COMPARISON OF COSMIC-RAY ENVIRONMENTS ON EARTH, MOON, MARS AND IN SPACECRAFT USING PHITS.

Estimation of cosmic-ray doses is of great importance not only in aircrew and astronaut dosimetry but also in evaluation of background radiation exposure to public. We therefore calculated the cosmic-ray doses on Earth, Moon and Mars as well as inside spacecraft, using Particle and Heavy Ion Transport code System PHITS. The same cosmic-ray models and dose conversion coefficients were employed in the calculation to properly compare between the simulation results for different environments.

Measurements of electron-induced neutrons as a tool for determination of electron temperature of fast electrons in the task of optimization laser-produced plasma ions acceleration.

High intensity laser-plasma interaction has attracted considerable interest for a number of years. The laser-plasma interaction is accompanied by generation of various charged particle beams, such as high-energy proton and ions with high charge to mass ratio (Q/M; same as multi-charged ions). Results of simultaneous novel measurements of electron-induced photonuclear neutrons (photoneutron), which are a diagnostic of the laser-plasma interaction, are proposed to use for optimization of the laser-plasma ion generation.

[Features of PHITS and its application to medical physics].

PHITS is a general purpose Monte Carlo particle transport simulation code to analyze the transport in three-dimensional phase space and collisions of nearly all particles, including heavy ions, over wide energy range up to 100 GeV/u. Various quantities, such as particle fluence and deposition energies in materials, can be deduced using estimator functions "tally". Recently, a microdosimetric tally function was also developed to apply PHITS to medical physics.

Development of a single-shot-imaging thin film for an online Thomson parabola spectrometer.

A single-shot-imaging thin scintillator film was developed for an online Thomson parabola (TP) spectrometer and the first analysis of laser accelerated ions, using the online TP spectrometer, was demonstrated at the JAEA-Kansai Advanced Relativistic Engineering Laser System (J-KAREN). An energy spectrum of ~4.0 MeV protons is obtained using only this imaging film without the need of a microchannel plate that is typically utilized in online ion analyses.

Applications of the microdosimetric function implemented in the macroscopic particle transport simulation code PHITS.

Purpose: Microdosimetric quantities such as lineal energy are generally considered to be better indices than linear energy transfer (LET) for expressing the relative biological effectiveness (RBE) of high charge and energy particles. To calculate their probability densities (PD) in macroscopic matter, it is necessary to integrate microdosimetric tools such as track-structure simulation codes with macroscopic particle transport simulation codes.

Methods: As an integration approach, the mathematical model for calculating the PD of microdosimetric quantities developed based on track-structure simulations was incorporated into the macroscopic particle transport simulation code PHITS (Particle and Heavy Ion Transport code System).

Impact of the introduction of ICRP Publication 103 on neutron dosimetry.

The impact of the introduction of ICRP Publication 103 on neutron dosimetry was analysed by calculating effective doses in various operational neutron fields, using dose conversion coefficients derived from the recommendations given in ICRP 103 and ICRP 60. It was found from the analysis that effective doses based on ICRP 103 are generally smaller than those based on ICRP 60, mainly owing to the revision of w(R) assigned to neutrons. The results also indicate that H*(10) can provide a conservative estimate for ICRP 103-based effective doses in most neutron fields.

Comparison of fluence-to-dose conversion coefficients for deuterons, tritons and helions.

Secondary radiation in aircraft and spacecraft includes deuterons, tritons and helions. Two sets of fluence-to-effective dose conversion coefficients for isotropic exposure to these particles were compared: one used the particle and heavy ion transport code system (PHITS) radiation transport code coupled with the International Commission on Radiological Protection (ICRP) reference phantoms (PHITS-ICRP) and the other the Monte Carlo N-Particle eXtended (MCNPX) radiation transport code coupled with modified BodyBuilder™ phantoms (MCNPX-BB). Also, two sets of fluence-to-effective dose equivalent conversion coefficients calculated using the PHITS-ICRP combination were compared: one used quality factors based on linear energy transfer; the other used quality factors based on lineal energy (y).

Analysis of cell-survival fractions for heavy-ion irradiations based on microdosimetric kinetic model implemented in the particle and heavy ion transport code system.

It is considered that the linear energy transfer (LET) may not be the ideal index for expressing the relative biological effectiveness (RBE) of cell killing for heavy-ion irradiation, as the ion-species dependencies have clearly been observed in the relation between LET and RBE derived from cell-survival fraction data. The previously measured survival fractions of four cell lines irradiated by various ion species, employing the saturation-corrected dose-mean lineal energy, y*, instead of LET as the index of the RBE were therefore re-analysed. In the analysis, the initial slopes of the survival fractions, the so-called α-parameter in the linear-quadratic model, were plotted as a function of y*, which was calculated by the microdosimetric kinetic (MK) model implemented in the Particle and Heavy Ion Transport code System.

Dose estimation for astronauts using dose conversion coefficients calculated with the PHITS code and the ICRP/ICRU adult reference computational phantoms.

Absorbed-dose and dose-equivalent rates for astronauts were estimated by multiplying fluence-to-dose conversion coefficients in the units of Gy.cm(2) and Sv.cm(2), respectively, and cosmic-ray fluxes around spacecrafts in the unit of cm(-2) s(-1).

Fluence-to-dose conversion coefficients for heavy ions calculated using the PHITS code and the ICRP/ICRU adult reference computational phantoms.

The fluence to organ-absorbed-dose and effective-dose conversion coefficients for heavy ions with atomic numbers up to 28 and energies from 1 MeV/nucleon to 100 GeV/nucleon were calculated using the PHITS code coupled to the ICRP/ICRU adult reference computational phantoms, following the instruction given in ICRP Publication 103 (2007 (Oxford: Pergamon)). The conversion coefficients for effective dose equivalents derived using the radiation quality factors of both Q(L) and Q(y) relationships were also estimated, utilizing the functions for calculating the probability densities of absorbed dose in terms of LET (L) and lineal energy (y), respectively, implemented in PHITS. The calculation results indicate that the effective dose can generally give a conservative estimation of the effective dose equivalent for heavy-ion exposure, although it is occasionally too conservative especially for high-energy lighter-ion irradiations.

Estimating neutron dose equivalent rates from heavy ion reactions around 10 MeV amu(-1) using the PHITS code.

It has been sometimes necessary for personnel to work in areas where low-energy heavy ions interact with targets or with beam transport equipment and thereby produce significant levels of radiation. Methods to predict doses and to assist shielding design are desirable. The Particle and Heavy Ion Transport code System (PHITS) has been typically used to predict radiation levels around high-energy (above 100 MeV amu(-1)) heavy ion accelerator facilities.

Fluence-to-dose conversion coefficients for neutrons and protons calculated using the PHITS code and ICRP/ICRU adult reference computational phantoms.

The fluence to organ-dose and effective-dose conversion coefficients for neutrons and protons with energies up to 100 GeV was calculated using the PHITS code coupled to male and female adult reference computational phantoms, which are to be released as a common ICRP/ICRU publication. For the calculation, the radiation and tissue weighting factors, w(R) and w(T), respectively, as revised in ICRP Publication 103 were employed. The conversion coefficients for effective dose equivalents derived using the radiation quality factors of both Q(L) and Q(y) relationships were also estimated, utilizing the functions for calculating the probability densities of the absorbed dose in terms of LET (L) and lineal energy (y), respectively, implemented in PHITS.

Biological dose estimation for charged-particle therapy using an improved PHITS code coupled with a microdosimetric kinetic model.

Microdosimetric quantities such as lineal energy, y, are better indexes for expressing the RBE of HZE particles in comparison to LET. However, the use of microdosimetric quantities in computational dosimetry is severely limited because of the difficulty in calculating their probability densities in macroscopic matter. We therefore improved the particle transport simulation code PHITS, providing it with the capability of estimating the microdosimetric probability densities in a macroscopic framework by incorporating a mathematical function that can instantaneously calculate the probability densities around the trajectory of HZE particles with a precision equivalent to that of a microscopic track-structure simulation.

Calculation of energy-deposition distributions and microdosimetric estimation of the biological effect of a 9C beam.

Among the alternative beams being recently considered for external cancer radiotherapy, (9)C has received some attention because it is expected that its biological effectiveness could be boosted by the beta-delayed emission of two alpha particles and a proton that takes place at the ion-stopping site. Experiments have been performed to characterise this exotic beam physically and models have been developed to estimate quantitatively its biological effect. Here, the particle and heavy-ion transport code system ( PHITS ) is used to calculate energy-deposition and linear energy transfer distributions for a (9)C beam in water and the results are compared with published data.

Development of PARMA: PHITS-based analytical radiation model in the atmosphere.

Estimation of cosmic-ray spectra in the atmosphere has been essential for the evaluation of aviation doses. We therefore calculated these spectra by performing Monte Carlo simulation of cosmic-ray propagation in the atmosphere using the PHITS code. The accuracy of the simulation was well verified by experimental data taken under various conditions, even near sea level.

Development of a calculation method for estimating specific energy distribution in complex radiation fields.

Estimation of the specific energy distribution in a human body exposed to complex radiation fields is of great importance in the planning of long-term space missions and heavy ion cancer therapies. With the aim of developing a tool for this estimation, the specific energy distributions in liquid water around the tracks of several HZE particles with energies up to 100 GeV n(-1) were calculated by performing track structure simulation with the Monte Carlo technique. In the simulation, the targets were assumed to be spherical sites with diameters from 1 nm to 1 microm.

Analytical functions to predict cosmic-ray neutron spectra in the atmosphere.

Estimation of cosmic-ray neutron spectra in the atmosphere has been an essential issue in the evaluation of the aircrew doses and the soft-error rates of semiconductor devices. We therefore performed Monte Carlo simulations for estimating neutron spectra using the PHITS code in adopting the nuclear data library JENDL-High-Energy file. Excellent agreements were observed between the calculated and measured spectra for a wide altitude range even at the ground level.

Comparison between calculation and measured data on secondary neutron energy spectra by heavy ion reactions from different thick targets.

Measured neutron energy fluences from high-energy heavy ion reactions through targets several centimeters to several hundred centimeters thick were compared with calculations made using the recently developed general-purpose particle and heavy ion transport code system (PHITS). It was confirmed that the PHITS represented neutron production by heavy ion reactions and neutron transport in thick shielding with good overall accuracy.

Simulations of an accelerator-based shielding experiment using the particle and heavy-ion transport code system PHITS.

In order to estimate the biological effects of HZE particles, an accurate knowledge of the physics of interaction of HZE particles is necessary. Since the heavy ion transport problem is a complex one, there is a need for both experimental and theoretical studies to develop accurate transport models. RIST and JAERI (Japan), GSI (Germany) and Chalmers (Sweden) are therefore currently developing and bench marking the General-Purpose Particle and Heavy-Ion Transport code System (PHITS), which is based on the NMTC and MCNP for nucleon/meson and neutron transport respectively, and the JAM hadron cascade model.

Analysis of dose-LET distribution in the human body irradiated by high energy hadrons.

For the purposes of radiological protection, it is important to analyse profiles of the particle field inside a human body irradiated by high energy hadrons, since they can produce a variety of secondary particles which play an important role in the energy deposition process, and characterise their radiation qualities. Therefore Monte Carlo calculations were performed to evaluate dose distributions in terms of the linear energy transfer of ionising particles (dose-LET distribution) using a newly developed particle transport code (Particle and Heavy Ion Transport code System, PHITS) for incidences of neutrons, protons and pions with energies from 100 MeV to 200 GeV. Based on these calculations, it was found that more than 80% and 90% of the total deposition energies are attributed to ionisation by particles with LET below 10 keV microm(-1) for the irradiations of neutrons and the charged particles, respectively.

Conversion coefficients from fluence to effective dose for heavy ions with energies up to 3 GeV/A.

Radiological protection against high-energy heavy ions has been an essential issue in the planning of long-term space missions. The fluence to effective dose conversion coefficients have been calculated for heavy ions using the particle and heavy ion transport code system PHITS coupled with an anthropomorphic phantom of the MIRD5 type. The calculations were performed for incidences of protons and typical space heavy ions--deuterons, tritons, 3He, alpha particles, 12C, 20Ne, 40Ar, 40Ca and 56Fe--with energies up to 3 GeV/A in the isotropic and anterior-posterior irradiation geometries.

Oxidative folding of human lysozyme: effects of the loss of two disulfide bonds and the introduction of a calcium-binding site.

Mutant human lysozymes (HLZ) lacking two disulfide bonds were constructed to study the importance of each disulfide bond on oxidative refolding. To avoid destabilization, a calcium-binding site was introduced. Five of the six species of two-disulfide mutants could be obtained with enzymatic activity.