The GALATEA test facility and a first study of alpha-induced surface events in a Germanium detector

Germanium detectors are a choice technology in fundamental
research. They are suitable for the search for rare events due to
their high sensitivity and excellent energy resolution. As an
example, the GERDA (GERmanium Detector Array) experiment searching
for neutrinoless double beta decay is described. The observation of
this decay would resolve the fundamental question whether the
neutrino is its own antiparticle. Especially adapted detector
technologies and low background rates needed to detect very rare
events such as neutrinoless double beta decays are discussed. The
identification of backgrounds originating from the interaction of
radiation, especially alpha-particles, is a focus of this thesis.
Low background experiments face problems from alpha-particles due
to unavoidable surface contaminations of the germanium detectors.
The segmentation of detectors is used to obtain information about
the special characteristics of selected events. The high precision
test stand GALATEA was especially designed for surface scans of
germanium detectors. As part of this work, GALATEA was completed
and commissioned. The final commissioning required major upgrades
of the original design which are described in detail. Collimator
studies with two commercial germanium detectors are presented.
Different collimation levels for a beta-source were investigated
and crystal axis effects were examined. The first scan with an
alpha-source of the passivated end-plate of a special 19-fold
segmented prototype detector mounted in GALATEA is described. The
alpha-induced surface events were studied and characterized.
Crosstalk and mirror pulses seen in the segments of the germanium
detector were analyzed. The detector studies presented in this
thesis will help to further improve the design of germanium
detectors for low background experiments.