[Studies in the small intestine of mice after fractionated neutron and x-ray irradiation].

Several groups of mice received a whole-body irradiation with X-rays and neutrons. The survival and the number of crypts per intestinal circumference was measured after one-time, two-time, three-time, and four-time fractionation. The irradiation interval was 24 hours. Survival rate and number of crypts were compared to one another. There were discrepancies which could be explained by determining the right moments of examination. Thus it seems not recommendable to use the system of small intestine crypts for experiences with fractionated irradiations. The RBE values increased with the rising number of fractions. If Dn-Dl values were calculated, they increased on the one hand with the rising fractionation, on the other hand with the rising total dose. This effect was more marked after X-ray irradiation, less after neutron irradiation. This may be explained by the fact that, contrary to neutron irradiation, the recovery following to sublethal lesion by X-rays had not been exhausted.