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.

Measurement of neutron-production double-differential cross sections of C, Al, Fe, and Pb by 20, 34, 48, 63, and 78 MeV protons in the most-forward direction

Satoh, Daiki; Iwamoto, Yosuke; Ogawa, Tatsuhiko

Nuclear Instruments and Methods in Physics Research A, 920, p.22 - 36, 2019/03

https://doi.org/10.1016/j.nima.2018.12.049

The Particle and Heavy Ion Transport code System (PHITS) is a general purpose particle transport simulation code developed by the Japan Atomic Energy Agency (JAEA). The PHITS is utilized in various areas including a shielding design of accelerator facilities. Unfortunately, it is known that theoretical models and evaluated nuclear data used in the PHITS cannot reproduce the neutron production in most-forward direction for proton incidences. Hence, the present study aimed to obtain the experimental data of neutron-production double-differential cross sections of C, Al, Fe, and Pb by 20, 34, 48, 63, and 78 MeV protons in most-forward direction for improvement of theoretical models and nuclear data. The experiment has been performed at the ion irradiation facility (TIARA) of the National Institutes for Quantum and Radiological Science and Technology. The proton beams provided by the cyclotron were incident to the target sample. The neutrons produced by nuclear reactions were pass through the collimator in the most-forward direction, and measured with an organic scintillator at the experimental room. The kinetic energy of those neutrons was determined by the time-of-flight method. The obtained results were compared with the results of the theoretical model INCL and the nuclear-data library JENDL-4.0/HE used in the PHITS. It was found that the INCL and JENDL-4.0/HE cannot reproduce the peak structures observed for light nuclei, because they do not consider the nuclear transition between discrete states of nucleus. In addition, the JENDL-4.0/HE agreed with the experimental data of energy-integrated cross section within a factor of 2, but the INCL gave approximately 6 times larger values.

A New detector system for the measurement of high-energy prompt -rays for low-energy neutron induced fission

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Lguillon, R.*; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; Ache, M.*; Astier, A.*; et al.

Nuclear Instruments and Methods in Physics Research A, 906, p.88 - 96, 2018/10

https://doi.org/10.1016/j.nima.2018.07.055

We have developed a new setup to measure prompt fission -ray spectra in neutron induced fission up to energies sufficient to reveal the structure associated with giant dipole resonances of fission fragments. The setup consists of multi-wire proportional counters, to detect both fission fragments in coincidence, and two large volume (101.6 mm in diameter and 127.0 mm in length) LaBr(Ce) scintillators, to measure the -rays. The setup was used to obtain the prompt fission -ray spectrum for thermal neutron induced fission of U at the PF1B cold-neutron beam facility of the Institut Laue-Langevin, Grenoble, France. We have successfully measured the -ray spectrum up to energies of about 20 MeV, what extends the currently known -ray spectrum limit to higher energies by approximately a factor of two.

Cluster formation in relativistic nucleus-nucleus collisions

Ogawa, Tatsuhiko; Sato, Tatsuhiko; Hashimoto, Shintaro; Niita, Koji*

Physical Review C, 98(2), p.024611_1 - 024611_15, 2018/08

https://doi.org/10.1103/PhysRevC.98.024611

Particle production by nucleus-nucleus reactions in the energy range from GeV to TeV is substantially important for safety evaluation in heavy ion accelerators and evaluation of space radiation dose. A lot of models and theories have been studied. In the models developed in the past, interaction between nucleons were dependent on the reference frame; therefore the moving incident nucleus and the target nucleus at rest transferred to the common frame were disintegrated. Previously, intentional bias was introduced to the calculation algorithms to supplement stability but residual nucleus mass and secondary particle production was underestimated. In this study, a reaction model JAMQMD was developed, in which intra-nucleon interaction was described in a frame-independent way. This model can reproduce the stability of nuclei regardless of the reference frame and the yield of residual nuclei as well as secondary particles including deuterons. JQMD Ver.2 developed 3 years ago can simulate nucleus-nucleus reactions up to 3 GeV/nucleon; therefore the development of JAMQMD is the doorway to simulate nucleus-nucleus reactions regardless of the incident energy. JAMQMD is an useful model for not only radiation protection studies but also analysis of fundamental physics studies.

2018 Annual Meeting of Japan Atomic Energy Society, Joint Session of Nuclear Data Subcommittee and Sigma Special Advisory Committee; Present status and future of nuclear data evaluation code in Japan, 4; Role and improvement of nuclear reaction models in the PHITS code

Hashimoto, Shintaro; Sato, Tatsuhiko; Iwamoto, Yosuke; Ogawa, Tatsuhiko; Furuta, Takuya; Abe, Shinichiro; Niita, Koji*

Kaku Deta Nyusu (Internet), (120), p.26 - 34, 2018/06

http://www.aesj.or.jp/~ndd/ndnews/No120.html

Particle and heavy-ion transport code system PHITS has been used for calculations of radiation shielding in accelerator facilities. PHITS describes physical phenomena induced by radiation as combination of transport and collision processes. The collision process including nuclear reactions is simulated by the three-step calculation: a generation of a reaction, pre-equilibrium, and compound processes. In the simulation, many physics models are used. This report explains roles of the models in PHITS and shows their developments we recently performed.

Comparison of heavy-ion transport simulations; Collision integral in a box

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

Physical Review C, 97(3), p.034625_1 - 034625_20, 2018/03

https://doi.org/10.1103/PhysRevC.97.034625

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 320 neutrons were packed in a 20-fm-large cube to calculate the number of particle-particle collisions as well as the energies of collisions during the time evolution. In addition to the calculation, their algorithms were compared. The author contributed to this study by running calculation using JQMD (JAERI Quantum Molecular Dynamics). The results were compared with those calculated by the other 15 codes from over the world. Algorithm comparison showed that JQMD calculates collision probabilities from protons at first and collisions by neutrons are simulated later, which might be unreasonable. On the other hand, it was clarified that the calculation by JQMD agrees with those by the others. Despite the fact that some codes deviate from the average by a factor of 2, JQMD exhibited stable performance.