Preliminary TDCR measurements at low energies using a miniature x-ray tube

International audienceDeveloped for radionuclide standardization using liquid scintillation, the TDCR method (Triple to Double Coincidence Ratio) is applied using coincidence counting obtained with a detection system composed of three photomultiplier tubes. For activity determination, a statistical model of light emission is classically used to establish a relation between the detection efficiency and the experimental TDCR value. Among the usual assumptions specified for the standard TDCR model, the condition of stochastic independence between PMTs is not explicitly mentioned. The validity of this condition can be tested using a stochastic approach of the TDCR modeling based on the Geant4 simulation code. The interest of this TDCR-Geant4 model is the possibility to simulate the propagation of optical photons from their creation in the scintillation vial to the production of photoelectrons in PMTs. Previous investigations revealed the existence of stochastic dependence between PMTs of geometrical origin in the case of low-energy depositions (lower than 20 keV). Not considered in the standard model, this effect can entail non-negligible deviations on calculated detection efficiencies and in turn on activity determination