Contemporary measurements of '*’Cs and other

surement data to make estimates of '’Cs deposition

long-lived radionuclides
Considerable amounts of data are available on the
total inventories of long-lived radionuclides at various
times as a result of soil sampling carried out by the
Department of Energy-sponsored Northern Marshall Islands Radiological Survey (Robison et al. 1981, 1997)
and soil sampling and in situ gamma spectrometry
surveys by the Republic of the Marshall Islands Nation-

individual tests. The resultant total '*’Cs deposited by all

wide Radiological Study (NWRS) (Graham and Simon
1996; Simon and Graham 1997; Simon et al. 1999).

the retrospective '*’Cs remaining in the soil as measured

Laboratory (HASL 1956). These various soil measure-

placed on estimating the fallout deposition in the 1950’s

from contemporary analyses of cumulative '°’Cs deposition at each atoll. Furthermore, in that work it was

assumed for purposes of simplicity that the total deposition was a result of a single nuclear test (the 1954 Bravo
test). In this paper, we use the various historical meadensity and fallout TOA for each atoll and for each of 20

tests from this analysis, after appropriate decay to account for the actual effective decay rate in the Marshall
Islands discussed previously, were then compared with
at variousatolls by different investigators in 1978 and in
1991-1993. This comparison was used to demonstrate

the validity and relative accuracy of our '*’Cs deposition
density estimates for individual tests.

Thetest- and atoll-specific estimates of '°’Cs fallout

were then used to estimate the deposition densities (Bq
m~) ofall other radionuclides considered in this study,
taking into account the estimated fallout transit times. A
nuclide mixture was assumedforall TN tests identical to
that for the Castle Bravo nuclear test (Hicks 1982),

adjusted for estimated fractionation effects, while a
nuclide mixture of a typical plutonium-fueled fission
device that was detonated at the Nevada Test Site (NTS)
was used for the non-TN tests (Hicks 1981).

The measurements we used for the estimation and

validation of the ground deposition of '*’Cs and other

radionuclides included:

e measurements in soil of '’Cs and other long-lived
radionuclides including "Sr, *°'*°Pu, and ™'Am,
carried out at least a decade after the last test;

e historical measurements of exposure rates, made soon
after the tests, from which the ground deposition of

'’Cs can be derived using calculated ratios of '°’Cs

deposition per unit exposure rate and information on
the TOA of fallout;
e historical measurementsof total beta activity deposited
on gummedfilm that were collected daily at several
locations after a numberof tests; and

e meteorological data on wind speed and direction,
which were used as input to an atmospheric transport
model to predict the geographic pattern of dispersion

Some data in other years are also available in reports
from University of Washington (Nelson 1977, 1979) and
the Atomic Energy Commission’s Health and Safety
ment data were used to validate the estimates of total

'’Cs deposition density inferred from measured expo-

sure rates and other data by comparing the estimated
inventories (from summing individual test depositions,
decay corrected to the year of soil analysis) with the
contemporary measurements of inventory. The decay
correction used for this comparison relied on an estimate
of the effective half-life, accounting for both physical
decay and loss of activity due to weathering and downward migration.
Historical measurements of exposure rates

Data on exposurerates after various tests in the 1952
Ivy and 1954 Castle series were obtained from Joint Task
Force 7 memoranda (JTF 1954a, b, c), Breslin and
Cassidy (1955), Klein (1952), Eisenbud (1953), Steton et
al. (1956), Martin and Rowland (1954), Heidt et al.
(1952), DNA (1979), Graves (1954), Graveson et al.

(1956), Dunning (1957), Held (1965) and SAIC (1981).*
During the years of testing, islands were generally
surveyed soon after individual detonations by aerial
reconnaissance using fixed-wing aircraft as a monitoring
platform, as well as by ground-level measurements with
gamma survey meters. Automatic gamma-ray monitors,
designed by HASL, were also located at Rongerik,
Kwajalein, Majuro and Ujelang during Operation Castle
(Breslin and Cassidy 1955). Additionally, the U.S. Public

Health Service (PHS) monitored fallout on Ujelang,

Utrik, Wotho, and Rongerik during the 1956 tests and
* Personal communication, SAIC, Calculated dose for individuals

on Kwajalein, SANDSTONE/Yoke (unpublished SAIC memo dated
23 July 1981—Revised 24 August 1981).

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