[en] The structural changes of LiFePO₄ and C-coated LiFePO₄ during charging at various C-rates and temperatures are investigated using synchrotron based in situ X-ray diffraction technique. The XRD patterns collected during cycling show the structural evidence of the positive effects of carbon coating on LiFePO₄ for the electrochemical performance improvements at different temperatures, especially at low temperatures. At -10 C, the C-coated LiFePO₄ shows comparable capacities with the sample cycled at room temperature when cycled at C/5 rate with a slight shift of the plateau to a higher voltage during charging. The in situ XRD patterns collected simultaneously show a complete phase transformation from triphylite to heterosite. At -20 C, the C-coated LiFePO₄ delivers 55.6% of its theoretical capacities at C/5 rate. However, the plateau in the charging curve becomes sloppy and shifts to a higher voltage. The in situ XRD patterns show that the phase transformation from triphylite to heterosite is not completed when charged to 4.5 V due to the larger polarization when charged at -20 C.

[en] The superconducting properties of as-grown and neutron irradiated MgB₂ were characterized. The analysis is performed by means of SQUID magnetometry. Low temperature Scanning Laser Microscopy (LTSLM) and Low temperature Scanning Hall Probe Microscopy (LTSHPM) were carried out to reveal the spatial distribution of the local resistive transition temperature and the local current density in commercial YBCO coated conductors near the superconducting transition. Neutron irradiation increased the critical current density of MgB₂ at high magnetic field. Using LTSLM and LTSHPM the current path in YBCO coated conductors of different patterns could be directly imaged

[en] Droplet dynamics and emission of a supercritical droplet in crossing gas stream are numerically investigated. Effects of ambient pressure and velocity of nitrogen gas on the dynamics of the supercritical oxygen droplet are parametrically examined. Unsteady conservative axisymmetric Navier-Stokes equations in curvilinear coordinates are preconditioned and solved by dual-time stepping method. A unified property evaluation scheme based on a fundamental equation of state and extended corresponding-state principle is established to deal with thermodynamic non-idealities and transport anomalies. At lower pressures and velocities of nitrogen cross flows, both the diffusion and the convection are important in determining the droplet dynamics. Relative flow motion causes a secondary breakup and cascading vortices, and the droplet lifetime is reduced with increasing in ambient pressure. At higher ambient pressures and velocities, however, the droplet dynamics become convection-controlled while the secondary breakup is hindered by reduced diffusivity of the oxygen. Gas-phase mixing depends on the convection and diffusion velocities in conjunction with corresponding droplet deformation and flow interaction. Supercritical droplet dynamics and emission is not similar with respect to the pressure and velocity of the ambient gas and thus provides no scale

[en] The first-cycle irreversibility of Li_1.048(Ni_1/3Co_1/3Mn_1/3)_0.952O₂ (LiMO₂) cathode material in lithium and lithium-ion cells has been studied using galvanostatic cycling and in situ synchrotron X-ray diffraction. The so-called 'lost capacity' of a Li/LiMO₂ cell observed during initial cycle in conventional voltage ranges (e.g., 3.0-4.3 V) could be completely recovered by discharging the cell to low voltages (<2 V). During the deep discharge, the lithium cell exhibited an additional voltage plateau, which is believed to result from the formation of Li₂MO₂-like phase on the oxide particle surface due to very sluggish lithium diffusion in Li_1-#Delta#MO₂ with Δ → 0 (i.e., near the end of discharge). Voltage relaxation curve and in situ X-ray diffraction patterns, measured during relaxation of the lithium cell after deep discharge to obtain 100% cycle efficiency, suggested that the oxide cathode returned to its original state after the following two-step relaxation processes: relatively quick disappearance of the Li₂MO₂-like phase on the particle surface, followed by slow lithium diffusion in the layered structure. Experiments conducted in Li₄Ti₅O₁₂/LiMO₂ lithium-ion cells confirmed that the physical loss of lithium (via surface film formation or parasitic electrochemical reactions, etc.) from LiMO₂ was negligible up to an oxide voltage of 4.3 V vs. Li⁺/Li.

[en] We are developing meander-shaped metallic magnetic calorimeters using micro-fabrication methods. A planar Nb coil in a meander shape was fabricated on a Si substrate. The coil was designed to have a persistent current using a metal heater evaporated on a part of the coil. A paramagnetic sensor, 5μm thick Au:Er foil, was glued on top of the meander structure with epoxy. The magnetization and heat capacity were measured at different temperatures, and applied field currents matched well with expected values. The detector showed an energy resolution of 4 keV FWHM for the 5.5 MeV alpha particles.

[en] Magnetization studies have been carried out on MgB₂ polycrystalline samples in the temperature range of 5 - 44 K and in the magnetic field up to 7 Tesla. The critical current density was calculated from hysteresis loops using the Bean's critical state model, and the highest value of J_c at 20 K was 2.7 x 10⁵ A/cm² at 2 Tesla. The hysteresis loops were carefully examined to determine the temperature and magnetic field range where flux jumps appeared. The first jump occurred typically at 1 Tesla. Due to the strong pinning, we observed the presence of flux jump below H = 1 Tesla at temperature below 30 K.

[en] We investigated the magnetic and transport properties of Co and Ni co-doped TiO₂ thin films grown by using a sol-gel method with Co and Ni concentrations from 0 % to 4 %. All the samples exhibited ferromagnetism at room temperature, but were highly resistive when annealed in vacuum at 650 .deg. C. The magnetic moment per ion increased with the Co concentration. After annealing at 850 .deg. C, the electrical conductance and the magnetic moment per ion of the films were enhanced, but a small Co metallic peak was observed in the X-ray diffraction pattern. The Hall effect study showed that the carriers were electrons with densities lower than 10¹⁹ cm^-3 at room temperature for the samples annealed at 850 .deg. C. A weak anomalous Hall effect was observed and increased with the Co concentration. We discuss the co-doping effect by comparing the results with those of films singly doped with Ni or Co.

[en] Cryogenic detectors using heat generation below 1 K have become an attractive alternative because of their outstanding energy resolution. Significant improvement in gamma spectroscopy has been achieved with high resolution transition edge sensors (TESs) for nuclear material analysis. In alpha spectroscopy, superior resolution to that of conventional detectors has been also demonstrated. Since all the deposited energy can be converted into thermal energy by surrounding a radioactive source with metal foil, alpha energy can be measured without any correction for selfattenuation. Accompanying electrons, x-rays, and/or γ-rays are also converted into thermal energy. Thus measurement of alpha decay in 4π geometry returns the Q value, the total decay energy, independent of decay branches without loss of energy and count, enabling Q spectroscopy.

[en] Metallic magnetic calorimeters (MMCs) are one of the most competitive low temperature detector (LTD) readout sensors. They have the advantages of high time resolution, no heat dissipation, and a wide range of operating temperature. We apply MMCs to our neutrinoless double beta decay (0cββ) search experiment. A CaMoO₄ crystal was employed as both a source of 0cββ and an energy absorber. The crystal was thermally connected to a MMC sensor. We set a simple thermal model for this detector and measured pulse shapes are compared with a numerical solution of the thermal model.

[en] Cryogenic particle detectors have recently been adopted in radiation detection and measurement because of their high energy resolution. Many of these detectors have demonstrated energy resolutions better than the theoretical limit of semiconductor detectors. We report the development of alpha spectrometer using a micro-fabricated magnetic calorimeter coupled to a large-area particle absorber. A piece of gold foil of was glued to the paramagnetic temperature sensor made of sputtered Au:Er film to serve as an absorber for incident alpha particles. We performed experiments with 241Am source at cryogen free adiabatic demagnetization refrigerator (CF-ADR). A high energy resolution of 6.8 keV in FWHM was obtained for 5.5 MeV alpha particles