Speaker
Description
At the very end of September and in October 2017 artificial radioactive isotope Ruthenium-106 has been detected in air over Europe. It was primarily found in Northern Italy and Central Europe. $^{106}$Ru was detected by means of aerosol sampling stations used in continuous monitoring of presence of radioactive isotopes in ground-level air. In Krakow, $^{106}$Ru was firstly detected on filter which had been exposed in period 25.09 - 02.10.2017 (standard week exposition) but in order to increase time resolution, next filters were changed every day. Early measurements involved assessment of activity concentration of $^{106}$Ru in collected samples. Soon traces of $^{103}$Ru were also found in the most active sample with $^{106}$Ru/$^{103}$Ru activity ratio close to 3500. Moreover, due to unknown reason and source of release, further study also focused on determination of $^{241}$Am, $^{90}$Sr, $^{238}$Pu and $^{239+240}$Pu in three samples with the highest activity concentration of $^{106}$Ru, collected in time periods: 25.09-02.10, 02-03.10 and 03-04.10.
Air filter samples were collected at the Institute of Nuclear Physics PAN in Krakow using aerosol sampler which works at nominal flow rate 500 m$^3$/h and utilizes Petryanov filter FPP-15-1.5 (polyvinyl chloride) with high efficiency for collecting aerosols. After exposition, filters were compressed into pellets (5 cm diameter, about 4 mm height) and measured using low background gamma-ray spectrometer with HPGe detector ($^{106}$Ru (half-life 373 days) is a pure beta-emitter but within few minutes achieves secular equilibrium with its daughter isotope - $^{106}$Rh (half-life 30 s) which decay is followed by gamma-ray emission). Subsequently, samples underwent radiochemical procedures in order to separate isotopes of Pu, Am (using Dowex-1x8 and TEVA) and Sr (using Sr-Resin). Determination of activity concentrations of actinides were carried out using alpha spectrometry and $^{90}$Sr was determined by means of LSC technique.
Investigations showed that the highest concentration of $^{106}$Ru in ground level air in Krakow was present in period 2-3 October 2017 and reached 16.7 ± 1.2 mBq/m$^3$. During following days its activity concentration was constantly declining and reached limit of detection on 5.10.2017. However, $^{106}$Ru was still detectable in following weeks at levels three order of magnitude lower.
Preliminary results of conducted radiochemical analyses demonstrated that the highest activity concentrations of $^{239+240}$Pu and $^{241}$Am were 2.42 ± 0.93 nBq/m$^3$ and 7.15 ± 5.45 nBq/m$^3$, respectively. The $^{238}$Pu concentrations were below detection limit (estimated at 0.77 nBq/m$^3$). Results of $^{90}$Sr concentrations, will be presented at the conference.
