Doctoral Dissertations

Date of Award

12-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Katherine Grzywacz-Jones

Committee Members

Daniel Bardayan, Michael Guidry, Thomas Papenbrock, Lawrence Townsend

Abstract

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*106 26Al/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 Γp[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.

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