Measurement of Radon Concentration in Super-Kamiokande's Buffer Gas

Abstract

To precisely measure radon concentrations in purified air supplied to the Super-Kamiokande detector as a buffer gas, we have developed a highly sensitive radon detector with an intrinsic background as low as 0.33$\pm$0.07 mBq/m${}^3$. In this article, we discuss the construction and calibration of this detector as well as results of its application to the measurement and monitoring of the buffer gas layer above Super-Kamiokande. In March 2013, the chilled activated charcoal system used to remove radon in the input buffer gas was upgraded. After this improvement, a dramatic reduction in the radon concentration of the supply gas down to 0.08 $\pm$ 0.07 mBq/m${}^3$. Additionally, the Rn concentration of the in-situ buffer gas has been measured 28.8$\pm$1.7 mBq/m${}^3$ using the new radon detector. Based on these measurements we have determined that the dominant source of Rn in the buffer gas arises from contamination from the Super-Kamiokande tank itself.

15 pages, 9 figures (accepted for publication in Nuclear Inst. and Methods in Physics Research, A)

References in corpus (4)

• Measurement of the solar neutrino capture rate with gallium metal. III: Results for the 2002--2007 data-taking period
• Solar neutrino measurements in Super-Kamiokande-II
• Solar Neutrino Measurements in Super-Kamiokande-IV
• 7Be Solar Neutrino Measurement with KamLAND

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• A Study on the radon removal performance of low background activated carbon
• Development of new radon monitoring systems in the Kamioka mine
• Evaluation of radon adsorption efficiency values in xenon with activated carbon fibers
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• The development of ${}^{222}$Rn detectors for JUNO prototype
• Developing the radium measurement system for the water Cherenkov detector of the Jiangmen Underground Neutrino Observatory
• Study of radon removal performance of silver-ion exchanged zeolite from air for underground experiments
• Development of a low-background HPGe detector at Kamioka Observatory
• Development of High-Sensitivity Radon Emanation Measurement Systems with Surface Treatment Optimization
• First Gadolinium Loading to Super-Kamiokande
• Radon emanation rate measurements using liquid scintillation counting
• Measurement of the solar neutrino interaction rate below 3.49 MeV in Super-Kamiokande-IV