The NEMO 3 experiment (NEMO = Neutrino Ettore Majorana Observatory) is devoted to the search for neutrinoless double beta decay (0νββ) and to the accurate measurement of two-neutrino double beta decay (2νββ). For this goal, the experiment combines two detection techniques: calorimetry and tracking. Such approach allows us at the same time unambiguous identification of e⁻, e⁺, γ, and α-particles provided by a wire tracking chamber and energy and time measurements of particles with a calorimeter.
The NEMO 3 detector is installed and currently running in the Fréjus Underground Laboratory (4800 m w.e.) in France. The experimental set-up is cylindrical in design, is divided into twenty equal sectors and with γ and neutron shielding it has about 6 m in diameter and 4 m in height.
The tracking wire chamber is made of 6180 open octagonal drift cells operating in Geiger mode (Geiger cells). It is filled with a gas mixture of 95% He, 4% ethyl-alcohol and 1% Ar. The Geiger cells provide a three-dimensional measurement of the charged particle tracks by recording the drift time and the two plasma propagation times.
The calorimeter, which surrounds the wire chamber, is composed of 1940 plastic scintillators coupled by light-guides to very low-radioactivity PMTs. The energy resolution σ_E/E of the calorimeter ranges from 6.0% to 7.5% for 1 MeV electrons, while the time resolution is 250 ps.
Seventeen sectors of NEMO 3 accommodate almost 10 kg of the following, highly enriched (95% – 99%) ββ decay isotopes: ¹⁰⁰Mo (6914 g), ⁸²Se (932 g), ¹¹⁶Cd (405 g), ¹³⁰Te (454 g), ¹⁵⁰Nd (34 g), ⁹⁶Zr (9 g), and ⁴⁸Ca (7 g). In addition, three sectors are also used for external background measurement and are equipped with pure Cu and natural Te. All these isotopes are produced in the form of thin foils and are placed in the central vertical plane of each sector.
For the e⁻ / e⁺ recognition, the detector is surrounded by a solenoidal coil which generates a vertical magnetic field of 25 Gauss. Moreover, NEMO 3 is covered by two types of shielding against external γ-rays and neutrons. Finally, the whole experimental set-up is closed inside a “tent”, which is supplied with radon-free air from a radon trapping facility. Radon is trapped and then decays inside a tank filled with 1 ton of charcoal (K48 from Silicarbon Aktivkohle) cooled down to −50˚C. This facility decreases the radon level of the air from the laboratory (15 – 20 Bq/m³) by a factor of ~1000. The radon trapping facility has been operating in the laboratory since October 2004.
 
Official web page of the NEMO 3 experiment.