Isoscalar monopole and dipole transitions in $^{24}$Mg, $^{26}$Mg and $^{28}$Si
| Autor: | Adsley, P., Nesterenko, V. O., Kimura, M., Donaldson, L. M., Neveling, R., Brümmer, J. W., Jenkins, D. G., Kheswa, N. Y., Kvasil, J., Li, K. C. W., Marin-Lámbarri, D. J., Mabika, Z., Papka, P., Pellegri, L., Pesudo, V., Rebeiro, B., Reinhard, P. -G., Smit, F. D., Yahia-Cherif, W. |
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| Rok vydání: | 2020 |
| Předmět: | |
| Zdroj: | Phys. Rev. C 103, 044315 (2021) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevC.103.044315 |
| Popis: | Nuclei in the $sd$-shell demonstrate a remarkable interplay of cluster and mean-field phenomena. The $N=Z$ nuclei, such as $^{24}$Mg and $^{28}$Si, have been the focus of the theoretical study of both these phenomena in the past. The cluster and vortical mean-field phenomena can be probed by excitation of isoscalar monopole and dipole states in scattering of isoscalar particles such as deuterons or $\alpha$ particles. Inelastically scattered $\alpha$ particles were momentum-analysed in the K600 magnetic spectrometer at iThemba LABS, Cape Town, South Africa. The scattered particles were detected in two multi-wire drift chambers and two plastic scintillators placed at the focal plane of the K600. In the theoretical discussion, the QRPA and AMD+GCM were used. The QRPA calculations lead us to conclude that: i) the mean-field vorticity appears mainly in dipole states with $K=1$, ii) the dipole (monopole) states should have strong deformation-induced octupole (quadrupole) admixtures, and iii) that near the $\alpha$-particle threshold, there should exist a collective state (with $K=0$ for prolate nuclei and $K=1$ for oblate nuclei) with an impressive octupole strength. The results of the AMD+GCM calculations suggest that some observed states may have a mixed (mean-field + cluster) character or correspond to particular cluster configurations. A tentative correspondence between observed states and theoretical states from QRPA and AMD+GCM was established. The QRPA and AMD+GCM analysis shows that low-energy isoscalar dipole states combine cluster and mean-field properties. The QRPA calculations show that the low-energy vorticity is well localized in $^{24}$Mg, fragmented in $^{26}$Mg, and absent in $^{28}$Si. Comment: 11 figures, 18ish pages, accepted in Phys Rev C |
| Databáze: | arXiv |
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