Innovation of radioactive nuclide determination by the SDM method

Oshima, Masumi*; Hayakawa, Takehito*; Asai, Masato; Goto, Jun*; Shinohara, Hirofumi*

Nihon Genshiryoku Gakkai-Shi ATOMO, 68(6), p.361 - 365, 2026/06

https://doi.org/10.3327/jaesjb.68.6_361

We have developed an innovative method named "spectral determination method (SDM method)" to analyze radiation spectra containing a number of radioactive isotopes with better accuracy than that of conventional analysis methods. We applied this method to -ray spectra measured with Ge detectors or scintillation detectors, -particle spectra measured with liquid scintillation counters, and - coincidence spectra. Furthermore, we found that the accuracy of the analysis results was much improved by unifying all these spectra and applying the SDM method to those unified spectra.

Differences between radiation dose values under wearing and non-wearing geometries of personal dosimeters during sleep

Hirouchi, Jun; Takahara, Shogo; Watanabe, Masatoshi*

Health Physics, 130(1), p.87 - 93, 2026/01

https://doi.org/10.1097/HP.0000000000002001

With the return of residents after the Fukushima Daiichi Nuclear Power Station accident, some residents' radiation doses have been measured to ensure their safety. However, personal radiation doses vary depending on the behavior and residential environment of each subject even for a group of subjects living in the same region at the same time. In past studies, subjects were required to wear a personal dosimeter on their chest outdoors, while they were not required to wear the device indoors. This study investigated the difference between the dose values indicated for the wearing and nonwearing conditions of personal dosimeters during sleep. In particular, an adult human phantom was used to compare the indicated dose values when personal dosimeters were placed on the chest (reproducing the wearing condition) and near the head (reproducing the nonwearing condition) in two houses with a high radiation dose. Furthermore, to understand the reason for the difference in the indicated dose values, the radiation dose during sleep was calculated using a radiation transport calculation code. The dose values for the wearing condition were approximately 4% lower on the first floor and approximately 15% lower on the second floor than those for the nonwearing condition. In addition, the radiation doses and radiation dose ratios (head/chest) differed by approximately 30% and 20%, respectively, depending on the distance from the nearest window (1-3 m).

Speciation of cesium in a radiocesium-bearing microparticle emitted from Unit 1 during the Fukushima nuclear accident by XANES spectroscopy using transition edge sensor

Takahashi, Yoshio*; Miura, Hikaru*; Yamada, Shinya*; Sekizawa, Oki*; Nitta, Kiyofumi*; Hashimoto, Tadashi*; Yomogida, Takumi; Yamaguchi, Akiko; Okada, Shinji*; Itai, Takaaki*; et al.

Journal of Hazardous Materials, 495, p.139031_1 - 139031_19, 2025/09

https://doi.org/10.1016/j.jhazmat.2025.139031

In this presentation, we analyzed the chemical state of cesium in radiocesium-bearing microparticles (CsMPs) released during the 2011 Fukushima Daiichi Nuclear Power Plant accident using high-resolution X-ray absorption spectroscopy (XANES) and micro X-ray fluorescence (-XRF). The results identified two forms of cesium: one dissolved in glass and the other enriched on the surfaces of internal voids. The latter is considered to have originally existed as a gas and became concentrated during the cooling and solidification of the molten glass. These findings are crucial for understanding the formation process of CsMPs during the accident, as well as for future decommissioning and safety assessments.

Evaluating the effect of temporal variations in wind speed on sheltering effectiveness and developing a simplified correction method to account for these variations

Hirouchi, Jun; Takahara, Shogo; Watanabe, Masatoshi*

Journal of Radiological Protection, 45(2), p.021506_1 - 021506_13, 2025/05

https://doi.org/10.1088/1361-6498/add53e

Sheltering is a key countermeasure for mitigating radiation exposures during nuclear power plant accidents. The effectiveness of sheltering in minimizing inhalation exposure is commonly expressed using the reduction factor, which is the ratio of indoor to outdoor cumulative doses. The indoor dose is primarily influenced by the air exchange rate, penetration factor, and indoor deposition rate. Additionally, the air exchange rate is dependent on wind speed. In previous studies, the reduction factor was often treated as a constant value or calculated under constant wind speed conditions. However, wind speed varies in reality. This study investigated the effect of temporal variations in wind speed on the reduction factor and developed a simplified correction method to account for these variations. The results revealed that temporal variations in wind speed caused the reduction factor to differ by a factor of approximately two. Using the simplified correction method, the corrected reduction factors agreed, on average, within 10% of those calculated using a method that explicitly considers temporal variations in actual wind speed. Additionally, the computational cost was reduced by more than 20 times.

Neutron spectroscopy study on crystalline electric field excitations in NdB

Yamauchi, Hiroki; Metoki, Naoto; Watanuki, Ryuta*; Hong, T.*; Fernandez-Baca, J. A.*; Hagihara, Masato; Masuda, Takatsugu*; Yoshizawa, Hideki*; Ito, Shinichi*

Journal of the Physical Society of Japan, 94(5), p.054705_1 - 054705_8, 2025/04

https://doi.org/10.7566/JPSJ.94.054705

Evaluation of exposure doses and reduction factor for sheltering for each nuclear site under each accident scenario (Contract research)

Hirouchi, Jun; Watanabe, Masatoshi*; Hayashi, Naho; Nagakubo, Azusa; Takahara, Shogo

JAEA-Research 2024-015, 114 Pages, 2025/03

JAEA-Research-2024-015.pdf:10.03MB

The public living in areas contaminated by nuclear accidents is exposed to radiation in the early phase and over the long term. Even under the same accident scenario, the exposure doses and the effectiveness of sheltering, which is one of the protective measures, vary depending on the meteorological condition and the surrounding environment. The exposure doses and sheltering effectiveness in the early phase are important information for the public and the national and local governments planning a nuclear emergency preparedness. In this report, we evaluate the exposure doses and sheltering effectiveness at sites with nuclear facilities in Japan using OSCAAR, one of the probabilistic risk assessment codes, for five accident scenarios: three scenarios from past severe accident studies; a scenario defined by the Nuclear Regulatory Authority; and a scenario assuming the Fukushima Daiichi Nuclear Power Station accident. The sheltering effectiveness differed by approximately 20% among the sites. This was due to the differences in wind speed among the sites.

Effect of the ratio of water to rice on the molecular dynamics of cooked rice starch during retrogradation; Implications for amorphous structure in gelatinized state

Hirata, Yoshinobu*; Nakagawa, Hiroshi; Yamauchi, Hiroki; Kaneko, Koji; Hagihara, Masato; Yamaguchi, Hideyuki*; Imaizumi, Teppei*; Nishizu, Takahisa*

International Journal of Biological Macromolecules, 306, p.141668_1 - 141668_7, 2025/03

https://doi.org/10.1016/j.ijbiomac.2025.141668

We used quasi-elastic neutron scattering (QENS) to investigate the effect of the ratio of water to rice on the molecular dynamics of cooked rice starch during retrogradation. X-ray diffraction and differential scanning calorimetric measurements revealed that the degree of recrystallization and change in enthalpy were smaller with an increase in the amount of water added for cooking rice, whereas little difference in the crystallinity of the gelatinized rice starch was detected. The QENS measurements determined that the elastic incoherent structure factor (EISF) values of gelatinized samples were smaller with an increase in the amount of water added for cooking rice, indicating that the molecular dynamics of gelatinized rice starch with higher added water content were spatially more extended.

Magnetic and quadrupole coupling emerging in NdB with geometrically frustrated orthogonal antiferromagnetic dimer

Metoki, Naoto; Yamauchi, Hiroki; Hagihara, Masato; Watanuki, Ryuta*; Kawamura, Seiko; Kofu, Maiko*; Nakajima, Kenji; Matsuda, Masaaki*

Physical Review B, 111(10), p.104424_1 - 104424_9, 2025/03

https://doi.org/10.1103/PhysRevB.111.104424

Inelastic neutron scattering experiments were carried out to understand the unusual successive order in NdB with the frustrated Shatry-Sutherland (SS) lattice. The pseudo-quartet with and splits into four levels in the magnetically ordered states. The spectra can be explained with the on-site magnetic interaction , the coupling of with quadrupole , and the uniaxial crystalline electric field. The -electron states reproduce the temperature dependences of the in-plane moment which is the primary order parameter, and a weakly induced as the secondary order parameter. The magnetic-quadrupole coupling emerges and play essential role under the geometrical frustration, where the Heisenberg interactions are cancelled out.

Unique magnetic transition process demonstrating the effectiveness of bond percolation theory in a quantum magnet

Zheng, X.-G.*; Yamauchi, Ichihiro*; Hagihara, Masato; Nishibori, Eiji*; Kawae, Tatsuya*; Watanabe, Isao*; Uchiyama, Tomoki*; Chen, Y.*; Xu, C.-N.*

Nature Communications (Internet), 15, p.9989_1 - 9989_12, 2024/11

https://doi.org/10.1038/s41467-024-54335-6

France-Japan collaboration on severe accident studies in sodium-cooled fast reactors, 2; Methodologies and calculations of severe accident phases

Sogabe, Joji; Ishida, Shinya; Tagami, Hirotaka; Okano, Yasushi; Kamiyama, Kenji; Onoda, Yuichi; Matsuba, Kenichi; Yamano, Hidemasa; Kubo, Shigenobu; Kubota, Ryuzaburo*; et al.

Proceedings of International Conference on Nuclear Fuel Cycle (GLOBAL2024) (Internet), 4 Pages, 2024/10

In the frame of France-Japan collaboration, the calculational methodologies were defined and assessed, and the phenomenology and the severe accident consequences were investigated in a pool-type sodium-cooled fast reactor.