Energy and efficiency calibration of an array of six Euroball Cluster detectors used for beta-decay studies

The use of an array of six Euroball Cluster detectors, i.e. 42 large-volume germanium detectors, for beta-decay studies is described. The solid angle with respect to a source placed in the center of the array amounts to 65% of 4π sr. The total photo-peak efficiency for 1.33 MeV γ-rays is 10.2(5)%, without “adding back” the Compton-scattered events. For this γ-ray energy, the energy resolution of the entire setup is 2.8 keV. The performance of the array up to γ-ray energies of 8 MeV is discussed, and alternative ways of determining the photo-peak efficiency are presented.