Life Shortening in Mice Exposed to Fission Neutrons and γ Rays: V. Further Studies with Single Low Doses

Data are presented on the mean aftersurvival of female ${\rm B}6{\rm CF}_{1}$ mice exposed to single doses of neutrons (1 to 40 rad) or γ rays (22.5, 45, and 90 rad). For γ-ray exposures and for neutron exposures up to 10 rad, the dose-response curves are indistinguishable from linear; higher neutron doses produce significant departures from linearity. Consequently, in these data, an upper limit of the relative biological effectiveness (RBE) exists for life shortening from all causes of death after single neutron exposures; this value is 15.0 ± 5.1. The RBE depends on the cause of death, ranging from 2 to 5 for lymphoreticular tumors to 23-24 for lung tumors.