Development of super-high sensitivity radon detector for the Super-Kamiokande detector

A super-high sensitivity radon detector for water which works as a real-time monitor of the radon concentration in water for the Super-Kamiokande detector was developed. Super-high sensitivity was achieved through the utilization of the membrane degassifier module, in addition to factors such as large detector volume, high electrostatic collection voltage, and high-quality electronics. As a result of the calibration study, a sensitivity of 14.6±2.1(stat.+syst.) (counts/day)/(mBq/m3) is achieved. The background level of the radon detector for water is 34.5±5.8(stat.) (counts/day). This corresponds to the detection limit of 0.7 mBq/m3 in a one-day measurement.