An actively vetoed Clover \gamma -detector for nuclear astrophysics at LUNA

An escape-suppressed, composite high-purity germanium detector of the Clover type has been installed at the Laboratory for Underground Nuclear Astrophysics (LUNA) facility, deep underground in the Gran Sasso Laboratory, Italy. The laboratory $ \gamma$ -ray background of the Clover detector has been studied underground at LUNA and, for comparison, also in an overground laboratory. Spectra have been recorded both for the single segments and for the virtual detector formed by online addition of all four segments. The effect of the escape suppression shield has been studied as well. Despite their generally higher intrinsic background, escape-suppressed detectors are found to be well suited for underground nuclear-astrophysics studies. As an example for the advantage of using a composite detector deep underground, the weak ground-state branching of the E _p = 223 keV resonance in the ²⁴Mg(p, $ \gamma$ )²⁵Al reaction is determined with improved precision.