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Nakamura, Tatsuya; Katagiri, Masaki; Chen, Y. E.*; Ukibe, Masahiro*; Okubo, Masataka*
Nuclear Instruments and Methods in Physics Research A, 559(2), p.766 - 768, 2006/04
Times Cited Count:13 Percentile:65.83(Instruments & Instrumentation)We have been developing a position-sensitive neutron detector, which exhibits a high spatial resolution of the order of 10 microns and high detection efficiency. The analysis on the pulse-heights or on the time-delay between the STJs gives incident positions of the neutrons. In this paper, the response of the STJs/LBO neutron detector measured using a cold neutron beam is presented. The two STJs have the same size of 50 50 m and their distance is 1.3 mm. The count intensity in the correlation map varied depending on the incident position of the neutron beam which gives an evidence for the position-sensitivity of the detector. These experimental results were qualitatively understood by a simple solid-angle model.
Nakamura, Tatsuya; Katagiri, Masaki; Soyama, Kazuhiko; Ukibe, Masahiro*; Ikeuchi, Takashi*; Okubo, Masataka*
Nuclear Instruments and Methods in Physics Research A, 529(1-3), p.402 - 404, 2004/08
Times Cited Count:8 Percentile:48.81(Instruments & Instrumentation)We evaluated the neutron--rays discrimination of the neutron detector comprising a superconducting tunnel junction (STJ) on the single crystal of LiBO. The neutron detector was irradiated with X-rays, -rays and neutrons, and the signal pulses were analyzed including pulse height distributions and rise times. It was found that the most of the signal pulses for the neutron-events exhibited slower rise times than those for X-rays and -rays. This indicated the capability of neutron--rays discrimination of the detector using the differences in the decay time of the signal current.
Nakamura, Tatsuya; Katagiri, Masaki; Ukibe, Masahiro*; Ikeuchi, Takashi*; Okubo, Masataka*
Nuclear Instruments and Methods in Physics Research A, 520(1-3), p.67 - 69, 2004/03
Times Cited Count:28 Percentile:84.49(Instruments & Instrumentation)We succeeded in detecting neutrons using superconducting tunnel junctions (STJs) fabricated on a single crystal of LiBO. Neutrons are captured in the crystal by the nuclear reactions Li + n T+ + 4.78 MeV and B + n Li + + 2.3 MeV, and generated phonons propagate in the absorber and are measured by the STJs. We selected a single crystal of LiBO as the absorber material because of properties such as the large neutron cross-section of Li and B, low -ray sensitivity, short particle range in the substrate, and fast phonon velocity. Series-connected or multiple STJs on the crystal would enable two-dimensional neutron imaging with high detection efficiency, low gamma-ray background, and a high spatial resolution of a few microns. We demonstrate neutron detection by the STJs and show their X-ray response and neutron detection. The correlation in pulse heights between two junctions located 1.3mm apart clearly indicates the possibility of neutron imaging.
Nakamura, Tatsuya; Katagiri, Masaki; Okubo, Masataka*; Pressler, H.*; Takahashi, Hiroyuki*; Nakazawa, Masaharu*
AIP Conference Proceedings 605, p.173 - 176, 2002/00
Periodical distribution of charge output in superconducting tunnel junction (STJ) having a structure of Nb/Al/AlO/Al/Nb with size of 200 x 200 was first observed by Low Temperature Scanning Synchrotron Microscope experiments. Two swelled parts were appeared in the distribution of charge output and the period of the swelled parts was about 100. It is found that this distribution was occurred under the conditions; (1) the size of the STJ is more than twice of Josephson characteristic length and (2) a bias voltage applied to the device is more than 0.2mV of about the energy gap of the trapping layers. It was confirmed that this anomalous distribution of charge output significantly distorts the shape of the photo peak and degrades the energy resolution of the STJ detector.
Katagiri, Masaki; Nakamura, Tatsuya; Okubo, Masataka*; Pressler, H.*; Takahashi, Hiroyuki*; Nakazawa, Masaharu*
AIP Conference Proceedings 605, p.177 - 180, 2002/00
no abstracts in English
Kishimoto, Maki; Katagiri, Masaki; Nakamura, Tatsuya; Okubo, Masataka*; Ukibe, Masahiro*; Kurakado, M.*; Kanno, Ikuo*; Fukuda, Daiji*; Takahashi, Hiroyuki*; Kraus, H.*; et al.
Nuclear Instruments and Methods in Physics Research A, 444(1-2), p.124 - 128, 2000/04
Times Cited Count:4 Percentile:36.74(Instruments & Instrumentation)no abstracts in English
Jiang, L.*; O'Rourke, B. E.*; Harada, Yoshihisa*; Takatsu, Shuhei*; Ito, Kenji*; Okubo, Masataka*; Hirade, Tetsuya; Uedono, Akira*; Suzuki, Ryoichi*; Takai, Kenichi*; et al.
no journal, ,
We are studying the depth dependence of the density of the defects induced by the electrical discharge machining (EDM) in SUS316L, using the electron probe microanalysis (EPMA), Positron annihilation lifetime spectroscopy (PALS) and X-ray diffraction (XRD). EPMA results show a large change in the composition over the first 10 m. This layer can be assumed to correspond to the recast layer. PALS and XRD results suggest a defect layer with a thickness of around 50 m. This depth can be assumed to correspond to the heat affected zone where dislocations and vacancy clusters exists. For PALS (and other methods) analysis, it is recommended to remove the topmost 100 m of the samples by chemical polishing after EDM.