I have heard on the Internet that there are at least three pear-shaped nuclei: radium-224, radon-220 (a direct product of the previous isotope), and barium-144. CERN has a webpage about this discovery https://home.cern/news/news/experiments/first-observations-short-lived-pear-shaped-atomic-nuclei and it calls them "short-lived". Their half-lives are all less than one week and I wonder if radium-224 is the most stable pear-shaped nucleus or if there are more stable ones that have that property in common.

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    $\begingroup$ Probably better on Physics SE. Even as a long-time supporter of Glen Seaborg's nuclear chemistry contributions, this one really is nuclear physics. $\endgroup$ – Jon Custer May 21 '19 at 13:18
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    $\begingroup$ I'm voting to close this question as off-topic because it's not about chemistry. $\endgroup$ – Mithoron Sep 21 '19 at 23:19