210 Pb-Atmospheric deposition in lichen-carpets in northern

The 210Pb-content of lichen-carpets collected in Northern Sweden (62.3 " N, 12.4 " E) from 1961 until 1969 has been studied. The analytical method used was wet ashing with nitric and perchloric acid and spontaneous deposition of zlOPo on silver discs. The a-activity of zlOPo was measured with a silicon-surface-barrier detector. No maximum P1oPb-content in lichen was found in 1963-1965 which could be com-pared with that previously found for 137Cs, 55Fe and 90Sr, which were released by nuclear-weapons tests during 1961-62. Thus there was no special evidence of any release of significant amounts of artificial,loPb into the atmosphere by these tests. The average Z'OPb-area-content of lichen during 1962-68 was found to be 16 k 2 nCi/m2 and the deposition rate of 210Pb was estimated to be 1.7k0.3 nCi/mz a. The effective half life for elimination of,loPb from the lichen-carpet was estimated to be 7 + 2 a. The vertical distribution of aloPb in the lichen-carpet was also studied, and the highest concentrations were found in the top layer