land area is about 6 km”, and the land height generally averages 3-5 m above mean sea level. The islands vary in size from small sandbars of a few hundred square meters in area to islands having areas of about 2 km? The islands of most importance for sweuiate Rhavitation ire Cikini and Unes islands. A total of 23 nuclear tests took place during the testing period. *oets were conducted on barges anchored in the lagoon or on the reef. uunjected to varying degrees of close-in fallout. Most of the All islands were Generally, the prevailing winds transported the radioactive debris clouds toward the southwest. One exception, however, occurred during the Bravo event when unexpected changes in the wind directions caused “he cloud to travel toward the east over 3ikini Island. Most of the radioactive con- “amination on Bikini Island is due to this event. This recent survey was designed to evaluate the potential external gamma doses associated with proposed housing locations on Bikini and Eneu Islands, and to evaluate the potential doses received through the major terrestrial food crops on the atoll. survey teams therefore directed their efforts in three major areas: The (1) Gamma-ray exposure rate measurements and surface soil collections will provide a means for evaluating the external gamma doses associated with proposed housing locations. Gamma spectral analyses of the soil samples will provide information on the fractional contributions of different radionuclides to the external dose. whole-body doses from this exposure pathway. This will enable us to evaluate long-term (2) Collection of lens water samples will opiy .nformacien un cue radionuclice activity levels in the groundwater anu on cycling of radionuclides in the atoll ecosystem. he In addition, salinity measurements and jens capacity measurements were made at each well to determine the quality and quantity ot water available to the Bikini people for irrigation and/or drinking. (3) Vegetation- soil collections will provide information concerning the radionuclide concentrations in sritical fcod products to evaluate the dose contribution via food chains. It will aiso provide information on the correlation between soil type, soil radionuclide concentrations, and radionuclide concentrations in key food plants and indicator plant species, which is necessary in order to develop predictive models. this is the 1irst in a series of reports which wiil be based upon the June 1975 survey data; it is directed only at preliminary estimates of the external gamma-ray doses. The report describes our techniques for measuring geographical variability of the gammaray exposure rates on Bikini and Eneu Islands and how we used the resulting data in conjunction with population statistics and expected living patterns to estimate the external gamma doses. Estimates of the integral first-year and 30-year doses associated with various options for housing locations on Bikini and Eneu Islands are presented and compared with appropriate guide values. The reader should note that these estimates are still preliminary in nature and may undergo changes when all of the results of the survey become available. Further information concerning radiation doses that may potentially be received via groundwater and various food chains will be published upon the completion of the analyses of the many soil, vegetation, and water samples that were collected during the survey. -2-