Papers by Keyword: Proton

Abstract: KENS-II is the second generation of the spallation neutron source at KEK which was operated from December 1, 2000 to March 22, 2006 supplying neutron beam to the neutron spectrometers of material science. The present paper reviews history of the KENS-II from its design to removal together with its performance for the neutron scattering experiments.

Abstract: Space exploitation and development need high-performance polymer based tribo-materials in order to reduce the weight and improve the reliability of mechanical moving components. However, the wear resistance of polymer composites will decrease after space irradiation. In order to improve the anti-irradiation and wear resistance, the high performance polyimide (PI) composites reinforced with aramid fibers (AF), filled with polytetrafluoroethylene (PTFE) and Al₂O₃ were designed and prepared using hot press sintering. The effect of the individual atomic oxygen or proton irradiation as well as both on the tribological properties of the PI composites were systematically investigated against Si₃N₄ ball on a ball-on-disk test rig under simulating space environment system, and coefficient of friction and wear rate were considered as responses. The worn surfaces of the composites were observed by scanning electrical microscopy to reveal wear mechanisms of the materials’ damage. Experimental results indicated that the wear rate of the PTFE/AF/PI greatly increased after atomic oxygen and proton irradiation due to oxidation degradation effect on the polymer matrix. However, filling Al₂O₃ nano-particles into polyimide matrix can improve the wear resistance because of oxidation layer, gradually formulated during the process of atomic oxygen irradiation, which can protect the polymer composites and avoid further oxidation. This study will expect to provide the helpful guidance for designing high performance polymer based frictional materials in the application of space science.

Abstract: The problems of hydrogen energetic as well as a method of high pure hydrogen obtaining are presented in the paper. It was suggested to use the reaction of aluminium nanopowder with water, as the reaction proceeds with high rate even at ambient conditions (the rate of hydrogen emission reached 18 ml/(s∙g)) and high degree of conversion (up to 100 %). The unreasonableness of the replacement of aluminium nanopowder to coarse-grained powder in this reaction due to the low efficiency is shown in the article. As a solution for pure hydrogen obtaining, a phenomenon of self-heating of aluminum nanoparticles and the resulting hydrogen, as well as the effect of its high-temperature diffusion through the membrane of ultrahigh molecular weight polyethylene were used.

Abstract: The electrical behaviour of irradiated and post-irradiation annealed nMOSFETs with an implanted p-type body and having a N₂O oxynitrided gate oxide is analysed in this work. This study reveals the existence of a “threshold fluence” which might change the predominant SiO₂/SiC interface charge trapping type from donors to acceptors at a given energy. The irradiation fluence and energy limit that guaranty a normal or improved operation of the MOSFETs are also given.

Abstract: Schottky-barrier diodes with a diameter of ~10 μm are fabricated on n-GaN epitaxial films grown by hydride vapor-phase epitaxy (HVPE) on sapphire substrates. The changes in the parameters of the diodes under irradiation with 15 MeV protons are studied. The carrier rate was found to be 130-145 cm^-1. The linear nature of the dependence N = F (D) (N is carrier concentration, and D, the irradiation dose) shows that compensation of the material is associated with transition of electrons from shallow donors to deep acceptor levels which are related to primary radiation defects.

Abstract: Electronic properties of radiation damage produced in 1700 V 4H-SiC MPS diodes by proton and carbon irradiation were investigated and compared. 4H-SiC epilayers, which formed the lowdoped N-base of MPS power diodes, were irradiated to identical depth with 670 keV protons and 9.6 MeV C⁴⁺ ions. Results show that irradiation with both projectiles produces strongly localized damage (deep levels) peaking at ion’s projected range. Compared to protons, heavier carbon ions introduce more defects with deeper levels in the SiC bandgap and more stable damage. Radiation damage act as electron traps and compensates donor doping of the epilayer and decreases electron mobility. Forward voltage drop of irradiated diodes then sharply increases when the peak concentration of introduced acceptor levels donor doping. The effect of both the proton and carbon irradiation can be simulated using a simple model accounting only for one dominant electron trap.

Abstract: High temperature solid oxide fuel cells (SOFCs) have high efficiency and low emissions and contribute to the saving of the fossil fuel and the decreasing of the CO₂ emission bringing about the global warning. As concerned about the development of electrolytes, oxide-ion conductors alternative to yttria-stabilized zirconia (YSZ) such as doped CeO₂, Sc-SZ and perovskite-type oxides (LaGaO₃) etc. have been reported to apply to the intermediate temperature SOFCs (IT-SOFCs).Some of perovskite-type oxides shows high proton conductivity at high temperature and are expected to the electrolyte materials for IT-SOFCs. In this paper we have investigated review the mixed electrical conductivity and the optical absorption spectrum of OH(D)-vibration of LaScO₃.We also evaluated its applicability to the electrolyte material for IT-SOFCs by testing the SOFC performance of Pt/LaScO₃/Pt single cell configuration.

Abstract: Electronic properties of radiation damage produced in 4H-SiC epilayer by proton and alpha particle irradiation were investigated and compared. 4H-SiC epilayers, which formed the low doped n-base of Schottky barrier power diodes, were irradiated to identical depth with 550 keV protons and 1.9 MeV alphas. Radiation defects were then characterized by capacitance deep-level transient spectroscopy and C-V measurements. Results show that both projectiles produce identical, strongly localized damage peaking at ion’s projected range. Radiation defects have a negligible effect on dynamic characteristic of irradiated 4H-SiC Schottky diodes, however acceptor character of introduced deep levels and their high introduction rates deteriorate diode’s ON-state resistance already at very low irradiation fluences.

Abstract: Carrier removal rate (Vd) in p-6H-SiC in its irradiation with 8 MeV protons has been studied. p-6H-SiC samples were produced by sublimation in a vacuum. Vd was determined by analysis of capacitance-voltage characteristics and from results of Hall effect measurements. It was found that full compensation of samples with initial value of Na-Nd 1.5 x1018 cm-3 occurs at an irradiation dose of ~1.1 1016 cm-2. In this case, the carrier removal rate was ~130 cm-1

Abstract: Poly(vinyl) chloride (PVC)-NH₄I-EC films have been prepared by solution cast technique. The sample containing 30 wt. % NH₄I exhibited highest room temperature conductivity of 4.60 × 10^-7 S cm^-1. The conductivity increased to 1.08 × 10^-6 Scm^-1 when 15 wt. % of ethylene carbonate (EC) was added to 70 wt. % PVC - 30 wt. % NH₄I. Fourier Transform Infrared (FTIR) showed evidence of polymer–salt complexation while DSC showed increase in glass transition temperature (T_g ) of PVC -NH₄I - EC polymer electrolytes. The conductivity behavior of the studied system could be accounted by the changes in T_g values.