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 microencapsulated with Parylene C to reduce its rate of dissolution. Averaged over the first hour of use, the pulse shape discrimination figure-of-merit was 1.4 and the detection efficiencies 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 rate in the alpha and beta pulse shape window was 0.17 and 0.004 cps, respectively. The resultant minimum detectable activity for a 30 second count time was 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 microencapsulation reduced CsI:Tl dissolution, the detection efficiency declined by a factor of two after 4.8 hours while the pulse shape resolution degraded slightly