Radioactive sources of isotopes 22Na, 137Cs, 60Co, 133Ba and decay chains of Th and U are analyzed by means of gamma spectroscopy. The instrument used, a cylindrical NaI(Tl) scintillator from Mirion Technologies (Canberra) with dimensions of 2 × 2, is characterized by its calibration and absolute efficiency. The peak energies of the gamma spectra obtained are identified and related to corresponding isotopes and matter-radiation interactions according to nuclear and atomic databases. From these data, spectroscopic methods are implemented to compute radioactive activities for each source.