Abstract
Spores were irradiated and cultured to measure their survival. Radiation damage could be modified by treating with NO, O2 and water during and after irradiation. The radiation damage in anoxically irradiated spores, stored in N2, remained open to full enhancement by O2 for several hours, but the rate of this process decreased with time. Enhancement of damage by O2 could be prevented by treatment with NO or water. The opposing effects of NO and O2 were used to titrate the rate of development of the radiobiological oxygen effect The behaviour of radiation-produced species could be described by a kinetic model. The modification of radiation damage by O2 involved the formation and the decay of a peroxy radical intermediate. A correlation of survival data with E.S.R. data is given in terms of the model.