[en] We measure the ac complex resistivity in the mixed state of amorphous Mo_xSi_1-x films with different thicknesses (t). For films with t=100 and 30 nm we can determine the vortex-glass-transition (VGT) line which persists down to low temperatures (T) up to high fields (B) near the upper critical field at T=0. In the liquid phase the vortex-relaxation time (τ_g) extracted from the frequency dependence of ac resistivity follows the power-law T dependence expected by the VG theory for three dimensions (3D). For the thinner (10, 6 nm) films, both the dc resistivity and τ_g follow the activated T dependence except for the very low-T region, suggestive of 2D VGT. For all of the films studied, τ_g in high B shows a decreased T dependence at lower T, indicating the quantum-driven fluctuations

[en] We present measurements of dc and ac complex resistivities for amorphous Mo_xSi_1-x films with different disorder and dimensionality (film thickness t). For thicker films with t=100 and 30 nm we determine the vortex-glass-transition (VGT) line B_g(T) which persists down to low enough temperatures T up to high fields B near B_c2(0), where B_c2(0) is an upper critical field at T=0. The finite quantum-vortex-liquid (QVL) phase at T=0, B_g(0)< B< B_c2(0), is observed for these films. We find a trend for the QVL phase to increase as the film becomes more resistive and/or thinner. This result is consistent with a view that the QVL phase is driven by strong quantum fluctuations, which are enhanced with increasing disorder and with decreasing dimensionality. For the thinnest film with t=6 nm, both the dc resistivity and vortex relaxation time follow the activated T dependence, suggestive of two-dimensional VGT

[en] Positronium (Ps) can be formed by the reaction of trapped electrons and free positrons at low temperatures in molecular solids. While Ps formation by spur process must be fast, Ps formation by trapped electrons and free positrons is possible even at positron age of several hundreds pico-seconds. Age-momentum correlation measurement of electron-positron pair annihilation γ-rays was applied to investigate the delayed Ps formation, and an evidence for the existence of the delayed Ps formation was successfully observed

[en] A practical multi-gyrotron oscillation system, using collector-potential depression, composed of six gyrotron tubes and 3 U of power supplies, was designed, fabricated and tested. This system was designed to generate power levels of 3 MW for pulse duration of 1-s at ∼168 GHz for electron cyclotron heating of LHD at the National Institute for Fusion Science. The all-solid-state power supply unit can drive a maximum of three gyrotrons by equipping the collector power supply with three pairs of the anode and body power supplies. The gyrotrons used a TE_31,8,1-mode interaction cavity. A single-stage depressed collector with sweeping coils was employed to increase system efficiency and reduce the heat flux to the collector surface. An internal converter produced a flattened Gaussian profile at a single-disk silicon-nitride window. The output mode was reconverted into the HE₁₁ mode by an MOU. We reconstructed a main circuit of the power supply unit because of stray capacitors in the actual circuit. There were some differences between the designed and measured output wave profiles. The tubes were tested for 1-s pulse with power levels of 500 kW; system efficiencies were 30% at the peak and 28% at the average and temperatures of the windows were ∼200 degree sign C

No abstract available

[en] Spin-polarized low-energy positrons were considered as useful probes for studying electron spin states of both surface and bulk materials. Due to the spin-dependent interactions between electrons and positrons, the formation of positronium (Ps), an electron-positron bound system, can be distinguished from different electron spin states. Recently, a positron source of ¹⁸F has been developed for a spin polarized slow positron beam at the institute of physical and chemical research (RIKEN). The design of an electrostatic positron beam will be discussed in conjunction with a spin rotator.

[en] The removal of oxygen from rare-earth metals (RE, RE=Gd, Tb, Dy, Er) by an electrochemical deoxidation method was investigated. A titanium basket containing the rare-earth metal sample, submerged in molten CaCl₂ electrolyte, formed the cathode of an electrolysis cell. A high-purity graphite anode was used. The calcium metal produced at the cathode effectively deoxidized the rare-earth metal. Carbon monoxide and dioxide were generated at the graphite anode. Rare-earth metals containing more than 2000 mass ppm oxygen were deoxidized to 10-50 mass ppm level by electrolysis at 1189 K for 36 ks (10 h). Cyclic voltammetry was used to characterize the molten salt at different stages of the process. The effectiveness of the process is discussed with the aid of a chemical potential diagram for RE-O solid solutions. The new electrochemical technique is compared with the conventional deoxidation methods reported in the literature. The possibility of nitrogen removal from the rare-earth metals by the electrochemical method is outlined. (orig.)

[en] The oxygen potentials of four rare-earth metal - oxygen (RE-O: RE=Gd, Dy, Tb, Er) solid solutions have been measured by equilibration with yttrium - oxygen (Y-O) and titanium - oxygen (Ti-O) solid solutions. Rare-earth metal, yttrium and titanium samples were immersed in calcium-saturated CaCl₂ melt at temperatures between 1093 and 1233 K. Homogeneous oxygen potential was established in the metallic samples through the fused salt, which contains some dissolved CaO. The metallic samples were analyzed for oxygen after quenching. The oxygen potentials of RE-O solid solutions were determined using either Y-O or Ti-O solid solution as the reference. This method enabled reliable measurement of extremely low oxygen potentials at high temperature (circa p_O2=10^-48 atm at 1173 K). It was found that the oxygen affinity of the metals decreases in the order: Y>Er>Dy>Tb>Gd>Ti. Values for the standard Gibbs energy of solution of oxygen in RE metals obtained in this study, permit assessment of the extent of deoxidation that can be achieved with various purification techniques. It may be possible to achieve an oxygen level of 10 mass ppm using an electrochemical deoxidation method. (orig.)

[en] A system which supplies an intense ¹⁸F (half life 110 min) positron source produced by an AVF cyclotron through ¹⁸O(p,n)¹⁸F reaction has been constructed. Produced ¹⁸F is transferred to a low background experiment hall through a capillary. It is electro-deposited on a graphite rod and used for a source of a slow positron beam. In the meantime the next batch of target ¹⁸O water is loaded and proton irradiation proceeds. This system makes it possible to perform continuous positron beam experiments using the 18 F positron source.

[en] Robot technologies for maintenance and inspection of various equipments in nuclear plants have been developed. The environment inside of the nuclear plants is very complex and out of order. Then, necessary skills for manipulators to work well in actual working environment are required to be developed. In this study, two technologies have been developed in addition to a contact moving type already developed; one is a virtual restricting type and another is a contact-restricting type. Modeling studies of the actual working environment and development of the teaching system have proceeded. Design studies on the total systems of various devices and techniques, and on the test working environment for demonstrating efficiency of the skills have also proceeded. (A. Hishinuma)