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The NEMO 3 detector is cylindrical in design and is composed of twenty equal sectors. The external dimensions of the detector with shields are 6 m in diameter and 4 m in height. NEMO 3 is based on the techniques tested on previous incarnations of the experiment NEMO 1 [13], and NEMO 2 [14]. 

The wire chamber is made of 6180 open octagonal drift cells which operate in Geiger mode (Geiger cells). A gas mixture of ∼ 95% helium, 4% ethyl-alcohol, 1% argon and 0.15% water at 10 mbar above atmospheric pressure is used as the filling gas of the wire chamber. Each drift cell provides a three-dimensional measurement of the charged particle tracks by recording the drift time and the two plasma propagation times. The transverse position is determined from the drift time, while the longitudinal position is deduced from the difference between the plasma propagation times at both ends of the cathode wires. The average vertex position resolution for the two-electron events is σ$_{t}$ = 0 . 5 cm in the transverse plane of the detector and σ$_{l}$ = 0 . 8 cm in the longitudinal plane. The Geiger cell information is treated by the track reconstruction program based on the cellular automaton algorithm, described in [15]. 

The calorimeter, which surrounds the wire chamber, is composed of 1940 plastic scintil- lator blocks coupled by light-guides to very low-radioactivity photomultiplier tubes (PMTs) 

