Biological effects of Cf-252 neutrons at low dose rates.

The EMT6 tumour of the Balb/c mouse and the LSA ascites lymphoma of the C57BL/YM mouse have been used to study the effects of Cf-252 neutrons at low dose rates. EMT6 and LSA cells were irradiated in vitro in a hypoxic state; EMT6/KY cells were plated after exposure for colony-forming ability assays, while TD50 assays were used to test the tumour-forming ability of LSA cells. EMT6 cells showed r.b.e.n values of 5.3, 4.7, and 3.0 for Cf-252 dose rates of 26.8, 10.2, and 5.2 cGy/hour (= rad/hour), respectively, when compared to Cs-137 irradiations at dose rates of 79.7, 25.7 and 12.1 cGy/hour, respectively. The LSA ascites gave r.b.e.n values of 5.6 and 5.2 at dose rates of 27.0 and 6.94 cGy/hour of Cf-252, when compared to Cs-137 irradiations at 79.6 and 24.9 cGy/hour, respectively. However, changes in r.b.e. values for both systems were entirely dependent on comparison with Cs-137 survival curves.