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 1m 3 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 222 Rn and 218 Po. 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 222 Rn of 2.5 µBq l −1 with current analysis efficiency, potentially opening up DRIFT technology as a new tool for sensitive radon assay of materials.

The novel properties of SF6 for directional dark matter experiments

“…The recent discovery of minority charge carriers in CS 2 + O 2 mixtures [19], has changed this by allowing the differences in their mobility to be used to derive the Z coordinate of the event (e.g., see Equation 7.1). This has transformed the DRIFT dark matter experiment [17], which, until this discovery, had operated for close to a decade with backgrounds from radon progeny recoils at the TPC cathode that severely impacted the dark matter search [16,[78][79][80][81].…”

A review of the discovery reach of directional Dark Matter detection

“…Hence, it constitutes an extension of direction-insensitive direct detection, for which only the energy is measured. Several directional detection strategies have been proposed: low pressure gaseous Time Projection Chambers (TPCs) [21][22][23][24][25][26][27][28][29], nuclear emulsions [30,31], columnar recombination in high-pressure gaseous Xenon TPCs [32][33][34], solid-state detectors [35][36][37], DNA-based detectors [38], graphene-based heterostructures [39] and polarized detectors [40]. Not all techniques are equally mature.…”

Direct detection of MeV-scale dark matter utilizing germanium internal amplification for the charge created by the ionization of impurities

“…For over three decades, many experiments have conducted searches for WIMPs using various targets [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. These experiments are all sensitive to WIMPs with masses greater than a few GeV/c 2 .…”