Wide-band gamma-ray burst monitor: GBM for the CALET mission

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Astrophysics with All-Sky X-Ray observations: 3rd International MAXI Workshop (RIKEN, 10-12 June 2008)

We are developing the gamma-ray burst monitor for the CALET (CALorimetric Electron Telescope) experiment which is proposed and studied (in phase A) to be a next experiment for the JEM/Exposure Facility of the ISS. The CALET GRB Monitor (CALET-GBM) is planned to measure wide-band energy spectra from GRB prompt emissions over nine decades in energy (from a few keV to a few TeV) together with the CALET Imaging Calorimeter (IMC) and the Total Absorption Calorimeter (TASC). To fulfill this requirement, we are planning to employ six LaBr3(Ce) crystals for the range from a few keV to about 1 MeV together with a thick BGO detector covering from several tens of keV to about 20 MeV. Since the light yield of LaBr3(Ce) is about twice as large as that of NaI(Tl), it is very attractive material. However it has not been yet used as a detector for long exposure in space. Therefore its radiation hardness and induced background due to trapped protons in the geomagnetic field are not fully understood. To evaluate its performance in high radiation environment in the ISS orbit, we carried out proton irradiation tests. Proton-induced radio-activation were measured from a few minutes after irradiation over a period longer than two months by a Germanium detector, and most of radioactive nuclei induced by protons are identified. We have manufactured a proto-type model, 3 inch in diameter x 0.5 inch thick with the entrance window of 220 micrometer beryllium. In preliminary measurements, 6.4 keV Fe K alpha fluorescence line is clearly detectable. We can expect that the lower energy threshold can be around 4 keV or even lower.

著者人数: 11人

Physical characteristics: Original contains color illustrations

資料番号: AA0064306074

レポート番号: JAXA-SP-08-014E

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