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Journal Articles

Atmospheric resuspension of insoluble radioactive cesium bearing particles found in the difficult-to-return area in Fukushima

Tang, P.*; Kita, Kazuyuki*; Igarashi, Yasuhito*; Satou, Yukihiko; Hatanaka, Kotaro*; Adachi, Koji*; Kinase, Takeshi*; Ninomiya, Kazuhiko*; Shinohara, Atsushi*

Progress in Earth and Planetary Science (Internet), 9(1), p.17_1 - 17_15, 2022/03

 Times Cited Count:0 Percentile:0.01(Geosciences, Multidisciplinary)

Journal Articles

Structural and compositional characteristics of Fukushima release particulate material from Units 1 and 3 elucidates release mechanisms, accident chronology and future decommissioning strategy

Martin, P. G.*; Jones, C. P.*; Bartlett, S.*; Ignatyev, K.*; Megson-Smith, D.*; Satou, Yukihiko; Cipiccia, S.*; Batey, D. J.*; Rau, C.*; Sueki, Keisuke*; et al.

Scientific Reports (Internet), 10, p.22056_1 - 22056_17, 2020/12

 Times Cited Count:0 Percentile:0.01(Multidisciplinary Sciences)

Journal Articles

Classification of the insoluble particles including radioactive Cs found in Okuma town and Futaba town, Fukushima prefecture

Igarashi, Junya*; Zhang, Z. J.*; Ninomiya, Kazuhiko*; Shinohara, Atsushi*; Satou, Yukihiko; Minowa, Haruka*; Yoshikawa, Hideki

KEK Proceedings 2019-2, p.54 - 59, 2019/11

no abstracts in English

Journal Articles

First determination of Pu isotopes ($$^{239}$$Pu, $$^{240}$$Pu and $$^{241}$$Pu) in radioactive particles derived from Fukushima Daiichi Nuclear Power Plant accident

Igarashi, Junya*; Zheng, J.*; Zhang, Z.*; Ninomiya, Kazuhiko*; Satou, Yukihiko; Fukuda, Miho*; Ni, Y.*; Aono, Tatsuo*; Shinohara, Atsushi*

Scientific Reports (Internet), 9(1), p.11807_1 - 11807_10, 2019/08

 Times Cited Count:15 Percentile:69.55(Multidisciplinary Sciences)

Radioactive particles were released into the environment during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Many studies have been conducted to elucidate the chemical composition of released radioactive particles in order to understand their formation process. However, whether radioactive particles contain nuclear fuel radionuclides remains to be investigated. Here, we report the first determination of Pu isotopes in radioactive particles. To determine the Pu isotopes ($$^{239}$$Pu, $$^{240}$$Pu and $$^{241}$$Pu) in radioactive particles derived from the FDNPP accident which were free from the influence of global fallout, radiochemical analysis and inductively coupled plasma-mass spectrometry measurements were conducted. Radioactive particles derived from unit 1 and unit 2 or 3 were analyzed. For the radioactive particles derived from unit 1, activities of $$^{239+240}$$Pu and $$^{241}$$Pu were (1.70-7.06)$$times$$10$$^{-5}$$ Bq and (4.10-8.10)$$times$$10$$^{-3}$$ Bq, respectively and atom ratios of $$^{240}$$Pu/$$^{239}$$Pu and $$^{241}$$Pu/$$^{239}$$Pu were 0.330-0.415 and 0.162-0.178, respectively. These ratios were consistent with the simulation results from ORIGEN code and measurements from various environmental samples. In contrast, Pu was not detected in the radioactive particles derived from unit 2 or 3. The difference in Pu contents is clear evidence towards different formation processes of radioactive particles, and detailed formation processes can be investigated from Pu analysis.

Journal Articles

Activity of $$^{90}$$Sr in fallout particles collected in the difficult-to-return zone around the Fukushima Daiichi Nuclear Power Plant

Zhang, Z.*; Igarashi, Junya*; Satou, Yukihiko; Ninomiya, Kazuhiko*; Sueki, Keisuke*; Shinohara, Atsushi*

Environmental Science & Technology, 53(10), p.5868 - 5876, 2019/05

 Times Cited Count:14 Percentile:69.55(Engineering, Environmental)

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released abundant radioactive particles into the surrounding environment. Herein, we analyzed the activity of $$^{90}$$Sr in these particles to estimate the contribution of this radionuclide to the overall radiation exposure and shed light on the processes that occurred during the accident. Seven radioactive particles were isolated from the dust and soil samples collected from areas surrounding the FDNPP, and the minimum/maximum $$^{137}$$Cs activities were determined as 224/4,100 Bq. Based on the size, specific activity, and $$^{134}$$Cs/$$^{137}$$Cs activity ratios, we concluded that six of the seven radioactive particles were released from the Unit 1 reactor, while one particle was released from the Unit 3 reactor by a hydrogen explosion. Strontium-90 was detected in all radioactive particles, and the minimal/maximal $$^{90}$$Sr activities were determined as 0.046/1.4 Bq. $$^{137}$$Cs/$$^{90}$$Sr activity ratios above 1000 were observed for all seven particles, that is, compared to $$^{137}$$Cs, $$^{90}$$Sr had negligible contribution to the overall radiation exposure. The $$^{137}$$Cs/$$^{90}$$Sr activity ratios of the radioactive particles were similar to those of terrestrial environmental samples and were higher for particles released from the Unit 1 reactor than for samples collected from the Unit 1 reactor building, which indicates possibility of additional $$^{90}$$Sr -rich contamination after release of the particles.

Journal Articles

Nondestructive elemental depth-profiling analysis by muonic X-ray measurement

Ninomiya, Kazuhiko*; Kubo, Kenya*; Nagatomo, Takashi*; Higemoto, Wataru; Ito, Takashi; Kawamura, Naritoshi*; Strasser, P.*; Shimomura, Koichiro*; Miyake, Yasuhiro*; Suzuki, Takao*; et al.

Analytical Chemistry, 87(9), p.4597 - 4600, 2015/05

 Times Cited Count:16 Percentile:55.49(Chemistry, Analytical)

Journal Articles

Study on index of erosion rate in inland mountains; Case study using old river valley around detached meander core

Yasue, Kenichi; Takatori, Ryoichi*; Tanikawa, Shinichi*; Ninomiya, Atsushi*; Tanase, Atsushi*; Furusawa, Akira*; Tajikara, Masayoshi*

Chishitsugaku Zasshi, 120(12), p.435 - 445, 2014/12

Estimating the rate of change in landforms and geological environments due to erosion is important when assessing the safety of the geological disposal of high-level radioactive waste in Japan. The aim of this study is to develop an index of erosion rates in inland mountains. We focused on circular abandoned channels, which are old river valleys around detached meander cores formed by the cut-off of incised meandering rivers. The channels can be useful for estimating incision rates because they occur at a range of elevations throughout the Japanese Islands. We undertook a case study to determine the incision rate using a circular abandoned channel in the middle reaches of the Kumanogawa River in the Kii Peninsula, where many circular abandoned channels have been identified. We obtained undisturbed core samples of old river channel deposits and angular gravel deposits that overlie the circular abandoned channel. The old river channel deposits have been emergent since at least MIS5, based on an analysis of the soil color in angular gravel deposits. The incision rate, as calculated from this age and the difference in elevation between the abandoned and present channels, is less than about 0.9 m/ky. This study shows that analyses of circular abandoned channels can yield estimates of incision rates and potentially also uplift rates. More accurate estimates of incision rates require further studies of the dating and evolution of sediments that overlie circular abandoned channels.

Journal Articles

Measurements of the neutron activation cross sections for Bi and Co at 386 MeV

Yashima, Hiroshi*; Sekimoto, Shun*; Ninomiya, Kazuhiko*; Kasamatsu, Yoshitaka*; Shima, Tatsushi*; Takahashi, Naruto*; Shinohara, Atsushi*; Matsumura, Hiroshi*; Satoh, Daiki; Iwamoto, Yosuke; et al.

Radiation Protection Dosimetry, 161(1-4), p.139 - 143, 2014/10

 Times Cited Count:2 Percentile:18.5(Environmental Sciences)

The neutron activation cross sections up to GeV are important for the neutron dosimetry of the radiation field in high-energy and high-intensity accelerator facilities for a project of intense spallation neutron source. But the evaluation of neutron activation cross section data is not enough above 20 MeV because experimental data are still scarce. This study aimed to measure the neutron activation cross sections of Bi and Co by using a quasi-monoenergetic neutron field. In this symposium, we will present obtained experimental cross section data with the other experimental data (neutron-induced and proton-induced), the calculated data by PHITS code and the evaluated nuclear data.

Journal Articles

Spatial variations in $$^{3}$$He/$$^{4}$$He ratios along a high strain rate zone, central Japan

Umeda, Koji; Kusano, Tomohiro; Ninomiya, Atsushi*; Asamori, Koichi; Nakajima, Junichi*

Journal of Asian Earth Sciences, 73, p.95 - 102, 2013/09

 Times Cited Count:4 Percentile:14.14(Geosciences, Multidisciplinary)

A linear zone with high strain rates along the Japan Sea coast, the Niigata-Kobe Tectonic Zone (NKTZ), is considered to be associated with rheological heterogeneities in the lower crust and/or upper mantle. Helium isotope variations along the NKTZ reveal a close association with the geophysical evidence for rheological heterogeneities in the crust and mantle. In the northern NKTZ where two large inland earthquakes occurred recently, there appear to be many samples with $$^{3}$$He/$$^{4}$$He ratios significantly higher than those observed in the fore-arc side of northeast Japan. A plausible source of mantle helium could be attributed to upward mobilization of aqueous fluids generated by dehydration of the subducting Pacific Plate slab.

Journal Articles

Helium isotope variations along the Niigata-Kobe Tectonic Zone

Ninomiya, Atsushi; Umeda, Koji; Asamori, Koichi

Gekkan Chikyu, 35(6), p.297 - 304, 2013/06

The seismic tomography study along the Niigata-Kobe Tectonic Zone revealed segmentations of the seismic velocity structure and suggests the variable origin of the high-strain-rate along the NKTZ. We compiled existing helium isotope data to inspect an implication of geographic distribution of helium isotope data to the geophysical structure of the NKTZ.

JAEA Reports

Development of database on circular abandoned channel in Japan

Takatori, Ryoichi; Yasue, Kenichi; Tanikawa, Shinichi*; Ninomiya, Atsushi*; Tanase, Atsushi*

JAEA-Data/Code 2012-028, 15 Pages, 2013/03

JAEA-Data-Code-2012-028.pdf:34.12MB
JAEA-Data-Code-2012-028-appendix(CD-ROM).zip:0.52MB

To develop a method for estimating late Quaternary uplift rates of inland mountainous terrains where fluvial terraces are poorly developed, we focused on "circular abandoned channels", formed by meander cut-offs or river capture of an incised meandering river. We studied about 1,000 circular abandoned channels distributed throughout the Islands of Japan, and developed GIS database on circular abandoned channel in Japan. This database contains formation process, relative heights, degree of dissection and bedrocks of circular abandoned channels. Circular abandoned channels are distributed in inland mountainous terrains, where late Quaternary uplift rates are unknown, and indicate different relative heights along the same river. Relative heights tend to correlate with degree of dissection of the circular abandoned channels, which may indicate that degree of dissection correlate with ages of abandonment of circular abandoned channels.

Journal Articles

Development of nondestructive and quantitative elemental analysis method using calibration curve between muonic X-ray intensity and elemental composition in bronze

Ninomiya, Kazuhiko; Nagatomo, Takashi*; Kubo, Kenya*; Ito, Takashi; Higemoto, Wataru; Kita, Makoto*; Shinohara, Atsushi*; Strasser, P.*; Kawamura, Naritoshi*; Shimomura, Koichiro*; et al.

Bulletin of the Chemical Society of Japan, 85(2), p.228 - 230, 2012/02

 Times Cited Count:21 Percentile:55.21(Chemistry, Multidisciplinary)

Elemental analysis of bulk materials can be performed by detecting the high-energy X-rays emitted from muonic atoms. Muon irradiation of standard bronze samples was performed to determine the muon capture probabilities for the elemental components from muonic X-ray spectra. Nondestructive elemental analysis of an ancient Chinese coin was also performed.

Journal Articles

Manifestations of upwelling mantle flow on the Earth's surface

Asamori, Koichi; Umeda, Koji; Ninomiya, Atsushi*; Negi, Tateyuki

The Earth's Core; Structure, Properties and Dynamics, p.79 - 94, 2011/07

Remarkable uplift of 1400 m during the Quaternary has been recognized in the Mesozoic crystalline mountains (Asahi Mountains) located on the back-arc side of the Northeast Japan Arc. Crustal and mantle structures beneath the mountains were imaged as a 2D resistivity model, using magnetotelluric survey. The resulting resistivity structure clearly indicates that an anomalous conductive body is present in the central part of the mountains. The conductor extends from the middle crust to the upper mantle. Also, helium isotope ratios were determined from free gas and groundwater samples collected in and around the mountains. The highest value is similar to those of MORB-type helium derived from mantle volatiles. These results provide strong evidence for the presence of a latent magma reservoir and related high-temperature aqueous fluids beneath the Asahi Mountains. The presence of a latent magma reservoir could lead to thinning of the brittle upper crust and the aqueous fluids could weaken the crustal rocks. Thus, contractive deformation could arise locally above the reservoir under compressive stress field. Although the uplift is considered to be controlled by active reverse faults on the west side of the mountains, the highest peak of the mountains is not located near the active faults, but rather is above the prominent conductive zone. It is concluded that the notable uplift of the mountains can mainly be attributed to locally anelastic deformation of the entire crust.

Journal Articles

Measurement of neutron cross sections for yttrium and terbium at 287 MeV

Sekimoto, Shun*; Utsunomiya, Takashi*; Yashima, Hiroshi*; Ninomiya, Kazuhiko*; Omoto, Takashi*; Nakagaki, Reiko*; Shima, Tatsushi*; Takahashi, Naruto*; Shinohara, Atsushi*; Kinoshita, Norikazu*; et al.

Progress in Nuclear Science and Technology (Internet), 1, p.89 - 93, 2011/02

In this work, we tried to determine reaction cross sections for Y and Tb induced by neutrons at 300 MeV, which have never been reported. The irradiations were carried out using neutrons produced through $$^{7}$$Li(p, n) reaction at N0 beam line in the Research Center for Nuclear Physics (RCNP), Osaka University. To estimate quasi-monoenergetic neutron induced cross sections, the target stacks of Y and Tb were irradiated on the two angles of 0 degree and 30 degree for the axis of the primary proton beam. Neutron cross sections were estimated by subtracting the activities produced in the samples placed on 30 degree from those of 0 degree to correct the contribution of the low energy tail in the neutron spectrum.

JAEA Reports

Annual report for research on long-term stability of geological environments in FY2008

Kusano, Tomohiro; Asamori, Koichi; Kurosawa, Hideki; Tanikawa, Shinichi; Ninomiya, Atsushi; Negi, Tateyuki; Hanamuro, Takahiro; Yasue, Kenichi; Yamada, Kunimi; Ishimaru, Tsuneari; et al.

JAEA-Research 2009-072, 72 Pages, 2010/03

JAEA-Research-2009-072.pdf:11.27MB

The Japanese islands are located in the tectonically active Circum-Pacific Mobile Belt. As a result, Japan has a high frequency of earthquakes and eruptions. Special consideration is given to the long-term stability of the geological environment, taking into account volcanism, faulting, uplift, denudation, climatic change and sea-level change in Japan. Development of research/prediction technologies for geotectonic events has been carried out to evaluate the long-term stability of the geological environment in Japan. In fiscal year 2008, we carried out the following researches. For studies on faulting and seismic activity, we developed investigation techniques for evolutional history and activity of fault, and carried out case studies for development of effective assessment model in the fault zones. For volcanological and geothermal studies, we provided an integrated approach for detecting crustal magma and/or geothermal fluid in deep underground using geophysical and geochemical data. For the general evaluation study on uplift/denudation and climatic/sea-level change, we arranged investigation techniques for reconstruction of paleo-topography and paleo-climate, and to establish a simulation model for landform development. For studies on the long-term stability of the geological environments, we developed simulation techniques for groundwater flow related by crustal movement.

JAEA Reports

Study on the method of fault zone survey by use of in-situ hydrogen gas measurement

Kurosawa, Hideki; Ishimaru, Tsuneari; Shimada, Koji; Niwa, Masakazu; Kosaka, Hideki*; Saito, Satoshi*; Ninomiya, Atsushi

JAEA-Research 2009-043, 144 Pages, 2010/01

JAEA-Research-2009-043-01.pdf:8.09MB
JAEA-Research-2009-043-02.pdf:46.22MB

Research on the influence of fault activity on deep geological environments contributes to the reliability of geological disposal systems for HLW. In this study, preliminary test shows that measured value within 1 hour after measurement start is supposed to include hydrogen gas generated by rock fracturing during the drilling of sampling holes and that stored in surrounding disturbed rocks, though the monitoring from a hand-drilled hole is effective for a rapid measurement. We investigated the concentration of hydrogen gas emitted from the Yamasaki fault zone, in southeast Japan. In our survey, the points where high concentrations of hydrogen gas emission was detected were unevenly distributed along the active fault, and in the southeast portion of the study area where small earthquakes frequently occurred.

Journal Articles

Release of mantle helium and its tectonic implications

Umeda, Koji; Ninomiya, Atsushi; Asamori, Koichi

Helium; Characteristics, Compounds, and Applications, 28 Pages, 2010/00

Helium is the lightest noble gas and both stable isotopes, $$^{3}$$He and $$^{4}$$He, are produced in the crust in a ratio of $$sim$$ 0.02 R$$_{rm A}$$, with R$$_{rm A}$$ being the atmospheric $$^{3}$$He/$$^{4}$$He ratio of 1.4$$times$$10$$^{-6}$$. Higher values are an indication of helium from the mantle where $$^{3}$$He captured during planetary accretion has been stored. It has been suspected for some time that degassing of the planet does not occur homogeneously over the Earth's surface, but is rather concentrated along plate boundaries, where the dynamics of the lithosphere are more intense and mantle helium from the Earth's interior can be more easily transported to the surface. We indicate that the spatial distribution of $$^{3}$$He/$$^{4}$$He ratios in gas samples from crustal fluids are considered to provide potentially useful information for determining not only latent magmatic activity but also potential pathways for mantle volatiles, such as in tectonically active zones.

JAEA Reports

Annual report for research on long-term stability of geological environments in FY2007

Kusano, Tomohiro; Nohara, Tsuyoshi; Umeda, Koji; Ishimaru, Tsuneari; Hanamuro, Takahiro; Saito, Tatsuo; Yasue, Kenichi; Niwa, Masakazu; Shimada, Koji; Yamada, Kunimi; et al.

JAEA-Research 2009-022, 47 Pages, 2009/09

JAEA-Research-2009-022.pdf:48.94MB

The Japanese islands are located in the tectonically active Circum-Pacific Mobile Belt. As a result, Japan has a high frequency of earthquakes and eruptions. Special consideration is given to the long-term stability of the geological environment, taking into account volcanism, faulting, uplift, denudation, climatic change and sea-level change in Japan. Development of research/prediction technologies for geotectonic events has been carried out to evaluate the long-term stability of the geological environment in Japan. In fiscal year 2007, we carried out the following researches, to confirm existence of the phenomena that have influences on geological disposal system (e.g., active faulting, volcanism), and to develop the investigation techniques to reconstruct the history of these phenomena. For studies of faulting and seismic activity, we developed the investigation techniques to research distribution of crush zone, process of faulting, activity, and so on. For volcanological and geothermal studies, we developed a technique for detecting crustal magma and/or geothermal fluid in deep underground. For studies of uplift/denudation and climatic/sea-level changes, we extracted investigation techniques for landform developments and uplift rate with river terraces.

Journal Articles

Helium isotopes as a tool for detecting concealed active faults

Umeda, Koji; Ninomiya, Atsushi

Geochemistry, Geophysics, Geosystems (Internet), 10(8), p.Q08010_1 - Q08010_10, 2009/08

A magnitude ($$M$$$$_{j}$$) 7.3 crustal earthquake occurred in western Tottori Prefecture, southwest Japan, on 6 October 2000. However, there was no indication of an earthquake surface fault corresponding to the 2000 earthquake. In order to elucidate the geographic distribution of the $$^{3}$$He/$$^{4}$$He ratios around the seismic source region, new helium isotope data for groundwater samples from drinking water wells were acquired. The maximum $$^{3}$$He/$$^{4}$$He ratio was observed from the well located nearest to the epicenter of the main shock. In addition, there appears to be a clear trend of decreasing $$^{3}$$He/$$^{4}$$He ratios with distance away from the main trace of the estimated fault segments. The observations provide significant evidence that the source fault of the 2000 earthquake is associated with leakage of mantle volatiles through the crust to the Earth's surface. We suggest that helium isotopes can be regarded as a tool for investigating concealed active faults with no surface expression.

Journal Articles

Heat source for an amagmatic hydrothermal system, Noto Peninsula, Central Japan

Umeda, Koji; Ninomiya, Atsushi; Negi, Tateyuki

Journal of Geophysical Research, 114(B1), p.B01202_1 - B01202_10, 2009/01

Although there is no geological evidence of volcanism during the Pliocene and Quaternary in the Noto Peninsula, Central Japan, the peninsula has long been known to be unusual and atypical of non-volcanic regions, as indicated by the presence of high-temperature hot springs and the high geothermal gradient values of more than 50 K/km. In this work, we present new helium isotope data from the Noto Peninsula and examine a possible source of excess heat in this non-volcanic region, including geophysical evidence such as seismic velocity, resistivity structures, and heat flow data.

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