In the present work, we have made Monte Carlo simulations of the response of 1″ × 1″ LaCb(Ce) and 1″ × 1″ LaBn(Ce) scintillation detectors using the radioactive sources emitting two gamma rays in cascade, namely, 60Co, 94Nb, 46Sc and 24Na for different values of source-detector separation. These simulations were done using GEANT4 toolkit that include radioactive decay module and general particle source (GPS) module. Energy spectra were generated for each of these double gamma emitters and absolute activities were calculated using conventional sum-peak method and modified sum-peak method proposed very recently. In order to validate the simulated results, we have carried out experimental investigations using a calibrated 60Co source. The measured activities are found to be in very good agreement with the simulated activities.
