The effect of multiple γ-ray interactions on ionisation quenching corrections in liquid scintillants

The effect of multiple γ-ray interactions within a liquid scintillation detector caused by a single radionuclide decay event on ionisation quenching corrections has been determined. Ionisation quenching corrections to the energy deposition spectrum have been carried out over all electron-generating gamma interactions of the decay event. Comparison has been made with the approximate method typically used to correct for ionisation quench. Both calculations were carried out using the Geant4 simulation package. The two models are compared using the values of detection efficiencies of the logical sum of double coincidence obtained for 131I, 123I and 177Lu measured using the Triple-to-Double Coincidence Ratio method of absolute activity measurement. Finally, predictions are made as to the circumstances under which the two quench correction approaches will be most discrepant.