[en] 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.

[en] Investigations of double beta decay processes to excited states of daughter nuclei were performed at the Modane underground laboratory (LSM, France, 4800 m w.e.) using the high sensitivity spectrometer OBELIX [1], which is a common activity of JINR Dubna, IEAP CTU in Prague and LSM. The spectrometer is based on the HPGe detector with the sensitive volume of 600 cm"3 and relative efficiency of 160%. Investigation of resonant neutrino-less double electron capture of "1"0"6Cd was performed with ∼23.2 g of "1"0"6Cd (enrichment of 99.57%) during ∼17 days. The experiment with natural Ni (∼21.7 kg of mass) was also carried out during ∼47 days. The preliminary experimental limits for 0νEC/EC resonant decay to the excited states of "1"0"6Pd and different modes of β β decay "5"8Ni are presented

[en] An ultra-low background coaxial HPGe detector for gamma-ray spectrometry with a relative efficiency of 160%, corresponding to a 600 cm"3 Ge crystal, was installed at the Laboratoire Souterrain de Modane, France (4800 m.w.e). To reduce the instrinsic detector background, all parts involved in the detector cryostat were selected for their low radioactivity contamination. A shielding, composed of an inner layer of roman lead and an external layer of regular lead was installed, together with a system to reduce the Rn level inside the sample chamber. The shielding was designed to allow the measurement of Marinelli-shaped samples. We present the constructional details which lead to a remarkable low detector background of 73 cts/kg·d in [40, 3000] keV. Measured samples showed that sensitivities about 100 μBq/kg in "2"2"6Ra and "2"2"8Th are reached for samples of some kg and 30 days of lifetime

[en] We present a new type of gaseous detectors, the spherical proportional counter. It consists of a small metallic ball, 16 mm in diameter, located at the centre of curvature of a large spherical vessel, acting as a proportional amplification structure. It allows high gas gains to be reached and operates from low to high gas pressure. This simple and robust structure allows large volumes to be read out with a single electronic channel. The detector performance presently achieved is already close to fulfil the demands of many challenging projects from low energy neutrino physics to dark matter detection with applications in neutron, alpha, gamma spectroscopy. Preliminary results of neutron flux measurements currently going on in underground laboratory will be presented.

[en] Several efforts are ongoing for the development of spherical gaseous time projection chamber detectors for the observation of rare phenomena such as weakly interacting massive particles or neutrino interactions. The proposed detector, thanks to its simplicity, low energy threshold and energy resolution, could be used to observe the ββ0ν process i.e. the neutrinoless double beta decay. In this work, a specific setup is presented for the measurement of ββ0ν on 50 kg of ¹³⁶Xe. The different backgrounds are studied, demonstrating the possibility to reach a total background per year in the detector mass at the level of 2 events per year. The obtained results are competitive with the present generation of experiments and could represent the first step of a more ambitious roadmap including the ββ0ν search with different gases with the same detector and therefore the same background sources. The constraints in terms of detector constructions and material purity are also addressed, showing that none of them represents a show stopper for the proposed experimental setup.

[en] The radioactivity levels in the air of the radionuclides released by the Fukushima accident were measured at the Laboratoire Souterrain de Modane, in the South-East of France, during the period 25 March–18 April 2011. Air-filters from the ventilation system exposed for one or two days were measured using low-background gamma-ray spectrometry. In this paper we present the activity concentrations obtained for the radionuclides ¹³¹I, ¹³²Te, ¹³⁴Cs, ¹³⁷Cs, ⁹⁵Nb, ⁹⁵Zr, ¹⁰⁶Ru, ¹⁴⁰Ba/La and ¹⁰³Ru. The activity concentration of ¹³¹I was of the order of 100 μBq/m³, more than 100 times higher than the activities of other fission products. The highest activities of ¹³¹I were measured as a first peak on 30 March and a second peak on 3–4 April. The activity concentrations of ¹³⁴Cs and ¹³⁷Cs varied from 5 to 30 μBq/m³. The highest activity concentration recorded for Cs corresponded to the same period as for ¹³¹I, with a peak on 2–3 April. The results of the radioactivity concentration levels in grass and mushrooms exposed to the air in the Modane region were also measured. Activity concentrations of ¹³¹I of about 100 mBq/m² were found in grass. - Highlights: ► Air activity concentration following Fukushima accident were measured in Modane, France. ► ¹³¹I level in the air was of the order 100 μBq/m³ and ¹³⁴Cs and ¹³⁷Cs levels were between 5 and 30 μBq/m³. ► The highest ¹³¹I, ¹³⁴Cs and ¹³⁷Cs levels were on 30 March and 2–4 April 2011. ► Peak activity levels explained by meteorological conditions and consistent with simulation models.