Particle And Heavy Ion Transport Code System Research Articles

Benchmark study of particle and heavy-ion transport code system using shielding integral benchmark archive and database for accelerator-shielding experiments

ABSTRACT To validate the accuracy of the general-purpose Monte Carlo Particle and Heavy-Ion Transport code System (PHITS), a benchmark study of the recent version (version 3.24) of PHITS has been conducted using neutron-shielding experiments listed in the Shielding Integral Benchmark Archive and Database (SINBAD). Five neutron sources were selected, which are generated from (1) 43- and 68-MeV proton-induced reaction on a thin lithium target, (2) 52-MeV proton-induced reaction on a thick graphite target, (3) 590-MeV proton-induced reaction on a thick lead target, (4) 500-MeV proton-induced reaction on a thick tungsten target, and (5) 800-MeV proton-induced reaction on a thick tantalum target. For all these cases, overall agreements between the experimental and calculated results were satisfactory to simulate neutron- and proton-induced reactions up to 200 MeV when using the Japanese evaluated nuclear data library JENDL-4.0/HE; however, using default settings in the code system made discrepancies between the results in neutron production and scatterings in shielding materials with energies lower than 100 MeV. The present study revealed that it is preferable to use JENDL-4.0/HE in the PHITS calculation.

Implementation of simplified stochastic microdosimetric kinetic models into PHITS for application to radiation treatment planning

Purpose The stochastic microdosimetric kinetic (SMK) model is one of the most sophisticated and precise models used in the estimation of the relative biological effectiveness of carbon-ion radiotherapy (CRT) and boron neutron capture therapy (BNCT). However, because of its complicated and time-consuming calculation procedures, it is nearly impractical to directly incorporate this model into a radiation treatment-planning system. Materials and methods Through the introduction of Taylor expansion (TE) or fast Fourier transform (FFT), we developed two simplified SMK models and implemented them into the Particle and Heavy Ion Transport code System (PHITS). To verify the implementation, we calculated the photon isoeffective doses in a cylindrical phantom placed in the radiation fields of passive CRT and accelerator-based BNCT. Results and discussion Our calculation suggested that both TE-based and FFT-based SMK models can reproduce the data obtained from the original SMK model very well for absorbed doses approximately below 5 Gy, whereas the TE-based SMK model overestimates the original data at higher doses. In terms of computational efficiency, the TE-based SMK model is much faster than the FFT-based SMK model. Conclusion This study enables the instantaneous calculation of the photo isoeffective dose for CRT and BNCT, considering their cellular-scale dose heterogeneities. Treatment-planning systems that use the improved PHITS as a dose-calculation engine are under development.

Medical application of particle and heavy ion transport code system PHITS.

The Particle and Heavy Ion Transport code System (PHITS) is a general-purpose Monte Carlo simulation code that has been applied in various areas of medical physics. These include application in different types of radiotherapy, shielding calculations, application to radiation biology, and research and development of medical tools. In this article, the useful features of PHITS are explained by referring to actual examples of various medical applications.

Development of local-scale high-resolution atmospheric dispersion model using large-eddy simulation part 6: introduction of detailed dose calculation method

ABSTRACT We developed a LOcal-scale High-resolution atmospheric DIspersion Model using Large-Eddy Simulation (LOHDIM-LES) for the safety assessment of nuclear facilities and emergency responses to accidental or deliberate releases of radioactive materials. In parts 1–5 of this series, the basic performance was examined by comparing with wind tunnel or field experimental results on plume dispersion over various complex surface geometries under ideal and realistic atmospheric conditions. In this study, we introduced a dose calculation method that can simulate air dose rate distributions by considering shielding effects and inhomogeneous distribution of radioactive materials in the air and on the ground and building surfaces. First, we conducted LESs of radioactive plume dispersion and dry deposition in building array and investigated the basic performance of the dose calculation method by comparison with that of Monte-Carlo based three-dimensional radiation transport simulations by Particle and Heavy-Ion Transport code System (PHITS). Then, we compared the LOHDIM-LES results with actual air dose rate obtained from the monitoring posts in a nuclear facility. The observed data were reasonably simulated. Thus, we completed LOHDIM-LES, which can simulate plume dispersion, dry deposition, and air dose rates from complex distributions of radionuclides considering the influence of individual buildings under realistic meteorological conditions.

Verification of KURBUC-based ion track structure mode for proton and carbon ions in the PHITS code

The particle and heavy ion transport code system (PHITS) is a general-purpose Monte Carlo radiation transport simulation code. It has the ability to handle diverse particle types over a wide range of energy. The latest PHITS development enables the generation of track structure for proton and carbon ions (1H+, 12C6+) based on the algorithms in the KURBUC code, which is considered as one of the most verified track-structure codes worldwide. This ion track-structure mode is referred to as the PHITS-KURBUC mode. In this study, the range, radial dose distributions, and microdosimetric distributions were calculated using the PHITS-KURBUC mode. Subsequently, they were compared with the corresponding data obtained from the original KURBUC and from other studies. These comparative studies confirm the successful inclusion of the KURBUC code in the PHITS code. As results of the synergistic effect between the macroscopic and microscopic radiation transport codes, this implementation enabled the detailed calculation of the microdosimetric and nanodosimetric quantities under complex radiation fields, such as proton beam therapy with the spread-out Bragg peak.

The analysis of X-Rays dose distribution in the 350 keV/10 mA electron beam machine (EBM) acility using PHITS computer code

The EBM 350 keV/10mA is an electron irradiation facility located at the Centre for Accelerator Science and Technology (PSTA). The EBM generates the electrons with energy of 350 keV and the beam current of 10 mA. This generated electron beam can induce x-rays radiation when passing through materials. It is dangerous for workers if the radiation dose exceeds the dose threshold. The previous study has investigated the x-rays radiation in the EBM facility. However, it implemented an analytical approach and applied the high-Z material tabulation data for the x-rays source definition. In this work, we present a different approach using particle transport simulation. The Particle and Heavy Ion Transport code System (PHITS) was utilised to obtain the x-rays source data as well as its dose distribution in the EBM facility. Based on the PHITS simulation, the x-rays are induced by the interaction between electron beams and the EBM’ window through atomic fluorescence and bremsstrahlung mechanism, with the total reaction rate density of 2.6437 × 1013 reactions/cm3s. The x-rays’ maximum dose rate of 1.4659 × 104 µSv/s is located around the window, and it decreases along with the position from the window. The x-rays dose rate in the preparation room (12 m away from the x-rays source, behind 45 cm concrete wall) was 7.4975 × 10−2 µSv/s. It exceeded the permissible dose threshold. Therefore, a radiation shield or the working-duration limits is required for the workers’ safety.

Optimization of a slab geometry type cold neutron moderator for RIKEN accelerator-driven compact neutron source

We have optimized a cold neutron moderator to be operated at the RIKEN accelerator-driven compact neutron source (RANS) to broaden cold neutron applications and provide more choices for RANS users. We selected a safe and easy to manage material, mesitylene, as the RANS cold moderator. An efficient moderator system was designed by studying and optimizing a coupled cold neutron moderator of mesitylene at 20 K with a polyethylene (PE) pre-moderator at room temperature in the slab geometry with Particle and Heavy Ion Transport code System (PHITS) simulations. The parameters of mesitylene and PE thickness, the reflector, and the shielding configuration were studied to increase cold neutron intensities within [0.1 meV, 10 meV] and thermal neutron intensities within [10 meV, 100 meV]. Consequently, an integrated cold neutron intensity of 1.15 ×103n/cm2∕μA at 2 m from the neutron-producing target was finally achieved, which was 12 times higher than that of the current RANS moderator with 4 cm PE according to simulation results. The cold and thermal neutron intensities of the optimized cold neutron moderator was compared with a cold neutron source based on solid methane, which has a beryllium target and the same proton energy as RANS. The results showed attractive application prospect of mesitylene as cold neutron moderator material.

Simulation code for estimating external gamma-ray doses from a radioactive plume and contaminated ground using a local-scale atmospheric dispersion model.

In this study, we developed a simulation code powered by lattice dose-response functions (hereinafter SIBYL), which helps in the quick and accurate estimation of external gamma-ray doses emitted from a radioactive plume and contaminated ground. SIBYL couples with atmospheric dispersion models and calculates gamma-ray dose distributions inside a target area based on a map of activity concentrations using pre-evaluated dose-response functions. Moreover, SIBYL considers radiation shielding due to obstructions such as buildings. To examine the reliability of SIBYL, we investigated five typical cases for steady-state and unsteady-state plume dispersions by coupling the Gaussian plume model and the local-scale high-resolution atmospheric dispersion model using large eddy simulation. The results of this coupled model were compared with those of full Monte Carlo simulations using the particle and heavy-ion transport code system (PHITS). The dose-distribution maps calculated using SIBYL differed by up to 10% from those calculated using PHITS in most target locations. The exceptions were locations far from the radioactive contamination and those behind the intricate structures of building arrays. In addition, SIBYL's computation time using 96 parallel processing elements was several tens of minutes even for the most computationally expensive tasks of this study. The computation using SIBYL was approximately 100 times faster than the same calculation using PHITS under the same computation conditions. From the results of the case studies, we concluded that SIBYL can estimate a ground-level dose-distribution map within one hour with accuracy that is comparable to that of the full Monte Carlo simulation.

Measurement of thick target neutron yield at 180°for a mercury target induced by 3-GeV protons

A thick target neutron yield (TTNY) for a mercury target at an angle of 180°from the incident beam direction was measured with the time-of-flight method using a 3-GeV proton beam at the Japan Proton Accelerator Research Complex (J-PARC). Comparison of the experimental results with a Monte Carlo particle transport simulation by the Particle and Heavy Ion Transport code System (PHITS) shows that the default spallation model of PHITS, the Liège intranuclear cascade model version 4.6 coupled with the generalized evaporation model (INCL4.6/GEM) reproduces the measured TTNY fairly well, whereas apparent overestimation is observed for the former default model, the Bertini intranuclear cascade model coupled with GEM (Bertini/GEM). These trends are consistent with the experimental results of neutron-induced reaction rates obtained using indium and niobium activation foils.

Multimodal Monte Carlo treatment system capable of microdosimetry with PHITS

Boron neutron capture therapy (BNCT) is a radiation therapy that combines neutrons and boron drugs. An industry-academia-government collaboration team is currently developing the linac-based treatment device and several peripheral devices to establish this therapy. In the project, a demonstration device, “iBNCT001”, for a linac-based neutron source applicable to BNCT treatment is being developed. We are developing Tsukuba Plan, a multimodal Monte Carlo-based treatment planning system, in addition to the linac-based neutron source device. Tsukuba-Plan has adopted a Particle and Heavy Ion Transport code System (PHITS) as the Monte Carlo-based dose calculation engine. PHITS has a microdosimetric function that can compute a lineal energy distribution and determine relative biological effectiveness through combination with the stochastic microdosimetric kinetic model parameters. By utilising these functions, Tsukuba-Plan is expected to estimate the weighted doses administered to the tumour region and normal tissues in the irradiation field more accurately.

Relation between biomolecular dissociation and energy of secondary electrons generated in liquid water by fast heavy ions

In this work, we measured and simulated the dissociation of biomolecules in liquid water induced by secondary electrons ejected from water molecules during fast heavy-ion irradiation. We calculated the energy spectra of secondary electrons generated along carbon ion tracks in liquid water in the Bragg peak region. The calculation was done using the Particle and Heavy Ion Transport code System (PHITS) in carbon track structure mode. This mode enables simulation of inelastic collisions along a carbon ion track based on the cross sections considered in the Monte Carlo code KURBUC. To understand the biomolecular dissociation processes in our previous MeV-SIMS experiments with microdroplet targets of glycine solution, we calculated the collision spectra of secondary electrons produced near liquid surfaces using PHITS. Furthermore, we examined the relationship between the secondary electron energy and formation of positive and negative glycine fragments. The results showed that the formation of methylene amine cations is caused by secondary electrons with energies of 13–100 eV. The formation of glycine-related negative ions such as cyanide anion, formate anion, and deprotonated glycine was found to be caused by low-energy (less than 13 eV) secondary electrons. These ions are known products of dissociative electron attachment.

Encapsulated Gamma Source Contact Dose Conversion Factors: Updating NCRP-40 Guidance.

Secondary electron generation on the surface of encapsulated gamma sources can play a large role in the dose measured near the surface of the encapsulation. The National Council on Radiation Protection and Measurements Report No. 40 contains contact dose rate conversion factors for encapsulated gamma sources, along with recommended secondary electron correction factors. However, secondary electron correction factors were based on experiments performed in the 1930s and 1940s with encapsulated radium sources, and the correction factors for the other sources listed in the report were estimated based on these radium source measurements. Monte Carlo simulations were performed using the Particle and Heavy Ion Transport code System (PHITS) to calculate the contact dose rate conversion factors for each encapsulated gamma source presented in NCRP-40, taking into account the dose from both gamma rays and secondary electrons. These simulations showed that the contact dose rate conversion factors are much lower than those presented in NCRP-40, and the secondary electron contribution was much greater than the values proposed by NCRP-40. The original research used results from encapsulated 226Ra experiments to determine the secondary electron correction factors for NCRP-40. To support the current Monte Carlo calculations, experiments were conducted using an encapsulated 137Cs source, rare earth magnet, and ion chamber detector to show that the secondary electron correction factors presented in NCRP-40 were not applicable to the geometry of tissue in direct contact with the encapsulation. In this work, contact dose conversion factors for common encapsulated radionuclide sources are presented.

Development of INC-ELF version 2 and incorporation into PHITS: Extension to lower incident energies down to 30 MeV

Version 2 of the Intranuclear Cascade with Emission of Light Fragments (INC-ELF) code is developed and incorporated into the Particle and Heavy Ion Transport code System (PHITS). The aim of INC-ELF2 is to expand it to the lower incident-energy range of 30–200 MeV, where the original INC theory is not applicable. The refinement of the code is based faithfully on the results of basic research on direct reactions within the framework of the INC model. INC-ELF2 can deal with the emission of light fragments from nuclear reactions induced by protons and neutrons. Double-differential cross-sections are calculated by a two-step model combining INC-ELF2 and GEM (generalized evaporation model) in PHITS, and they are compared with experimental data to examine the predictive ability. Excellent agreement is confirmed for various reactions over a wide range of target masses and over the incident-energy range of 30–200 MeV.

Dose Analysis of Boron Neutron Capture Therapy (BNCT) Treatment for Lung Cancer Based on Particle and Heavy Ion Transport Code System (PHITS)

The objectives of this study were to determine the effect of boron concentration on total dose rate for lung cancer treatment, and to determine the effect of boron concentration on the length of irradiation time for lung cancer treatment. This study was computer simulation-based using the Particle and Heavy Ion Transport code System (PHITS) by defining the geometry and components of lung cancer and the surrounding organism as the object being studied and the source of radiation used. The type of phantom used was the ORNL of an adult Asian male. The neutron source used was Kartini Reactor. The independent variable was the boron concentration of 30, 40, 50, 60, and 70 ?g/g cancer tissue and the dependent variables were the dose rate and the irradiation time. The results of this study indicated that the larger the amount of boron concentration that was injected, the higher the rate of total dose the organ received, where the total dose rate for each variation of boron concentration were 1.34 × 10-3 Gy/s, 1.71 × 10-3 Gy/s, 2.07 × 10-3 Gy/s, 2.42 × 10-3 Gy/s, and 2.78 × 10-3 Gy/s, and the larger the amount of boron concentration that was injected, the faster the irradiation time for the treatment of lung cancer was, where the irradiation time required for each variation of boron concentration was 37294 s, 29240 s, 24180 s, 20633 s, and 17996 s.

Conceptual design of a subcritical research reactor for inertial fusion energy with the J-EPoCH facility

The Japan Establishment for a Power-laser Community Harvest (J-EPoCH) is proposed as a next generation laser facility having multi-purpose high repetition laser beams at the maximum rate of 100 Hz. One of the experimental areas is assigned for laser fusion research. The omnidirectional 12 laser beams with 8 kJ and a 5 PW heating laser are arranged. A Large High Aspect Ratio Target (LHART) with the laser beams would yield ~1013 neutrons. The fusion energy corresponds to ~22 J/shot. As one of the J-EPoCH applications, a laser fusion subcritical research reactor with replaceable cores has been conceptually designed based on existing technologies. Moreover,we can conduct a variety of fusion engineering studies: energy conversion, tritium breeding, neutron irradiation effects and other subjects. The feasibility of tritium breeding and preliminary energy conversion studies are proven according to calculations by the Particle and Heavy Ion Transport code System (PHITS).

Internal exposure rate conversion coefficients and absorbed fractions of mouse for 137Cs, 134Cs and 90Sr contamination in body.

The aim of this study was to determine parameters for estimating the internal exposure of all organs in mouse experiments from the radioactivity concentration in organs. The estimation of internal exposure rate conversion coefficients and absorbed fractions for 137Cs, 134Cs and 90Sr by the Particle and Heavy Ion Transport code System (PHITS) with a voxel-based mouse phantom is presented. The geometry of the voxel phantom is constructed from computer tomography images of a mouse 9cm in length weighing 23.9g. The voxel-based mouse phantom has the following organs: brain, skull, heart, lungs, liver, stomach, spleen, kidneys, bladder, testis and tissue (tissue and other organs). Gamma- and beta-rays from 137Cs, 134Cs and 90Sr sources in each source organ are generated and scored for every target organ. The internal exposure rate conversion coefficients and absorbed fractions are calculated from deposition energies in each target organ from each source organ and are used to generate an internal exposure rate conversion coefficient matrix and an absorbed fraction matrix. The absorbed fractions of beta-rays in the source organs are roughly 0.5-0.8 for 137Cs and 134Cs, and the absorbed fractions of gamma-rays are <0.04 for 137Cs and <0.03 for 134Cs. The internal exposure rate conversion coefficient matrix is defined using the absorbed fractions. The calculated internal exposure rate coefficient matrix is tested under a uniform radioactivity concentration of 1Bq/kg for 137Cs, 134Cs and 90Sr. The estimated internal exposure rates in the mouse whole body for 137Cs, 134Cs and 90Sr are 3.28×10-3, 2.55×10-3 and 1.20×10-2 μGy/d, respectively. These values are very similar to those for an ellipsoid frog (31.4g) and an ellipsoid crab egg mass (12.6g) reported in ICRP Publication 108.

Estimation of reliable displacements-per-atom based on athermal-recombination-corrected model in radiation environments at nuclear fission, fusion, and accelerator facilities

The displacements-per-atom (dpa) is widely used as an exposure unit to predict the operating lifetime of materials in radiation environments. Because the athermal-recombination-corrected dpa (arc-dpa) model is a more realistic model than the standard Norgett–Robinson–Torrens (NRT) model, new evaluation of radiation damage for various applications at nuclear fission, fusion, and accelerator facilities will be performed using the arc-dpa model as a standard. Determination of the rescaling factor from the NRT-dpa to arc-dpa model for various applications is also important. In this work, the recent arc-dpa model of various materials including C, Al, Si, Fe, Cu, and W are incorporated in the Particle and Heavy Ion Transport code System (PHITS), and the rescaling factors (NRT-dpa/arc-dpa) over a wide energy range are reported. For neutron incidences with the energy spectrum determined in selected nuclear facilities and proton incidences with energies of 600 MeV–50 GeV, the rescaling factor for each material is independent of these irradiation conditions with almost the same value for each material. This value is mainly determined by the saturation in the damage production efficiency in the damage energy region over approximately 1 keV. Our findings will be beneficial for rescaling the NRT-dpa used for radiation damage applications over a wide energy region at various facilities.

Evaluation of a back-illuminated solid state detector with thin dead layer for super heavy element research

The precise energy measurement of charged particles using a silicon semiconductor detector (SSD) is very important in studies of the characteristics of superheavy elements (SHEs). It is necessary to evaluate the dead layer thickness of the SSD to measure the recoil energy of charged particles, such as SHEs, and α particles or fission fragments that are emitted upon the successive decay from the SHEs. Since the energy resolution of the SSD depends on the thickness of the dead layer, a back-illuminated SSD with a thin dead layer has been introduced for SHE research. To evaluate the dead layer thickness of the SSD, energy spectra were first investigated by irradiating 241Am α particles at incident angles of 0° and 45° for two types of SSD. The dead layer thicknesses of the SSDs were deduced by a computer simulation using the particle and heavy ion transport code system (PHITS).

Evaluation for gamma-ray rejection ability affecting neutron discrimination property in scintillating-fiber type of fast neutron detector

Scintillating-fiber (Sci-Fi) detector has been employed to measure 14 MeV neutrons in the magnetic confinement fusion experiment. Design of the Sci-Fi detector reduces response to gamma-rays, compared to bulk scintillators, while at the same time enabling directional responses to energetic neutrons. Ability of gamma-ray rejection is an important parameter to judge the discrimination property for a fast neutron detector. In order to investigate the gamma-ray rejection abilities in the case of 2.45 MeV neutron and higher-energy neutrons, the pulse height spectra (PHS) of four different-head detectors in different diameter and with/without the aluminum (Al) matrix have been measured by using the accelerator-based neutron source with d–D reaction. Four different-head detectors show the different pulse height properties and the gamma-ray rejection abilities, which impact upon the neutron discrimination abilities. Meanwhile, simulations of detector responses have been performed using the Particle and Heavy Ion Transport code System (PHITS) to analyze the experimental results. Neutron discrimination abilities of small diameter Sci-Fi is better than that of large diameter Sci-Fi. Al matrix is beneficial to enhance 6.6–10 times difference of the gamma-ray rejection affecting the neutron discrimination ability in the case of Sci-Fi with/without Al matrix. It is also found that the neutron discrimination abilities of the Sci-Fi without the Al matrix and a plastic scintillator are the same.

Development of a predictive capability of short-pulse laser-driven broadband x-ray radiography

High intensity, short-pulse laser interaction with a solid metal target produces broadband hard x-rays potentially for various applications of x-ray radiography. Here experimental benchmarking of numerical modelling for short-pulse laser-driven broadband x-ray radiography is presented. Angular dependent x-ray spectra are first calculated with a hybrid particle-in-cell code, Large Scale Plasma (LSP), using fast electron parameters inferred from an analysis of measured bremsstrahlung signals. Subsequently, a calculated x-ray spectrum in the direction of radiography is used in photon transport calculations using a Monte Carlo code, Particle and Heavy Ion Transport code System (PHITS), to simulate a radiographic image including a modelled 3D test object, an x-ray attenuation filter and an image plate detector. Simulated radiographic images are compared with measurements obtained in an experiment using a 50-TW Leopard short-pulse laser at the University of Nevada Reno. Results show that simulations reproduce the experimental images well for three different attenuation filters (plastic, aluminium, and brass), while 1D transmission profiles for the plastic and aluminium filters are quantitatively in good agreement. The modelling approach established in this work could be used as a predictive tool to simulate radiographic images of complex 3D solid objects at any arbitrary angular position or to optimize experimental components such as the source spectrum, x-ray attenuation filters and a detector type depending on a radiographic object without carrying out radiographic experiments.