Eur. Phys. J. A (2019) 55: 109
https://doi.org/10.1140/epja/i2019-12791-5

Letter

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

¹ Department of Physics, University of Surrey, GU2 7XH, Guildford, UK
² National Physical Laboratory, TW11 0LW, Teddington, Middlesex, UK
³ Argonne National Laboratory, 60439, Argonne, Illinois, USA
⁴ Department of Chemistry and Biochemistry, University of Maryland, 20742, College Park, Maryland, USA
⁵ Department of Physics & Astronomy, University of North Carolina at Chapel Hill, 27599, Chapel Hill, North Carolina, USA
⁶ Triangle Universities Nuclear Laboratory, Duke University, 27708, Durham, North Carolina, USA
⁷ School of Physics & Astronomy, University of Edinburgh, EH9 3JZ, Edinburgh, UK

^* e-mail: g.lotay@surrey.ac.uk

Received: 20 February 2019
Accepted: 3 June 2019
Published online: 18 July 2019

Abstract

The ²²Ne(, 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(,)²⁶Mg reaction. Here, the ¹¹B(¹⁶O,p) fusion-evaporation reaction was used to identify -decay transitions from ²²Ne + resonant states in ²⁶Mg. Spin-parity restrictions have been placed on a number of -unbound excited states in ²⁶ Mg and their role in the ²²Ne(,)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 -cluster character, was observed to decay. Furthermore, a known resonance at keV has been definitively assigned 2⁺ spin and parity. Consequently, uncertainties in the ²²Ne(,) stellar reaction rate have been reduced by a factor of ∼ 20 for temperatures ∼ 0.2 GK.