INJURY ACCUMULATION IN SHEEP DURING PROTRACTED GAMMA RADIATION

Abstract : The study describes the injury accumulation and recovery in sheep exposed to Co60 gamma rays (2/3 LD50/30) at dose rates of 0.5 to 3.9 R/hour. Immediately following the protracted exposure (165 R), no injury as defined by the lethality of a second exposure could be detected for those animals exposed to gamma radiation at dose rates of 0.5 and 0.95 R/hour. However, when animals were subjected to a similar total protracted exposure but at dose rates of 1.85 and 3.9 R/hour, significant amounts of injury could be detected immediately following the protracted exposure. Approximately 75 R (45%) and 104 R (63%) of the remaining injury was detected in animals exposed at dose rates of 1.95 and 3.9 R/hour, respectively. This suggests a threshold exposure rate, probably between 1.0 and 1.85 R/hour, for injury accumulation in sheep. Further experiments to relate the size of the conditioning exposure (protracted) to injury accumulation indicate that at an exposure rate of 3.6 R/hour, injury accumulation is a linear function of the total protracted dose. (Author)