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Developments and results from the new Hungarian graphite target line
Nuclear Instruments and Methods in Physics Research B 268 (2010) 940–942
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Developments and results from the new Hungarian graphite target line Mihály Molnár a,c,*, Lászlo Rinyu a, Tamás Nagy a, Éva Svingor a, István Futó a, Mihály Veres b, A.J. Timothy Jull c, George S. Burr c, Richard Cruz c, Dana Biddulph c a
Hertelendi Ede Laboratory of Environmental Studies, Institute of Nuclear Research of the Hungarian Academy of Sciences, Bem ter 18/c, Debrecen 4026, Hungary Isotoptech Zrt, Piac u. 53, Debrecen 4025, Hungary c NSF Arizona AMS Laboratory, University of Arizona, 1118 East Fourth St., Tucson, AZ 85721, United States b
a r t i c l e
i n f o
Article history: Available online 8 October 2009 Keywords: 14 C Graphite AMS Catalyst Hydrogen
a b s t r a c t This paper describes upgrades to the first Hungarian graphite line, including improvements to the hydrogen reduction graphitization protocol. Several sets of blanks and known-activity graphite samples were processed in ATOMKI and successfully tested in the NSF Arizona 14C AMS facility in Tucson, Arizona. The test graphites were processed in a completely different manner than normally used at the Arizona Lab. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Radiocarbon dating by gas proportional counting has a long tradition in the Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI). Our Institute would like to enlarge its 14 C dating capabilities by the installation of a tandetron accelerator mass spectrometer, obtained from the Oxford Radiocarbon Accelerator Unit (ORAU). Our laboratory is currently developing sample preparation systems for AMS radiocarbon dating measurements. A Hungarian AMS graphite production facility was established in ATOMKI in 2005. After the first promising results [1], the complete vacuum system was upgraded and the hydrogen-based reduction graphitization protocol was revised and improved. In addition, the entire laboratory building was completely renewed implementing an enhanced air filtration and conditioning system. Several sets of blanks and known-activity graphite samples were processed and tested in cooperation with the NSF Arizona 14C AMS facility in Tucson, Arizona.
The gas handling line (Fig. 1) is made of stainless steel with Swagelok valves and fittings. Using a newly installed Pfeiffer turbo molecular pump (TMU 071 P) we have reached a pressure of <1 103 mbar at the connections for gas ampoules and graphitization rigs. The graphite target production system is similar to the one used at ORAU in Oxford [2], developed by Special Control Devices Company, Debrecen, Hungary. The system consists of two independent furnaces and two Peltier cooler units, each of which contains five positions for reaction rigs [1]. Temperatures of the furnaces and Peltier coolers are set by the digital control system (GTP system) (Fig. 2). Set-point accuracy of the furnace is 1 and 0.1 °C for the Peltier cooler. Graphite targets were prepared by reduction of carbon dioxide gas samples using Fe catalyst and hydrogen gas. The Fe powder we used was less than 325 mesh, 98% purity (Alfa Aesar). The reaction rig consists of a Hy-Lok plug valve, a Swagelok Vacuum Ultra-TorrÒ Union Tee fitting, a quartz tube designed to limit carbon contamination [3], and a glass reusable water trap tube. The volume of the reaction rig is 7 cm3. Before the beginning of the graphitization process, iron powder was activated by pre-reduction in 0.7 bar H2 atmosphere at 450 °C for 90 min. The H2:CO2 ratio was fixed at 2:1 according to our earlier results [1], which suggest that this ratio avoids hydrocarbon formation during graphitization. The initial pressure of a carbon dioxide gas sample was 300–500 mbar. The temperature of the
* Corresponding author. Address: Hertelendi Ede Laboratory of Environmental Studies, Institute of Nuclear Research of the Hungarian Academy of Sciences, Bem ter 18/c, H-4026 Debrecen, Hungary. Tel.: +36 52 509 213; fax: +36 52 416 181. E-mail address: [email protected] (M. Molnár). 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.10.069
941
M. Molnár et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 940–942
powder applied in a graphitization process, suggests that they do not seem to be correlated (Fig. 3). Finally, we tested our whole graphitization process using only Fe powder in the reaction rig in the absence of CO2. It was observed that during reduction steps in H2 atmosphere the iron itself also experiences a significant weight loss (Fig. 4). Most of the blank graphite targets produced in ATOMKI (graphite ID: DeA-) with hydrogen reduction gave good background
Fig. 1. Gas handling line in ATOMKI developed for graphitization of CO2 samples.
Fig. 3. Gravimetric yield deficit vs. amount of applied Fe catalyst.
Fig. 2. Digital control system of ATOMKI graphitization units Block 1 and 2.
water trap during the iron powder activation and the graphitization process was 5 °C. The minimum graphitization time was 300 min, however a typical sample was processed overnight. The 14C background of the gas handling line and the graphite target production system were tested by graphitization of 14C free, old borehole carbon dioxide gas (d13C = 3.4 ± 0.2‰ PDB, purity 4.5, Linde AG, Répcelak, Hungary). We also checked the reliability of the system by graphitizing gas produced from an intercalibration sample VIRI B (consensus 14C age value: 2820 yr BP) [4]. Total conversion of CO2 to graphite was monitored by pressure yield control and also by gravimetric yield data, which was calculated as follows [5]:
Gravimetric yield ð%Þ ¼
weightðmgÞ ½ðFe and C and tubeÞ-ðFe and tubeÞ 100 CO2 sample ðmmolÞ 12 ðmg=mmolÞ
3. Results and discussion Typical pressure yields were 96 ± 2%. Gravimetric yield measurements gave systematically smaller values compared to the actual pressure yields. Comparing this deficit to the amount of Fe
Fig. 4. Weight loss during pre-reduction and graphitization in the absence of CO2.
Table 1 Summary of NSF Arizona Lab
14
C results for ATOMKI produced graphites.
Lab code
Graphite ID
14
Graphite from fossil CO2 gas AA80306 AA80307 AA80308 AA80309 AA80310 AA80314 AA80315 AA80316 AA80317 AA80318 AA80319 AA80320 AA80321 AA80322 AA80323
DeA-75 DeA-76 DeA-77 DeA-78 DeA-79 DeA-98 DeA-99 DeA-100 DeA-102 DeA-103 DeA-104 DeA-105 DeA-106 DeA-107 DeA-108
>49900 >49800 >49800 >49900 >49900 >49600 >47400 >47400 >46500 >49800 >49900 >46900 >46900 >45800 >47200
Graphite from VIRI B sample CO2 gas AA80311 DeA-80 AA80312 DeA-81 AA80313 DeA-82
C age (yr BP)
2893 ± 36 2857 ± 36 2878 ± 36
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M. Molnár et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 940–942
results in comparison with zinc-reduced graphite blanks that are routinely produced in the NSF Arizona Lab (Table 1). Although all of the graphite samples from ATOMKI were processed in a different manner than is usual at the NSF Arizona Lab [6], the mean value of the VIRI B samples measured by the NSF Arizona AMS is consistent with measured by gas proportional counting technique in ATOMKI (2810 ± 30 yr BP) and with the consensus value for this sample (2820 yr BP) as published in the first report of the VIRI project [4]. 4. Conclusions Several sets of blanks and known-activity graphite samples were successfully processed in the ATOMKI upgraded graphite line
and tested in the NSF Arizona 14C AMS facility in Tucson, Arizona. ATOMKI graphites produced comparable results to the Arizona blanks and also agreed with the consensus value of a known-age (VIRI B) sample. References [1] L. Rinyu, I. Futó, Á.Z. Kiss, M. Molnár, É. Svingor, G. Quarta, L. Calcagnile, Radiocarbon 49 (2) (2007) 217. [2] C.R. Bronk, R.E.M. Hedges, Nucl. Instrum. Methods B 123 (1997) 539. [3] J.S. Vogel, J.R. Southon, D.E. Nelson, Nucl. Instrum. Methods B 29 (1987) 50. [4] E.M. Scott, G.T. Cook, P. Naysmith, C. Bryant, D. O’Donnell, Radiocarbon 49 (2) (2007) 409. [5] E.A. Osborne, A.P. McNichol, A.R. Gagnon, D.L. Hutton, G.A. Jones, Nucl. Instrum. Methods B 92 (1994) 158. [6] P.J. Slota, A.J.T. Jull, T.W. Linick, L.J. Toolin, Radiocarbon 29 (2) (1987) 303.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Developments and results from the new Hungarian graphite target line Mihály Molnár a,c,*, Lászlo Rinyu a, Tamás Nagy a, Éva Svingor a, István Futó a, Mihály Veres b, A.J. Timothy Jull c, George S. Burr c, Richard Cruz c, Dana Biddulph c a
Hertelendi Ede Laboratory of Environmental Studies, Institute of Nuclear Research of the Hungarian Academy of Sciences, Bem ter 18/c, Debrecen 4026, Hungary Isotoptech Zrt, Piac u. 53, Debrecen 4025, Hungary c NSF Arizona AMS Laboratory, University of Arizona, 1118 East Fourth St., Tucson, AZ 85721, United States b
a r t i c l e
i n f o
Article history: Available online 8 October 2009 Keywords: 14 C Graphite AMS Catalyst Hydrogen
a b s t r a c t This paper describes upgrades to the first Hungarian graphite line, including improvements to the hydrogen reduction graphitization protocol. Several sets of blanks and known-activity graphite samples were processed in ATOMKI and successfully tested in the NSF Arizona 14C AMS facility in Tucson, Arizona. The test graphites were processed in a completely different manner than normally used at the Arizona Lab. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Radiocarbon dating by gas proportional counting has a long tradition in the Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI). Our Institute would like to enlarge its 14 C dating capabilities by the installation of a tandetron accelerator mass spectrometer, obtained from the Oxford Radiocarbon Accelerator Unit (ORAU). Our laboratory is currently developing sample preparation systems for AMS radiocarbon dating measurements. A Hungarian AMS graphite production facility was established in ATOMKI in 2005. After the first promising results [1], the complete vacuum system was upgraded and the hydrogen-based reduction graphitization protocol was revised and improved. In addition, the entire laboratory building was completely renewed implementing an enhanced air filtration and conditioning system. Several sets of blanks and known-activity graphite samples were processed and tested in cooperation with the NSF Arizona 14C AMS facility in Tucson, Arizona.
The gas handling line (Fig. 1) is made of stainless steel with Swagelok valves and fittings. Using a newly installed Pfeiffer turbo molecular pump (TMU 071 P) we have reached a pressure of <1 103 mbar at the connections for gas ampoules and graphitization rigs. The graphite target production system is similar to the one used at ORAU in Oxford [2], developed by Special Control Devices Company, Debrecen, Hungary. The system consists of two independent furnaces and two Peltier cooler units, each of which contains five positions for reaction rigs [1]. Temperatures of the furnaces and Peltier coolers are set by the digital control system (GTP system) (Fig. 2). Set-point accuracy of the furnace is 1 and 0.1 °C for the Peltier cooler. Graphite targets were prepared by reduction of carbon dioxide gas samples using Fe catalyst and hydrogen gas. The Fe powder we used was less than 325 mesh, 98% purity (Alfa Aesar). The reaction rig consists of a Hy-Lok plug valve, a Swagelok Vacuum Ultra-TorrÒ Union Tee fitting, a quartz tube designed to limit carbon contamination [3], and a glass reusable water trap tube. The volume of the reaction rig is 7 cm3. Before the beginning of the graphitization process, iron powder was activated by pre-reduction in 0.7 bar H2 atmosphere at 450 °C for 90 min. The H2:CO2 ratio was fixed at 2:1 according to our earlier results [1], which suggest that this ratio avoids hydrocarbon formation during graphitization. The initial pressure of a carbon dioxide gas sample was 300–500 mbar. The temperature of the
* Corresponding author. Address: Hertelendi Ede Laboratory of Environmental Studies, Institute of Nuclear Research of the Hungarian Academy of Sciences, Bem ter 18/c, H-4026 Debrecen, Hungary. Tel.: +36 52 509 213; fax: +36 52 416 181. E-mail address: [email protected] (M. Molnár). 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.10.069
941
M. Molnár et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 940–942
powder applied in a graphitization process, suggests that they do not seem to be correlated (Fig. 3). Finally, we tested our whole graphitization process using only Fe powder in the reaction rig in the absence of CO2. It was observed that during reduction steps in H2 atmosphere the iron itself also experiences a significant weight loss (Fig. 4). Most of the blank graphite targets produced in ATOMKI (graphite ID: DeA-) with hydrogen reduction gave good background
Fig. 1. Gas handling line in ATOMKI developed for graphitization of CO2 samples.
Fig. 3. Gravimetric yield deficit vs. amount of applied Fe catalyst.
Fig. 2. Digital control system of ATOMKI graphitization units Block 1 and 2.
water trap during the iron powder activation and the graphitization process was 5 °C. The minimum graphitization time was 300 min, however a typical sample was processed overnight. The 14C background of the gas handling line and the graphite target production system were tested by graphitization of 14C free, old borehole carbon dioxide gas (d13C = 3.4 ± 0.2‰ PDB, purity 4.5, Linde AG, Répcelak, Hungary). We also checked the reliability of the system by graphitizing gas produced from an intercalibration sample VIRI B (consensus 14C age value: 2820 yr BP) [4]. Total conversion of CO2 to graphite was monitored by pressure yield control and also by gravimetric yield data, which was calculated as follows [5]:
Gravimetric yield ð%Þ ¼
weightðmgÞ ½ðFe and C and tubeÞ-ðFe and tubeÞ 100 CO2 sample ðmmolÞ 12 ðmg=mmolÞ
3. Results and discussion Typical pressure yields were 96 ± 2%. Gravimetric yield measurements gave systematically smaller values compared to the actual pressure yields. Comparing this deficit to the amount of Fe
Fig. 4. Weight loss during pre-reduction and graphitization in the absence of CO2.
Table 1 Summary of NSF Arizona Lab
14
C results for ATOMKI produced graphites.
Lab code
Graphite ID
14
Graphite from fossil CO2 gas AA80306 AA80307 AA80308 AA80309 AA80310 AA80314 AA80315 AA80316 AA80317 AA80318 AA80319 AA80320 AA80321 AA80322 AA80323
DeA-75 DeA-76 DeA-77 DeA-78 DeA-79 DeA-98 DeA-99 DeA-100 DeA-102 DeA-103 DeA-104 DeA-105 DeA-106 DeA-107 DeA-108
>49900 >49800 >49800 >49900 >49900 >49600 >47400 >47400 >46500 >49800 >49900 >46900 >46900 >45800 >47200
Graphite from VIRI B sample CO2 gas AA80311 DeA-80 AA80312 DeA-81 AA80313 DeA-82
C age (yr BP)
2893 ± 36 2857 ± 36 2878 ± 36
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M. Molnár et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 940–942
results in comparison with zinc-reduced graphite blanks that are routinely produced in the NSF Arizona Lab (Table 1). Although all of the graphite samples from ATOMKI were processed in a different manner than is usual at the NSF Arizona Lab [6], the mean value of the VIRI B samples measured by the NSF Arizona AMS is consistent with measured by gas proportional counting technique in ATOMKI (2810 ± 30 yr BP) and with the consensus value for this sample (2820 yr BP) as published in the first report of the VIRI project [4]. 4. Conclusions Several sets of blanks and known-activity graphite samples were successfully processed in the ATOMKI upgraded graphite line
and tested in the NSF Arizona 14C AMS facility in Tucson, Arizona. ATOMKI graphites produced comparable results to the Arizona blanks and also agreed with the consensus value of a known-age (VIRI B) sample. References [1] L. Rinyu, I. Futó, Á.Z. Kiss, M. Molnár, É. Svingor, G. Quarta, L. Calcagnile, Radiocarbon 49 (2) (2007) 217. [2] C.R. Bronk, R.E.M. Hedges, Nucl. Instrum. Methods B 123 (1997) 539. [3] J.S. Vogel, J.R. Southon, D.E. Nelson, Nucl. Instrum. Methods B 29 (1987) 50. [4] E.M. Scott, G.T. Cook, P. Naysmith, C. Bryant, D. O’Donnell, Radiocarbon 49 (2) (2007) 409. [5] E.A. Osborne, A.P. McNichol, A.R. Gagnon, D.L. Hutton, G.A. Jones, Nucl. Instrum. Methods B 92 (1994) 158. [6] P.J. Slota, A.J.T. Jull, T.W. Linick, L.J. Toolin, Radiocarbon 29 (2) (1987) 303.