Dose-mortality Studies for Mice Irradiated with X-rays, Gamma-rays and 15 MeV Neutrons

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Abstract
Acute mortality in mice, occurring within 5 or within 30 days after the end of the exposure, was studied after irradiation with x-rays, gamma-rays or 15 MeV neutrons in either 2-hour or 8-hour exposures. Death due to the haematopoietic syndrome occurred mainly between 8 and 14 days after exposure, whereas a mean survival time of 4·5 days was found for the intestinal syndrome. For 15 MeV neutron irradiations and 2-hour exposure time, the LD50-values for the two syndromes differed by nearly 300 rads. Mortality due to the intestinal syndrome was not observed in the range of the lowest lethal doses. RBE-values of 1·1 and 1·4 with respect to 250 kVp x-rays were obtained for haematopoietic death and intestinal death, respectively. The effect of protraction of the exposures to gamma-rays and neutrons suggests that there are intrinsic differences between the cellular radiosensitivity of intestinal cells and bone-marrow cells.