An Array of 12 Planar Germanium Detectors for in Situ Gamma Spectroscopy

There is a continuing need at the Nevada Test Site (NTS) for sensitive instruments that quantify surface concentrations of radionuclides. We have designed, fabricated, and field tested an array of 12 high-purity germanium planar detectors in a single cryostat. The detector system has a total surface area of 120 cm2 and internal shielding. The detectors are 0.8-cm thick and are individually encapsulated. This system was primarily designed for in situ detection of plutonium via the 241Am 60-keV gamma ray; however, it will also be used for in vivo lung counting and sample counting. We have fielded it at the NTS and found it to have a minimum detectable activity (MDA) for 241Am of about a factor of four lower than that of our four-detector system.