EVALUATION OF POLYMER-COATED CSI-TL AS AN ALPHA BETA PULSE-SHAPE DISCRIMINATING FLOW CELL/

A pulse shape discriminating flow-cell radiation detection system cons tructed with polymer-coated CsI:TI was evaluated for simultaneous gros s alpha/gross beta quantification, The CsI:TI scintillator was crushed and sieved to 63-90-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 detect ion efficiencies (+/-1 sigma) were 64.9+/-5.7%, 52.5+/-4.5%, and 4.5%/-0.2% for U-233, Sr-90/Y-90, and C-14, respectively, The typical back ground count rates in the alpha and beta pulse shape window were 0.004 and 0.17 cps, respectively, The resultant minimum detectable activiti es (+/-1 sigma) 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 U-233, Sr-90/Y-90, and C-14, respectively. Although the 3-mu m-thick encapsulation slowed Cs I: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:TI is a good candidate for a heterogeneou s pulse shape discriminating flow-cell.