The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments - ABOX, ABA and hypy
The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments - ABOX, ABA and hypy
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DOI：
10.1016/j.quageo.2014.02.003
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发表时间：
2014-08-01
影响因子：
2.7
通讯作者：
Apperley, David C.
中科院分区：
文献类型：
--
作者：
Bird, Michael I.;Levchenko, Vladimir;Apperley, David C.
在这里，我们报告了三种放射性碳前处理技术去除放射性碳污染能力的直接内部比较的结果，这些技术是通过将在三种不同温度(300、400和500摄氏度)下制成的已知不含放射性碳的木炭暴露在热带雨林地面上的环境污染中一到三年而引入的。最初的木炭没有可测量的放射性碳，但在环境暴露后，C-14活性增加，一年后接近1PMC(表观年龄类似于40,000年BP)，三年后类似于5 PMC(表观年龄类似于25,000年)。对于400摄氏度和500摄氏度的样品，所有技术都能够减少90%的污染。酸碱氧化(ABOX)提供了最可靠的去污方法，将一年样品的放射性碳活度降至本底，并将三年样品的放射性碳活度降至0.04+/-0.02PMC或更低(表观年龄56,900年BP)。ABOX处理的效果优于酸碱酸(ABA)和氢热裂解(HHY)处理，其中ABA在大多数情况下表现优于HHYY。没有一种技术能够完全去除300摄氏度木炭的污染(尽管ABOX再次去除了大部分污染)，这可能是由于木炭的不完全热解性质，它主要是由环状小尺寸的芳香族簇主导的。所有技术都依赖于比本土碳更快地去除污染物碳，而在低于350摄氏度的温度下生产的木炭不符合这一条件。虽然所有的前处理对常规样品处理都是有用的，但结果表明，ABOX是唯一可以对接近放射性碳测年技术年龄限制的木炭进行可靠去污的技术。(C)2014爱思唯尔B.V.保留所有权利。
Here we report results of a direct inter-comparison of the ability of three radiocarbon pre-treatment techniques to remove radiocarbon contamination introduced by exposing known-radiocarbon-free charcoal made at three different temperatures (300, 400 and 500 degrees C) to environmental contamination on a rainforest floor for one to three years. The initial charcoal had no measureable radiocarbon, but C-14 activity increased after environmental exposure to similar to 1 pMC after one year (apparent age of similar to 40,000 yrs BP) and similar to 5 pMC after three years (apparent age of similar to 25,000 years). For the 400 and 500 degrees C samples, all techniques were able to reduce contamination by >90%. Acid base oxidation (ABOX) provided the most reliable decontamination, reducing the radiocarbon activity of the one year samples to background, and reducing the radiocarbon activity of the three year samples to 0.04 +/- 0.02 pMC or less (apparent age >56,900 yrs BP). The performance of ABOX was superior to that of both acid-base-acid (ABA) and hydrogen pyrolysis (hypy) treatments, with ABA performing better than hypy in most cases. No technique was able to fully remove decontamination from the 300 degrees C charcoal (although ABOX again removed the most contamination), likely due to the incompletely pyrolized nature of the charcoal which is dominated by aromatic clusters of small ring size. All the techniques rely on removing contaminant carbon faster than indigenous carbon and this condition is not met in the case of charcoal produced at temperatures below similar to 350 degrees C. While all pre-treatments are useful for routine sample processing, the results suggest that ABOX is the only technique that can provide reliable decontamination of charcoal of an age close to the dating limit of the radiocarbon dating technique. (c) 2014 Elsevier B.V. All rights reserved.