GeDet: Development of germanium detectors
Germanium detectors in basic research
In basic research, germanium detectors are used in spectroscopy, in the search for dark matter, and in the search for neutrinoless double-beta decay. The isotope germanium 76 is a candidate for neutrinoless double-beta decay, and this allows detectors to be constructed which simultaneously serve as the source of the phenomenon and also as its means of detection, thus making them particularly efficient.
Neutrinoless double-beta decay is possible only if neutrinos are their own antiparticle. Neutrinos are key particles in nuclear fission and nuclear fusion and also in the evolution of matter after the Big Bang. If they are their own antiparticle, this opens up one possibility to explain the disappearance of antimatter.
Neutrinoless double-beta decay is an extremely rare phenomenon, if indeed it exists at all. It would never be possible to observe it in the presence of normal radioactive background radiation. These experiments have therefore to be extremely well screened from the ambient radiation. All parts of an experiment have to be made of materials which radiate as little as possible. The cosmic radiation causes a further background which the Group analyzes with the aid of measurements.
The experiments must be conducted deep underground in order to minimize this background. The appropriate conditions exist at the SNOLAB in Canada or at the CJPL in China. The Group is involved in planning a future experiment which is to have a ton of germanium and thus extend the search by at least one order of magnitude compared to existing experiments such as GERDA.
Technology of the germanium detectors:
Germanium is a semiconductor that can only be used as detector material at low temperatures. Germanium detectors are typically operated at around 100 kelvin (-173°C), cooled by liquid nitrogen. The temperature dependence of the operation of germanium detectors is one of the main aspects of the work.
A number of different types of detectors are being used in the search for neutrinoless double-beta decay. All are cylindrical and roughly the size of a tea cup. The electric pulses generated by radiation are used not only to determine the energy deposited, but also to differentiate signal events from background events. The form of the pulses depends on the way contact is made to the crystal.
The study of the pulses and their simulation is one focus of the work. Segmented germanium detectors are also used for this purpose, where the detector mantle is divided up into several contact zones.
The segmentation itself can also be used to identify background events.
The Group operates several test stands, for example GALATEA, in which novel germanium detectors are examined for their characteristics.
Further information on the GeDet group
The GALATEA test-facility for high purity germanium detectors
Nucl.Instrum.Meth. A 782 (2015) 56
Measurement of the temperature dependence of pulse lengths in an n-type germanium detector
Eur. Phys. J. Appl. Phys. 56 (2011) 10104
Pulse shape simulation for segmented true-coaxial HPGe detectors
Eur. Phys. J. C 68, 609-618 (2010)
Neutron Interactions as Seen by A Segmented Germanium Detector
Eur. Phys. J. A 36, 139-149 (2008)
Characterization of the first true coaxial 18-fold segmented n-type prototype detector for the GERDA project Nucl.Instrum.Meth. A 577 (2007) 574