TORSIONAL MULTIPOLE MAGNETIC RESPONSE OF A HEAVY SPHERICAL NUCLEUS

The predictions of the distorted Fermi-sphere model for magnetic isosc alar resonances are summarized. In this model a heavy spherical nucleu s is thought of as a charged piece of spin and isospin saturated nucle ar Fermi-continuum possessing properties of an elastic-like matter. Th e magnetic resonances are described in fluid-dynamical terms and inter preted as manifestations of elastic torsional vibrations of the nucleu s. The process of nuclear magnetization induced by inelastically scatt ered electrons is described as a transition from a currentless ground state to a magnetized excited one which is characterized by a non-zero magnetic multipole moment. We present calculations of a complete set of integral characteristic parameters of M lambda, T = 0 resonances su ch as position of energy peak, excitation probability and magnetic osc illator strength computed as functions of mass number and multipole de gree lambda greater than or equal to 2. An analytic form is given for collective transition current density and the PWBA computed form facto rs that may be used for analysis of measurements with inelastically sc attered electrons. Numerical estimates are performed with use of the D WBA code. Theoretical predictions are presented in juxtaposition with the DALINAC data available on M2 giant resonance in spherical nuclei. We briefly discuss the microscopic effects of two-particle correlation s between nucleons occupying two different single-particle orbits of s hell structured mean field that may, in our opinion, be responsible fo r the collective torsional magnetic response predicted by the model in question.