Application of TDCR-Geant4 modeling to standardization of 63Ni

► A TDCR model based on Geant4 is described in the case of standardization of 63Ni. ► All the optical effects (refraction, reflection) in the TDCR counter are simulated. ► The problem of the resolving time duration is also investigated. ► Activity measurements are compared with the classical TDCR model.