The development of $$^{222}\hbox {Rn}$$ 222 Rn detectors for JUNO prototype

JUNO (The Jiangmen Underground Neutrino Observatory) is a multipurpose neutrino experiment, and it has very strict requirements for the detector. According to the MC simulation for JUNO experiment requirements, the Rn concentration in the water of the veto detector should be less than 0.2Bq/m $$^{3}$$ . In order to measure such low Rn concentration, two kinds of high-sensitivity Rn measurement systems have been developed. Based on the water system of JUNO prototype, two kinds of high-sensitivity Rn detectors have been developed, namely the Si-PIN Rn detector and the LS Rn detector. The Si-PIN Rn detector uses a Si-PIN photodiode to detect the $$\alpha $$ from $$^{214}$$ Po decay and the LS Rn detector detects the coincident signals of $$\beta $$ from $$^{214}$$ Bi decay and $$\beta $$ from $$^{214}$$ Po decay. The background measurement of Si-PIN Rn detector and LS Rn detector is performed to estimate the sensitivity. The sensitivity of Si-PIN Rn detector is around 9.0mBq/m $$^{3}$$ and the sensitivity of LS Rn detector is around 64.0Bq/m $$^{3}$$ . Both of the Si-PIN Rn detector and the LS Rn detector are working well with the JUNO prototype at present, and both of them can be developed as an online Rn concentration monitoring device for JUNO veto detector.