GERDA has been a pioneering experiment in the search for the still undetected neutrinoless double beta (0𝜈𝛽𝛽)-decay of 76Ge. The discovery of this extremely rare process would prove the Majorana character of neutrinos and consequently physics beyond Standard Model. For an explicit identification of a signal caused by the 0𝜈𝛽𝛽-decay a precise understanding of the background components is crucial. Indeed, a previous work of Camp and Foster [1] indicates that germanium itself could be a candidate of potential background for all 76Ge 0𝜈𝛽𝛽-decay experiments near the 𝑄 value of 2039 keV. The experiment first established the existence of a 𝐸𝛾 = (2040.70 ± 0.25) keV 𝛾-ray which is emitted during the de-excitation of 76Ge. This 𝛾-line was observed during the decay of 76Ga which was produced with 76Ge(𝑛, 𝑝)76Ga reactions. Since this experiment was performed in 1971, several experiments attempt to verify the existence of the 2040 keV 𝛾-line, but no significant indications could be achieved. Therefore, a repetition of the previous work is crucial.
For the investigation of this potential background enriched germanium is activated by quasi mono-energetic neutrons of 14.1 MeV from a DT generator. The 𝛾-rays emitted by the activated sample are detected by two germanium detectors of high relative efficiencies, whereby one of them is surrounded by an additional anti-Compton shield. Furthermore, dedicated Monte Carlo simulation are developed for the optimization of the detector setup and to support the analysis procedure.
The accumulated data is already sufficient to observe the 2040 keV 𝛾-line at an energy of 𝐸𝛾 = (2040.5 ± 0.4) keV with an emission probability of 𝜈𝛾 = (0.43 ± 0.11) %. The results of the previous experiment could be successfully confirmed.