TEMPERATURE DEPENDENCE OF RADIATION SENSITIVITY IN DRY STATE - A MODEL DERIVED FROM EXPERIMENTS USING ATOMIC HYDROGEN

The effect of temperature on the inactivation rate of phage T1 in vacuo by radiation-induced diffusible radicals has been studied. Reactive species were liberated by 2-MeV protons impinging on thin foils of organic material and permitted to reach phage samples arranged at some distance. Thus, the sites of radical production and radical reaction were separated in space. Two different modes of exposure were used: the temperature either of phage samples only (method A), or both of foil and samples (method B), could be varied from 100°K to 340°K. Activation energies of 0·65 ± 0·1 kcal/mole and 0·95 ± 0·1 kcal/mole, respectively, were derived from the temperature dependence of damage. The latter value, simulating inactivation by secondary processes in ionizing radiation, strongly supports the hypothesis that the activation energy of 1 kcal/mole, frequently reported in the literature for radiation damage, is related to H radical action. Using the results of both experiments, an interpretation of the temperature effect is given by separating the overall activation energy into components of 0·3 kcal/mole necessary for H atoms to overcome 'cage-effects at the parent-molecule' and of 0·65 kcal/mole to maintain diffusion by freeing the radicals from trapping sites. © 1969 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.