Speaker
Description
Traces of radioactive isotopes of ruthenium in the atmosphere were reported in the beginning of October 2017 by several European stations monitoring the airborne concentrations of gamma emitters (e.g., IRSN, 2017). As of February 2018, the source in Eastern Europe has not been publically identified. $^{106}$Ru is a fission product with a half-life of 371.5 days. It is used as a medical isotope and despite its relatively short half-life, also its use as radionuclide thermoelectric generator was suggested (IRSN, 2017). $^{106}$Ru values, up to dozens of mBq•m$^{-3}$ have been detected in Czech stations (SURO, 2017), where also the isotope $^{103}$Ru was detected in levels 3−4 orders of magnitude lower.
In October 2017 we collected grass samples from four stations in Liberec region in northern Czechia. The samples were taken in order to test, if radioisotopes related to wet deposition during the period of positive $^{106}$Ru atmospheric detection, can be measured in detectable amounts and whether a deposition ratio could be derived. Grass is an environmental medium, in which radionuclide fallout would be concentrated after emission followed by wet deposition. Grass is at the same time an important part of the terrestrial food chain. For both reasons, grass is one of the first environmental media to be investigated in emergency plans. Our grass samples contained $^{106}$Ru detectable by standard gamma spectrometric procedures in the range of hundreds of mBq•m$^{-2}$. The observed activities of ruthenium and natural radionuclides were evaluated using a simple deposition model in context of the reported airborne activities and meteorological conditions.
Acknowledgements
We thank to citizen scientists Rudolf Makeľ and Marie Matoušková for collecting the grass samples, and to Miroslav Kudrna and the Technical College for Economy and Forestry in Frýdlant for the data from their meteorological station.
References
IRSN, 2017, Detection of ruthenium 106 in the air in the east and southeast of Europe - Update of October 9, 2017, accessed 07.11.2017, http://www.irsn.fr/EN/newsroom/News/Pages/20171009_Detection-of-ruthenium-106-in-the-air-in-the-east-and-southeast-of-Europe.aspx#1
SURO, 2017. Czech National Radiation Protection Institute, Information on ruthenium occurrence in the atmosphere (In Czech: Informace o výskytu ruthenia v ovzduší), accessed 07.11.2017, https://www.suro.cz/cz/publikace/aktuality/informace-o-vyskytu-ru-106-v-ovzdusi
