Late Effects of Fast Neutrons versus X-Rays in Mice: Nephrosclerosis, Tumors, Longevity

Groups of mice exposed to sublethal doses of fast neutrons or to lethal doses of x-rays were followed until natural death in order to study long-term irradiation effects. The x-irradiated mice were protected against acute death by injection of hematopoietic cells or limb shielding. Gastrointestinal carcinomas were much more common in the neutron-irradiated than in the x-irradiated mice. However, in the small group of mice surviving superalethal doses of x rays of 1000 to 1100 r following thigh shielding during exposure, 21% exhibited intestinal carcinomas. A neutron RBE value of 2 to 3 is therefore indicated for these tumors, as late effects. Nephrosclerosis, on the other hand, was more common in the x-irradiated mice, with an apparent neutron RBE value close to unity for this late lesion. (auth)