LET LET. < 10 MeV/u H He MeV/u C. Keywords: Water radiolysis, ion beam, track structure, G value, intratrack reaction, LET, scavenger

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1 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 aq, OH and H 2 O 2, 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 Université desherbrooke, 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 OH detection with HPLC connected fluorometry. Keywords: Water radiolysis, ion beam, track structure, G value, intratrack reaction, LET, scavenger 1 Radiation Chemical Reactions in Water Radiolysis with Therapeutic Heavy Ion Beams Shinichi Yamashita (Advanced Science Research Center, Japan Atomic Energy Agency) , TEL: , FAX: , yamashita.shinichi@jaea.go.jp LET LET < 10 MeV/u HHe MeV/u C event time /s H 2 O physical physicochemical chemical biological excitation 1 H 2 O* H 2 O+ aq ionization + OH, e -, H, etc. aq e - thermalization, solvation, etc. intra-track reactions, diffusion OH, e -, H+, H 2 O 2, H 2, etc.? minutes, hours, days, months, years

2 LET 1 1ps OH OHe aq H 1ps 2 OH e aq OH + OH H 2 O 2 OH + e aq OH 2e aq (+2H 2O) H 2 (+2OH ) dm 3 /mol/s (1) dm 3 /mol/s (2) dm 3 /mol/s (3) 100 ns primary yield G C Fe 1 ps 100 ns 100 ns 100 ns 5 Yamashita 2) LaVerne 3) MeV/u NIRS HIMACHeavy Ion Medical Accelerator in Chiba 12 C MeV/u 4 He MeV/u 56 Fe MeV/u LET ev/nm 4) HIMAC 100 MeV/u scavenger e aq NaNO 3 Na 2 HPO 3 e aq NO C 290 MeV/u e āq 1 µm Blow-up OH, etc. 200 nm Fe 500 MeV/u 2 1ps 1) Blow-up e aq + NO 3 NO dm 3 /mol/s (4) NO H 2 O NO 2 + 2OH dm 3 /mol/s (5) NO 2 + HPO2 3 HNO 2 + PO dm 3 /mol/s (6) HNO 2 NO 2 90 (2010) 12

3 OH H OH + HPO 2 3 H 2 O + PO dm 3 /mol/s (7) H + HPO 2 3 H 2 + PO dm 3 /mol/s (8) Radical + Scavenger Products k S dm 3 /mol/s (9) k S [S] s 1 [S] mol/dm 3 Radical Products k S [S] s 1 (10) k S [S] s ns 10 7 s HIMAC e aq OHH 2 O 2 3 4, 5) LET e aq OH (1) H 2 O 2 Jay-Gerin Universitéde Sherbrooke H 2 O 2 LET < 100 ev/nm LET LET LET LET : 4,5) : 4 He 2+ : 12 C 6+ : 20 Ne 10+ : 28 Si 14+ : 40 Ar 18+ : 56 Fe 26+ : 1) LET (Z eff /β) 2 4 Z eff β 4 3 (Z eff /β) MeV/u LET Zeff 2 Z2 eff β 2 β 2 LET 13

4 MV MV 2+ e aq + MV 2+ MV dm 3 /mol/s (11) OH H HCOO OH + HCOO H 2 O + COO H + HCOO H 2 + COO dm 3 /mol/s (12) dm 3 /mol/s (13) COO MV 2+ COO + MV 2+ MV + + CO dm 3 /mol/s (14) 3 MV MV + MV + HCOO mol/dm 3 (12) (13) 100 ns ns MV (Z eff /β) 2 4) 3 (Z eff /β) 2 < 10 MeV/u 1 H + 4 He 2+ (Z eff /β) 2 MZ eff /E 0 LaVerne M E 0 3) 4 MV Cl 2 HCOONa 6) e aq G(MV +. ) /(100 ev) Scavenging time scale for. OH, t S /ns Low-LET (0.2), reported He (2.2) C (13) Ne (31) Si (54) Ar (92) Fe (185) (LET ev/nm) Symbols: Lines: experimental simulation Concentration of HCOO - /mol/dm 3 5 MV + 6) 3 HCOO MV + OH H 4 He Fe 26+ LET 90 (2010) 14

5 MV + 3 (1) (3) 17 COO + COO products dm 3 /mol/s (15) 5 MV + COO + OH products (16) MV + + OH products (17) (12) OH COO (1) (16) e aq MV+ (2) (17) 5 LET (16) (17) 6 MV (15) (15) LET 6 COO (14) (15) COO (15) COO OH OH 6) 5 OH 10 6 mol/dm 3 CEA BALDACCHINO OH 7) OH -3-Coumarin-3-carboxylic acid: C3CA 0.5g/100g mol/dm 3 ns C3CA C3CA OH e aq dm 3 /mol/s hydroxyl-coumarin-3-carboxylic acid: 7OH-C3CA OH C3CA 5%7OH-C3CA e aq 7OH-C3CA cgy 60 Co-γ 7OH- C3CA 7OH-C3CA C3CA HPLC ns μs OH 7) 15

6 6 GeV HIMAC LET (Z eff /β) 2 MV + OH OH OH (3) 1ps O 2 HIMAC NIRSJean-Paul JAY- GERIN Jintana MEESUNGNOEN Université de Sherbrooke Gérard BALDACCHINO CEA COE 1) J. Meesungnoen and J.-P. Jay-Gerin, J. Phys. Chem. A 109, 6406 (2005). 2) S. Yamashita, M. Taguchi, G. Baldacchino, Y. Katsumura, Radiation Chemistry of Liquid Water with Heavy Ions: Steady-State and Pulse Radiolysis Studies, in Charged Particle and Photon Interactions with Matter: Recent Advances, Applications, and Interfaces, Y. Hatano, Y. Katsumura, A. Mozumder, Eds., Taylor & Francis, in press. 3) J. A. LaVerne, Radiation Chemical Effects of Heavy Ions, in Charged Particle and Photon Interactions with Matter: Chemical, Physicochemical, and Biological Consequences with Applications, Y. Hatano, A. Mozumder, Eds., Marcel Dekker (2004). 4) S. Yamashita, Y. Katsumura, M. Lin, et al., Radiat. Phys. Chem. 77, 439 (2008). 5) S. Yamashita, Y. Katsumura, M. Lin, et al., Radiat. Phys. Chem. 77, 1224 (2008). 6) S. Yamashita, Y. Katsumura, M. Lin, et al., Radiat. Res. 170, 521 (2008). 7) G. Baldacchino, T. Maeyama, S. Yamashita, et al., Chem. Phys. Lett. 275, 468 (2009) (2010) 16