Large quadrupole deformation in $^{20}$Ne challenges rotor model and modern theory: urging for $\alpha$ clusters in nuclei
| Autor: | Mehl, C. V., Orce, J. N., Ngwetsheni, C., Marević, P., Brown, B. A., Holt, J. D., Raju, M. Kumar, Lawrie, E. A., Abrahams, K. J., Adsley, P., Akakpo, E. H., Bark, R. A., Bernier, N., Bucher, T. D., Yahia-Cherif, W., Dinoko, T. S., Ebran, J. -P., Erasmus, N., Jones, P. M., Khan, E., Kheswa, N. Y., Khumalo, N. A., Lawrie, J. J., Majola, S. N. T., Malatji, K. L., Mavela, D. L., Mokgolobotho, M. J., Nikšić, T., Ntshangase, S. S., Pesudo, V., Rebeiro, B., Shirinda, O., Vretenar, D., Wiedeking, M. |
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| Rok vydání: | 2024 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | The spectroscopic quadrupole moment of the first excited state, $Q_{_S}(2^{+}_{1})$, at 1.634 MeV in $^{20}$Ne was determined from sensitive reorientation-effect Coulomb-excitation measurements using a heavy target and safe energies well below the Coulomb barrier. Particle-$\gamma$ coincidence measurements were collected at iThemba LABS with a digital data-acquisition system using the {\sc AFRODITE} array coupled to an annular, doubled-sided silicon detector. A precise value of $Q_{_S}(2^{+}_{1})=-0.22(2)$ eb was determined at backward angles in agreement with the only safe-energy measurement prior to this work, $Q_{_S}(2^{+}_{1})=-0.23(8)$ eb. This result adopts 1$\hbar\omega$ shell-model calculations of the nuclear dipole polarizability of the 2$^+_1$ state that contributes to the effective quadrupole interaction and determination of $Q_{_S}(2^{+}_{1})$. It disagrees, however, with the ideal rotor model for axially-symmetric nuclei by almost $3\sigma$. Larger discrepancies are computed by modern state-of-the-art calculations performed in this and prior work, including {\it ab initio} shell model with chiral effective interactions and the multi-reference relativistic energy density functional ({\sc MR-EDF}) model. The intrinsic nucleon density of the 2$^+_1$ state in $^{20}$Ne calculated with the {\sc MR-EDF} model illustrates the presence of $\alpha$ clustering, which explains the largest discrepancy with the rotor model found in the nuclear chart and motivates the explicit inclusion of $\alpha$ clustering for full convergence of $E2$ collective properties. Comment: 8 pages, 8 figures |
| Databáze: | arXiv |
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