²¹⁰Pb-Atmospheric deposition in lichen-carpets in northern Sweden during 1961–1969

Abstract

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 210Po on silver dises. The ∝-activity of ²¹⁰Po was measured with a silicon-surface-barrier detector.

No maximum ²¹⁰Pb-content in lichen was found in 1963–1965 which could be compared 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 ²¹⁰Pb into the atmosphere by these tests.

The average ²¹⁰Pb-area-content of lichen during 1962–68 was found to be 16±2 nCi/m² and the deposition rate of ²¹⁰Pb was estimated to be 1.7±0.3 nCi/m² a. The effective half life for elimination of ²¹⁰Pb from the lichen-carpet was estimated to be 7±2 a.

The vertical distribution of ²¹⁰Pb in the lichen-carpet was also studied, and the highest concentrations were found in the top layer.