New sensitive technique for measurement of krypton-85 based on absorption in polycarbonates and liquid scintillation counting

The objective of this work is to present the liquid scintillation counting (LSC) as a new technique to be used within the polycarbonate method for measurements of ⁸⁵Kr activity concentrations in air or water. Currently, the polycarbonate method employs the high absorption ability of some polycarbonates to noble gases for sampling them from the environment and then to measure the absorbed activity. This work explores the applicability of LSC for measurement of ⁸⁵Kr beta particles emitted from the exposed polycarbonates. Experiments with exposure of polycarbonates to Kr-85 in water and subsequent LSC counting are presented. The results from these experiments demonstrate good linear correlation between the measured net LS counting rate and the activity concentration of ⁸⁵Kr at the exposure. The usage of the proposed technique leads to approximately 10 times better sensitivity for ⁸⁵Kr compared to gross beta counting or gamma-spectrometry of the exposed polycarbonates. A particularly advantageous feature that has been identified in the present work is that the polycarbonate material is largely transparent for the LS cocktail light, thus adding polycarbonate in the LS cocktail do not result in a strong adverse effect on the light output. The results from the conducted experiments imply that quantitative measurements of ⁸⁵Kr activity concentrations in air or water by LS counting of polycarbonates are feasible. The technique is applicable for monitoring of ⁸⁵Kr concentrations in air or water in nuclear power plants (including at-reactor pools), spent fuel storage facilities and reprocessing plants. It allows simultaneous monitoring of ⁸⁵Kr concentrations in a large number of points in these facilities.