The NEMO 3 experiment
Neutrino Ettore Majorana Observatory
is devoted to the search for
neutrinoless double beta decay
and to the accurate measurement of
two-neutrino double beta decay
For this goal,
the experiment combines two detection techniques:
calorimetry and tracking.
Such approach allows us at the same time
, 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.
which surrounds the wire chamber,
is composed of 1940 plastic scintillators coupled by light-guides
to very low-radioactivity PMTs.
The energy resolution σE
/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:
Mo (6914 g), 82
Se (932 g),
Cd (405 g), 130
Te (454 g),
Nd (34 g), 96
Zr (9 g),
Ca (7 g).
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−
the detector is surrounded by a solenoidal coil
which generates a vertical magnetic field of 25 Gauss.
NEMO 3 is covered by two types of shielding
against external γ-rays and neutrons.
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.