In situ calibration of a low-level, in-line, flow liquid scintillation analyzer

A new method to calibrate a flow liquid scintillation detector in an in-line waste water monitor was developed and its operation was verified. The liquid scintillation detector for detecting low energy beta emitters was one of three detectors of the monitor that aimed to analyze radionuclide concentrations in the waste water before draining it into sewer. To calibrate the liquid scintillation detector, a 20-cm3 calibration vial containing a reference solution was connected to the water sampling channel with a three-way valve. Ten measurements needed to define a quench correction curve required only 200 cm3 solution. The counting efficiencies of the liquid scintillation detector for 3H and for 14C under the average quenching level of the waste waters were estimated at 27% and 58%, respectively. The calibration using the vial took into account the sampling and mixing system, which would not be the case with sealed quenched standards. Although active solution was used, the method was simple, generated little active waste, had low possibility of contamination, and reduced costs and labor for the calibration.