INITIAL ACTIONS OF IONIZING RADIATIONS

The initial process of radiation damage is described beginning with the formation of ionized molecules along the tracks of the radiation particles. These ions immediately dissociate to form free radicals, and the free radicals react to produce permanent damage to some key molecules. The tracks of ionized molecules may pass through some sensitive region or target in which a single ionization may inactivate the molecule, the particle, or the cell. The larger the target, the easier it is to hit. The dose required for inactivation decreases with increasing target size. The role which free radicals play in radiation damage is investigated by electron spin resonance. Experiments indicate that changes induced in these free radicals will alter the course and extent of the radiation damage. It is pointed out that the problem of the high sensitivity of cells to radiation damage may be solved by a further understanding of the initial action of radiation. (N.W.R.)