To exploit natural and artificial activity of tritium, H3 (half-life, 12.3 y.), as a tracer for the study of the large-scale circulation of air in the tropo-sphere, water balance and characteristics of ground water, systematic measurements of its activity in wet precipitations, surface and subsurface waters have been carried out since 1961. The levels of tritium activities in such samples vary over a wide range, factors of 104 or more. Due to large dilution with hydrogen of the tropospheric water, the specific activities in surface and subsurface waters are very low, and employment of sensitive detection techniques becomes necessary.
In this paper, we report on the techniques adopted for the measurement of tritium which permit an accurate determination of T/H ratios exceeding 10−17, without carrying out an electrolytic enrichment. A factor of twenty enrichment then suffices to measure natural levels of tritium in ground waters of up to 25 years “age” corresponding to T/H ratios of ca. 5 × 10−19.