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High-resolution study of levels in the astrophysically important nucleus 26Mg and resulting updated level assignments

P. Adsley, J. W. Brümmer, T. Faestermann, S. P. Fox, F. Hammache, R. Hertenberger, A. Meyer, R. Neveling, D. Seiler, N. de Séréville, and H.-F. Wirth

Background : The 22Ne(α,n)25Mg reaction is an important source of neutrons for the s-process. Direct measurement of this reaction and the competing 22Ne(α,γ)26Mg reaction are challenging due to the gaseous nature of both reactants, the low cross section and the experimental challenges of detecting neutrons and high-energy γ rays. Detailed knowledge of the resonance properties enables the rates to be constrained for s-process models.

Purpose : Previous experimental studies have demonstrated a lack of agreement in both the number and excitation energy of levels in 26Mg. To try to resolve the disagreement between different experiments, proton and deuteron inelastic scattering from 26Mg have been used to identify excited states.

Method : Proton and deuteron beams from the tandem accelerator at the Maier-Leibnitz Laboratorium at Garching, Munich, were incident upon enriched 26MgO targets. Scattered particles were momentum-analyzed in the Q3D magnetic spectrograph and detected at the focal plane.

Results : Reassignments of states around Ex=10.810.83 MeV in 26Mg suggested in previous works have been confirmed. In addition, new states in 26Mg have been observed, two below and two above the neutron threshold. Up to six additional states above the neutron threshold may have been observed compared to experimental studies of neutron reactions on 25Mg, but some or all of these states may be due to 24Mg contamination in the target. Finally, inconsistencies between measured resonance strengths and some previously accepted Jπ assignments of excited 26Mg states have been noted.

Conclusion : There are still a large number of nuclear properties in 26Mg that have yet to be determined and levels that are, at present, not included in calculations of the reaction rates. In addition, some inconsistencies between existing nuclear data exist that must be resolved in order for the reaction rates to be properly calculated.

Voir en ligne : Phys. Rev. C 97, 045807



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