Thick-target Yield of ${}^{65}$Cu($\alpha ,n{)}^{68}$Ga Near Threshold and Implications for Nuclear Medicine, Deep Underground Detector Backgrounds, and Nucleosynthesis

We report thick target yields of ${}^{65}\mathrm{C}\mathrm{u}(\alpha ,n{)}^{68}\mathrm{G}\mathrm{a}$ from $\alpha$ energies $E_{\alpha }$$=$6.5–8~MeV measured via neutron-counting at the Edwards Accelerator Laboratory at Ohio University. Our results agree with prior results based on single-foil irradiations, while disagreeing with thick-target yields inferred from stacked-foil irradiations by up to an order of magnitude. Based on comparisons of our and prior measurements to Hauser-Feshbach calculations, we estimate the thick-target yield for ${}^{68}\mathrm{G}\mathrm{a}$ from $E_{\alpha }$=14~MeV impinging on 100%-enriched copper (${}^{65}\mathrm{C}\mathrm{u}$) is 161${}_{-24}^{+5}$~MBq/$\mu$Ah (for He${}^{++}$), which is in agreement with the current IAEA estimate of 156~MBq/$\mu$Ah. At $E_{\alpha }$$=$8~MeV, where radioimpurity-free production of ${}^{68}\mathrm{G}\mathrm{a}$ could be realized with a natural copper target, our yield estimate is nearly 4$\times$ lower than the IAEA estimate. We find that the ${}^{65}\mathrm{C}\mathrm{u}(\alpha ,n)$ cross section estimates presently employed for neutrino and dark matter detector backgrounds and the ${}^{65}\mathrm{C}\mathrm{u}(\alpha ,n)$ astrophysical reaction rate recently recommended for nucleosynthesis calculations are in agreement with our measurement results.