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Journal Articles

Features of accelerator-based neutron source for boron neutron capture therapy calculated by Particle and Heavy Ion Transport code System (PHITS)

Matsuya, Yusuke; Kusumoto, Tamon*; Yachi, Yoshie*; Hirata, Yuho; Miwa, Misako*; Ishikawa, Masayori*; Date, Hiroyuki*; Iwamoto, Yosuke; Matsuyama, Shigeo*; Fukunaga, Hisanori*

AIP Advances (Internet), 12(2), p.025013_1 - 025013_9, 2022/02

Boron Neutron Capture Therapy (BNCT) is a radiation therapy, which can selectively eradicate solid tumors by $$alpha$$-particles and Li ions generated through the nuclear reaction between thermal neutron and $$^{10}$$B in tumor cells. With the development of accelerator-based neutron sources that can be installed in medical institutions, accelerator-based boron neutron capture therapy is expected to become available at several medical institutes around the world in the near future. Lithium is one of the targets that can produce thermal neutrons from the $$^{7}$$Li(p,n)$$^{7}$$Be near-threshold reaction. Particle and Heavy Ion Transport code System (PHITS) is a general-purpose Monte Carlo code, which can simulate a variety of diverse particle types and nuclear reactions. The latest PHITS code enables simulating the generation of neutrons from the $$^{7}$$Li(p,n)$$^{7}$$Be reactions by using Japanese Evaluated Nuclear Data Library (JENDL-4.0/HE). In this study, we evaluated the neutron fluence using the PHITS code by comparing it to reference data. The subsequent neutron transport simulations were also performed to evaluate the boron trifluoride (BF$$_{3}$$) detector responses and the recoiled proton fluence detected by a CR-39 plastic detector. As a result, these comparative studies confirmed that the PHITS code can accurately simulate neutrons generated from an accelerator using a Li target. The PHITS code has a significant potential for contributing to more precise evaluating accelerator-based neutron fields and understandings of therapeutic effects of BNCT.

Journal Articles

Track-structure modes in Particle and Heavy Ion Transport code System (PHITS); Application to radiobiological research

Matsuya, Yusuke; Kai, Takeshi; Sato, Tatsuhiko; Ogawa, Tatsuhiko; Hirata, Yuho; Yoshii, Yuji*; Parisi, A.*; Liamsuwan, T.*

International Journal of Radiation Biology, 98(2), p.148 - 157, 2022/02

When investigating radiation-induced biological effects, it is essential to perform detailed track-structure simulations explicitly by considering each atomic interaction in liquid water (which is equivalent to human tissues) at sub-cellular and DNA scales. The Particle and Heavy Ion Transport code System (PHITS) is a Monte Carlo code which can be used for track structure calculations by employing an original electron track-structure mode (etsmode) and the world-famous KURBUC algorithms (PHITS-KURBUC mode) for protons and carbon ions. In this study, the physical features (i.e., range, radial dose and microdosimetry) of these modes have been verified by comparing to the available experimental data and Monte Carlo simulation results reported in literature. In addition, applying the etsmode to radiobiological study, we estimated the yields of single-strand breaks (SSBs), double-strand breaks (DSBs) and complex DSBs, and evaluated the dependencies of DNA damage yields on incident electron energy. As a result, the simulations suggested that DNA damage types are intrinsically related with the spatial patterns of ionization and electronic excitations and that approximately 500 eV electron can cause much complex DSBs. In this paper, we show the development status of the PHITS track-structure modes and its application to radiobiological research, which would be expected to identify the underlying mechanisms of radiation effects based on physics.

Journal Articles

Theoretical and experimental estimation of the relative optically stimulated luminescence efficiency of an optical-fiber-based BaFBr:Eu detector for swift ions

Hirata, Yuho; Sato, Tatsuhiko; Watanabe, Kenichi*; Ogawa, Tatsuhiko; Parisi, A.*; Uritani, Akira*

Journal of Nuclear Science and Technology, 10 Pages, 2022/01

The reliability of dose assessment with radiation detectors is an important feature in various fields, such as radiotherapy, radiation protection, and high-energy physics. However, many detectors irradiated by high linear energy transfer (LET) radiations exhibit decreased efficiency called the quenching effect. This quenching effect depends not only on the particle LET but strongly on the ion species and its microscopic pattern of energy deposition. Recently, a computational method for estimating the relative efficiency of luminescence detectors was proposed following analysis of microdosimetric specific energy distributions simulated using the particle and heavy ion transport code system (PHITS). This study applied the model to estimate the relative optically stimulated luminescence (OSL) efficiency of BaFBr:Eu detectors. Additionally, we measured the luminescence intensity of BaFBr:Eu detectors exposed to $$^{4}$$He, $$^{12}$$C and $$^{20}$$Ne ions to verify the calculated data. The model reproduced the experimental data in the cases of adopting a microdosimetric target diameter of approximately 30-50 nm. The calculated relative efficiency exhibit ion-species dependence in addition to LET. This result shows that the microdosimetric calculation from specific energy is a successful method for accurately understanding the results of OSL measurements with BaFBr:Eu detectors irradiated by various particles.

Journal Articles

Development and validation of proton track-structure model applicable to arbitrary materials

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

Scientific Reports (Internet), 11(1), p.24401_1 - 24401_10, 2021/12

Track-structure calculation, a method to simulate every secondary electron production reaction explicitly, has been extensively used as an important techniques in various fields such as radiation biology, material irradiation effect, and radiation detection. However, it requires the dielectric function of the target materials, which is not well known except for liquid water. Therefore we developed a model to perform track-structure calculation based on a systematic formula of secondary electron production cross section and that of stopping power. The model can therefore perform track-structure calculation regardless of the availability of dielectric function measurement data. Stopping range, and energy deposition radial distribution calculated by this model agreed well with the earlier experimental data and calculation by precedent codes. The lineal energy in tissue-equivalent gas calculated by this model agreed with measurement data taken from literature, showing distinct difference from that in liquid water. This model was implemented to PHITS Ver3.25, the general-purpose radiation transport simulation code of JAEA, being distributed to users as the first track-structure calculation model applicable to arbitrary materials available in general-purpose transport code.

Journal Articles

Track-structure mode for electrons, protons and carbon ions in the PHITS code

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

Hoshasen Kagaku (Internet), (112), p.15 - 20, 2021/11

Particle and Heavy Ion Transport code System (PHITS) is a general-purpose Monte Carlo code enabling radiation kinetics, which is often used in diverse research fields, such as atomic energy, engineering, medicine and science. After released in 2010, the PHITS code has been developed to expand its functions and to improve its convenience. In the few years, track-structure mode has been introduced in PHITS that can simulate each atomic interaction by electrons, positions, protons and carbon ions in liquid water. Thanks to the development of track-structure mode, the latest PHITS code enables microscopic dose calculations by decomposing it to the scale of DNA. Aiming at realizing the track-structure mode with high precision, the further developments of electron and ion track-structure mode for arbitrary materials are recently ongoing. This review shows the development history and future prospect of PHITS track-structure mode, which can expect to be further applied to the research fields of atomic physics, radiation chemistry, and quantum life science.

Oral presentation

Crystallographic characterization on different types of structure (Tsukurikomi) of Japanese swords using pulsed neutron imaging and diffraction methods

Oikawa, Kenichi; Kiyanagi, Yoshiaki*; Shinohara, Takenao; Kai, Tetsuya; Watanabe, Kenichi*; Uritani, Akira*; Hori, Genki*; Hirata, Yuho*

no journal, , 

Oral presentation

Application to the calculation of detector response function

Hirata, Yuho

no journal, , 

Detectors such as scintillators show a decrease in sensitivity to high-energy charged particles, however, conventional radiation behavior calculation codes cannot accurately reproduce these decreases. We focused on the concentration of energy applied to minute regions related to sensitivity reduction and developed a model that predicts the response function of the detector using PHITS. In this presentation, we introduce a method to predict the response of a detector by calculating the energy deposition density using the microdosimetry function implemented in PHITS. We measured the response of the radiation-induced phosphor BaFBr:Eu used as a detector to high-energy charged particles and calculated the energy deposition density by PHITS. We have developed a method to calculate the luminescence efficiency by combining the calculated energy deposition density and the response to gamma-ray irradiation and succeeded in reproducing the measured value of the luminescence efficiency of BaFBr:Eu for high-energy charged particles. We will develop a method for theoretically predicting the response of phosphors using the track structure analysis mode of PHITS.

Oral presentation

Extension of PHITS track structure calculation mode

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

no journal, , 

Track structure calculation is a technique to predict energy deposition in sub-micro meter to nano meter scale by tracking electrons down to a few eVs. Conventional track structure calculation codes predict electron transport using the cross section of target materials calculated based on dielectric functions, in other words, response to electro-magnetic waves. Owing to this procedure, they are applicable merely to materials whose dielectric function is measured in a wide frequency range. Therefore in this study, a track structure mode is developed by using stopping power formula and secondary electron energy distribution systematics. In this study, stopping power and secondary electron energy were calculated by ATIMA and Rudd's formula, respectively. Stopping range, radial dose distribution, and stochastic energy deposition distribution calculated by our code agreed well with literature data indicating validity of our model. This model is going to be implemented to the next release of PHITS to be used by users.

Oral presentation

Development of electron track structure simulation code for evaluating the radiation effect on Si material

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

no journal, , 

The pulse-height defect in the heavy-ions measurement by the Si semiconductor detector is a problem of accurate measurement. Besides, soft errors that cause malfunctions of electronic devices are caused by the radiation interaction of Si semiconductor memory. To study the mechanism of these phenomena, we developed an electron track structure simulation code for Si material. In this work, we prepared the cross-sections for the track structure simulation for Si and calculated the energy transfer process of the radiation down to very low energy. The developed simulation code was implemented in PHITS and succeeded in calculating the electron track in Si. The epsilon value that is the energy required to generate an electron carrier, was calculated as 3.62 eV, which corresponds to the experimental value. For future work, we will analyze the pulse-height defect in the Si semiconductor detector using the developed track structure simulation code.

Oral presentation

Development of track structure calculation mode for detector response simulation

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

no journal, , 

Track-structure calculation, a method to simulate every secondary electron production reaction explicitly, has been extensively used as an important techniques in various fields such as radiation biology, material irradiation effect, and radiation detection. However, it requires the dielectric function of the target materials, which is not well known except for liquid water. Therefore we developed a model to perform track-structure calculation based on a systematic formula of secondary electron production cross section and that of stopping power. The model can therefore perform track-structure calculation regardless of the availability of dielectric function measurement data. Stopping range, and energy deposition radial distribution calculated by this model agreed well with the earlier experimental data and calculation by precedent codes. The lineal energy in tissue-equivalent gas calculated by this model agreed with measurement data taken from literature, showing distinct difference from that in liquid water. This model was implemented to PHITS Ver3.25, the general-purpose radiation transport simulation code of JAEA, being distributed to users as the first track-structure calculation model applicable to arbitrary materials available in general-purpose transport code.

Oral presentation

Development of response prediction model for luminescence radiation detectors focusing on the microscopic energy deposition

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

no journal, , 

Luminescence detectors (LD) are widely used for evaluating the radiation field, however, these detectors show a decrease in sensitivity to high-energy charged particles. We developed predicting and analyzing functions of the LD response using PHITS. First, we predicted the detector response using the microdosimetric function installed in PHITS. We reproduced the response of the LD to some of the high-energy charged particles. To analyze the physical process of the change of detector response, the investigation of the radiation behavior in the detector material is necessary. We developed the track structure code applied to Si which is widely used as detector materials. The developed code reproduced the electron behavior in Si, such as the electron ranges, and the number of emitted electrons. We developed a model which can predict the response mechanism of the luminescence radiation detector.

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