MUTAGENIC EFFECTS AT HPRT LOCUS INDUCED IN CHINESE-HAMSTER OVARY CELLS BY THERMAL-NEUTRONS WITH OR WITHOUT BORON COMPOUND

CHO cells were exposed to thermal neutrons and their mutation frequenc y was determined. The Kyoto University Research Reactor (KUR), which h as a very low level of contamination by gamma-rays and fast neutrons w as used as a thermal neutron source. Cells were irradiated in the pres ence or absence of boric acid to determine mutation frequency and cell survival. Thermal neutron irradiation was 2.5 times as mutagenic as g amma-irradiation without boron. In the presence of boron, however, the rmal neutron irradiation was from 4.2 to 4.5 times as mutagenic as gam ma-irradiation. When the mutation frequency was plotted against the su rvival fraction, a higher degree of mutagenicity was observed in the p resence than in the absence of boron. These results suggest that the e nhancement of thermal neutron-induced mutation with boron is strongly associated with alpha-particles released by B-10(n,alpha)Li-7 reaction .