New approach in nuclear data evaluation through Bayesian machine learning

Iwamoto, Hiroki

JAEA-Conf 2026-001, p.34 - 37, 2026/06

https://doi.org/10.11484/jaea-conf-2026-001

Nuclear data are essential for the research and development of nuclear energy systems and accelerator facilities, and applications involving radioactive isotopes. However, the increasing complexity of theoretical models and the demands of large-scale computations have made sustainable nuclear data evaluation challenging with limited human resources. To overcome these difficulties and continue providing reliable nuclear data, it is crucial to advance nuclear data evaluation methods. In this talk, I will explore possible solutions to these issues through Bayesian machine learning, using examples from our recent work.

A Machine leaning-based approach to estimate nuclide production cross sections

Iwamoto, Hiroki; Meigo, Shinichiro; Sugihara, Kenta*

JPS Conference Proceedings (Internet), 45, p.011179_1 - 011179_7, 2026/06

https://doi.org/10.7566/JPSCP.45.011179

The nuclide production cross sections are crucial for evaluating the radioactivity of activation products in accelerators and nuclear facilities. Although the production of radionuclides in spallation reactions can be explained using physics models like the nuclear cascade plus evaporation model, accurately and comprehensively reproducing experimental values remains challenging. To address this problem, we have developed a machine learning (ML) model to comprehensively estimate nuclide production cross sections for target materials. The model is trained on experimental data from the nuclear reaction database EXFOR and can estimate nuclide production cross sections even in data-poor regions by utilizing transfer learning. In a previous study, we demonstrated that our model can comprehensively estimate Be ( d) and H ( y) production cross sections for a wide range of targets. In this study, we apply the ML model to nuclides important for accelerator facility design and astrophysics, such as He, Be ( y), Na ( y), and Na ( h), showing that it can comprehensively estimate their production cross sections.

Design policy of pilot plant for accelerator-driven system

Nishihara, Kenji; Sugawara, Takanori; Fukushima, Masahiro; Iwamoto, Hiroki; Katano, Ryota; Abe, Takumi

Progress in Nuclear Science and Technology (Internet), 8, p.185 - 190, 2025/09

https://doi.org/10.15669/pnst.8.185

A pilot plant for the accelerator-driven system is proposed as a scaled-down version of a lead-bismuth cooled ADS with 800 MW thermal output for transmutation of minor actinides. In this article, the design policy of the pilot plant is elaborated for each design area: safety, subcritical management, sub-critical core, accelerator, target and in-core components. The conceptual design of the pilot ADS is also presented: 200 MW of thermal output, keff below 0.95, introduction of control rod, 1.0 GeV-10mA accelerator and roughly-estimated size of in-core components.

Built-in physics models and proton-induced nuclear data validation using MCNP, PHITS, and FLUKA; Impact on the shielding design for proton accelerator facilities

elik, Y.*; Stankovskiy, A.*; Iwamoto, Hiroki; Iwamoto, Yosuke; Van den Eynde, G.*

Annals of Nuclear Energy, 212, p.111048_1 - 111048_12, 2025/03

https://doi.org/10.1016/j.anucene.2024.111048

Measurements of displacement cross sections of metals for 120-GeV proton beam irradiation

Iwamoto, Yosuke; Matsuda, Hiroki*; Meigo, Shinichiro; Yonehara, Katsuya*; Pellemoine, F.*; Liu, Z.*; Lynch, K.*; Yoshida, Makoto*; Yabuuchi, Atsushi*; Yoshiie, Toshimasa*; et al.

Nuclear Instruments and Methods in Physics Research B, 557, p.165543_1 - 165543_8, 2024/12

https://doi.org/10.1016/j.nimb.2024.165543

The number of displacements per atom is widely used as an indicator of irradiation damage to materials in proton accelerator facilities. Experiments have been carried out on protons below 3 GeV to verify the dpa of metallic materials. However, the dpa for high-energy protons above 3 GeV has not been measured. In order to validate the displacement cross sections of metals in the high-energy region, the electrical resistivity changes of aluminium, copper and tungsten wires at a temperature of 8 K were measured using protons with energy of 120 GeV. The results show that the conventional irradiation damage model of PHITS overestimates the experimental data. On the other hand, the calculation results using the athermal recombination correction model were in agreement with the experimental data.

Proton beam utilization for space development equipment at J-PARC

Meigo, Shinichiro; Yamaguchi, Yuji; Iwamoto, Hiroki

Proceedings of 21st Annual Meeting of Particle Accelerator Society of Japan (Internet), p.32 - 37, 2024/10

https://www.pasj.jp/web_publish/pasj2024/proceedings/PDF/WEOA/WEOA01.pdf

no abstracts in English

Comprehensive estimation of nuclide production cross sections using a phenomenological approach

Iwamoto, Hiroki; Meigo, Shinichiro; Sugihara, Kenta*

Physical Review C, 109(5), p.054610_1 - 054610_12, 2024/05

https://doi.org/10.1103/PhysRevC.109.054610

Nuclide production cross sections are crucial in nuclear research, development, space exploration, and astrophysical investigations. Despite their importance, limited experimental data availability restricts the practicality of phenomenological approaches to comprehensive cross-section estimation. To address this, we propose a Gaussian process-based machine learning (ML) model capable of transferring knowledge from elements with abundant data to those with limited or no experimental data. Our ML model not only enables comprehensive cross-section estimations for various elements but also demonstrates predictive capabilities akin to physics models, even in regions with scarce training data.

Measurement of 100 MeV-range nuclear reaction data using the fixed-field alternating gradient accelerator at Kyoto University

Iwamoto, Hiroki

JAEA-Conf 2023-001, p.40 - 45, 2024/02

https://doi.org/10.11484/jaea-conf-2023-001

no abstracts in English

Neutron-production double-differential cross sections of Pb and Bi in proton-induced reactions near 100 MeV

Iwamoto, Hiroki; Meigo, Shinichiro; Satoh, Daiki; Iwamoto, Yosuke; Ishi, Yoshihiro*; Uesugi, Tomonori*; Yashima, Hiroshi*; Nishio, Katsuhisa; Sugihara, Kenta*; elik, Y.*; et al.

Nuclear Instruments and Methods in Physics Research B, 544, p.165107_1 - 165107_15, 2023/11

https://doi.org/10.1016/j.nimb.2023.165107

The lack of double-differential cross-section (DDX) data for neutron production below the incident proton energy of 200 MeV hinders the validation of spallation models in technical applications, such as research and development of accelerator-driven systems (ADSs). The present study aims to obtain experimental DDX data for ADS spallation target materials in this energy region and identify issues related to the spallation models by comparing them with the analytical predictions. The DDXs for the () reactions of Pb and Bi in the 100-MeV region were measured over an angular range of 30 to 150 using the time-of-flight method. The measurements were conducted at Kyoto University utilizing the FFAG accelerator. The DDXs obtained were compared with calculation results from Monte Carlo-based spallation models and the evaluated nuclear data library, JENDL-5. Comparison between the measured DDX and analytical values based on the spallation models and evaluated nuclear data library indicated that, in general, the CEM03.03 model demonstrated the closest match to the experimental values. Additionally, the comparison highlighted several issues that need to be addressed in order to improve the reproducibility of the proton-induced neutron-production DDX in the 100 MeV region by these spallation models and evaluated nuclear data library.

Measurement of displacement cross-sections of Nb irradiated by protons with kinetic energy range between 0.4 and 3 GeV

Meigo, Shinichiro; Nakano, Keita*; Matsuda, Hiroki; Iwamoto, Yosuke; Yoshida, Makoto*

EPJ Web of Conferences, 284, p.05001_1 - 05001_4, 2023/05

https://doi.org/10.1051/epjconf/202328405001

In high-intensity proton accelerator facilities such as Accelerator Driven System (ADS) and the spallation neutron source, it is crucial to evaluate the damage of beam-interception materials and accelerator components, such as a magnet coil. The displacement per atom (dpa) is used as a damage index, which is derived by integrating the particle flux and the displacement cross section based on the NRT model. Although the dpa is employed as the standard, the experimental data of displacement cross section are scarce for a proton in the energy region above 20 MeV. To obtain the data for superconducting materials for high-intensity accelerators and magnets, the displacement cross section of Nb for proton irradiation with a kinetic energy range between 0.4 and 3 GeV was measured. For sustaining damage in the sample, the Nb sample was cooled at a cryogenic temperature (8 K), where the recombination of Frenkel pairs due to thermal motion was well suppressed with maintaining the normal conductivity to maintain Matthiessen's rule. The displacement cross section of Nb was calculated using the PHITS code, and was compared with the present experimental results. It was found that the widely utilized NRT model overestimates the cross section by a factor of 2, as suggested by the previous works. It was also found that the calculation with a recently proposed athermal recombination corrected (arc) model based on Molecular Dynamics (MD) shows good agreement with the present data.