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Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tsuchida, Hidetsugu*; Yokoya, Akinari*
Hoshasen Seibutsu Kenkyu, 61(2), p.112 - 126, 2026/06
This review introduces a chemical calculation code which can quantitatively evaluate the indirect effects of DNA damage. Radiation DNA damage is formed from direct and indirect effects. The direct effect is the interaction between DNA and a radiation, while the indirect effect is the chemical reaction between DNA and radiolytic chemical species. The damage reduces repair efficiency and induces biological effects. In this study, DNA damage induced by only indirect effects was quantitatively evaluated. Our results indicated that the multiple damage is formed when only tens of eV energy is deposited to water in the vicinity of DNA, although its formation probability is less than 1%. In other words, the possibility of late biological effects cannot be excluded by imparting energy to water in the extreme vicinity of DNA. Our results are one of the most important findings for understanding low-dose radiation risk.
Kyriakou, I.*; Papadopoulos, A.*; Polopetrakis, I.*; Kotroumbelou, C.*; Plante, I.*; Matsuya, Yusuke; Kai, Takeshi; Qiu, R.*; Li, J.*; Kundr
t, P.*; et al.
Physics in Medicine & Biology, 71(8), p.085009_1 - 085009_25, 2026/04
Times Cited Count：0Several Monte Carlo Track-Structure (MCTS) codes for liquid water have been developed worldwide over the last 40 years; however, use the different interaction cross sections. This study evaluates the uncertainties of physical features (electronic stopping power, pathlength, dose-point-kernel, and microdosimetry) of low-energy electron transport in liquid water by using 6 types of MCTS codes. The intercomparison results reveal significant differences among MCTS codes at low energies, especially below ~100 eV, potentially compromising the accuracy of DNA damage simulations where such electrons play a key role. The present work highlights the need for further development of the physics models used in MCTS codes to reduce the uncertainties associated with low-energy electron transport calculations in liquid water.
Tamura, Jun; Kondo, Yasuhiro; Yee-Rendon, B.; Meigo, Shinichiro; Maekawa, Fujio; Kako, Eiji*; Umemori, Kensei*; Sakai, Hiroshi*; Domae, Takeshi*
Proceedings of 22nd International Conference on RF Superconductivity (SRF2025) (Internet), p.691 - 694, 2026/04
Japan Atomic Energy Agency (JAEA) has been proposing an accelerator-driven nuclear transmutation system (ADS) as a future nuclear system to efficiently reduce high-level radioactive waste generated in nuclear power plants. As the first step toward the full-scale CW proton linac for the JAEA-ADS, we are currently prototyping a low-beta (around 0.2) single-spoke cavity. Since there is no experience in manufacturing superconducting spoke cavities in Japan, prototyping and performance evaluation of the cavity are essential to ensure the feasibility of the JAEA-ADS. The actual cavity fabrication started in 2020, and the cavity assembly by electron beam welding was finally completed in fiscal year 2024. In this assembly, the target resonance frequency of 324 MHz was achieved by trimming the ends of the cavity parts several times before the final welding. In the final welding, smooth weld beads were obtained by combining circular-correction and end-thinning for the cavity parts to be welded. The fabrication of the prototype spoke cavity is presented.
:Ce using PHITS track-structure simulationsHirata, 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
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)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.
value of hydrated electrons updated by a dynamic Monte Carlo simulationKai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tsuchida, Hidetsugu*; Yokoya, Akinari*
RSC Advances (Internet), 16(15), p.13886 - 13895, 2026/03
Times Cited Count：0 Percentile：0.00(Chemistry, Multidisciplinary)Water is one of the most interesting subjects of research in life sciences and the power industry, yet the ratio of ionization to electron excitation in water radiolysis remains unclear. This ratio determines the yield of radiolytic chemical species, but currently, it is parameterized. We challenged this long-standing fundamental scientific problem using computer simulations and successfully evaluated the primary electron energy dependence of the initial yield of hydrated electrons without relying on conventional model parameters. Contrary to conventional concepts, this study revealed that defining cross sections for water ionization and electron excitation is unnecessary. Instead, the dynamic motion calculation of secondary electrons generated by water radiolysis determines the final ratio of ionization to excitation. Our novel analytical approach is expected to gradually recognized as a new method for analyzing general liquid radiolysis.
Villagrasa, C.*; Baiocco, G.*; Chaoui, Z.-E.-A.*; Dingfelder, M.*; Incerti, S.*; Kundrt, P.*; Kyriakou, I.*; Matsuya, Yusuke; Kai, Takeshi; Parisi, A.*; et al.
PLOS ONE (Internet), 21(1), p.e0340500_1 - e0340500_22, 2026/01
Times Cited Count：3 Percentile：97.87(Multidisciplinary Sciences)Nanodosimetry, which is important for understanding the biological effects after ionizing radiation exposure, can be evaluated using Monte Carlo Track Structure (MCTS) codes that can reproduce atomic interactions at the molecular scale. Various MCTS codes, developed independently over decades, have used different physical models and cross section data sets for electron interactions in liquid water, that is the main component of biological tissues. In this study, we evaluated the uncertainties in nanodosimetric calculations due to the variation of interaction cross sections used in various MCTS codes. The calculation results of seven MCTS codes (i.e., Geant4-DNA, PARTRAC, PHITS, MCwater, and PTra) revealed that there were large differences in physical quantities at molecular scale, such as the average number of ionizations and the probability of two or more ionizations. The largest differences were observed for low-energy electrons, where the contribution of the interaction cross section was found to be the main cause of uncertainty. These results highlight that difference in the cross section have a non-negligible impact on biological effects, such as complex DNA damage induction.
CMatsuya, Yusuke; Yoshii, Yuji*; Kusumoto, Tamon*; Wang, Y.*; Ogawa, Tatsuhiko; Sato, Tatsuhiko; Kai, Takeshi
Scientific Reports (Internet), 24 Pages, 2026/00
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.
Ogawa, Tatsuhiko; Hirata, Yuho; Matsuya, Yusuke; Kai, Takeshi
Computer Physics Communications, 316, p.109758_1 - 109758_15, 2025/11
Times Cited Count：1 Percentile：51.60(Computer Science, Interdisciplinary Applications)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.
Sekikawa, Takuya; Takada, Kazuki*; Kai, Takeshi; Ono, Yoshiaki*
Journal of Applied Physics, 137(20), p.203901_1 - 203901_10, 2025/05
Times Cited Count：0 Percentile：0.00(Physics, Applied)no abstracts in English
Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tsuchida, Hidetsugu*; Yokoya, Akinari*
Journal of Chemical Physics, 162(15), p.154102_1 - 154102_11, 2025/04
Times Cited Count：1 Percentile：41.78(Chemistry, Physical)Scientific knowledge of low-energy electrons resulting from water radiolysis is required to estimate radiation DNA damage. However, since the analysis of water radiolysis is very complex, this study focuses on the experimental values of low-energy electrons related to simple water photolysis and those generated by photoirradiation of electrodes in water. Both experimental analyses involve the presence or absence of a Coulomb field in the parent ion. In this study, we analyzed these experimental values using a calculation code that combines Monte Carlo and molecular dynamics methods. As a result, it was shown that the code reproduced the experimental values even under different experimental conditions, and the code was validated. The calculation code will be a powerful tool for analyzing the interaction between low-energy electrons and DNA, and is expected to be applied to elucidate the formation mechanism of radiation DNA damage.
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
Times Cited Count：3 Percentile：79.67(Chemistry, Physical)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.
Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tsuchida, Hidetsugu*; Ito, Yuma*; Yokoya, Akinari*
Communications Chemistry (Internet), 8, p.60_1 - 60_9, 2025/03
Times Cited Count：4 Percentile：65.29(Chemistry, Multidisciplinary)Radiation DNA damage is formed from direct and indirect effects. The direct effect is the interaction between DNA and a radiation, while the indirect effect is the chemical reaction between DNA and radiolytic chemical species. We believed that when the direct effect is induced, multiple lesions are formed within 10 base pairs (about 3.4 nm) of DNA. The damage reduces repair efficiency and induces biological effects. In this study, DNA damage induced by only indirect effects was quantitatively evaluated. Our results indicated that the multiple damage is formed when only 10s of eV energy is deposited to water in the vicinity of DNA, although its formation probability is less than 1%. In other words, the possibility of late biological effects cannot be excluded simply by imparting energy to water in the extreme vicinity of DNA without direct interaction between radiation and DNA. Our results are one of the most important findings for understanding low-dose radiation risk.
C and 500CTakagi, Honoka*; Yabutsuka, Takeshi*; Hayashida, Hirotoshi*; Song, F.; Kai, Tetsuya; Shinohara, Takenao; Kurita, Keisuke; Iikura, Hiroshi; Yamamoto, Norio*; Nakajima, Minoru*; et al.
Solid State Ionics, 417, p.116716_1 - 116716_7, 2024/12
Times Cited Count：3 Percentile：28.45(Chemistry, Physical)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
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.
Matsuya, Yusuke; Kai, Takeshi; Sato, Tatsuhiko
Shototsu, 21(3), p.R008_1 - R008_8, 2024/11
Particle and Heavy Ion Transport code System PHITS is a Monte Carlo code that enables the simulation of the behavior of radiation using a computer. Since 2018, a track-structure mode has been developed that allows the simulation of each atomic interaction in liquid water, which is a main component of living organisms. This development has made it possible to perform high-spatial resolution radiation track-structure analysis on the DNA scale. Meanwhile, based on the spatial information of atomic interactions calculated in the track-structure mode, we have also succeeded in developing an analysis code that enables the estimate of the various types of DNA damage yields efficiently and with high accuracy. In this review, we introduce an overview of the track-structure mode and DNA damage estimation model implemented in the latest version of PHITS, and show examples of applications of PHITS in the field of life sciences.
Hirata, Yuho; Kai, Takeshi; Ogawa, Tatsuhiko; Matsuya, Yusuke; Sato, Tatsuhiko
Hoshasen Kagaku (Internet), (118), p.21 - 28, 2024/10
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.
Tamura, Jun; Kondo, Yasuhiro; Yee-Rendon, B.; Meigo, Shinichiro; Maekawa, Fujio; Kako, Eiji*; Umemori, Kensei*; Sakai, Hiroshi*; Domae, Takeshi*
Proceedings of 32nd Linear Accelerator Conference (LINAC 2024) (Internet), p.496 - 498, 2024/10
Kai, Takeshi; Toigawa, Tomohiro; Matsuya, Yusuke*; Hirata, Yuho; Tezuka, Tomoya*; Tsuchida, Hidetsugu*; Yokoya, Akinari*
Scientific Reports (Internet), 14, p.24722_1 - 24722_15, 2024/10
Times Cited Count：5 Percentile：38.08(Multidisciplinary Sciences)Scientific insight of water radiolysis is essential to estimate the direct and indirect effects of radiation DNA damage. Secondary electrons produced by water radiolysis are responsible for both effects. Here, we use a first-principles code to calculate the femtosecond dynamics of secondary electrons produced as a result of 20-30 eV energy deposition to water and analyze the formation mechanism of radiolytic chemical species produced in a nano-size ultra-small space region. From the results, it was clarified that the chemical species produced by water radiolysis begin to densify in the ultra-small region of a few nanometers when the deposition energy exceeds 25 eV. Our results provide important scientific insights into the formation of clustered DNA damage, which is believed to cause biological effects such as cell death.
Tsuchida, Hidetsugu*; Tezuka, Tomoya*; Kai, Takeshi; Matsuya, Yusuke*; Majima, Takuya*; Saito, Manabu*
Journal of Chemical Physics, 161(10), p.104503_1 - 104503_8, 2024/09
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)Although fast ion beams can damage DNA by chemical products such as secondary electrons produced by their interaction with water in living cells, the process of formation of these chemical products in the Bragg peak region used in particle therapy is not fully understood. To investigate this process, we performed experiments to evaluate the yields of radiolytic products produced when a liquid water jet in vacuum is irradiated with a MeV-energy carbon beam. In addition, ionization processes in water due to incident ions and secondary electrons were simulated using a radiation transport Monte Carlo code. The results indicated that the primary source of ionization in water is secondary electrons. Finally, we show that these elementary processes contribute to the development of radiation biophysics and biochemistry to study the formation mechanism of DNA damage.
Uchida, Kazuto*; Masuda, Tsukuru*; Hara, Shintaro*; Matsuo, Yoichi*; Liu, Y.*; Aoki, Hiroyuki; Asano, Yoshihiko*; Miyata, Kazuki*; Fukuma, Takeshi*; Ono, Toshiya*; et al.
ACS Applied Materials & Interfaces, 16(30), p.39104 - 39116, 2024/07
Times Cited Count：11 Percentile：70.39(Nanoscience & Nanotechnology)