Quantitative analysis of ionization quenching in CaF:Ce using PHITS track-structure simulations

Hirata, Yuho; Kai, Takeshi; Ogawa, Tatsuhiko; Matsuya, Yusuke; Sato, Tatsuhiko; Watanabe, Kenichi*; Kato, Takumi*; Kawaguchi, Noriaki*; Yanagida, Takayuki*

Radiation Measurements, 193, p.107651_1 - 107651_8, 2026/04

https://doi.org/10.1016/j.radmeas.2026.107651

CaF:Ce has a high potential to be used as a dosimeter due to its high optically stimulated luminescence (OSL) intensity. However, when phosphors such as CaF:Ce are irradiated with swift ions, the OSL intensity per dose decreases due to quenching effects. Traditionally, quenching effects in phosphors have been evaluated based on energy deposition density, using linear energy transfer (LET) as a metric. However, the relationship between quenching effects and LET varies with ion type, complicating unified evaluations. The track structure in PHITS can precisely simulate the radiation interactions. In this study, we simulated the detector response of CaF:Ce irradiated with swift-ions and compared these results with experimental data. The comparison suggests that the quantum yield of OSL is a critical parameter influencing the quenching effect in CaF:Ce. These findings are expected to contribute to the development of improved phosphor detectors.

Development of a temperature-dependent chemical simulation code based on PHITS for water radiolysis from 0 to 350C

Matsuya, Yusuke; Yoshii, Yuji*; Kusumoto, Tamon*; Wang, Y.*; Ogawa, Tatsuhiko; Sato, Tatsuhiko; Kai, Takeshi

Scientific Reports (Internet), 24 Pages, 2026/00

https://doi.org/10.1038/s41598-026-52128-z

Water radiolysis plays an important role in radiation effects on materials, such as DNA damage in the human body and corrosion processes in nuclear reactors. Conventional chemical simulation codes are generally limited to around room temperature, which differs significantly from the temperature conditions encountered in reactor environments. In this study, we developed a chemical simulation code (PHITS-Chem) based on the general-purpose Monte Carlo code, the Particle and Heavy Ion Transport code System (PHITS), applicable over a temperature range 0 to 350C. The code explicitly considers the temperature dependence of diffusion coefficients and reaction rate constants, and its performance was validated by comparing the calculated G-values with previously reported experimental and theoretical data for low-LET (0.2 keV/m), medium-LET (11.9 keV/m), and high-LET (63.4 keV/m) radiation. The developed code enables high-precision evaluation of the reaction kinetics of radiolytic species over a wide temperature range and is expected to be useful for assessing in-core material degradation and for studies related to severe accident mitigation in nuclear reactors.

Development and validation of generalized Monte Carlo track-structure simulation model applicable to arbitrary ions in arbitrary materials

Ogawa, Tatsuhiko; Hirata, Yuho; Matsuya, Yusuke; Kai, Takeshi

Computer Physics Communications, 316, p.109758_1 - 109758_15, 2025/11

https://doi.org/10.1016/j.cpc.2025.109758

A track structure simulation model, ITSART Ver.2, has been developed to simulate the transport of arbitrary ions in arbitrary materials, accounting for every atomic interaction on an event-by-event basis. Unlike conventional track structure models, which are typically designed for therapeutic particle beams or bio-molecular targets, ITSART Ver.2 uniquely enables track structure calculations for any ion-material combination across an energy range from 10 eV/n to 1 TeV/n. To validate the developed model, the energy-angular distributions of secondary electrons, ion stopping ranges, radial dose distributions, and microscopic dose distributions calculated by ITSART Ver.2 were benchmarked against literature data. The unique features of ITSART Ver.2, including kinetic modeling of secondary electrons above 1 keV, modeling of secondary electron angular distribution, consideration of momentum transfer to target atoms, and interface with an atomic de-excitation model, resulted in calculations that were consistent with the benchmarking data. Furthermore, this benchmarking calculation demonstrated that ITSART Ver.2 can reproduce target-specific quantities such as Auger electron production and penumbra radial dose, which cannot be simulated with conventional codes that approximate the target as water. The capability of ITSART Ver.2 to perform track structure calculations under unconventional conditions paves the way for simulating various irradiation eff ects, such as reactor material irradiation damage, semiconductor device degradation, and other complex interactions.

Development of a chemical code applicable to ions based on the PHITS code for efficient and visual radiolysis simulations

Matsuya, Yusuke; Yoshii, Yuji*; Kusumoto, Tamon*; Ogawa, Tatsuhiko; Onishi, Seiki*; Hirata, Yuho; Sato, Tatsuhiko; Kai, Takeshi

Physical Chemistry Chemical Physics, 27(14), p.6887 - 6898, 2025/04

https://doi.org/10.1039/D4CP04216F

Radicals by water radiolysis play an important role in evaluating radiation-induced biological effects, such as DNA damage induction, chromosomal aberrations, and carcinogenesis. In the Particle and Heavy Ion Transport code System (PHITS), a track-structure simulation mode enabling the estimation of each atomic interactions in water and a chemical simulation code (PHITS-Chem) dedicated to electron beams that can simulate radical dynamics have been developed in our previous study. Here, we developed the PHITS-Chem code applicable to any ion species, considering a space partitioning method to detect radical reactions more efficiently and the 4D visualization function. The updated PHITS-Chem code was verified by comparing the simulated G values of proton beams, particle beams, and carbon ion beams to the corresponding values in the literature. We succeeded in intuitively evaluating the diffusion dynamics of radicals using the PHITS 3D drawing software, PHIG-3D. The time to calculate the G values was reduced (e.g., about 28 times faster) while maintaining its calculation accuracy. The developed PHITS-Chem code is expected to contribute to precise and intuitive understanding of the biological effects induced by radicals in ion-beam radiotherapy.

Overview of PHITS Ver.3.34 with particular focus on track-structure calculation

Ogawa, Tatsuhiko; Hirata, Yuho; Matsuya, Yusuke; Kai, Takeshi; Sato, Tatsuhiko; Iwamoto, Yosuke; Hashimoto, Shintaro; Furuta, Takuya; Abe, Shinichiro; Matsuda, Norihiro; et al.

EPJ Nuclear Sciences & Technologies (Internet), 10, p.13_1 - 13_8, 2024/11

https://doi.org/10.1051/epjn/2024012

The latest updates on PHITS, a versatile radiation transport code, focusing specifically on track-structure models are presented. Track structure calculations are methods used to simulate the movement of charged particles while explicitly considering each atomic reaction. Initially developed for radiation biology, these calculation methods aimed to analyze the radiation-induced damage to DNA and chromosomes. Several track-structure calculation models, including PHITS-ETS, PHITS-ETS for Si, PHITS-KURBUC, ETSART, and ITSART, have been developed and implemented to PHITS. These models allow users to study the behavior of various particles at the nano-scale across a wide range of materials. Furthermore, potential applications of track-structure calculations have also been proposed so far. This collection of track-structure calculation models, which encompasses diverse conditions, opens up new avenues for research in the field of radiation effects.

Development and application of PHITS track structure calculations to elucidate the response mechanisms of radiation detectors

Hirata, Yuho; Kai, Takeshi; Ogawa, Tatsuhiko; Matsuya, Yusuke; Sato, Tatsuhiko

Hoshasen Kagaku (Internet), (118), p.21 - 28, 2024/10

https://radiation-chemistry.org/kaishi/118pdf/RC118.pdf

Accurate dose evaluation by radiation detectors is crucial for the safe use of radiation. However, with certain types of radiation, the output from detectors can be nonlinear relative to the dose, thereby hindering correct dose assessments. To address these issues, it is vital to theoretically analyze the mechanisms affecting detector outputs. The radiation transport code PHITS includes a track structure analysis mode that precisely tracks radiation behavior. This review paper introduces the newly developed Electron Trajectory Structure Analysis Mode for Arbitrary Materials (ETSART), which facilitates the tracking of electron beams in various detector materials. Additionally, we present an example of phosphor quenching under ion beam irradiation, as analyzed using the PHITS track structure mode.

Formation behavior of gaseous iodine from sodium iodide under SFR severe accidental condition

Kikuchi, Shin; Kondo, Toshiki; Doi, Daisuke; Seino, Hiroshi; Ogawa, Kengo*; Nakagawa, Takeshi*

Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NUTHOS-14) (Internet), 12 Pages, 2024/08

Three-dimensional electrical resistivity structure beneath a strain concentration area in the back-arc side of the northeastern Japan Arc

Usui, Yoshiya*; Ueshima, Makoto*; Hase, Hideaki*; Ichihara, Hiroshi*; Aizawa, Koki*; Koyama, Takao*; Sakanaka, Shinya*; Ogawa, Tsutomu*; Yamaya, Yusuke*; Nishitani, Tadashi*; et al.

Journal of Geophysical Research; Solid Earth, 129(5), p.e2023JB028522_1 - e2023JB028522_22, 2024/05

https://doi.org/10.1029/2023JB028522

We elucidated the crustal heterogeneities beneath a strain concentration area on the back-arc side of the northeastern Japan Arc based on electrical resistivity. By deploying magnetotelluric surveys, we revealed the three-dimensional electrical resistivity structure in the crust, suggesting the coexistence of two types of strain-concentration mechanisms in the strain-concentration area. The shallow conductive layers and lower-crustal conductors appear to act as low-elastic-modulus and low-viscosity areas, respectively, and are responsible for the strain concentration. We found a spatial correlation between the edges of the lower-crustal conductors and the epicenters of large intraplate earthquakes. Weak shear zones in the conductive lower crust may cause stress loading on faults in the brittle upper crust, resulting in large earthquakes. We also identified vertical conductors ranging from the lower crust to Quaternary volcanoes, which may indicate fluid paths to these volcanoes.

Benchmark analysis by Beremin model and GTN model in CAF Subcommittee

Nagoshi, Yasuto*; Fukahori, Takuya*; Okada, Hiroshi*; Takahashi, Akiyuki*; Shimodaira, Masaki; Ueda, Takashi*; Ogawa, Takuya*; Yashirodai, Kenji*; Takahashi, Yukio*; Ohata, Mitsuru*

Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 9 Pages, 2024/03

no abstracts in English

Recent improvements of the Particle and Heavy Ion Transport code System; PHITS version 3.33

Sato, Tatsuhiko; Iwamoto, Yosuke; Hashimoto, Shintaro; Ogawa, Tatsuhiko; Furuta, Takuya; Abe, Shinichiro; Kai, Takeshi; Matsuya, Yusuke; Matsuda, Norihiro; Hirata, Yuho; et al.

Journal of Nuclear Science and Technology, 61(1), p.127 - 135, 2024/01

https://doi.org/10.1080/00223131.2023.2275736

The Particle and Heavy Ion Transport code System (PHITS) is a general-purpose Monte Carlo radiation transport code that can simulate the behavior of most particle species with energies up to 1 TeV (per nucleon for ions). Its new version, PHITS3.31, was recently developed and released to the public. In the new version, the compatibility with high-energy nuclear data libraries and the algorithm of the track-structure modes have been improved. In this paper, we summarize the upgraded features of PHITS3.31 with respect to the physics models, utility functions, and application software introduced since the release of PHITS3.02 in 2017.