Lethal Effects on Rats of Single and Multiple Exposures of 400-Kv and 22-Mv X-Radiation

The relative effectiveness of different kinds of ionizing radiation is usually studied in rats and mice by comparing the amounts of these radiations required (1) to produce 50% deaths in 30 days (LD50) and (2) to reduce the survival time of individuals. Quastler (1), Harvey (2), and others have found a quantitative difference in effects among various types of radiations in mice and in rats. This difference in relative biologic effectiveness (RBE) of radiations which vary in energy has been found in a variety of biologic objects (Moos, 3; Lorenz, 4; Lacassagne, 5; and others). It is apparently related to the differences in linear energy transfer (or specific ionization) correlated with the change in the energy of the radiation. The purpose of the experiments in the present report was to compare the lethal response of rats to single and multiple exposures of 400-kv and 22-Myv X-radiation. Weights and gross pathologic findings were recorded, but histologic findings will be reported elsewhere.