The trigger detector for APEX: An array of position-sensitive NaI(Tl) detectors for the imaging of positrons from heavy-ion collisions

Abstract

We describe a 24-element position-sensitive cylindrical NaI(Tl) detector which allows positron imaging with an on-axis position resolution of 3 cm FWHM and annihilation radiation energy resolution of 13% FWHM. Two such detectors will provide the trigger for the APEX experiment at Argonne National Laboratory, which is exploring anomalous positron and electron production observed in heavy-ion collisions.