Comparative Testing of Various Flow-Cell Detectors Fabricated using CaF₂ Solid Scintillator

A monitoring system based on a flow-cell detector was developed for measuring the tritium concentration in water. The flow-cell detector was fabricated using a granular CaF₂ solid scintillator. This system does not use a liquid scintillation cocktail and does not generate radioactive organic liquid waste. Moreover, continuous real-time measurements are possible, in contrast to a liquid scintillation counting system, which requires batch measurements. For further development of the system, four flow-cell detectors were fabricated. They included a single 3-mm-diameter cell, three 3-mm-diameter cells in series, a single 5-mm-diameter cell, and three 5-mm-diameter cells in series. Continuously flowing water containing tritium at various concentrations was passed through the flow cells, and tritium count were measured for 600 and 10000 s. Investigating the relation between the count rate and concentration, the three 5-mm-diameter cells were most sensitive, with a linear relation maintained down to approximately 2 Bq/mL and 10 Bq/mL for 10000- and 600-s measurements, respectively.