This collaboration has already obtained encouraging results about the perfo
rmance of 200 and 600 mum thick semiinsulating GaAs detectors, in terms of
charge collection efficiency (c.c.e.), detection efficiency and imaging cap
abilities, to be used as single photon counting detectors with photons in t
he radiographic energy range. The possible use of such detectors in nuclear
medicine implies detection of more energetic photons, up to the 140 keV of
the Tc-99m source; thus efficient detectors must be thicker than those pre
viously studied. In this paper, we present the results of the investigation
of electrical and detection properties (spectra, c.c.e., energy resolution
) of a series of detectors, whose thickness ranges from 200 to 1000 mum, wh
en irradiated with radioactive sources over the energy range used in nuclea
r medicine. (C) 2001 Elsevier Science B.V. All rights reserved.