Toward an Experimentally Determined {sup 26m}Al(p,{gamma}){sup 27}Si Reaction Rate in ONe Novae
- Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520 (United States)
Evidence of the ongoing nucleosynthesis of {sup 26}Al in our galaxy has been found in presolar grains and in observations of the 1.809-MeV {gamma} ray, which results from the {beta} decay of the ground state of {sup 26}Al({sup 26g}Al; t{sub 1/2} = 7.2x 10{sup 5} yrs) to an excited state in {sup 26}Mg. The nucleosynthesis of {sup 26}Al is complicated by the existence of the isomeric state, {sup 26m}Al, at 228 keV (t{sub 1/2} = 6.3 s), which must be treated independently from {sup 26g}Al in certain stellar environments, such as ONe novae, where temperatures are below 0.4 GK [1]. {sup 26m}Al{beta} decays directly to {sup 26g}Mg, bypassing the emission of the 1.809-MeV {gamma} ray. The {sup 26g}Al(p,{gamma}){sup 27}Si and {sup 26m}Al(p,{gamma}){sup 27}Si reactions destroy {sup 26}Al in novae and have a direct impact on the net amount of {sup 26}Al produced. While the {sup 26g}Al(p,{gamma}){sup 27}Si reaction rate has been studied extensively, there has been virtually no information published on resonances of the {sup 26m}Al(p,{gamma}){sup 27}Si reaction and previously published reaction rates [2] have been based on {sup 26g}Al+p resonances and Hauser-Feshbach calculations. The {sup 27}Al({sup 3}He,t){sup 27}Si*(p){sup 26}Al and {sup 28}Si({sup 3}He,{alpha}){sup 27}Si*(p){sup 26}Al reactions have been studied at the Wright Nuclear Structure Laboratory at Yale University. Proton decays from the excited states in {sup 27}Si populated via the {sup 27}Al({sup 3}He,t){sup 27}Si and {sup 28}Si({sup 3}He,{alpha}){sup 27}Si transfer reactions were detected in coincidence with the reaction products of interest, which were detected at the focal plane of the Yale Enge spectrograph. Angular correlations were measured to constrain spins and determine proton branching ratios for {sup 26m}Al+p resonances with E{sub cm}>450 keV and excitation energies of {sup 27}Si were measured. Using this information a {sup 26m}Al(p,{gamma}){sup 27}Si reaction rate based on experimental information has been calculated for the first time. The extreme differences in proton decays from excited states in {sup 27}Si to {sup 26g}Al and {sup 26m}Al show that {sup 26m}Al(p,{gamma}){sup 27}Si reaction rates found using experimental data for {sup 26g}Al+p resonances are not valid, and a direct {sup 26m}Al(p,{gamma}){sup 27}Si measurement must be made to reliably determine the strengths of low-energy resonances, which most likely dominate the reaction rate.
- OSTI ID:
- 21289455
- Journal Information:
- AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 1098; ISSN 0094-243X; ISSN APCPCS
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM 26
ALUMINIUM 26 TARGET
ALUMINIUM 27
ALUMINIUM 27 TARGET
ANGULAR CORRELATION
BETA DECAY
BRANCHING RATIO
EXCITED STATES
GROUND STATES
HAUSER-FESHBACH THEORY
HELIUM 3 REACTIONS
NOVAE
NUCLEAR STRUCTURE
NUCLEOSYNTHESIS
PROTON REACTIONS
PROTON-EMISSION DECAY
SILICON 27
SILICON 28 TARGET
TRANSFER REACTIONS