Backgrounds: Thallium-201 is produced through ²⁰³Tl (p, 3n) ²⁰¹pb ²⁰¹Tl reaction by cyclotron. This radioisotope has known as one of the cyclotron radioisotopes which is used for myocardial perfusion in the coronary artery disease, Tl-201 after chemical purification and quality control in the form of ²⁰¹Tl-chlorid is ready to send to the hospitals.

Materials and methods: In this work the effect of the proton energy on quality of Tl-201, was studied. Radionucleidic purity was determined by high purity Ge (HPGe) detector Gamma spectrometer, in production time and after one half-life (73h). The targets were coated with Enriched Thallium-203 (97%).

Results: The Variation of thickness of targets was 18.3 ± 1.3µm. The different energies of bombardment on quality of Tl-201 and Tl-200, Tl-202, and Pb-203 (as impurity) were studied. The results have shown that optimum energy for proton was 28.5 MeV.

Conclusion: The variation energy of bombardment can change the purity of Tl-201 but all results were in the standard range according to the United States Pharmacopoeia (USP) and European Pharmacopoeia. Iran . J. Radiat. Res. 2003 1(1): 51 - 54.