Radiobiology of Large Animals.
Annual rept. 1 Aug 72-31 Jul 73,
STANFORD RESEARCH INST MENLO PARK CALIF LIFE SCIENCES DIV
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Hematologic changes occurring during and after complex sequences of low-dose-rate exposure of sheep to gamma radiation Cobalt 60 have been evaluated. Erythrocytic values were depressed early in the irradiation sequence, with further gradual depression after cessation of exposure. Leukocytic values decreased in a stepwise fashion during the irradiation sequence, with the patterns of decrease and post-irradiation recovery dependent on the particular parameters of radiation exposure. Studies of bone-marrow cell kinetics in mice receiving single exposures have shown that post-irradiation changes in total cellularity depend on dose rate. Further studies of lethality in sheep irradiated at low dose rates have indicated that a previously developed mathematical model relating exposure parameters to lethality may require modification when the exposure dose rate is of the order of 10 Rhr or higher. Author