Ten year time series of Kr-85 in air on the southern hemisphere

In July 2025 CSIRO Waite Campus will have measured Kr-85 in air for a continuous period of 10 years.

Kr-85 is the only anthropogenic isotope of the three radioactive noble gas isotopes (the other two are Kr-81 and Ar-39). Kr-85 is ‘the ash of the nuclear fire’ and produced in nuclear reactors when uranium atoms undergo fission. When the fuel is re-processed and the fuel rods are cut into pieces and dissolved in acid, the gaseous Kr-85 escapes into the atmosphere. Its activity in the atmosphere therefore varies with space and time according to the global reprocessing activity. A global network exists of stations taking weekly samples for Kr-85, since it can also be used to detect clandestine nuclear activities (Bollhöfer et al. 2019). There have been several sample collection stations on the southern hemisphere, but the last one in Darwin ceased operation in 2010. Since 1/7/2015 weekly air samples are collected at CSIRO Waite Campus and sent to the Bundesamt für Strahlenschutz (BFS) in Freiburg, Germany for measurement.

For the application of Kr-85 as a dating tracer in the hydrosphere, establishing a time series of Kr-85 in the atmosphere is necessary as this provides the input function for estimation of modern groundwater recharge. An additional benefit is that the data may be used for non-proliferation detection of clandestine nuclear activities.