Physicochemical characterization of the youngest active domain in major fault zones using the weathering index and X-ray computed tomography

Iwamori, Akiyuki*; Ogita, Yasuhiro; Shimada, Koji; Tateishi, Ryo*; Takagi, Hideo*; Ota, Toru*; Cho, T.*; Kudo, Shunsuke*; Nojiri, Keisuke*; Shigemitsu, Yasumune*; et al.

Engineering Geology, 344, p.107821_1 - 107821_20, 2025/01

https://doi.org/10.1016/j.enggeo.2024.107821

Clarification of the physicochemical characterization of brittle fault rocks is important not only for understanding the history of the fault activity and deformation mechanisms, but also for assessing the siting conditions of important facilities such as nuclear power plants, radioactive waste disposal sites, and oil storage bases. Here, we apply the chemical weathering index (W values) to the brittle fault rocks of the Shiraki-Nyu fault (granite), the Tsuruga fault (geological boundary between granite and greenstone), and the Yamada fault (adamellite), which are active faults in the peripheral area of Wakasa Bay, and their respective protoliths (hard rocks), and investigate the physicochemical characteristics of the youngest active domain of brittle fault rocks based on the relationship between computed tomography data (CT numbers) and alteration intensity (AI values). The W values of the fault rocks are mainly affected by changes in NaO and CaO, corresponding to the elution or deposition of plagioclase and calsite for granite, clinopyroxene and hornblende for greenstone, and plagioclase for adamellite. The W values mainly indicate the effects of hydrothermal alteration up to 50 60 percent and of weathering at over 60 percent. On the other hand, the CT values of the fault rocks are lowest in the fault gouge corresponding to the latest active zone, which was identified as the lowest density zone. In addition, fresh plagioclase fragments are present in each fault gouge of the latest active zone of the active faults in this study. The application of W values to brittle fault rocks is an effective method for understanding the trends of mineralogical variations associated with hydrothermal alteration and weathering in fault rocks, and it is highly possible to improve the accuracy of identifying the youngest active domain in major fault zones through joint analyses of CT numbers.

Level structures of Ca cast doubt on a doubly magic Ca

Chen, S.*; Browne, F.*; Doornenbal, P.*; Lee, J.*; Obertelli, A.*; Tsunoda, Yusuke*; Otsuka, Takaharu*; Chazono, Yoshiki*; Hagen, G.*; Holt, J. D.*; et al.

Physics Letters B, 843, p.138025_1 - 138025_7, 2023/08

https://doi.org/10.1016/j.physletb.2023.138025

Gamma decays were observed in Ca and Ca following quasi-free one-proton knockout reactions from Sc. For Ca, a ray transition was measured to be 1456(12) keV, while for Ca an indication for a transition was observed at 1115(34) keV. Both transitions were tentatively assigned as the decays. A shell-model calculation in a wide model space with a marginally modified effective nucleon-nucleon interaction depicts excellent agreement with experiment for level energies, two-neutron separation energies, and reaction cross sections, corroborating the formation of a new nuclear shell above the N = 34 shell. Its constituents, the and orbitals, are almost degenerate. This degeneracy precludes the possibility for a doubly magic Ca and potentially drives the dripline of Ca isotopes to Ca or even beyond.

Controlled release of radioactive krypton gas

Watanabe, Kazuki; Kimura, Norimichi*; Okada, Jumpei; Furuuchi, Yuta; Kuwana, Hideharu*; Otani, Takehisa; Yokota, Satoru; Nakamura, Yoshinobu

JAEA-Technology 2023-010, 29 Pages, 2023/06

JAEA-Technology-2023-010.pdf:3.12MB

The Krypton Recovery Development Facility reached an intended technical target (krypton purity of over 90% and recovery rate of over 90%) by separation and rectification of krypton gas from receiving off-gas produced by the shearing and the dissolution process in the spent fuel reprocessing at the Tokai Reprocessing Plant (TRP) between 1988 and 2001. In addition, the feasibility of the technology was confirmed through immobilization test with ion-implantation in a small test vessel from 2000 to 2002, using a part of recovered krypton gas. As there were no intentions to use the remaining radioactive krypton gas in the krypton storage cylinders, we planned to release this gas by controlling the release amount from the main stack, and conducted it from February 14 to April 26, 2022. In this work, all the radioactive krypton gas in the cylinders (about 7.110 GBq) was released at the rate of 50 GBq/min or less lower than the maximum release rate from the main stuck stipulated in safety regulations (3.710 GBq/min). Then, the equipment used in the controlled release of radioactive krypton gas and the main process (all systems, including branch pipes connected to the main process) were cleaned with nitrogen gas. Although there were delays due to weather, we were able to complete the controlled release of radioactive krypton gas by the end of April 2022, as originally targeted without any problems such as equipment failure.

"Southwestern" boundary of the island of inversion; First study of low-lying bound excited states in V and V

Elekes, Z.*; Juhsz, M. M.*; Sohler, D.*; Sieja, K.*; Yoshida, Kazuki; Ogata, Kazuyuki*; Doornenbal, P.*; Obertelli, A.*; Achouri, N. L.*; Baba, Hidetada*; et al.

Physical Review C, 106(6), p.064321_1 - 064321_10, 2022/12

https://doi.org/10.1103/PhysRevC.106.064321

The low-lying level structure of V and V was investigated for the first time. The neutron knockout reaction and inelastic proton scattering were applied for V while the neutron knock-out reaction provided the data for V. Four and five new transitions were determined for V and V, respectively. Based on the comparison to our shell-model calculations using the Lenzi-Nowacki-Poves-Sieja (LNPS) interaction, three of the observed rays for each isotope could be placed in the level scheme and assigned to the decay of the first 11/2 and 9/2 levels. The (,) excitation cross sections for V were analyzed by the coupled-channels formalism assuming quadrupole plus hexadecapole deformations. Due to the role of the hexadecapole deformation, V could not be unambiguously placed on the island of inversion.

A First glimpse at the shell structure beyond Ca; Spectroscopy of K, Ca, and Ca

Koiwai, Takuma*; Wimmer, K.*; Doornenbal, P.*; Obertelli, A.*; Barbieri, C.*; Duguet, T.*; Holt, J. D.*; Miyagi, Takayuki*; Navrtil, P.*; Ogata, Kazuyuki*; et al.

Physics Letters B, 827, p.136953_1 - 136953_7, 2022/04

AA2021-0775.pdf:0.62MB

https://doi.org/10.1016/j.physletb.2022.136953

no abstracts in English

Dynamics of radiocaesium within forests in Fukushima; Results and analysis of a model inter-comparison

Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi; Nishina, Kazuya*; Ota, Masakazu; Ohashi, Shinta*; Calmon, P.*; et al.

Journal of Environmental Radioactivity, 238-239, p.106721_1 - 106721_10, 2021/11

https://doi.org/10.1016/j.jenvrad.2021.106721

This study was aimed at analysing performance of models for radiocesium migration mainly in evergreen coniferous forest in Fukushima, by inter-comparison between models of several research teams. The exercise included two scenarios of countermeasures against the contamination, namely removal of soil surface litter and forest renewal, and a specific konara oak forest scenario in addition to the evergreen forest scenario. All the models reproduced trend of time evolution of radiocesium inventories and concentrations in each of the components in forest such as leaf and organic soil layer. However, the variations between models enlarged in long-term predictions over 50 years after the fallout, meaning continuous field monitoring and model verification/validation is necessary.

Evaluation of brittle crack arrest toughness for highly-irradiated reactor pressure vessel steels

Iwata, Keiko; Hata, Kuniki; Tobita, Toru; Hirota, Takatoshi*; Takamizawa, Hisashi; Chimi, Yasuhiro; Nishiyama, Yutaka

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 7 Pages, 2021/07

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

https://doi.org/10.1038/s41550-020-01271-2

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Quasifree neutron knockout reaction reveals a small -Orbital component in the Borromean nucleus B

Yang, Z. H.*; Kubota, Yuki*; Corsi, A.*; Yoshida, Kazuki; Sun, X.-X.*; Li, J. G.*; Kimura, Masaaki*; Michel, N.*; Ogata, Kazuyuki*; Yuan, C. X.*; et al.

Physical Review Letters, 126(8), p.082501_1 - 082501_8, 2021/02

AA2020-0819.pdf:1.29MB

https://doi.org/10.1103/PhysRevLett.126.082501

A quasifree (,) experiment was performed to study the structure of the Borromean nucleus B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for and orbitals, and a surprisingly small percentage of 9(2)% was determined for . Our finding of such a small component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in B. The present work gives the smallest - or -orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of or orbitals is not a prerequisite for the occurrence of a neutron halo.

= 32 shell closure below calcium; Low-lying structure of Ar

Corts, M. L.*; Rodriguez, W.*; Doornenbal, P.*; Obertelli, A.*; Holt, J. D.*; Menndez, J.*; Ogata, Kazuyuki*; Schwenk, A.*; Shimizu, Noritaka*; Simonis, J.*; et al.

Physical Review C, 102(6), p.064320_1 - 064320_9, 2020/12

AA2020-0748.pdf:0.75MB

https://doi.org/10.1103/PhysRevC.102.064320

Low-lying excited states in the = 32 isotope Ar were investigated by in-beam -ray spectroscopy following proton- and neutron-knockout, multinucleon removal, and proton inelastic scattering at the RIKEN Radioactive Isotope Beam Factory. The energies of the two previously reported transitions have been confirmed, and five additional states are presented for the first time, including a candidate for a 3 state. The level scheme built using coincidences was compared to shell-model calculations in the model space and to predictions based on chiral two- and three-nucleon interactions. Theoretical proton- and neutron-knockout cross sections suggest that two of the new transitions correspond to 2 states, while the previously proposed 4 state could also correspond to a 2 state.