Determination of surface activity and radiation spectrum characteristics inside buildings by a gamma locator

A gamma locator designed to conduct contamination survey inside buildings connected with nuclear production is developed. The device consists of a detector head and a remote control unit connected with a cable (>150 m). The detector head (200 × 200 × 250 mm3; the weight is nearly 40 kg) is a collimated scintillated gamma detector installed on a scanning unit. The gamma detector is placed in a lead shielding with the collimator having an entrance angle near 10°. The detector head contains a TV camera and laser distance device. The remote control unit provides operation and processing of the acquired information. The gamma detector is based on a system of CsI(Tl) scintillators and an Si photodiode. The detector energy resolution (nearly 9% for radiation of 137Cs) provides identification of gamma radiating isotopes such as 57Co, 137Cs, 40K, 60Co, 131I and 154Eu. The gamma locator threshold of determination is 250 Bq/cm2 for a 10 cm3 scintillator and 137Cs radiation. The system allows one to measure the effective surface activity density (for 137Cs radiation) of all building surfaces and to reconstruct an exposed dose rate distribution within the volume of the investigated space.