Abstract
Mg18 was observed, for the first time, by the invariant-mass reconstruction of O14+4p events. The ground-state decay energy and width are ET=4.865(34) MeV and Γ=115(100) keV, respectively. The observed momentum correlations between the five particles are consistent with two sequential steps of prompt 2p decay passing through the ground state of Ne16. The invariant-mass spectrum also provides evidence for an excited state at an excitation energy of 1.84(14) MeV, which is likely the first excited 2+ state. As this energy exceeds that for the 2+ state in Mg20, this observation provides an argument for the demise of the N=8 shell closure in nuclei far from stability. However, in open systems this classical argument for shell strength is compromised by Thomas-Ehrman shifts.Received 30 August 2021Revised 18 October 2021Accepted 16 November 2021DOI:https://doi.org/10.1103/PhysRevLett.127.262502© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLifetimes & widthsNuclear structure & decaysProton emissionRare & new isotopesProperties6 ≤ A ≤ 19TechniquesRadioactive beamsNuclear Physics
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