RESUMO
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 in explaining the 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 six 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.
RESUMO
The nuclear magnetic dipole moment mu and electric quadrupole moment Q of the beta-emitting 16N(Ipi = 2(-), T(1/2) = 7.13 s) nucleus have been determined for the first time by detecting its beta-NMR in a MgO crystal and beta-NQR (nuclear quadrupole resonance) in a TiO (2) crystal to be /mu/ = (1.9859+/-0.0011) mu(N) and /Q/ = (17.9+/-1.7) mb, respectively. Although the prediction of mu given by the Hartree-Fock calculation agrees well with the experiment, an abnormally small effective charge for neutrons is required to account for the experimental Q.
