Background characteristics of the underground laboratory of the Hydrogeology and Engineering-Geology Section of the Academy of Sciences of the Georgian SSR

A low-background underground laboratory outfitted with equipment for determining ultra-small amounts of radionuclides in rock and water samples and in the structural materials of nuclear-radiation detectors has been built in the Hydrogeology and Engineering-Geology Section (SGIG) of the Academy of Sciences of the Georgian SSR. A detector based on a NaI(T1) crystal 100 mm in diameter and 100 mm long with a well 33 mm in diameter and 60 mm long was used to measure the background gamma radiation. The crystal was connected to an FEU-100 photomultiplier through a quartz optical waveguide. The body of the scintillation unit was made of grade M1 copper, which was then chrome plated. The energy resolution of the detector is 9.5 ± 0.1% for the 137Cs peak. Primary measurements were made with an AI-1024 analyzer. The measurement time for multiple exposures was 1000 sec outside passive shielding, while the measurement time in the shielding was 7 h of operating time daily for half a year. The results of the measurements were compared with data obtained from a similar detector in one of the low-background facilities of the Baksan Neutrino Observatory (BNO) of the Academy of Sciences of the USSR. The content of natural radionuclides in samples taken from the rocks surrounding the low-background loaboratories BNO and SGIG is shown in a table