Interference Effects in Gamma-Gamma Angular Correlations

The theory of the directional correlation of successive nuclear gamma-rays is extended to include transitions in which mixtures of multipoles are present. For such cases interference effects can radically modify the angular correlation from what is predicted in the usual theory assuming pure multipole transitions. Correlation functions are tabulated for all possible cascade emissions in which one of the transitions is a mixture of magnetic dipole and electric quadrupole and the other either dipole or quadrupole. It is shown that the experimental data on ${\mathrm{Sr}}^{88}$ which had previously seemed anomalous can be consistently interpreted with the mixture theory developed here, but the agreement with the observed angular correlation in ${\mathrm{Pd}}^{106}$ is not possible if the highest gamma-multipole order is assumed to be quadrupole.