How Robust is the N=34 Subshell Closure? First Spectroscopy of Ar 52

7 pags., 3 figs., 1 tab. -- Open Access funded by Creative Commons Atribution Licence 4.0
The first γ-ray spectroscopy of Ar52, with the neutron number N=34, was measured using the K53(p,2p) one-proton removal reaction at ∼210 MeV/u at the RIBF facility. The 21+ excitation energy is found at 1656(18) keV, the highest among the Ar isotopes with N>20. This result is the first experimental signature of the persistence of the N=34 subshell closure beyond Ca54, i.e., below the magic proton number Z=20. Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 21+ systematics of neutron-rich Ar isotopes, and support a N=34 subshell closure in Ar52.
We thank the RIKEN Nishina Center accelerator staff for their work in the primary beam delivery and the Big RIP Steam for preparing the secondary beams. The development of MINOS has been supported by the European Research Council through the ERC Grant No. MINOS 258567. Acknowledges the support from the Enhanced Eurotalents program (PCOFUND-GA-2013-600382) co-funded by CEA and the European Union. H.N.L., A.O. and A.S. acknowledge the support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project No. 279384907- SFB 1245. C.A.B. acknowledges support from the U.S. NSF Grant No. 1415656 and the U.S. DOE Grant No.DE-FG02-08ER41533.J.D.H.and R.S.acknowledge the support from NSERC and the National Research Council Canada. Y.L.S. acknowledges the support of Marie Skłodowska-Curie Individual Fellowship (H2020-MSCAIF-2015-705023) from the European Union. I.G. has been supported by HIC for FAIR andCroatianScienceFoundation. L.X.C. and B.D.L. have been supported by the Vietnam MOST through the Physics Development Program Grant No. ĐTĐLCN.25/18. K.I.H., D.K. and S.Y.P. have been supported by the NRF grant funded by the Korea government (No. 2017R1A2B2012382 and 2018R1A5A1025563). This work was supported in part by JSPS KAKENHI Grant No. 16H02179, MEXT KAKENHI Grants No. 24105005 and No. 18H05404. This work was also supported by the Office of Nuclear Physics,U.S.Department of Energy,under Grants No.de-sc 0018223 (NUCLEISciDAC-4collaboration) and the Field Work Proposal ERKBP72 at Oak Ridge National Laboratory (ORNL). Computer time was provided by the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program. Thisresearch used resources of the Oak Ridge Leadership Computing Facility located at ORNL, which is supported by the Office of Science of the Department of Energy under Contract No. DE-AC0500OR22725.