Dipole response in neutron-rich nuclei with new Skyrme interactions

Abstract

We investigate the isoscalar and isovector E1 response of neutron-rich nuclei, within a semiclassical transport model employing effective interactions for the nuclear mean-field. In particular, we adopt the recently introduced SAMi-J Skyrme interactions, whose parameters are specifically tuned to improve the description of spin-isospin properties of nuclei. Our analysis evidences a relevant degree of isoscalar/isovector mixing of the collective excitations developing in neutron-rich systems. Focusing on the low-lying strength emerging in the isovector response, we show that this energy region essentially corresponds to the excitation of isoscalar-like modes, which also contribute to the isovector response owing to their mixed character. Considering effective interactions which mostly differ in the isovector channels, we observe that these mixing effects increase with the slope L of the symmetry energy at saturation density, leading to a larger strength in the low-energy region of the isovector response. This result appears connected to the increase, with L, of the neutron/proton asymmetry at the surface of the considered nuclei, i.e., to the extension of the neutron skin.

Constraining simultaneously nuclear symmetry energy and neutron-proton effective mass splitting with nucleus giant resonances using a dynamical approach

“…As a breathing oscillation mode in the radial direction of a nucleus, the isoscalar giant monopole resonance (GMR) is a good probe of the incompressibility of nuclear matter [24][25][26][27][28], while the isoscalar giant quadruple resonance (IS-GQR), an oscillation mode with quadruple deformation of a nucleus, has been found to be much affected by the isoscalar nucleon effective mass m * s [29][30][31][32][33][34]. On the other hand, the isovector giant dipole resonance (IVGDR) and the pygmy dipole resonance (PDR), with the former an oscillation mode between the centers of mass of neutrons and protons and the latter that between the neutron skin and the nucleus core, are valuable probes of the nuclear symmetry energy at subsaturation densities [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]. Since the nuclear symmetry energy acts as a restoring force for the IVGDR, the main frequency of the IVGDR oscillation, i.e., the centroid energy E −1 , is related to E sym at subsaturation densities or its slope parameter L at the saturation density [36,45,49].…”

“…On the other hand, the isovector giant dipole resonance (IVGDR) and the pygmy dipole resonance (PDR), with the former an oscillation mode between the centers of mass of neutrons and protons and the latter that between the neutron skin and the nucleus core, are valuable probes of the nuclear symmetry energy at subsaturation densities [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]. Since the nuclear symmetry energy acts as a restoring force for the IVGDR, the main frequency of the IVGDR oscillation, i.e., the centroid energy E −1 , is related to E sym at subsaturation densities or its slope parameter L at the saturation density [36,45,49]. The electric dipole polarizability α D has a strong correlation with the neutron skin thickness ∆r np [38,49], and α D times E sym at the saturation density shows a good linear dependence on L [44,47,48].…”

“…Since the nuclear symmetry energy acts as a restoring force for the IVGDR, the main frequency of the IVGDR oscillation, i.e., the centroid energy E −1 , is related to E sym at subsaturation densities or its slope parameter L at the saturation density [36,45,49]. The electric dipole polarizability α D has a strong correlation with the neutron skin thickness ∆r np [38,49], and α D times E sym at the saturation density shows a good linear dependence on L [44,47,48]. It was argued that the accurate knowl-edge of α D and ∆r np can help constrain significantly the nuclear symmetry energy at subsaturation densities [40].…”

Collision dynamics at medium and relativistic energies

“…Then the value, J, of the symmetry energy at saturation density is different in the three cases, being equal to 27 MeV Fig.3(a). It would be interesting to explore the effects of these interactions, which provide a nice reproduction of nuclear ground state and structure properties, also in transport simulations [99,100,101]. Figure 3: (Color online) (a) Three effective parameterizations of the symmetry energy, as given by the Skyrme SAMi-J family [96].…”

Structure of Exotic Nuclei: a Theoretical Review

“…There are also lots of theoretical investigations on the soft dipole modes [101,102,103,104,105,106,107,108,109,110,111]. In Ref.…”