DETERMINATION OF SURFACE-ACTIVITY AND RADIATION SPECTRUM CHARACTERISTICS INSIDE BUILDINGS BY A GAMMA-LOCATOR

A gamma locator designed to conduct contamination sun ev inside buildi ngs connected with nuclear production is developed. The device consist s of a detector head and a remote control unit connected with a cable ( > 150 m). Tile detector head (200 x 200 x 250 mm(3); the weight is n early 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 degrees. The detector head contains a TV camera and laser distance device. The remote contr ol 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 radiat ion of Cs-137) provides identification of gamma radiating isotopes suc h as Co-57, Cs-137, K-40, Co-60, I-131 and Eu-154. The gamma locator t hreshold of determination is 250 Bq/cm(2) for a IO cm(3) scintillator and Cs-137 radiation. The system allows one to measure the effective s urface activity density (for Cs-137 radiation) of all building surface s and to reconstruct an exposed dose rate distribution within the volu me of the investigated space.