An electrostatic radon detector designed for water radioactivity measurements

The Sudbury Neutrino Observatory contains 1000 t of ultra-pure heavy water and 7000 t of very pure light water. In order to achieve the goal of determining accurately the total number of neutrinos emitted by the sun regardless of type, the radioactivity in the water must be maintained with a radiopurity of less than 10−14 g/g of 232Th and 238U in secular equilibrium with their daughters. This paper describes the design and application of an electrostatic radon detector which determines the amount of radon emanating from a column containing MnO2 used to extract radium from the water. This electrostatic radon detector has a total efficiency of 35% for detecting 222Rn and 22% for 220Rn.