Digital alpha/beta pulse shape discrimination of CsI : Tl for on-line measurement of aqueous radioactivity

A digital pulse shape discrimination data acquisition system developed arou nd a commercially available digital oscilloscope card and data acquisition software was applied to on-line measurement of aqueous radioactivity. The r adiation detector consisted of a flow-cell containing granular 63-90 mu m P arylene C polymer coated CsI:T1 and two Burle 8850 photomultiplier tubes (P MTs). The PMTs were connected in a software-realized coincidence mode. The digital data acquisition system consisted of a GaGe CompuScope 8012A/PCI 12 -bit dual channel 50-MHz digital oscilloscope card residing in a Pentium II I 450 MHz personal computer and:the:LabVIEW 5.1 data acquisition software. The individual fast anode scintillation pulses were digitized by the oscill oscope, transferred from on-board memory to computer memory, and processed by the LabVIEW Virtual Instrument (VI). The coincidence resolving time was set to 100 ns to reduce background. Pulse shape discrimination was achieved using the charge integration technique. Experimental tests showed very goo d pulse shape discrimination between alpha and beta particles. The alpha to beta and beta to alpha spillover were 2.1% and 1.4% respectively for singl e parameter analysis which yielded a figure of merit (FOM) of 1.65. The alp ha to beta and beta to alpha spillover for dual parameter; analysis were 1. 3% and 0.3%, respectively. The alpha and beta detection efficiencies for th e CsI:T1 flow-cell were typically 31% and 26%, respectively. This system wa s also coupled to a liquid ion chromatography system for online measurement of aqueous alpha/beta radionuclides.