The plutonium concentration of surface air at Vienna in the period 1962 to 1979

Air filters for the period 1962 to 1979 from a monitoring station in Vienna (Wien/Hohe Warte), which is operated as part of the Austrian network for measuring environmental radioactivity, were analysed for plutonium by chemical separation and alpha spectrometry. Several filters, all having been exposed for 24 hours, were combined, so that the analysis of each sample gave the average plutonium concentration in air for a period of two or three months. The sup(239(240))Pu concentration of surface air was found to have reached the highest values (up to 1 fCi/m3) in the spring of 1963, i.e. some months after the high yield nuclear weapon tests in the Fall of 1962. Afterwards the Pu concentration decreased, reaching about 0.03 fCi/m3 in 1967. This was a result of the Test Ban Treaty coming into force. The annual course of the Pu-concentration showed ''spring maxima'' especially in 1963, 1964 and 1965, such maxima having been observed also for other fallout radionuclides. In 1968 and 1976 the Pu concentration increased again (up to 0.06 fCi/m3), this being due to French and Chinese weapon tests in the atmosphere. In the last years of the period investigated, the Pu concentration was around 0,01 to 0,02 fCi/m3. In 1963 and 1964 the 238Pu activity was between 2 and 6% of the sup(239(240))Pu activity, such ratios being in agreement with those expected for fallout plutonium from weapon tests. Beginning in 1967 the activity ratio 238Pu/sup(239(240))Pu increased to values of 20 to 80%. This was a consequence of the release of 238Pu when the satellite SNAP-9A burnt up in the atmosphere (on 21 April 1964). From the Pu determinations and from gammaspectrometric measurements on the air filters the activity ratios 144Ce/239Pu and 137Cs/239Pu were obtained. From the change of the ratio 144Ce/239Pu with time, some information as to the date of formation of the radionuclide mixture was deduced. The ratio 137Cs/239Pu was on the average around 100 for the period investigated, but with considerable variation from sample to sample. (author)