The decay products of ²²⁹Th (t_1/2 = 7932 y), specifically ²²⁵Ac (t_1/2 = 9.92 d) and ²¹³Bi (t_1/2 = 45.61 min), are important alpha-emitting radioisotopes for treating cancer. These radionuclides are in high demand but have a limited supply that includes existing ²²⁹Th sources and accelerator-produced ²²⁵Ac. To address this shortage, we evaluated a novel method to produce ²²⁹Th through the proton irradiation of ²³⁰Th (t_1/2 = 75,400 y). We first developed a uniformly distributed ²³⁰Th target that is optimal for charged particle cross section measurements. The electrophoretic deposition of preformed Th nanoparticles with Ni as the electroactive species was used. Direct electrodeposition of Th is problematic because of the difficulty of reducing Th⁴⁺ ions and has led to many researchers attempting the use of aprotic solvents, molten salts, and ionic liquid electrolytes. The codeposited Ni serves a second important function: it will act as an in situ beam monitor through the measurement of the prompt gamma activity of ⁶¹Cu (t_1/2 = 3.339 h) postirradiation. Using Ce as a cold surrogate for Th, we investigated three Ce-based compositions (e.g., CeO₂, CePO₄, and CeVO₄) to assess which nanoparticle suspension provides the most uniform co-deposition with Ni metal ions. After establishing the electrophoretic deposition of Ce-based nanoparticles, the uniformly deposited ²³⁰Th target(s) will be fabricated and irradiated at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Postirradiation, the target(s) will be processed at Oak Ridge National Laboratory to separate the ²²⁹Th decay precursor, ²²⁹Pa (t_1/2 = 1.5 d), from impurities using ion exchange chromatography methods. After measuring ²²⁹Pa yield via gamma ray spectroscopy, we will report the ²³⁰Th(p,2n)²²⁹Pa reaction cross section.

Mike Zach

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