High-performance superconducting-tunnel-junction X-ray detector with resonant reading function

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Superconducting tunnel junction x-ray detectors are desired to have a wide active area for practical use. We attempt to study the usefulness of resonant biasing and reading method for tunnel junctions, for improving the performance in x-ray detection.It is know that large-area tunnel junctions are not completely stable in current-voltage characteristics. The current-voltage characteristics are, therefore, investigated to understand their behavior from the viewpoint of mixture of high frequency phase- difference of superconductors (ac Josephson effect). It was made clear that behavior of high frequency phase difference tends to lead to non-linear dc leakage current, when junctions are operated in high impedance biasing. Since the resonant method making use of inductance (L) and capacitance (C) produces low impedance situation, it is expected to give more stable operation.Experiments with LC biasing and reading were carried out. The experimental electronic resolution for 6-keV x-rays was 800 eV at a conventional room and 240 eV at an electromagnetical shielded condition. The value of 240eV was one order in magnitude as high as the resolution ideally expected. It was concluded that the complete electromagnetical shielding circumstance is essential important to obtain the ideal good performance.