decay of proton-rich nucleus ²³Al and astrophysical consequences

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V. E. Iacob, Y. Zhai, T. Al-Abdullah, C. Fu, J. C. Hardy, N. Nica, H. I. Park, G. Tabacaru, L. Trache, and R. E. Tribble
Cyclotron Institute, Texas A&M University, College Station, Texas 77843, USA

Received 25 July 2006; published 31 October 2006

Wepresent the first study of the beta decay of ²³Alundertaken with pure samples. The study was motivated by nuclearastrophysics questions. Pure samples of ²³Al were obtained from themomentum achromat recoil separator (MARS) of Texas A&M University, collectedon a fast tape-transport system, and moved to a shieldedlocation where beta and beta - gamma coincidence measurements were made. Wededuced beta branching ratios and log ft values for transitionsto states in ²³Mg, and from them determined unambiguously thespin and parity of the ²³Al ground state to beJ=5/2⁺. We discuss how this excludes the large increases inthe radiative proton capture cross section for the reaction ²²Mg(p, gamma )²³Alat astrophysical energies, which were implied by claims that thespin and parity is J=1/2⁺. The log ft for theFermi transition to its isobaric analog state (IAS) in ²³Mgis also determined for the first time. This IAS anda state 16 keV below it are observed, well separatedin the same experiment for the first time. We cannow solve a number of inconsistencies in the literature, excludestrong isospin mixing claimed before, and obtain a new determinationof the resonance strength. Both states are resonances in the²²Na(p, gamma )²³Mg reaction at energies important in novae. The reactions ²²Mg(p, gamma )²³Aland ²²Na(p, gamma )²³Mg have both been suggested as possible candidates fordiverting some of the flux in oxygen-neon novae explosions fromthe A=22 into the A=23 mass chain.

URL:	http://link.aps.org/doi/10.1103/PhysRevC.74.045810
DOI:	10.1103/PhysRevC.74.045810
PACS:	26.50.+x; 23.40.-s; 27.30.+t; 26.30.+k 26.50.+x Nuclear physics aspects of novae, supernovae, and other explosive environments 23.40.-s B decay; double decay; electron and muon capture 27.30.+t Properties of nuclei with 20 A 38 26.30.+k Nucleosynthesis in novae, supernovae, and other explosive environments YEAR: 2006

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