Water radiolysis with heavy ions

重粒子線による水の放射線分解

山下 真一; 勝村 庸介; 前山 拓哉*; Lin, M.; 室屋 裕佐*; 村上 健*; Meesungnoen, J.*; Jay-Gerin, J.-P.*

Yamashita, Shinichi; Katsumura, Yosuke; Maeyama, Takuya*; Lin, M.; Muroya, Yusa*; Murakami, Takeshi*; Meesungnoen, J.*; Jay-Gerin, J.-P.*

生成物収量測定とトラック内反応シミュレーションにより高エネルギー重粒子線による水の放射線分解について調べた。核子あたりのエネルギーが最大で500MeVのヘリウムからキセノンまでのイオンを放射線医学総合研究所の重粒子加速器HIMACにおいて照射に用いた。高エネルギー重粒子線の長い飛程(10cm以上)を利用し、トラックセグメント収量を主要生成物であるe, OH, HOについて測定した。さらに、PMMA製のエネルギー吸収材を利用してイオンのエネルギーを核子あたり約10MeVまで減少させ、LETを約2500eV/nmまで増加させて測定を実施した。また、捕捉剤濃度の効果も検討し、モンテカルロシミュレーションによる再現やトラック構造及びトラック内ダイナミクスに関する検討も実施した。

Water radiolysis with high-energy heavy ions has been investigated through measurement of product yield and simulation of intra-track reactions. Ions from helium to xenon of energies up to 500 MeV per nucleon were taken for irradiation at the biological irradiation port of HIMAC installed at NIRS, Japan. Taking long range of the ions, typically longer than 10 cm, as an advantage, track-segment yields of main water decomposition products, e, OH and HO, have been determined. Utilizing energy absorber made of PMMA, ion energies were decreased down to about 10 MeV per nucleon to vary beam properties in sample solutions, and then, product yields for wide ranges of ion types and energies were accumulated. Influences of scavenger concentration have also been discussed and yield of approximate sum of OH, H and e was measured. In parallel to these measurements, Monte-Carlo simulation of intra-track reactions has been conducted not only to reproduce the experimental results but also to discuss further track structure and its dynamics from microscopic viewpoint.