Identification of \(\gamma\)-decaying resonant states in ²⁶Mg and their importance for the astrophysical s process

The ²²Ne(\( \alpha\), n) reaction is expected to provide the dominant neutron source for the weak s process in massive stars and intermediate-mass (IM) Asymptotic Giant Branch (AGB) stars. However, the production of neutrons in such environments is hindered by the competing ²²Ne(\(\alpha\),\(\gamma\))²⁶Mg reaction. Here, the ¹¹B(¹⁶O,p) fusion-evaporation reaction was used to identify \(\gamma\)-decay transitions from ²²Ne + \(\alpha\) resonant states in ²⁶Mg. Spin-parity restrictions have been placed on a number of \( \alpha\)-unbound excited states in ²⁶ Mg and their role in the ²²Ne(\(\alpha\),\(\gamma\))²⁶Mg reaction has been investigated. In particular, a suspected natural-parity resonance at E_c.m. = 557(3) keV, that lies above the neutron threshold in ²⁶Mg, and is known to exhibit a strong \( \alpha\)-cluster character, was observed to \( \gamma\) decay. Furthermore, a known resonance at \( E_{c.m.} = 466(4)\) keV has been definitively assigned 2⁺ spin and parity. Consequently, uncertainties in the ²²Ne(\( \alpha\),\( \gamma\)) stellar reaction rate have been reduced by a factor of ∼ 20 for temperatures ∼ 0.2 GK.

1. S. Almaraz-Calderon

   Present address: Present address: Department of Physics, Florida State University, 32306, Tallahassee, Florida, USA

2. C. J. Chiara

   Present address: Present address: U.S. Army Research Laboratory, 20783, Adelphi, Maryland, USA

3. H. M. David

   Present address: Present address: GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany

4. A. Kankainen

   Present address: Present address: Department of Physics, University of Jyväskylä, FI-40014, Jyväskylä, Finland

Authors and Affiliations

1. Department of Physics, University of Surrey, GU2 7XH, Guildford, UK

   G. Lotay, D. T. Doherty & R. Wilkinson

2. National Physical Laboratory, TW11 0LW, Teddington, Middlesex, UK

   G. Lotay

3. Argonne National Laboratory, 60439, Argonne, Illinois, USA

   D. Seweryniak, S. Almaraz-Calderon, M. P. Carpenter, C. J. Chiara, H. M. David, C. R. Hoffman, T. Lauritsen & S. Zhu

4. Department of Chemistry and Biochemistry, University of Maryland, 20742, College Park, Maryland, USA

   C. J. Chiara

5. Department of Physics & Astronomy, University of North Carolina at Chapel Hill, 27599, Chapel Hill, North Carolina, USA

   R. V. F. Janssens

6. Triangle Universities Nuclear Laboratory, Duke University, 27708, Durham, North Carolina, USA

   R. V. F. Janssens

7. School of Physics & Astronomy, University of Edinburgh, EH9 3JZ, Edinburgh, UK

   A. Kankainen & P. J. Woods

Corresponding author

Correspondence to G. Lotay.

Communicated by A. Jokinen

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This manuscript has no associated data or the data will not be deposited. [Authors’ comment: Data may be made available upon request.]

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