[en] Targeted alpha therapy (TAT) is a treatment method of increasing interest to the clinical oncology community that utilizes α-emitting radionuclides conjugated to biomolecules for the selective killing of tumor cells. Proton irradiation of thorium generates a number of α-emitting radionuclides with therapeutic potential for application via TAT. In particular, the radionuclide "2"3"0Pa is formed via the "2"3"2Th(p, 3n) nuclear reaction and partially decays to "2"3"0U, an α emitter which has recently received attention as a possible therapy nuclide. In this study, we estimate production yields for "2"3"0Pa and other Pa isotopes from proton-irradiated thorium based on cross section measurements. We adopt existing methods for the chromatographic separation of protactinium isotopes from proton irradiated thorium matrices to combine and optimize them for effective fission product decontamination.

[en] Highlights: • Degradation of proton beam energy within a target stack was monitored via product nuclide ratios. • Nuclear reactions employed included ^natNi(p,x)⁵⁷Co and ^natNi(p,x)⁵⁷Ni. • Natural nickel foils were used to determine proton beam energies ranging from 15 to 30 MeV. • Proton energies determined serve as a basis to optimize radionuclide production. -- Abstract: The degradation of proton beam energy within a target stack was monitored via product nuclide ratios at the Los Alamos Isotope Production Facility (LANL-IPF). Nuclear reaction channels employed as energy monitors included ^NatNi(p,x)⁵⁷Co and ^NatNi(p,x)⁵⁷Ni. Natural nickel foils (thicknesses 0.025 mm) were used to determine proton beam energies ranging from 15 to 30 MeV. Energy values were estimated from a fitted ⁵⁷Ni/⁵⁷Co production activity ratio curve, which, in turn, was calculated from formation cross section data. Isotope production yields in the low energy “C” slot at LANL-IPF are very sensitive to beam energy, and differences of several MeV can translate into a drastic effect on overall production yields and radiochemical purity. Proton energies determined in this target stack position using nickel foils will serve as a basis to optimize radionuclide production in terms of product yield maximization and by-product minimization.