Life Shortening in Mice Exposed to Fission Neutrons and γ Rays: VI. Studies with the White-Footed Mouse, Peromyscus leucopus

Some of the studies on late effects of neutron and γ radiation previously carried out with the C57BL6 × BALB/c ${\rm F_{1}}$ hybrids of Mus musculus have been repeated with the white-footed mouse, Peromyscus leucopus, a cricetid rodent of a different subfamily, with differing physiological characteristics and a different spectrum of pathologies. Among the more important findings were the following: (1) For both species, the life shortening per rad at low doses of either radiation was the same percentage of the life span. (2) The limiting values of the relative biological effectiveness for life shortening from all causes of death were about the same for the two species, ranging from 8 to 16, depending on the method of calculation. (3) Fractionated neutron exposures failed to produce significant life shortening in Peromyscus over that observed at single doses. (4) Tumor-related deaths accounted for at least 70 to 75% of the radiation-specific excess mortality in Peromyscus.