Extra low-level radiocesium determination by a Compton suppressed Ge γ spectrometer

Detection limits for 137Cs using our low-level detection system with active and passive shielding is determined. The HPGe 'Canberra' detector, 25% nominal efficiency was placed inside Φ=7.62 cm diameter hole of 22.5 x 22.5 cm annular 'Bicron' made NaI(Tl) crystal. The other end of the hole was closed by the 7.6 x 7.6 cm NaI(Tl) plug detector. The whole assembly was shielded by the 25 cm thick shield made from pre W.W.II iron. Using advantages of low-background detection system and high efficiency of chemical separation of 137Cs from water it is estimated that the lowest concentration of 137Cs activity which can be detected in our laboratory is 0.5 mBq/l in 24 h measurement time. This limit could satisfy all requirements for determination of 137Cs in any environmental sample of water. (author)