RELATIVE BIOLOGICAL EFFECTIVENESS (RBE) OF CF-252 FISSION NEUTRONS FOR THE INDUCTION OF CHROMOSOME-DAMAGE IN HUMAN SPERMATOZOA

Effects of Co-60 gamma-rays and Cf-252 neutrons on human sperm chromos omes were studied using our interspecific in vitro fertilization syste m to estimate relative biological effectiveness (RBE) of neutrons. Sem en samples were exposed to 0.5, 1.0 and 2.0 Gy of Co-60 gamma-rays at 1.7 cGy/min and 0.25, 0.5 and 1.0 Gy of Cf-252 radiation at 1.3-1.7 cG y/min. In the Co-60 experiment, 509 spermatozoa from controls and 902 spermatozoa from the irradiated groups were karyotyped, while in the C f-252 experiment 460 control and 804 irradiated spermatozoa were analy sed. In both Co-60 and Cf-252 experiments, incidences of spermatozoa w ith radiation-induced structural chromosome aberrations increased line arly with increase of dosage. The RBE of Cf-252 neutrons for the induc tion of chromosomally abnormal spermatozoa. was estimated to be 1.6. T he number of induced structural chromosome aberrations per spermatozoo n also increased linearly. The RBE of neutrons for this index was 2.0. Among structural chromosome aberrations observed, chromosome-type bre aks were predominant in both Co-60 and Cf-252 experiments, and they sh owed a significant linear dose-dependent increase. Other types of aber rations such as chromosome-type exchanges and chromatid-type breaks al so increased linearly with increase in dose. The RBEs of Cf-252 neutro ns for the induction of these three types of aberrations were 1.6, 3.2 and 3.9, respectively. Thus, the RBEs of neutrons for the induction o f chromosome aberrations were smaller in human spermatozoa than in hum an lymphocytes, and mouse spermatogonia and embryos. This result is di scussed from the point of view of DNA-repairing capacity of oocytes.