Early Mortality in the Young Chicken after Exposure to Fast Neutrons or Gamma Rays

Two-day-old White Leghorn cockerels were exposed to various doses of60Co gamma radiation or high energy (14.5 MeV mean energy) neutrons from the Naval Research Laboratory, Isochronous Cyclotron in Washington DC. Early deaths (within 30 hr of exposure) were observed after exposure to both types of radiation. Chicks exposed to neutrons died in two distinct and separate time periods. These two modes of death were not apparent after the gamma irradiations. After either neutron or gamma ray exposure, survival time decreased as mortality level increased, reaching a minimum of approximately 5 hr. The 30-hr LD50values were 519 ± 5.6 rads of neutrons and 939 ± 8.0 rads of gamma radiation; the relative biological effectiveness (RBE) at this mortality level was 1.81.