Water radiolysis with heavy ions of energies up to 28 GeV.: 1. Measurements of primary g values as track segment yields

Water radiolysis has been investigated with heavy ions having energies up to 28 GeV provided from the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Sciences (NIRS). Beams of 4He2+, 12C6+, 20Ne10+, 28Si14+, 40Ar18+ and 56Fe26+ with respective energies of 150, 400, 400, 490, 500 and 500 MeV/u corresponding LET values of 2.2, 13, 30, 54, 92 and 183 eV/nm, respectively, were taken for the irradiation. The LET changes in sample solutions can be neglected due to their high energies for the irradiation of 1-cm cells. Primary g values have been determined for three important products, hydrated electron (e−aq), hydroxyl radical (·OH), and hydrogen peroxide (H2O2) as track segment yields (differential yields) under the conditions of neutral pH.With increasing LET, the g values of e−aq and ·OH decrease from 2.4 and 2.6 in 4He2+ radiolysis to 0.9 and 1.1 (100 eV)−1 in 56Fe26+ radiolysis, respectively. It was also found that the primary g value of e−aq is smaller than that of ·OH for any type of ion beam. For the 12C6+ beam, other energies such as 290, 220, 135 MeV/u were taken for the irradiation to investigate the effects of type or atomic number of ions on the measured yields. Furthermore, effects of dissolved oxygen on enhancement of H2O2 production have also been investigated with aerated NaNO3 solutions. The presence of dissolved oxygen caused 15–35% enhancement in H2O2 yields for all beams. In addition, the results of the present work were compared with reported track segment yields.