Beam tests of a 3-D position sensitive scintillation detector

An array of 30 position-sensitive scintillator bars has been tested in a gamma-ray beam. The gamma-ray energies range from 6 MeV to 17 MeV. The bars are similar to those proposed for use in the GRASP gamma-ray telescope satellite imaging plane. They are manufactured from CsI(Tl) covered with a highly reflective diffusive wrapping, and are read out using large-area PIN photodiodes. Each bar measures 15.0 cm by 1.3 cm by 1.3 cm. The beam test unit comprised 30 bars stacked in a 5 by 6 array. The photodiodes were optically coupled to the end face of each bar and were connected to a processing chain consisting of a low-noise preamplifier, a high-gain shaping amplifier, and a digitization and data collection system. Several experiments were performed with the unit to assess the spectral response position resolution, and background-rejection capabilities of the complete detector. The precision of the lateral position for an interaction measurement of lower energy photons was typically 10 mm. The position of interaction in the plane perpendicular to the beam has been shown to be well defined by the position of the bar in which the interaction closest to the front of the detector occurred. The resolution of the energy deposit in the whole detector at 6.14 MeV is 5%