The optimisation of small CsI(Tl) gamma-ray detectors

As part of the INTEGRAL (International Gamma-Ray Astrophysical Laboratory) project, CsI(Tl) scintillation elements with a cross-sectional area of 1 cm/sup 2/ and between 1 and 6 cm in length were developed to form the basis of the image detector plane. The crystal preparation and wrapping, crystal geometry, optical coupling, and matching to the photodiode were optimized in order to maximize the light output from the crystal, and hence produce the lowest energy threshold and best spectral resolution for any given readout electronics. Energy resolutions of 18% at 122 keV and 5.5% at 662 keV were obtained using a 1-cm/sup 3/ crystal on a 10-mm*10-mm photodiode. With standard laboratory electronics, a low energy threshold of approximately 35 keV was obtained.<
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