Ivana Stojković

Improvement of measuring methods and instrumentation concerning 222Rn determination in drinking waters – RAD7 and LSC technique comparison

A procedure for the determination of (222)Rn in environmental water samples using liquid scintillation counting (LSC) was applied and optimized. A minimum detectable activity of 0.029Bql(-1) in a 20ml glass vial (10ml water sample mixed with 10ml of liquid scintillation cocktail) has been achieved during 300min of measurement time. The procedure was compared with RAD7 radon detector measurements. (226)Ra content in the water was determined by gamma-ray spectroscopy. Applications to drinking waters collected from public drinking fountains in the Vojvodina (Serbia) are presented with annual effective dose for ingestion and inhalation for adults calculated.

Possibilities and limitations of color quench correction methods for gross alpha/beta measurements

Gross alpha/beta activity determination is utilized as a very popular Liquid Scintillation Counting (LSC) technique widely used in routine monitoring of drinking, surface and waste waters. Since quenching phenomena are most problematic effect during LSC measurements, the objectives of this paper are to present, consider and evaluate two methods for color quench correction as a proposal for supplement to the ASTM D 7283-06 method for gross α/β determination. The first method is PSA adjustment: application of previously established dependence of optimal PSA discriminator between alpha and beta events on quench level of sample. The second method assumes counting on usual optimal PSA setting and application of previously determined quench calibration curves in order to correct count rates in alpha and beta channels afterwards. Application on obtained activity results of few artesian well water samples and colored spiked samples, based on the measured SQP(E) value of samples, has been demonstrated, as the opportunity to compare the validity, reliability and limitations of both methods. All samples have been counted on low-background liquid scintilllation counter Quantulus 1220™.

PSA discriminator influence on 222Rn efficiency detection in waters by liquid scintillation counting

A procedure for the (222)Rn determination in aqueous samples using liquid scintillation counting (LSC) was evaluated and optimized. Measurements were performed by ultra-low background spectrometer Quantulus 1220™ equipped with PSA (Pulse Shape Analysis) circuit which discriminates alpha/beta spectra. Since calibration procedure is carried out with (226)Ra standard, which has both alpha and beta progenies, it is clear that PSA discriminator has vital importance in order to provide precise spectra separation. Improvement of calibration procedure was done through investigation of PSA discriminator level and, consequentially, the activity of (226)Ra calibration standard influence on (222)Rn efficiency detection. Quench effects on generated spectra i.e. determination of radon efficiency detection were also investigated with quench calibration curve obtained. Radon determination in waters based on modified procedure according to the activity of (226)Ra standard used, dependent on PSA setup, was evaluated with prepared (226)Ra solution samples and drinking water samples with assessment of measurement uncertainty variation included.