Radon in the DRIFT-II directional dark matter TPC: emanation, detection and mitigation

Abstract

Radon gas emanating from materials is of interest in environmental science and also a major concern in rare event non-accelerator particle physics experiments such as dark matter and double beta decay searches, where it is a major source of background. Notable for dark matter experiments is the production of radon progeny recoils (RPRs), the low energy (~100 keV) recoils of radon daughter isotopes, which can mimic the signal expected from WIMP interactions. Presented here are results of measurements of radon emanation from detector materials in the 1 metre cubed DRIFT-II directional dark matter gas time projection chamber experiment. Construction and operation of a radon emanation facility for this work is described, along with an analysis to continuously monitor DRIFT data for the presence of internal 222Rn and 218Po. Applying this analysis to historical DRIFT data, we show how systematic substitution of detector materials for alternatives, selected by this device for low radon emanation, has resulted in a factor of ~10 reduction in internal radon rates. Levels are found to be consistent with the sum from separate radon emanation measurements of the internal materials and also with direct measurement using an attached alpha spectrometer. The current DRIFT detector, DRIFT-IId, is found to have sensitivity to 222Rn of 2.5 μBq/l with current analysis efficiency, potentially opening up DRIFT technology as a new tool for sensitive radon assay of materials.

arXiv comment16 pages, 10 figures, 2 tables

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• Reducing DRIFT Backgrounds with a Submicron Aluminized-Mylar Cathode
• Long-term study of backgrounds in the DRIFT-II directional dark matter experiment
• Directional Detection of Dark Matter Using Solid-State Quantum Sensing
• First background-free limit from a directional dark matter experiment: results from a fully fiducialised DRIFT detector
• Demonstration of radon removal from SF${}_6$ using molecular sieves
• Improved Sensitivity of the DRIFT-IId Directional Dark Matter Experiment using Machine Learning
• Observables for Recoil Identification in High-Definition Gas Time Projection Chambers
• Dark Matter phenomenology : from simplified WIMP models to refined alternative solutions
• Test of low radioactive molecular sieves for radon filtration in SF6 gas-based rare-event physics experiments
• Measurements of Radon Concentrations Using CR-39 Detectors in China JinPing Underground Laboratory (2015-2016)
• Primary track recovery in high-definition gas time projection chambers
• Remote Reactor Ranging via Antineutrino Oscillations