Survival of cultured human cells exposed to californium 252Cf radiation at low dose rates.

Human T-1 cells were used to determine the rbe of low dose rate 252Cf (n + gamma) radiation, compared to low dose rate gamma radiation. The T-1 cells were irradiated hypoxically at room temperature, and the dose rates were as follows: a) 252Cf (n + gamma), 0.045, 0.090, and 0.270 Gy/hour; and b) 137Cs gamma radiation, 0.117, 0.246, and 0.765 Gy/hour. The RBE was obtained as the ratio of the initial slope of the 137Cs survival curves (approximately the same for all three dose rates), and the initial slope of the 252Cf survival curves (same for all three dose rates). The RBE was 5.0 +/- 1.0 for all components of the 252Cf radiation and 7.1 +/- 1.7 for the neutron components. As the dose increased, an inverse dose rate effect (more sensitive at lower dose rates) for the 137Cs survival curves was observed.