INVESTIGATION ON HIGH-RESOLUTION RADIATION-DETECTORS BY THE USE OF Nb-BASED TUNNEL JUNCTIONS

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It has been presumed that superconducting tunnel junctions for radiation detection show better energy resolution than semiconductor detectors. We made a basic research for applying niobium-based tunnel junctions to radiation detection.Nb/A1-A10x/Nb junctions of a simple structure was fabricated by photolithographic technique, and 5.9 keV X-ray was measured by them. Non-linear interaction between quasi-particles and phonons was analyzed by the coupled Boltzmann equations, and the behavior of quasiparticles and phonons in the superconductor was elucidated.In order to obtain better energy resolution under the present technical constraint, a study was made on the design method for the optimum niobium-based tunnel junctions. It was found that there exists an optimum value of normal resistance: The energy resolution is deteriorated when junctions have the normal resistance different from the optimum value.Finally, discussion about advanced tunnel junctions was made from the viewpoint of both multilayer tunnel junctions and materials suitable for radiation detection.