Dose Rate Effects on Lethality of Mice Exposed to Fission Neutrons; SM-44/13

15 pages. Footnotes. Tables. Figure. References. Ink correction on pages 11 and 12. Ex-library copy with usual markings. Ink number and name in pencil on front page. Latest publication in the references were from 1961. This work was performed under the auspices of the U. S. Atomic Energy Commission. The unusual radiation environment that man may encounter during future space ventures from such sources as primary cosmic rays, solar flares, natural radiation belts circling the earth, and nuclear propulsion systems designed for extended space flights was cause for concern and a need for a better understanding of radiation effects was recognized. This was particularly true with regard to dose rate effects of ionizing agents of different qualities. This study was designed to complete existing information by extending neutron dose rates to both fractionations and delivery times of microseconds. To obtain relative biological effects under the above dose rate conditions, CO 60 gamma-ray studies were also done. The median lethal dose determinations for fission neutrons and gamma rays delivered by the fractionation method (single, acute sub-lethal exposures at 14-day intervals) were done. The study found that the repair half-time for biological repair from fission neutron injury was estimated at 6 days for the RF strain female mouse.…