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Yang, S.*; Katsumura, Yosuke*; Yamashita, Shinichi*; Matsuura, Chihiro*; Hiroishi, Daisuke*; Lertnaisat, P.*; Taguchi, Mitsumasa
Radiation Physics and Chemistry, 123, p.14 - 19, 2016/06
Times Cited Count：2 Percentile：19.71(Chemistry, Physical)
-radiolysis of boiling water has been investigated. The G-value of H
evolution was found to be very sensitive to the purity of water. In high-purity water, both H and O gases were formed in the stoichiometric ratio of 2:1; a negligible amount of HO remained in the liquid phase. The G-values of H and O gas evolution depend on the dose rate: lower dose rates produce larger yields. To clarify the importance of the interface between liquid and gas phase for gas evolution, the gas evolution under Ar gas bubbling was measured. A large amount of H was detected, similar to the radiolysis of boiling water. The evolution of gas was enhanced in a 0.5 M NaCl aqueous solution. Deterministic chemical kinetics simulations elucidated the mechanism of radiolysis in boiling water.
Iwamatsu, Kazuhiro*; Muroya, Yusa*; Yamashita, Shinichi*; Kimura, Atsushi; Taguchi, Mitsumasa; Katsumura, Yosuke*
Radiation Physics and Chemistry, 119, p.213 - 217, 2016/02
Times Cited Count：1 Percentile：10.71(Chemistry, Physical)A quick measurement system of a continuous absorption spectrum covering a wide range from 200 to 950 nm was constructed by employing an optical multi-channel detector. Ion beam pulse radiolysis with 12.5 MeV/u He, 18.3 MeV/u C and 17.5 MeV/u Ne ions were performed with the measurement system. Transient absorption spectrum of (SCN)
was clearly observed in KSCN aqueous solutions within a few minutes in spite of their very small absorbance, demonstrating high sensitivity of 0.001-0.003 in absorbance in the range from 260 to 660 nm as well as short measurement time of a few minutes. Two different absorption peaks attributed to Br and Br
were observed simultaneously in NaBr aqueous solutions, showing powerfulness of the measurement system in overviewing chemical kinetics under ion beam irradiation especially in not well investigated chemical systems.
Hiroki, Akihiro; Yamashita, Shinichi*; Kimura, Atsushi; Nagasawa, Naotsugu; Taguchi, Mitsumasa
Nuclear Instruments and Methods in Physics Research B, 365(Part B), p.583 - 586, 2015/12
Effects of liner energy transfer (LET) and dose rate on the optical property of polymer gel dosimeters were investigated. The dosimeter prepared by using a radiation-crosslinked hydroxypropyl cellulose gel and methacrylate monomers such as 2-hydroxyethyl methacrylate and nonaethylene glycol dimethacrylate showed the color change from colorless to white with the He, C, Fe ions irradiation. Absorbance of the irradiated dosimeters increased with the dose up to 10 Gy. The absorbance of the dosimeters at the same total dose decreased with increasing dose rate in the range of 0.1 to 6.8 Gy/min. The absorbance decreased in order of He, C, Fe ions, which was in agreement with a change of LET. The increase in LET affected the decrease in the number of polymerization initiator such as OH radical and hydrated electron, resulting in the reduction of the absorbance of the dosimeters.
Yamashita, Shinichi*; Iwamatsu, Kazuhiro; Maehashi, Yuki*; Taguchi, Mitsumasa; Hata, Kuniki; Muroya, Yusa*; Katsumura, Yosuke*
RSC Advances (Internet), 5(33), p.25877 - 25886, 2015/02
Times Cited Count：12 Percentile：38(Chemistry, Multidisciplinary)Pulse radiolysis experiments were carried out to observe transient absorptions of reaction intermediates produced in NO and Ar-saturated aqueous solutions containing 0.9-900 mM NaBr. The most important species among the reaction intermediates are BrOH 
and Br , which commonly have absorption peaks around 360 nm. The experimental results were compared with the results of simulation based on a spur diffusion model. Each of several complicated sequential radiation-induced chemical reactions was carefully considered, optimizing its rate constant within a range of reported values. All the experimental results were able to be universally reproduced by the simulation, assuming a reaction not yet reported, 2BrOH 
Br + 2OH, with a rate constant of 3.8 
10
M
s, which is significant only within 10 micro-s for rather high bromide concentrations (
10 mM). Primary 
values, which are yields after sufficient diffusion from the spur to the perimeter region during 100 ns, of major water decomposition products, as well as of the reaction intermediates, were calculated for NO and Ar-saturated conditions as a function of NaBr concentration.
Hiroki, Akihiro; Yamashita, Shinichi*; Taguchi, Mitsumasa
Journal of Physics; Conference Series, 573(1), p.012028_1 - 012028_4, 2015/01
Times Cited Count：4 Percentile：79.08(Engineering, Biomedical)Polymer gel dosimeters based on radiation-crosslinked hydroxypropyl cellulose gel were prepared, which comprised 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol dimethacrylate (9G) as less toxic monomers and tetrakis (hydroxymethyl) phosphoniumu chloride (THPC) as an antioxidant. The dosimeters exposed to 
Co -rays became cloudy at only 1 Gy. The irradiated dosimeters were optically analyzed by using a UV-vis spectrophotometer to evaluate dose response. Absorbance of the dosimeters linearly increased in the dose range from 0 to 10 Gy. The dose sensitivity increased with increasing 9G concentration. The dosimeter with 2 wt% HEMA, 3 wt% 9G, and 0.16 wt% THPC exhibited about 0.04 Abs Gy of the dose sensitivity. The dose sensitivity of the dosimeters was also enhanced by increment in THPC, reached about 0.06 Abs Gy at 0.40 wt% THPC.
Yamashita, Shinichi*; Hiroki, Akihiro; Taguchi, Mitsumasa
Radiation Physics and Chemistry, 101, p.53 - 58, 2014/08
Times Cited Count：10 Percentile：60.98(Chemistry, Physical)Hiroki, Akihiro; Yamashita, Shinichi; Sato, Yuichi*; Nagasawa, Naotsugu; Taguchi, Mitsumasa
Journal of Physics; Conference Series, 444, p.012028_1 - 012028_4, 2013/06
Times Cited Count：10 Percentile：91.72(Physics, Multidisciplinary)Polymer gel dosimeters consisting of less toxic methacrylate-type monomers such as 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol 400 dimethacrylate (9G) with hydroxypropyl cellulose (HPC) gel were prepared. We investigated the effect of monomer compositions on the dose response of the polymer gel dosimeter. The HPC gels as a matrix for the polymer gel dosimeter were obtained by electron beam irradiation to 20wt% of HPC aqueous solution. The dried HPC gels were immersed into mixed monomer solutions, and then the swollen gels were vacuum-packed to prepare the polymer gel dosimeters. The polymer gel dosimeters showed cloudiness by exposing to Co -ray, in which the cloudiness increased with the dose up to 10 Gy. At the same dose, the increase in the cloudiness appeared with increasing concentration of 9G. It was found that the dose response depended on the composition ratio between HEMA and 9G.
Fujibuchi, Toshio*; Kawamura, Taku*; Yamanashi, Koichi*; Hiroki, Akihiro; Yamashita, Shinichi*; Taguchi, Mitsumasa; Sato, Yuichi*; Mimura, Koichi*; Ushiba, Hiroaki*; Okihara, Toru*
Journal of Physics; Conference Series, 444(1), p.012089_1 - 012089_4, 2013/06
Times Cited Count：3 Percentile：71.54(Physics, Multidisciplinary)Yamashita, Shinichi; Baldacchino, G.*; Maeyama, Takuya*; Taguchi, Mitsumasa; Muroya, Yusa*; Lin, M.*; Kimura, Atsushi; Murakami, Takeshi*; Katsumura, Yosuke
Free Radical Research, 46(7), p.861 - 871, 2012/07
Times Cited Count：24 Percentile：53.66(Biochemistry & Molecular Biology)Radiation-induced reactions in aqueous solutions of a water-soluble coumarin derivative, coumarin-3-carboxyl acid (C3CA), have been investigated by pulse radiolysis with 35-MeV electron beam, final product analysis after Co 
-irradiations, and deterministic model simulations. It was found that C3CA reacts with the hydroxyl radical (
OH) as well as the hydrated electron at nearly diffusion-controlled rate constants: 6.8
10 and 2.110
Ms, respectively. Reactivity of C3CA toward O was not confirmed. Production of a fluorescent molecule 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA) was detected by a fluorescence spectrometer coupled with high performance liquid chromatography. Production yields of 7OH-C3CA were in a range from 0.025 to 0.18 (100 eV), depending on irradiation conditions. A variety of the yield with saturating gas, additive, and C3CA concentration implied that there are at least two pathways from scavenging reaction of C3CA toward OH to 7OH-C3CA: peroxidation reaction followed by elimination of perhydroxyl radical and disproportionation reaction. A reaction mechanism involving the two pathways was proposed and incorporated into the simulations, showing good explanation of experimentally measured 7OH-C3CA yields with a constant conversion factor from OH scavenging to 7OH-C3CA production, 4.7%, unless 
-BuOH is not added.
Maeyama, Takuya*; Yamashita, Shinichi; Taguchi, Mitsumasa; Baldacchino, G.*; Sihver, L.*; Murakami, Takeshi*; Katsumura, Yosuke
Radiation Physics and Chemistry, 80(12), p.1352 - 1357, 2011/12
Times Cited Count：14 Percentile：71.96(Chemistry, Physical)Coumari-3-carboxylic acid scavenges OH radical produced in water radiolysis, leading to production of a fluorescence probe at almost constant ratio relative to the amount of the scavenged OH radicals. This was applied in estimation of OH radical yield in water radiolysis especially with therapeutic heavy ions of GeV-class energies, i.e. 
C
beams of 135, 290 and 400 MeV/u. OH yields upstream of the Bragg peaks decreased with increasing penetration depth of the projectile ions while that downstream suddenly jumped up to near the value for low-LET radiations such as -rays. This is due to low-LET secondary fragmentation ions produced during long trajectory of the primary projectile C ion. Quantitative explanation by nuclear fragmentation simulations with PHITS code was attempted and resulted in 15-45% underestimation in the region behind the Bragg peaks, which would be due to the difference in geometries between irradiations of the sample solutions and dosimetry with a small ionization chamber.
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Taguchi, Mitsumasa; Kimura, Atsushi; Murakami, Takeshi*; Katsumura, Yosuke
Radiation Physics and Chemistry, 80(4), p.535 - 539, 2011/04
Times Cited Count：33 Percentile：91.42(Chemistry, Physical)Aqueous coumarin-3-carboxylic Acid (3CCA) solutions were irradiated with eight different ion beams covering LET range from 0.5 to above 2000 eV/nm. -values of 7OH-3CCA, one of hydroxylated products in radiolysis of the solutions, have been determined by fluorescence-HPLC technique in 3CCA concentration range from 0.1 to 26 mM. The formation yield of 7OH-3CCA increased with increasing concentration of 3CCA while it decreased with increasing LET value of ion beam. Compared with our previous reports on (OH) at a scavenging capacity of 10
s with absorption spectroscopy, it was found that (7OH-3CCA) is about (4.7
0.6)% of (OH), which is consistent for all of the ion beams used in the present study. However, 7OH-3CCA yields in high CCA concentration region, especially by using extremely high LET ions, were much higher than expected values based on the above conversion factor and (OH) value predicted in theoretical work.
Yamashita, Shinichi; Taguchi, Mitsumasa; Baldacchino, G.*; Katsumura, Yosuke
Charged Particle and Photon Interactions with Matter; Recent Advances, Applications, and Interfaces, p.325 - 354, 2010/12
Irradiation effects induced by heavy ions are much different from those by low-LET radiations. Such distinctiveness has been applied to cancer therapy, surface processing, analytical techniques, and so on. However, detailed mechanism through which such distinctiveness appears has not been clarified yet. In this chapter, what have experimentally been found recently, especially within these five years, in water radiolysis with positively-charged atomic heavy ions are shown. Steady-state radiolysis studies and pulse radiolysis studies are separately summarized because these two approaches inherently involve own advantages and limitations. Gathering reported products yields and kinetics, track structures and intra-track dynamics are discussed. One of the most characteristic features of recent studies is that track-segment or -differential yields were intensively measured compared to earlier studies.
Baldacchino, G.*; Maeyama, Takuya*; Yamashita, Shinichi; Taguchi, Mitsumasa; Kimura, Atsushi; Katsumura, Yosuke; Murakami, Takeshi*
Chemical Physics Letters, 468(4-6), p.275 - 279, 2009/01
Times Cited Count：38 Percentile：79.07(Chemistry, Physical)This paper reports a sensitive method using HPLC-fluorescence detection of OH in liquid water under high-energy heavy-ion irradiation. The coumarin-3-carboxylic-acid (3CCA) molecule was selected for probing OH and providing the fluorescent 7-hydroxy-coumarin-3-carboxylic-acid (7OH-3CCA). Since the concentration limit achievable is better than 1 nM, the radiolytic yields were determined with a sensitivity of 210
mol/J for 4.8-GeV-C of and 20-GeV-
Ar
in the ns time-range. They decrease with the linear energy transfer from 2.810
to 1.310 mol/J (C of 11 eV/nm) and 1.510 to 0.910 mol/J (Ar of 90 eV/nm) which is in agreement with the literature data.
OH yields with fluorescent probe, 1; Investigation into reaction mechanism and reactivity toward water decomposition radicals of coumarin-3-carboxylic acidMaeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Muroya, Yusa*; Taguchi, Mitsumasa; Kimura, Atsushi; Katsumura, Yosuke
no journal, ,
no abstracts in English
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Taguchi, Mitsumasa; Kimura, Atsushi; Katsumura, Yosuke; Murakami, Takeshi*
no journal, ,
no abstracts in English
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Katsumura, Yosuke; Taguchi, Mitsumasa; Kimura, Atsushi; Muroya, Yusa*; Murakami, Takeshi*
no journal, ,
Detailed mechanism in which effectiveness of heavy ions in cancer therapy are derived from is not known well. It is inevitably important to examine water radiolysis with high-energy heavy ions because water is main component of human body. Among several water decomposition products, OH is known to be most responsible for radiation induced cell death in indirect actions. OH yield has been reported for heavy-ion irradiations in several works employing absorption analyses. With increasing LET, OH yield decreases monotonically (at least up to several hundred eV per nm). Then, more sensitive way to determine OH yield is preferable for higher LET region. In this work, a fluorescent probe, coumarin-3-carboxylic acid, was applied for OH-yield determination as a sensitive way of quantification of OH radical production. Especially, OH yield near the Bragg peaks was discussed.
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Katsumura, Yosuke; Muroya, Yusa*; Taguchi, Mitsumasa; Kimura, Atsushi; Murakami, Takeshi*
no journal, ,
Fluorescent probe 7-Hydroxy-coumarin-3-carboxylic acid, which is a product of reaction between Coumarin-3-carboxylic acid (CCA) and hydroxyl radical (OH), was applied to estimation of the yield of OH produced in water radiolysis with heavy ions of energies up to 28 GeV provided from HIMAC (Heavy Ion Medical Accelerator in Chiba). LET was varied from 0.2 for -ray or fast electron beam to 346 eV/nm for iron ion beam. With changing the concentration of CCA in the range from 0.1 to 26 mM, scavenging time scale was varied from 4 ns to 1 
s, at which time scale intra-track reactions between water decomposition radicals including OH are significant.
OH yield near the Bragg peakMaeyama, Takuya*; Yamashita, Shinichi; Katsumura, Yosuke; Baldacchino, G.*; Taguchi, Mitsumasa; Kimura, Atsushi; Murakami, Takeshi*
no journal, ,
Aqueous solution of Coumarin-3-carboxylic acid (CCA) has been applied to yield measurement of OH in water. 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. Taking sensitiveness of fluorometry as an advantage, OH yields near the Bragg peaks, which are known very small compared to those in plateau LET region, have been measured. Contribution of fragmentations, which are known to be significant near the Bragg peaks of high-energy heavy ions, is also being discussed.
Maeyama, Takuya*; Yamashita, Shinichi*; Baldacchino, G.*; Katsumura, Yosuke*; Taguchi, Mitsumasa; Kimura, Atsushi; Muroya, Yusa*; Murakami, Takeshi*
no journal, ,
no abstracts in English
Yamashita, Shinichi; Maeyama, Takuya*; Baldacchino, G.*; Katsumura, Yosuke; Muroya, Yusa*; Taguchi, Mitsumasa; Kimura, Atsushi; Murakami, Takeshi*
no journal, ,
A novel sensitive method to determine OH yield in water radiolysis has been developed and has been applied for heavy-ion irradiations. In this work, this method was extended to measurement near the Bragg peak. It was found that OH yield has minimum value near the Bragg peak and is different even for the same ion irradiation of different acceleration energies.
