Study of the relative calibration system of the NEMO 3 calorimeter and research of 2β0ν and 2β2ν 100Mo decay periods

The NEMO3 experiment is running since 2003 and aims at the research of the neutrinoless double beta decay signal (2β0ν) with an expected sensitivity of 0.1 eV on the effective mass. The discovery of this signal, forbidden by the Standard Model, would imply the non-conservation of the leptonic number and the existence of Majorana massive neutrinos. Experimental technique associates a tracking detector with a calorimeter and allows the identification of the two electrons and their energy measurement. With a period sensitivity over 1023 years few events are expected. Background reduction and knowledge are fundamental. An accurate check of the gains of all the photomultipliers from the calorimeter is also necessary. The first part of this work consisted with the exploitation of the information obtained by the relative energy calibrations carried out daily with a laser light. This study led to an application method of the relative calibrations results for the NEMO3 data analysis. The second part of this work concerned the study of the different backgrounds of the 2β2ν and 2β0ν decays. The analysis of data taken with a neutron source in different shields configurations of the NEMO3 detector validated a program of photon generation produced by fast neutron interactions. Finally, this work has determined the 2β2ν 100Mo decay period (∼ 7.2*108 years) and a limit on the 100Mo 2β0ν decay period (> ∼ 3.5*1023 years). (author)