Low-backround gamma- and beta-spectrometry laboratory


This laboratory consists of two ultralow-background liquid scintillation counters (LSCs) and two ultralow-background gamma spectrometers, all of which are among the best of their kinds. The laboratory has been designed and configured for low-level and low-background activity measurements. The equipment in this facility can be used for the detection of gamma-emitters as well as pure-beta isotopes such as 3H, 14C, 36Cl, 90Sr, 99Tc with low detection limits. One of the possible applications is the tracing of the residue of the nuclear weapon tests and that of the Chernobyl NPP accident in sediment sequences.

The HPGe detector of the Canberra-Packard made BE5030-7915-30ULB thin-windowed, broad-energy gamma-spectrometer is situated in high-purity lead shielding. For sediment samples of about 10 g (dispersed in a thin layer), the detection efficiency of the natural fallout 210Pb is about 18%, while the Compton background in this region is around 0.3 cpm. This enables the quantification of 2-3 Bq/kg excess 210Pb, compared to the 226Ra baseline. From the same measurement the MDA for the anthropogenic (e.g. nuclear weapon tests and Chernobyl NPP accident) fallout 241Am-re and 137Cs is around 1-2 Bq/kg, in case of 36 hours counting time.

The Tri-Carb 3180 TR/SL is a computer-controlled benchtop liquid scintillation counter by Perkin-Elmer for   detecting small amounts of beta radioactivity with multi-parameter linear MCA. Special proprietary “Surround TR-LSC” BGO (Bismuth Germanium Oxide) detector guard surrounds the sample in the counting chamber, enhances discrimination against background and yields the   highest E2/B values available in  a  multipurpose liquid scintillation counting system. It is specially designed for counting extremely low activity samples in disposable glass and plastic vials. Background for 3H and 14C is 1,0 – 0,75 cpm and 0,3 cpm, respectively.

Super low level counting is available for extremely low activity beta samples, increasing system sensitivity (E2/B) to a factory test minimum of 880 for 3H and 6,000 for 14C. The detection limit for 3H without enrichment is ≤ 1 Bq/l, in case of 500 minutes counting time.

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