my THE SHORT TERM BIOLOGICAL FATE AND PERSISTENCE OF RADIOACTIVE FALLOUT AS MEASURED AT VARIOUS LOCATIONS WITUIN FALLOUT PATTERNS By BR. G. lanprera and K. H. Larson Radio-Ecology Division, Atomic Energy Project, University of California at Los Angeles The problem of assessing the biological hazards of radioactive fallout may be arbi- trarily divided into two parts; one, the acute or immediate hazard arising primarily fram ex- ternal radiation and secondarily from the metabolism of certain fission products; and two, the chronic or long term hazards arising primarily from the metabolizedfission products, and secondarily from external radiation. The division of the problem is real. The exact duration of each phase is not. The Alamagordo Section and the succeeding Radio-Ecology Division at the Atomic Energy natural environments relatively unaffected by human exploitations. Jn these native, stable communities the occurrence of fission products originating from fallout have been documented as they oecur in the various components of the environment. The particular components studied during weapons testing programs have been air, soil, plants, native rodents, andfallout, Fromthesedata, collected serially over a period of time, the cycling of bomb debris may be followed as the contamination passes from one A reasonably continuous record is available of the fate of plutonium contamination near the New Mexico TestSite from 1947 tu the present, componentof the environmentto another. The kangaroo rat, genus Dipodomys, and the jack rabbit, genus Lepus, have been used as indicators of the biological availability of radioactive fallout to other mammals. These animals are abundant in most areas and are easily collected by trapping or shooting. The ’ kangaroo ratis of particular interest because of its sedentary nature. In other words, the body contamination in several areas adjacent to the Nevada Test Site from 1951 to the present. is within one or two hundredfeet of the point of Project, Universityof California at Los Angeles, has been engaged in part in studying the fate and persistence of radioactive fallout in areas adjacent to continental test sites since 1947, A record of the fate of repeated fission product also available. Lest we stray from the “short term’' objectives of the symposium, the data presented below will emphasize data collected during weapons testing programs and up to one year following fallout contamination of an environment. During the course of these studies many kinds of environments have been sampled varying from the semiarid desert valleys, to juniper and pifiion pine covered slopes, to relativelyrich agricultural areas. Byandlarge the sampling has emphasized the study of burdenof fission products in any particular rat is the result of that animal living its entire life collection. Therefore, knowledge of the conditions of contamination within this area provides us with parameters for estimating the biological significance of any particular fallout condition. The plant species and plant parts which go to make up the primary forage of the kangaroo rat and jack rabbit in any particular area are the ones chosen fer documenting the oceurrence of fallout materials in or on plants. Experience has shown that radioactive fallout originating from continental weapons tests tends to remain in the surface inch or two of soil in 197