Interference Phenomena in Perturbed Angular Correlations (Theory of Time — Independent Interactions)

TLDR: In this paper, the theory of perturbed angular correlations of time independent interactions is formulated in such a way as to display explicitly the interference properties of the individual energy levels of the intermediate state.

Abstract: The theory of perturbed angular correlations of time — independent interactions is formulated in such a way as to display explicitly the interference properties of the individual energy levels of the intermediate state. In time — differential angular correlation experiments, interfering energy eigenstates give rise to oscillations whose period is a direct measure of the energy difference of the corresponding levels. Two energy levels that cross as a function of an external magnetic field may produce a resonance in a time — integrated angular correlation experiment, because of interference between the two states. From general symmetry properties of the extranuclear interactions, a number of selection rules for interference is derived. Based on these rules and the level structure of the intermediate system in the extranuclear field, general properties of the angular correlation function can be derived without calculation. The method is illustrated by discussing hitherto unobserved effects in angular correlations due to the hyperfine interaction in free atoms and in paramagnetic crystals. Characteristic effects produced by the mixing of states in the vicinity of repulsive energy levels are also discussed.