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$N = 8$ Shell Breaking in ${}^{12}{Be}$ from a Single-Particle Perspective

J. Chen ^1,2,*, B. P. Kay², D. K. Sharp³, L. P. Gaffney⁴, S. J. Freeman^3,5, S. M. Wang^6,7, J. G. Li^8,9,10, P. T. MacGregor^3,5, C. R. Hoffman² et al. (ISOLDE Collaboration)

C. R. Hoffman², Y. Ayyad¹¹, P. A. Butler⁴, S. Carollo^12,13, A. Ceulemans¹⁴, D. J. Clarke³, A. J. Dolan⁴, C. Everett⁴, Z. Favier⁵, K. Garrett³, J. Geng¹⁵, H. Jayatissa², M. Labiche¹⁶, I. Lazarus¹⁶, W. P. Liu¹, Y. F. Niu¹⁵, B. Olaizola^5,17, J. Ojala⁴, C. A. A. Page^18,5, R. D. Page⁴, O. Poleshchuk¹⁴, R. Raabe¹⁴, M. R. Xie^8,9, C. X. Yuan¹⁹, Z. Yue^18,5, and Y. N. Zhang¹⁹ (ISOLDE Collaboration)

¹Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, Guangdong, China
²Physics Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
³Department of Physics, University of Manchester, M13 9PL Manchester, United Kingdom
⁴Department of Physics, University of Liverpool, Liverpool L69 3BX, United Kingdom
⁵EP Department, CERN, Geneva CH-1211, Switzerland
⁶Key Laboratory of Nuclear Physics and Ion-beam Application (MOE), Institute of Modern Physics, Fudan University, Shanghai 200433, China
⁷Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University, Shanghai 200438, China
⁸Heavy Ion Science and Technology Key Laboratory, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
⁹School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
¹⁰Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences, Huizhou 516000, China
¹¹IGFAE, Universidade de Santiago de Compostela, E-15782, Santiago de Compostela, Spain
¹²Dipartimento di Fisica e Astronomia, Universit degli Studi di Padova, I-35131 Padova, Italy
¹³Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova, Padova, Italy
¹⁴KU Leuven, Intituut voor Kern-en Stralingsfysica, Celestijnenlaan 200D, 3001 Leuven, Belgium
¹⁵Frontier Science Center for Rare Isotopes, Lanzhou University, Lanzhou 730000, China
¹⁶Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, United Kingdom
¹⁷Instituto de Estructura de la Materia, CSIC, E-28006 Madrid, Spain
¹⁸School of Physics, University of York, York YO10 5DD, North Yorkshire, United Kingdom
¹⁹Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082, China

^*Contact author: chenjie@sustech.edu.cn

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Phys. Rev. Lett. 136, 222501 – Published 2 June, 2026

DOI: https://doi.org/10.1103/3vts-dwst

Abstract

Experimental observations of the low-lying states in ${}^{12}{Be}$ 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 ${}^{11}{Be}$ using the ISOLDE Solenoidal Spectrometer at CERN’s HIE-ISOLDE facility. The single-particle energies of $1 s_{1 / 2}$ , $0 d_{5 / 2}$ , and $0 p_{1 / 2}$ orbitals in ${}^{12}{Be}$ have been determined from the extracted spectroscopic factors. A significant reduction between the separation of $1 s_{1 / 2}$ and $0 p_{1 / 2}$ 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 ${}^{12}{Be}$ , including the narrow unnatural-parity resonance $0_{1}^{-}$ and the possible halolike nature of the $0_{2}^{+}$ isomer.

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Phys. Rev. Lett. 136, 222501– Published 2 June, 2026

Vol. 136, Iss. 22 — 5 June 2026

Received 9 September 2025
Accepted 21 April 2026

DOI: https://doi.org/10.1103/3vts-dwst

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by CERN.

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$N = 8$ Shell Breaking in ${}^{12}{Be}$ from a Single-Particle Perspective

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N=8 Shell Breaking in Be12 from a Single-Particle Perspective

Abstract

Physics Subject Headings (PhySH)

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References (70)

$N = 8$ Shell Breaking in ${}^{12}{Be}$ from a Single-Particle Perspective