On the "Oxygen in Heavy-Ion Tracks" Hypothesis

Abstract

Two well-known chemical systems, the Fricke (system I) and the Fricke + ethanol (system II), were irradiated with intermediate-energy 12C and 40Ca ion beams. A vertical beam allowed us to study radiation phenomena in the bulk of a stirred solution and in the motionless surface layer in contact with air. The G value of the formation of Fe3+ in system II compared to system I allowed us to distinguish between oxygenated and hypoxic conditions in the reaction zone, i.e., in our case, in the vicinity of the heavy-ion path. Our results for nonstirred solutions that are open to air indicate an oxygen deficiency in the reaction zones even for medium-intensity ion fluences. The origin of this effect is not completely clear at present. Nevertheless, it is evident that postulated mechanisms for the generation of O2 in heavy-ion tracks are not sufficient to keep an oxygenated condition in nonstirred solutions. We cannot exclude the possibility that the low oxygen enhancement ratio observed in experiments with high-LET radiation may arise, at least partly, from an insufficiency rather than an excess of oxygen.