摘要：Two groups of normal human blood cells, one stimulated with phytohaemaglutinin (PHA) for 24 hr (G 1 -S phase of the cell cycle) and one unstimulated (G 0 phase), were irradiated with 60 Co gamma rays or 252 Cf radiation. A comparison of radiation-induced micronucleus frequencies showed that the high-dose-rate gamma rays were more effective in inducing micronuclei than low-dose-rate gamma rays. In the cells exposed to low-dose-rate irradiation, there was little difference between the frequency of micronuclei in the G 0 phase and the G 1 -S phase. However, cells in the G 1 -S phase were more sensitive than G 0 -phase cells to high-doserate gamma rays. The relative biological effectiveness of 252 Cf neutron irradiation measured in micronucleus assays was consistent with the value obtained for the lethal effect of 252 Cf on cultured cells.
