The effect of impurities on calculated activity in the triple-to-double coincidence ratio liquid scintillation method

In the triple-to-double coincidence ratio (TDCR) method of liquid scintillation counting, unaccounted or improperly accounted impurities can result in lower-than-expected or higher-than-expected recovered activities, depending on the counting efficiency of the nuclide of interest, the counting efficiency of the radionuclidic impurity, and the amount of impurity present. We describe these general dependences using a simple model. The trends predicted by the model are tested experimentally using a series of mixed 241Am/3H and 63Ni/3H sources. An “impurity surface” is derived to facilitate an intuitive grasp of impurity phenomena in TDCR.

► Improperly accounting for impurities can have counterintuitive effects in TDCR LS counting.
► We model the variation of the ratio of recovered and actual activities with impurity fraction.
► Our model reproduces trends observed in experiments with mixed 241Am/3H and 63Ni/3H sources.
► A 3D surface is derived to promote a more intuitive grasp of impurity effects in TDCR counting.