SURFACE-ACTIVITY AND DOSE-RATE DISTRIBUTION INSIDE 4-TH REACTOR HALL OF CHERNOBYL NPP

A Gamma Locator designed to conduct contamination surveys inside the r eactor hall of the Chernobyl NNP 4-th unit is developed. The device co nsists of detector head and remote control computer connected with a c able (> 150 m). The detector head is a collimated scintillator-based g amma-ray detector. It is installed on a scanning unit and is placed in side the reactor hall. The Gamma Locator scans all hall surfaces with a certain angle step and measures quantum flux from these directions. These data are used to determine the effective surface activity of con taminated surfaces. A distance between the detector head and surveyed surface is measured by a laser distance device. There is a small CCD c amera inside the collimator. It obtains a visible image of the measure d surface. Au exposed dose rate distribution within the investigated v olume is reconstructed by using the measured Cs-137 effective surface activity.