| 刘圣华,史慧霞,蒋雅欣,徐胜,刘冰冰.加速器质谱14C分析石墨制备技术研究进展[J].岩矿测试,2019,38(5):583-597 |
| LIU Sheng-hua,SHI Hui-xia,JIANG Ya-xin,XU Sheng,LIU Bing-bing.Research Progress on Graphite Target Preparation for Accelerator Mass Spectrometry 14C Analysis[J].Rock and Mineral Analysis,2019,38(5):583-597.DOI:10.15898/j.cnki.11-2131/td.201807100082 |
| 加速器质谱14C分析石墨制备技术研究进展 |
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| Research Progress on Graphite Target Preparation for Accelerator Mass Spectrometry 14C Analysis |
| 投稿时间：2018-07-10 修订日期：2019-04-28 |
| DOI：10.15898/j.cnki.11-2131/td.201807100082 |
| 中文关键词: 加速器质谱 14C 石墨制备 微量样品 碳污染 |
| 英文关键词: accelerator mass spectrometry radiocarbon graphite preparation small (ultra-small) sample carbon contamination |
| 基金项目:中国地质科学院基本科研业务费项目（YYWF201517，SK201603） |
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| 中文摘要: |
| 加速器质谱（AMS）是进行14C同位素分析的主要技术手段，而高精度低本底加速器质谱14C分析主要受样品制备技术限制，因此探讨如何提高石墨制备的稳定性和控制碳污染降低本底将有助于产出高质量14C分析数据，突破14C测年上限（约5.0万年），进一步拓宽14C年代学和同位素示踪的应用范畴。本文详细阐述了催化还原法（H2/Fe法、Zn/Fe法和Zn-TiH2/Fe法）制备石墨样品的真空装置和主要工作原理，指出了微量样品石墨制备过程中同位素分馏、石墨产率、束流强度以及精密度与样品量之间存在严重的依赖关系及其抑制方法。着重探讨了石墨制备技术实验条件（还原剂、催化剂、温度等）的优化选择及其与石墨产率、同位素分馏、束流性能之间的内在联系，总结分析了碳污染来源并探寻合适的碳污染控制技术。目前的研究表明最佳实验条件为：H2/Fe法宜采用还原剂H2/CO2（体积比2~2.5），催化剂为源自氢还原单质铁粉（-325目球粒，Fe/C=2~5），温度500~550℃；Zn/Fe法宜采用还原剂Zn/C（质量比50~80），催化剂为源自氢还原单质铁粉（-325目球粒，Fe/C=2~5），Zn反应管温度400~450℃，Fe反应管温度500~550℃。碳污染来源于制备过程中的各个方面，除采用高温除碳的方式外还可采用适当的数学模型加以校正，但还需要更多详细的实验工作来加强现有认识，以期更好地消除碳污染对测试结果的影响。对测年目标组分不稳定的样品（如地下水中的溶解无机碳）应避免样品直接暴露于大气，以减少野外采样过程中现代大气CO2对测量结果的影响。 |
| 英文摘要: |
BACKGROUND:Accelerator mass spectrometry (AMS) is the most popular technique for radiocarbon analysis. However, yielding high precision and low background 14C data by AMS is hindered by sample preparation. Therefore, improving the stability of graphitization and reducing the carbon contamination in the background helps to produce high quality 14C data and break through the 14C dating upper limit (about 50000ya), further broadening the application range of 14C chronology and isotope tracer.
OBJECTIVES:To provide basic reference for beginners or more experienced scientists who are going to set up a radiocarbon sample preparation vacuum line and methods.
METHODS:The development of graphite preparation technology with respect to sample preparation vacuum line apparatus and the underlying principle of H2/Fe, Zn/Fe and Zn-TiH2/Fe methods were reviewed. The advantages and drawbacks of these methods were also discussed. Additionally, the optimization of experimental conditions from the perspective of reductant, catalyst and graphitization temperature, accompanied by the inner relationship with the graphite yield, isotope fractionation and beam performance were emphatically discussed. The sources of carbon contamination and suitable control technology were also argued.
RESULTS:The optimized graphitization conditions by H2/Fe method was H2/CO2=2-2.5 (V/V), -325 meshes ion powder derived from hydrogen reduction with Fe/C=2-5 (m/m), and graphitization temperature of 500-550℃, while by Zn/Fe method it was Zn/C=50-80 (m/m), -325 meshes ion powder derived from hydrogen reduction with Fe/C=2-5 (m/m), and graphitization temperature of 400-450℃ for Zn reaction tube and 500-550℃ for Fe reaction tube. The carbon contamination originated from each step in the sample preparation procedure, which could be either reduced by high-temperature bake or calibrated by mathematical model, but it required more detailed study to strengthen our knowledge and eliminate the effects on results.
CONCLUSIONS:Both of the sample preparation methods used and the optimum of graphitization conditions are critical for good performance of the graphite target and the final precision and accuracy of the measurement, especially for ultra-small size samples. However, these effects could be reduced or even eliminated by optimizing the experimental procedures and the graphitization conditions or subtracting by mathematical models. |
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