Effect of Graded Acute Exposures of Gamma Rays or Fission Neutrons on Survival in Subsequent Protracted Gamma-Ray Exposures

Abstract

Female mice (528) were randomly divided into 12 groups and given fractionated doses of gamma-rays ranging from 240 to 1200 rads, and fission neutrons ranging from 92 to 451 rads. After 90 days, they were placed in a continuous field of gamma-rays (50 rads per 24 hours), until death. The mean accumulated dose for each group was determined and correlated with the insult dose. Results showed that: radiation-induced damage in the mouse has one component that is permanent and irreversible; at least a fraction of this irreversible damage is proportional to the magnitude of the insult dose and is measurable in terms of a reduction in survival time in a continuous gamma-radiation field; the fraction of permanent injury produced by fission neutrons is approximately 5 times as great as that produced by gamma-rays.