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

Abstract

A digital pulse shape discrimination data acquisition system developed around a commercially available digital oscilloscope card and data acquisition software was applied to on-line measurement of aqueous radioactivity. The radiation detector consisted of a flow-cell containing granular 63-90 /spl mu/m Parylene C polymer coated CsI:Tl and two Burle 8850 photomultiplier tubes (PMTs). The PMTs were connected in a software-realized coincidence mode. The digital data acquisition system consisted of a GaCe CompuScope 8012A/PCI 12-bit dual channel 50-MHz digital oscilloscope card residing in a Pentium III 450 MHz personal computer and the LabVIEW 5.1 data acquisition software. The individual fast anode scintillation pulses were digitized by the oscilloscope, 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 good 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 single parameter analysis which yielded a figure of merit (FOM) of 1.65. The alpha 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 the CsI:Tl flow-cell were typically 31% and 26%, respectively. This system was also coupled to a liquid ion chromatography system for online measurement of aqueous alpha/beta radionuclides.