Introduction

Abstract

The charge distribution of an atomic nucleus interacts with the electromagnetic fields produced by the extranuclear charges of the shell electrons or the constituents of the solid-state surroundings, or by totally external sources such as an applied magnetic field. This hyperfine interaction results in a shift and a splitting of the nuclear and atomic levels. The hyperfine interaction Hamiltonian H_hf can be expressed conveniently in terms of a multipole expansion:

$$ {{H}_{{hf}}} = H(EO) + H(M1) + H(E2) + \ldots , $$

(1.1)

where H(E0) denotes the electric monopole, H(M1) the magnetic dipole, H(E2) the electric quadrupole term, etc. They correspond to the moments of the nucleus not required by symmetry to vanish.