The Reorientation Effect

Abstract

The reorientation effect in Coulomb excitation is discussed as a tool to measure static quadrupole moments in excited nuclear states. Since the electromagnetic field produced in a Coulomb excitation is well known, the method is free from the ambiguities inherent in methods employing the fields produced by the atomic electrons. In order to furnish a basis for the interpretation of experiments an outline of the theory is given in the framework of a perturbation expansion. Even if the assumptions underlying the perturbation approach are not strictly satisfied, the explicit nature of its solutions provides an indispensable guide for designing an experiment. For the actual evaluation one has to utilize the numerical solution obtained from a direct treatment of the time-dependent Schrodinger equation. Some care is devoted to the discussion of other effects which might contribute to the excitation and thus affect the measurement of the quadrupole moment. Both magnetic dipole reorientation and excitation via the giant dipole resonance turn out to be innocuous within present experimental accuracies. Various possible experiments and experimental techniques are treated in some detail, and the results obtained so far are presented and discussed. The appendix aims to facilitate the planning of experiments by compiling numerical formulas, tables, and graphs.