加速器质谱~(14)C制样真空系统及石墨制备方法研究
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摘要
~(14)C制样真空系统和石墨制备方法是高精度低本底~(14)C加速器质谱(AMS)测量的关键,而碳污染、石墨产率不稳定和同位素分馏等问题是限制该技术发展的主要难题。为了降低传统在线还原法对制样系统长时间静态真空的要求和解决Zn-TiH_2/Fe火焰封管法中不可控的CH_4等问题,提高石墨合成的稳定性和控制本底,本文建立了基于Zn/Fe火焰封管法的~(14)C制样真空系统和石墨制备方法。通过比较Zn/Fe在线法和Zn/Fe火焰封管法对石墨束流性能以及标样的影响,发现Zn/Fe火焰封管法相较Zn/Fe在线法能明显克服大气泄漏问题,改善化学流程本底(0.24～0.32pMC),提高方法测年上限(47000～48000ya),同时石墨束流输出稳定。进一步利用标准样品和本底样品评估了Zn/Fe火焰封管法的技术特点,实验结果表明该法的精密度好(RSD=0.35%,n=20,标样OXⅡ),准确度高(IAEA系列标样的测定值与认定值线性拟合方程y=0.9969x+0.0013,R~2=1),实验本底低(无机碳46296±271ya和有机碳48341±356ya)。因此,该石墨样品制备真空系统及Zn/Fe火焰封管法技术具有石墨品质优、化学流程本底低、准确度和精密度高等特点,满足高精度低本底~(14)C-AMS测定石墨样品制备要求。
BACKGROUND: The technical keys of high-quality ~(14)C-Accelerator Mass Spectrometry(AMS) analysis with low-background is the sample preparation method and the vacuum line rigs. However, the development of the graphite target preparation method is impeded by extraneous source carbon contamination, unsteady graphitization yield and isotope fractionation.OBJECTIVES: To reduce the requirement of the traditional on-line method on the long-term statical vacuum performance of the sample preparation line, solve the problem of CH_4 produced in the Zn-TiH_2/Fe sealed tube method, while improving the stability of graphitization, and control carbon contamination.METHODS: ~(14)C sample preparation vacuum system and graphite preparation method based on Zn/Fe flame sealing method was established. The effects on the beam current and values of graphite(prepared from OXⅡ and blank samples) between the Zn/Fe on-line method and the Zn/Fe flame sealed tube method were compared. The precision of the Zn/Fe flame sealed tube method was checked with OXⅡ as the unknown sample. Two ‘in-house' blank standards IHEG-Cal and IHEG-Coal were used to evaluate the chemical procedure background of both methods. The other ‘known-value' reference materials of IAEA C2, C3, C5, C7, C8 and C9 were used to validate the accuracy of the Zn/Fe flame sealed tube method.RESULTS: Zn/Fe on-line method can obviously overcome the air leakage, which yields a lower chemical process background(0.24-0.32 pMC) and higher ultimate radiocarbon age(47000-48000 ya) observed in Zn/Fe flame sealed tube method with long-term stable beam current output. It was demonstrated that Zn/Fe sealed tube method was more suitable for graphite target preparation than Zn/Fe on-line method. The results illustrated that the Zn/Fe flame sealed tube method had good reproducibility(RSD=0.35%, n=20, OXⅡ), and high accuracy for a variety of natural samples ranging from dead carbon samples to modern carbon samples(linear fitting formula y=0.9969x+0.0013, R~2=1) with a low background(radiocarbon age of blank 46296±271 ya for inorganic carbon and 48341±356 ya for organic carbon).CONCLUSIONS: The graphite sample preparation vacuum system and the Zn/Fe flame sealing method have the characteristics of excellent graphite quality, low chemical procedure background, high accuracy and high precision, and meet the sample preparation requirements of high-precision and low-background ~(14)C-AMS determination for graphite.
BACKGROUND: The technical keys of high-quality ~(14)C-Accelerator Mass Spectrometry(AMS) analysis with low-background is the sample preparation method and the vacuum line rigs. However, the development of the graphite target preparation method is impeded by extraneous source carbon contamination, unsteady graphitization yield and isotope fractionation.OBJECTIVES: To reduce the requirement of the traditional on-line method on the long-term statical vacuum performance of the sample preparation line, solve the problem of CH_4 produced in the Zn-TiH_2/Fe sealed tube method, while improving the stability of graphitization, and control carbon contamination.METHODS: ~(14)C sample preparation vacuum system and graphite preparation method based on Zn/Fe flame sealing method was established. The effects on the beam current and values of graphite(prepared from OXⅡ and blank samples) between the Zn/Fe on-line method and the Zn/Fe flame sealed tube method were compared. The precision of the Zn/Fe flame sealed tube method was checked with OXⅡ as the unknown sample. Two ‘in-house' blank standards IHEG-Cal and IHEG-Coal were used to evaluate the chemical procedure background of both methods. The other ‘known-value' reference materials of IAEA C2, C3, C5, C7, C8 and C9 were used to validate the accuracy of the Zn/Fe flame sealed tube method.RESULTS: Zn/Fe on-line method can obviously overcome the air leakage, which yields a lower chemical process background(0.24-0.32 pMC) and higher ultimate radiocarbon age(47000-48000 ya) observed in Zn/Fe flame sealed tube method with long-term stable beam current output. It was demonstrated that Zn/Fe sealed tube method was more suitable for graphite target preparation than Zn/Fe on-line method. The results illustrated that the Zn/Fe flame sealed tube method had good reproducibility(RSD=0.35%, n=20, OXⅡ), and high accuracy for a variety of natural samples ranging from dead carbon samples to modern carbon samples(linear fitting formula y=0.9969x+0.0013, R~2=1) with a low background(radiocarbon age of blank 46296±271 ya for inorganic carbon and 48341±356 ya for organic carbon).CONCLUSIONS: The graphite sample preparation vacuum system and the Zn/Fe flame sealing method have the characteristics of excellent graphite quality, low chemical procedure background, high accuracy and high precision, and meet the sample preparation requirements of high-precision and low-background ~(14)C-AMS determination for graphite.
引文
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[19] Krajcar Bronic' I,Horvatincˇic' N,Sironic' A,et al.A new graphite preparation line for AMS 14C dating in the Zagreb Radiocarbon Laboratory[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2010,268(7-8):943-946.
[20] Wacker L,Němec M,Bourquin J.A revolutionary graph-itisation system:Fully automated,compact and simple[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2010,268(7):931-934.
[21] Zoppi U,Crye J,Song Q,et al.Performance evaluation of the new AMS system at Accium BioSciences[J].Radiocarbon,2016,49(1):171-180.
[22] 庞义俊,何明,杨旭冉,等.基于小型单极加速器质谱测量14C的样品制备技术研究[J].原子能科学技术,2017,51(10):1866-1873.Pang Y J,He M,Yang X R,et al.14C sample preparation for compact single stage AMS[J].Atomic Energy Science and Technology,2017,51(10):1866-1873.
[23] Yuan S,Wu X,Gao S,et al.The CO2 preparation system for AMS dating at Peking University[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2000,172(1-4):458-461.
[24] Aerts-Bijma A T,Meijer H A J,van Der Plicht J.AMS sample handling in Groningen[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,1997,123(1-4):221-225.
[2] Kutschera W.Applications of accelerator mass spectrometry[J].International Journal of Mass Spectrometry,2013,349-350(1):203-218.
[3] Fink D.AMS-11 in Rome,2008:Past achievements,current and future trends[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2010,268(7-8):1334-1342.
[4] 管永精,王慧娟,鞠志萍,等.加速器质谱技术及其在地球科学中的应用[J].岩矿测试,2005,24(4):41-47.Guan Y J,Wang H J,Ju Z P,et al.Acclerator mass spectrometry and its applications in geosciences[J].Rock and Mineral Analysis,2005,24(4):41-47.
[5] Synal H-A.Developments in accelerator mass spectrometry[J].International Journal of Mass Spectrometry,2013,349-350:192-202.
[6] Vogel J S,Southon J R,Nelson D E,et al.Performance of catalytically condensed carbon for use in accelerator mass spectrometry[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,1984,5(2):289-293.
[7] Jull A,Donahue D,Hatheway A,et al.Production of graphite targets by deposition from CO/H2 for precision accelerator 14C measurements[J].Radiocarbon,1986,28(2A):191-197.
[8] Slota P,Jull A T,Linick T,et al.Preparation of small samples for 14C accelerator targets by catalytic reduction of CO[J].Radiocarbon,1987,29(2):303-306.
[9] Ertunc T,Xu S,Bryant C L,et al.Progress in AMS target production of sub-milligram samples at the NERC radiocarbon laboratory[J].Radiocarbon,2005,47(3):453-464.
[10] Xu X,Trumbore S E,Zheng S,et al.Modifying a sealed tube zinc reduction method for preparation of AMS graphite targets:Reducing background and attaining high precision[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2007,259(1):320-329.
[11] Khosh M S,Xu X,Trumbore S E.Small-mass graphite preparation by sealed tube zinc reduction method for AMS 14C measurements[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2010,268(7-8):927-930.
[12] Macario K D,Alves E Q,Oliveira F M,et al.Graphitization reaction via zinc reduction:How low can you go?[J].International Journal of Mass Spectrometry,2016,410(1):47-51.
[13] Ding P,Shen C D,Yi W X,et al.Small-mass graphite preparation for AMS 14C measurements performed at GIGCAS,China[J].Radiocarbon,2017,59(3):705-711.
[14] Cheng P,Zhou W,Burr G S,et al.Authentication of Chinese vintage liquors using bomb-pulse 14C[J].Scientific Reports,2016,6:38381-38388.
[15] D’Elia M,Calcagnile L,Quarta G,et al.Sample preparation and blank values at the AMS radiocarbon facility of the University of Lecce[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2004,223-224:278-283.
[16] Marzaioli F,Borriello G,Passariello I,et al.Zinc reduction as an alternative method for AMS radiocarbon dating:Process optimization at CIRCE[J].Radiocarbon,2008,50(1):139-149.
[17] Orsovszki G,Rinyu L.Flame-sealed tube graphitization using zinc as the sole reduction agent:Precision improvement of environMICADAS 14C measurements on graphite targets[J].Radiocarbon,2015,57(5):979-990.
[18] Xu X,Gao P,Salamanca E G.Ultra small-mass graphitization by sealed tube zinc reduction method for AMS 14C measurements[J].Radiocarbon,2013,55(2-3):608-616.
[19] Krajcar Bronic' I,Horvatincˇic' N,Sironic' A,et al.A new graphite preparation line for AMS 14C dating in the Zagreb Radiocarbon Laboratory[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2010,268(7-8):943-946.
[20] Wacker L,Němec M,Bourquin J.A revolutionary graph-itisation system:Fully automated,compact and simple[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2010,268(7):931-934.
[21] Zoppi U,Crye J,Song Q,et al.Performance evaluation of the new AMS system at Accium BioSciences[J].Radiocarbon,2016,49(1):171-180.
[22] 庞义俊,何明,杨旭冉,等.基于小型单极加速器质谱测量14C的样品制备技术研究[J].原子能科学技术,2017,51(10):1866-1873.Pang Y J,He M,Yang X R,et al.14C sample preparation for compact single stage AMS[J].Atomic Energy Science and Technology,2017,51(10):1866-1873.
[23] Yuan S,Wu X,Gao S,et al.The CO2 preparation system for AMS dating at Peking University[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,2000,172(1-4):458-461.
[24] Aerts-Bijma A T,Meijer H A J,van Der Plicht J.AMS sample handling in Groningen[J].Nuclear Instruments and Methods in Physics Research Section B:Beam Interactions with Materials and Atoms,1997,123(1-4):221-225.