The Relative Biological Effectiveness of Fast Neutrons and X-Rays for Life Shortening in Mice

Abstract

The relative biological effectiveness (RBE) of fast neutrons versus x rays has been measured for the shortening of the life span in mice. Three experiments were performed comparing these two radiations, and in each the ratio of K rays to neutrons was such as to produce the same 30-day mortality. The first experiment employed large single doses of Ihe radiations; the second, four smaller doses at 7-day intervals; and the third, four smaller doses at 14-day intervals. All animals were kept until natural death. The RBE was found to be the same (1.7) for acute lethal effects as for shortening of life span in all three experiments. The animals receiving neutron treatments did not gain weight - as fast as the x-ray-treated animals, however. In view of previously reported high values of RBE for chronic neutron versus x irradiation, it is concluded that the relative recovery rates for neutrons versus x rays are different for small doses from those for large doses.