Analysis of ²⁶Al + p elastic and inelastic scattering reactions and Galactic abundances of ²⁶Al

²⁶Al(p,p)²⁶Al and ²⁶Al(p,p’)²⁶Al^* scattering reactions were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) at the Oak Ridge National Laboratory (ORNL). The purpose of the elastic scattering study was to determine properties of previously uncharacterized ²⁷Si levels above the proton threshold in the energy range E(c.m.) ~ 0.5 - 1.5 MeV and to calculate reaction rates for the ²⁶Al(p,γ[gamma])²⁷Si reaction that destroys ²⁶Al. The inelastic scattering reaction was also evaluated to investigate the reaction that produces the metastable state of ²⁶Al at E(c.m.) = 228 keV, which would in turn destroy ²⁶Al in the stellar environment.

Pure ²⁶Al beams (E(beam) = 13 - 41 MeV) with intensities of ~2*10^{6 26}Al/s bombarded a thin polypropylene target of 46 μ[micro]g/cm² thickness for 7 days. Scattered protons were detected in the Silicon Detector Array (SIDAR), covering laboratory angles 18 to 41 degrees. Background events were rejected by detecting these protons in coincidence with recoiled ²⁶Al particles in an ionization chamber, and proton yields were measured at 45 energies from E(c.m.) = 0.49 - 1.53 MeV. A thick 2.4 mg/cm² polypropylene target was also bombarded with a 32 MeV ²⁶Al beam for 1.5 days for comparison with thin-target excitation functions.

Little evidence for the inelastic scattering reaction was observed, indicating that this is not a significant destruction pathway. For the first time, however, an upper limit for the cross section of this reaction was estimated, and it has been set at 5*10^-2 barns. The first upper limits were also established for possible resonances of the elastic scattering reaction with angular momentum transfers up to L = 3 that were not directly observed by this study. Thin-target elastic scattering data suggested a potential resonance at E(r) = 544 keV, which had not been previously observed, with (9/2, 11/2)+ spin and proton width Γ_p[Gamma_p] ≤ 1 keV. Thick-target analysis appeared to confirm this result. An upper limit for the strength of this resonance was estimated to be 1.4*10^-5 keV or 1.6*10^-5 keV for a 9/2+ or 11/2+ state, respectively, moderately increasing the total ²⁶Al(p,γ[gamma])²⁷Si resonant reaction rate at supernova temperatures.