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Journal Articles

Development of the multi-cubic $$gamma$$-ray spectrometer and its performance under intense $$^{137}$$Cs and $$^{60}$$Co radiation fields

Kaburagi, Masaaki; Shimazoe, Kenji*; Kato, Masahiro*; Kurosawa, Tadahiro*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*

Nuclear Instruments and Methods in Physics Research A, 1010, p.165544_1 - 165544_9, 2021/09

 Times Cited Count:0 Percentile:0.03(Instruments & Instrumentation)

The number of nuclear facilities being decommissioned has been increasing worldwide, in particular following the accident of the Tokyo Electric Power Company Holdings' Fukushima Daiichi Nuclear Power Station in 2011. In these nuclear facilities, proper management of radioactive materials is required. Then, A $$gamma$$-ray spectrometer with four segmentations using small volume CeBr$$_{3}$$ scintillators with a dimension of $$5 times 5 times 5$$ $$rm{mm}^3$$ was developed. The four scintillators were coupled to a multi-anode photomultiplier tube specific to intense radiation fields. We performed the $$gamma$$-ray exposure study under $$^{137}$$Cs and $$^{60}$$Co radiation fields. Under the $$^{137}$$Cs radiation field, the relative energy resolution at 1375 mSv/h was the relative energy resolution at 1375 mSv/h was 9.2$$pm$$0.05%, 8.0$$pm$$0.08%, 8.0$$pm$$0.03%, and 9.0$$pm$$0.04% for the four channels, respectively.

Journal Articles

Gamma-ray spectroscopy with a CeBr$$_3$$ scintillator under intense $$gamma$$-ray fields for nuclear decommissioning

Kaburagi, Masaaki; Shimazoe, Kenji*; Kato, Masahiro*; Kurosawa, Tadahiro*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*; et al.

Nuclear Instruments and Methods in Physics Research A, 988, p.164900_1 - 164900_8, 2021/02

 Times Cited Count:1 Percentile:81.22(Instruments & Instrumentation)

An increasing number of nuclear facilities have been decommissioned worldwide following the 2011 accident of the TEPCO' Fukushima Daiichi Nuclear Power Station. During the decommissioning, radioactive materials have to be retrieved under proper management. In this study, a small cubic CeBr$$_3$$ spectrometer with dimensions of 5 mm $$times$$ 5 mm $$times$$ 5 mm was manufactured to perform $$gamma$$-ray spectroscopy under intense $$gamma$$-ray fields. Furthermore, thanks to a fast digital process unit and a customized photomultiplier, the device could perform $$gamma$$-ray spectroscopy at dose rates of over 1 Sv/h. The energy resolution (FWHM) at 662 keV ranged from 4.4% at 22 mSv/h to 5.2% at 1407 mSv/h for a $$^{137}$$Cs radiation field. Correspondingly, at 1333 keV, it ranged from 3.1% at 26 mSv/h to 4.2% at 2221 mSv/h for a $$^{60}$$Co radiation field, which suggested to realize $$gamma$$-ray assessment of $$^{134}$$Cs, $$^{137}$$Cs, $$^{60}$$Co, and $$^{154}$$Eu at dose rates of over 1 Sv/h.

Journal Articles

A Cubic CeBr$$_{3}$$ gamma-ray spectrometer suitable for the decommissioning of the Fukushima Daiichi Nuclear Power Station

Kaburagi, Masaaki; Shimazoe, Kenji*; Otaka, Yutaka*; Uenomachi, Mizuki*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*; et al.

Nuclear Instruments and Methods in Physics Research A, 971, p.164118_1 - 164118_8, 2020/08

 Times Cited Count:3 Percentile:76.41(Instruments & Instrumentation)

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

 Times Cited Count:140 Percentile:99.81(Multidisciplinary Sciences)

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Journal Articles

Field test around Fukushima Daiichi Nuclear Power Plant site using improved Ce:Gd$$_{3}$$(Al,Ga)$$_{5}$$O$$_{12}$$ scintillator Compton camera mounted on an unmanned helicopter

Shikaze, Yoshiaki; Nishizawa, Yukiyasu; Sanada, Yukihisa; Torii, Tatsuo; Jiang, J.*; Shimazoe, Kenji*; Takahashi, Hiroyuki*; Yoshino, Masao*; Ito, Shigeki*; Endo, Takanori*; et al.

Journal of Nuclear Science and Technology, 53(12), p.1907 - 1918, 2016/12

 Times Cited Count:24 Percentile:96.18(Nuclear Science & Technology)

The Compton camera was improved for use with the unmanned helicopter. Increase of the scintillator array from 4$$times$$4 to 8$$times$$8 and expanse of the distance between the two layers contributed to the improvements of detection efficiency and angular resolution, respectively. Measurements were performed over the riverbed of the Ukedo river of Namie town in Fukushima Prefecture. By programming of flight path and speed, the areas of 65 m $$times$$ 60 m and 65 m $$times$$ 180 m were measured during about 20 and 30 minutes, respectively. By the analysis the air dose rate maps at 1 m height were obtained precisely with the angular resolution corresponding to the position resolution of about 10 m from 10 m height. Hovering flights were executed over the hot spot areas for 10-20 minutes at 5-20 m height. By using the reconstruction software the $$gamma$$-ray images including the hot spots were obtained with the angular resolution same as that evaluated in the laboratory (about 10$$^{circ}$$).

Journal Articles

Fabrication of Pt nanoparticle incorporated polymer nanowires by high energy ion and electron beam irradiation

Tsukuda, Satoshi*; Takahashi, Ryota*; Seki, Shuhei*; Sugimoto, Masaki; Idesaki, Akira; Yoshikawa, Masahito; Tanaka, Shunichiro*

Radiation Physics and Chemistry, 118, p.16 - 20, 2016/01

 Times Cited Count:1 Percentile:14.27(Chemistry, Physical)

Polyvinylpyrrolidone (PVP)-Pt nanoparticles (NPs) hybrid nanowires were fabricated by high energy ion beam irradiation to PVP thin films including H$$_{2}$$PtCl$$_{6}$$. Single ion hitting caused crosslinking reactions of PVP and reduction of Pt ions within local cylindrical area along an ion trajectory (ion track); therefore, the PVP nanowires including Pt NPs were formed and isolated on Si substrate after wet-development procedure. The number of Pt NPs was easily controlled by the mixed ratio of PVP and H$$_{2}$$PtCl$$_{6}$$. However, increasing the amount of H$$_{2}$$PtCl$$_{6}$$ led to decreasing the radial size and separation of the hybrid nanowires during the wet-development. Additional electron beam irradiation after ion beam improved separation of the nanowires and controlled radial sizes due to an increase in the density of crosslinking points inner the nanowires.

Journal Articles

Swelling of radiation-cured polymer precursor powder for silicon carbide by pyrolysis

Takeyama, Akinori; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito

Journal of Asian Ceramic Societies (Internet), 3(4), p.402 - 406, 2015/12

Journal Articles

Progress of divertor simulation research toward the realization of detached plasma using a large tandem mirror device

Nakashima, Yosuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Oki, Kensuke*; Sakamoto, Mizuki*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; Imai, Tsuyoshi*; et al.

Journal of Nuclear Materials, 463, p.537 - 540, 2015/08

 Times Cited Count:17 Percentile:88.2(Materials Science, Multidisciplinary)

JAEA Reports

Enhancement of the methodology of repository design and post-closure performance assessment for preliminary investigation stage, 3; Progress report on NUMO-JAEA collaborative research in FY2013 (Joint research)

Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Makino, Hitoshi; Wakasugi, Keiichiro; Mitsui, Seiichiro; Kitamura, Akira; Yoshikawa, Hideki; Oda, Chie; Ishidera, Takamitsu; et al.

JAEA-Research 2014-030, 457 Pages, 2015/03

JAEA-Research-2014-030.pdf:199.23MB

JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and post-closure performance assessment in preliminary investigation stage. With regard to (1) study on rock suitability in terms of hydrology, based on some examples of developing method of hydro-geological structure model, acquired knowledge are arranged using the tree diagram, and model uncertainty and its influence on the evaluation items were discussed. With regard to (2) study on scenario development, the developed approach for "defining conditions" has been reevaluated and improved from practical viewpoints. In addition, the uncertainty evaluation for the effect of use of cementitious material, as well as glass dissolution model, was conducted with analytical evaluation. With regard to (3) study on setting radionuclide migration parameters, based on survey of precedent procedures, multiple-approach for distribution coefficient of rocks was established, and the adequacy of the approach was confirmed though its application to sedimentary rock and granitic rock. Besides, an approach for solubility setting was developed including the procedure of selection of solubility limiting solid phase. The adequacy of the approach was confirmed though its application to key radionuclides.

Journal Articles

Development of divertor simulation research in the GAMMA 10/PDX tandem mirror

Nakashima, Yosuke*; Sakamoto, Mizuki*; Yoshikawa, Masayuki*; Oki, Kensuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; et al.

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10

Journal Articles

Thermodynamic model for the solubility of Ba(SeO$$_{4}$$, SO$$_{4}$$) precipitates

Rai, D.*; Felmy, A. R.*; Moore, D. A.*; Kitamura, Akira; Yoshikawa, Hideki; Doi, Reisuke; Yoshida, Yasushi*

Radiochimica Acta, 102(8), p.711 - 721, 2014/08

 Times Cited Count:1 Percentile:10.7(Chemistry, Inorganic & Nuclear)

The solubility of Ba(SeO$$_{4}$$, SO$$_{4}$$) precipitates was determined as a function of the BaSeO$$_{4}$$ mole fractions, ranging from 0.0015 to 0.3830, and time with an equilibration period extending to as long as 302 days. Equilibrium/steady state conditions in this system are reached in $$leq$$ 65 days. Pitzer's ion interaction model was used to calculate solid and aqueous phase activity coefficients. Thermodynamic analyses showed that the data do not satisfy Gibbs-Duhem equation, thereby demonstrating that a single-solid solution phase does not control both the selenate and sulfate concentrations. Our extensive data with [Ba], [SeO$$_{4}$$], and [SO$$_{4}$$] can be explained with the formation of an ideal BaSeO$$_{4}$$ solid solution phase that controls the selenium concentrations and a slightly disordered/less-crystalline BaSO$$_{4}$$(s) that controls the sulfate concentrations. In these experiments the BaSO$$_{4}$$ component of the solid solution phase never reaches thermodynamic equilibrium with the aqueous phase. Thermodynamic interpretations of the data show that both the ideal BaSeO$$_{4}$$ solid solution phase and less-crystalline BaSO$$_{4}$$(s) phase are in equilibrium with each other in the entire range of BaSeO$$_{4}$$ mole fractions investigated in this study.

Journal Articles

Thermodynamic model for the solubility of BaSeO$$_{4}$$(cr) in the aqueous Ba$$^{2+}$$-SeO$$_{4}$$$$^{2-}$$-Na$$^{+}$$-H$$^{+}$$-OH$$^{-}$$-H$$_{2}$$O system; Extending to high selenate concentrations

Rai, D.*; Felmy, A. R.*; Moore, D. A.*; Kitamura, Akira; Yoshikawa, Hideki; Doi, Reisuke; Yoshida, Yasushi*

Radiochimica Acta, 102(9), p.817 - 830, 2014/04

 Times Cited Count:0 Percentile:0.01(Chemistry, Inorganic & Nuclear)

The aqueous solubility of BaSeO$$_{4}$$(cr) was studied in Na$$_{2}$$SeO$$_{4}$$ solutions ranging in concentration from 0.0001 to 4.1 mol.kg$$^{-1}$$ and maintained in a N$$_{2}$$ atmosphere at room temperature (296 $$pm$$ 2 K). The studies were conducted from both the undersaturation and oversaturation directions, with equilibration periods ranging from 3 to 596 days. The equilibrium in this system was reached rather rapidly ($$leq$$ 3 days). The SIT and Pitzer's ion-interaction models were used to interpret these data and the predictions based on both of these models agreed closely with the experimental data.

Journal Articles

A Macroporous SiC material synthesized from preceramic polymer with direct foaming and radiation curing

Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito

JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 42, 2014/03

A macroporous SiC material was synthesized from polycarbosilane (PCS) by direct foaming and radiation curing. A mixture of PCS and biurea, a blowing agent, was heat-treated in Ar to obtain foamed PCS body, irradiated by $$gamma$$-rays to fix the shaped body and finally pyrolyzed at 1000$$^{circ}$$C in Ar. In this work, effects of foaming temperature (280-320$$^{circ}$$C) and biurea content (0-1wt%) on the properties of obtained porous SiC material such as average cell size, porosity, compressive strength were investigated. It was found that the average cell size increased as foaming temperature and/or biurea content increased. Corresponding to increasing in average cell size, total porosity and open porosity increased and bulk density, closed porosity and compressive strength decreased. In case of the foaming at 280$$^{circ}$$C with biurea content of 1wt%, obtained porous SiC material showed average cell size of 0.5 mm, total porosity of 74% and compressive strength of 3.2 MPa.

Journal Articles

Synthesis of a porous SiC material from polycarbosilane by direct foaming and radiation curing

Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito

Innovative Processing and Manufacturing of Advanced Ceramics and Composites II; Ceramic Transactions, Vol.243, p.61 - 69, 2014/01

A macroporous SiC material was synthesized from polycarbosilane (PCS) by direct foaming and radiation curing. A mixture of PCS and biurea, a blowing agent, was heat-treated in Ar to obtain foamed PCS body, irradiated by $$gamma$$-rays to fix the shaped body and finally pyrolyzed at 1000$$^{circ}$$C in Ar. In this work, effects of foaming temperature (280-320$$^{circ}$$C) and biurea content (0-1wt%) on the properties of obtained porous SiC material such as average cell size, porosity, compressive strength were investigated. It was found that the average cell size increased as foaming temperature and/or biurea content increased. Corresponding to increasing in average cell size, total porosity and open porosity increased and bulk density, closed porosity and compressive strength decreased. In case of the foaming at 280$$^{circ}$$C with biurea content of 1wt%, obtained porous SiC material showed average cell size of 0.5 mm, total porosity of 74% and compressive strength of 3.2 MPa.

Journal Articles

Decontamination of school facilities in Fukushima-city

Yoshikawa, Hideki; Iijima, Kazuki; Sasamoto, Hiroshi; Fujiwara, Kenso; Mitsui, Seiichiro; Kitamura, Akira; Kurikami, Hiroshi; Tokizawa, Takayuki; Yui, Mikazu; Nakayama, Shinichi

Materials Research Society Symposium Proceedings, Vol.1518, p.269 - 275, 2013/10

Following the release of radionuclides into the environment as a result of the accident at Fukushima Daiichi Nuclear Power Plant, Japan Atomic Energy Agency (JAEA) had to develop an immediate and effective method of reducing the dose rate received by students in school facilities. A demonstration of a reducing method was carried out by JAEA at a junior high school ground and kindergarten yard in the center of Fukushima-city. Dose rates of the released radionuclides are largely controlled by the ground level contamination and accumulation of mainly cesium-137 ($$^{137}$$Cs) and cesium-134 ($$^{134}$$Cs) in populated areas. An effective means of reducing dose rate was to remove the surface soil and to bury it on-site under fresh uncontaminated soil or soil collected under deep depth at the site for shielding. The dose rate at1 m above ground level was reduced from 2.5 $$mu$$Sv/h to 0.15 $$mu$$Sv/h.

Journal Articles

Scintillation properties of Yb$$^{3+}$$-doped YAlO$$_{3}$$ in the temperature range from 4.2 to 175 K

Yasumune, Takashi; Kurihara, Masakazu*; Maehata, Keisuke*; Ishibashi, Kenji*; Yoshikawa, Akira*

Nuclear Instruments and Methods in Physics Research A, 726, p.37 - 40, 2013/08

 Times Cited Count:1 Percentile:12.7(Instruments & Instrumentation)

Yb$$^{3+}$$-doped yttrium-aluminum perovskites (YAP:Yb) are expected to be scintillator materials with high light yield and short scintillation decay time because of their charge transfer (CT) luminescence. Since the CT luminescence of Yb$$^{3+}$$ is strongly affected by thermal quenching, to use YAP:Yb as a scintillator material, it is necessary to measure the scintillation properties of YAP:Yb at low temperatures. Since it is difficult to detect scintillation light at low temperatures, scintillation properties of YAP:Yb characterized by irradiating with $$gamma$$-rays or other radiation below 100 K have not been reported. We conducted measurements of the temperature dependence of emission wavelength spectrum of YAP:Yb by irradiating with $$beta$$-rays from a $$^{90}$$Sr/$$^{90}$$Y source in the temperature range from 4.2 K to 175 K. The emission peak at around 340-350 nm and 500-520 nm were observed in the emission wavelength spectra. The light yield of YAP:Yb was characterized by using an avalanche photodiode in detection of 662 keV $$gamma$$-rays from a $$^{137}$$Cs source in the temperature range from 50 K to 175 K. The light yield increased with decreasing temperature and reached 11,000 photons/MeV at a temperature of 4.2 K.

Journal Articles

Development of utility for on-site recording of dose rate and program for data accumulation, mapping and management using GPS and GIS (DRaMM-GiGs)

Kitamura, Akira; Fujiwara, Kenso; Yoshikawa, Hideki; Gomi, Katsuhiko*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 20(1), p.15 - 19, 2013/06

We developed an integrated system on setting many monitoring spots in playgrounds and fields and simultaneously recording of monitored results with spot, date and time for a decontamination project. This system enables to set grid squares containing many spots to be monitored and to integrate all the monitored spots using a geographic information system (GIS). Furthermore, we could easily access to the monitoring spots in pre-set grid squares using a personal digital assistant with a highly accurate global positioning system (GPS) and a camera. All the monitored results are linked up with location, date and time, and photos taken around the spot, and could be efficiently managed in an integrated fashion in a personal computer. As a result, we saved many times and manpowers for monitoring and data summarizing, and succeeded to conduct the monitoring quickly and accurately.

Journal Articles

The Present situation and future prospects of groundwater colloids studies on the performance assessment of geological disposal of radioactive wastes in Japan

Nagao, Seiya*; Niibori, Yuichi*; Tanaka, Tadao; Sasaki, Takayuki*; Saito, Takumi*; Kirishima, Akira*; Yoshikawa, Hideki; Iijima, Kazuki; Hama, Katsuhiro; Iwatsuki, Teruki; et al.

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 20(1), p.3 - 14, 2013/06

This paper shows a current status of groundwater colloids studies on the performance assessment of geological disposal of radioactive wastes in Japan, and summaries realistic approach of the colloids studies at a substantial research network for Japanese universities and institutes.

JAEA Reports

Study of cable ageing mechanism for nuclear power plant (Contract research)

Seguchi, Tadao*; Tamura, Kiyotoshi*; Watashi, Katsumi; Suzuki, Masahide; Shimada, Akihiko; Sugimoto, Masaki; Idesaki, Akira; Yoshikawa, Masahito; Oshima, Takeshi; Kudo, Hisaaki*

JAEA-Research 2012-029, 158 Pages, 2012/12

JAEA-Research-2012-029.pdf:9.4MB

The degradation mechanisms of ethylene-propylene rubber (EPR), crosslinked polyethylene (XLPE), polyvinylchloride (PVC), and silicone rubber (SiR) as the cable insulation materials were investigated for the cable ageing research of the nuclear power plant. The materials as same insulations for the practical cable (practical formulation) and as the model formulation containing specific additive were selected. They were exposed to the accelerated radiation and thermal environments. The mechanical properties, the crosslinking and chain scission, and the distribution of antioxidant and of oxidative products were measured and analyzed.

JAEA Reports

Ageing research of cable insulation materials

Seguchi, Tadao*; Tamura, Kiyotoshi; Kudo, Hisaaki*; Shimada, Akihiko; Sugimoto, Masaki; Idesaki, Akira; Oshima, Takeshi; Yoshikawa, Masahito

JAEA-Review 2012-027, 46 Pages, 2012/08

JAEA-Review-2012-027.pdf:5.87MB

The research on cable degradation mechanisms was conducted for 5 years in 2006 - 2010 as the project research of plant life management for nuclear power plant by NISA (Nuclear and Industrial Safety Agency) of METI (Ministry of Economy, Trade, and Industry). At the finish of above research, the degradation mechanisms were reviewed on the analysis of many reports on cable degradation. The reports published after 1970 were mainly surveyed and the facts or data containing the experimental accuracy were selected. The verified facts, the reasonable interpretation of the facts, unresolved aspects were checked on the view points of recent techniques or analysis, and proposed the new model of degradation mechanisms was proposed.

134 (Records 1-20 displayed on this page)