CsI calorimeter with 3-D position resolution

New gamma-ray calorimeter have been developed for the MEGA Compton camera. They consist of arrays of small CsI(Tl) scintillator bars read out by Silic on PIN-diodes and low noise, self-triggering frontend electronics. The leng th of the bars (the thickness of the calorimeter) can be varied for differe nt applications to fit the stopping power needed and the light loss tolerab le. In this paper we present calibration results from 2 cm long bars with d iodes on one side, and 8 cm long bars with diodes on two opposite sides. Do uble-sided readout gives 3-D information of interactions which will be used to overcome the limited position resolution in Anger-cameras at high energ ies. Simpler detection devices like Anger-cameras might finally resolve onl y the centre of gravity. As events from gamma-rays with energies of MeV do extend over several cm, it is a prerequisite for an imaging device to resol ve the interaction structure in detail. Combining CsI(Tl) scintillators, Si licon PIN-photodiodes and frontend electronics inside the housing results i n a cheap rugged design. While the development in our institute is mainly d one for the Compton camera prototype, many other applications are conceivab le. (C) 2000 Elsevier Science B.V. All rights reserved.