The Study of Rn in the JUNO Prototype Water System

Abstract

In order to reduce and monitor the Rn concentration in pure water supplied to the JUNO detector, the vacuum degasses membrane device had been installed in the JUNO prototype water system. Meanwhile, two high sensitivity detectors for Rn measurement in water and gas have been set up and calibrated using a known concentration of Rn source. The measurement results of the two detectors are consistent with each other. The background level of the PIN detector was measured by using pure evaporated nitrogen. As a result, Rn concentration of detector background is $0.07 \pm 0.04$ Bq/m$^{3}$ for the PIN detector and $5.44 \pm 0.43$ Bq/m$^{3}$ for the LS detector (only statistical errors are reported). The activated charcoal was used to enrich Rn for improving Rn signal rate as well as signal-to-noise ratio in the LS detector. The removal Rn efficiency of one degassing by one degasser membrane is $59\%$. A better results will be obtained by optimizing the degasser and, as it can be seen, it fulfills JUNO’s requirements.