M. Heisel

Optimisation of the MC-model of a p-type Ge-spectrometer for the purpose of efficiency determination

An optimisation of the geometrical model of a p-type detector used for material screening was carried out to improve the accuracy of Monte Carlo simulations in reproducing spectrometric measurements. Gamma-ray sources were measured to determine the dimensions of the detector dead layer and borehole. An agreement between simulations and measurement within 3% was achieved at energies above 100 keV. In contrast, discrepancies on the order of 23% were encountered using the nominal parameters from the detector manufacturer.

Gamma-ray spectrometry of ultra low levels of radioactivity within the material screening program for the GERDA experiment

In present and future experiments in the field of rare events physics a background index of 10(-3) counts/(keV kg a) or better in the region of interest is envisaged. A thorough material screening is mandatory in order to achieve this goal. The results of a systematic study of radioactive trace impurities in selected materials using ultra low-level gamma-ray spectrometry in the framework of the GERDA experiment are reported.

Statistical analysis of low-level material screening measurements via gamma-spectroscopy.

Background estimations in neutrinoless double beta decay experiments (0nubetabeta) require reliable statistical limits on gamma-spectrometric low-level material screening measurements. For this purpose a custom method based on Bayesian statistics with reference to the international standard ISO 11929-7 is presented. The analysis combines the data from sample- and background spectra and comprises the physical knowledge of non-negative counting rates. It allows to incorporate multiple gamma lines of radionuclides. The confidence intervals pass continuously from two-sided intervals into single-sided upper limits.

Status of the Germanium Detector Array (GERDA) in the search of neutrinoless ββ decays of 76Ge at LNGS

The Germanium Detector Array (GERDA) in the search for neutrinoless ββ decays of 76Ge at LNGS will operate bare germanium diodes enriched in 76Ge in an (optional active) cryogenic fluid shield to investigate neutrinoless ββ decay with a sensitivity of T1/2 > 2 × 1026 yr after an exposure of 100 kg yr. Recent progress includes the installation of the first underground infrastructures at Gran Sasso, the completion of the enrichment of 37.5 kg of germanium material for detector construction, prototyping of low-mass detector support and contacts, and front-end and DAQ electronics, as well as the preparation for construction of the cryogenic vessel and water tank.

A Comparison of Low-level Gamma-spectrometers within the GERDA Collaboration

In low‐level gamma spectrometry, one of the main goals is the improvement of detection sensitivity. However, ensuring the accuracy and compatibility of the measurement results in different laboratories is also very important. This has been particularly highlighted within the GERDA collaboration, which incorporates several low‐level material screening laboratories. For this reason a comparison of gamma‐spectrometers situated at MPIK Heidelberg, IRMM Geel, LNGS Assergi and JINR Dubna was performed. This comparison was based on the National Physical Laboratory’s “Environmental Radioactivity Comparison 2005” exercise, in which MPIK Heidelberg and IRMM Geel participated. The exercise allowed comparing the accuracy of the measurements and the different evaluation techniques between many low‐level laboratories, using the same standard mixture of low‐radioactivity nuclides. The results of the internal comparison are presented and discussed, as well as the implementation of the Monte‐Carlo simulations in the evalu...