Fall-out plutonium in Austrian soil samples

Plutonium concentration in soil samples coming from different locations in the Austrian mountain region was determined. Sampling points were selected from areas strongly differing in the amount of mean annual rainfall and in height above the sea level. Investigations were performed with soil samples taken down to a depth of 10 cm including all surface vegetation. After ashing the soil samples at 4500C in a muffle furnace and leaching with nitric acid, chemical separation of Pu was carried out using anionic exchange extraction with trilaurylamine in xylene. For alphaspectrometric measurements with a silicon surface barrier detector samples were prepared electrolytically from slightly acidic ammonium chloride solution on stainless steel disks. In order to check the Pu recovery of the chemical procedure before ashing each soil sample was spiked with 236Pu. The results show that 239Pu concentrations in the soil are varying from 2 to about 30 fCi/g. Fall-out deposition can be estimated in some mountain regions up to 5 mCi/km2 well correlated with rainfall and height above sea level. Beyond this some values from disturbed areas like farmed soils or dry riverbottoms show that fall-out deposition predominantly must be fixed in the upper layer of the soils