Paper FALLOUT DEPOSITION IN THE MARSHALL ISLANDS FROM BIKINI AND ENEWETAK NUCLEAR WEAPONSTESTS Harold L. Beck,* André Bouville,” Brian E. Moroz,” and Steven L. Simon’ Bravo, a 15-Mt test conducted on | March (local time) 1954, on Bikini Atoll, which, as a result of an unexpected Abstract—Deposition densities (Bq m~’) ofall important dosecontributing radionuclides occurring in nuclear weaponstesting fallout from tests conducted at Bikini and Enewetak Atolls (1946-1958) have been estimated on a test-specific basis for 32 atolls and separate reef islands of the Marshall Islands. A complete review of various historical and contemporary data, as well as meteorological analysis, was used to make judgments regarding which tests deposited fallout in the Marshall Islands and to estimate fallout deposition density. Our analysis suggested that only 20 of the 66 nuclear tests conducted in or near the Marshall Islands resulted in substantial fallout deposition on any of the 23 inhabited atolls. This analysis was confirmed wind shear condition, resulted in heavy fallout on atolls east of the site and high radiation doses to the populations of those atolls. Numerous studies have been conducted to monitor the islands and people, to develop land remediation strategies, and to assess contemporary and possible future doses that might be received by inhabitants of certain atolls in the Marshall Islands. Particular emphasis has been given to the northern Marshall Islands. Many of these studies were chronicled in a July 1997 special by the fact that the sum of our estimates of *’Cs deposition edition of Health Physics. However, while there have been numerous measure- from these 20 tests at each atoll is in good agreement with the total *’Cs deposited as estimated from contemporary soil sample analyses. The monitoring data and meteorological analyses were used to quantitatively estimate the deposition density of 63 activation and fission products for each nuclear ments made over the decades of radioactivity in soil collected from many ofthe atolls (particularly the northern atolls and primarily for '*’Cs), no assessment of the deposition of all of the many radionuclides contributing to radiation exposure from each test has ever been made for all of the atolls of the Marshall Islands. Someof the difficulties in estimating deposition of the many fallout nuclides at the more than 30 atolls and separate reef islands has been the absence of measurement data of nuclides other than '°’Cs, lack of a reliable model for predicting the relative deposition of deposited test, plus the cumulative deposition of *’*™°Pu at each atoll. Estimates of the degree of fractionation of fallout from each test at each atoll, as well as of the fallout transit times from the test sites to the atolls were used in this analysis. The estimates of radionuclide deposition density, fractionation, and transit times reported here are the most complete available anywhere and are suitable for estimations of both external and internal dose to representative persons as described in companion papers. Health Phys. 99(2):124-142; 2010 Key words: '’Cs; fallout; Marshall Islands; nuclear weapons nuclides for both thermonuclear (TN) and nonthermonuclear (non-TN)tests, and absence of good data INTRODUCTION on time of transit for fallout from each test to reach the atolls from the test sites. There has also been little information regarding the effects of weathering that From 1946 through 1958, 66 nuclear weaponstests were conducted in or near the Marshall Islands, including 23 at Bikini Islands, 42 at Enewetak, and one at a nearby open-ocean site (DNA 1979; Simon 1997; Simon and reduced residual radioactivity, particularly soil '°’Cs levels, more quickly than would be expected by radioactive decay alone. In this work, all available historical and contemporary measurement data were collected and reviewed, including data not previously published in the open literature. An analysis of these measurements along with model calculations of relative nuclide activity and estimated fractionation, supplemented by meteorological modeling, have allowed us to make deposition estimates of all important fallout radionuclides at all atolls from eachtest. Robison 1997). Of special significance was the test * New York, NY 10014 (retired from the U.S. DOE); * Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892. For correspondence contact: Steven L. Simon, National Cancer Institute, National Institutes of Health, 6120 Executive Blvd., Bethesda, MD 20892, or email at ssimon@mail.nih.gov. (Manuscript accepted 11 August 2009) 0017-9078/10/0 Copyright © 2010 Health Physics Society DOI: 10.1097/HP.0b013e3 18 lbbbfbd 124