Deformation and magicity in heavy actinides; First observation of the ground-state rotational band of Fm

Orlandi, R.; Asai, Masato; Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Tsukada, Kazuaki; Sato, Tetsuya; Ito, Yuta; Suzaki, Fumi; Nagame, Yuichiro*; et al.

Physical Review Letters, 137(8), p.082501_1 - 082501_6, 2026/08

https://doi.org/10.1103/7gzt-ldn5

J-PARC LINAC 50 Hz operation verification study

Kondo, Yasuhiro; Chimura, Motoki; Cicek, E.*; Fukui, Yuji*; Futatsukawa, Kenta*; Fuwa, Yasuhiro; Goto, Rikuto*; Hirano, Koichiro; Ishikawa, Masaki*; Ito, Takashi; et al.

Proceedings of 22nd Annual Meeting of Particle Accelerator Society of Japan (Internet), p.124 - 129, 2026/03

https://www.pasj.jp/web_publish/pasj2025/proceedings/PDF/FRO6/FRO601.pdf

Various upgrade plans of the J-PARC linac are underway, and repetition-rate doubling project is one of the most important part. Currently, the linac supplies a 400~MeV H ion beam to the 3~GeV synchrotron (RCS) at a repetition rate of 25~Hz. However, to deliver the beam to both RCS and proton-beam irradiation facility under planning, it is necessary to raise the repetition rate from 25~Hz to 50~Hz. Prior to construction of the beamline to the irradiation facility, we conducted a verification of the 50~Hz operation of all the linac apparatus simultaneously within the current operational limits in May 2025. And also, the verification of the 50~Hz operation of the particle counter system, which is one of the most important safety device of the J-PARC accelerator, was conducted. As a result, any significant problems were not found out, and it is now ready for the upcoming 50~Hz-beam acceleration demonstration. This paper describes this details of the demonstration of the 50~Hz operation, without beam acceleration, of the J-PARC linac.

Investigating the N(,)O reaction rates via the F(,)F reaction

Kim, S. H.*; Chae, K. Y.*; Asai, Masato; Hirose, Kentaro; Sato, Tetsuya; Makii, Hiroyuki; Nishio, Katsuhisa; Orlandi, R.; Smallcombe, J.; Suzaki, Fumi; et al.

Journal of the Korean Physical Society, 6 Pages, 2026/00

https://doi.org/10.1007/s40042-026-01643-3

no abstracts in English

None

Yokozuka, Eri*; Seito, Hajime*; Oka, Toshitaka; Kumagai, Yuta; Nagasawa, Naotsugu*

Isotope News, (801), p.46 - 48, 2025/10

https://www.jrias.or.jp/books/cat3/2025/801.html

no abstracts in English

Fabrication of low-O/M fast reactor MOX fuel and analysis on its oxygen potential behaviors

Hirooka, Shun; Vauchy, R.; Horii, Yuta; Sunaoshi, Takeo*; Saito, Kosuke

Proceedings of TopFuel 2025; Nuclear Reactor Fuel Performance Conference (Internet), 10 Pages, 2025/10

Reducing the oxygen-to-metal (O/M) ratio in MOX fuels plays an important role in suppressing the corrosion depth in the cladding due to fuel-cladding chemical interaction (FCCI), which is the key to determining the lifetime of fast reactor MOX fuels. Owing to a number of irradiation and post-irradiation experiments, a clear decreasing trend in the corrosion depth with lower O/M ratio in the as-fabricated MOX pellet was reported, whereas a significant redistribution of the O/M ratio in a pellet driven by the radial temperature gradient during irradiation could supply a higher oxygen potential near the pellet periphery where the FCCI should occur. The reduction of the O/M ratio in the MOX pellet fabrication processes can be achieved by heat treatment by taking high temperature, longer time, and lower oxygen partial pressure in the gas into account; the properties governing the reduction are not sufficiently studied. This study demonstrated the variation of O/M ratio in MOX pellets and the in-situ O/M ratio during the heat treatment was analyzed by using a thermogravimeter, which revealed a decreasing behavior during heating and dwell as well as an increasing behavior in the O/M ratio during the cooling step. Furthermore, the redistribution of O/M ratio, analyzed by Sari's model, was discussed to investigate the O/M ratio and the oxygen potential near the pellet periphery which is likely to have a more direct influence on the FCCI than the as-fabricated O/M ratio. By using the recent oxygen potential data on MOX, it is found that the oxygen potential profile in the radial direction is especially drastic near the pellet periphery and is sensitive to the as-fabricated O/M ratio.

Upper limit for the Cm(Ti,xn)Og reaction cross section

Gall, B. J.-P.*; Asai, Masato; Ito, Yuta; Toyoshima, Atsushi*; 30 of others*

Journal of the Physical Society of Japan, 94(9), p.094201_1 - 094201_9, 2025/09

https://doi.org/10.7566/JPSJ.94.094201

An experiment to search for Og isotopes using the Ti beam impinging on Cm target was performed at RIKEN Nishina Center. The optimal beam energy was determined from the quasielastic barrier distribution extracted from the excitation function of quasielastic backscattering. As a result, no Og decay was found, enabling only an estimation of the sensitivity for one event of 0.27 pb, and the 1 cross section upper limit of 0.50 pb.

Control and irradiation behaviors of oxygen potential of MOX fuel

Hirooka, Shun; Vauchy, R.; Horii, Yuta; Sunaoshi, Takeo*; Saito, Kosuke; Ozawa, Takayuki

Proceedings of Workshop on Fuel Performance Assessment and Behaviour for Liquid Metal Cooled Fast Reactors (Internet), 8 Pages, 2025/07

no abstracts in English

A Multi-reflection time-of-flight mass spectrograph for superheavy nuclei

Schury, P.*; Ito, Yuta; Wada, Michiharu*

Nihon Butsuri Gakkai-Shi, 80(2), p.72 - 78, 2025/02

https://doi.org/10.11316/butsuri.80.2_72

The multi-reflection time-of-flight mass spectrograph has recently become of great utility in the study of superheavy nuclei. The device efficiently uses each ion and its operation is amenable to the inclusion of a decay detector being coupled into the time-of-flight (TOF) ion impact detector. In this way, TOF-decay correlation can be measured to unambiguously differentiate low-yield radioactive ions from stable molecular ions or dark counts. This will eventually allow the technique to be applied to the study of extremely low-yield nuclei such as those of Nh and Mc isotopes.

Pulsed muon facility of J-PARC MUSE

Shimomura, Koichiro*; Koda, Akihiro*; Pant, A. D.*; Sunagawa, Hikaru*; Fujimori, Hiroshi*; Umegaki, Izumi*; Nakamura, Jumpei*; Fujihara, Masayoshi; Tampo, Motonobu*; Kawamura, Naritoshi*; et al.

Interactions (Internet), 245(1), p.31_1 - 31_6, 2024/12

https://doi.org/10.1007/s10751-024-01863-8

Creep deformation and rupture behavior of 9Cr-ODS steel cladding tube at high temperatures from 700C to 1000C

Imagawa, Yuya; Hashidate, Ryuta; Miyazawa, Takeshi; Onizawa, Takashi; Otsuka, Satoshi; Yano, Yasuhide; Tanno, Takashi; Kaito, Takeji; Onuma, Masato*; Mitsuhara, Masatoshi*; et al.

Journal of Nuclear Science and Technology, 61(6), p.762 - 777, 2024/06

https://doi.org/10.1080/00223131.2023.2269178

The Japan Atomic Energy Agency has been developing 9Cr-oxide dispersion strengthened (ODS) steel as a fuel cladding material for sodium-cooled fast reactors (SFRs). Previous studies have formulated the creep rupture equation for 650C to 850C. However, little data have been obtained above 850C, and no equation has been formulated. This study conducted creep tests to evaluate creep strength at 700C to 1000C. Two creep test methods, the internal pressure and ring creep tests under development, were used, and the validation of the ring creep test method was conducted. The results showed that 9Cr-ODS steel undergoes almost no strength change due to the matrix's phase transformation, and a single equation can express a creep rupture strength from 700C to 1000C. In validating the ring creep test method, analysis clarified the effect of stress concentration on the specimen. Plastic deformation occurs at high initial stress and may lead to early rupture. The results will be essential for future creep testing and evaluation of neutron-irradiated 9Cr-ODS steel.