AUTOMATIC SYSTEM FOR REMOTE MEASUREMENTS OF GAMMA-RAY FIELD CHARACTERISTICS FOR ACCIDENT BUILDINGS

An automatic gamma-locator was developed for measuring the Cs-137 surf ace activity inside the reactor hall of the destroyed fourth unit of t he Chernobyl Nuclear Power Plant. The gamma-locator consists of two co llimated scintillation detectors mounted on scanning devices and a con trol unit connected by the detectors with 200-m-long coaxial cables. T he energy resolution of the detectors is similar to 8% for Cs-137 (662 keV). The gamma-locator measures the surface activity of the Cs-137-r adionuclide contamination in the 3.7 x 10(6)-3.7 x 10(12)-Bq/m(2) rang e. Each detector is equipped with a TV-camera to observe an object und er investigation. For measuring the distances from the detector to the radiating surface, one of the detectors has a laser range finder and the other one has a laser pointer. The software makes it possible to d etermine the surface activity of radiation sources and to compute the distribution of the effective-dose rate from the spectra measured in t he accident building.