First Observation of the Four-Proton Unbound Nucleus ^{18}Mg

Y Jin; C Y Niu; K W Brown; Z H Li; H Hua; A K Anthony; J Barney; R J Charity; J Crosby; D Dell'Aquila; J M Elson; J Estee; M Ghazali; G Jhang; J G Li; W G Lynch; N Michel; L G Sobotka; S Sweany; F C E Teh; A Thomas; C Y Tsang; M B Tsang; S M Wang; H Y Wu; C X Yuan; K Zhu

doi:10.1103/PhysRevLett.127.262502

First Observation of the Four-Proton Unbound Nucleus ^{18}Mg

Phys Rev Lett. 2021 Dec 24;127(26):262502. doi: 10.1103/PhysRevLett.127.262502.

Authors

Y Jin¹, C Y Niu², K W Brown^{2

3}, Z H Li¹, H Hua¹, A K Anthony^{2

4}, J Barney^{2

4}, R J Charity⁵, J Crosby^{2

4}, D Dell'Aquila², J M Elson⁵, J Estee^{2

4}, M Ghazali^{2

4}, G Jhang², J G Li^{1

6

7}, W G Lynch^{2

4}, N Michel^{6

7}, L G Sobotka^{5

8}, S Sweany^{2

4}, F C E Teh^{2

4}, A Thomas⁵, C Y Tsang^{2

4}, M B Tsang^{2

4}, S M Wang^{9

10}, H Y Wu¹, C X Yuan¹¹, K Zhu^{2

4}

Affiliations

¹ School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China.
² National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
³ Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
⁴ Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.
⁵ Department of Chemistry, Washington University, St. Louis, Missouri 63130, USA.
⁶ Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China.
⁷ School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China.
⁸ Department of Physics, Washington University, St. Louis, Missouri 63130, USA.
⁹ Institute of Modern Physics, Fudan University, Shanghai 200433, China.
¹⁰ FRIB Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
¹¹ Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082, China.

PMID: 35029460
DOI: 10.1103/PhysRevLett.127.262502

Abstract

^{18}Mg was observed, for the first time, by the invariant-mass reconstruction of ^{14}O+4p events. The ground-state decay energy and width are E_{T}=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 ^{16}Ne. 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 ^{20}Mg, 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.