Large quadrupole deformation in 20Ne challenges rotor model and modern theory
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Date
2025
Journal Title
Journal ISSN
Volume Title
Publisher
American Physical Society
Abstract
The spectroscopic quadrupole moment of the first excited state, QS (2+1 ), at 1.634 MeV in 20Ne was determined from sensitive reorientation-effect Coulomb-excitation measurements using a heavy target and safe energies well below the Coulomb barrier. Particle-γ coincidence measurements were collected at iThemba LABS with a digital data-acquisition system using the AFRODITE array coupled to an annular, doubled-sided silicon detector. A precise value of QS (2+1 ) = −0.22(2) eb was determined at backward angles in agreement with the only safe energy measurement prior to this work, QS (2+1 ) = −0.23(8) eb. This result adopts 1 ¯hω shell-model calculations of the nuclear dipole polarizability of the 2+1 state that contributes to the effective quadrupole interaction and determination of QS (2+1 ). It disagrees, however, with the ideal rotor model for axially symmetric nuclei by almost 3σ. Larger discrepancies are computed by modern state-of-the-art calculations performed in this and prior work, including ab initio shell model with chiral effective interactions and the multireference relativistic energy density functional (MR-EDF) model. The intrinsic nucleon density of the 2+1 state in 20Ne calculated with the MR-EDF model illustrates the presence of α clustering, which explains the largest discrepancy with the rotor model found in the nuclear chart and motivates the explicit inclusion of α clustering for full convergence of E2 collective properties.
Description
Keywords
IThemba labs, Spectroscopic quadrupole, Rotor model, Light ions, Modern theory
Citation
Mehl, C.V., Orce, J.N., Ngwetsheni, C., Marević, P., Brown, B.A., Holt, J.D., Raju, M.K., Lawrie, E.A., Abrahams, K.J., Adsley, P. and Akakpo, E.H., 2024. Large quadrupole deformation in $^{20} $ Ne challenges rotor model and modern theory: urging for $\alpha $ clusters in nuclei. arXiv preprint arXiv:2411.10598.