A Compton coincidence study of liquid scintillator response to low-energy electrons

Abstract

Liquid scintillation counting is used in the Laboratoire Primaire des Rayonnements Ionisants (LPRI) for the standardisation of electron emitters by the triple to double coincidence ratio (TDCR) method. For low-energy emitters, the main uncertainty comes from the imperfect model of the non-linear liquid scintillator response to low energy electrons caused by the ionisation quenching effect. Many semi-empirical models have been published in the literature to describe the phenomenon but all of these formulae use parameters that are difficult to define. An experimental study of the LS response has been undertaken to describe these phenomena and to measure the mean number and the statistical distribution of the light photons emitted by the cocktail after the interaction of monoenergetic electrons. These electrons have been simulated by using a Compton coincidence detection system. The LS-cocktail was irradiated by an external gamma-ray source to create a Compton interaction. A brief description is given of the experimental system and the method used to analyse the statistical distribution of the photons detected by the photomultiplier tube. Furthermore, the response of commercial and home-made cocktails is presented for various chemical quenching conditions. The study shows that the kB coefficient of the Birks' formula depends on the chemical quencher concentration and an alternative approach is discussed which provides a better fit to the experimental results.