Sometime ago a number of $\gamma-\gamma$, $\beta-\gamma$ and $\alpha-\gamma$ angular correlation studies were carried out to infer spin-parity assignments for cascades of decays from excited nuclear states (e.g., this one). A typical study would have a fixed detector and a moveable detector, with an angle $\vartheta$ subtended between them in relation to a radioactive source. Two $\gamma$ photons were recorded in coincidence, and the path of the first one, detected in the fixed detector, was chosen as the $z$-axis. The intensity of the correlation was measured as a function of $\vartheta$ as the moveable detector was moved around the source. The anisotropy in the intensity that was found as a function of $\vartheta$ was then used to infer things like the multipole order of the second $\gamma$ that had been emitted.
Suppose in a specific case an E1 (electric dipole) transition was determined (or perhaps an M1+E2 transition). Is there a semiclassical explanation for the anisotropy in the coincidence measurement around the radioactive source, or do we only understand the mathematics? Is there an intuitive explanation for the fact that the second $\gamma$ photon is preferentially emitted at specific angles in relation to the first $\gamma$?