Development of the ultra-low background HPGe spectrometer OBELIX at Modane underground laboratory

Abstract

A new ultra low-background spectrometer based on a HPGe detector with a sensitive volume of 600 cm3 was developed to investigate rare nuclear processes, such as resonant neutrino-less double electron capture (0νEC/EC) and double beta decay processes (2ν2β−, 2νβ+EC, 2νEC/EC) to the excited states of daughter nuclei. The spectrometer was installed at the Modane underground laboratory (LSM, France, 4800 m w.e.). Sensitivity of the spectrometer and its background were tested. A new method for the efficiency calibration in measurements of low-active samples was developed. The spectrometer was used for the measurements of low active materials and samples. Results obtained in 395 h investigation of resonant 0νEC/EC decay of 106Cd to the 2718 keV and 2741 keV excited states of 106Pd with ∼23.2 g of enriched 106Cd and 2ν2β− decay of 100Mo sample with a mass of 2588 g to the 0+, 1130 keV and 2+, 539.5 keV excited states of 100Ru are presented.