Evaluation of polymer-coated CsI:Tl as an alpha/beta pulse shape discriminating flow cell

A pulse shape discriminating flow-cell radiation detection system constructed with polymer-coated CsI:Tl was evaluated for simultaneous gross alpha/gross beta quantification. The CsI:Tl scintillator was crushed and sieved to 63-90-μm particle size and encapsulated with Parylene C to slow its dissolution rate. Averaged over the first hour of use, the pulse shape discrimination figure of merit was 1.4, and the detection efficiencies (±1σ) were 64.9±5.7%, 52.5±4.5%, and 4.5±0.2% for ²³³U, ⁹⁰Sr/⁹⁰Y, and ¹⁴C, respectively. The typical background count rates in the alpha and beta pulse shape window were 0.004 and 0.17 cps, respectively. The resultant minimum detectable activities (±1σ) for a 30-s count time were calculated to be 0.19±0.01 Bq, 0.9±0.1 Bq, and 11.4±0.6 Bq for ²³³U, ⁹⁰Sr/⁹⁰Y, and ¹⁴C, respectively. Although the 3-μm-thick encapsulation slowed CsI:Tl dissolution, the detection efficiency declined by a factor of two after 4.8 h, while the pulse shape resolution degraded slightly. With an appropriate coating, CsI:Tl is a good candidate for a heterogeneous pulse shape discriminating flow-cell