Special nuclear materials monitoring - An application of CdxZn1-xTe detectors

Special nuclear materials (SNMs) are radioactive sources containing either U-235 or Pu-239; materials that can be used in nuclear weapons. To monitor the extensive stockpiles of these materials in the US and former Soviet Union requires specialized instrumentation. This instrumentation must contain a sensor capable of detecting the gamma emissions from U-235 or Pu-239, yet the instrument must be extremely reliable and consume little power. The performance of a SNM monitoring system, developed under project ''Straight-line'' at Sandia National Laboratories will be discussed. The system makes use of room temperature CdxZn1-xTe (CZT) detectors. CZT detectors are a good choice for this application because they have excellent stopping power for U-235 or Pu-239 photon emissions, and they draw very little current. Particular emphasis will be given to the problem of providing a suitable charge sensitive preamplifier and electronic readout system for a CZT detector that consumes little power.