Optimization of low-level LS counter Quantulus 1220 for tritium determination in water samples Ivana Jakonić a,n , Natasa Todorović b , Jovana Nikolov b , Ines Krajcar Bronić c , Branislava Tenjović d , Miroslav Vesković b a University of Novi Sad, Faculty of Technical Sciences, Novi Sad, Serbia b University of Novi Sad, Faculty of Sciences, Department of Physics, Novi Sad, Serbia c Laboratory for Measurements of Low-Level Radioactivity, Ruđer Bošković Institute, Zagreb, Croatia d University of Novi Sad, Faculty of Sciences, Department of Chemistry, Novi Sad, Serbia HIGHLIGHTS  The goal of this paper is to demonstrate development of new direct LSC method in our laboratory.  The optimization of tritium analysis in water samples by Quantulus 1220 was performed.  Sample/scintillant ratio, choice of appropriate scintillation cocktail and comparison of their efficiency were performed.  The effect of chemi- and photoluminescence and combination of scintillant/vial were performed.  Tritium activity concentration was determined in Danube river samples and in several intercomparison samples. article info Article history: Received 10 October 2013 Accepted 11 January 2014 Available online 22 January 2014 Keywords: Tritium measurement Liquid scintillation counting Scintillation cocktails Optimization abstract Liquid scintillation counting (LSC) is the most commonly used technique for measuring tritium. To optimize tritium analysis in waters by ultra-low background liquid scintillation spectrometer Quantulus 1220 the optimization of sample/scintillant ratio, choice of appropriate scintillation cocktail and comparison of their efficiency, background and minimal detectable activity (MDA), the effect of chemi- and photoluminescence and combination of scintillant/vial were performed. ASTM D4107-08 (2006) method had been successfully applied in our laboratory for two years. During our last preparation of samples a serious quench effect in count rates of samples that could be consequence of possible contamination by DMSO was noticed. The goal of this paper is to demonstrate development of new direct method in our laboratory proposed by Pujol and Sanchez-Cabeza (1999), which turned out to be faster and simpler than ASTM method while we are dealing with problem of neutralization of DMSO in apparatus. The minimum detectable activity achieved was 2.0 Bq l 1 for a total counting time of 300 min. In order to test the optimization of system for this method tritium level was determined in Danube river samples and also for several samples within intercomparison with Ruđer Bošković Institute (IRB). & 2014 Elsevier Ltd. All rights reserved. 1. Introduction According to European Commission the upper limit for tritium in drinking water is 100 Bq l 1 (European Commission, 1998). This value is not based on health effect relative to its consumption but rather on monitoring value which would indicate leakage or release from power plant that needs further check if other radio- nuclides are present in water. Activity concentration value that is commonly used as limit based on health concerns is 10,000 Bq l 1 (for a 70 kg man who drinks 2 l of water per day), as recom- mended by World Health Organization (WHO) (2011). Taking into account the tritium low level in the environment, special conditions have to be fulfilled in order to obtain accurate and reliable tritium measurements. The activity concentration of natural water samples is so low, that for obtaining accurate measurements, any counting system must have a high and stable overall efficiency for the detection of low energy beta particles together with a low and stable background (Varlam et al., 2009). Liquid scintillation counting (LSC) is the most commonly used technique for measuring low-energy beta emitters, namely for tritium (José Madruga et al., 2008). The radioactive sample is combined with a liquid scintillation cocktail and the decaying Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/radphyschem Radiation Physics and Chemistry 0969-806X/$ - see front matter & 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radphyschem.2014.01.012 n Corresponding author. E-mail address: ijakonic@uns.ac.rs (I. Jakonić). Radiation Physics and Chemistry 98 (2014) 69–76