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Description
BALOO (BAsement scintillation LOw-backgrOund detector) is a low-background scintillation set-up constructed in a basement room at the Institute for Nuclear Research of NASU for assessment of materials radiopurity, R&D of radiopure scintillation materials and small scale low counting experiments. A CdWO4 crystal scintillator 7 cm in diameter and 7 cm height is viewed by a low-background photomultiplier through a high-purity quartz light-guide 10 cm length. The detector is shielded by layers of OFHC copper (6-12 cm) and low radioactive lead (15 cm). The set-up construction allows an easy access to the sample volume of the detector by shift of the passive-shield upper part. A plastic scintillator counter 100 × 100 × 12 cm is placed above the set-up to veto cosmic muons. The detector background counting rate is reduced by 3 orders of magnitude in the energy interval 0.5 – 2.6 MeV and by an order of magnitude above 3 MeV in comparison with the unshielded detector at the Earth surface. Thanks to the low level of background and a very high gamma-ray quanta detection efficiency of the CdWO4 scintillator, the sensitivity of the detector is comparable to the characteristics of low-background HPGe detectors located underground: for instance, 90% C.L. activity upper limits are on the level of 5 mBq/kg (40K), 1 mBq/kg (137Cs), 3 mBq/kg (226Ra), and 0.8 mBq/kg (228Th) for a 3-kg titanium sample in the Marinelli geometry over 30 days of measurements. Assembling of anti-radon system and additional muon-veto counters is in progress to improve the set-up sensitivity further.
