RadChem 2018

Determination of Pu-238,239+240, Am-241 and Sr-90 in air filters affected by Ruthenium isotopes and collected in autumn 2017

15 May 2018, 17:15

1h 30m

Gallery (Casino Conference Centre)

Poster Radionuclides in the Environment, Radioecology Poster RER

Speaker

Mr Krzysztof Gorzkiewicz (Institute of Nuclear Physics Polish Academy of Sciences)

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.