Observation of radon mitigation in MicroBooNE by a liquid argon filtration system

Abstract

The MicroBooNE liquid argon time projection chamber (LArTPC) maintains a high level of liquid argon purity through the use of a filtration system that removes electronegative contaminants in continuously-circulated liquid, recondensed boil off, and externally supplied argon gas. We use the MicroBooNE LArTPC to reconstruct MeV-scale radiological decays. Using this technique we measure the liquid argon filtration system's efficacy at removing radon. This is studied by placing a 500 kBq 222Rn source upstream of the filters and searching for a time-dependent increase in the number of radiological decays in the LArTPC. In the context of two models for radon mitigation via a liquid argon filtration system, a slowing mechanism and a trapping mechanism, MicroBooNE data supports a radon reduction factor of greater than 97% or 99.999%, respectively. Furthermore, a radiological survey of the filters found that the copper-based filter material was the primary medium that removed the 222Rn. This is the first observation of radon mitigation in liquid argon with a large-scale copper-based filter and could offer a radon mitigation solution for future large LArTPCs.

Large low background kTon-scale liquid argon time projection chambers

“…New materials such as Metal-organic frameworks could improve the capture potential beyond charcoal, allowing a potential shrinkage of the footprint of a radon-capture facility to fit the existing cavern designs. Recent evidence from MicroBoone [19] indicates that a copper filter purification system similar to that planned for DUNE may remove greater than 97% or 99.999% of the radon (depending on whether slowed or trapped) in the system without the need for additional removal techniques. • Emanation measurement materials campaign.…”

Convolutional neural network for multiple particle identification in the MicroBooNE liquid argon time projection chamber

“…The most frequent type of neutron interaction leaves the argon nucleus in an excited state without producing another visible signature. In principle, MicroBooNE has the LArTPC detector response attributes and existing low-energy reconstruction tools [29,30] to tag neutrons through de-excitation photons. While previous demonstrations of identifying such events have been produced [14], these interactions present unique challenges that complicate their application to the problem of neutrino calorimetry [31].…”

“…However, due to the lack of hits from other particles in the same location, these isolated charge depositions can be reconstructed at significantly lower energies in principle. Further work to lower the proton threshold, including leveraging newly developed low-threshold reconstruction capabilities [29,30], would lead to significant efficiency gains. Additionally, the selection could be expanded to consider protons not reconstructed as part of the neu- trino slice -around 60% of neutron-induced protons in our sample.…”