137Cs direct measurement in water via LSC techniques

This work explores the screening technique of 137Cs concentration dissolved in water via the Cherenkov counting method on a Liquid Scintillation Counter Quantulus 1220. In the event of a nuclear emergency or the potential radioactive leakage from the power plants, the prompt detection of two long-lived fission products, 90Sr/90Y and 137Cs, is of the greatest radiological concern. Here we present an innovative, rapid, and simple LSC method for 137Cs content determination that enables quick evaluation of the radioactive contamination status of water samples without any sample pre-treatment. The novelty in the presented Cherenkov counting technique is the addition of ionic liquid 1-butyl-3-methylimidazolium salicylate in a sample vial. Its presence in the amount of ∼1 g increases efficiency up to ∼30% via a wavelength-shifting mechanism, thus reducing the detection limit of the method more than 4 times. Without the ionic liquid's addition, the method's main parameters were detection efficiency of 6.98(11)% and a detection limit of 2.6 Bq L−1 for 300 min of counting in a 20 mL sample volume. Interference with 90Sr/90Y, a radionuclide that can contribute to the Cherenkov radiation spectrum, was also investigated. The method of distinguishing individual radionuclides (137Cs and 90Sr/90Y) in the cumulative Cherenkov spectrum is presented as well.