Relativistic transport approach to collective nuclear dynamics

Journal Article · Thu Dec 15 00:00:00 EST 2005 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PhysRevC.72.064317· OSTI ID:20771093

Yildirim, Serbuelent ^[1]; Gaitanos, Theodoros ^[2]; Di Toro, Massimo; Greco, Vincenzo ^[3]

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1. Fizik Boeluemue, Mersin Ueniversitesi, TR-33343 Mersin (Turkey)
2. Dept. fuer Physik, Universitaet Muenchen, Am Coulombwall 1, D-85748 Garching (Germany)
3. Laboratori Nazionali del Sud, INFN, Via S. Sofia 62, I-95123 Catania (Italy) and Dipartimento di Fisica e Astronomia, Universita degli Studi di Catania, Catania (Italy)

The isoscalar giant monopole resonance (ISGMR) and isovector giant dipole resonance (IVGDR) in finite nuclei are studied within the framework of a relativistic transport approach. Small-amplitude oscillations are analyzed with the relativistic Vlasov equation, i.e., neglecting nucleon collision terms. The excitation energies of ISGMR and IVGDR are obtained for spherical nuclei with various sets of Lagrangian parameters. In the case of {sup 208}Pb we study in detail the dependence of the monopole response on the effective mass and symmetry energy at saturation a{sub 4} given by the used covariant effective interaction. We show that a reduced m* and a larger a{sub 4} can compensate for the effect on the ISGMR energy centroid of a much larger compressibility modulus K{sub nm}. The role of the symmetry energy is confirmed by the observation of reduced corrections for the more symmetric {sup 90}Zr. This result is important for overcoming the conflicting determination of nuclear compressibility between nonrelativistic and relativistic effective interactions. For symmetry-energy dynamical effects, we analyze the influence of the inclusion of an effective isovector-scalar channel, {delta}-meson field, with constant- and density-dependent couplings. We show that the {delta}-meson contribution, keeping fixed the equilibrium a{sub 4} value, leads to a reduction in the centroid energy of the ISGMR and IVGDR for {sup 208}Pb. The same mechanism can account for the apparent paradox of a decrease of the frequency of a IVGDR mode in heavy nuclei (of volume type) even in presence of a larger a{sub 4}. All that in fact reveals the sensitivity of the ISGMR and IVGDR collective motions for neutron-rich systems on the slope (or pressure) of the symmetry energy at saturation. Density-dependent vertices do not much affect our conclusions. Following as a guidance the dispersion relations in nuclear matter, we see two main reasons for that: The smoothness of the density dependences around saturation and the presence of compensation effects coming from rearrangement terms.

• OSTI ID: 20771093
• Journal Information: Physical Review. C, Nuclear Physics, Vol. 72, Issue 6; Other Information: DOI: 10.1103/PhysRevC.72.064317; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
AMPLITUDES
BOLTZMANN-VLASOV EQUATION
COLLECTIVE MODEL
COMPRESSIBILITY
CORRECTIONS
DENSITY
DIPOLES
DISPERSION RELATIONS
EFFECTIVE MASS
EXCITATION
GIANT RESONANCE
ISOVECTORS
LAGRANGIAN FUNCTION
LEAD 208
MASS NUMBER
MESONS
NEUTRONS
NUCLEAR FORCES
NUCLEAR MATTER
QUANTUM FIELD THEORY
RELATIVISTIC RANGE
ROUGHNESS
SATURATION
SCALARS
SENSITIVITY
SPHERICAL CONFIGURATION
SYMMETRY
ZIRCONIUM 90