Calculation of extrapolation curves in the 4π(LS)β-γ coincidence technique with the Monte Carlo code Geant4

At LNE-LNHB, a liquid scintillation (LS) detection setup designed for Triple to Double Coincidence Ratio (TDCR) measurements is also used in the β-channel of a 4π(LS)β-γ coincidence system. This LS counter based on 3 photomultipliers was first modeled using the Monte Carlo code Geant4 to enable the simulation of optical photons produced by scintillation and Cerenkov effects. This stochastic modeling was especially designed for the calculation of double and triple coincidences between photomultipliers in TDCR measurements. In the present paper, this TDCR-Geant4 model is extended to 4π(LS)β-γ coincidence counting to enable the simulation of the efficiency-extrapolation technique by the addition of a γ-channel. This simulation tool aims at the prediction of systematic biases in activity determination due to eventual non-linearity of efficiency-extrapolation curves. First results are described in the case of the standardization (59)Fe. The variation of the γ-efficiency in the β-channel due to the Cerenkov emission is investigated in the case of the activity measurements of (54)Mn. The problem of the non-linearity between β-efficiencies is featured in the case of the efficiency tracing technique for the activity measurements of (14)C using (60)Co as a tracer.

Simulation technique for extrapolation curves in 4πβ-γ coincidence counting method using EGS5 code

A simulation technique was developed for the extrapolation technique in 4πβ-γ coincidence counting method. Simultaneous emissions of β and γ rays were calculated using EGS5 code to obtain coincidence counting between both β and γ channels. The simulated extrapolation curves were compared with experimental data obtained with (134)Cs measurements using a plastic scintillator in the β channel. The variation of the extrapolation curves with γ-gate configuration was investigated by the simulation technique.