Extending the Hoyle-State Paradigm to

Carbon burning is a key step in the evolution of massive stars, Type 1a supernovae and superbursts in x-ray binary systems. Determining the ^{12}C+^{12}C fusion cross section at relevant energies by extrapolation of direct measurements is challenging due to resonances at and below the Coulomb barrier. A study of the ^{24}Mg(α,α^{'})^{24}Mg reaction has identified several 0^{+} states in ^{24}Mg, close to the ^{12}C+^{12}C threshold, which predominantly decay to ^{20}Ne(ground state)+α. These states were not observed in ^{20}Ne(α,α_{0})^{20}Ne resonance scattering suggesting that they may have a dominant ^{12}C+^{12}C cluster structure. Given the very low angular momentum associated with sub-barrier fusion, these states may play a decisive role in ^{12}C+^{12}C fusion in analogy to the Hoyle state in helium burning. We present estimates of updated ^{12}C+^{12}C fusion reaction rates.

Pairing of thorium with selected primary target materials in tandem configurations: Co-production of 225Ac/213Bi and 230U/226Th 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 225Ac/213Bi and 230U/226Th 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 natMg(p,x)22Na, natGa(p,x)68Ge, and natRb(p,x)82Sr 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 225Ac, 225Ra, and 230Pa in Th + p reactions as well as 22,24Na in natMg + 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 22Na, 68Ge, 82Sr, 225Ac, and 230Pa. It is concluded that 225Ac/213Bi 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 225Ac are similar to those found in higher proton-energy windows. The scope for 230U/226Th generators, via bulk production of the precursor 230Pa, seems to be more limited due to a lower yield but can nevertheless be produced in clinically relevant quantities.

Large-scale production of 88Y and 88Zr/88Y generators: A proof of concept study for a 70 MeV H- cyclotron.

The large-scale production of 88Y with proton-induced reactions has been investigated from the perspective of new generation 70 MeV H- cyclotrons. Tandem target configurations are presented for both the direct production of 88Y as well as for producing 88Zr/88Y generators. Based on the relevant excitation functions, physical yields have been derived for 88Y production with Y2O3/SrCO3 tandem targets and 88Zr production with Zr/Y2O3 tandem targets. Yields are presented for optimized targets (i.e. optimum yield) as well as for balanced thermal loads on the individual targets. Liquid 88Zr/88Y generators have been produced using both natural Zr and Nb target materials, the former for dedicated productions and the latter as a byproduct by processing spent irradiated Nb capsules which normally would constitute radioactive waste. These stock solutions, which contain both the target material and 88Zr precursor, are retained virtually unchanged after processing except for the removal of 88Y on AG MP-50 macroporous cation-exchange resin. Methods are presented for the preparation of Nb stock solutions in hydrofluoric acid and Zr stock solutions in sulphuric acid. It is shown that multi-Ci productions of 88Y are feasible at a 70 MeV cyclotron facility, suitable for the needs of fracking applications. In addition, 88Zr/88Y generators can provide 88Y with very high specific activity, suitable for labelling of biomolecules. LA-UR-20-24305.