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In radiation physics, Monte Carlo radiation transport simulations are powerful tools to evaluate the cellular responses after irradiation. When investigating such radiation-induced biological effects, it is essential to perform track structure simulations by explicitly considering each atomic interaction in liquid water at the sub-cellular and DNA scales. The Particle and Heavy-Ion Transport code System (PHITS) is a Monte Carlo code which enables to calculate track structure at DNA scale by employing the track-structure modes for electrons, protons and carbon ions. In this paper, we review the recent development status and future prospects of the track-structure modes in the PHITS code.To date, the physical features of these modes have been verified using the available experimental data and Monte Carlo simulation results reported in literature. These track-structure modes can be used for calculating microdosimetric distributions to estimate cell survival and for estimating initial DNA damage yields. The use of PHITS track-structure mode is expected not only to clarify the underlying mechanisms of radiation effects but also to predict curative effects in radiation therapy. The results of PHITS simulations coupled with biophysical models will contribute to the radiobiological studies by precisely predicting radiation-induced biological effects based on the Monte Carlo approach.

In the present work, the authors propose a standard analytical method to estimate systematic uncertainties in the Monte Carlo particle transport simulation based on analysis of variance (ANOVA). As...

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 ...

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.

We have constructed models for muon interactions (i.e., bremsstrahlung, electron–positron pair production, muon photonuclear interaction, and negative muon capture reaction) and implemented these models in the particle and heavy ion transport code system (PHITS). The PHITS2.86 agrees well with experimental data for the vertical intensities of cosmic-ray muons in water and standard rock. The calculated results for neutron production by muon photonuclear interaction and negative muon capture reaction are in good agreement with measured data, except in the case of lead target. PHITS2.86 can also reproduce the cross-section of radionuclide production by muons passing through a concrete wall very well. These results indicate the applicability of PHITS2.86 to the shielding design of muon facilities in which estimations of attenuation length and induced radioactivity are important.

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.

The impact of different spallation models and parametrisation of nucleon–nucleus interactions in the particle transport code PHITS on the nuclear characteristics of an accelerator-driven system (ADS) is investigated. Cut-off neutrons below 20 MeV calculated using the default option of the current spallation model (i.e. Liege intranuclear cascade (INC) model version 4.6, INCL4.6) are found to be 14% less than those calculated by the old spallation model (i.e. Bertini INC model). This decrease increases the proton beam current that drives the 800-MW thermal power and impacts various ADS parameters, including material damage, nuclear heating of the proton beam window and the inventory of spallation products. To validate these options based on the ADS neutronics design, we conduct benchmark calculations of the total and non-elastic cross sections, thick target neutron yields and activation reaction rate distributions. The results suggest that Pearlstein–Niita systematics, which is a default option of ...

Secondary cosmic-ray neutron-induced soft errors in an n-type metal-oxide-semiconductor field-effect transistor are analyzed based on the multiple sensitive volume (MSV) model using Particle and He...

To improve radiation safety in high-energy accelerator facilities, the authors have been developing the new radiation dose monitor device DARWIN: Dose monitoring system Applicable to various Radiations with WIde energy raNges. DARWIN is composed of (a) a phoswitch-type scintillation detector, which consists of liquid organic scintillator BC501A coupled with ZnS(Ag) scintillation sheets doped with 6 Li, and (b) a data acquisition (DAQ) system for digital analysis of the waveform of the scintillator signals. The DAQ system was recently updated in order to apply DARWIN in monitoring dose rates in radiation fields having time structure, introducing an originally developed module based on a field-programmable gate array. To examine the performance of DARWIN placed in radiation fields composed of varieties of particles over wide energy ranges, the authors mounted DARWIN on a jet aircraft and measured neutron, photon, muon, electron, and positron dose rates at high altitudes. The measured dose rates excellently agreed with the corresponding data calculated by EXPACS over a wide altitude range. This agreement indicates the applicability of DARWIN to dose monitoring in complex radiation fields such as those in high-energy accelerator facilities and aircrafts.

Response functions of a BC501A liquid organic scintillator for neutrons up to 800 MeV have been measured at the heavy-ion accelerator of the National Institute of Radiological Sciences, Japan. A thick graphite target was bombarded with 400-MeV/u C ions and 800-MeV/u Si ions to produce high-energy neutrons whose kinetic energy was determined by the time-of-flight method. The measured response functions were compared with the results obtained using SCINFUL-QMD code, and the accuracy of the code was experimentally verified up to 800 MeV. This work will contribute to extending the energies measurable with our new radiation dose-monitoring system (DARWIN), which is based on the BC501A scintillator.

Photoneutron spectra produced from thin targets bombarded with 2.04 GeV electrons were measured in the range from 9 MeV to 300 MeV by using the time of flight technique. The measurements were carried out for thin C, Al, Cu, Sn, and Pb targets at a fixed angle of 900 to the beam direction. In this data reduction a removal cross-section was newly calculated for compensating the effect of the Pb attenuator which was set to suppress γ-flash signal. The double differential yields per incident electron were obtained from the spectra as a function of the mass number of target elements. For neutron energies larger than 20 MeV the yields decreased with higher mass number of the target, which was consistent with other authors’ published results.

Photo-neutron spectra produced by 2.04 GeV electron incident on thick A1, Cu, Sn and Pb targets were measured by TOF method. An efficiency of used detector PILOT-U was calculated by SCINFUL and Cecil’s code. The efficiency was also measured for neutron energies at 14.9, 33, 66.0, 86.5, and 132.0 MeV to confirm the calculated results. However, there is a discrepancy between those two results. A Pb attenuator was placed at the middle point of the flight path to suppress γ-flash signals. The thickness of the attenuator was changed from 10 cm to 30 cm for each target, and the effects of the attenuator on the neutron spectra were calculated by a combination of small changed LAHET code and ENDF-HE/VI data. Obtained neutron spectra from each attenuator case were agreed with each other for neutron energy from 10 MeV to 300 MeV.

Thick beam stops were bombarded by 2-25 GeV electrons. The Al foils and liquid containers were placed at the several depth in 10-radiation-length thick beam stop made of Cu plates. The containers were filled with the water or xylene (C8H10). The residual radioactivity was measured using activation gamma-ray spectroscopy. Tritium production yields in Al, O and C were measured using liquid scintillation counters. Depth distribution of the residual activity in the beam dumps were calculated using EGS4 and PICA3 Monte Carlo code.

Tatsuhiko Sato, Kazuyuki Emi, Yui Osawa, Hajime Bando Osaka Rosai Hospital Clinical Research Center for Occupational Sensory Organ Disability, Sakai, Japan Background: Fundus autofluorescence studies in eyes with macular holes (MHs) have shown a hyperautofluorescent spot corresponding to the hole and a hypoautofluorescent ring corresponding to the fluid cuff surrounding the hole. The purpose of this report is to present three cases of MH with a different fundus autofluorescence pattern. Case reports: Case 1 was a 62-year-old woman who did not know the duration of the MH in her left eye. Her decimal best-corrected visual acuity (BCVA) was 0.08. The left eye had a one-half disc diameter MH with a depigmented ring surrounding the area of the fluid cuff. Fundus autofluorescence showed a hyperautofluorescent ring corresponding to the depigmented ring. After vitrectomy, fundus autofluorescence showed the same size hyperautofluorescent ring despite the decreased size of the opened MH. Case 2 was a 69-year-old woman who had been diagnosed with MH in the right eye 13 years earlier. Her decimal BCVA was 0.1. The right eye had a one-half disc diameter MH with a depigmented ring surrounding the area of the fluid cuff. Fundus autofluorescence showed a hyperautofluorescent ring corresponding to the depigmented ring. Postoperative fundus autofluorescence showed the same size hyperautofluorescent ring despite the hole being closed. The decimal BCVA was 0.2 in her right eye 6 months after vitrectomy. Case 3 was a 71-year-old woman who had been diagnosed with MH in the right eye 15 years earlier. Her decimal BCVA was 0.1. The right eye had a one-half disc diameter MH with a depigmented ring which corresponded with a hyperautofluorescent ring. Postoperative fundus autofluorescence showed the same size hyperautofluorescent ring despite the hole being closed. The decimal BCVA was 0.2 in her right eye 6 months after vitrectomy. Conclusion: Our findings suggest that a hyperautofluorescent ring in eyes with MHs may be an indicator of a poor surgical prognosis both anatomically and functionally. Keywords: macular hole, fundus autofluorescence, vitrectomy, predictor

Tatsuhiko Sato, Kazuyuki Emi, Hajime Bando, Toshihide IkedaOsaka Rosai Hospital Clinical Research Center for Occupational Sensory Organ Disability, Sakai, JapanBackground and methods: We compared surgical procedures and outcomes, including duration of recovery period, in eyes with proliferative diabetic retinopathy that underwent 25-gauge microincision vitrectomy surgery with those that underwent 20-gauge vitrectomy. Seventy-two eyes from 53 patients that underwent 20-gauge vitrectomy in 2006 and 87 eyes from 55 patients that underwent 25-gauge vitrectomy in 2010 were studied. The surgical procedures, ie, number of vitreous procedures, operating time, and ratio of type of intraocular tamponade were compared between the two groups. In addition, the outcomes, ie, postoperative complications, anatomical success, postoperative best-corrected visual acuity (BCVA), and duration of hospitalization as an indicator of the postoperative recovery period were also compared.Results: There were no significant differences in surgical procedures or ratio of cases with postoperative complications between cases with 20-gauge and 25-gauge vitrectomy. The final anatomical success rate was 100% in the two groups. BCVA at 6 months after the final vitrectomy was significantly better than the preoperative BCVA for both types of vitrectomy (P < 0.05), and was not significantly different between the two groups. The average duration of hospitalization was 19.5 days after 20-gauge vitrectomy, which was significantly longer than the 11.0 days after 25-gauge vitrectomy (P < 0.001).Conclusion: These results indicate that the anatomical and functional improvements after 25-gauge microincision vitrectomy surgery are not significantly different from those after 20-gauge vitrectomy in eyes with proliferative diabetic retinopathy. However, the significantly shorter recovery period after 25-gauge microincision vitrectomy surgery suggests that it is less traumatic than 20-gauge vitrectomy.Keywords: vitrectomy, 25-gauge vitrectomy, microincision vitrectomy surgery, diabetic retinopathy, postoperative recovery