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Structures of exotic 131,133Sn isotopes and effect on r-process nucleosynthesis...

by Shisheng Zhang, Michael S Smith, Goran Arbanas, R. Kozub
Publication Type
Journal
Journal Name
Physical Review C
Publication Date
Volume
86
Issue
3

Background: Four strong single-particle bound levels with strikingly similar level spacings have recently been measured in 131Sn and 133Sn. This similarity has not yet been addressed with a theoretical nuclear structure model. Information on these single particle bound levels, as well as on resonant levels above the neutron capture threshold, are also needed to determine neutron capture cross sections -- and corresponding capture reaction rates -- on 130,132Sn. The 130Sn(n,gamma) rate was shown in a recent sensitivity study to significantly impact the synthesis of heavy elements in the r-process in supernovae.
Purpose: Understand the structure of bound and resonant levels in 131,133Sn, and determine if the densities of unbound resonant levels are sufficiently high to warrant statistical model treatments of neutron capture on 130,132Sn.
Method: Single-particle bound and resonant levels for 131,133Sn are self-consistently calculated by the analytical continuation of the coupling constant (ACCC) based on a relativistic mean field (RMF) theory with BCS approximation.
Results: We obtain four strong single-particle bound levels in both 131,133Sn with an ordering that agrees with experiments and spacings that, while differing from experiment, are consistent between the Sn isotopes. We also find at most one single-particle level in the effective energy range for neutron captures in the r-process.
Conclusions: Our RMF+ACCC+BCS model successfully reproduces observed single-particle bound levels in 131,133Sn and self-consistently predicts single-particle resonant levels with densities too low for widely used traditional statistical model treatments of neutron capture cross sections on 130,132Sn employing Fermi gas level density formulations.