The development of a digital gamma-gamma coincidence/anticoincidence spectrometer and its applications to monitor low-level atmospheric 22Na/7Be activity ratios in Resolute Bay, Canada

Using a previously developed digital gamma-gamma coincidence/anticoincidence spectrometer, daily aerosol samples collected at Resolute Bay, Canada (74.71 degrees N, 94.97 degrees W) from May 2016 to April 2017 were analysed for activity concentrations of Na-22 and Be-7. The spectrometer design allows a more selective measurement of Na-22 with a significant background reduction by gamma-gamma coincidence events processing. It has been demonstrated that the improved spectrometer provides a more sensitive and effective way to quantify trace amounts of Na-22 and Be-7 with a critical limit of 3 mBq and 5 Bq respectively for a 20 h counting. The Be-7/Na-22 ratio data set obtained in this study showed significant annual variation, which has a distinct spring (typically from February to May) maximum and winter (from September to February of next calendar year) minimum, which suggest that it could be used as a radiochronometer for studying the atmospheric processes. The Be-7/Na-22 ratios are most likely connected to deep stratosphere-to-troposphere transport (STT) exchange events where air with a higher Be-7/Na-22 ratio originates from downward flow from stratosphere to the troposphere. The aerosols with lower Be-7/Na-22 ratios located between two oscillation peaks may have longer residence time. The correlations between Be-7 and Na-22 activity concentration were the high during these time periods. Compared with other studies based on weekly collected aerosol samples, the techniques greatly improve the temporal resolution of Be-7/Na-22 data set that will be able to provide more detailed information to study various atmospheric phenomena.