Year: 2016
Type: article
Abstract: Background: The sharp ${1}^{\ensuremath{-}}$ resonances with enhanced isoscalar dipole transition strengths are observed in many light nuclei at relatively small excitation energies, but their nature has been unclear.Purpose: We show those resonances can be attributed to the cluster states with asymmetric configurations such as $\ensuremath{\alpha}+^{16}\mathrm{O}$. We explain why asymmetric cluster states are strongly excited by the isoscalar dipole transition. We also provide a theoretical prediction of the isoscalar dipole transitions in $^{20}\mathrm{Ne}$ and $^{44}\mathrm{Ti}$.Method: The transition matrix is analytically derived to clarify the excitation mechanism. The nuclear model calculations by Brink--Bloch wave function and antisymmetrized molecular dynamics are also performed to provide a theoretical prediction for $^{20}\mathrm{Ne}$ and $^{44}\mathrm{Ti}$.Results: It is shown that the transition matrix is as large as the Weisskopf estimate even though the ground state is an ideal shell-model state. Furthermore, it is considerably amplified if the ground state has cluster correlation. The nuclear model calculations predict large transition matrix to the $\ensuremath{\alpha}+^{16}\mathrm{O}$ and $\ensuremath{\alpha}+^{40}\mathrm{Ca}$ cluster states comparable with or larger than the Weisskopf estimate.Conclusions: We conclude that the asymmetric cluster states are strongly excited by the isoscalar dipole transition. Combined with the isoscalar monopole transition that populates the ${0}^{+}$ cluster states, the isoscalar transitions are promising probes for asymmetric clusters.
Source: Physical Review C
Authors: Y. Chiba, M. Kimura, Y. Taniguchi
Institutions: Hokkaido University, Nihon Institute of Medical Science
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: Study of Neutron-halo and shape coexistence near the neutron-drip line, G2539256395, G5795264350, G6471540087, Drastic changes of nuclear structure induced by many-body correlations, Study of cluster resonances probed by monopole and dipole transitions, and its application to Carbon burning process, G7270080624
OpenAlex ID: W2219450366