Measurement of ambient radon progeny decay rates and energy spectra in liquid argon using the MicroBooNE detector
Abstract
We report measurements of radon progeny in liquid argon within the MicroBooNE time projection chamber (LArTPC). The presence of specific radon daughters in MicroBooNE's 85 metric tons of active liquid argon bulk is probed with newly developed charge-based low-energy reconstruction tools and analysis techniques to detect correlated 214Bi-214Po radioactive decays. Special datasets taken during periods of active radon doping enable new demonstrations of the calorimetric capabilities of single-phase neutrino LArTPCs for β and α particles with electron-equivalent energies ranging from 0.1 to 3.0 MeV. By applying 214Bi-214Po detection algorithms to data recorded over a 46-day period, no statistically significant presence of radioactive 214Bi is detected, and a limit on the activity is placed at <0.35 mBq/kg at the 95% confidence level. This bulk 214Bi radiopurity limit -- the first ever reported for a liquid argon detector incorporating liquid-phase purification -- is then further discussed in relation to the targeted upper limit of 1 mBq/kg on bulk 222Rn activity for the DUNE neutrino detector.
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