shyORRRMESIRE8 2 TERETEOY nae AOR, radiations while their shorter range beta particles will contribute a muchless biologically significant exposure to the skin. Of the radionuclides that contribute to external radiation, the most important single one is cesium 137. Its radioactive half-life is approximately 30 years. Thus, it is possible for cesium 137 to remain in our environment for long periods of time without losing muchofits activity, although there can be loss or reduction in availability of the material through normal weathering processes. Still cesium 137 does have a short enoughhalf-life so that most of the radiations are released within the lifetime of a man. All radioactive materials in fallout, except cesium 137, which remain outside the body may be conveniently lumped together to estimate their contribution to external exposures. These usually are called “short-lived” even though some do havehalflives of upwards of one year. In spite of the fact that nearly all of the radiation exposure received from these short-lived radionuclides is completed within a year after the radionu- clides are created the total amount of exposure during the year may be greater than that received from cesium 137 within 30 years. Cesium 137 also is one of the two (carbon 14 is the other) principal radionuclides deposited internally that irradiate the whole body. It is not a major source of the total whole radiation dose except in such cases as that of Eskimos whose diet is largely caribou or reindeer meat. The food chain (liichen-caribou-Eskimo) reflects the relatively high surface contamination of cesium 137 on the lichens. The Data The highest whole body exposures from nuclear weapons tests ever reported by the United States were about 175 roentgens to 64 Marshallese following the March 1, 1954 surface nuclear test detonation at the Pacific Proving Ground.’ This situation resulted from a shifting of the winds so that the local heavy fallout from this large yield surface burst occurred, in part, across the islands instead of the open sea. The Marshallese were evacuated, given medical treatment and returned to their homeisland of Rongelap on June 29, 1957 after radiation levels had subsided to acceptable levels 5 (fig. 3). From 1956 to 1962 about 24 children have been born —all normal—and four persons have died from natural causes.® (One of these had been on anotherisland and received 69 roent- gens exposure.) Four deaths have occurred in the comparison population of like size. There were, of course, noticeable effects immediately after the irradiation such as nausea and 5