Low-level tritium concentration measurements by liquid scintillation counting in environmental water samples

As it is shown in the literature, the concentration of 3 H bomb in the environment gradually decreases and 'peak' 3 H model calculations lose their significance because of the small differences in the 3 H content in waters of various ages. The method for 3 H analysis is now a routine, although special conditions have to be fulfilled in order to obtain accurate and reliable tritium measurements. Tritium is probably the most commonly used isotope for hydrological studies because of its ease of collecting and analysis. The 'age' of ground water has important implications for water resource management. Groundwater, that is part of the modern hydrological cycle, is continuously renewed. Only tritium is part of the water molecule and can thus actually 'dates' the water. All other dating methods rely on dissolved constituents whose abundance in water is controlled by physicochemical and biological processes. Tritium can be considered a conservative tracer for most hydrological studies. There are two standard recommendations that specify a method for determining tritium concentration in water by liquid scintillation counting. Basically, the principle is the same with small differences between the two chemical treatments of water samples. In the present work, a low background liquid scintillation system detector Quantulus 1220 is used to determine tritium concentration in different types of water: drinking water, precipitation, surface water and wastewater. All samples were measured according to the two studied standards, but we observed several parameters that were important for good scintillation measurement, namely pH, conductivity and holding time of sample: scintillator mixture. There is some interference in the measurement process that leads to different results for the same water sample prepared by the two methods. Establishing the most appropriate routine procedure for tritium measurement in water sample was the main goal of our study. The results obtained in the Sixth IAEA Inter-comparison of Low-level Tritium Measurements in Water (TRIC2000) confirm the settled procedure. Even if the uncertainty of the method is high and even if tritium levels in the environment continue to decrease, the direct measurement of tritium concentration in water sample can still be a more rapid and cheaper measurement method for environment. (authors)