Effect of counting vials and scintillators on the detection of low-level 14C by liquid scintillation spectrometry
The low-level 14C detection efficiencies and background count rates of glass and commercially available copper-Teflon (C-T) vials have been determined. The C-T vials gave better results and their spectral characteristics were investigated using four different scintillators. The highest figure of merit was obtained using sample benzene with a butyl- PBD scintillator, confirming results reported in the literature. However, some undesirable characteristics of C-T vials have come to light. We have investigated and overcome the high benzene (sample) vapour loss and the between vials variable 14C spectral end point. These factors dictate that care as well as individual vial calibration is needed for their successful application to low-level 14C counting. The sample volume to background relationship determined for the C-T vials indicates that a 4 ml counting volume is near to optimal for low-level 14C detection.