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-/spl mu/m 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 (/spl plusmn/1/spl sigma/) were 64.9/spl plusmn/5.7%, 52.5/spl plusmn/4.5%, and 4.5/spl plusmn/0.2% for /sup 233/U, /sup 90/Sr//sup 90/Y, and /sup 14/C, 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 (/spl plusmn/1/spl sigma/) for a 30-s count time were calculated to be 0.19/spl plusmn/0.01 Bq, 0.9/spl plusmn/0.1 Bq, and 11.4/spl plusmn/0.6 Bq for /sup 233/U, /sup 90/Sr//sup 90/Y, and /sup 14/C, respectively. Although the 3-/spl mu/m-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.