A multi-detector array for high energy nuclear e+e? pair spectroscopy

A multi-detector array has been constructed for the simultaneous measurement of energy and angular correlation of electron–positron pairs produced in internal pair conversion (IPC) of nuclear transitions up to 18 MeV. The response functions of the individual detectors have been measured with mono-energetic beams of electrons. Experimental results obtained with 1.6 MeV protons on targets containing 11B and 19F show clear IPC over a wide angular range. A comparison with GEANT simulations demonstrates that angular correlations of e+e− pairs of transitions in the energy range between 6 and 18 MeV can be determined with sufficient resolution and efficiency to search for deviations from IPC due to the creation and subsequent decay into e+e− of a hypothetical short-lived neutral boson.