A very low background HPGe detector operating deep underground at 4800 m water equivalent.
A very low background HPGe detector has been installed in the Fréjus underground laboratory in order to investigate radioactive contaminations. The main features and capabilities of the detector are described here.
Development of the ultra-low background HPGe spectrometer OBELIX at Modane underground laboratory
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.
Geiger tube planes as a trigger for the nucleon lifetime experiment in the Frejus tunnel (France)
Abstract Geiger tubes 6 m long made of extruded aluminium and assembled in 6m × 6m planes have been developed at Orsay and will be used as a trigger for the nucleon lifetime experiment in the Frejus tunnel (Aachen-Orsay-Palaiseau-Saclay-Wuppertal Collaboration) which will start in the spring of 1983. There will be 185 trigger planes which correspond to about 65 000 tubes. The use of aluminium tubes is advantageous because of their low cost mass production, but obtaining a stable Geiger mode operation of aluminium tubes of such dimensions is difficult and requires a preliminary mechanical treatment of the surface. Safety regulations in the tunnel limit the choice of gas. The gas used is a non-inflammable mixture of argon, ethyl-alcohol (2%) and freon (0.05%). The two characteristic parts of the Geiger pulse: steep rise in about 50 ns, followed by a long part lasting about 30–70 ≃s, are both advantageously used, the first to build a fast trigger, the second as a kind of natural memory. Moreover the relatively high Geiger signal reduces amplification requirements, thereby simplifying the electronics.