The ionization quenching function for coincident electrons.

When two electrons interact simultaneously with a liquid scintillator, they generate two distributions of solvent excited molecules. These distributions can overlap totally, partially or not overlap at all. The overlap produces an increase of the excitation density, and consequently a modification of the ionization quenching. A theoretical description that calculates the mean overlap and the ionization quench function for multiple electron coincidences is presented. We analyse the overlapping factor for electrons of similar energies. Two overlap models, two dimensional (2D) and three dimensional (3D), have been developed. Both Birks and Voltz formulae have been applied to a KLM atomic rearrangement model to compute the ionization quenching function. The counting efficiency for (125)I obtained by applying the overlapping correction is about 1% lower than that computed without this correction.