The Distance That a Radical Formed by Ionizing Radiation Can Diffuse in a Yeast Cell

from water by ionizing radiation. The intermediates can diffuse through an aqueous medium and inactivate a molecule at a distance from where the energy was originally absorbed; hence the name of effect. Intermediates which are commonly assumed to be involved are H, OH, HO2, H202, and, in media containing organic molecules, organic peroxides. The magnitude of the indirect effect on a given substance depends partly on the inherent sensitivity of the substance to attack by the diffusible intermediates and partly on the competition for the intermediates by other materials in the irradiated medium. A theory for determining the magnitude of the indirect effect on spherical molecules has been given by Zirkle and Tobias (1). The effect of the surroundings in modifying the indirect action is shown by these authors to be expressible as a mean distance through which the radicals formed can diffuse. Zirkle and Tobias did not measure directly a value for this distance but showed that the data they obtained on haploid and diploid yeast cells were consistent with a value of the order of hundreds of angstroms, which was not impossible to reconcile with experimental data available at the time on the various radicals. This paper is concerned mostly with the calculation of such a mean radical diffusion distance in yeast cells from the radiation data on enzymes in cells given in an