The carbon-14 concentration in tree-ring cellulose of an 80-year-old pine tree which has been used for tritium measurement was measured during the 1941-1987 period. This was done to determine the formation year of each tree ring in order to study the pathway of tritium uptake into the tree rings. In the 1941 to 1953 period, the A14C value remained slightly lower than 0%o. It began to increase from 1954 to a small broad peak of 250%o between 1959 and 1961, followed by rapid increase to the highest value of approximately 800%o in 1964. Since 1964, it had been diminishing year by year to reach a level of 190%o in 1987. The two peak years coincided with those in the known carbon-14 patterns in tree rings. However, there existed a difference in the amplitude of the A14C values during the period of 1963 1967.

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