Tatsuhiko Ogawa

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.

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.

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.

Development of general nuclear resonance fluorescence model

ABSTRACT A model to simulate nuclear resonance fluorescence (NRF) reactions of various nuclear species and their various excitation levels was developed. There is a strong need for the simulation of NRF applications using general purpose radiation transport codes; however, NRF reaction cross section data are available only for a few excited states for certain nuclear species. In this study, based on the generalized gamma de-excitation model, an NRF model that can simulate NRF reactions associated with all the levels included in the nuclear structure database was developed. Absorption cross sections calculated by the developed NRF model agree with the experimental data typically within one order of magnitude. To illustrate that this model can be used for simulation studies on NRF applications, the demonstration of the developed NRF model for non-destructive nuclear material assay and isomer production is shown.

Measurement of the stochastic radial dose distribution for a 30-MeV proton beam using a wall-less tissue-equivalent proportional counter

The frequency distribution of the lineal energy, y, of a 30-MeV proton beam was measured as a function of the radial distance from the beam path, and the dosed mean of y, y¯(D), was obtained to investigate the radial dependence of y¯(D). A wall-less tissue-equivalent proportional counter, in a cylindrical volume with simulated diameters of 0.36, 0.72 and 1.44 µm was used for the measurement of y distributions, yf(y). The measured values of yf(y) summed in the radial direction agreed fairly well with the corresponding data taken from the microdosimetric calculations using the PHITS code. The y¯(D) value of the 30-MeV proton beam presented its smallest value at r = 0.0 and gradually increased with radial distance, and the y¯(D) values of heavy ions such as iron showed rapid decrease with radial distance. This experimental result demonstrated that the stochastic deposited energy distribution of high-energy protons in the microscopic region is rather constant in the core as well as in the penumbra region of the track structure.

Analysis of scintillation light intensity by microscopic radiation transport calculation and Förster quenching model

The scintillation light yield of plastic scintillator considering the quenching effect is reproduced by a calculation model based on a track-structure simulation code and the Förster effect. Energy deposition and its nm-scale spatial arrangement in the irradiation by electrons, protons, and heavy ions (4He to 81Br) in an NE-102A scintillator were simulated by a track-structure simulation code. The spatial arrangements of the excited molecules emitting scintillation light and those dissipating the excitation energy were then obtained to calculate the strength of the quenching effect. Light emission from the excited molecules was integrated to finally obtain the observable light yield. The calculated light yields are in good agreement with the earlier measurement data. Moreover, in the case of low-LET particle incidence, a statistical micro-dosimetric model can substitute the track-structure simulation code for reproducing the light yield.

Improvements and developments of physics models in PHITS for space applications

Precise predictions of the radiation environment inside space vehicles, and inside the human body, are essential when planning for long term deep space missions. Since these predictions include complex geometries, as well as the contributions from many different types of radiation, including neutrons, 3-D Monte Carlo codes with precise physics models are needed. In this paper, we present improvements and developments of some physics models used in the general purpose 3-D Monte Carlo code PHITS [1]. The total reaction cross section (σR) and the decay lifetime of a projectile particle are the first essential quantities in MC calculations, since these determine the mean free path of the transported particles and the probability function according to which a projectile particle will collide within a certain distance in the matter depends on the σR. This will also scale the calculated partial fragmentation cross sections. In this paper we present comparisons of calculated and measured σR using the Kurotama Hybrid σR, model [2] which is incorporated into PHITS. The prediction of the fragmentation reactions of relativistic heavy ions is also essential for ensuring radiation safety of astronauts. The default model for nuclear-nuclear reactions is JQMD in PHITS. However, JQMD cannot accurately enough describe the nucleon and d, t, 3He and 4He induced reactions. Therefore the Intra-Nuclear Cascade of Liège (INCL) [3] has been selected as the default model for these reactions. Moreover, it has been realized that the production of light fragments is underestimated by conventional simulation codes based on a combination of intranuclear cascade and statistical decay models. This is because this combination cannot reproduce the high multiplicity events that are responsible for the production of light fragments. To better reproduce high multiplicity events, we have simulated fragmentation cross sections using a combination of JQMD/INCL, statistical multi-fragmentation model (SMM) [4,5] and the generalized evaporation model (GEM). Examples of these simulations will be presented. A new approach to describe neutron spectra of deuteron-induced reactions in the Monte Carlo simulations has also been developed by combining the INCL and the Distorted Wave Born Approximation (DWBA) calculation [6]. We have incorporated this combined method into PHITS and applied it to estimate (d,xn) spectra on light targets at incident energies ranging from 10 to 40 MeV. In this paper, we will show that the double differential cross sections obtained by INCL and DWBA successfully reproduced broad peaks and discrete peaks, respectively.