Radiopurity assessment of the energy readout for the NEXT double beta decay experiment

Abstract

The Neutrino Experiment with a Xenon Time-Projection Chamber (NEXT) experiment intends to investigate the neutrinoless double beta decay of 136Xe, and therefore requires a severe suppression of potential backgrounds. An extensive material screening and selection process was undertaken to quantify the radioactivity of the materials used in the experiment. Separate energy and tracking readout planes using different sensors allow us to combine the measurement of the topological signature of the event for background discrimination with the energy resolution optimization. The design of radiopure readout planes, in direct contact with the gas detector medium, was especially challenging since the required components typically have activities too large for experiments demanding ultra-low background conditions. After studying the tracking plane, here the radiopurity control of the energy plane is presented, mainly based on gamma-ray spectroscopy using ultra-low background germanium detectors at the Laboratorio Subterráneo de Canfranc (Spain). All the available units of the selected model of photomultiplier have been screened together with most of the components for the bases, enclosures and windows. According to these results for the activity of the relevant radioisotopes, the selected components of the energy plane would give a contribution to the overall background level in the region of interest of at most 2.4 x 10-4 counts keV-1 kg-1 y-1, satisfying the sensitivity requirements of the NEXT experiment.

arXiv commentFinal version for publication

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• The Next White (NEW) detector
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• Ultra-low radioactivity Kapton and copper-Kapton laminates
• Evaluation of radon adsorption efficiency values in xenon with activated carbon fibers
• Status of ArDM-1t: First observations from operation with a full ton-scale liquid argon target
• Measurement of radon-induced backgrounds in the NEXT double beta decay experiment
• The electronics of the energy plane of the NEXT-White detector
• Double Beta Decay Experiments at Canfranc Underground Laboratory
• Mass spectrometric analyses of high performance polymers to assess radiopurity as ultra low background materials for rare event physics detectors
• A Novel Low-Background Photomultiplier Tube Developed for Xenon Based Detectors
• AlphaCAMM, a Micromegas-based camera for high-sensitivity screening of alpha surface contamination