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Low-density films of single-walled carbon nanotubes (SWNTs) can be used as a semi-transparent top electrode for all-solution-processed film devices; however, their semiconductor characteristics vary depending on the experimental factors in their dispersion into solvents, and the sublayers are damaged as a result of solvent incompatibility. In this study, we report a solvent-compatible filter-transfer method for SWNT films stacked with silver nanowires (AgNWs), and evaluate the semiconductor characteristics through the p/n heterojunction with a Si wafer (SWNT/Si). AgNWs and SWNTs were successively filtered through their aqueous dispersion solutions using a membrane filter. The stacked semi-transparent films (AgNW/SWNT films with controlled densities) were successfully transferred onto glass plates and Si wafers. The transmittance at 550 nm revealed a window between 60% and 80% with a narrow sheet resistance range between 11 and 23 Ω □

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 accidenta...

The personal dose equivalent was calculated for the public (newborns; 1-, 5-, 10-, and 15-year-old children; and adults) in an environment contaminated with radioactive cesium (134Cs and 137Cs) distributed in a soil at specific depths of 0.0, 0.5, 2.5, 5.0, 10.0, and 50.0 g/cm2, and the conversion coefficients for converting activity concentration to personal dose equivalent rate were provided for each age group. Monte Carlo calculations were performed using pediatric and adult computational phantoms incorporated into a particle and heavy ion transport code system. Compared with the effective dose and ambient dose equivalent at a height of 100 cm above the ground, the personal dose equivalent was found to provide a good estimate as a measurable quantity for the effective dose and did not exceed the ambient dose equivalent even in the environmental radiation fields, while the personal dose equivalent values increased for younger subjects. The weighted-integral method to obtain the personal dose equ...

To estimate effective doses for members of the public exposed to external radiation from radioactive cesium (134Cs and 137Cs) deposited on the ground by the Fukushima nuclear accident, we calculate the conversion coefficients for converting activity concentration to effective dose rate by using the Particle and Heavy Ion Transport Code System. The data were produced from different age groups within the public (newborns; 1-, 5-, 10-, and 15-year-old children; and adults) for the situations in which radioactive cesium is distributed uniformly in the soil over a planar area and at specific depths of 0.0, 0.5, 2.5, 5.0, 10.0, and 50.0 g/cm2. On the basis of the results, we also derive the conversion coefficients for exponentially distributed volumetric sources. In addition, we obtain the conversion coefficients that give the effective dose accumulated over the first and second months, the first year, and over a lifetime (50 years) because of the contamination remaining on the ground. These calculations indica...

A calculation system for the estimation of decontamination effects (CDE) is developed in the present work to aid in the effective planning of decontamination procedures. This system calculates dose...

At the Fukui Prefectural Hospital Proton Therapy Center, neutron doses behind the concrete shields and at the maze were measured with three types of radiation monitors (DARWIN, Wendi-2, and a rem meter) along with solid-state nuclear track detectors. The measured data were compared with estimations of analytical models and the Monte Carlo code, Particle and Heavy-Ion Transport code System (PHITS). The analytical model, using the parameters employed in the shielding design of the facility, gave considerably larger values than the measured data. This means that the facility was designed with a sufficient margin of safety. The results calculated by PHITS were less than those of the analytical model and were about three times larger than the measured data. From a perspective that seeks conservative estimation with less margin, the Monte Carlo simulation is a good tool for shielding design of accelerator-based proton treatment facilities.

A simulation method to analyze all particle behavior inside a human body upon neutron exposure has been developed by incorporating the Japanese voxel phantoms into the Monte Carlo particle transport code PHITS. The absorbed doses in organs were calculated for idealized irradiation geometries in the energy range from 10−9 to 150MeV, and compared with the data of ICRP Publication 74 and the Visible Chinese Human phantom. While they agreed within 30% in most organs, some deviations due to variations in the internal structure of anthropomorphic phantoms were observed. The contributions of particle types and their energy distributions to absorbed doses were quantitatively clarified by utilizing the event generator mode of PHITS. It was found that the ratio of energies imparted to organs by charged particles significantly varies with the depth of target organs from the surface of the body. Upon 10−8 MeV irradiation, the proton contribution was about 10 times higher in the skin than in the stomach.

A shielding benchmark experiment has been performed to obtain the spectra of neutrons penetrating 10- to 100-cm-thick iron shields and 25- to 200-cm-thick concrete shields and to investigate the accuracy of various calculation codes using a 137-MeV quasi-monoenergetic neutron source. The source neutrons are produced from a 1.0-cm-thick lithium target bombarded with 140-MeV protons, and the energy spectra are measured with the time-of-flight (TOF) method using a NE213 organic liquid scintillator. The neutrons emitted in the forward direction were collimated with a 150-cm-thick iron collimator with 10- X 12-cm aperture. TOF and unfolding methods are applied to obtain the energy spectra behind the shield for the peak energy region and continuous-energy region, respectively. Monte Carlo calculations with PHITS and MCNPX are compared with the measured data. The comparison shows that the calculated spectra are in good agreement with the measured spectra.

A shielding benchmark experiment has been performed to obtain the experimental data of neutrons penetrated through iron and concrete shields by using 140-, 250-, and 350-MeV p-Li quasi-monoenergeti...

Neutron energy spectra at 90 deg produced from stopping-length graphite, aluminum, iron, and lead targets and at 180 deg produced from a thin lithium target bombarded with 140-MeV protons were measured in the irradiation room of the neutron time-of-flight (TOF) course at the Research Center of Nuclear Physics of Osaka University. The neutron energy spectra were obtained by using the TOF technique in the energy range from 10 MeV to the incident proton energy of 140 MeV. The experimental data for a thick target at 90 deg were compared with calculations performed with the Particle and Heavy Ion Transport code System (PHITS) using the evaluated nuclear data. It was shown that PHITS using the evaluated nuclear data is able to reproduce the secondary neutron spectra at 90 deg. The experimental data for a thin target at 180 deg were compared with calculations using the nuclear physics models in PHITS and the Monte Carlo N-Particle eXtended code (MCNPX). We found that the two codes work well at 180 deg in the neutron energy region above 10 MeV.

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.

Neutron-production double-differential cross sections of iron and lead for 0.8 and 1.5 GeV protons incidences were measured in the most-forward direction. Neutrons were measured by the time-of-flight (TOF) method. An NE213 liquid organic scintillator was set at 0° as a neutron detector. Neutron detection efficiencies were obtained by calculations with a Monte Carlo simulation code SCINFUL-QMD. The present experimental data were compared with other reported experimental data and the results of calculation codes based on Intranuclear-Cascade-Evaporation (INC/E) and Quantum Molecular Dynamics (QMD) models. For neutrons associated with Δ formation, the present data deviated from predictions of these codes, and gave magnitudes between them in both 0.8 and 1.5 GeV incidences.

The Monte Carlo code, designeted SCINFUL-QMD, has been developed to calculate neutron detection efficiency up to 3 GeV for liquid organic scintillators such as NE-213. The existing Monte Carlo code, SCINFUL, is known to reproduce a response function and detection efficiency at incident neutron energies below 80 MeV. We incorporate the quantum molecular dynamics plus statistical decay model (QMD+SDM) into SCINFUL to extend the upper limit of incident neutron energy to 3 GeV. The results by SCINFUL-QMD are compared with experimental data and those of CECIL. The SCINFUL-QMD exhibits an increase in detection efficiency above 300 MeV. This tendency agrees with one of the experimental data. The increase is achived by taking charged pion production into account.

Neutron-production double-differential cross sections in the most-forward directions were measured for proton-induced reactions on Fe and Pb targets at 0.8 and 1.5 GeV. The experiment was performed...

Neutron-production double-differential cross sections for 870-MeV π+ and π− and 2.1-GeV π+ mesons incident on iron and lead targets were measured with NE213 liquid scintillators by time-of-flight technique. NE213 liquid scintillators 12.7 cm in diameter and 12.7 cm thick were placed in directions of 15, 30, 60, 90, 120 and 150°. The typical flight path length was 1.5 m. Neutron detection efficiencies were derived from the calculation results of SCINFUL and CECIL codes. The experimental results were compared with the JAM code. The double differential cross sections calculated by the JAM code disagree with experimental data at neutron energies below about 30 MeV. JAM overestimates π+-incident neutron-production cross sections in forward angles at neutron energies of 100 to 500 MeV.