Single scintillation crystal versus Phoswich detectors for in vivo low- energy photon detection

The development of in vivo body-count measurement systems for the detection of low-energy photons from americium and plutonium has stressed the importance of low background counting rates for better sensitivity. The measurement systems are develeped for use in the body-counting facility, which has been in operation at the Rocky Flats Plant, to detect exposures in humans from radioactive materials. The facility is in a separate building and houses the body courter which consists of thick steel walls. The detectors within the body counter section are arranged over a table or couch and can be positioned over various parts of the body of an individual being checked for the presence of radioactive materials. The systems in current use provide an improvement in background counting rates for sodium-iodide thallium detectors with the two- crystal sandwich or Phoswich scintillator. The two types of electronic configurations used with the Phoswich detectors demonstrate improvements in background counting rates over results from a single crystal detector. Tabulated data comparing the operating parameters of a single crystal and a dual-crystal configuration are included. (auth