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Experimental technique is used to study the variation of intrinsic as well as absolute detection efficiencies of NaI(Tl) scintillator detector with the source-detector distance and the energy of incident radiation. Usually it is believed that intrinsic efficiency is material property and is independent of geometrical configuration of source and detector. However experiments have shown that the intrinsic efficiency varies with source-detector distance. Detailed analysis is performed using two point sources Cs-137 and Co-60 to study the variation of intrinsic efficiency with source detector distance. Moreover, the variation of the absolute efficiency is also presented with source-detector distance and the efficiencies are compared for incident gamma energies of 0.662 1.173 and 1.332 MeV.