Effect of 60Co gamma radiation dose rate on 30-day mortality in swine

SUMMARY One hundred and sixty-three 8-month-old Duroc swine which averaged 114 kg. in body weight were exposed to 60 Co gamma radiation. Radiation doses were given at rates of 1, 10, and 50 rads per minute. The clinical syndrome and 30-day mortality were studied. The median lethal doses causing 30-day mortality ( ld 50/30 ) in swine subjected to dose rates of 1, 10, and 50 rads per minute were 710, 435, and 360 rads (tissue doses in air), respectively. Mean survival time for all decedents was 16 days, with the earliest death occurring at 9 days and latest death at 30 days after irradiation. Although dose rate significantly affected the dose-mortality curves, it did not affect survival time or the general clinical syndrome. The relative effectiveness of 10 rads per minute and that of 50 rads per minute in causing 30-day mortality were 1.63 and 1.97, respectively, where 1 rad per minute was assigned the value of 1. The higher dose rates were also more effective in causing decrease of leukocyte and platelet concentrations in the peripheral blood.