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Low background techniques for the SuperNEMO experiment

Liu, XR; (2017) Low background techniques for the SuperNEMO experiment. Doctoral thesis , UCL (University College London). Green open access

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Abstract

SuperNEMO is a 0uββ experiment aiming to reach a half-life sensi¬tivity of 1026 years corresponding to an effective Majorana neutrino mass of (mββ) < 50 - 100 meV. Stringent radio-purity constraints are therefore placed on the detector construction material as well as the gases used in the central detector tracking volume. Radon, 222Rn, is one of the most problematic backgrounds for SuperNEMO due to its decay daughter, 214Bi, having a high Qββ value. Hence the radon level within the SuperNEMO tracker gas mixture must not exceed 150 pBq/m3. This activity is beyond the measurement capability of standard radon detectors, therefore a “Radon Concentration Line” was designed and constructed. This instrument has demonstrated the ability to measure the SuperNEMO tracker gas to a sensitivity of 20 pBq/m3. For large volume of gases the 222Rn activity can be measured with a sensitivity of <5 pBq/m3. Measurements of the fully instrumented quarter trackers and its subsystems have been performed. Radon emanation chambers have also been built to be used with the electrostatic detector which has demonstrated sensitivities of <190 pBq. High-purity germanium detectors offer a standard method to mea-sure material contamination. A dedicated screening facility has been established at Boulby Underground Laboratory with four detectors fully commissioned for low background material measurements. Such a detector can be used to make a highly sensitive measurement of 96Zr decay to the 0+ 1 excited state. Simulations of an experimental setup using 20 kg of 96Zr have shown a sensitivity of 1021yrs can be achieved with a 1 year measurement, a factor of 3 improvement on current world’s best limit.

Type: Thesis (Doctoral)
Title: Low background techniques for the SuperNEMO experiment
Event: University College London
Open access status: An open access version is available from UCL Discovery
Language: English
Keywords: Radon, Low-background, Germanium, SuperNEMO, Boulby
UCL classification: UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: http://discovery.ucl.ac.uk/id/eprint/1544146
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