The superconducting properties of Ti-Nb-Ta ternary alloys were investigated. The upper critical field of Ti-Nb-Ta alloy is about 125kG, which is the highest of known alloy superconductors. Ti-Nb-Ta alloy with fixed Ta content to 5 at % maintains higher transition temperature, it being about 10°K. It has been found that the heat-treatment at 400°C for a long time is optimum for H-Ic characteristic of Ti-25Nb-5Ta alloy, and that this heat-treatment precipitates α-Ti in the matrix. This precipitate was sustained by transmission electron micrograph examination. The magnet wound with Ti-25Nb-5Ta wire produces 60kG without instability and with relatively small current degradation.
With the recent remarkable development of cryogenic appliances data for mechanical properties of various materials at cryogenic temperature have been required. Under these circums tances, our efforts were concentrated to the test method for materials at cryogenic temperature and collecting data on mechanical properties of materials in cryogenic use. In this report, we introduce the test methods and the mechanical properties of materials at temperatures of room to the liquid nitrogen. As for the test methods, we mainly discuss the construction of various cryostats for tensile tests, hardness tests, impact tests and fatigue tests. By using the methods established in this study, we investigated on the mechanical properties of aluminum, copper, 18-8 stainless steel and other metals. Besides these two subjects, we also explain the relation between the martensite transformation in austenitic stainless steels and peculiar behavior of their mechanical properties at cryogenic temperature.
This short note describes briefly on a cryostat of the polarized hydrogen target by means of so-called dynamic nuclear orientation, which was constructed for proton-proton scattering experiment with the 50MeV synchrocyclotron at Institute for Nuclear Study, University of Tokyo. The entire system consisted of a liquid helium dewar at the top and a cryostat part involving a target cavity. Liquid helium stored in the dewar was guided downwards through a thin pipe and spurted out continuously at the target cavity. Temperature of the target was easily adjusted by changing flow of liquid helium with a needle valve. The lowest temperature obtained was about 1.2°K and 1.5°K with and without the microwave power (about 75mW, 70kMc/s). The average helium loss was approximately 1.2l/hour., not involving losses during transfer of liquid helium to the dewar from outside. Average polarization obtained through 300 hours' experimental run was about 30%.
The splitting of the ground state of Fe57 in iron corresponds to 2.2 millidegrees. At a very low temperature, the population in the m=-1/2 level will become greater than that in the m=+1/2. For an iron absorber, the ratio of the intensities of transitions arising from the m=-1/2 level to those from the m=+1/2 level is increased as the temperature approaches to 2.2 millidegrees. Utilizing this effect, we have measured the temperature of an iron absorber to be 7.9 millidegrees without any ambiguity of depolarization effects through β decay, which might be experienced in the Mössbauer Effect thermometer with the source kept at very low temperature.
Superconducting tunneling effect as a method of determination of the energy gap of superconductors is reviewed and the research programs on the effect in Electrotechnical Laboratory are presented together with the preliminary results: the anisotropy of the energy gap in Ga single crystal is only 10% although Ga has a highly anisotropic crystal structure.