The development of the NEMO3 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 NEMO3 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.

After analysis of 5797 h of data from the detector NEMO3, new limits on neutrinoless double beta decay of 100Mo (T1/2>3.1×1023y, 90% CL) and 82Se (T1/2>1.4×1023y, 90% CL) have been obtained. The corresponding limits on the effective majorana neutrino mass are: 〈mv〉<(0.8–1.2) eV and 〈mv〉<(1.5–3.1) eV, respectively. Also the limits on double-beta decay with Majoron emission are: T1/2>1.4×1022y (90% CL) for 100Mo and T1/2>1.2×1022y (90% CL) for 82Se. Corresponding bounds on the Majoron-neutrino coupling constant are 〈 gee〉<(0.5–0.9)×10−4 and <(0.7−1.6)×10−4. Two-neutrino 2β-decay half-lives have been measured with a high accuracy, \(T_{1/2}^{100_{Mo} } = [7.68 \pm 0.02(stat) \pm 0.54(syst)] \times 10^{18} y\) and \(T_{1/2}^{82_{Se} } = [10.3 \pm 0.3(stat) \pm 0.7(syst)] \times 10^{19} y\).

After analysis of 5797 h of data from the detector NEMO3, new limits on neutrinoless double beta decay of (100)Mo (T(1/2) > 3.1 x 10(23) y, 90% CL) and (82)Se (T(1/2) > 1.4 x 10(23) y, 90% CL) have been obtained. The corresponding limits on the effective majorana neutrino mass are: < (0.8-1.2) eV and < (1.5-3.1) eV, respectively. Also the limits on double-beta decay with Majoron emission are: T(1/2) > 1.4 x 10(22) y (90% CL) for (100)Mo and T(1/2) > 1.2 x 10(22) y (90% CL) for (82)Se. Corresponding bounds on the Majoron-neutrino coupling constant are < (0.5-0.9) x 10(- 4) and <(0.7-1.6) x 10(- 4). Two-neutrino 2beta-decay half-lives have been measured with a high accuracy, T(1/2)(100)Mo = [7.68 +/- 0.02(stat) +/- 0.54(syst)] x 10(18) y and T(1/2)(82)Se = [10.3 +/- 0.3(stat) +/- 0.7(syst)] x 10(19) y. (C) 2004 MAIK "Nauka/Interperiodica".

To be sensitive to an effective Majorana neutrino mass, 〈mν〉, on the order of 0.1 eV, the NEMO 3 double beta (ββ(0ν)) decay experiment requires precise knowledge and control of the backgrounds. The effect of neutrons and γ-rays from the Fréjus underground laboratory (LSM, Laboratoire Souterrain de Modane) has been studied during 10700 h of data collection. The data were taken with a NEMO 2 prototype detector using different shield configurations. Monte Carlo calculations with GEANT/MICAP code and a new library of γ-rays from neutron captures are presented. The implied consequences for the NEMO 3 detector which is under construction are discussed. The neutrinoless double beta decay background induced by neutrons and γ-rays within the LSM will be suppressed to the very suitable level of 0.1 event in a live time of five years given the appropriate shield and magnetic field.

Most currently, viable double beta decay experiments require highly enriched isotopic sources. These sources must be extraordinarily free of radioactive contamination. The double beta decay experiment NEMO 3 will study 100Mo, for which physical and chemical purification techniques have been investigated. The success of the chemical purification process is discussed in the context of ultra-low background, high-purity germanium spectrometer measurements.

The NEMO-2 tracking detector located in the Fréjus Underground Laboratory was designed as a prototype for the NEMO-3 detector and to study different modes of double beta decay. Measurements with 100 Mo, 116 Cd, 82 Se and 96 Zr were carried out. Presented here are the experimental half-life limits on double beta decays for new Majoron emission modes and limits on effective neutrino–Majoron coupling constants.

: The Pauli Exclusion Principle (PEP) was tested with the NEMO-2 detector. Limits at the 90% C.L. on the violation of PEP for p-shell nucleons in 12 C were obtained. Specifically, transitions to the fully occupied 1 s 1/2 -shell yielded a limit of 4.2 · 10 24 y for the process with emission of a γ-quantum. Similarly limits of 3.1 · 10 24 y for β − and 2.6 · 10 24 y for β + Pauli-forbidden transitions of 12 C → 12 Ñ 12 B) are reported here.

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.

The NEMO-2 tracking detector located in the Fréjus 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 T12 = (0.83 ± 0.10(stat) ± 0.07 (syst)) × 1020 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.

A cellular automaton for track searching and an elastic net for charged particle trajectory fitting are presented. The advantages of the methods are: simplicity of the algorithms, fast and stable convergence to real tracks, and a reconstruction efficiency close to 100%. Demonstration programs are available at http://nuweb.jinr.dubna.su/LNP/NEMO using a Java enabled browser.

In the double beta decay (ββ) experiment NEMO-2, the 214Bi radioactivity has been measured as background for the ββ processes. The analysis of the 214Bi contamination has been performed via the signature of 214Po alpha decay. This method has been applied to data taken with enriched 100Mo and 116Cd sources. At the level of NEMO-2's sensitivity, in a 1.0 mole yr study of enriched material, the contamination of the sources can be measured in the range of 2.0 mBq kg−1. The effects of deposited contamination by 222Rn are also discussed and estimated at the level of 0.3 mBq per square meter of source foil. Backgrounds for neutrinoless double beta decay (ββ0v) are deduced from these measurements and the consequences for the higher sensitivity ββ experiment NEMO-3 are drawn.

The NEMO-2 tracking detector located in the Fréjus Underground Laboratory was designed as a prototype of the detector NEMO-3 to study 0ν and 2ν double-beta decay (ββ) physics. After ten months of nearly continuous running with an enriched cadmium source (0.92 mol·y of116Cd) aββ2ν half-life ofT 1/2=(3.75±0.35(stat)±0.21(syst))·1019 y was measured. Limits with 90% CL on the116Cd half-lives of 5.0·1021 y forββ0ν decay and of 1.2·1021 y forββ0νχ 0 decay with a Majoron (χ 0) were obtained. Theoretical predictions for 0ν and 2ν decays of116Cd are also presented.

Decay products emitted in highly dissipative Pb+Au reactions at 29 MeV/nucleon have been detected using a large area array. Multiplicities of fragments as large as 8 have been detected with a sizeable cross section. The m-fragment exit channels are fully compatible with the formation of a transient excited dinuclear system formed in damped collisions. The excitation energy function shows that fully damped collisions are achieved even for m = 2 indicating that heavy nuclei are able to sustain high excitation energy and end up as evaporation residues.

From data accumulated over 6140 h with 172 g of enriched molybdenum (1.18 mol yr of 100Mo) with the NEMO 2 detector in the Fréjus Underground Laboratory, a clear ββ2ν signal (1433 events) is observed, leading to a half-life T1/2=0.95±0.04(stat)±0.09(syst) 1019 yr. The experimental two-electron energy spectrum and the two-electron angular distribution are in agreement with the expected ones. Limits for ββ0ν decays to the ground state, excited states (2+1 and 0+1), and also with Majoron emission are given.Received 29 June 1994DOI:https://doi.org/10.1103/PhysRevD.51.2090©1995 American Physical Society

To investigate double beta decay processes, the NEMO collaboration began a long-range research and development program in 1988. The NEMO 2 detector, which is now running in the Fréjus underground laboratory (L.S.M. Laboratoire Souterrain de Modane), is the second prototype. It consists of a 1 m2 source foil sandwiched between Geiger cell drift chambers for electron tracking and two plastic scintillator walls for energy and time-of-flight measurements. The technical description of the detector is followed by the study of the various sources of background.

The lifetime, τ, with respect to multifragmentation of highly excited nuclei is deduced from the analysis of strongly damped Pb + Au collisions at 29 MeV/u. The method is based on the study of space-time correlations induced by “proximity” effects between fragments emitted by the two primary products of the reaction and gives the time between the reseparation of the two primary products and the subsequent multifragment decay of one partner. A lifetime significantly longer than the interaction time is found. It is compared with time scales corresponding to different types of dynamical instabilities which may be responsible for nuclear disassembly.

Three fragment production has been studied in peripheral 208Pb + 197Au collisions at 29 MeV/u. The data suggests the formation and subsequent decay of necklike structures producing a small fragment emitted at mid-rapidity in between the two partners of a deep inelastic scattering. Data and trajectory calculations suggest also the existence of a competing process in which the neck is absorbed by one of the reactants, this latter decaying further by binary fission.