The Szilard–Chalmers effect in macrocyclic ligands to increase the specific activity of reactor-produced radiolanthanides: Experiments and explanations

Abstract

Abstract Successful utilization of medical isotopes in the radiolabeling reactions to a significant degree depends on the technically achievable specific activity. In this respect, the Szilard-Chalmers effect is considered in detail as a radiochemical tool to increase the specific activity of radionuclides produced by direct nuclear reactions. In the present study, a physico-chemical model is described utilizing the specific aspects of thermodynamically and kinetically stabilised metal-ligand complexes. The approach is applied as a proofof- principle study to increase the specific activity of 166Ho, produced via the (n, γ) nuclear reaction. As a target material, 165Ho-DOTA is used. In this case, 166Ho, the product nucleus of the neutron capture reaction, is obtained chemically as non-complexed cationic 166HoIII species in situ. Consequently, it can effectively and quantitatively be separated from the inactive 165Ho-DOTA target material by means of fast and simple chromatographic, column-based methods. We were able to verify the physico-chemical model by the experimentally obtained data. For the first time we quantitatively describe the interaction of the ligand-framework of the target material (e.g. the Ho-DOTA complex) with the radiation field of the nuclear reactor. The analysis of the experimental data allows to assume that radionuclides with half-lives of T1/2 < 64 h can be produced at a TRIGA II nuclear reactor via the Szilard-Chalmers effect with specific activities higher than in the case of direct irradiation of common target materials such as oxides.