RETROSPECTIVE EVALUATION OF TRITIUM FALLOUT BY TREE-RING ANALYSIS

Tritium analyses of tree-ring cellulose were made to test its suitabil ity for retrospective evaluation of a local tritium fallout. Several s pruce trees were taken from an Austrian alpine area where tritium cont amination of May 1974 precipitation had been detected. Wood from the a nnual growth rings of 1973, 1974 and 1975 was separated and the cellul ose extracted. After isotopic equilibration with dead water, cellulose was combusted to yield water whose tritium concentration was measured by liquid scintillation counting. Rigorous statistical treatment prov ed the significance of the increased tritium concentration caused by t he tritium anomaly, which occurred during the growing season. The long -term trends of local atmospheric tritium, including the 1974 peak, we re also well reflected by analysis of a 24-year ring sequence from a s ingle tree in the contaminated area. The tritium data gained by the gi ven method can be used at present qualitatively and a better understan ding of the possible sources of contamination is required in order tha t the quantitative criteria be satisfied