Results of the BiPo-1 prototype for radiopurity measurements for the SuperNEMO double beta decay source foils

The development of BiPo detectors is dedicated to the measurement of extremely high radiopurity in $^{208}$Tl and $^{214}$Bi for the SuperNEMO double beta decay source foils. A modular prototype, called BiPo-1, with 0.8 $m^2$ of sensitive surface area, has been running in the Modane Underground Laboratory since February, 2008. The goal of BiPo-1 is to measure the different components of the background and in particular the surface radiopurity of the plastic scintillators that make up the detector. The first phase of data collection has been dedicated to the measurement of the radiopurity in $^{208}$Tl. After more than one year of background measurement, a surface activity of the scintillators of $\mathcal{A}$($^{208}$Tl) $=$ 1.5 $\mu$Bq/m$^2$ is reported here. Given this level of background, a larger BiPo detector having 12 m$^2$ of active surface area, is able to qualify the radiopurity of the SuperNEMO selenium double beta decay foils with the required sensitivity of $\mathcal{A}$($^{208}$Tl) $<$ 2 $\mu$Bq/kg (90% C.L.) with a six month measurement.Comment: 24 pages, submitted to N.I.M.

Spectral modeling of scintillator for the NEMO-3 and SuperNEMO detectors

We have constructed a GEANT4-based detailed software model of photon transport in plastic scintillator blocks and have used it to study the NEMO-3 and SuperNEMO calorimeters employed in experiments designed to search for neutrinoless double beta decay. We compare our simulations to measurements using conversion electrons from a calibration source of $\rm ^{207}Bi$ and show that the agreement is improved if wavelength-dependent properties of the calorimeter are taken into account. In this article, we briefly describe our modeling approach and results of our studies.Comment: 16 pages, 10 figure

Investigating the Double Beta Decay of 58^{58}Ni

International audienceDouble beta decay (β + EC, EC/EC) of$^{58}$Ni is investigated at France’s Modane Underground Laboratory (4800 m water equivalent) using the OBELIX ultralow-background HPGe detector with a sensitive volume of 600 cm$^{3}$ and a natural nickel sample of ~68% 58Ni with a mass of ~21.7 kg. After preliminary analysis of the experimental data accumulated over ~144 days, new experimental limits are obtained for the 2νβ$^{+}$EC decay of$^{58}$Ni to the 0$^{+}$ ground state and the 2$_{1}^{+}$ , 811 keV excited state of$^{58}$Fe, and for the 2νEC/EC decay of$^{58}$Ni to the 2$_{1}^{+}$ , 811 keV and 2$_{2}^{+}$ , 1675 keV excited states of$^{58}$Fe. The limits are T$_{1/2}$(β$^{+}$EC,0→0$^{+}$) > 1.7 × 10$^{22}$ yr, T$_{1/2}$(β$^{+}$EC,0→2$_{1}^{+}$ ) > 2.3 × 10$^{22}$ yr, T$_{1/2}$(EC/EC,0→2$_{1}^{+}$ ) > 3.3 × 10$^{22}$ yr, and T$_{1/2}$(EC/EC,0→2$_{2}^{+}$ ) > 3.4 × 10$^{22}$ yr. Experimental limit T$_{1/2}$(0νEC/EC–res, 1918 keV > 4.1 × 10$^{22}$ yr is obtained for resonant neutrinoless radiative EC/EC decay with an energy of 1918.3 keV. All limits are at 90% CL

Investigation of double beta decay of 58^{58}Ni at the Modane Underground Laboratory

International audienceInvestigation of double beta decay processes (β+EC, EC/EC) of 58Ni was performed at the Modane underground laboratory (LSM, France, 4800 m w.e.). A sample of natural nickel, containing ∼68% of 58Ni and a mass of ∼21.7 kg, was measured using ultra low-background HPGe detector Obelix (sensitive volume of 600 cm3) during ∼143.8 days. New experimental limits on 2νβ+EC decay of 58Ni to the ground 0+ and (math), 811 keV excited state of 58Fe, and 2νEC/EC decay of 58Ni to (math), 811 keV and (maht), 1 675 keV excited states of 58Fe were obtained in this measurement. There are -T1/2(β+EC, 0+ → 0+) > 1.7 × 1022 y; (math), (math), (math). For resonant neutrino-less radiative EC/EC decay with energy of 1 918.3 keV a new experimental limit of T1/2 (0νEC/EC – res, 1918KeV) > 4.1 ×1022 y was also obtained. All limits are at 90 % CL

Improved limits on β+\beta^+EC and ECEC processes in 74^{74}Se

International audienceNew limits on β+ EC and ECEC processes in 74 Se have been obtained using a 600 cm 3 HPGe detector and an external source consisting of 1600 g of a natural selenium powder. For different β+ EC and ECEC transitions (to the ground and excited states) obtained limits are on the level ∼(0.2−4.8)×1019yr at 90% C.L. In particular, for the potentially resonant transition into the 1204.2 keV excited state of 74 Ge a lower half-life limit of 1.1×1019yr at 90% C.L. has been obtained. Possibility to increase the sensitivity of such measurements is discussed

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

International audienceA new ultra low-background spectrometer based on a HPGe detector with a sensitive volume of 600 cm(3) 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 (106)Cd to the 2718 keV and 2741 keV excited states of (106)Pd with ~23.2 g of enriched (106)Cd and 2ν2β(−) decay of (100)Mo sample with a mass of 2588 g to the 0(+), 1130 keV and 2(+), 539.5 keV excited states of (100)Ru are presented