Mass Measurements of Exotic <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>Ar</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>48</mn><mo>−</mo><mn>50</mn></mrow></mmultiscripts></mrow></math> Isotopes: Probing Proton-Neutron Interaction of the Doubly Magic <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>Ca</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>52</mn></mrow></mmultiscripts></mrow></math> and the Robustness of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>N</mi><mo>=</mo><mn>32</mn></mrow></math> Subshell

C. Y. Fu; W. D. Xian; T. Niwase; M. Rosenbusch; M. Wada; A. Scalesi; V. Somà; J. Lee; H. Ishiyama; S. Nishimura; S. Yoshida; A. Takamine; P. Schury; D. S. Hou; S. Kimura; Y. Hirayama; Y. Ito; S. Iimura; J. M. Yap; Y. X. Watanabe; Q. B. Zeng; V. H. Phong; T. T. Yeung; H. Ueno; H. Haba; T. Duguet; M. Frosini; Z. H. Li; H. Y. Wu; A. Estrade; M. Khandelwal; Y. Jang; J. Lee; A. I. Morales; R. Kanungo; M. Tanaka; D. Suzuki; H. J. Ong; H. Sakurai; S. Michimasa; N. Fukuda; H. Takeda; H. Suzuki; Y. Shimizu; M. Ohtake; K. Kusaka; Y. Yanagisawa; Y. Togano; M. Yoshimoto; B. Hong; Y. H. Kim; X. Ma; B. Moon; J. Park; F. F. Zeng; J. Z. Zhang

doi:10.1103/krq1-t8pr

Mass Measurements of Exotic ${}^{48 - 50}{Ar}$ Isotopes: Probing Proton-Neutron Interaction of the Doubly Magic ${}^{52}{Ca}$ and the Robustness of $N = 32$ Subshell

C. Y. Fu ^1,2,*, W. D. Xian ^1,3,4, T. Niwase⁵, M. Rosenbusch ⁶, M. Wada ^2,3,7, A. Scalesi ^8,9, V. Somà ⁹, J. Lee¹, H. Ishiyama⁶ et al.

S. Nishimura⁶, S. Yoshida ^6,10, A. Takamine ^6,11, P. Schury ³, D. S. Hou ¹, S. Kimura³, Y. Hirayama ³, Y. Ito ³, S. Iimura ¹², J. M. Yap ¹, Y. X. Watanabe ³, Q. B. Zeng^2,6, V. H. Phong ⁶, T. T. Yeung ¹³, H. Ueno ⁶, H. Haba⁶, T. Duguet ⁹, M. Frosini ¹⁴, Z. H. Li¹⁵, H. Y. Wu ^15,16, A. Estrade ¹⁷, M. Khandelwal ¹⁸, Y. Jang ¹⁹, J. Lee ¹⁹, A. I. Morales ^6,20, R. Kanungo²¹, M. Tanaka²², D. Suzuki ^6,13,23, H. J. Ong², H. Sakurai ⁶, S. Michimasa⁶, N. Fukuda⁶, H. Takeda⁶, H. Suzuki⁶, Y. Shimizu⁶, M. Ohtake⁶, K. Kusaka⁶, Y. Yanagisawa⁶, Y. Togano ⁶, M. Yoshimoto ⁶, B. Hong ¹⁹, Y. H. Kim ²⁴, X. Ma ², B. Moon ²⁴, J. Park ^24,25, F. F. Zeng ², and J. Z. Zhang¹⁵

¹Department of Physics, The University of Hong Kong, Pokfulam, Hong Kong, China
²Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
³Wako Nuclear Science Center (WNSC), Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK), Wako, Saitama 351-0198, Japan
⁴Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082, Guangdong, China
⁵Department of Physics, Meiji University, Kawasaki, Kanagawa 214-8571, Japan
⁶RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
⁷Advanced Energy Science And Technology GuangDong Laboratory, Huizhou, China
⁸Department of Physics, Chalmers University of Technology, 412 96 Göteborg, Sweden
⁹Université Paris-Saclay, CEA, IRFU, 91191 Gif-sur-Yvette, France
¹⁰School of Data Science and Management, Utsunomiya University, Mine, Utsunomiya 321-8505, Japan
¹¹Department of Physics, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan
¹²Department of Physics, Rikkyo University, Toshima, Tokyo 171-8501, Japan
¹³Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
¹⁴CEA, DES, IRESNE, DER, SPRC, LEPh, 13108 Saint-Paul-lès-Durance, France
¹⁵School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China
¹⁶Key Laboratory of Nuclear Data, China Institute of Atomic Energy, Beijing 102413, China
¹⁷Department of Physics and Science of Advanced Materials Program, Central Michigan University, Mount Pleasant, Michigan 48859, USA
¹⁸RCNP, The University of Osaka, Ibaraki, Osaka 567-0047, Japan
¹⁹Department of Physics, Korea University, Seoul 02841, Republic of Korea
²⁰Instituto de Física Corpuscular, CSIC-Universitat de València, 46071 València, Spain
²¹TRIUMF, Vancouver, British Columbia V6T 2A3, Canada
²²Faculty of Arts and Science, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan
²³Quark Nuclear Science Institute, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
²⁴Center for Exotic Nuclear Studies, Institute for Basic Science, Daejeon 34126, Republic of Korea
²⁵Department of Physics, Hope College, Holland, Michigan 49423, USA

^*Contact author: fucy@impcas.ac.cn

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Phys. Rev. Lett. 137, 062502 – Published 6 August, 2026

DOI: https://doi.org/10.1103/krq1-t8pr

Abstract

High-precision multireflection time-of-flight mass spectrometry has been applied at BigRIPS-SLOWRI of the Radioactive Isotope Beam Factory (RIBF). The atomic mass of ${}^{50}{Ar}$ was measured for the first time, and the mass value of ${}^{49}{Ar}$ was determined to be 674 keV lower than the one from a previous $B ρ -$ TOF measurement, with a precision improved by a factor of 250. The new mass data enable us to determine the empirical proton-neutron interaction strength in the unconventional doubly magic nucleus ${}^{52}{Ca}$ . This strength exhibits a conspicuous variation across shell closures, analogously to what observed in classical doubly magic nuclei. Meanwhile, our measurements support the existence of a weak shell effect at $N = 32$ in Ar isotopes. To supplement these experimental findings, theoretical calculations were performed for the isotopes of interest, which, compared with data, illustrate the capacity of ab initio expansion methods to capture key quadrupole correlations in doubly open-shell nuclei via an explicit account of nuclear deformation.

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Mass Measurements of Exotic ${}^{48 - 50}{Ar}$ Isotopes: Probing Proton-Neutron Interaction of the Doubly Magic ${}^{52}{Ca}$ and the Robustness of $N = 32$ Subshell

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Mass Measurements of Exotic Ar48−50 Isotopes: Probing Proton-Neutron Interaction of the Doubly Magic Ca52 and the Robustness of N=32 Subshell

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Mass Measurements of Exotic ${}^{48 - 50}{Ar}$ Isotopes: Probing Proton-Neutron Interaction of the Doubly Magic ${}^{52}{Ca}$ and the Robustness of $N = 32$ Subshell