In the present work, we have carried out realistic Monte Carlo simulations of the response of a 1 scintillation detector using mono energetic gamma emitter Cs and double-gamma emitter $^{\mathbf{60}}$\textbf{Co. These simulations were done using GEANT4 toolkit that include radioactive decay module, low energy EM package and general particle source (GPS) module. Apparent efficiencies (both total detection and full energy absorption) so obtained for $^{\mathbf{60}}$Co have been corrected for coincidence summing using the method proposed by Vidmar $et al$\textbf{. [6]. The simulations have also been carried out for the same energies assuming mono-energetic point sources, for comparison. Experimental measurements have also been carried out using calibrated point sources of $^{\mathbf{137}}$\textbf{Cs and $^{\mathbf{60}}$\textbf{Co. The simulated and the experimental results are found to be in good agreement. This demonstrates the reliability of the correction method, originally proposed for HPGe detector, for efficiency calibration of CeBr$_{\mathbf{3}}$ detector.
