Richards, BJ; (2013) Double beta decay of 48Ca with NEMO3 and calibration development for SuperNEMO. Doctoral thesis (PhD), UCL (University College London).

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Abstract

The two neutrino double beta ( 2 ) decay half-life of the 48Ca to 48Ti ground state transition has been measured by analysing 1555 days of NEMO3 data with 6.99g of 48Ca and was found to be T1=2 = 4:11+0:23 0:20(stat:) 0:26(syst:) 1019 years. This is the world's most accurate result for this isotope from which the matrix element for 2 has been calculated M2 = 0:0247 0:0015. A limit on the neutrinoless double beta ( 0 ) decay half-life for 48Ca has also been obtained at T1=2 > 1:8 1022 years at 90% CL.. This corresponds to an upper bound on the e ective Majorana neutrino mass of hm i < 19:8 eV for a 0 matrix element of M0 = 0.72 which is comparable with the best present results for this isotope. The next incarnation of the NEMO3 technology is SuperNEMO which has its demonstrator module currently under construction and is due to begin operation in 2014. SuperNEMO aims to achieve a half-life sensitivity of 1026 years (90% CL) which corresponds to a neutrino mass of 40-100 meV. Calibration of the SuperNEMO detector sub-systems, especially the calorimeter, is important in order to maintain the required sensitivity and determine the detector design. The absolute calibration of SuperNEMO was shown to be achievable with a 6x4 con guration of 207Bi sources inside the detector. The calibration sources strength, position in the detector and the length and periodicity of the calibration runs have been optimised.

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