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Tominaga, Masahide*; Nagayasu, Yukari*; Sasaki, Motoharu*; Furuta, Takuya; Hayashi, Hiroaki*; Oita, Masataka*; Nishiyama, Yuichi*; Haga, Akihiro*
Radiological Physics and Technology, 14(4), p.381 - 389, 2021/12
Due to recent advance of diagnostic radiology, the increase of diagnostic radiation exposure to patient becomes problem. Diagnostic Reference Levels has been released to optimized the radiation exposure to patients in Japan recently. The evaluation of entrance surface dose (ESD) is recommended to assess the dose level for general X-ray examination. The ESD can be easily evaluated by multiplying the backscatter factor of the patient body on the free-in-air air kerma. The air kerma free-in-air value used to estimate ESD may contain X-rays scattered from obstacles located at the time of measurement, which may induce non-minor error in assessments. We therefore studied the influence of scattered X-rays on air kerma measurement under various environments (distances, field sizes, and materials). It was found that the dependence on the X-ray energy and field size was different for different materials. The X-ray contamination can be ignored for all the materials when the distance to the scatterer exceeds 35 cm.
Fukuda, Kenji; Watanabe, Yusuke; Murakami, Hiroaki; Amano, Yuki; Hayashida, Kazuki*; Aosai, Daisuke*; Kumamoto, Yoshiharu*; Iwatsuki, Teruki
JAEA-Data/Code 2018-021, 76 Pages, 2019/03
JAEA-Data-Code-2018-021.pdf:3.78MB
Japan Atomic Energy Agency has been investigating groundwater chemistry to understand the influence of excavation and maintenance of underground facilities as part of the Mizunami Underground Research Laboratory (MIU) Project in Mizunami, Gifu, Japan. In this report, we compiled data of groundwater chemistry and microbiology obtained at the MIU in the fiscal year 2017. In terms of ensuring traceability of data, basic information (e.g. sampling location, sampling time, sampling method and analytical method) and methodology for quality control are described.
Hayashida, Kazuki; Kato, Toshihiro*; Kubota, Mitsuru*; Murakami, Hiroaki; Amano, Yuki; Iwatsuki, Teruki
Chikyu Kagaku, 52(1), p.55 - 71, 2018/03
In this study, the simulated experimental drift was constructed in the granite of 500 m depth at Mizunami Underground Research Laboratory, and the hydrochemical process after the drift closure was observed. The groundwater chemistry around the drift changed with the change of the groundwater flow in the fractures when the gallery was constructed. The redox potential increased due to the infiltration of oxygen from the drift into the rock. After closing the drift, the redox potential of the groundwater plunged due to microbial activity, while the groundwater became alkalized conditon due to the influence of cement material such as shotcrete. The amount of cement material consumed for this alkalization was small, and it was considered that its influence would last long in accordance with the amount of cement used.
Sasaki, Takayuki*; Kokami, Takayuki*; Kobayashi, Taishi*; Kirishima, Akira*; Murakami, Hiroaki; Amano, Yuki; Mizuno, Takashi; Iwatsuki, Teruki; Sasamoto, Hiroshi; Miyakawa, Kazuya
Journal of Nuclear Science and Technology, 54(3), p.373 - 381, 2017/03
Trace amounts of natural thorium and uranium in deep groundwater were investigated at two underground research laboratories situated at Horonobe and Mizunami, Japan. The groundwater was sampled from underground boreholes, and the colloid contribution was checked by in situ two size-fractionated ultrafiltration systems. A decrease in the concentration after in situ filtration suggested the presence of natural colloids and suspended matter that were carriers of a portion of the elements. The result of the Th and U concentrations in groundwater after 10 kDa filtration was analyzed thermodynamically using existing hydrogeological and geochemical data such as the mineral components in the groundwater at a given pH, ionic strength, concentration of co-existing ions, redox potential, and solid phase assumed. A crystalline solid phase made the solubility very low compared with that of the amorphous phase, and the solubility agreed well with the concentrations measured.
measurements of neutron-rich nuclei far from the 
-stability lineHayashi, Hiroaki*; Shibata, Michihiro*; Asai, Masato; Osa, Akihiko; Sato, Tetsuya; Koizumi, Mitsuo; Kimura, Atsushi; Oshima, Masumi*
Nuclear Instruments and Methods in Physics Research A, 747, p.41 - 51, 2014/05
Times Cited Count：10 Percentile：60.98(Instruments & Instrumentation)To measure -decay energy of short-lived fission products with good accuracy and high efficiency, we have developed a new total absorption clover detector and demonstrated its performance. Using a large-volume clover-type Ge detector having a through-hole in its center, we could measure total absorption spectra of + 
rays with extremely high efficiency and high energy resolution, and could determine values with 
30 keV accuracy. Using this detector, we have determined the values of 
Eu and 
Gd for the first time, and of 
Eu and 
Gd with better accuracies. In addition, we have observed a new isomeric state in Gd, and determined its half-life and excitation energy.
Katsuyama, Chie*; Nashimoto, Hiroaki*; Nagaosa, Kazuyo*; Ishibashi, Tomotaka*; Furuta, Kazuki*; Kinoshita, Takeshi*; Yoshikawa, Hideki; Aoki, Kazuhiro; Asano, Takahiro*; Sasaki, Yoshito; et al.
FEMS Microbiology Ecology, 86(3), p.532 - 543, 2013/12
Times Cited Count：14 Percentile：36.72(Microbiology)Anaerobic microbial activity has a major influence on the subsurface environment, and should be considered in subsurface activities including the construction of radioactive waste repositories. We investigated denitrification and methanogenesis in anoxic groundwater from 140 m depth in two boreholes, where the redox potential fluctuated. The average maximum potential denitrification rates, measured under anaerobic conditions in the two boreholes using an 
N tracer. Methanogenesis candidates were detected by 16S rRNA gene analysis. Although the stable isotope signatures suggested that some of the dissolved methane was of biogenic origin, no potential for methane production was evident during the incubations. The groundwater at 140 m depth did not contain oxygen, had an Eh ranging from -144 to 6.8 mV, and was found to be a potential field for denitrification.
nucleus 
NoAsai, Masato; Tsukada, Kazuaki; Sakama, Minoru*; Haba, Hiromitsu*; Ichikawa, Takatoshi*; Ishii, Yasuo; Toyoshima, Atsushi; Ishii, Tetsuro; Nishinaka, Ichiro; Nagame, Yuichiro; et al.
Physical Review C, 87(1), p.014332_1 - 014332_6, 2013/01
Times Cited Count：6 Percentile：43.66(Physics, Nuclear)The spin-parity and neutron configuration of the ground state of No have been identified through 
-decay spectroscopy. The No is the nucleus with the largest neutron number whose spin-parities and single-particle configurations have ever been identified. The neutron 9/2
[615] configuration was assigned to the ground state of No as well as to the 231.4 keV level in 
Fm. This allowed us to establish energy spacings and order of the neutron single-particle orbitals in such heaviest nuclear region. The appearance of the 9/2[615] ground state at 
=157 implies that the order of the neutron orbitals between the =152 and 162 deformed shell gaps should change considerably with increasing neutron number.
N(n,)N reaction as a -ray intensity standard up to 11 MeVMiyazaki, Itaru*; Sakane, Hitoshi*; Takayama, Hirokazu*; Kasaishi, Masafumi*; Tojo, Akinori*; Furuta, Masataka*; Hayashi, Hiroaki*; Suematsu, Osamu*; Narasaki, Hiromichi*; Shimizu, Toshiaki*; et al.
Journal of Nuclear Science and Technology, 45(6), p.481 - 486, 2008/06
Times Cited Count：5 Percentile：35.07(Nuclear Science & Technology)The intensities of the prompt rays from the N(n,)N reaction have been precisely measured. As the samples, a liquid nitrogen target and a deuterated melamine (C
D
N) were used. The previous values widely used as intensity standards agreed with those obtained in this study within 4-5% in the 2-11 MeV region, however, showed a monotonous decrease with the increase of -ray energy.
measurements of 
Pm, 
Sm, Eu, Gd and Tb using a total absorption BGO detectorHayashi, Hiroaki*; Akita, Yukinori*; Suematsu, Osamu*; Shibata, Michihiro*; Asai, Masato; Sato, Tetsuya; Ichikawa, Shinichi; Nishinaka, Ichiro; Nagame, Yuichiro; Osa, Akihiko; et al.
European Physical Journal A, 34(4), p.363 - 370, 2007/12
Times Cited Count：16 Percentile：71.35(Physics, Nuclear) values of Eu and Gd were measured for the first time using a total absorption BGO detector, and the data of Pm, Sm, and Tb obtained previously were reanalyzed. These nuclei were produced by the proton-induced fission of 
U at the JAEA-Tokai tandem accelerator facility, and separated from the reaction products using an on-line isotope separator. The deduced mass excesses and two-neutron separation energies were compared with those of atomic mass evaluations and theoretical predictions.
EuSato, Tetsuya; Osa, Akihiko; Asai, Masato; Ichikawa, Shinichi; Tsukada, Kazuaki; Shibata, Michihiro*; Hayashi, Hiroaki*; Kojima, Yasuaki*
no journal, ,
no abstracts in English
- spectroscopy of NoAsai, Masato; Tsukada, Kazuaki; Sakama, Minoru*; Ishii, Yasuo; Toyoshima, Atsushi; Ishii, Tetsuro; Nishinaka, Ichiro; Nagame, Yuichiro; Kasamatsu, Yoshitaka; Shibata, Michihiro*; et al.
no journal, ,
- coincidence spectroscopy for the decay of No has been performed at the JAEA tandem accelerator facility to study nuclear shell structure of superheavy nuclei. The decay scheme of No has been established for the first time, and spin-parity and neutron single-particle configuration of the ground state of No have been identified. It was found that many theoretical calculations could not reproduce the ground-state configuration of the nuclei with 157 neutrons, which implies that the deformation of the nuclei with more than 157 neutrons would be substantially different from theoretical predictions.
-decay half-lives of four new neutron-rich isotopes 
Eu and levels in GdSato, Tetsuya; Asai, Masato; Osa, Akihiko; Tsukada, Kazuaki; Hayashi, Hiroaki*; Shibata, Michihiro*; Kojima, Yasuaki*; Ichikawa, Shinichi
no journal, ,
-decay half-lives of four new neutron-rich isotopes Eu produced in the proton-induced fission of U have been determined, using an on-line isotope separator at JAEA. The measured half-life values are 7.7(4) s for Eu, 4.6(7) s for 
Eu, 2.7(6) s for Eu and 1.7(4) s for Eu. And we determined the 
, 
energies of Gd
which is most neutron-rich Gd isotope to be 69.7(1) keV and 230.5(1) keV, respectively.
spectroscopy of N = 155 and 157 nuclei using a gas-jet transport techniqueAsai, Masato; Tsukada, Kazuaki; Sakama, Minoru*; Ishii, Yasuo; Toyoshima, Atsushi; Ishii, Tetsuro; Nishinaka, Ichiro; Nagame, Yuichiro; Kasamatsu, Yoshitaka; Haba, Hiromitsu*; et al.
no journal, ,
Alpha- spectroscopy of 
No and 
Rf nuclei with the neutron number N=155 and 157 have been performed for the first time at the JAEA tandem accelerator using a gas-jet transport technique. Spin-parities and neutron single-particle configurations of ground states of these nuclei as well as excited states in their daughter nuclei have been identified. On the basis of these experimental results, energy spacings and order of neutron single-particle orbitals between N=153 and 161 were evaluated. The result implies that the order of the neutron orbitals between N=153 and 161 should be inverted between lighter nuclei around 
Fm and heavier ones around 
Hs.
-decay half-life of new neutron rich isotope Eu and levels in GdSato, Tetsuya; Osa, Akihiko; Asai, Masato; Tsukada, Kazuaki; Hayashi, Hiroaki*; Shibata, Michihiro*; Kojima, Yasuaki*; Ichikawa, Shinichi
no journal, ,
New neutron-rich rare-earth isotope Eu produce in the proton-induced fisson of U were identified using the JAEA on-line isotope separator at the JAEA tandem accelerator and its half-life was determined to be 1.7(4) s. Excited state in Gd was established for the first time.
-ray spectroscopy of the heaviest nuclei at JAEA tandem acceleratorAsai, Masato; Tsukada, Kazuaki; Sakama, Minoru*; Ishii, Yasuo; Toyoshima, Atsushi; Ishii, Tetsuro; Nishinaka, Ichiro; Nagame, Yuichiro; Kasamatsu, Yoshitaka; Haba, Hiromitsu*; et al.
no journal, ,
Recent results on the -ray spectroscopic studies of the heaviest nuclei at the JAEA tandem accelerator are reviewed. The nuclei 
No, No, and Rf studied in the present work are the heaviest and the most neutron-rich nuclei that -ray spectroscopic studies have ever been performed for. Excited-state energies, spin-parities, and single-particle configurations of those nuclei and their daughters have been established by means of - coincidence spectroscopy. The deduced energy spacings and order of neutron single-particle orbitals suggest that the higher-order deformations play an important role in level structure of the superheavy nuclei in this region.
Gd using a total absorption detectorAsai, Masato; Hayashi, Hiroaki*; Osa, Akihiko; Sato, Tetsuya; Otokawa, Yoshinori; Nagae, Daisuke; Tsukada, Kazuaki; Miyashita, Yuji*; Ouchi, Hiroyuki*; Izumi, Sayaka*; et al.
no journal, ,
We have developed a new method to measure lifetime of long-lived isomers populated through the decay, using a total absorption detector. Using this method, we have determined lifetime of the K isomers in 
Gd and Gd for the first time. The short-lived neutron-rich nuclei Eu and Eu were produced and mass-separated by the on-line isotope separator (ISOL) at JAEA tandem accelerator facility. Beta- and rays emitted by the decay of Eu were total-absorbed by the detector, and all the events were recorded with time stamps. This method enabled us to determine lifetime of the isomers with more than 100-
s lifetime.
measurementsHayashi, Hiroaki*; Shibata, Michihiro*; Asai, Masato; Osa, Akihiko; Oshima, Masumi; Kimura, Atsushi; Koizumi, Mitsuo; Sato, Tetsuya
no journal, ,
A new total absorption detector composed of a large Clover-type Ge detector and BGO Compton suppressors has been developed to measure 
values of nuclei far from the -stability line. The Clover detector has a through-hole with a 15-mm inner diameter at its center to put radioactive sources in it. Because of its high detection efficiencies for both and rays, the value can be directly determined from the endpoint of an observed total sum spectrum for and rays without information on the decay scheme. Using this detector, values of 
Eu and 
Gd produced in the proton-induced fission of U and mass-separated by an on-line isotope separator at the JAEA-Tokai Tandem Accelerator have been determined with accuracies of 30-300 keV.
Sasaki, Takayuki*; Kokami, Takayuki*; Amamiya, Hiroki; Murakami, Hiroaki; Amano, Yuki; Iwatsuki, Teruki; Mizuno, Takashi; Kobayashi, Taishi*; Kirishima, Akira*
no journal, ,
For thermodynamic analysis of the trace metals in groundwater, concentrations of Th, U, and rare earth elements (REEs) were investigated at Horonobe Underground Research Laboratory. Groundwater was sampled in anaerobic condition directly from a packed section in the boreholes drilled to 140 m and 250 m depth in drift. The colloidal distribution was checked by an on-site batch ultrafiltration unit using 0.2 m or 10 kDa membranes. As the result, both Th and U concentrations could be estimated by thermodynamic calculations, assuming that the soluble solid phases are restricted to ThO
(cr) and UO(cr), respectively. Meanwhile, the concentrations of REEs were also very low, and significant colloidal distribution for lighter REEs was observed. In the thermodynamic analysis where the lanthanide phosphate was assumed to be a solid phase, the experimental plots matched better with the calculated one, even though the changing trend differs from each other.
Iwatsuki, Teruki; Hayashida, Kazuki; Murakami, Hiroaki; Watanabe, Yusuke
no journal, ,
Geochemical condition and solutes transport property in and around a simulated closure tunnel were studied by observing the behavior of REEs at Mizunami Underground Research Laboratory. Results show that the REEs in the closure tunnel tend to be immobilized by absorbing to shotcrete and the colloidal flocculation.
Watanabe, Yusuke; Hayashida, Kazuki; Murakami, Hiroaki; Iwatsuki, Teruki
no journal, ,
In the geological disposal project of high-level radioactive waste, a disposal facility will be constructed in depths deeper than 300 m. In this study, the simulated experimental tunnel was constructed in the granite of 500 m depth at Mizunami Underground Research Laboratory, and the hydrochemical process after the tunnel closure was observed.
