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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.
Hiroki, Akihiro
Cellulose Communications, 22(3), p.143 - 145, 2015/09
no abstracts in English
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.
Nakagawa, Seiko*; Taguchi, Mitsumasa; Kimura, Atsushi; Nagasawa, Naotsugu; Hiroki, Akihiro
Nuclear Instruments and Methods in Physics Research B, 334, p.64 - 68, 2014/09
Times Cited Count：2 Percentile：19.23(Instruments & Instrumentation)N
-saturated 2-propanol solutions containing styrene and maleimide were gelled by the addition of hydroxypropylcellulose and irradiated by proton, He and C-ion beams. The trend in the dose rate and LET effects on the yield and molecular weight distribution of the polymer produced in the gel was almost the same in the solution. On the contrary, the dose rate effect in the gel was higher than that in the solution. This effect was accelerated for irradiations by proton as well as heavier ion with a higher LET value.
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
Hoshasen To Sangyo, (135), p.15 - 18, 2013/12
no abstracts in English
Hiroki, Akihiro; Sato, Yuichi*; Nagasawa, Naotsugu; Ota, Akio*; Seito, Hajime; Yamabayashi, Hisamichi*; Yamamoto, Takayoshi*; Taguchi, Mitsumasa; Tamada, Masao; Kojima, Takuji
Physics in Medicine & Biology, 58(20), p.7131 - 7141, 2013/10
Times Cited Count：17 Percentile：54.54(Engineering, Biomedical)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)Hiroki, Akihiro; Hong, P. T. T.*; Nagasawa, Naotsugu; Tamada, Masao
Transactions of the Materials Research Society of Japan, 36(3), p.397 - 400, 2011/09
Properties such as a degree of swelling (Sw) and biodegradability of blend hydrogels based on carboxymethyl cellulose (CMC) and carboxymethyl starch (CMS) were investigated. The irradiations of 40wt% of CMC/CMS aqueous solution (blend ratio of CMC/CMS: 100/0, 75/25, 50/50, 25/75, 0/100) were carried out using Co -ray source to obtain the blend hydrogels. The gel fraction of CMC/CMS blend hydrogels increased sharply up to 10 kGy and reached a constant value at 30 kGy. Increase in the ratio of CMC increased the gel fraction of blend hydrogel. These hydrogels reached the equilibrium swelling state from initial dried gel in about 2 hours. The blend hydrogels with the maximum Sw of about 800 were obtained at 2 kGy. The Sw decreased significantly with increasing the dose, and leveled off in the range of 20-40 kGy. As a result of the biodegradability test in soil, the discharge of carbon oxide generated by the biodegradation of the blend hydrogels (the Sw of about 100) gradually increased with increasing the ratio of CMS, resulting in the decomposition ratio in the range of 5 to 20% at 30 days. Therefore, the biodegradability of the blend hydrogels was controlled by adjusting the composition of the CMC/CMS and irradiation doses.
O
nanoparticles on radiolytic HO production in waterRoth, O.*; Hiroki, Akihiro; LaVerne, J. A.*
Journal of Physical Chemistry C, 115(16), p.8144 - 8149, 2011/04
Times Cited Count：14 Percentile：42.26(Chemistry, Physical)Hydrogen peroxide, HO, is the major stable oxidizing species produced in the radiolysis of water and understanding the mechanisms involved in its production is important both from a fundamental science perspective and for engineering purposes, in particular within the nuclear power industry. In this work, the yields of HO were determined in aqueous slurries in the pH range of 1-13 with various amounts of added AlO nanoparticles. The addition of AlO generally decreased HO yields at all pH values within this range in the radiolysis of both deaerated and aerated slurries, except at very high pH. Very little effect of pH was observed in the radiolysis of deaerated systems in the pH range of 3-8, whereas a large increase in HO yields was observed in aerated AlO slurries at the extreme pH values. Scavenger capacity studies using methanol as an OH radical scavenger show that the decrease in HO yields with added AlO occurs at relatively long time scales and is probably due to reaction of the solid nanoparticles with OH radicals.
N117CS membranesIwai, Yasunori; Hiroki, Akihiro; Tamada, Masao
Journal of Membrane Science, 369(1-2), p.397 - 403, 2011/03
Times Cited Count：19 Percentile：53.45(Engineering, Chemical)The successful formation of radiation-induced crosslinking in Nafion N117CS membranes was clearly demonstrated by tensile testing, a methanol uptake measurement, thermo-mechanical analysis (TMA) and fluorine-19 MAS NMR (
F NMR). The possibility of radiation-induced crosslinking of Nafion never had been considered with regard to the thermal stability of Nafion membranes, since the scission of PFAE pendant-chains in Nafion membranes in their protonated form begins at 523 K. To improve the thermal stability of Nafion membranes, Nafion membranes were soaked in sodium chloride prior to irradiation. The sodium-exchange Nafion membranes were irradiated with rays in an argon atmosphere at temperatures ranging from room temperature to 618 K. The irradiated membranes were re-exchanged to the protonated form. Fluorine-19 MAS NMR results for the alcohol-swollen membranes indicate peaks which originated due to radiation-induced crosslinking. An increase in percent elongation at break, a decrease in methanol uptake, and a decrease in the softening temperature at a differential TMA peak for membranes irradiated at 598 K compared to received membranes also add support for our new finding.
Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Kudo, Hisaaki*; Katsumura, Yosuke*
Radiation Physics and Chemistry, 80(2), p.149 - 152, 2011/02
Times Cited Count：18 Percentile：77.43(Chemistry, Physical)Carboxymethyl cellulose (CMC), one of polysaccharide derivatives, at highly concentrated aqueous solution undergoes radiation-crosslinking reactions. In this topic, CMC radical, formed by reaction with OH radical attributed to radiation-induced crosslinking reaction, were studied by ESR method to understand the radiation-induced reaction mechanism of CMC aqueous solution. At first, it was succeeded to observe ESR spectra of the CMC radical using photolysis of hydrogen peroxide as the origin of OH radical. Observed ESR spectra were identified as radicals located on the secondary carbon of carboxymethyl groups. Secondly, NO saturated CMC aqueous solution 6 min after electron beam irradiation was measured by ESR method. The spectra were almost same shape as the case of photolysis of hydrogen peroxide, and were assigned as long-lived radicals located on carboxymethyl groups. Next, in the case of N and O saturation, spectra intensity become half or 0. This means that these long-lived radicals are produced by reaction with OH radical.
Iwai, Yasunori; Sato, Katsumi; Hiroki, Akihiro; Tamada, Masao; Hayashi, Takumi; Yamanishi, Toshihiko
Fusion Engineering and Design, 85(7-9), p.1421 - 1425, 2010/12
Times Cited Count：3 Percentile：24.08(Nuclear Science & Technology)The deteriorations of polymeric materials for a SPE-type high-level tritiated water electrolyzer composed of the Water Detritiation System (WDS) against sulfonic acid environment and radiation environment were discussed. A long-term durability of VITON, AFLAS, denaturated polyphenylene ether, and Kapton polyimide immersed in a sulfonic acid was demonstrated. Negligible degradation in percent elongation at break of these polymeric materials was observed up to the immersing period of 2 years. The detectable radiation deterioration in ionic conductivity of Nafion N117CS ion exchange membrane irradiated with electron beams up to the integrated dose of 1500 kGy was measured. The ionic conductivity of Nafion N117CS ion exchange membrane irradiated at more than 1000 kGy was slightly deteriorated. As for the elastomers for its use as a seal, the radiation degradation in hardness of VITON, AFLAS was investigated. Negligible degradation in hardness of these rubbers was observed up to the integrated dose of 1500 kGy. The water uptake of rubbers was generally increased as the integrated dose was increased. However, irradiated VITON rubbers had constant water uptake up to the integrated dose of 1500 kGy.
Takigami, Machiko*; Nagasawa, Naotsugu; Hiroki, Akihiro; Kasai, Noboru; Yoshii, Fumio; Tamada, Masao; Takigami, Shoji*; Shibata, Takuya*; Aketagawa, Yasushi*; Ozaki, Masuo*
Transactions of the Materials Research Society of Japan, 35(3), p.647 - 650, 2010/09
There are many livestock farmers in Gunma Prefecture. Many of the farms are located under Mt. Akagi and Haruna, which attract tourists. Furthermore, rivers around the mountains are source of water supply to metropolitan area. Therefore, the waste treatments are very important. Regulations of smell and COD (chemical oxygen demand) are severe in Gunma Prefecture. Although there is no regulation for color of drain water, color in secondary treated water from livestock urine waste has been one of the major concerns for livestock farmers. The color is a metabolite of microorganisms and not easy to be removed. People have tried to remove the color by ozone treatment, absorption using activated carbon or soils. An absorbent was prepared by radiation grafting; fibers were irradiated with Co -rays and some kinds of monomers were grafted onto the fibers. The absorbent thus prepared were used to decolorize the secondary treated water. The color and COD were removed by the absorbent, however, COD removal was more difficult than decolorization. Degree of grafting (weight increase expressed in % by grafting reaction to initial weight of the fiber), treated water/absorbent ratio, flow rate of treated water, and direction of flow affected color and COD removal. The used absorbent could be used repeatedly after washing.
Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Muroya, Yusa*; Kudo, Hisaaki*; Katsumura, Yosuke*
Radiation Physics and Chemistry, 79(3), p.276 - 278, 2010/03
Times Cited Count：12 Percentile：59.22(Chemistry, Physical)Carboxymethyl chitosan (CMCTS) is one kind of polysaccharide derivatives and has a good water-solubility. At a high concentrated aqueous solution, CMCTS forms gel by ionizing irradiation, though polysaccharide derivatives are generally radiation-degradation type. In general, OH radical, which is one of main water radiolysis products and very oxidative species, is said to induce crosslinking reaction of polymer solution. The purpose of this study is to understand the radiation-crosslinking mechanism of CMCTS at a high concentrated aqueous solution. In this study, identification of CMCTS radical produced by reaction with OH radical was introduced. CMCTS radical in an aqueous solution was observed directly by ESR method using photolysis of hydrogen peroxide. The ESR spectra have a large doublet split and small triplet split like [Triplet 
Doublet]. However, some species seemed to be overlapped on ESR spectra, because right-and-left triplet spectra are not equiform. Compared with some radicals, which have analogical structure to CMCTS, about hyperfine coupling constant, [Triplet Doublet], assigned as radical on carboxymethyl group linked to C6, and [Doublet], assigned as radical on carboxymethyl group linked to C2 or C3, were isolated from ESR spectra of experimental results. In conclusion, these spectra were identified as radicals located on secondary carbon of carboxymethyl groups.
Iwai, Yasunori; Hiroki, Akihiro; Tamada, Masao; Isobe, Kanetsugu; Yamanishi, Toshihiko
Radiation Physics and Chemistry, 79(1), p.46 - 51, 2010/01
Times Cited Count：16 Percentile：72.36(Chemistry, Physical)The cation-exchange Nafion N117CS membranes swelling in electrolyte solution were irradiated with -rays or electron beams at various doses up to 1500 kGy in the temperature range from room temperature to 343 K to obtain detailed information on the effect of ion-exchange on the radiation deterioration in mechanical properties and ion exchange capacity. Considerable deterioration in mechanical properties was observed when the Nafion membranes swelling in electrolyte solution were irradiated. A reason is the promotion of degradation with oxygen molecules produced by the irradiation of electrolyte solution. The concentration of electrolyte solution influenced strongly the radiation deterioration in mechanical properties. Keeping the concentration of metal ions to be negligible is important when electrolyzed highly radioactive solution in the light of the durability of polyperfluorosulfonic acid membrane. A sort of cation in electrolyte solution negligibly influenced radiation deterioration in mechanical properties. A sort of anion in electrolyte solution had negligible effect on radiation deterioration in mechanical properties and ion exchange capacity.
irradiationHiroki, Akihiro; Tran, H. T.*; Nagasawa, Naotsugu; Yagi, Toshiaki*; Tamada, Masao
Radiation Physics and Chemistry, 78(12), p.1076 - 1080, 2009/12
Times Cited Count：58 Percentile：96.39(Chemistry, Physical)To investigate an adsorption of Pb and Au ions, blend hydrogels based on the carboxymethyl cellulose (CMC) and carboxymethyl chitosan (CMCts) were prepared by -irradiation of a high concentrated CMC/CMCts aqueous solution. The blend hydrogels showed a degree of swelling in the range of 30 to about 550 g -water/g -dried gel. The gel fraction of the blend hydrogels increased sharply up to 30 kGy and reached a constant value in the range of 100-200 kGy. The gel fraction of the blend hydrogel decreased with increasing the ratio of CMCts. Nitrogen content in the hydrogels was determined by means of elemental analysis. The nitrogen content in the obtained hydrogels was proportional to the ratio of CMCts in the mixture, which was almost equal with theoretical ones. This is indicated that the obtained hydrogels were constructed at the initial ratio of CMC/CMCts. The rate of the metal ions adsorbed to the blend hydrogels increased with increasing the composition of CMCts. In the case of Pb, the CMC/CMCts blend gels showed the enhancement of the adsorption rate in the range of 55% to 80%. Although the adsorption rate of Au ions was only 10% at CMC/CMCts 100/0, it reached at 60% at 75/25, and then increased up to about 90% at 0/100. The obtained blend hydrogels had high adsorption performance which was controlled by adjusting the composition of CMC/CMCts.
Hiroki, Akihiro
FBNews, (394), p.3 - 7, 2009/10
no abstracts in English
Takigami, Machiko*; Hiroki, Akihiro; Nagasawa, Naotsugu; Kasahara, Takamitsu*; Takigami, Shoji*; Tamada, Masao
Transactions of the Materials Research Society of Japan, 34(3), p.391 - 394, 2009/09
Carboxymethyl cellulose (CMC) with different molar mass was prepared by acid hydrolysis at 121
C. CMC thus prepared was mixed with citric acid aqueous solution to form CMC-acid gel. By replacing sodium existing as counter ion in carboxymethyl group with hydrogen, CMC molecules coagulate and hydrogen bonds are formed among CMC molecules. The CMC-acid gel prepared in that way was subjected to evaluation of gel fraction, water absorption and mechanical properties. Gel fraction was higher in CMC with higher molar mass than that in CMC with lower molar mass at short incubation time. However, there was no difference in gel fraction attributable to molar mass of CMC after long time incubation. CMC with higher molar mass crosslinked more easily than CMC with lower molar mass. The gel made of CMC with lower molar mass was softer and absorbed more amount of water than that with higher molar mass. All the results were elucidated by number of hydrogen bonds in CMC molecule. The gel made of higher molar mass CMC becomes stiff and brittle after long time incubation, however, the gel made of lower molar mass CMC keeps softness and strength longer.
