国分 紀秀

ASTRO-E Hard X-ray Detector (HXD) is characterized by well-type phoswich counters[1] in a compound-eye configuration which reduce the detector background to lower level than any other past hard X-ray mission. When operating in Low Earth Orbit, the expected background of the HXD is an order of 10 -5 counts/s/kcV/cm 2, mainly caused from the radioactivity induced within the detector materials by geomagnetically trapped protons. Results are presented from measurements of induced radioactivity in two phoswich scintillators, GSO (Gd 2SiO 5:Ce 0.5% mol) and BGO (Bi 4Ge 3O 12), irradiated by mono-energetic protons at an accelerator facility. Radiation transport computer codes are used to build the detector response functions for emissions from decays of spallation products. Based on the comparison between experimental and simulation results, the activation background level of HXD in the orbit is estimated. © 1999 IEEE.

The Hard X-ray Detector (HXD) is one of the three experiments of the Astro-E mission, the fifth Japanese X-ray satellite devoted to studies of high energy phenomena in the universe in the X-ray to soft gamma-ray region.(1-3) Prepared for launch at the beginning of 2000 via the newly developed M-V launch vehicle of the Institute of Space and Astronautical Science, the Astro-E is to be thrown into a near-circular orbit of 550 km altitude, with an inclination of 31 degrees. The flight model has been finished assembled this year, and we carried out various tests to verify the performance. We acquired the background spectrum at sea level, and confirmed that our system is operating effectively in reducing the background level. The HXD will observe photons in the energy range of 10-600 keV, and the calculations based on the preflight calibration suggest that the HXD will have the highest sensitivity ever achieved in this energy range. We also verified that our electronic system will maintain its performance against charged particle events expected in orbit.