The Effects of Accelerated Carbon Nuclei and Other Radiations on the Survival of Haploid Yeast: II. Biological Experiments

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Abstract
The radiation sensitivity for the inhibition of colony formation in the haploid yeast, Saccharomyces cerevisiae, has been measured with a series of radiations that cover a range in linear energy transfer from 20 to 5000 Mev cm2/gm. In addition to X-rays and Po210 alpha particles, the radiations employed include cyclotron deuterons, alpha particles, and carbon nuclei with a charge of 6. The radiation sensitivity increases with increasing LET until it reaches a maximum corresponding to a relative biological effectiveness of 2 for 3.4-Mev alpha particles. At still higher LET values, the radiosensitivity decreases progressively and corresponds to an approximately constant inactivation cross section of 1 [mu]2. Implications of the experimental results are considered in terms of target theory, the migration model, and the track-segment calculation.