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Soft breathing modes in neutron-rich nuclei with the subtracted second random-phase approximation

D. Gambacurta, M. Grasso, and O. Sorlin

We analyze the isoscalar response related to breathing modes with particular attention being paid to low-lying excitations in neutron-rich nuclei. We use the subtracted second random-phase approximation (SSRPA) to describe microscopically the response. By increasing the neutron excess, we study the evolution of the response in Ca isotopes going from 40Ca to 48Ca and to 60Ca as well as in N=20 isotones going from 40Ca to 36S and to 34Si. Finally, the case of 68Ni is investigated. We predict soft monopole modes in neutron-rich nuclei which are driven by neutron excitations. At variance with dipole pygmy modes, these neutron excitations are not only strongly dominant at the surface of the nucleus but over its entire volume. The effect of the mixing with two particle–two hole configurations induced by the SSRPA model is analyzed. The properties of such soft neutron modes are investigated in terms of their excitation energies, transition densities and wave-function components. Their collectivity is also discussed as a function of the isospin asymmetry and of the mass of the nucleus. The link between such low-energy compression modes and a compressibility modulus introduced for neutron-rich infinite matter is finally studied.

See online : Phys. Rev. C 100, 014317 (2019)


 

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