Relative biological effectiveness of Cf-252 with teratogenicity as index

The teratogenicity of fission neutron (Cf-252) having a radioactive composition similar to the Hiroshima-type atomic bomb on rat embryo was evoluated. As method, a single whole body irradiation of Cf-252 in various doses was given to pregnant rats on day 7, 8, 9, 10 and 11 of pregnancy and the external and visceral anomalies were studied by microscopic autopsy of embryos on day 18 of pregnancy. For comparison, an experiment was made irradiating standard γ ray of Co-60 at the same dose rate (1 rad/min). As a result, on RBE of 3.1 - 3.3 was obtained from the line given on modifying the frequency curve of anomalous embryos among implanted and survival embryos by the method of least squares. Further, the anomalies in Cf-252 and Co-60 irradiated cases were similar to each other in substance. Using LD50 of embryos as index, RBE was 2.3 in cases irradiated at 8 days of fetal age and 3.2 in cases irradiated at 9 days of fetal age. The above results show that Cf-252 has strong teratogenicity. (author)