At the crossroad of particle physics and nuclear physics, the NEMO group at CENBG aim to reveal the true nature of neutrino particle et to measure its mass. The succeed of this project would a more complete understanding of the particle physics models and to clarified the role of neutrinos in the missing mass mystery and in the creation of the universe. The international NEMO experiment (Neutrinoless Ettore Majorana Observator) seek the existence of a particular, never observed, disintegration of nuclei: the double neutrinoless beta disintegration. The observation of this process would show that neutrinos and anti-neutrinos are a same state of matter (majorana particle) and would give an evaluation of its mass. The non-observation would put and upper limit to its mass. The NEMO3 detector, installed in the underground laboratory of Modane is already accumulating data. The very first results gave a first values of half-time of β β 2 ν decay for 100Mo and 82 Se The main goal of the R&D at CENBG for the next calorimeter is to improve the energy resolution of the detector.
The instrumentation department is managing the construction of a colorimeter demonstrator for the superNEMO experiment. This demonstrator will show the feasibility of the experiment by validating the results from the R&D stage. It will also check sources of background noise for the detectors. This will be a 1/22 of the complete superNEMO detector. The calorimeter includes 500 counters which is 80% of the total demonstrator counters. Each one is made of a scintillator (to convert electrons into photons) coupled to a 8’’ photomultiplier. These couples are manufactured and assembled to math the performance obtained during the R&D phase: 7%(FWHM) for 1 MeV electrons. These counters will include calibration devices: an α source as part of the block and optical fiber to conduct photon from a LED to the detector. They will cover a wall that is 5.4 meter long and 3.8 meter tall. We are working on mounting and checking procedures. The department is, as well, in charge of the redaction of the product quality management plan (risks assessment and management), that well be added to the Technical Design Report. At the same time we are managing the conception of manufacturing equipment (as: press for gluing, rotation table to wrap the counter and outgazing bench for glue). These tasks should be validated by the second semester of 2010 with the manufacturing of 20 pre-production detectors. The department is the main technical partner of the CENBG superNEMO collaboration and thus is present during the collaboration workshop and meeting.
The instrumentation department was involved, in collaboration with other department, in developing 3 test benches for this project. Two benches are electrons spectrometers to test scintillator- Photomultiplier (PM) coupling. The two benches have similar characteristics but are different in size: the first one it to test 30cm scintillator with Photomultiplier, the second is to test larger device, as bar, coupled to one or two photomultipliers. Each spectrometer is made with an electron source (90Sr – 370 MBq), an electromagnetic dipole and collimators, allowing to get electron beam in the range of 400KeV- 2MeV with a size of about one millimeter on the scintillator. The device is motorized and coupled to a computed, allowing a automated scan of the scintillator surface, thus the homogeneity of the scintillator-PM coupling can be tested. At Delta-E veto detector has been added to reject signals from background. This detector is a 110µm think scintillator foil coupled to two PM. The detector is on the electron trajectory and show that the signal from the tested device is associated to an incoming electron. Each spectrometer is remotely controlled (Electrons energy X-Y position of the beam, veto detector in-out position, beam stop). we tested and calibrated these benches during 2008.
The department did the R&D of a LASER-LED measurement bench dedicated to the measurement of the PM gain as a function of the wavelength of the incident photons. This bench consist mainly in a remote controlled (intensity – frequency) monochromatic light flasher with optic lines to the PM.. These flashes are similar in duration and intensity to the signal produced by a particle in a scintillator. The results from this test bench are crucial for the calibrating device of the future SuperNEMO detector. For this bench the LED option was introduced by the department as an alternative solution to a laser test bench. The prototype was made, optimized and build in collaboration with the electronics and mechanics departments. The bench is in work since September 2009. The bench has 4 monochromatic flasher (410,420,440,460nm) coupled by optical fibre to the PM. The remote control of the flashers was developed by the electronic department.