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The growing field of nuclear medicine theranostics relies on radionuclides that combine diagnostic and therapeutic functions [1]. Among these, the four isotopes of Terbium Tb-149, Tb-152, Tb-155, and Tb-161 offer complementary decay modes suitable for PET, SPECT, and targeted alpha and beta therapy, earning Terbium the title of the “Swiss army knife” of nuclear medicine [2,3].
To produce non-conventional medical radionuclides with high-molar purity, CERN established the MEDICIS (MEDical Isotopes Collected from ISOLDE) facility in 2017. Operating in synergy with ISOLDE, MEDICIS utilizes the unused fraction of the 1.4 GeV proton beam from the Proton-Synchrotron Booster to irradiate dedicated targets. After irradiation, targets are heated up to 2000 - 2300 °C to release the reaction products, which are then ionized and mass-separated to obtain isotopically pure samples [4]. MEDICIS has successfully delivered several radionuclides - including Tb-149, Tb-152, Tb-155, Sm-153 and Ac-225 - for medical research. However, despite recent advancements in mass separation at CERN-MEDICIS and other different facilities, the efficiency and yield for some radionuclides known as “difficult to extract” such as Tb, remain sub-optimal for medically relevant activities [5].
The selection of the target material is critical for optimizing isotope yield and release efficiency. Tantalum remains a preferred choice due to its high atomic mass, excellent thermal stability, and suitability for producing terbium isotopes and other lanthanides. However, despite these favourable properties, the mass separation efficiency has been observed to decrease by approximately an order of magnitude after the first use of the target material.
This study compares the mass separation efficiency of terbium radionuclides produced using tantalum foils and tantalum carbide pellets as target materials. Recent developments at the CERN-MEDICIS facility have demonstrated significant improvements in the production of high-purity Tb samples, with mass separation efficiencies for Tb-155 reaching nearly 2% as well as providing first pure Tb-149 samples to partner institutes. In addition, sintering studies conducted on Ta foils and TaC targets provide insights into the structural and microstructural changes occurring after repeated use, offering possible explanations for the observed reduction in mass separation efficiency during subsequent heating cycles.
[1] Zhang, Siqi, et al. "Radiopharmaceuticals and their applications in medicine." Signal transduction and targeted therapy 10.1 (2025): 1.
[2] Van Laere, Camille, et al. "Terbium radionuclides for theranostic applications in nuclear medicine: from atom to bedside." Theranostics 14.4 (2024): 1720.
[3] Müller, Cristina, and Nicholas P. van der Meulen. "Terbium “Sisters”: More Than just a “Swiss Army Knife”." Beyond Becquerel and Biology to Precision Radiomolecular Oncology: Festschrift in Honor of Richard P. Baum. Cham: Springer International Publishing, 2024. 225-236.
[4] Duchemin, Charlotte, et al. "CERN-MEDICIS: a unique facility for the production of non-conventional radionuclides for the medical research." 11th International Particle Accelerator Conference (IPAC2020). 2020.
[5] Bernerd, C., et al. "Production of innovative radionuclides for medical applications at the CERN-MEDICIS facility." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 542 (2023): 137-143.
