Re-examining the ${}^{26}$Mg($\hat{I}\pm ,\hat{I}{\pm }^{\prime }$)${}^{26}$Mg reaction - probing astrophysically important states in ${}^{26}$Mg

Abstract

Background: The ${}^{22}$Ne($\hat{I}\pm ,n$)${}^{25}$Mg reaction is one of the neutron sources for the $s$-process in massive stars. The properties of levels in ${}^{26}$Mg above the $\hat{I}\pm$-particle threshold control the strengths of the ${}^{22}$Ne($\hat{I}\pm ,n$)${}^{25}$Mg and ${}^{22}$Ne($\hat{I}\pm ,{\hat{I}}^3$)${}^{26}$Mg reactions. The strengths of these reactions as functions of temperature are one of the major uncertainties in the $s$-process. Methods: Inelastically scattered $\hat{I}\pm$ 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 $\hat{I}\pm$ 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 $J^{\ddot{I}}€$ 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 $J^{\ddot{I}}€$ 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 $\hat{I}\pm$-particle threshold at 10.615 MeV and the neutron threshold at 11.319 MeV.

8 pages, 3 figures, submitted to Physical Review C, fixed a typo in a figure caption and some improvements for clarity in Figure 2, added information on rate implications for alpha-particle radiative capture on Ne-22