Abstract
The first γ-ray spectroscopy of ^{52}Ar, with the neutron number N=34, was measured using the ^{53}K(p,2p) one-proton removal reaction at ∼210 MeV/u at the RIBF facility. The 2_{1}^{+} 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 ^{54}Ca, i.e., below the magic proton number Z=20. Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 2_{1}^{+} systematics of neutron-rich Ar isotopes, and support a N=34 subshell closure in ^{52}Ar.
Highlights
The first γ-ray spectroscopy of 52Ar, with the neutron number N 1⁄4 34, was measured using the 53Kðp; 2pÞ one-proton removal reaction at ∼210 MeV=u at the RIBF facility
A few prominent examples are the breakdown of the conventional N 1⁄4 20, 28 magic numbers [3,4,5] and the emergence of a new N 1⁄4 16 magic number [6,7] in neutron-rich nuclei
In the present Letter, we report on the first spectroscopy of 52Ar, the most neutron-rich even-even N 1⁄4 34 isotone accessible today and possibly for the decades
Summary
Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 2þ1 systematics of neutron-rich Ar isotopes, and support a N 1⁄4 34 subshell closure in 52Ar. In the shell-model description of atomic nuclei, magic numbers of nucleons correspond to fully occupied energy shells below the Fermi surface [1], and present the backbone of our understanding of nuclei. The measured Eð2þ1 Þ of 54Ca was 2043(19) keV, ∼0.5 MeV lower than 52Ca [24] Despite this lower Eð2þ1 Þ, 54Ca was concluded to be a doubly magic nucleus from a phenomenological shell-model interpretation [24], whereas ab initio coupled-cluster calculations indicated a weak N 1⁄4 34 subshell closure [29]. Phenomenological shell-model calculations [16,30] reproducing the available Eð2þ1 Þ data for neutron-rich Ar isotopes predict a relatively high-lying 2þ1 state in 52Ar, and suggest that the N 1⁄4 34 subshell closure in. A clear enhancement of Eð2þ1 Þ at N 1⁄4 34 is found, supporting the persistence of the N 1⁄4 34 magic number in Z < 20 nuclei
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