Abstract: The quality of the gamma spectrometer results depends directly on the accuracy of the detection efficiency in the specific configuration of the concern. In this research, measurement conditions. In γ-ray spectroscopy using scintillation detectors, one usually needs to know the full-energy peak efficiency for any specific source where the detectors are calibrated for measuring point sources are placed in succession at constant distance from the considered detector to optimize the detection. Experimental calibration is limited to many measurement geometries and can not be directly applied to all measurement configurations. Hence, an alternative possibility of being able to calculate efficiency is highly desirable. The purpose of this research is calibration. The Nal (T1) scintillation detector practically by using radioactive point sources in the development of axial dimensions from the surface of detector and with varying photon energies.