Low capacitance large volume shaped-field germanium detector

Large-mass ultralow noise germanium detectors: performance and applications in neutrino and astroparticle physics

“…Another important application of a modified electrode HPGe arises from exploiting the characteristic temporal features of the preamplifier traces in this electrode configuration, features already noted in [17]: Fig. 10 displays two sets of traces, the top panel for a conventional coaxial electrode detector, the bottom panel for the prototype under discussion, both crystals roughly the same mass and dimensions.…”

“…Material with these characteristics is actually commonly present in germanium ingots as a result of segregation processes during crystal growth [18]. The detector in [17] was inspired by searches for the "Cosmion" [19], a low-mass particle dark matter candidate thought at the time to be able to explain the now defunct "solar neutrino problem". Due to their light mass (∼ 1 GeV) these particles were expected to produce relatively soft recoils.…”

“…Besides the mentioned improvements to the electronics, another departure from the approach in [17] was the choice of p-type rather than n-type electrode configuration. The first reason for this was to enjoy a diminished sensitivity to very low energy minimum ionizing backgrounds (surface betas, x-rays, etc.…”

“…The mentioned limited performance in this respect from conventional coaxial crystals has lead these experimental efforts to consider complex multi-electrode segmented germanium detectors, where the additional spatial granularity helps improve the background rejection ability. Evidently, the prohibitive energy resolution degradation observed in ntype modified electrode schemes [17] would never allow one to consider a neutrinoless double-beta decay application, where the signature sought is a very precisely defined energy deposition corresponding to the Q-value of the nuclear transition (2039 keV for 76 Ge). The optimal charge collection observed in a p-type design leads on the other hand to excellent prospects.…”

Energy reconstruction of an n-type segmented inverted coaxial point-contact HPGe detector

“…Furthermore, the pronounced weighting field around the electrode leads to a characteristic pulse shape. This pulse shape together with the variation in drift time can be used to determine the number of interactions in the detector [2]. The addition of a bore hole in the detector bypasses the volume limitations of cylindrical point-contact detectors, which if too large cannot be fully depleted at a reasonable bias voltage (a few thousand volts).…”