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Nagaishi, Ryuji; Aoyagi, Noboru; Taguchi, Mitsumasa; Kondo, Takafumi*; Yang, J.*; Yoshida, Yoichi*
no journal, ,
Radiolytic reactions in ionic liquids of thiocyanate salts were studied by means of the pulse radiolysis technique. In the imidazolium salts, transient absorption of dimer radical anion of thiocyanate was observed as well as that originated from imidazolium cation. In the ammonium salts containing two anions, the initial absorption of dimer increased with increasing the concentration of thiocyanate anion in the salts. These suggest that one of the main ionization sites of ionic liquids is thiocyanate anion to generate electron and thiocyanate radical, and then that the rapid formation of dimer is mainly due to the direct dimerization between the radical and its surrounding anion, not via their diffusion encounter.
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Katsumura, Yosuke; Taguchi, Mitsumasa; Kimura, Atsushi; Muroya, Yusa*; Murakami, Takeshi*
no journal, ,
Cancer therapy needs ions of several GeV to attain sufficiently long penetration depth into human body (normally 30 cm) to treat cancer in deep position. While advantages of heavy ion therapy are well-known phenomenologically, details of mechanism in which heavy ion irradiation leads to distinctive biological effectiveness have not been clarified yet. Then, understanding of water radiolysis with heavy ions is necessary because water is main component of human body. Aqueous solution of Coumarin-3-carboxylic acid (CCA) has been applied to yield-measurement of 
OH produced in water radiolysis with therapeutic carbon ion beam provided from HIMAC at NIRS. Production yield of a fluorescent probe, 7OH-CCA, which is a stable product produced after scavenging reaction for OH by CCA, was determined by using HPLC connected to a fluorometer. By using this chemical system, OH yields near the Bragg peak have been measured. Contribution of fragmentations, which are known to be significant near the Bragg peak of high-energy heavy ions, is also discussed by conducting fragmentation simulation.
Kumagai, Yuta; Nagaishi, Ryuji; Yamada, Reiji; Muroya, Yusa*; Katsumura, Yosuke*
no journal, ,
Reactions of hydrated electron and OH radical in the presence of colloidal silica were studied by pulse-radiolysis technique to understand the addition effect of silica based materials on the radiolysis of aqueous solutions, which has been observed as changes in yields of final products in steady-state radiolysis. The results shows that there is an interaction between OH radical and silica particles, which scavenged OH radical and inhibited oxidation of ferrocyanide ion by OH radical. On the other hand, addition of silica particles had almost no effect on the decay kinetics of hydrated electron. These results indicate that scavenging of OH radical has a significant role in the addition effect of silica based materials on radiation-induced reactions.
Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Kudo, Hisaaki*; Katsumura, Yosuke*
no journal, ,
Yamashita, Shinichi; Katsumura, Yosuke; Maeyama, Takuya*; Lin, M.; Muroya, Yusa*; Murakami, Takeshi*; Meesungnoen, J.*; Jay-Gerin, J.-P.*
no journal, ,
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 H
O, 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.