Influence of the symmetry energy on the giant monopole resonance of neutron-rich nuclei

Abstract

We analyze the influence of the density dependence of the symmetry energy on the average excitation energy of the isoscalar giant monopole resonance (GMR) in stable and exotic neutron-rich nuclei by applying the relativistic extended Thomas-Fermi method in scaling and constrained calculations. For the effective nuclear interaction, we employ the relativistic mean field model supplemented by an isoscalar-isovector meson coupling that allows one to modify the density dependence of the symmetry energy without compromising the success of the model for binding energies and charge radii. The semiclassical estimates of the average energy of the GMR are known to be in good agreement with the results obtained in full RPA calculations. The present analysis is performed along the Pb and Zr isotopic chains. In the scaling calculations, the excitation energy is larger when the symmetry energy is softer. The same happens in the constrained calculations for nuclei with small and moderate neutron excess. However, for nuclei of large isospin the constrained excitation energy becomes smaller in models having a soft symmetry energy. This effect is mainly due to the presence of loosely-bound outer neutrons in these isotopes. A sharp increase of the estimated width of the resonance is found in largely neutron-rich isotopes, even for heavy nuclei, which is enhanced when the symmetry energy of the model is soft. The results indicate that at large neutron numbers the structure of the low-energy region of the GMR strength distribution changes considerably with the density dependence of the nuclear symmetry energy, which may be worthy of further characterization in RPA calculations of the response function.

25 pages, 5 figures; modifications in text

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• Origin of the neutron skin thickness of 208Pb in nuclear mean-field models
• Microscopic Study of the Isoscalar Giant Monopole Resonance in Cd, Sn and Pb Isotopes
• Giant Monopole Resonances and nuclear incompressibilities studied for the zero-range and separable pairing interactions
• Sensitivity of the fusion cross section to the density dependence of the symmetry energy
• Effect of isospin asymmetry in nuclear system
• Single-Λ Hypernuclei in the Relativistic Mean-Field Theory with parameter set FSU
• Neutron-skin thickness of 208Pb from the energy of the anti-analog giant dipole resonance
• Giant monopole energies from a constrained relativistic mean-field approach
• Constraining the relativistic mean-field models from PREX-2 data: Effective forces revisited
• Softness of Sn isotopes in relativistic semi-classical approximation
• Symmetry energy effects on isovector properties of neutron rich nuclei with a Thomas-Fermi approach