Evaluation of SNOLAB background mitigation procedures through the use of an ICP-MS based dust monitoring methodology

TL;DR

This study employs ICP-MS to directly measure radionuclide fallout rates in SNOLAB, validating dust mitigation procedures and providing detailed background levels crucial for rare-event search experiments.

Contribution

It introduces an ICP-MS based methodology for direct radionuclide fallout measurement, offering a more accurate assessment of dust backgrounds at SNOLAB.

Findings

Radionuclide fallout rates are significantly lower in clean areas.

Handling of lead bricks increases stable Pb fallout by two orders of magnitude.

Particulate-generating activities raise K-40, Th-232, and U-238 levels.

Abstract

Dust particulate fallout on materials in use for rare-event searches is a concerning source of radioactive backgrounds due to the presence of naturally occurring radionuclides K-40, Th-232, U-238, and their progeny in dust. Much effort is dedicated to inform radioactive backgrounds from dust and evaluate the efficacy of mitigation procedures. A great portion of such effort relies on fallout models and assumed dust composition. In this work, an ICP-MS based methodology was employed for a direct determination of fallout rates of radionuclides and stable isotopes of interest from dust particulate at the SNOLAB facility. Hosted in an active mine, the SNOLAB underground laboratory strives to maintain experimental areas at class 2000 cleanroom level. This work validates the mitigation procedures in place at SNOLAB, and informs dust backgrounds during laboratory activities. Fallout rates of major constituent of the local rock were measured two to three orders of magnitude lower in the clean experimental areas compared to non-clean transition areas from the mine to the laboratory. A ca. two order of magnitude increase in stable Pb fallout rate was determined in an experimental area during activities involving handling of Pb bricks. Increased K-40, Th-232, and U-238 fallout rates were measured in clean experimental areas during activities generating particulate.