Yosuke Iwamoto

Particle and Heavy Ion Transport code System, PHITS, version 2.52

An upgraded version of the Particle and Heavy Ion Transport code System, PHITS2.52, was developed and released to the public. The new version has been greatly improved from the previously released version, PHITS2.24, in terms of not only the code itself but also the contents of its package, such as the attached data libraries. In the new version, a higher accuracy of simulation was achieved by implementing several latest nuclear reaction models. The reliability of the simulation was improved by modifying both the algorithms for the electron-, positron-, and photon-transport simulations and the procedure for calculating the statistical uncertainties of the tally results. Estimation of the time evolution of radioactivity became feasible by incorporating the activation calculation program DCHAIN-SP into the new package. The efficiency of the simulation was also improved as a result of the implementation of shared-memory parallelization and the optimization of several time-consuming algorithms. Furthermore, a number of new user-support tools and functions that help users to intuitively and effectively perform PHITS simulations were developed and incorporated. Due to these improvements, PHITS is now a more powerful tool for particle transport simulation applicable to various research and development fields, such as nuclear technology, accelerator design, medical physics, and cosmic-ray research.

Design of superconducting combined function magnets for the 50 GeV proton beam line for the J-PARC neutrino experiment

Superconducting combined function magnets will be utilized for the 50 GeV-750 kW proton beam line for the J-PARC neutrino experiment and an R&D program has been launched at KEK. The magnet is designed to provide a combined function with a dipole field of 2.59 T and a quadrupole field of 18.7 T/m in a coil aperture of 173.4 mm. A single layer coil is proposed to reduce the fabrication cost and the coil arrangement in the 2D cross-section results in left-right asymmetry. This paper reports the design study of the magnet.

Evaluation of the White Neutron Beam Spectrum for Single-Event Effects Testing at the RCNP Cyclotron Facility

Abstract The 30-deg white neutron beam at the Research Center for Nuclear Physics (RCNP) cyclotron facility has been characterized as a probe suitable for testing of single-event effects (SEE) in semiconductor devices in the neutron energy range from 1 to 300 MeV using the 392-MeV proton incident reaction on a 6.5-cm-thick tungsten target. The neutron spectrum obtained by time-of-flight measurements reproduced the terrestrial neutron flux distribution at sea level, and neutron intensity increased by a factor of 1.5 × 108 became available. The average neutron intensity and spectrum in the energy region from 10 to 100 MeV at RCNP were almost the same as those at the Weapons Neutron Research (WNR). The calculated RCNP neutron flux using Particle and Heavy Ion Transport code System (PHITS) generally agreed with the measured RCNP data within a factor of 2. The neutron density per pulse at RCNP, which is around 500 times lower than that for WNR, has the advantage in reduction of the pileup probability of single-event transient currents and false multiple-bit upsets. Such conditions at RCNP are suitable for accelerated SEE testing to get meaningful results in a realistic time frame.

Features of Particle and Heavy Ion Transport code System (PHITS) version 3.02

ABSTRACT 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 user-supportive 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.

Development of a prototype of Superconducting combined function magnet for the 50 GeV proton beam line for the J-PARC neutrino experiment

Superconducting combined function magnets will be utilized for the 50 GeV, 750 kW proton beam line for the J-PARC neutrino experiment and an R&D program has been launched at KEK. The magnet is designed to provide a combined function of a dipole field of 2.6 T with a quadrupole field of 19 T/m in a coil aperture of 173.4 mm. Critical magnet components including glass-fiber reinforced phenolic plastic spacers have been successfully developed. The mechanical design has been verified by a 100 mm long short-cut model, and coils have been wound for the first full-length prototype.

Experimental studies of shielding and irradiation effects at high-energy accelerator facilities

Abstract Experimental studies of shielding and radiation effects are carried out at Fermi National Accelerator Laboratory (FNAL) under collaboration between FNAL and Japan, aiming at benchmarking simulation codes and studying irradiation effects for the upgrade and design of new high-energy accelerator facilities. The purposes of this collaboration are (a) acquisition of shielding data in a proton beam energy region above 100 GeV, (b) further evaluation of predictive accuracy of the PHITS and MARS codes, (c) modification of physics models and data in these codes if needed, (d) characterization of radiation fields for studies of radiation effects, and (e) development of a code module for an improved description of radiation effects. The first campaign of the experiment was carried out at the Pbar target station and NuMI experimental station at FNAL, which use irradiation of targets with 120-GeV protons for antiproton and neutrino production, respectively. The generated secondary particles passing through steel, concrete, and rock were measured by activation methods as well as by other detectors such as a scintillator with a veto counter, phoswich detector, and a Bonner ball counter on trial. Preliminary experimental and calculated results are presented.

Superconducting combined function magnet system for J-PARC neutrino experiment

The J-PARC Neutrino Experiment, the construction of which starts in JFY 2004, will use a superconducting magnet system for its primary proton beam line. The system, which bends the 50 GeV 0.75 MW proton beam by about 80 degrees, consists of 28 superconducting combined function magnets. The magnets utilize single layer left/right asymmetric coils that generate a dipole field of 2.6 T and a quadrupole field of 18.6 T/m with the operation current of about 7.35 kA. The system also contains a few conduction cooled superconducting corrector magnets that serve as vertical and horizontal steering magnets. All the magnets are designed to provide a physical beam aperture of 130 mm in order to achieve a large beam acceptance. Extensive care is also required to achieve safe operation with the high power proton beam. The paper summarizes the system design as well as some safety analysis results.

Neutron Dosimetry in Quasi-Monoenergetic Fields of 244 and 387 MeV

This paper describes the results of neutron spectrometry and dose measurements using a Bonner Sphere Spectrometer (BSS) at the ring cyclotron facility of the Research Center for Nuclear Physics (RCNP), Osaka University, Japan. Quasi-monoenergetic neutron fields were generated using the 7Li (p,n)7Be reaction and 246 and 389 MeV protons. Neutrons produced at 0° and 30° emission angles were extracted into a time-of-flight (TOF) tunnel, and the energy spectra were measured at a distance of 35 m from the target. To deduce the corresponding neutron spectra from thermal to the nominal maximum energy, the BSS data were unfolded using the MSANDB code and response functions were calculated by Monte Carlo (MC) methods. These spectra are compared to spectral measurements using NE213 organic liquid scintillators applying the TOF method. The results are discussed in terms of ambient dose equivalent H* (10) and compared with the readings of other instruments operated during the experiment.

Evaluation of dose rate reduction in a spacecraft compartment due to additional water shield

The dose reduction rates brought about by the installation of additional water shielding in a spacecraft are calculated in the paper using the particles and heavy ion transport code system PHITS, which can deal with transport of all kinds of hadrons and heavy ions with energies up to 100 GeV/n in three-dimensional phase spaces. In the PHITS simulation, an imaginary spacecraft was irradiated isotropically by cosmic rays with charges up to 28 and energies up to 100 GeV/n, and the dose reduction rates due to water shielding were evaluated for 5 types of doses: the dose equivalents obtained from the LET and linear energy spectra, the dose equivalents to skin and red bone marrow, and the effective dose equivalent. The results of the simulation indicate that the dose reduction rates differ according to the type of dose evaluated. For example, 5 g/cm2 water shielding reduces the effective dose equivalent and the LET dose equivalent by approximately 14% and 32%, respectively. Such degrees of dose reduction can be regarded to make water shielding worth the efforts required to install it.

Benchmark study of the recent version of the PHITS code

ABSTRACT We performed a benchmark study for 58 cases (22 cases reported in this paper and 36 cases reported in online as supplementary materials of this paper) using the recent version (version 2.88) of the Particle and Heavy-Ion Transport code System (PHITS) in the following fields: (1) particle production cross-sections for nuclear reactions from 20 MeV to 1 GeV, (2) thick-target neutron yields and neutron shielding, (3) depth–dose distribution in water using 12C beam, and (4) electron and photon transportation over a wide-energy range from keV to GeV. Overall agreements were found to be sufficiently satisfactory; however, several discrepancies are observed, particularly in particle productions with energies below 100 MeV, neutron production for 7Li(p,n)7Be, and photonuclear reactions. To overcome these inaccuracies and to further improve the code, it will be necessary to incorporate a high-energy version of the evaluated nuclear data library JENDL-4.0/HE and the photonuclear data file JENDL-PD in the PHITS package.