Effects of low energy of 252Cf neutrons on lymphocyte chromosomes in human

Effects of Cf-252 neutrons on human lymphocyte chromosomes were examined in the absence or presence of iron shielding. In an irradiation experiment at dose rates of 2 cGy/min and 0.02 cGy/min, Cf-252 neutrons were found to be independent of dose rates. The values of relative biological effectiveness (RBE) of Cf-252 neutrons were 3.9 at a dose rate of 2 cGy/min and 15 at a dose rate of 0.02 cGy/min, revealing higher RBE values at lower dose rates. When an iron material 15 cm in thickness was used to produce low energy of Cf-252 neutrons, RBE of low energy of neutrons to dicentric and ring chromosomes was 17. This was not statistically significant, as compared with 15 at a dose rate of 0.02 cGy/min. Low energy of Cf-252 neutrons had few effects on the formation of exchange type of chromosomal aberration, but had an effect on the formation of deletion type. These findings may have important implications for the reassessment of radiation doses of A-bombing and the formation mechanism of radiation-induced chromosomal aberration. (N.K.)