(a) The Polaris J detector setup to measure 137Cs, 22Na, and 60Co point sources placed back-to-back for simultaneous measurement of all γs. The inset shows the single source measurement setup. Black squares indicate CZT array location in the box. Detector stages 1, 2, 3, and 4 are placed at (0, −123 mm, 0), (0, −250 mm, −48 mm), (0, −250 mm, 48 mm) and (0, −377 mm, 0) respectively. (b) Schematic showing the point sources for the single source measurements and 3-point source measurement with respect to stage 1 of the CC (not drawn to scale). Also, (c) single-stage mode and (d) multi-stage mode double/triple scatter events are shown.