Biological Effects of Cf-252 Neutrons at Low Dose Rates

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Abstract
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.