Benchmark shielding calculations for fusion and accelerator-driven sub-critical systems

Iwamoto, Yosuke; Tsuda, Shuichi; Ogawa, Tatsuhiko

Frontiers in Energy Research (Internet), 11, p.1085264_1 - 1085264_11, 2023/01

https://doi.org/10.3389/fenrg.2023.1085264

This review describes experimental data useful for validation of radiation shielding design in advanced reactor systems such as nuclear fusion and accelerator-driven subcritical systems (ADS) and calculations using the PHITS code and JENDL-4.0/HE. The relevant experiments have been conducted mainly in Japan and include (1) neutron spectra in iron shields using 14 MeV neutron sources, (2) leakage neutron spectra from spherical piles of various materials using 14 MeV neutron sources, (3) neutron spectra after penetration through shields using several tens of MeV neutron sources, (4) neutron spectra produced from the target by high-energy heavy-ion bombardment, and (5) induced radioactivity in concrete using heavy-ion nuclear reaction product particles as a source. Throughout, the experimental and calculated values were agreed well. These experimental data are also useful for the validation of all radiation transport calculation codes used in the design of advanced reactor systems.

Implementation of the electron track-structure mode for silicon into PHITS for investigating the radiation effects in semiconductor devices

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

Japanese Journal of Applied Physics, 61(10), p.106004_1 - 106004_6, 2022/10

https://doi.org/10.35848/1347-4065/ac8ae9

Some radiation effects such as pulse-height defects and soft errors can cause problems in silicon (Si) devices. Local energy deposition in microscopic scales is essential information to elucidate the mechanism of these radiation effects. We, therefore, developed an electron track-structure model, which can simulate local energy deposition down to nano-scales, dedicated to Si and implemented it into PHITS. Then, we verified the accuracy of our developed model by comparing the ranges and depth-dose distributions of electrons obtained from this study with the corresponding experimental values and other simulated results. As an application of the model, we calculated the mean energies required to create an electron-hole pair, the so-called epsilon value. We found that the threshold energy for generating secondary electrons reproducing the epsilon value is 2.75 eV, consistent with the corresponding data deduced from past theoretical and computational studies. Since the magnitudes of the radiation effects on Si devices largely depend on the epsilon value, the developed code is expected to contribute to precisely understanding the mechanisms of pulse-height defects and semiconductor soft errors.

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, 59(7), p.915 - 924, 2022/07

https://doi.org/10.1080/00223131.2021.2017372

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 He, C and 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.

Mesospheric ionization during substorm growth phase

Murase, Kiyoka*; Kataoka, Ryuho*; Nishiyama, Takanori*; Nishimura, Koji*; Hashimoto, Taishi*; Tanaka, Yoshimasa*; Kadokura, Akira*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Ogawa, Yasunobu*; et al.

Journal of Space Weather and Space Climate (Internet), 12, p.18_1 - 18_16, 2022/06

https://doi.org/10.1051/swsc/2022012

We identified two energetic electron precipitation (EEP) events during the growth phase of moderate substorms and estimated the mesospheric ionization rate for an EEP event for which the most comprehensive dataset from ground-based and space-born instruments was available. The mesospheric ionization signature reached below 70 km altitude and continued for ~15 min until the substorm onset, as observed by the PANSY radar and imaging riometer at Syowa Station in the Antarctic region. We also used energetic electron flux observed by the Arase and POES 15 satellites as the input for the air-shower simulation code PHITS to quantitatively estimate the mesospheric ionization rate. Combining the cutting-edge observations and simulations, we shed new light on the space weather impact of the EEP events during geomagnetically quiet times, which is important to understand the possible link between the space environment and climate.

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

https://doi.org/10.1038/s41598-021-01822-1

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.

Optimization of a 9 MeV electron accelerator bremsstrahlung flux for photofission-based assay techniques using PHITS and MCNP6 Monte Carlo codes

Meleshenkovskii, I.*; Ogawa, Tatsuhiko; Sari, A.*; Carrel, F.*; Boudergui, K.*

Nuclear Instruments and Methods in Physics Research B, 483, p.5 - 14, 2020/11

https://doi.org/10.1016/j.nimb.2020.10.002

For the purpose of fissile material detection, the technique to observe neutrons ejected from photo-fission induced by bremsstrahlung X-rays is being developed. This technique is advantageous in the sense that the machine can be compact compared to conventional neutron generators. However, photo-fission reaction cross sections are generally smaller than those of neutron-induced fission cross sections therefore optimization of the beam line is of high importance. In this study, we investigated the factors necessary to be optimized by using Monte-Carlo transport codes MCNP and PHITS. It was found that high-Z materials are advantageous to effectively produce bremsstrahlung X-rays but photons produce neutrons by secondary (,n) reactions resulting in mixing of prompt and delayed fission reactions. Moreover, secondary neutrons are produced not only inside the target but also in the materials surrounding the target. Therefore it is necessary to select elements whose neutron separation energy is high to suppress parasitic secondary neutrons.

Estimation of observables

Ogawa, Tatsuhiko; Iwamoto, Yosuke

Hoshasen Shahei Handobukku; Oyohen, p.68 - 74, 2020/03

Atomic Energy Society of Japan is going to compile a book entitled "The handbook of radiation shielding -Advanced Edition-" as the guideline for researchers and engineers working on radiation shielding in Japan. The authors are responsible for a chapter dedicated to "Evaluation of observables". Conventionally, in radiation shielding calculation, the quantities averaged over a lot of radiation particles are assessed; however, fluctuation around the average matters for detector response calculation, and radiation-induced damage. Therefore, algorithms to recover the details on fluctuations, such as the event generator mode of PHITS, are needed. This publication is intended to explain the significance of fluctuation evaluation in radiation transport, the principle to calculate the fluctuation, and the effect of the fluctuation on observables.

Depth profiles of energy deposition near incident surface irradiated with swift heavy ions

Ogawa, Tatsuhiko; Ishikawa, Norito; Kai, Takeshi

Nuclear Instruments and Methods in Physics Research B, 461, p.272 - 275, 2019/12

https://doi.org/10.1016/j.nimb.2019.10.010

Heavy ion irradiation, which deposits energy locally in materials, is widely used to study new material modification and radiation-induced damage. So far, radial distribution of energy deposition by heavy ions were well studied. By contrast, depth profile of energy deposition was usually assumed to be uniform but the energy deposition near the incident surface is likely suppressed because the delta-rays are pushed by the incident heavy ions. In this study, spatial distribution of energy deposition in the materials exposed to heavy ions is calculated by using a track structure simulation code RITRACKS. The result showed that energy deposition is suppressed in the first 2 nm of water and that beyond 2 nm is uniform. This result can be applied to the materials other than water by scaling with electron density. It is indicated that reactor fuel pins damaged by fission products and the materials modified by heavy ions receive less energy deposition and less radiation effect in the first 2 nm.

Comparison of heavy-ion transport simulations; Collision integral with pions and resonances in a box

Ono, Akira*; Xu, J.*; Colonna, M.*; Danielewicz, P.*; Ko, C. M.*; Tsang, M. B.*; Wang, Y,-J.*; Wolter, H.*; Zhang, Y.-X.*; Chen, L.-W.*; et al.

Physical Review C, 100(4), p.044617_1 - 044617_35, 2019/10

AA2019-0025.pdf:2.76MB

https://doi.org/10.1103/PhysRevC.100.044617

International comparison of heavy-ion induced reaction models were discussed in the international conference "Transport2017" held in April 2017. Owing to their importance for safety assessment of heavy-ion accelerators and dosimetry of astronauts, various models to simulate heavy-ion induced reaction models are developed. This study is intended to clarify the difference among them to pinpoint their problems. In the comparison study, 320 protons and neutrons were packed in a 20-fm-large cube to calculate the number and energies of collisions during the time evolution. The author contributed to this study by running calculation using JQMD (JAERI Quantum Molecular Dynamics). This study showed that time step in the calculation is one of the biggest causes of the discrepancies. For example, the calculation by JQMD comprises 1-fm/c time steps, each of which is composed of transport, scattering and decay phases. Therefore a sequence of scattering, and decay followed by another scattering in 1 fm/c cannot be considered. Moreover, in JQMD particles are labeled by sequential numbers and scattering reactions are simulated by the order. Therefore scattering between low ID numbers, that between high ID numbers and that between the first (low ID) pair is overlooked in JQMD. Above indications obtained in this study must be kept in our mind for future JQMD upgrades.

Measurement of neutron-production double-differential cross sections in most-forward direction by proton incidences

Satoh, Daiki; Iwamoto, Yosuke; Ogawa, Tatsuhiko

2017-Nendo Ryoshi Kagaku Gijutsu Kenkyu Kaihatsu Kiko Shisetu Kyoyo Jisshi Hokokusho (Internet), 1 Pages, 2019/08

Many neutrons are produced in forward directions by intermediate-energy proton-induced reactions. While it is known that collective motion in a target nucleus plays important role in this neutron production, validity of theoretical model and nuclear-data library has not been examined well due to a lack of experimental data. Hence, we obtained systematic data of neutron-production double-differential cross section in the most-forward direction. The experiment was performed at TIARA of Takasaki Advanced Radiation Research Institute, QST. 34-MeV proton beams were bombarded upon thin carbon, aluminum, iron, and lead target, and the neutrons produced in the most-forward direction were led to experimental room passing through a collimator. Scintillation detectors were used to the neutron detection. In comparison with the calculation results of PHITS, it was found that the theoretical model INCL always overestimate the cross sections, and the evaluated nuclear-data library JENDL-4.0/HE reproduce the measure spectra better than the INCL does.