| Popis: |
The relationships between dose rate and radiation response were studied in sheep and in mice. For sheep, the LD 50/60 varies inversely with dose rate, even when the dose rate is several hundreds of R/hr. An initial exposure to as little as 10 R (midline-air) at a high dose rate appears to affect the pattern of injury accumulation during subsequent low dose-rate exposure. The LD 50/60 for sheep exposed at 0.84 R/hr appears to be well in excess of 800 R. Continuous exposure to death at 3.8 R/hr results in a compression in survival time, so that all animals die within a period of seven days. Studies in mice indicate that there is no simple direct dependency of LD 50/30 on fractional survival of hematopoietic stem cells as the LD 50/30 increases with decreasing dose rate. A technique for evaluating erythroid activity in the bone marrow has been used to demonstrate that increased erythroid activity can occur in mice at a time post-irradiation when marrow cellularity is depressed. This technique has been found to be feasible for future irradiation studies using sheep. (Author) |
