Preparation of an Actinium-228 Generator.

Advances in targeted α-therapies have increased the interest in actinium (Ac), whose chemistry is poorly defined due to scarcity and radiological hazards. Challenges associated with characterizing Ac chemistry are magnified by its 5f6d electronic configuration, which precludes the use of many spectroscopic methods amenable to small amounts of material and low concentrations (like EPR, UV-vis, fluorescence). In terms of nuclear spectroscopy, many actinium isotopes (Ac and Ac) are equally "unfriendly" because the actinium α-, β-, and γ-emissions are difficult to resolve from the actinium daughters. To address these issues, we developed a method for isolating an actinium isotope (Ac) whose nuclear properties are well-suited for γ-spectroscopy. This four-step procedure isolates Ra from naturally occurring Th. The relatively long-lived Ra ( = 5.75(3) years) radioisotope subsequently decays to Ac. Because the Ac decay rate [ = 6.15(2) h] is fast, Ac rapidly regenerates after being harvested from the Ra parent. The resulting Ac generator provides frequent and long-term access (of many years) to the spectroscopically "friendly" Ac radionuclide. We have demonstrated that the Ac product can be routinely "milked" from this generator on a daily basis, in chemically pure form, with high specific activity and in excellent yield (∼95%). Hence, in the same way that developing synthesis routes to new starting materials has advanced coordination chemistry for many metals by broadening access, this Ac generator has the potential to broaden actinium access for the inorganic community, facilitating the characterization of actinium chemical behavior.