Detector Performance

Measurements made with a single-cell prototype of the modular neutron detector. Two isotopes were used for the tests: cesium-137 (red), which emits gamma rays, and californium-252 (green), which emits alpha particles, neutrons, and gamma rays. The horizontal axis is the charge produced in the detection cell by the radiation packets, which include gamma rays and the tritons and alpha particles emitted from neutron-absorbing reactions in the cell's lithium layer. (Californium-252's alpha particles are absorbed by the source's container before they reach the detector.) The vertical axis is the number of radiation packets that produce a given value of charge. The two sharp peaks on the left are produced by the sources' gamma rays. The remaining data is from neutrons. When the detection threshold is set at the white line, the detector responds only to neutron-emitting materials such as plutonium and rejects gamma-ray-emitting materials such as radioactive pharmaceuticals or radioactive elements in the environment. By discriminating between these two types of radioactive materials, the detector yields fewer false positives, increasing inspection efficiency.

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