Portable gamma-ray monitor composed of a compact electrically cooled Ge detector and a mini-MCA system

A portable gamma-ray monitor composed of a compact electrically cooled germanium detector and a mini-MCA system was developed for in situ gamma-ray monitoring with very fast starting time and easy operation. This detector is suitable for an accident, an emergency, a fast inspection, and an easy analysis since the detector could acquire data after a 51 min cooling time. The size of Ge detector cryostat was 10.2 cmφ×39.3 cm and the weight 5.2 kg. A small Stirling refrigerator could cool down a 14 cm³ planar-type high purity Ge detector with the relative detection efficiency of 1% automatically with low power driving electronics. After cooling down, gamma-ray data were acquired and analyzed repeatedly by a mini-MCA system interfaced to a very small hand held computer. The energy resolution of the detector was 2.46 keV at an energy of 1.33 MeV. Consequently, a user can comfortably analyze a gamma-ray spectrum with radionuclide identification and quantitative analysis by watching the display on the hand held computer.