Extreme Shape Coexistence Observed in $^{70}$Co
Abstract
The shape of the atomic nucleus is a property which 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 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 spherical and deformed states in Co, separated by less than 275~keV. This close degeneracy of levels with the same 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.
Cite
@article{arxiv.2502.12681,
title = {Extreme Shape Coexistence Observed in $^{70}$Co},
author = {Cade Dembski and Artemis Spyrou and B. Alex Brown and Sean N. Liddick and Hannah C. Berg and Darren L. Bleuel and Katherine Childers and Benjamin P. Crider and Alexander C. Dombos and Erin C. Good and Caley Harris and Ann-Cecilie Larsen and Rebecca Lewis and Stephanie Lyons and Alicia Palmisano-Kyle and Jorge Pereira and Andrea L. Richard and Debra Richman and Nicholas Scielzo and Anna Simon and Mallory K. Smith and Chris Sullivan and Adriana Sweet and Antonius Torode and Remco Zegers},
journal= {arXiv preprint arXiv:2502.12681},
year = {2025}
}