IAEA-MEL's underground counting laboratory -The design and main characteristics

摘要

An underground counting laboratory designed for low-level gamma- and beta-ray spectrometry of anthropogenic and natural radionuclides in environmental samples has been constructed at the depth of 35 m water equivalent (w.e.) at the IAEA's Marine Environment Laboratory in Monaco. The laboratory is equipped with 4 large volume HPGe detectors placed in a common lead shield with anti-cosmic plastic scintillator shielding, a coincidence—anticoincidence gamma-ray spectrometer, comprising an HPGe detector and NaI(Tl) shielding, a HPGe-HPGe telescope (sandwich) detector system, and a Quantulus liquid scintillation spectrometer. The laboratory design is presented and performance of the gamma-ray spectrometers under different coincidence-anticoincidence modes of operation are discussed. The anti-cosmic shielding has proved to be a valuable investment as the backgrounds of HPGe detectors operating at shallow depths are comparable with backgrounds of detectors placed in laboratories operating at moderate depths of about 250 m w.e.