Measurement of the Th230(p,2n)Pa229 and Th230(p,3n)Pa228 reaction cross sections from 14.1 to 16.9 MeV

Background: Actinium-225 is of interest for medical isotope production and there is on-going research into methods of producing $^{225}\mathrm{Ac}$, either directly or via the decay of its parent isotopes ($^{229}\mathrm{Th}, ^{229}\mathrm{Pa}$, and $^{225}\mathrm{Ra}$). One method that has been suggested is the $^{230}\mathrm{Th}(p,2n)^{229}\mathrm{Pa}$ reaction. However, there is no available cross-section data for this reaction in the literature.Purpose: Measure the $^{230}\mathrm{Th}(p,2n)$ and $^{230}\mathrm{Th}(p,3n)$ reaction cross sections in the energy range where the $(p,2n)$ reaction is predicted to peak to determine the feasibility of $^{225}\mathrm{Ac}$ production via the $^{230}\mathrm{Th}(p,2n)$ reaction.Methods: Targets naturally enriched in $^{230}\mathrm{Th}$ were irradiated at the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory with energies ranging from 14.1 to 16.9 MeV. Chemical processing was used to separate the protactinium activation products, followed by $\ensuremath{\gamma}$-ray spectroscopy to measure the activities of $^{228,229,230,232}\mathrm{Pa}$ produced in the irradiation.Results: Excitation functions are reported for the first time in the literature for the $^{230}\mathrm{Th}(p,2n)$ and $^{230}\mathrm{Th}(p,3n)$ reactions in this energy range. The peak measured value of the $^{230}\mathrm{Th}(p,2n)$ reaction was found to be $182\ifmmode\pm\else\textpm\fi{}12$ mb at $14.4\ifmmode\pm\else\textpm\fi{}0.1$ MeV. The $^{232}\mathrm{Th}(p,n)^{232}\mathrm{Pa}$ reaction was used to verify the experimental conditions, the measured values are reported and are comparable to the existing literature values. From the $\ensuremath{\gamma}$-ray spectrometry data, the half-life of $^{229}\mathrm{Pa}$ was measured as $1.5\ifmmode\pm\else\textpm\fi{}0.1$ days, which is within the error of the half-life reported in the evaluated nuclear data as well as in the recent measurements, and the half-life of $^{228}\mathrm{Pa}$ was measured as $19.5\ifmmode\pm\else\textpm\fi{}0.4$ hours.Conclusions: The $^{230}\mathrm{Th}(p,2n)^{229}\mathrm{Pa}$ reaction could reasonably be used for $^{225}\mathrm{Ac}$ isotope production, although significant amounts of relatively isotopically pure $^{230}\mathrm{Th}$ would be needed for significant production because the low alpha-decay branching ratio of $^{229}\mathrm{Pa}$ and long half-life of $^{229}\mathrm{Th}$ inhibit the in-growth of significant amounts of $^{225}\mathrm{Ac}$.