Re-examining the 26Mg(α,α')26Mg reaction: Probing astrophysically important states in 26Mg.

Background: The 22Ne(α,n)25Mg reaction is one of the neutron sources for the s process in massive stars. The properties of levels in 26Mg above the α-particle threshold control the strengths of the 22Ne(α,n)25Mg and 22Ne(α,γ)26Mg reactions. The strengths of these reactions as functions of temperature are one of the major uncertainties in the s process. Purpose: Information on the existence, spin, and parity of levels in 26Mg can assist in constraining the strengths of the 22Ne(α,γ)26Mg and 22Ne(α,n)25Mg reactions, and therefore in constraining s-process abundances. Methods: Inelastically scattered α particles from a 26Mg target were momentum-analyzed in the K600 magnetic spectrometer at iThemba LABS, South Africa. The differential cross sections of states were deduced from the focal-plane trajectory of the scattered α particles. Based on the differential cross sections, spin and parity assignments to states are made. Results: A newly assigned 0+ state was observed in addition to a number of other states, some of which can be associated with states observed in other experiments. Some of the deduced Jπ values of the states observed in the present study show discrepancies with those assigned in a similar experiment performed at RCNP Osaka. The reassignments and additions of the various states can strongly affect the reaction rate at low temperatures. Conclusion: The number, location, and assignment of levels in 26Mg that may contribute to the 22Ne+α reactions are not clear. Future experimental investigations of 26Mg must have an extremely good energy resolution to separate the contributions from different levels. Coincidence experiments of 26Mg provide a possible route for future investigations. [ABSTRACT FROM AUTHOR]