Patent ID: 7502442

Claim:
A material discrimination system including a high energy X-ray source, a first detector component in the form of a thin scintillation crystal for registering an amount of energy deposited by an X-ray that is essentially independent of the X-ray energy, a thicker one-piece downstream scintillation crystal, a low-Z converter situated between the thin crystal and the thicker crystal to stop electrons produced by X-ray interactions downstream of the thin crystal from being significantly backscattered into the thin crystal and prevent electrons leaving the thin crystal from returning and depositing more energy in the thin crystal, and a plurality of read-out devices for detecting light energy emitted by the crystals and generating respective electrical output signals in response thereto, wherein a pair of read-out devices is provided to read out from opposite sides of the thin crystal, and further pairs of read-out devices are provided to read out from opposite sides of the thicker crystal at different respective depths in the beam direction, and wherein the output signal from one read-out device of each pair is added to the output signal from the other read-out device of the pair on the opposite side of the crystal to reduce any left/right asymmetry in the output signals.