Uppfångning och kvarhållning av 134Cs och 85Sr i olika växtutvecklingsstadier

Abstract: Emissions of radionuclides to the atmosphere can lead to wet deposition on plants in the event of rainfall. An increased level of radioactivity in the plants may occur due to interception and retention of the radionuclides. If the content of the plants is above the threshold limit value, entire yields may have to be destroyed. In order to prevent contamination or decrease the content countermeasures can be taken. The impact of the biomass, leaf area index (LAI) and growth stage of the plant on the interception and retention is important to know in order to decide which countermeasures to use. Weather may also be an important factor. In this work the interception and retention of 134Cs and 85Sr by spring wheat, ley and spring oil-seed rape was studied. The impact of the biomass, LAI and growth stage of the plant and precipitation after deposition was also studied. The work was conducted as a field study with plots of the size 1 x 1 m. The plants were wet deposited with 134Cs and 85Sr by using a rain simulator. A total activity of 40 kBq/m2 for both radionuclides was deposited on each plot. Depositions were performed during four different growth stages and the plants were sampled approximately four hours, one and five days after deposition. Activities of the dried plant samples were measured with a High Purity Germanium (HPGe) detector. Finally the interception fraction and the retention factor were calculated. The study showed that the interception fraction was highest for the third growth stage for both wheat and oil-seed rape; dough ripeness for wheat and ripening for oil-seed rape. Ley, which was harvested after two depositions, had the highest interception fraction at the second growth stage, flowering. Oil-seed rape and ley seemed to have a slightly higher interception fraction for 85Sr at all growth stages. There was a positive relationship for the biomass and interception fraction, for the LAI and interception fraction the relationship wasn’t significant. The retention showed a weak trend of decreasing with time, with the decrease being largest during the first day after the interception. However, the standard deviation was large and consequently the values uncertain.