The Mechanisms of the Liquid Scintillation Process

Abstract

This chapter discusses various mechanisms that comprise the liquid scintillation process. The liquid scintillation process is based upon the conversion of a part of the kinetic energy of an ionizing particle into photons. In all liquid scintillation counting with homogeneous distribution of the radionuclide, there is always a fraction of radionuclides near the walls of the container. A part of these radiations can reach the wall before losing all of their energy. Thus, the response produced is less than that produced by a particle of the same energy which releases all of its energy to the liquid scintillation medium. This is often called the wall effect. The wall effect has a slight effect on counting in a wide open counting channel, but can markedly alter the relative counts in narrow counting channels. In liquid scintillator solutions, the primary excitations occur in the solvent part of the solution. The final response is directly proportional to the number of excited solvent molecules produced in this initial step. Quenching is a term commonly used to denote some process that causes a decrease in the photon yield of a liquid scintillator solution relative to no quenching. These quenching mechanisms can be divided into four main categories: energy absorption, dilution-concentration, impurity (sometimes called chemical), and color.