Two mini-orange spectrometers were used to view ${\mathrm{e}}^{+}$-${\mathrm{e}}^{\mathrm{-}}$ pairs from a positron source and a Th scatterer from opposite directions, 180° apart. No statistically significant evidence for peaks previously reported was found in the coincidence spectra.

• Received 8 July 1987

DOI:https://doi.org/10.1103/PhysRevC.36.2136