Radon and material radiopurity assessment for the NEXT double beta decay experiment

Abstract

The "Neutrino Experiment with a Xenon TPC" (NEXT), intended to investigate the neutrinoless double beta decay using a high-pressure xenon gas TPC filled with Xe enriched in 136 Xe at the Canfranc Underground Laboratory in Spain, requires ultra-low background conditions demanding an exhaustive control of material radiopurity and environmental radon levels. An extensive material screening process is underway for several years based mainly on gamma-ray spectroscopy using ultra-low background germanium detectors in Canfranc but also on mass spectrometry techniques like GDMS and ICPMS. Components from shielding, pressure vessel, electroluminescence and high voltage elements and energy and tracking readout planes have been analyzed, helping in the final design of the experiment and in the construction of the background model. The latest measurements carried out will be presented and the implication on NEXT of their results will be discussed. The commissioning of the NEW detector, as a first step towards NEXT, has started in Canfranc; in-situ measurements of airborne radon levels were taken there to optimize the system for radon mitigation and will be shown too.

Radon background in liquid xenon detectors

“…The radioactive daughter isotopes of radon form an important background source in many low-event rate experiments. Among those neutrino and dark matter experiments rank and we will focus on the ones using liquid xenon as detection medium (for example [1] - [5]). Radon is created by the decay of radium that, being part of the primordial decay chains of thorium and uranium, is present in many materials used for detector construction.…”