Radiation chemical reactions in water radiolysis with therapeutic heavy ion beams

Water radiolysis with heavy-ion beams of energies up to 28 GeV provided from HIMAC (Heavy Ion Medical Accelerator in Chiba), NIRS (National Institute of Radiological Sciences) has been investigated from the viewpoint of correlation of products yields with track structure and its dynamics. For wide variety of heavy-ion beams in terms of LET, velocity, charge, etc., primary yields of major products in water radiolysis, e_eq^-, radical OH and H₂O₂, have been measured by employing scavenging method to convert transient water radicals into stable and easily detectable species. Temporal behavior of approximate sum of water radicals has also been experimentally measured by a scavenging method with methyl viologen cation and formate anion. A Monte-Carlo simulation code of water radiolysis developed by a group of Universite de Sherbrooke, Canada was complementally used in discussion of microscopic track structure and its dynamics. In addition, a fluorescent probe, 7-hydroxyl-coumarin-3-carboxylic acid, was utilized in sensitive radical OH detection with HPLC connected fluorometry. (author)