Machine learning molecular dynamics reveals the structural origin of the first sharp diffraction peak in high-density silica glasses

Kobayashi, Keita; Okumura, Masahiko; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Urata, Shingo*; Suzuya, Kentaro

Scientific Reports (Internet), 13, p.18721_1 - 18721_12, 2023/11

https://doi.org/10.1038/s41598-023-44732-0

The first sharp peak diffraction peak (FSDP) in the structure factor of amorphous materials is thought to reflect the medium-range order structure in amorphous materials, and the structural origin of the FSDP has been a subject of ongoing debate. In this study, we employed machine learning molecular dynamics (MLMD) with nearly first-principles calculation accuracy to investigate the structural origin of the FSDP in high-density silica glass. First, we successfully reproduced various experimental data of high-density silica glass using MLMD. Furthermore, we revealed that the development (or reduction) of the FSDP in high-density silica glass is characterized by the deformation behavior of ring structures in Si-O covalent bond networks under compression.

Decommissioning of Pre-dismantling Temporary Waste Storage Facility 3 (FPG-03a,b,c) in Plutonium Fuel Production Facility

Shinozaki, Masaru; Aita, Takahiro; Iso, Takahito*; Odakura, Manabu*; Haginoya, Masahiro*; Kadowaki, Hiroyuki*; Kobayashi, Shingo*; Inagawa, Takumu*; Morimoto, Taisei*; Iso, Hidetoshi; et al.

JAEA-Technology 2021-043, 100 Pages, 2022/03

JAEA-Technology-2021-043.pdf:7.49MB

It is planned that the MOX (Mixed Oxide) from the decommissioned facilities in Nuclear Fuel Cycle Engineering Laboratories is going to be consolidated and stored stably and safely for a long term in Plutonium Fuel Production Facility of the Plutonium Fuel Development Center of Nuclear Fuel Cycle Engineering Laboratories. For this purpose, it is necessary to pelletize nuclear fuel materials in the facility and store them in the assembly storage (hereinafter referred to as "waste packaging work") to secure storage space in the plutonium material storage. As a countermeasure to reduce the facility risk in this waste packing work, it was decided to construct a new powder weighing and homogenization mixing facility to physically limit the amount (batch size) of nuclear fuel materials handled at the entrance of the process. In order to secure the installation space for the new facility in the powder preparation room (1) (FP-101), the pre-dismantling temporary waste storage facility 3 (FPG-03a, b, c) was dismantled and removed. This facility consists of a granulating and sizing facility, an additive mixing facility, and a receiving and delivering guided facility, which started to be used from January 1993, and was discontinued on February 3, 2012 and became a waste facility. Subsequently, the dismantling and removal of the interior equipment was carried out by pellet fabrication section for glove operation to reduce the amount of hold-up, and before the main dismantling and removal, there was almost no interior equipment except for large machinery. This report describes the dismantling and removal of the glove box and some interior equipment and peripherals of the facility, as well as the Green House setup method, dismantling and removal procedures, and issues specific to powder process equipment (dust, etc.).

Pressure-temperature-field phase diagram in the ferromagnet UP

Araki, Shingo*; Hayashida, Minami*; Nishiumi, Naoto*; Manabe, Hiroki*; Ikeda, Yoichi*; Kobayashi, Tatsuo*; Murata, Keizo*; Inada, Yoshihiko*; Winiewski, P.*; Aoki, Dai*; et al.

Journal of the Physical Society of Japan, 84(2), p.024705_1 - 024705_8, 2015/02

https://doi.org/10.7566/JPSJ.84.024705

Collective structural changes in vermiculite clay suspensions induced by cesium ions

Motokawa, Ryuhei; Endo, Hitoshi*; Yokoyama, Shingo*; Nishitsuji, Shotaro*; Kobayashi, Toru; Suzuki, Shinichi; Yaita, Tsuyoshi

Scientific Reports (Internet), 4, p.6585_1 - 6585_6, 2014/10

https://doi.org/10.1038/srep06585

Detection and activity of iodine-131 in brown algae collected in the Japanese coastal areas

Morita, Takami*; Niwa, Kentaro*; Fujimoto, Ken*; Kasai, Hiromi*; Yamada, Haruya*; Nishiuchi, Ko*; Sakamoto, Tatsuya*; Godo, Waichiro*; Taino, Seiya*; Hayashi, Yoshihiro*; et al.

Science of the Total Environment, 408(16), p.3443 - 3447, 2010/06

https://doi.org/10.1016/j.scitotenv.2010.04.001

Iodine-131 (I) was detected in brown algae collected off the Japanese coast. The maximum measured specific activity of I in brown algae was 0.370.010 Bq/kg-wet. Cesium-137 (Cs) was also detected in all brown algal samples used in this study. There was no correlation between specific activities of I and Cs in these seaweeds. Low specific activity and minimal variability of Cs in brown algae indicated that past nuclear weapon tests were the source of Cs. Although nuclear power facilities are known to be pollution sources of I, there was no relationship between the sites where I was detected and the locations of nuclear power facilities. Most of the sites where I was detected were near big cities with large populations. On the basis of the results, we suggest that the likely pollution source of I, detected in brown seaweeds, is not nuclear power facilities, but nuclear medicine procedures.

Single crystal growth and fermi surface properties of an antiferromagnet UPdGa

Ikeda, Shugo; Matsuda, Tatsuma; Haga, Yoshinori; Yamamoto, Etsuji; Nakashima, Miho*; Kirita, Shingo*; Kobayashi, Tatsuo*; Hedo, Masato*; Uwatoko, Yoshiya*; Yamagami, Hiroshi*; et al.

Journal of the Physical Society of Japan, 74(8), p.2277 - 2281, 2005/08

https://doi.org/10.1143/JPSJ.74.2277

We have succeeded in growing a high-quality single crystal of an antiferromagnet UPdGa by the Ga-flux method with the off-stoichiometric composition of U : Pd : Ga = 1 : 2 : 7.3. The electronic state has been investigated by the de Haas-van Alphen experiment, indicating the similar cylindrical Fermi surfaces as in an antiferromagnet UPtGa. We have also studied the pressure effect by measuring the electrical resistivity. The Nel temperature decreases with increasing pressure and becomes zero at 3.1 GPa. The antiferromagnetic state is changed into the paramagnetic state above 3.1 GPa.

Depth dependency of neutron density produced by galactic cosmic rays in the lunar subsurface

Ota, Shuya; Sihver, L.*; Kobayashi, Shingo*; Hasebe, Nobuyuki*

no journal, , 

Neutron production by galactic cosmic rays (GCR) in the lunar subsurface plays an important role in the radiation environment on the surface and subsurface of the Moon and to make its accurate estimation is therefore very important for lunar and planetary nuclear spectroscopy and space dosimetry. In this work, the depth dependency of neutron production from protons and alpha particles in galactic cosmic ray (GCR) was estimated using the three-dimensional particle and heavy ion transport simulation code PHITS incorporating the latest high energy nuclear data, JENDL-HE. Our estimation of equilibrium neutron density profiles in the lunar subsurface was compared with the experimental data obtained by Apollo 17 Lunar Neutron Probe Experiment (LNPE). As the results, our calculation successfully reproduced the LNPE data within experimental errors of 15% (measurement) + 30% (systematic).

Mesoscopic structure of vermiculite and weathered biotite clays in suspension with and without cesium ions; Small-angle X-ray and neutron scattering studies

Motokawa, Ryuhei; Endo, Hitoshi*; Yokoyama, Shingo*; Nishitsuji, Shotaro*; Yaita, Tsuyoshi; Kobayashi, Toru; Suzuki, Shinichi

no journal, , 

no abstracts in English