THE OPTIMIZATION OF SMALL CSI(TL) GAMMA-RAY DETECTORS

As a part of the INTEGRAL (International Gamma-Ray Astrophysical Labor atory) project, CsI(Tl) scintillation elements with a cross-sectional area of 1cm2, and between 1 and 6 cm in length have been developed to form the basis of the imager detector plane. The crystal preparation a nd wrapping, crystal geometry, optical coupling and matching to the ph otodiode have all been optimised in order to maximise the light output from the crystal, and hence produce the lowest energy threshold and b est spectral resolution for any given readout electronics. Energy reso lutions of 18% at 122 keV and 5.5% at 662 keV have been obtained using a 1cm3 crystal on a 10x10mm photodiode. With standard laboratory elec tronics, a low energy threshold of approximately 35 keV has been obtai ned.