A vertical radiation sensitive detector array (114) includes at least one detector leaf (118). The detector leaf includes a scintillator array (210, 502, 807, 907), including, at least, a top side (212) which receives radiation, a bottom side (218) and a rear side (214) and a photo-sensor circuit board (200, 803, 903), including a photo-sensitive region (202, 508, 803, 903), optically coupled to the rear side of the scintillator array. The detector leaf further includes processing electronics (406) disposed below the scintillator array, a flexible circuit board (220) electrically coupling the photo-sensitive region and the processing electronics, and a radiation shield (236) disposed below the bottom of the scintillator array, between the scintillator and the processing electronics, thereby shielding the processing electronics from residual radiation passing through the scintillator array. Some embodiments incorporate rare earth iodides such as SrI 2 (Eu).