Research Progress on Graphite Target Preparation for Accelerator Mass Spectrometry <sup>14</sup>C Analysis

Sheng-hua LIU; Hui-xia SHI; Ya-xin JIANG; Sheng XU; Bing-bing LIU

doi:10.15898/j.cnki.11-2131/td.201807100082

2019 Vol. 38, No. 5

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Sheng-hua LIU, Hui-xia SHI, Ya-xin JIANG, Sheng XU, Bing-bing LIU. 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

Citation:

Sheng-hua LIU, Hui-xia SHI, Ya-xin JIANG, Sheng XU, Bing-bing LIU. 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

Research Progress on Graphite Target Preparation for Accelerator Mass Spectrometry ¹⁴C Analysis

1.
School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
2.
Institute of Hydrology and Environmental Geology, China Academy of Geological Sciences, Shijiazhuang 050061, China
3.
Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China

More Information

Corresponding author: Bing-bing LIU, 408729357@qq.com

Received Date: 10 July 2018

Revised Date: 28 April 2019

Accepted Date: 16 July 2019

Abstract

Abstract

BACKGROUNDAccelerator 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. OBJECTIVESTo provide basic reference for beginners or more experienced scientists who are going to set up a radiocarbon sample preparation vacuum line and methods. METHODSThe 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. RESULTSThe 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. CONCLUSIONSBoth 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.
- accelerator mass spectrometry /
- radiocarbon /
- graphite preparation /
- small (ultra-small) sample /
- carbon contamination

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References

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