Fusion Science and Technology / Volume 48 / Number 1 / July 2005 / Pages 409-412
Technical Paper / Tritium Science and Technology - Tritium Measurement, Monitoring, and Accountancy
Traditionally the amount of tritium on a surface is determined by swiping the surface with a material such as filter paper and counting the removed tritium by scintillation. While effective, this method can be time consuming, can alter the surface, only measures removable tritium and produces radioactive waste. For a given application each of these considerations may or may not be a disadvantage. A solid state monitor, on the other hand, has the potential to provide rapid analysis, not alter the surface, measure all tritium on a surface and produce little or not radioactive waste. This allure has promoted open wall ion chamber and PIN diode-based tritium surface monitor development, and these techniques have enjoyed certain success. Recently the first tests were performed with an avalanche photodiode (APD) for surface tritium measurement. While quite similar in concept to PIN diode based measurements, side-by-side testing showed that the APD provided substantially better counting efficiency. Considerations included count rate, background, sensitivity, stability and effect of ambient light. Of particular importance in the US, the APD was able to measure concentrations down to the "free release" limit, i.e., the concentration below which items can be removed from radiological control areas.