Abstract
Water radiolysis with heavy ions having energies up to 28 GeV has been investigated. Beams of 4He2+, 12C6+, 20Ne10+, 28Si14+, 40Ar18+ and 56Fe26+ were taken for irradiations at HIMAC, NIRS. Corresponding LET values vary widely from 2 to 183 keV/μm. Aqueous solutions of MV (Methyl viologen) containing various concentrations of formate (0.01-2 M HCOO-) were irradiated and the production G values of MV+• were determined by absorption spectroscopy. Intra-track reactions were discussed from the MV+• yields because they can approximately be regarded as the sum of the yields of e-aq, •OH and H•. With increasing LET and with increasing HCOO- concentration, the MV+• yield decreased, reflecting increase of track density and development of intra-track reactions, respectively.
In parallel to above measurement, a Monte-Carlo simulation has been conducted not only to reproduce experimental results but also to discuss track structures more deeply. After selection of additional reactions concerning scavengers, experimental results were reproduced well. Then, attention was paid to each intra-track reaction and there were two findings. The first was that reactions between the products in scavenging reactions as well as reactions between water decomposition radicals become significant in high LET track. The second was that one of such reactions, COO-• + COO-•, showed similar LET dependence with RBE value and this similarity could be an explanation of highly effective cell-killing induced by heavy ion irradiation. Such an explanation by using radiation chemical calculation has not been shown yet although further investigation is necessary.
