Evidence for Z=6 `magic number' in neutron-rich carbon isotopes

Abstract

The nuclear shell structure, which originates in the nearly independent motion of nucleons in an average potential, provides an important guide for our understanding of nuclear structure and the underlying nuclear forces. Its most remarkable fingerprint is the existence of the so-called `magic numbers' of protons and neutrons associated with extra stability. Although the introduction of a phenomenological spin-orbit (SO) coupling force in 1949 helped explain the nuclear magic numbers, its origins are still open questions. Here, we present experimental evidence for the smallest SO-originated magic number (subshell closure) at the proton number 6 in 13-20C obtained from systematic analysis of point-proton distribution radii, electromagnetic transition rates and atomic masses of light nuclei. Performing ab initio calculations on 14,15C, we show that the observed proton distribution radii and subshell closure can be explained by the state-of-the-art nuclear theory with chiral nucleon-nucleon and three-nucleon forces, which are rooted in the quantum chromodynamics.

arXiv comment7 pages, 5 figures

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• Study of ground state properties of carbon isotopes with deformed relativistic Hartree-Bogoliubov theory in continuum
• Swelling of doubly magic ${}^{48}$Ca core in Ca isotopes beyond $N=28$
• Angular momentum projection in the deformed relativistic Hartree-Bogoliubov theory in continuum
• Nuclear matter distributions in the neutron-rich carbon isotopes ${}^{14-17}$C from intermediate-energy proton elastic scattering in inverse kinematics
• Charge-changing cross sections for ${}^{42\text{–}51}$Ca and effect of charged-particle evaporation induced by neutron removal reaction
• Ab initio no-core shell model description of ${}^{10-14}$C isotopes
• Nuclear ground-state properties probed by the relativistic Hartree-Bogoliubov approach
• Neutron quadrupole transition strength in ${}^{10}$C deduced from the ${}^{10}$C$(\alpha ,{\alpha }^{\prime })$ measurement with the MAIKo active target
• Accuracy of the mean-field theory in describing ground-state properties of light nuclei
• Probing the Z = 6 spin-orbit shell gap with (p,2p) quasi-free scattering reactions
• Ab initio no-core shell model study of neutron-rich ${}^{18,19,20}$C isotopes
• Unbound states in 17C and p-sd shell-model interactions
• Ab initio study of Z(N) = 6 magicity
• Quenching of the proton $\pi 0p_{3/2}$-$\pi 0p_{1/2}$ spin-orbit splitting in ${}^{20}$O and the effect of the tensor force
• Novel multi-layer plastic-scintillator-based solid active proton target for inverse-kinematics experiments