Paramagnetische Felder am Kernort

Abstract

A theory of the paramagnetic correction of an external magnetic field at the site of the nucleus is developed. This effect is important especially for the experimental method of perturbed angular correlations, by which magnetic moments of excited nuclei are measured. It occurs if an “inner” electron shell is not closed, e. g. for the Lanthanons (4f-shell) or the Actinons (5f-shell).

The ion in view, considered to be isolated, is described by a single particle model with central field (e. g. Hartree's self consistent field), so that l is a good quantum number. Russell-Saunders coupling is assumed. For the ground multiplet L and S are evaluated by Hund's rule. The excited multiplets may be disregarded as they are not occupied at usual temperatures. Saturation, diamagnetic and other nonlinear effects in the magnetic field strength are neglected. Corrections to this model are discussed in the last section.

In the L-S-scheme, the strengths of the multiplet splitting and of the induced magnetic field are determined by two coefficients η and ξ, which depend on the electron configuration ι^itq. A detailed derivation of the expressions η(l, q) and ξ(l, q) is presented. At last, the quantum mechanical and thermodynamical average of the paramagnetic field in question is calculated.