[en] A new concept of a Charge Sensitive Amplifier without a high-value resistor in the feedback loop is presented. Basic spectroscopic parameters of the amplifier coupled to a coaxial High Purity Germanium detector (HPGe) are discussed. The amplifier signal input is realized with an n-channel J-FET transistor. The feedback capacitor is discharged continuously by the second, forward biased n-channel J-FET, driven by an RC low–pass filter. Both the analog—with a standard spectroscopy amplifier and a multi-channel analyzer—and the digital—by applying a Flash Analog to Digital Converter—signal readouts were tested. The achieved resolution in the analog and the digital readouts was 0.17% and 0.21%, respectively, at the Full Width at Half Maximum of the registered "6"0Co 1332.5 keV gamma line.

[en] We performed Pulse Shape Analysis to separate single-scattered gamma energy deposition events from multiple-scattered photons in a high-sensitivity γ-ray spectrometer. The spectrometer is based on a Broad Energy High Purity Germanium detector and the developed technique uses multivariate analysis by an application of the Multi-Layer Perceptron Neural Network. A very good separation of the single-site- and multi-site events was achieved leading to a significant reduction of the background level of the investigated spectrometer - the double escape peak, rich in single-site events, was reduced by 95%, while the full energy peaks lost at most 25% of their counts. The peak to Compton ratio, calculated for the 2614.5 keV gamma line from ²⁰⁸Tl, was improved by 114.3%. (orig.)

[en] The Gerda collaboration is performing a sensitive search for neutrinoless double beta decay of ⁷⁶Ge at the INFN Laboratori Nazionali del Gran Sasso, Italy. The upgrade of the Gerda experiment from Phase I to Phase II has been concluded in December 2015. The first Phase II data release shows that the goal to suppress the background by one order of magnitude compared to Phase I has been achieved. Gerda is thus the first experiment that will remain ''background-free'' up to its design exposure (100 kg year). It will reach thereby a half-life sensitivity of more than 10²⁶ year within 3 years of data collection. This paper describes in detail the modifications and improvements of the experimental setup for Phase II and discusses the performance of individual detector components. (orig.)

[en] A search for neutrinoless ββ decay processes accompanied with Majoron emission has been performed using data collected during Phase I of the GERmanium Detector Array (GERDA) experiment at the Laboratori Nazionali del Gran Sasso of INFN (Italy). Processes with spectral indices n = 1, 2, 3, 7 were searched for. No signals were found and lower limits of the order of 10²³ yr on their half-lives were derived, yielding substantially improved results compared to previous experiments with ⁷⁶Ge. A new result for the half-life of the neutrino-accompanied ββ decay of ⁷⁶Ge with significantly reduced uncertainties is also given, resulting in T_1/2^2ν = (1.926 ± 0.094) @ x 10²¹ yr. (orig.)

[en] An optimized digital shaping filter has been developed for the Gerda experiment which searches for neutrinoless double beta decay in ⁷⁶Ge. The GERDA Phase I energy calibration data have been reprocessed and an average improvement of 0.3 keV in energy resolution (FWHM) corresponding to 10% at the Q value for 0νββ decay in ⁷⁶Ge is obtained. This is possible thanks to the enhanced low-frequency noise rejection of this Zero Area Cusp (ZAC) signal shaping filter. (orig.)

[en] Neutrinoless double electron capture is a process that, if detected, would give evidence of lepton number violation and the Majorana nature of neutrinos. A search for neutrinoless double electron capture of "3"6Ar has been performed with germanium detectors installed in liquid argon using data from Phase I of the GERmanium Detector Array (Gerda) experiment at the Gran Sasso Laboratory of INFN, Italy. No signal was observed and an experimental lower limit on the half-life of the radiative neutrinoless double electron capture of "3"6Ar was established: T_1_/_2 > 3.6 x 10"2"1 years at 90% CI. (orig.)