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Ogawa, Tatsuhiko; Iwamoto, Yosuke
Nuclear Instruments and Methods in Physics Research B, 549, p.165255_1 - 165255_4, 2024/04
Times Cited Count：0 Percentile：0.11Atomic defect is one of the critical factors that determines the irradiation effects in materials. The atoms are recoiled by the impulse of incoming radiation, which changes the mechanical, electrical and chemical properties of the target materials. Methods to calculate atomic displacement based on nuclear reaction cross sections and Rutherford scattering cross sections were proposed but they were dedicated to calculation of the defect density in macroscopic scale whereas some phenomena are attributed to the topological arrangements of defects in microscopic scale. Application of a track-structure calculation model, ITSART implemented to a general-purpose radiation transport code PHITS for calculation of the topological arrangement of radiation-induced defects is proposed in this study. To verify the defect production calculated by ITSART, DPA (Displacement Per Atom) cross section in Cu was calculated and compared with literature data. The agreement indicates the accuracy of ITSART for calculating atomic displacement. By using the same methodology to a smaller volume, the defects in SiO
exposed to 600 MeV proton beam was calculated. PHITS users can make use of the outputs by forwarding them to other tools, such as molecular dynamics codes, to analyse the further evolution of the defects.
C ions based on first-principles calculationsSekikawa, Takuya; Matsuya, Yusuke; Hwang, B.*; Ishizaka, Masato*; Kawai, Hiroyuki*; Ono, Yoshiaki*; Sato, Tatsuhiko; Kai, Takeshi
Nuclear Instruments and Methods in Physics Research B, 548, p.165231_1 - 165231_6, 2024/03
Times Cited Count：0 Percentile：0.11(Instruments & Instrumentation)One of the main causes of radiation effects on the human body is thought to be damage to DNA, which carries genetic information. However, it is not fully understood what kind of molecular structural changes DNA undergoes upon radiation damage. Since it has been reported that various types of DNA damage are formed when DNA is irradiated, our group has investigated the relationship between DNA damage and various patterns of radiation-induced ionization induced by radiation. Although we have so far analyzed DNA damage in a simple system using a rigid body model of DNA, more detailed calculations are required to analyze the molecular structural changes in DNA, which are considered to be important in considering the effects on the human body. In this study, we attempted to clarify the molecular conformational changes of DNA using OpenMX, a first-principles calculation software that can discuss electronic states based on molecular structures. Specifically, we calculated the most stable structure, band dispersion, and wave function of DNA under the assumption that one and two electrons are ionized by various radiation. In the presentation, we will discuss the relationship between the energy dependence of each incident radiation type and the molecular conformational change of DNA. In addition, the radiation-induced changes in the basic physical properties of DNA (corresponding to the initial stage of DNA damage) will be discussed from the viewpoints of both radiation physics and solid state physics.
Shaimerdenov, A.*; Gizatulin, Sh.*; Sairanbayev, D.*; Bugybay, Zh.*; Silnyagin, P.*; Akhanov, A.*; Fuyushima, Takumi; Hirota, Noriaki; Tsuchiya, Kunihiko
Nuclear Instruments and Methods in Physics Research B, 548, p.165235_1 - 165235_6, 2024/03
Times Cited Count：0 Percentile：0.11(Instruments & Instrumentation)Compared to conditions in other types of installations, cable insulation in nuclear reactors is exposed to mixed conditions (high temperatures, radiation, pressure, humidity, aggressive environments) and at the same time they must maintain their performance characteristics for a long time (about 40-50 years). As a result of irradiation to such conditions, the electrical properties of the cable insulation are degraded, which leads to an increase in current loss. This is because the charge is induced by radiation into the insulator. At the WWR-K reactor, studies were started on the radiation resistance of signal cables with two types of mineral insulation (MgO and AlO
). As part of these studies, new experimental data will be obtained on the behavior of signal cables with mineral insulation of two types in mixed operating conditions (radiation field and high temperature). It is planned to accumulate fluence of fast neutrons 
10
cm
in cables. The irradiation temperature will be (500 
50)
C). The study of the degradation of the electrical properties of the insulation of signal cables will be carried out in real time (in-situ). For this, a special design of the experimental device and a technique for in-reactor measurement of electrical characteristics were developed. This paper presents a sketch of the capsule design, the results of complex calculations for the development of the capsule design, the expected neutron fluences, the dpa in steel, the technique for in-reactor measurement of electrical characteristics, and a work plan for the future indicating the expected results. The cable irradiation time until the target neutron fluence is reached will be about 100 effective days. This research is funded by the International Scientific-Technical Center.
Hirata, Yuho; Kai, Takeshi; Ogawa, Tatsuhiko; Matsuya, Yusuke; Sato, Tatsuhiko
Nuclear Instruments and Methods in Physics Research B, 547, p.165183_1 - 165183_7, 2024/02
Times Cited Count：0 Percentile：0.02(Instruments & Instrumentation)The luminescence efficiency of the phosphors for swift ions is known to decrease because of the quenching effects. To obtain the precise dose distributions using phosphor detectors, understanding the mechanisms of quenching effects is mandatory. Here, we developed a new model for estimating the luminescence intensity of phosphors based on the track-structure modes for arbitrary materials implemented in PHITS. The developed model enabled the simulation of the quenching effects of the BaFBr detector and was verified by comparing the results to the corresponding measured data. The present model is expected to contribute to developing phosphor detectors worldwide.
Ishikawa, Norito; Fukuda, Shoma; Nakajima, Toru; Ogawa, Hiroaki; Fujimura, Yuki; Taguchi, Tomitsugu*
no journal, ,
In the present study, natural zirconia (Baddeleyite) and pure zirconia in nanoparticle form were irradiated with 340 MeV and 200 MeV Au ions, respectively, and the irradiation-induced nanostructures, i.e. ion tracks and nanohillocks, were observed by TEM. Based on the TEM observation results, nanohillocks and ion tracks are created both in natural zirconia and in nanoparticle zirconia samples. We analysed the size and shape of ion tracks as well as the size of nanohillocks in two zirconia-based oxides. It is found that the size of nanohillocks directly reflects the size of the melt. In both samples, the ion tracks are found to have two concentric damage zones; low-density core region and outer damaged region, suggesting that the recrystallization process plays an important role in ion track formation. In natural zirconia, the cross-section of the outer region is found to have rectangular shape, while rectangular shape is not observed for nanoparticle pure zirconia.
Okubo, Nariaki; Tomobe, Masakatsu*; Ishikawa, Norito
no journal, ,
no abstracts in English
irradiated with swift heavy ionsIshikawa, Norito; Taguchi, Tomitsugu*; Toimil-Molares, M. E.*; Trautmann, C.*; Ogawa, Hiroaki
no journal, ,
In this study we have characterized by transmission electron microscopy (TEM) very thin crystalline-SiO (c-SiO) irradiated with swift heavy ions, imaging ion tracks exhibiting concentric regions of different contrast that suggest an inhomogeneous track structure especially for very thin samples. In the thinner parts of the c-SiO samples, the ion tracks are found to be composed of a low-density core and a surrounding damaged region. Amorphous-SiO irradiated with swift heavy ions was also characterized by TEM. In the very thin part of the samples, low-density cores similar to those observed in c-SiO are imaged. The results demonstrate that TEM observation of thin samples is a useful approach to investigate the formation mechanism of concentric structure of ion tracks.
Matsumura, Daiju; Okazaki, Hiroyuki*; Idesaki, Akira*; Ishii, Kenji*; Yamaki, Tetsuya*
no journal, ,
