Angular correlations of electron-positron pairs in internal electric monopole conversion of aligned heavy nuclei

We consider the influence of the nuclear alignment which, e.g., may be caused by Coulomb excitation on the spatial distribution of the electron-positron pairs resulting from electric monopole conversion processes. E0 conversion is a pure penetration effect, i.e., there is no virtual photon exchange. Approximating the nucleus by a homogeneously charged sphere we find that the angular distribution of electrons and positrons is independent on the alignment axis of the excited nucleus and is determined solely by the opening angle of the emitted lepton pairs. (orig.)