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Open Access item Evidence for a spin-aligned neutron–proton paired phase from the level structure of 92Pd

Authors:Cederwall, B.
Algora, Alejandro
Gadea, Andrés
Jungclaus, Andrea
Williams, S.
Issue Date:Jan-2011
Publisher:Nature Publishing Group
Citation:Nature 469: 68-71 (2011)
Abstract:Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work that introduced a strong spin–orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron–proton pairing, in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus 92Pd. Gamma rays emitted following the 58Ni(36Ar,2n)92Pd fusion–evaporation reaction were identified using a combination of state-of-the-art high-resolution γ-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron–proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron–proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.
Description:4 páginas, 4 figuras.-- El Pdf es la versión pre-print.-- et al.
Publisher version (URL):http://dx.doi.org/10.1038/nature09644
URI:http://hdl.handle.net/10261/41677
ISSN:0028-0836
E-ISSNmetadata.dc.identifier.doi = DOI:1476-4687
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