Improving sensitivity of a BEGe-based high-purity germanium spectrometer through pulse shape analysis

Abstract

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 singlesite 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 208 Tl, was improved by 114.3%.

Fabrication, characterization and analysis of a prototype high purity germanium detector for $$^{76}$$Ge-based neutrinoless double beta decay experiments

“…By analyzing survival probabilities in SEPs and FEPs it can be concluded that for this prototype detector the ANN-based PSA provides better multi-site events rejection efficiency. A similar behaviour was observed for the analysis described in [20]. However, it should be noted that for much more massive (≈ 0.5 kg−0.7 kg) BEGe detectors used in Gerda the A/E method provides much better multi-site events rejection efficiencies [17] as obtained here.…”

“…In the γ -ray spectrometry the situation is different: as the signal one considers MSEs (characteristic for the full energy peaks used to evaluate the activities) and SSEs, like e.g. the Compton scattered γ -rays contributing to the continuum need to be rejected as background events [20].…”

“…Thus, different options for training and validation of the PSA are possible. A detailed description of the applied analysis method can be found in [20] -since it was followed exactly as described, it will not be explained here.…”

“…However, the small BEGe-type (Broad Energy Germanium) detectors [17] used in Gerda Phase II may not be an optimal choice because, with their average mass of about 0.7 kg, one would need more than 1300 readout channels (large number of electronic components, which may constitute a potential background source). On the other hand, classical semi-coaxial detectors (masses up to ∼2.7 kg) show much poorer pulse shape analysis (PSA) abilities [18][19][20][21]. Recently developed the so-called Inverted Coaxial (IC) detectors, which offer larger mass and the BEGe-like PSA performance [22,23], thus they are considered to be applied in Legend-200.…”

“…In the second part of the paper we discuss the efficiency of a PSA method developed by our group [20] and applied to the prototype. It is compared with analysis based on simulated signals.…”