Life Shortening in Mice Exposed to Fission Neutrons and γ Rays: IV. Further Studies with Fractionated Neutron Exposures

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Abstract
When mice were exposed to a total dose of 240 rad of fission neutrons divided into 2, 4, or 6 fractions given at 1-wk intervals, more life shortening was observed than was seen after a single exposure. Maximum life shortening was observed with 4 fractions, although the value for 6 fractions was not significantly lower. Much of the augmentation effect was attributable to an increase in early deaths during the 1st 200-300 days after exposure, although differences persisted throughout the lifetime of the animals. The changes in life shortening were associated with changes in the distribution of causes of death; however, decrementation of the populations for any given specific cause of death failed to eliminate completely the differences in mean aftersurvival time.