Well-type phoswich counter for low-flux X-ray/ gamma -ray detection

Phoswich counters that can detect low-flux hard-X-ray/ gamma -ray from localized sources are described. The counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). The first model counter was built by using a new scintillator, gadolinium silicate (GSO), in the decision part and CsI(Tl) in the shielding part. A detector system consisting of 64 such phoswich counters (total area approximately 740 cm/sup 2/) was flown onboard a balloon, setting a limit to the /sup 57/Co line flux from SN 1987A, at approximately 10/sup -4/ cm/sup -2/ s The sensitivity for continuum flux was around a few *10/sup -6/ cm/sup -2/ s/sup -1/ keV/sup -1/ between 100 and 200 keV. In the second model, CsI(Tl) was replaced by bismuth germanate (BGO), and radioactive contaminations in GSO were reduced. Improvements are planned to reach a sensitivity (3 sigma ) around 5*10/sup -7/ cm/sup -1/ s/sup -1/ keV/sup -1/ for the continuum.<
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