Radiometric techniques for the detection and assessment of tritium in aqueous media - a review

Tritium (3H) is one of the hardest isotopes to detect by most traditional radiometric means due to the low energy of the β− emission, (β−MEAN 5.67 keV, β−MAX 18.59 keV). The high mobility of the isotope in groundwater environments and subsequent entry into the food chain constitutes a radiation safety risk justifying assessment. Accordingly, there is a need to measure 3H accurately and efficiently, often in low concentrations, both in laboratory settings and on-line flow-cells for potential in situ measurement requirements. This review covers technologies developed to assess aqueous tritium-containing samples. Of the techniques reviewed, liquid scintillation counting (LSC) is the best performing means of aqueous 3H detection with a minimal detectable activity of 6 × 10−4 Bq L−1 for a 195-min counting time. LSC is also established as the industry standard and is the basis of the first, commercially-available, real-time 3H detection system. This review also covers the other means described in literature for the detection of tritium in aqueous samples, including the use of plastic and inorganic scintillators, imaging plates, both in off-line and on-line modes of operation. Whilst most of these techniques lag LSC in terms of technological maturity, several offer detection sensitivities that could rival LSC, without the need for the sample preparation and waste generation associated with LSC, and providing real-time in situ measurements.