126 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 paragraphs. 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).