High-LET Pulse Radiolysis: O 2 - and Oxygen Production in Tracks

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Abstract
The production of O2- in the radiolysis of water at pH 7 and 11 was investigated using pulses of 20 MeV deuterons and 40 MeV .alpha. particles. The G-values [number of ions reacted/100 eV energy absorbed] of O2- [super oxide anion] are estimated by comparing the observed optical absorptions at approximately 252 nm with the absorptions calculated on the basis of known reaction rate constants and absorption coefficients of species produced in water radiolysis. The experimental observations can be explained reasonably well without invoking primary yields of O2- or O2, although there is room, within the limits of error, for a contribution from such primary yields. The observations are discussed in relation to the O2 in the track hypothesis and arguments are presented showing that species formed in the track (e.g., O2, O2-) with small G-values do not allow an explanation of the known effects of radiation quality on the relative biological effectiveness and the O2 enhancement ratio in terms of this hypothesis.

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