München 2019 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 27: Structure and Dynamics of Nuclei V

HK 27.2: Talk

Tuesday, March 19, 2019, 17:00–17:15, HS 14

How robust is the N = 34 subshell closure? First spectroscopy of ⁵²Ar — •Hongna Liu for the SEASTAR17 collaboration — Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany

It is now well known that magic numbers are not universal across the nuclear landscape and that new shell closures may emerge in exotic nuclei. For example, a new N=34 subshell closure was predicted for neutron-rich pf-shell nuclei. However, on the experimental side, the N=34 subshell closure has been so far reported only in ⁵⁴Ca. The systematics of E(2₁⁺) along the Ti and Cr isotopes show no local maximum at N=34. It is thus very natural to ask how the N=34 subshell evolves below Z=20 towards more neutron-rich systems, such as ⁵²Ar.

In this talk, we will report on the first γ-ray spectroscopy of ⁵²Ar measured using the ⁵³K(p,2p) reaction at ∼210 MeV/u at RIBF. The 2₁⁺ excitation energy was measured to be 1656(18) keV, the highest among the Ar isotopes with N>20, providing the first experimental signature of the persistence of the N = 34 subshell closure below Z=20. Shell-model calculations with phenomenological and the chiral interaction 1.8/2.0 (EM) both reproduce the measured 2₁⁺ systematics of the neutron-rich Ar isotopes, and surpport a N=34 subshell closure in ⁵²Ar. However, coupled-cluster calculations based on the same chiral interaction underestimate E(2₁⁺) in ⁵²Ar. The data measured in current work serves as an important benchmark to understand the uncertainties of the employed many-body methods and chiral effective-field-theory interactions.