Hiroshi Iwase - Academia.edu (original) (raw)

Papers by Hiroshi Iwase

Lawrence Berkeley National Laboratory, Apr 9, 2002

Neutron production cross sections have been measured from 290 MeV/nucleon C and 600 MeV/nucleon N... more Neutron production cross sections have been measured from 290 MeV/nucleon C and 600 MeV/nucleon Ne interacting in a slab of simulated Martian regolith/polyethylene composite, and from 400 MeV/nucleon Ne interacting in a section of wall materials from the International Space Station. Neutron spectra were measured at 7 angles between 5º and 80º, and for neutron energies 5 MeV and greater. Spectra at forward angles are dominated by the breakup of the projectile, whereas spectra at back angles show the typical exponential falloff with energy that is indicative of decay from the overlap region and the target remnant. The measured total neutron production cross sections indicate that the regolith/polyethylene composite may be a more effective shielding material than the ISS wall materials, in terms of the number of neutrons produced.

Lawrence Berkeley National Laboratory, 2002

Neutron production cross sections have been measured from290 MeV/nucleon C and 600 MeV/nucleon Ne... more Neutron production cross sections have been measured from290 MeV/nucleon C and 600 MeV/nucleon Ne interacting in a slab ofsimulated Martian regolith/polyethylene composite, and from 400MeV/nucleon Ne interacting in a section of wall materials from theInternational Space Station. Neutron spectra were measured at 7 anglesbetween 5 degrees and 80 degrees, and for neutron energies 5 MeV andgreater. Spectra at forward angles are dominated by the breakup of theprojectile, whereas spectra at back angles show the typical exponentialfalloff with energy that is indicative of decay from the overlap regionand the target remnant. The measured total neutron production crosssections indicate that the regolith/polyethylene composite may be a moreeffective shielding material than the ISS wall materials, in terms of thenumber of neutrons produced.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2001

We measured angular energy spectra of secondary neutrons from large Cu and Pb targets bombarded b... more We measured angular energy spectra of secondary neutrons from large Cu and Pb targets bombarded by 400 MeV/nucleon Fe ions to obtain the benchmark data for the newly-developed heavy ion transport Monte Carlo code HETC-CYRIC. The HETC-CYRIC code is made by incorporating a heavy ion reaction calculation routine, which consists of the HIC code, the SPAR code, and the Shen's formula, into the hadron transport Monte Carlo code HETC-3STEP. The results calculated with the HETC-CYRIC were compared with the measured data and the HETC-CYRIC gave good agreement with the experiment.

Progress in nuclear science and technology, 2014

A shielding benchmark experiment has been performed using a quasi-monoenergetic 7 Li(p,n) neutron... more A shielding benchmark experiment has been performed using a quasi-monoenergetic 7 Li(p,n) neutron source with 246 and 389 MeV protons at the Research Center for Nuclear Physics (RCNP) of Osaka University, in order to investigate the accuracy of nuclear data libraries and calculation codes for hundreds of MeV neutrons. Time-of-flight and energy spectra behind bulk shields of 10-to 100-cm-thick iron, 25-to 300-cm-thick concrete and their composite are measured using a NE213 organic liquid scintillator with a diameter and thickness of 25.4 cm each. A time-of-flight and an unfolding method are applied to obtain the energy spectra transmitted through the shields for the peak energy region and continuous energy region, respectively. The simulations with the PHITS code coupled with the JENDL-HE nuclear data library are performed for comparison with the measured data. The measured attenuation lengths of peak neutrons with energies of 244 and 387 MeV are in good agreement with the calculation result by the PHITS code within 6 %.

Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2020

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Aug 1, 2010

ABSTRACT Electron backscattering coefficients, ηη, obtained from several targets in the MeV range... more ABSTRACT Electron backscattering coefficients, ηη, obtained from several targets in the MeV range were calculated by using electron–photon Monte Carlo transport calculation codes, i.e., EGS5 and ITS 3.0. These calculated values were compared with those obtained from the electron backscattering experiment performed by Tabata using an ionization chamber [15]. We found that Tabata’s estimation of the multiplication factor of the ionization chamber, f, had a non-negligible error. Then, we calculated the ionization chamber output, I, which is a product of ηη and f. The ratios of I between the experimental and the calculated values were within 1.5 and 1.3 for the EGS5 code and the ITS 3.0 code, respectively. The ratios of ηη between the experimental and the calculated values were within 2.4 and 1.5 for the EGS5 code and the ITS 3.0 code, respectively. The differences between the experimental and the calculated values of I and ηη are large for low-Z targets (Be and C). Here, the ratios obtained by using the ITS 3.0 code are closer to unity than those obtained by using the EGS5 code. The reason of this is the fact that the calculated value obtained by using the ITS 3.0 code is underestimated for low-Z targets; this underestimation can, in turn, be attributed to the use of the default value of the number of steps in the electron transport algorithm in the ITS 3.0 code.

日本原子力学会春の年会予稿集(CD-ROM), 2016

Journal of Radiation Research, 2012

Heavy ion/Lineal energy/Tissue equivalent proportional counter/LET. The frequency distributions o... more Heavy ion/Lineal energy/Tissue equivalent proportional counter/LET. The frequency distributions of the lineal energy, y, of 160 MeV proton, 150 MeV/u helium, and 490 MeV/u silicon ion beams were measured using a wall-less tissue equivalent proportional counter (TEPC) with a site size of 0.72 μm. The measured frequency distributions of y as well as the dose-mean values, , agree with the corresponding data calculated using the microdosimetric function of the particle and heavy ion transport code system PHITS. The values of increase in the range of LET below ~10 keV μm-1 because of discrete energy deposition by delta rays, while the relation is reversed above ~10 keV μm-1 as the amount of energy escaping via delta rays increases. These results indicate that care should be taken with the difference between and LET when estimating the ionization density that usually relates to relative biological effectiveness (RBE) of energetic heavy ions.

Physics in Medicine and Biology, Aug 11, 2010

The frequency distribution of the lineal energy, y, of a 290 MeV/u carbon beam was measured to ob... more The frequency distribution of the lineal energy, y, of a 290 MeV/u carbon beam was measured to obtain the dose-weighted mean of y and compare it with the linear energy transfer (LET). In the experiment, a wall-less tissue-equivalent proportional counter (TEPC) in a cylindrical volume with a simulated diameter of 0.72 microm was used. The measured frequency distribution of y as well as its dose-mean value agrees within 10% uncertainty with the corresponding data from microdosimetric calculations using the PHITS code. The ratio of the measured dose-mean lineal energy to the LET of the 290 MeV/u carbon beam is 0.73, which is much smaller than the corresponding data obtained by a wall TEPC. This result demonstrates that a wall-less TEPC is necessary to precisely measure the dose-mean of y for energetic heavy ion beams.

Progress in nuclear science and technology, Jan 31, 2019

In electron accelerator facility, neutron production induced by high energy electron above 1 GeV ... more In electron accelerator facility, neutron production induced by high energy electron above 1 GeV hitting on thick target, and the neutron deep penetration for concrete shielding can be calculated by the Jenkins formula. In the formula, the neutron source term is divided into three energy regions of GR, MID, and HE, and neutron deep penetration is solved by summing up the attenuation of the three individual source terms with different attenuation length. In this study, the concept of Jenkins formula is verified by using recent Monte Carlo codes with evaluated data and cross sections, and some parameters of Jenkins formula are revised.

Journal of Nuclear Science and Technology, Feb 1, 2012

In a nuclear power plant accident, radioactive nuclides may be released which are distributed uni... more In a nuclear power plant accident, radioactive nuclides may be released which are distributed uniformly on the ground. If estimation of dose rate from such a source by a Monte Carlo calculation is attempted, some difficulty is encountered because the calculation efficiency is very low. To solve this low efficiency problem, we show that a plane isotropic source can be transformed into a point isotropic source by changing the detector shape from a unit sphere to a plane. We verified the validity of this transformation by the numerical comparison of unscattered photon fluence. As an example of this transformation, the ambient dose rate D i was calculated from the uniform radioactive nuclide distribution on the ground using the EGS5 Monte Carlo code. We also measured the radioactivity and ambient dose rate (M) on the KEK campus within a month after the releases from the Fukushima No. 1 Nuclear Power Plant accident. Using radioactivity data and D i, we calculated the ambient dose rate (C). The calculated and measured ambient dose rates agreed reasonably well; their ratio (C/M) was 0.62 to 1.28.

Nuclear Technology, Nov 1, 2009

ABSTRACT

The concept of a compact ion particle accelerator has become attractive in view of recent progres... more The concept of a compact ion particle accelerator has become attractive in view of recent progress in laser-driven hadrons acceleration. The Photo Medical Research Centre (PMRC) of JAEA was established to address the challenge of laser-driven ion accelerator development for hadrons therapeutic. In the development of the instrument, it is necessary to do the bench-mark of the amount of the different types of radiation by the simulation code for shielding. The Monte Carlo Particle and Heavy Ion Transport code (PHITS) was used for bench-mark the dose on laser-shot radiations of short duration. The code predicts reasonably well the observed total dose as measured with a glass dosimeter in the laser-driven radiations.

Proceedings of International Workshop on Fast Neutron Detectors and Applications — PoS(FNDA2006), 2007

The radiation field of heavy-ion beams used for radiotherapy applications is significantly affect... more The radiation field of heavy-ion beams used for radiotherapy applications is significantly affected by nuclear fragmentation processes along the penetration path in tissue, causing an attenuation of the primary ion beam flux and the build-up of light fragments including fast neutrons. The emission of secondary fragments from 200 MeV/u carbon ions delivered from the synchrotron SIS-18 at GSI was investigated using a water absorber as tissue-equivalent beam stopping target. Energy spectra, angular distributions and yields of fast neutrons and charged particles emerging from the absorber downstream were investigated by using fast scintillation detectors and time-of-flight techniques. From the resulting yield of 0.54 neutrons (E n >10 MeV) per primary 12 C ion a neutron dose of 5.4 mSv per Cobalt Gray Equivalent (GyE) delivered to the target volume is estimated. Additional measurements employing a wide-energy neutron detector (WENDI-II) under identical irradiation conditions were found to be in fair agreement with the dose estimate based on the measured fast neutron fluences.

Proceedings of International Workshop on Fast Neutron Detectors and Applications — PoS(FNDA2006), 2007

The neutron fields generated by high-energy heavy ions in a production target are of key importan... more The neutron fields generated by high-energy heavy ions in a production target are of key importance as they are used as source terms for further transport calculations. Various calculations of secondary neutron fields generated by high-energy heavy-ion reactions, such as benchmarks with systematic data, neutron energy spectra and doses compared with data measured recently in GSI, and calculations for the Super-FRS project, are done. Comparison of measured neutron fields with calculations performed by the PHITS code will be included for more precise predictions for secondary neutron productions.

Journal of Nuclear Science and Technology, 2018

We have upgraded many features of the Particle and Heavy Ion Transport code System (PHITS) and re... more We have upgraded many features of the Particle and Heavy Ion Transport code System (PHITS) and released the new version as PHITS3.02. The accuracy and the applicable energy ranges of the code were greatly improved and extended, respectively, owing to the revisions to the nuclear reaction models and the incorporation of new atomic interaction models. Both condense history and track-structure methods were implemented to handle the electron and positron transport, although the latter is reliable only for simulations in liquid water. In addition, several usersupportive functions were developed, such as new tallies to efficiently obtain statistically better results, radioisotope source-generation function, and software tools useful for applying PHITS to medical physics. Owing to the continuous improvement and promotion of the code, the number of registered users has exceeded 3,000, and it is being used in diverse areas of study, including accelerator design, radiation shielding and protection, medical physics, and cosmic-ray research. In this paper, we summarize the basic features of PHITS3.02, especially those of the physics models and the functions implemented after the release of PHITS2.52 in 2013.

Nuclear Technology, 2009

Abstract We performed a systematic benchmark study of several Monte Carlo codes for neutron deep ... more Abstract We performed a systematic benchmark study of several Monte Carlo codes for neutron deep penetration experiments at 0 deg, which were previously performed using 40-, 65-, and 137-MeV quasi-monoenergetic neutrons and using continuous-energy neutrons up to 400 MeV. Neutron energy spectra behind shields and the attenuation lengths of the neutron flux are compared between the experiments and the calculations. All calculations generally well reproduce the energy spectra and the attenuation lengths measured in the experiments. The attenuation length obtained as a function of the incident neutron energy in this study rapidly increases with the incident energy.

EPJ Web of Conferences, 2017

Neutron energy spectra behind concrete and iron shields were measured for quasi-monoenergetic neu... more Neutron energy spectra behind concrete and iron shields were measured for quasi-monoenergetic neutrons above 200 MeV using a Bonner sphere spectrometer (BSS). Quasi-monoenergetic neutrons were produced by the 7 Li(p,xn) reaction with 246-MeV and 389-MeV protons. Shielding materials are concrete blocks with thicknesses from 25 cm to 300 cm and iron blocks with thicknesses from 10 cm to 100 cm. The response function of BSS was also measured at neutron energies from 100 MeV to 387 MeV. In data analysis, the measured response function was used and the pingpong scattering effect between the BSS and the shielding material was considered. The neutron energy spectra behind the concrete and iron shields were obtained by the unfolding method using the MAXED code. Ambient dose equivalents were obtained as a function of a shield thickness successfully.

Lawrence Berkeley National Laboratory, Apr 9, 2002

Neutron production cross sections have been measured from 290 MeV/nucleon C and 600 MeV/nucleon N... more Neutron production cross sections have been measured from 290 MeV/nucleon C and 600 MeV/nucleon Ne interacting in a slab of simulated Martian regolith/polyethylene composite, and from 400 MeV/nucleon Ne interacting in a section of wall materials from the International Space Station. Neutron spectra were measured at 7 angles between 5º and 80º, and for neutron energies 5 MeV and greater. Spectra at forward angles are dominated by the breakup of the projectile, whereas spectra at back angles show the typical exponential falloff with energy that is indicative of decay from the overlap region and the target remnant. The measured total neutron production cross sections indicate that the regolith/polyethylene composite may be a more effective shielding material than the ISS wall materials, in terms of the number of neutrons produced.

Lawrence Berkeley National Laboratory, 2002

Neutron production cross sections have been measured from290 MeV/nucleon C and 600 MeV/nucleon Ne... more Neutron production cross sections have been measured from290 MeV/nucleon C and 600 MeV/nucleon Ne interacting in a slab ofsimulated Martian regolith/polyethylene composite, and from 400MeV/nucleon Ne interacting in a section of wall materials from theInternational Space Station. Neutron spectra were measured at 7 anglesbetween 5 degrees and 80 degrees, and for neutron energies 5 MeV andgreater. Spectra at forward angles are dominated by the breakup of theprojectile, whereas spectra at back angles show the typical exponentialfalloff with energy that is indicative of decay from the overlap regionand the target remnant. The measured total neutron production crosssections indicate that the regolith/polyethylene composite may be a moreeffective shielding material than the ISS wall materials, in terms of thenumber of neutrons produced.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2001

We measured angular energy spectra of secondary neutrons from large Cu and Pb targets bombarded b... more We measured angular energy spectra of secondary neutrons from large Cu and Pb targets bombarded by 400 MeV/nucleon Fe ions to obtain the benchmark data for the newly-developed heavy ion transport Monte Carlo code HETC-CYRIC. The HETC-CYRIC code is made by incorporating a heavy ion reaction calculation routine, which consists of the HIC code, the SPAR code, and the Shen's formula, into the hadron transport Monte Carlo code HETC-3STEP. The results calculated with the HETC-CYRIC were compared with the measured data and the HETC-CYRIC gave good agreement with the experiment.

Progress in nuclear science and technology, 2014

A shielding benchmark experiment has been performed using a quasi-monoenergetic 7 Li(p,n) neutron... more A shielding benchmark experiment has been performed using a quasi-monoenergetic 7 Li(p,n) neutron source with 246 and 389 MeV protons at the Research Center for Nuclear Physics (RCNP) of Osaka University, in order to investigate the accuracy of nuclear data libraries and calculation codes for hundreds of MeV neutrons. Time-of-flight and energy spectra behind bulk shields of 10-to 100-cm-thick iron, 25-to 300-cm-thick concrete and their composite are measured using a NE213 organic liquid scintillator with a diameter and thickness of 25.4 cm each. A time-of-flight and an unfolding method are applied to obtain the energy spectra transmitted through the shields for the peak energy region and continuous energy region, respectively. The simulations with the PHITS code coupled with the JENDL-HE nuclear data library are performed for comparison with the measured data. The measured attenuation lengths of peak neutrons with energies of 244 and 387 MeV are in good agreement with the calculation result by the PHITS code within 6 %.

Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2020

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Aug 1, 2010

ABSTRACT Electron backscattering coefficients, ηη, obtained from several targets in the MeV range... more ABSTRACT Electron backscattering coefficients, ηη, obtained from several targets in the MeV range were calculated by using electron–photon Monte Carlo transport calculation codes, i.e., EGS5 and ITS 3.0. These calculated values were compared with those obtained from the electron backscattering experiment performed by Tabata using an ionization chamber [15]. We found that Tabata’s estimation of the multiplication factor of the ionization chamber, f, had a non-negligible error. Then, we calculated the ionization chamber output, I, which is a product of ηη and f. The ratios of I between the experimental and the calculated values were within 1.5 and 1.3 for the EGS5 code and the ITS 3.0 code, respectively. The ratios of ηη between the experimental and the calculated values were within 2.4 and 1.5 for the EGS5 code and the ITS 3.0 code, respectively. The differences between the experimental and the calculated values of I and ηη are large for low-Z targets (Be and C). Here, the ratios obtained by using the ITS 3.0 code are closer to unity than those obtained by using the EGS5 code. The reason of this is the fact that the calculated value obtained by using the ITS 3.0 code is underestimated for low-Z targets; this underestimation can, in turn, be attributed to the use of the default value of the number of steps in the electron transport algorithm in the ITS 3.0 code.

日本原子力学会春の年会予稿集(CD-ROM), 2016

Journal of Radiation Research, 2012

Heavy ion/Lineal energy/Tissue equivalent proportional counter/LET. The frequency distributions o... more Heavy ion/Lineal energy/Tissue equivalent proportional counter/LET. The frequency distributions of the lineal energy, y, of 160 MeV proton, 150 MeV/u helium, and 490 MeV/u silicon ion beams were measured using a wall-less tissue equivalent proportional counter (TEPC) with a site size of 0.72 μm. The measured frequency distributions of y as well as the dose-mean values, , agree with the corresponding data calculated using the microdosimetric function of the particle and heavy ion transport code system PHITS. The values of increase in the range of LET below ~10 keV μm-1 because of discrete energy deposition by delta rays, while the relation is reversed above ~10 keV μm-1 as the amount of energy escaping via delta rays increases. These results indicate that care should be taken with the difference between and LET when estimating the ionization density that usually relates to relative biological effectiveness (RBE) of energetic heavy ions.

Physics in Medicine and Biology, Aug 11, 2010

The frequency distribution of the lineal energy, y, of a 290 MeV/u carbon beam was measured to ob... more The frequency distribution of the lineal energy, y, of a 290 MeV/u carbon beam was measured to obtain the dose-weighted mean of y and compare it with the linear energy transfer (LET). In the experiment, a wall-less tissue-equivalent proportional counter (TEPC) in a cylindrical volume with a simulated diameter of 0.72 microm was used. The measured frequency distribution of y as well as its dose-mean value agrees within 10% uncertainty with the corresponding data from microdosimetric calculations using the PHITS code. The ratio of the measured dose-mean lineal energy to the LET of the 290 MeV/u carbon beam is 0.73, which is much smaller than the corresponding data obtained by a wall TEPC. This result demonstrates that a wall-less TEPC is necessary to precisely measure the dose-mean of y for energetic heavy ion beams.

Progress in nuclear science and technology, Jan 31, 2019

In electron accelerator facility, neutron production induced by high energy electron above 1 GeV ... more In electron accelerator facility, neutron production induced by high energy electron above 1 GeV hitting on thick target, and the neutron deep penetration for concrete shielding can be calculated by the Jenkins formula. In the formula, the neutron source term is divided into three energy regions of GR, MID, and HE, and neutron deep penetration is solved by summing up the attenuation of the three individual source terms with different attenuation length. In this study, the concept of Jenkins formula is verified by using recent Monte Carlo codes with evaluated data and cross sections, and some parameters of Jenkins formula are revised.

Journal of Nuclear Science and Technology, Feb 1, 2012

In a nuclear power plant accident, radioactive nuclides may be released which are distributed uni... more In a nuclear power plant accident, radioactive nuclides may be released which are distributed uniformly on the ground. If estimation of dose rate from such a source by a Monte Carlo calculation is attempted, some difficulty is encountered because the calculation efficiency is very low. To solve this low efficiency problem, we show that a plane isotropic source can be transformed into a point isotropic source by changing the detector shape from a unit sphere to a plane. We verified the validity of this transformation by the numerical comparison of unscattered photon fluence. As an example of this transformation, the ambient dose rate D i was calculated from the uniform radioactive nuclide distribution on the ground using the EGS5 Monte Carlo code. We also measured the radioactivity and ambient dose rate (M) on the KEK campus within a month after the releases from the Fukushima No. 1 Nuclear Power Plant accident. Using radioactivity data and D i, we calculated the ambient dose rate (C). The calculated and measured ambient dose rates agreed reasonably well; their ratio (C/M) was 0.62 to 1.28.

Nuclear Technology, Nov 1, 2009

ABSTRACT

The concept of a compact ion particle accelerator has become attractive in view of recent progres... more The concept of a compact ion particle accelerator has become attractive in view of recent progress in laser-driven hadrons acceleration. The Photo Medical Research Centre (PMRC) of JAEA was established to address the challenge of laser-driven ion accelerator development for hadrons therapeutic. In the development of the instrument, it is necessary to do the bench-mark of the amount of the different types of radiation by the simulation code for shielding. The Monte Carlo Particle and Heavy Ion Transport code (PHITS) was used for bench-mark the dose on laser-shot radiations of short duration. The code predicts reasonably well the observed total dose as measured with a glass dosimeter in the laser-driven radiations.

Proceedings of International Workshop on Fast Neutron Detectors and Applications — PoS(FNDA2006), 2007

The radiation field of heavy-ion beams used for radiotherapy applications is significantly affect... more The radiation field of heavy-ion beams used for radiotherapy applications is significantly affected by nuclear fragmentation processes along the penetration path in tissue, causing an attenuation of the primary ion beam flux and the build-up of light fragments including fast neutrons. The emission of secondary fragments from 200 MeV/u carbon ions delivered from the synchrotron SIS-18 at GSI was investigated using a water absorber as tissue-equivalent beam stopping target. Energy spectra, angular distributions and yields of fast neutrons and charged particles emerging from the absorber downstream were investigated by using fast scintillation detectors and time-of-flight techniques. From the resulting yield of 0.54 neutrons (E n >10 MeV) per primary 12 C ion a neutron dose of 5.4 mSv per Cobalt Gray Equivalent (GyE) delivered to the target volume is estimated. Additional measurements employing a wide-energy neutron detector (WENDI-II) under identical irradiation conditions were found to be in fair agreement with the dose estimate based on the measured fast neutron fluences.

Proceedings of International Workshop on Fast Neutron Detectors and Applications — PoS(FNDA2006), 2007

The neutron fields generated by high-energy heavy ions in a production target are of key importan... more The neutron fields generated by high-energy heavy ions in a production target are of key importance as they are used as source terms for further transport calculations. Various calculations of secondary neutron fields generated by high-energy heavy-ion reactions, such as benchmarks with systematic data, neutron energy spectra and doses compared with data measured recently in GSI, and calculations for the Super-FRS project, are done. Comparison of measured neutron fields with calculations performed by the PHITS code will be included for more precise predictions for secondary neutron productions.

Journal of Nuclear Science and Technology, 2018

We have upgraded many features of the Particle and Heavy Ion Transport code System (PHITS) and re... more We have upgraded many features of the Particle and Heavy Ion Transport code System (PHITS) and released the new version as PHITS3.02. The accuracy and the applicable energy ranges of the code were greatly improved and extended, respectively, owing to the revisions to the nuclear reaction models and the incorporation of new atomic interaction models. Both condense history and track-structure methods were implemented to handle the electron and positron transport, although the latter is reliable only for simulations in liquid water. In addition, several usersupportive functions were developed, such as new tallies to efficiently obtain statistically better results, radioisotope source-generation function, and software tools useful for applying PHITS to medical physics. Owing to the continuous improvement and promotion of the code, the number of registered users has exceeded 3,000, and it is being used in diverse areas of study, including accelerator design, radiation shielding and protection, medical physics, and cosmic-ray research. In this paper, we summarize the basic features of PHITS3.02, especially those of the physics models and the functions implemented after the release of PHITS2.52 in 2013.

Nuclear Technology, 2009

Abstract We performed a systematic benchmark study of several Monte Carlo codes for neutron deep ... more Abstract We performed a systematic benchmark study of several Monte Carlo codes for neutron deep penetration experiments at 0 deg, which were previously performed using 40-, 65-, and 137-MeV quasi-monoenergetic neutrons and using continuous-energy neutrons up to 400 MeV. Neutron energy spectra behind shields and the attenuation lengths of the neutron flux are compared between the experiments and the calculations. All calculations generally well reproduce the energy spectra and the attenuation lengths measured in the experiments. The attenuation length obtained as a function of the incident neutron energy in this study rapidly increases with the incident energy.

EPJ Web of Conferences, 2017

Neutron energy spectra behind concrete and iron shields were measured for quasi-monoenergetic neu... more Neutron energy spectra behind concrete and iron shields were measured for quasi-monoenergetic neutrons above 200 MeV using a Bonner sphere spectrometer (BSS). Quasi-monoenergetic neutrons were produced by the 7 Li(p,xn) reaction with 246-MeV and 389-MeV protons. Shielding materials are concrete blocks with thicknesses from 25 cm to 300 cm and iron blocks with thicknesses from 10 cm to 100 cm. The response function of BSS was also measured at neutron energies from 100 MeV to 387 MeV. In data analysis, the measured response function was used and the pingpong scattering effect between the BSS and the shielding material was considered. The neutron energy spectra behind the concrete and iron shields were obtained by the unfolding method using the MAXED code. Ambient dose equivalents were obtained as a function of a shield thickness successfully.