Extreme shape coexistence observed in 70Co

Résumé fourni par la source

The shape of the atomic nucleus is a property that underpins our understanding of nuclear systems, impacts the limits of nuclear existence, and enables probes of physics beyond the Standard Model. Nuclei can adopt a variety of shapes, including spheres, axially deformed spheroids, and pear shapes. In some regions of the nuclear chart where a spherical nucleus would naively be expected, deformed nuclear states can result from the collective action of constituent protons and neutrons. In a small subset of nuclei both spherical and deformed nuclear states have been experimentally observed, a phenomenon termed shape coexistence. We present spectroscopic evidence for the coexistence of Jπ = 1+ spherical and deformed states in 70Co, separated by less than 275 keV. This close degeneracy of levels with the same Jπ and different shapes demonstrates an extreme example of shape coexistence resulting from the interplay of independent particle motion and collective behavior in highly unstable nuclear systems and identifies the Co isotopes as a transition point between deformed ground states observed in the Cr isotopes and spherical configurations observed in the closed-shell Ni isotopes. The atomic nucleus can adopt a variety of shapes, and instances where a single nucleus exhibits multiple shape profiles are termed shape coexistence. Here, using a combined experimental and theoretical analysis, the authors claim a rare case of shape coexistence between two states with the same spin/parity quantum numbers in the neutron-rich isotope 70Co.

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