Absolute standardization of the impurity 121Te associated to the production of the radiopharmaceutical 123I

123I is widely used for radiodiagnostic procedures. It is produced by reaction of 124Xe (p,2n) 123Cs →123Xe →123I in cyclotrons. 121Te and 125I appear in a photon energy spectrum as impurities. An activity of 121Te was calibrated absolutely by sum-peak method and its photon emitting probability was estimated, whose results were consistent with published results.