Monte Carlo simulations by using GEANT4 and PHITS are performed for studying neutron shielding abilities of several materials, such as graphite, iron, polyethylene, NS-4-FR and KRAFTON-HB. As a neutron source 252 Cf is considered. For the Monte Carlo simulations by using GEANT4, high precision (G4HP) models with G4NDL 4.2 based on ENDF/B-VII data are used. For the simulations by using PHITS, JENDL-4.0 library are used. The neutron dose equivalent rates with or without five different shielding materials are estimated and compared with the experimental values. It is found that the differences between the shielding abilities calculated by using GEANT4 with G4NDL 4.2 and PHITS with JENDL-4.0 library are not significant for all the cases considered in this work. We investigate the accuracy of the neutron dose equivalent rates obtained by GEANT4 and PHITS by comparing our simulation results with experimental data and other values calculated earlier. The calculated neutron dose equivalent rates agree well with the experimental dose equivalent rates within 20% errors except for polyethylene. For polyethylene material, discrepancy between our calculations and the experiments are up to 40%, but all simulations show consistent features.
In order to improve energy efficiency by increasing heat dissipation performance of bus-bar which distributes the current in high-power switchboard, the heat dissipation effects of the shape modification and surface treatment of Cu bus-bar were studied. The surface temperatures of the conventional plate-type bus-bar, and the improved tunnel-type bus-bar were compared by using electromagnetic and thermal analyses. The optimum thickness of tunnel-type bus-bar and the spacing and array among three bus-bars were calculated; and the surface temperature of tunnel-type bus-bar showed 7.9 °C lower than that of plate-type bus-bar in a 3-phase array condition. In addition, the surface and internal temperatures of the uncoated, CNT (Carbon nanotube)-coated, and BN (Boron nitride)-coated Cu bus-bars were measured with thermal imaging camera and the experiment using a hot plate. It was confirmed that the difference in the internal temperature between uncoated and BN-coated Cu was 19.4 °C. The application of the bus-bar improved from this study might contribute to the increase in power energy efficiency.
Our group has recently developed α-fluoroamine synthesis using dioxaphospholenes derived from various 1,2-diketones and the dealkylation-resistant phosphoramidite as carbene surrogates that enabled the formal insertion into the N–F bond of (PhSO2)2NF. This full account presents the scope and limitation in terms of the reactivity and the site-selectivity, which were rationalized through the computational analysis. In addition, the efforts to broaden the synthetic utility of the current process by incorporating other nitrogen nucleophiles and halogen electrophiles are described.
Neutron shielding has been a worldwide concern for decades and appropriate methods in nuclear reactors and associated facilities for shielding have been developed. Light materials such as paraffin and water cannot be used in neutron radiography due to structural and fire concerns, and a material in the solid form is needed for effective neutron shielding. Therefore, the present study developed a new neutron shielding design for fixed industrial radiography facilities with solid structures based on material combination. Different materials were investigated to find the most appropriate combination design to shield the spontaneous neutron emitted from a Cf-252 source (with an energy in the range from several keV up to 20 MeV). The combination of iron, graphite, boron (or borate materials), and lead in this order, respectively, were found to be the most appropriate shielding structure for an open Cf-252 source used in fixed industrial radiography. As iron is characterized by a high removal cross section, its use in shielding the californium spontaneous neutron source is the key outcome of the present study. These results were confirmed with the Monte Carlo simulation-based particle and heavy ion transport code system.
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