N=8 Shell Breaking in 12Be from a Single-Particle Perspective

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Chen, J, Kay, BP, Sharp, DK, Gaffney, LP ORCID: 0000-0002-2938-3696, Freeman, SJ, Wang, SM, Li, JG, MacGregor, PT, Hoffman, CR, Ayyad, Y et al (show 24 more authors) , Butler, PA ORCID: 0000-0001-6080-9205, Carollo, S, Ceulemans, A, Clarke, DJ, Dolan, AJ, Everett, C, Favier, Z, Garrett, K, Geng, J, Jayatissa, H, Labiche, M, Lazarus, I, Liu, WP, Niu, YF, Olaizola, B, Ojala, J, Page, CAA, Page, RD ORCID: 0009-0009-7062-711X, Poleshchuk, O, Raabe, R, Xie, MR, Yuan, CX, Yue, Z and Zhang, YN (2026) N=8 Shell Breaking in 12Be from a Single-Particle Perspective PHYSICAL REVIEW LETTERS, 136 (22). 222501-. ISSN 0031-9007, 1079-7114

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Abstract

Experimental observations of the low-lying states in Be¹² and their accurate modeling play an essential role in understanding the disappearance of the N=8 magic number. Long-standing experimental ambiguities have been clarified using an one-neutron adding (d, p) reaction on Be¹¹ using the ISOLDE Solenoidal Spectrometer at CERN’s HIE-ISOLDE facility. The single-particle energies of 1s<inf>1/2</inf>, 0d<inf>5/2</inf>, and 0p<inf>1/2</inf> orbitals in Be¹² have been determined from the extracted spectroscopic factors. A significant reduction between the separation of 1s<inf>1/2</inf> and 0p<inf>1/2</inf> orbitals is found in comparison with the carbon isotones, highlighting the breakdown of the N=8 shell. These observations serve as an important test of different effects incorporated in theoretical models. It is found that two synergistic mechanisms, core deformation and weak binding, are responsible for the N=8 shell breaking and the exotic near-threshold phenomena observed in Be¹², including the narrow unnatural-parity resonance 0<inf>1</inf>^- and the possible halolike nature of the 0<inf>2</inf>⁺ isomer.

Item Type:	Article
Uncontrolled Keywords:	ISOLDE Collaboration
Divisions:	Faculty of Science & Engineering Faculty of Science & Engineering > School of Physical Sciences Faculty of Science & Engineering > School of Physical Sciences > Physics
Depositing User:	Symplectic Admin
Date Deposited:	15 Jun 2026 15:26
Last Modified:	05 Jul 2026 19:49
DOI:	10.1103/3vts-dwst
Open Access URL:	https://doi.org/10.1103/3vts-dwst
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3198947
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