Tritium determination in aqueous samples by using LSC Quantulus in CDTN - Brazilian Development Center for Nuclear Technology, Brazil

Tritium is the radioisotope of hydrogen which disintegrates by emission of beta particle to 3He. Its determination is important in several applications such as in oil recovery, where tritiated tracers are added to injection fluids, or in groundwater surveys, to estimate the recharging of aquifers, among others applications. Liquid scintillation spectrometry is an appropriate method for determining low-level contents of tritium in aqueous samples. We used a low background liquid scintillation system detector, Perkin Elmer - Wallac QuantulusTM 1220, recently acquired by Nuclear Technology Development Center (CDTN). The purpose of this work is the optimization of the counting performance for tritium determination in water samples by direct counting. For definition of optimum parameters we compare two cocktails, Instagel PlusTM and Optiphase HisafeTM 3. The ratios of sample/cocktail studied were 8/10, 10/10 and 10/12. The stability of the sample/cocktail mixture was also analysed by the loss of mass and by the luminescence spectrum. The counting conditions were 60 minutes counts for each vial, in the selected counting windows 50-200 and 1-200 channels. The vial used was 20 mL polyethylene. For background estimation we used a very old water (dead water) from Thermas Antonio Carlos, Pocos de Caldas, Brazil. The good results obtained in national and international laboratory intercomparison programs indicate the excellence of the tritium analysis at CDTN. (author)