Abstract
Summary
1. Plutonium 239, polonium 210, uranium 233, and thorium 228 were 20 times as effective as radium 226 in killing 50% of a population of CF No. 1 female mice in 20 to 100 days after intravenous administration. At levels approaching those that produced no effect, polonium was 3 times as effective, plutonium was equally effective, and uranium 233 was slightly less effective than radium in decreasing the expectation of life. The ratios relative to radium of the proportion of mice that developed malignant bone tumors after the latent period were 7:1 for plutonium and 2:1 for uranium 232. Uranium 233 and polonium were less effective than radium in this instance. 2. On the basis of these criteria, the best present estimate of the relative biological effectiveness at near-tolerance levels in CF No. 1 female mice is 7 (plutonium 239):3? (polonium 210): 2, (uranium 232): 1 uranium 233): 1 (radium 226).
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