Neutrino Ettore Majorana Observatory
Encyclopedia
The Neutrino Ettore Majorana
Observatory (NEMO experiment) is an international collaboration of scientists searching for neutrino
less double beta decay
. The observation of neutrinoless double beta decay would be evidence that neutrino
s are Majorana particles
and could be used to measure the neutrino mass. It is located in the Modane Underground Laboratory (LSM) in the Fréjus Road Tunnel
. Data taking started in January 2003 and ended in January 2011.
s in the form of thin foils with a total surface of about 20 m2. The main isotopes used for the neutrinoless double beta decay search are about 7 kg of enriched
molybdenum-100 and about 1 kg of selenium-82. The experiment also contains smaller amounts of cadmium-116, neodymium-150, zirconium-96 and calcium-48
foils. Tellurium and copper
foils are used for background measurements.
A tracking detector on each side of the foil detects electron
s and positron
s from the double beta decay. Electrons and positrons are identified through their curvature in a magnetic field. The energy of the electrons and positron is then measured in a calorimeter
. In neutrinoless double beta decay, the sum of the electron and positron energies will be the same as the energy (Q value) released in the double beta decay process. For the standard double beta decay process the two neutrinos, which cannot be observed directly, will take some of the energy thereby reducing the energy sum for the electron and positron.
No neutrinoless double beta decays have been observed during about 5 years of data taking. In 2009, the NEMO-3 experiment therefore reported that the half life for neutrinoless double beta decay of molybdenum-100 is greater than 1024 years. This can be translated into an upper limit on the neutrino mass of about 0.5–1.0 eV, depending on the nuclear model used to calculate the neutrino mass from the half-life.
. The installation of a first module in the LSM is expected in 2012.
Ettore Majorana
Ettore Majorana was an Italian theoretical physicist who began work on neutrino masses. He disappeared suddenly in mysterious circumstances. He is noted for the eponymous Majorana equation and for Majorana fermions.-Gifted in mathematics:Majorana was born in Catania, Sicily...
Observatory (NEMO experiment) is an international collaboration of scientists searching for neutrino
Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
less double beta decay
Double beta decay
Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted...
. The observation of neutrinoless double beta decay would be evidence that neutrino
Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
s are Majorana particles
Majorana fermion
In physics, a Majorana fermion is a fermion which is its own anti-particle. The term is used in opposition to Dirac fermion, which describes particles that differ from their antiparticles...
and could be used to measure the neutrino mass. It is located in the Modane Underground Laboratory (LSM) in the Fréjus Road Tunnel
Fréjus Road Tunnel
The Fréjus Road Tunnel is a tunnel that connects France and Italy. It runs under Col du Fréjus in the Cottian Alps between Modane in France and Bardonecchia in Italy...
. Data taking started in January 2003 and ended in January 2011.
Experiment
The experiment has a cylindrical shape with 20 sectors that contain different isotopeIsotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s in the form of thin foils with a total surface of about 20 m2. The main isotopes used for the neutrinoless double beta decay search are about 7 kg of enriched
Isotope separation
Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes, for example separating natural uranium into enriched uranium and depleted uranium. This is a crucial process in the manufacture of uranium fuel for nuclear power stations, and is...
molybdenum-100 and about 1 kg of selenium-82. The experiment also contains smaller amounts of cadmium-116, neodymium-150, zirconium-96 and calcium-48
Calcium-48
Calcium-48 is a rare isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, the only radioactive decay pathway open to it is the extremely rare process of double beta decay...
foils. Tellurium and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
foils are used for background measurements.
A tracking detector on each side of the foil detects electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s and positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
s from the double beta decay. Electrons and positrons are identified through their curvature in a magnetic field. The energy of the electrons and positron is then measured in a calorimeter
Calorimeter (particle physics)
In particle physics, a calorimeter is an experimental apparatus that measures the energy of particles. Most particles enter the calorimeter and initiate a particle shower and the particles' energy is deposited in the calorimeter, collected, and measured. The energy may be measured in its...
. In neutrinoless double beta decay, the sum of the electron and positron energies will be the same as the energy (Q value) released in the double beta decay process. For the standard double beta decay process the two neutrinos, which cannot be observed directly, will take some of the energy thereby reducing the energy sum for the electron and positron.
No neutrinoless double beta decays have been observed during about 5 years of data taking. In 2009, the NEMO-3 experiment therefore reported that the half life for neutrinoless double beta decay of molybdenum-100 is greater than 1024 years. This can be translated into an upper limit on the neutrino mass of about 0.5–1.0 eV, depending on the nuclear model used to calculate the neutrino mass from the half-life.
SuperNEMO
A next generation experiment, SuperNEMO, is currently under construction. It is based on technology used by the NEMO-3 experiment, but will be more than a factor of ten bigger. The SuperNEMO detector will consist of 20 modules each containing approximately 5 kg of enriched double beta decay emitting isotope in the form of a thin foil. Isotopes under consideration for SuperNEMO are selenium-82, neodymium-150 and calcium-48Calcium-48
Calcium-48 is a rare isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, the only radioactive decay pathway open to it is the extremely rare process of double beta decay...
. The installation of a first module in the LSM is expected in 2012.