J. L. Reyss

First results of the search for neutrinoless double-beta decay with the NEMO 3 detector.

The NEMO 3 detector, which has been operating in the Frejus underground laboratory since February 2003, is devoted to the search for neutrinoless double beta decay (bb0nu). Half-lives of the two neutrino double beta decays (bb2nu) have been measured for 100Mo and 82Se. After 389 effective days of data collection from February 2003 until September 2004 (Phase I), no evidence for neutrinoless double beta decay was found from ~7kg of 100Mo and ~1 kg of 82Se. The corresponding lower limits for the half-lives are 4.6 x 10^23 years for 100Mo and 1.0 x10^23 years for 82Se (90% C.L.). Depending on the nuclear matrix elements calculation, limits for the effective Majorana neutrino mass are<0.7-2.8 eV for 100Mo and<1.7-4.9 eV for 82Se

Large, low background well-type detectors for measurements of environmental radioactivity

During the two last decades, the development of γ counting techniques has led to the application of natural radioactivity to the study of numerous processes occurring in the environment. Such work flourished particularly when large HP germanium detectors with low background became available. For some studies, the sample to be measured is small (e.g. sediment, BaSO4 precipitate). In such cases, the use of high efficiency well-type detectors, when compared with similar detectors of conventional shape, provides the best choice. This paper describes three large, well-type detectors used for environmental studies. The background of the crystals has been lowered by: i) placing the detectors in an underground laboratory (Laboratoire Souterrain de Modane, LSM), shielded from cosmic radiation by 1700 m of rocks; ii) using only very low activity materials for the detector assembly and copper-lead shield. Results from various oceanic samples such as particles, sediments, water and hydrothermal sulphides are presented to illustrate the usefulness of this kind of detector for the measurement of environmental radioactivity. For sample volumes of about 10 cm3, these installations are shown to be the most sensitive way to measure nuclides as 226Ra, 228Ra, 228Th and 137Cs.

Technical design and performance of the NEMO 3 detector

Abstract The development of the Neutrino Ettore Majorana Observatory (NEMO ∼ 3 ) detector, which is now running in the Frejus Underground Laboratory (L.S.M. Laboratoire Souterrain de Modane), was begun more than ten years ago. The NEMO 3 detector uses a tracking-calorimeter technique in order to investigate double beta decay processes for several isotopes. The technical description of the detector is followed by the presentation of its performance.

Measurement of the Double Beta Decay Half-life of Nd-150 and Search for Neutrinoless Decay Modes with the NEMO-3 Detector

The half-life for double-{beta} decay of {sup 150}Nd has been measured by the NEMO-3 experiment at the Modane Underground Laboratory. Using 924.7 days of data recorded with 36.55 g of {sup 150}Nd, we measured the half-life for 2{nu}{beta}{beta} decay to be T{sub 1/2}{sup 2{nu}}=(9.11{sub -0.22}{sup +0.25}(stat.){+-}0.63(syst.))x10{sup 18} yr. The observed limit on the half-life for neutrinoless double-{beta} decay is found to be T{sub 1/2}{sup 0{nu}}>1.8x10{sup 22} yr at 90% confidence level. This translates into a limit on the effective Majorana neutrino mass of <4.0-6.3 eV if the nuclear deformation is taken into account. We also set limits on models involving Majoron emission, right-handed currents, and transitions to excited states.

Recent sedimentation and sedimentary budgets on the western Iberian shelf

Abstract Thus study is based on 31 box-core samples collected mainly from the mud-patches of the Galician and North-Portuguese shelf. Each of these cores, some decimetres in length, have been described, radiographied and sampled each centimetre for grain-size analysis and measurement of the particulate organic carbon (Corg) content. 210Pb excess profiles have been measured using gamma spectrometry, which, combined with the analysis of the vertical variations of the sedimentary facies, have allowed estimates of sedimentation rates. These rates were found to vary between 0.05 and 0.40 cm yr−1. Considering the latitudinal variation of sedimentation rates around the 100m contour, we note that the maximum rates occurred off the Douro estuary in the southern sector and also near the Galician rias to the north. The organic content (Corg) of sediments varied between 0.4 and 2%. Latitudinally Corg showed a decrease from the South to the North. These results coupled with the sedimentary map (see Dias, Gonzalez, Garcia & Diaz del Rio, 2001 ) have permitted us to establish the detrital mass budget and an inventory of Corg burial.

Double-β decay of 82Se

Abstract The NEMO-2 tracking detector located in the Frejus Underground Laboratory was designed as a prototype of the NEMO-3 detector to study neutrinoless (Oν) and two neutrino (2ν) double-beta decay (ββ) physics. After 10357 h of running with an isotopically enriched selenium source (2.17 mol yr of 82Se) a ββ2ν decay half-life of T 1 2 = (0.83 ± 0.10( stat ) ± 0.07 ( syst )) × 10 20 yr was measured. Limits with a 90% C.L. on the 82Se half-lives of 9.5 × 1021 yr for ββ0ν decay to the ground state, 2.8 × 1021 yr to the (2+) excited state and 2.4 × 1021 yr for ββ0νχ0 decay with a Majoron (χ0) were also obtained.

Late Quaternary changes in biogenic opal fluxes in the Southern Indian Ocean

Abstract Late Quaternary sedimentary and paleoenvironmental conditions in the southern Indian Ocean have been reconstructed from radioisotope and proxy element profiles (biogenic opal and organic carbon) measured on five sediment cores taken along a transect across the Indian sector of the Antarctic Circumpolar Current. Dissolution-corrected opal rain rates were used to reconstruct past changes of opal productivity for this region. Records from these five cores indicate that opal productivity during glacial periods was lower than presently recorded south of the Antarctic Polar Front (APF), probably due to increased ice cover. North of APF, opal productivity was slightly greater during glacial periods than during the Holocene, probably in response to (1) the northward migration of the APF by approximately 5° latitude, (2) a northward transport of Si from the Antarctic Zone, and (3) an increase of Fe, necessary for opal-producing organisms, via upwelling and the erosion of the Kerguelen Plateau. We also invoke a decoupling between opal burial and organic carbon flux to the seabed to explain the variation in buried Si/C ratio between glacial and interglacial sediment. This decoupling is principally explained by better organic carbon preservation in the glacial sediments due to strong sediment focussing. An increase in glacial export paleoproductivity is not supported by the data, implying that bioproductivity variations in the Southern Indian Ocean are unlikely to have contributed to the glacial drawdown of atmospheric CO 2 inferred from ice core data.

Double beta decay of 96Zr

Abstract After 10357 h of running the NEMO-2 tracking detector with an isotopically enriched zirconium source (0.084 mol yr of 96Zr), a ββ2ν decay half-life of T1/2=(2.1+0.8(stat)−0.4(stat)±0.2(syst))·1019 y was measured. Limits with a 90% C.L. on the 96Zr half-lives of 1.0·1021 y for ββ0ν decay to the ground state, 3.9·1020 y to the 2+ excited state and 3.5·1020 y for ββ0νχ0 decay with a Majoron (χ0) were obtained. The data also provide direct limits at the 90% C.L. for the 94Zr half-lives. These limits are 1.1·1017 y for ββ2ν decay to the ground state, 1.9·1019 y for ββ0ν decay to the ground state and 2.3·1018 y for ββ0νχ0 decay to ground state.

Limits on different Majoron decay modes of Mo-100 and Se-82 for neutrinoless double beta decays in the NEMO-3 experiment

Abstract The NEMO-3 tracking detector is located in the Frejus Underground Laboratory. It was designed to study double beta decay in a number of different isotopes. Presented here are the experimental half-life limits on the double beta decay process for the isotopes 100Mo and 82Se for different majoron emission modes and limits on the effective neutrino–majoron coupling constants. In particular, new limits on “ordinary” majoron (spectral index 1) decay of 100Mo ( T 1 / 2 > 2.7 × 10 22 yr ) and 82Se ( T 1 / 2 > 1.5 × 10 22 yr ) have been obtained. Corresponding bounds on the majoron–neutrino coupling constant are 〈 g e e 〉 ( 0.4 – 1.8 ) × 10 −4 and ( 0.66 – 1.9 ) × 10 −4 .

Particulate matter distribution and Th-234/U-238 disequilibrium along the Northern Iberian Margin: implications for particulate organic carbon export

Light beam attenuation and scattering profiles were obtained from a total of 94 stations from the shelf edge and slope of the Iberian Margin in the early summer of 1997 and winter of 1998. Hydrographic and satellite data suggest that the summer cruise took place just prior to the seasonal upwelling period present along this margin. Our results from the slope show well-developed, high-concentration, intermediate nepheloid layers (INL) present in North Atlantic Central Water, underlain by relatively clear Mediterranean Water, which, at its salinity maximum, shows an off-shelf decrease in particle load to clear water at the outer edge of the water mass. Only low-concentration INL and weak bottom nepheloid layer (BNL) activity is observed in North Atlantic Deep Water. The presence of low BNL activity suggests weak off-shelf transport of material and weak bottom current resuspension. Good agreement between particulate matter concentration estimated from the empirical calibration of beam attenuation and scattering is found in clear water, while differences in instrumental response within the BNL and surface layer are most likely related to the differing nature of the particles present. In the upper ocean particle load calculated from beam attenuation shows a considerable excess over that calculated by scattering. Offshore spatial and temporal differences in the relationship between both measurements are consistent with a response to large particle sized biological material present in the surface layer. The upper ocean View the MathML source activity was measured at a total of 23 stations and particulate organic carbon (POC) and particulate organic nitrogen (PON) at each station occupied during the summer cruise. The broadly uniform distribution of total View the MathML source, and more variable particulate View the MathML source, suggests that during pre-upwelling conditions on the Iberian Margin, View the MathML source distribution is strongly influenced by particle type. As a consequence, particle residence times derived from View the MathML source/ View the MathML source disequilibria show a considerable range between 4 and 193 d. Estimates of export flux of POC and PON from the upper 50 m were made using the View the MathML source, POC and PON results. POC and PON export ranged from 1–56 mmol C m−2 d−1 and 0.15–7.7 mmol N m−2 d−1 respectively, showing a broad offshore decrease. Comparison of the POC export with estimates of carbon fixation measured during the same period suggests that an average of 19% of the primary production is lost as a sinking particulate flux. Overall, the pre-upwelling situation observed during CD-105 was characterised by low phytoplankton biomass, primary production and low POC export fluxes.