The Relative Effectiveness of Fission Neutrons for Miniature Pig Performance Decrement.
ARMED FORCES RADIOBIOLOGY RESEARCH INST BETHESDA MD
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Trained miniature pigs were whole-body irradiated in a nuclear reactor-produced neutron field incident neutron to gamma ratio of 10. Their postirradiation performance was compared to that of pigs similarly irradiated in a gamma ray field from the same reactor incident neutron to gamma ratio of 0.06. The dose rate at the midline of the brain was approximately 2000 radsmin for all irradiations midbrain doses ranged from 1500 to 36,500 rads. Response of the pigs to supralethal doses from the neutron field notably differed from their response to similar doses from the gamma ray field. Early performance decrement, early transient incapacitation, and immediate permanent incapacitation occurred following much lower doses from the gamma ray field than from the neutron field. At doses greater than 11,000 rads, survival times of the neutron-irradiated pigs were on the average much longer than those of the gamma-irradiated pigs. Thus, the gamma rays were markedly more effective than the fission neutrons for producing the severe central nervous system damage manifested by pronounced early performance decrement and death within 48 hours. The relative effectiveness of the neutron field was 0.23 using the reactor-produced gamma ray field as the reference radiation and the 50 percentile midbrain dose 9ED50 for early performance decrement as the biological end point. Author