The presence of some low-lying (pygmy) strength in the dipole spectrum, at excitation energy well below the isovector giant dipole energy, has been confirmed in several nuclei. The microscopic structure and the nature of these states, in particular the possible collective nature and the isospin character, are currently under strong debate. In addition, a relation with the isovector properties of the equation of state of nuclear matter, such as the symmetry energy or its slope, has been proposed. We present a detailed analysis of Skyrme Hartree–Fock plus random phase approximation (RPA) predictions for both the isoscalar and isovector dipole responses, of different neutron-rich nuclei (68Ni, 132Sn and 208Pb). All of them show a low-energy peak that increases in magnitude with increasing values of the slope of the symmetry energy at saturation. Eventually, the collectivity associated with the RPA states contributing to this peak is more pronounced in the isoscalar than in the isovector channel.

Low-lying dipole response in stable and unstable nuclei / M. Brenna, X. Roca-Maza, G. Colò, P.F. Bortignon, K. Mizuyama, G. Pozzi. - In: PHYSICA SCRIPTA. - ISSN 0031-8949. - T154:154(2013 May 02), pp. 014020.1-014020.5. ((Intervento presentato al 19. convegno Nuclear physics workshop Marie and Pierre Curie tenutosi a Kazimierz , Polonia nel 2012 [10.1088/0031-8949/2013/T154/014020].

Low-lying dipole response in stable and unstable nuclei

M. Brenna
Primo
;
X. Roca-Maza;G. Colò;P.F. Bortignon;
2013

Abstract

The presence of some low-lying (pygmy) strength in the dipole spectrum, at excitation energy well below the isovector giant dipole energy, has been confirmed in several nuclei. The microscopic structure and the nature of these states, in particular the possible collective nature and the isospin character, are currently under strong debate. In addition, a relation with the isovector properties of the equation of state of nuclear matter, such as the symmetry energy or its slope, has been proposed. We present a detailed analysis of Skyrme Hartree–Fock plus random phase approximation (RPA) predictions for both the isoscalar and isovector dipole responses, of different neutron-rich nuclei (68Ni, 132Sn and 208Pb). All of them show a low-energy peak that increases in magnitude with increasing values of the slope of the symmetry energy at saturation. Eventually, the collectivity associated with the RPA states contributing to this peak is more pronounced in the isoscalar than in the isovector channel.
Settore FIS/04 - Fisica Nucleare e Subnucleare
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/222593
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