Magnetic Susceptibilities of Octacoordinated Uranium (IV) Complexes

Interstitial halogen centers in X-irradiated CsBr

Measurements of reflectivity, photoluminescence and cathodoluminescence for various electron beam voltages were performed on p-type single crystals at liquid nitrogen, hydrogen and helium temperatures. By an application of the microreversibility principle and consideration of the reflectivity data, the nature and the energies of the transitions were determined. In addition, we identify the lines due to the annihilation of exciton-neutral defect complexes, in ground or excited state. When the luminescence is modulated by a CO2 laser (hνIR ~ 130 meV) effects are observed at liquid helium temperature. A quenching effect is observed for the free-to-bound and pair recombinations. Quenching of the luminescence due to the annihilation of exciton isoelectronic oxygen complexes is a direct corroboration of the binding-in-two-step theory.

23 - THE CHANGE OF RESISTANCE OF GOLD CRYSTALS AT VERY LOW TEMPERATURES IN A MAGNETIC FIELD AND SUPRA-CONDUCTIVITY: CRITICAL REMARKS REGARDING THE RECENT WORK OF MEISSNER AND SCHEFFERS

Dose tolerance at helium and nitrogen temperatures for whole cell electron tomography

A beryllium-walled cryostat is described which allows collection of nearly a full sphere of accurate three-dimensional X-ray diffractometer data at liquid-nitrogen (LN2) and liquid-helium (LHe) temperatures. Cryogen consumption is 0.3–0.4 liters of LHe per hour at 30°K and 0.1–0.2 liters of LN2 per hour at 78°K. The specimen is mounted on a copper block, the temperature of which is controlled to within 0.1°. Measurements with a powder sample of TbVO4 show that at 33°K the specimen temperature is within 2° of the temperature of the copper block. The cryostat has been used for the collection of several low-temperature data sets. Some special modifications in data-collection and data-processing software are described.

We have investigated the performance of a few silicon photomultipliers to readout inorganic scintillators operated at cryogenic temperatures. Such detectors, that would need to operate close to liquid helium (LHe) temperatures and in a magnetic field of a few Tesla, have been proposed by our group as a way to build an active polarized target to be used for neutrino physics, for the search of axions and CP violation, as suggested by some theoretical papers. In the present work we investigate in some details the performance of a few different silicon photomultipliers produced by Hamamatsu and Advansid down to liquid helium temperature, to verify the temperature range of usability of these devices and their performance at cryogenic temperatures.

The emission spectra from NaI(T1) excited by X-Rays at the temperature of liquid hydrogen showed the peaks at approximately 616, 546, 437, 379, 332, 299 and 285 m µ. The 332 m µ band is predominant at only the temperatures of liquid hydrogen and liquid helium, and is thought to arise from the T1 dimers, consisting of a pair of T1 + ions substitutionally displacing two alkali ions in the nearest neighbour (<110> direction). T1 dimer becomes an effective luminescent emission center at very low temperature. The emission spectra from CsI(T1) excited by X-rays at the temperature of liquid helium showed a superposition of 595, 537 and 474 m µ bands. The luminescence being weaker at lower temperature than at the room temperature, it shows no band in the ultraviolet region. In the following, temperature dependence of emission spectra from NaI(T1) and CsI(T1) excited by X-rays are reported and some discussion concerning with also some experiments carried out by other authors are presented.

The photoluminescence (PL), optical reflectance, optical transmittance and piezoelectric photothermal spectra were successfully observed between liquid helium and room temperatures for high quality p-type P-doped ZnTe substrates. In the PL spectrum of the ZnTe substrate (1 × 1018 cm—3), three distinct kinds of peaks which were due to the radiative recombination of the exciton bound to a neutral acceptor (I1) and free to a neutral acceptor (FA) with longitudinal optical phonon replicas were present at liquid helium temperature. The bandgap energy was estimated to be 2.394 eV by adding the reflection peak (2.381 eV) to the exciton binding energy. Furthermore, the activation energy of the phosphor acceptor impurity was estimated to be 65 meV. On the other hand, in the higher carrier concentration substrate (8 × 1018 cm—3), the PL intensity was much smaller than in that of the lower carrier concentration substrate. This means that radiative recombination processes decrease with increasing carrier concentrations.

The visualization of macromolecular structures on voxels provides the basis for insights in dynamic events in assembly. Certain macromolecules arise as well organized frameworks. Symmetry or crystalline arrays arise through a strict geometry of subunits. Single asymmetric motifs can be superimposed on themselves taking such geometric constraints into account. Biological molecules are often composed of subunits arranged in a symmetrical manner Such conformations provide an opportunity for signal enhancement originating from the repetition of molecules in a larger configuration. Such repetitions require not only specific interactions among protein motifs, but also a built-in flexibility to accommodate conformational changes. Thus, it is advantageous to analyze critical molecular interactions with detailed protein folding information rooted in the volume density as a whole. Two-dimensional image projections can be collected in electron microscopes at temperatures of liquid nitrogen or helium. Using low-dose electron beams, viral assemblies of large lattices have been studied in vitreous ice to localize function-specific domains identified through difference imaging. Robust algorithms have been implemented based on various grid transformations to allow effective averaging of massive image data sets.

Neutron diffraction studies have been made on a powdered NaUO3 sample. It has been shown that an octahedron composed of six oxygen atoms around pentavalent uranium in this compound is distorted and four of six oxygen atoms are much closer to an uranium atom (U-O distance of 2.15Å) than the other two (U-O distance of 2.24Å). A unit of the UO2 + ion does not exist in the crystal, though the pentavalent uranium has been expected to be in the form of UO2 + as in the case of UO2 2+ of a hexavalent uranium Ion. A neutron diffraction pattern at temperature of liquid helium has shown no appreciable difference from that at temperature of liquid nitrogen.

Many insulating materials and systems for superconducting electrical equipment have been developed in response to the severe demands of safe usage, such as in cryogenic temperature, high mechanical stresses, high radiation, etc. They have been designed to fulfill very extreme service conditions, either at liquid helium or liquid nitrogen temperatures. Whatever the future industrial development, there is already abundant knowledge about insulating materials at cryogenic temperatures, and the feasibility has been proven. Many laboratories in the world continue research to increase this knowledge and to fill in the remaining gaps.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

First Tests of Twisted-Pair HTS 1 kA Range Cables for Use in Superconducting Links

Transient analysis and burnout of high temperature superconducting current leads

The effect of zinc displacement on the luminescence of zinc sulphide

[Abstract] The objective of this work is to investigate the interlaminar fracture and damage behavior of woven glass fiber reinforced polymer (GFRP) laminates for mixed-mode bending (MMB) configuration at cryogenic temperatures. The crack length corresponding to critical load is determined using measured specimen compliance of the damage states via finite element analysis (FEA), and the critical mixed-mode energy release rates of MMB specimen at room temperature (RT), liquid nitrogen temperature (77 K) and liquid helium temperature (4 K) are calculated. The values of the critical energy release rate (mixed-mode interlaminar fracture toughness) obtained from the beam theory and FEA are then compared. A FEA coupled with damage is also employed to study the damage distributions within the MMB specimen. Moreover, the results for the special cases of pure mode I and mode II loading of woven GFRP laminates are presented.