Measurement of low 222Rn concentration in N2 using an activated charcoal trap

222 Rn is a limiting background in many leading dark matter and low energy neutrino experiments. One way to mitigate 222 Rn is to fill external experimental components with a clean cover gas such as N 2 . At the SNOLAB facility in Canada, the 222 Rn concentration in the cover gas systems of the experiments are monitored using a radon assay board developed by the SNO collaboration. To improve the sensitivity of N 2 radon assays, a new trapping mechanism based on activated charcoal has been developed. The trap was purified and tested at SNOLAB. Additionally, a radon calibration source from floor tiles was developed and characterized. This calibration source was used to measure the efficiency of the activated charcoal trap. The methods for determining the efficiency, background, and sensitivity of the trap are described.