Re-examining the $^{26}$Mg($alpha,alpha^prime$)$^{26}$Mg reaction - probing astrophysically important states in $^{26}$Mg
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abstract
Background: The $^{22}$Ne($alpha,n$)$^{25}$Mg reaction is one of the neutron sources for the $s$-process in massive stars. The properties of levels in $^{26}$Mg above the $alpha$-particle threshold control the strengths of the $^{22}$Ne($alpha,n$)$^{25}$Mg and $^{22}$Ne($alpha,gamma$)$^{26}$Mg reactions. The strengths of these reactions as functions of temperature are one of the major uncertainties in the $s$-process. Methods: Inelastically scattered $alpha$ particles from a $^{26}$Mg target were momentum-analysed 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 $alpha$ particles. Based on the differential cross sections, spin and parity assignments to states are made. Results: A new $0^+$ 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 $J^pi$ values of the states observed in the present study show discrepancies with those assigned in an experiment performed at RCNP Osaka. Conclusion: The high level density at this excitation energy in $^{26}$Mg makes assigning $J^pi$ values to observed states difficult. Further experimental investigations with superior experimental energy resolution are required to clarify the number of levels in $^{26}$Mg, especially between the $alpha$-particle threshold at 10.615 MeV and the neutron threshold at 11.319 MeV.
