Study of radioactive impurities in solids. Pt.1: Radiation characteristics

The theoretical problem of the emission of radiation by radioactive nuclei is usually treated in a very general form adapted to nuclear physics. In this paper we approach it within a much narrower scope, but with the aim of using the resulting formulae in solid state physics studies. For this reason we give a unified treatment of both perturbed angular correlations and nuclear orientation, so as to permit an easy comparison between these two types of experiments. Also we resort systematically to Fano formalism (multipole expansion of the density matrix), which, in the second part of this work, will appear as particularly suitable for the computation of relaxation and radiofrequency effects.