Nature 569, 53–58 (2019)

When atomic nuclei have particularly stable configurations with fully occupied energy shells, their nucleon numbers are said to be magic. However, experiments suggest that the shell-closure criterion need not apply for magic nuclei with vastly different proton and neutron numbers. The 78Ni isotope has 28 protons and 50 neutrons — both magic numbers — making it a unique testbed to investigate this question.

Ryo Taniuchi and colleagues studied 78Ni spectroscopically at the Radioactive Isotope Beam Factory, confirming predictions of its doubly magic nature and spherical shape despite asymmetric nucleon numbers. What came as a surprise was that the spherical shape competes with a prolate deformation. As a result, heavier nickel isotopes with 28 protons or lighter isotones with 50 neutrons should not have spherical shapes despite their magicity. The onset of shape deformations in these neutron-rich nuclei may influence the synthesis of elements heavier than iron via rapid neutron capture in the Universe.