5th International Symposium on Nuclear Symmetry Energy NuSYM15, June 29 - July 2, 2015 Kraków, POLAND

Klaus Morawetz
Münster University of Applied Sciences Steinfurt, GERMANY

Damping of giant resonances in (a)symmetric nuclei

Klaus Morawetz$^{1,2,3}$
$^1$Münster University of Applied Sciences, Stegerwaldstrasse 39, 48565 Steinfurt, Germany
$^2$International Institute of Physics (IIP) Av. Odilon Gomes de Lima 1722, 59078-400 Natal, Brazil
$^3$Max-Planck-Institute for the Physics of Complex Systems, 01187 Dresden, Germany

Abstract
The giant resonances in symmetric and asymmetric nuclear matter [1] are described using a conserving relaxation time approximation to include collision effects and compared with experimental data of hot resonances. The isovector and isoscalar modes are coupled due to asymmetric nuclear meanfield acting on neutrons and protons differently. A further coupling is observed caused by collisional correlations. The latter one leads to the appearance of a third mode [2]. We had suggested that this mode might be observable in neutron rich systems like $^{11}Be$ while in proton rich isobars this mode should appear with strong damping which was observed later as Pygmy resonances. Using a pseudoparticle simulation technique we simulate large amplitude isoscalar octupole excitations in a finite nuclear system [3]. Dependent on the initialization we can either observe clear octupole modes or overdamped octupole modes which decay immediately into quadrupole ones. Octupole modes should be present in central asymmetric collisions of heavy ions with mass relation 3:7. The contribution of surface scattering is compared with the contribution from the interparticle collisions. A unified response function is derived which includes surface damping via the Lyapunov exponent [4] as well as collisional damping. The former one is calculated for different shape deformations of quadrupole and octupole type [5]. The surface as well as the collisional contribution each reproduce the experimental value, therefore we propose a proper weighting between both contributions related to their relative occurrence due to collision frequency between particles and of particles with the surface. We find that for low and high temperatures the collisional contribution dominates whereas the surface damping is dominant around temperatures of a third of the centroid energy [5].

[1] U. Fuhrmann, K. Morawetz, R. Walke, Phys. Rev. C 58 (1995), 1473
[2] K. Morawetz, U. Fuhrmann, R. Walke, M. DiToro, Phys. Rev. C 57 } (1998), R2813
[3] R. Walke, K. Morawetz, Phys. Rev. C 60 (1998) 17301; K. Morawetz, U. Fuhrmann, R. Walke, Nucl. Phys. A 649 (1998) 348c
[4] K. Morawetz, Phys. Rev. E 61 (1998) 2555
[5] K. Morawetz, M. Vogt, U. Fuhrmann, P. Lipavský, V. Spicka, Phys. Rev. C 60 (1999) 54601