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Bomb-Produced 14C in Tree Rings

Published online by Cambridge University Press:  18 July 2016

Dai Kaimei ,
Qian Youneng  and
C. Y. Fan
Dai Kaimei
Affiliation:
Department of Physics, Nanjing University, Nanjing, China
Qian Youneng
Affiliation:
Department of Physics, Nanjing University, Nanjing, China
C. Y. Fan
Affiliation:
Department of Physics, The University of Arizona, Tucson, Arizona 85721 USA
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Abstract

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The 14C content in 1961–1967 and 1970–1983 tree rings of a spruce grown in Dailing, China (47°N, 129°E) was measured by liquid scintillation. As a result of USSR bomb tests at Novaya Zemlya (72°N, 53°E), Δ14C values rose dramatically from 250‰ in 1961 to a maximum 909‰ in 1964, and then gradually decreased to 238‰ in 1983. We compared Δ14C values in the rings of an oak tree grown at 43°N, 74°W and that of a pine grown at 49°N, 9°E, and atmospheric Δ14C values in both northern and southern hemispheres. We observe that: 1) annual tree rings grown in the same latitude zone have the same Δ14C values, reflecting rapid longitudinal mixing of the atmosphere; 2) atmospheric 14C concentrations reached a global equilibrium distribution at the end of 1968, and tree ring 14C content reflects atmospheric 14C concentration; 3) 1976–1982 rings of the Dailing spruce show excessive 14C, likely due to the effect of 1976 and 1980 Chinese bomb tests; 4) Δ14C decreases exponentially, halving every 17 yr.

Type
III. Global 14C Production and Variation
Information
Radiocarbon , Volume 34 , Issue 3: Proceedings of the 14th International Radiocarbon Conference , 1992 , pp. 753 - 756
Copyright
Copyright © The American Journal of Science 

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