Pairing of thorium with selected primary target materials in tandem configurations: Co-production of Ac/Bi and U/Th generators with a 70 MeV H cyclotron.

Several radionuclide production facilities based on a new generation of high-current, 70 MeV H cyclotrons have been established in recent years and a number of new facilities are either under construction or being planned. In this study, the feasibility to produce Ac/Bi and U/Th generators via Th + p reactions at such a facility has been investigated. From the perspective of production yields, it has been found useful to compare the relevant reactions on thorium with those on other targets regularly employed in this energy region, in particular the Mg(p,x)Na, Ga(p,x)Ge, and Rb(p,x)Sr reactions that have been exploited with 66 MeV proton beams at iThemba LABS for many years. Therefore, various tandem configurations of thorium with magnesium, gallium and rubidium are discussed based on the relevant nuclear data. In a few cases, the available data were judged to be insufficient in this energy region. New experimental cross sections are presented for Ac, Ra, and Pa in Th + p reactions as well as Na in Mg + p reactions. Integral yields have been derived for those radionuclides of main interest. Production yields expected from extended 70 MeV proton bombardments, on selected tandem-target configurations, are presented for Na, Ge, Sr, Ac, and Pa. It is concluded that Ac/Bi generators can, in principle, be added to a production programme based at a 70 MeV H cyclotron facility as the production rate is of similar magnitude to those of other well-established radionuclides in this energy region. Also, radio-contaminant levels for Ac are similar to those found in higher proton-energy windows. The scope for U/Th generators, via bulk production of the precursor Pa, seems to be more limited due to a lower yield but can nevertheless be produced in clinically relevant quantities.