Measurements of 236U in Ancient and Modern Peat Samples and Implications for Postdepositional Migration of Fallout Radionuclides

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• 作者：Francesca Quinto ; Erich Hrnecek ; Michael Krachler ; William Shotyk ; Peter Steier ; Stephan R. Winkler
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：May 21, 2013
• 年：2013
• 卷：47
• 期：10
• 页码：5243-5250
• 全文大小：287K
• 年卷期：v.47,no.10(May 21, 2013)
• ISSN：1520-5851

文摘

²³⁶U was analyzed in an ombrotrophic peat core representing the last 80 years of atmospheric deposition and a minerotrophic peat sample from the last interglacial period. The determination of ²³⁶U at levels of 10⁷ atoms/g was possible by using ultraclean laboratory procedures and accelerator mass spectrometry. The vertical profile of the ²³⁶U/²³⁸U isotopic ratio along the ombrotrophic peat core represents the first observation of the ²³⁶U bomb peak in a terrestrial environment. A constant level of anthropogenic ²³⁶U with an average ²³⁶U/²³⁸U isotopic ratio of (1.24 卤 0.08) 脳 10^鈥? in the top layers of the core was observed. Comparing the abundances of the global fallout derived ²³⁶U and ²³⁹Pu along the peat core, the post depositional migration of plutonium clearly exceeds that of uranium. However, the cumulative ²³⁶U/²³⁹Pu ratio of 0.62 卤 0.31 is in agreement with previous studies on the global fallout uranium and plutonium. In the interglacial peat samples a ²³⁶U/²³⁸U isotopic ratio of (3.3 卤 0.7) 脳 10^鈥?2 was detected; although this measurement is an upper limit, it constitutes a significant step forward in the experimental determination of the natural ²³⁶U abundance and represents a true background sample for the ombrotrophic peat core.