Dipole torus mode in nuclear fluid-dynamics

Abstract

The nuclear fluid-dynamics is applied to the study of a dipole electric response related to the transverse poloidal oscillations of a particle flow. This response is associated with excitation in the nucleus volume of the spherical Hill vortex-torus-like current structure harmonically oscillating in time; the nucleus shape remains spherical. The energy evaluated within the distorted Fermi-surface model is predicted to be E(1 torus −) = 65–85A −1 3 MeV , i.e. the torus excitation is expected to be identified experimentally as 2khω isoscalar dipole resonance. An analytic form is derived for the electric form factor and numerical calculations of the transition current density are presented. The contribution to the cross section of photoabsorption computed in the PWBA is estimated to be σ γ(1 torus −)= 10 −3−10 −4Z 2 A MeV·fm 2 . Some hints for further experiments are suggested.