Dynamics of nuclear fluid. VI. Nuclear giant resonances as elastic vibrations

Starting with the previous result that the equation of motion for some collective motion of the nuclear fluid can be approximated by the Lame equation, we consider the nuclear giant resonances as elastic vibrations of a nucleus, the properties of elasticity being a peculiar manifestation of the quantum stress tensor. The nucleus is taken to be compressible and endowed with elastic moduli, surface tension, Coulombic charge, and two-body viscosity. Eigenenergies and widths for the isoscalar electric multipole states (0+,1-,2+,3-,4+,...) and the isoscalar magnetic multipole states (1+,2-,3+,4-,...) are obtained. The energies and widths of the 0+, 2+, and 3- states agree well with those of the observed giant resonances. Such agreement lends support to the present macroscopic description of the collective excitation of a nucleus. Nuclear viscosity coefficients and the incompressibility of nuclear matter are extracted. In the present unified approach, the high-lying electric multipole ''giant resonance'' states and the low-lying ''liquid-drop'' states emerge as eigenstates of the same characteristic equation. Similarities and differences between these two types of states are assessed