Study and development of analytical methods for the determination of natural radioactivity in waters

Radon content in water samples was determined by both the emanation method and alpha counting with liquid scintillation detectors. In the first method common erlenmeyer flasks were succesfully employed as scintillation chambers by internally linning their walls with ZnS(Ag). The radon separation and concentration process showed high efficiency and supplied reproducible results. Only 0,06% of the 222Rn originally dissolved in the water sample was lost by retention into the system. The detection limit attained with the emanation method corresponded to a 222Rn concentration of 4.1pCi/l for 95% confidence level. The liquid scintillation counting technique provided rapid and reliable results. Insta-gel (commercial product) and toluene solutions of PPO and DMPOPOP were used as liquid scintillation counters. It was found that 95% of the 222Rn gas contained in the water sample remained dissolved in the liquid phase of the counting 'cocktail'. The detection limits were 117 pCi/l and 26pCi/l for Insta-gel and toluene solutions, respectively, for 95% confidence level. The radon concentrations measured in different water springs of Sao Paulo State, Brazil, were below 9.000pCi/l which is the maximum limit recommended for drinkable water. (Author)