Research Article Received: 1 October 2014
Revised: 21 October 2014
Accepted: 22 October 2014
Published online in Wiley Online Library
Rapid Commun. Mass Spectrom. 2015, 29, 115–118 (wileyonlinelibrary.com) DOI: 10.1002/rcm.7083
Detection of
135Cs
by accelerator mass spectrometry
C. MacDonald1*, C. R. J. Charles1, R. J. Cornett2, X. L. Zhao1, W. E. Kieser1 and A. E. Litherland3 1
Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, ON, K1N 6N5, Canada Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, ON, K1N 6 N5, Canada 3 IsoTrace Laboratory, University of Toronto, 60 St. George St., Toronto, ON, M5S 1A7, Canada 2
RATIONALE: The ability to measure both 135Cs and 137Cs can provide an estimate of the age and source of Cs isotopes in
an environmental sample. Accelerator mass spectrometry (AMS) consistently reports lower abundance sensitivities than other techniques and, with the addition of an on-line reaction cell, simpler isobaric suppression. Therefore, an AMS methodology was developed to measure Cs isotopes using CsF2 as the initial anion. METHODS: The ion beam is passed through the Isobar Separator for Anions (ISA) where it is captured by radiofrequency quadrupoles in a gas cell before injection into the tandem accelerator. In the ISA, the beam reacts with O2 gas, selectively removing the BaF2 and leaving the Cs analyte to be reaccelerated and sent through the remainder of the AMS system. RESULTS: The BaF2 signal was attenuated by a factor of 105 in the ISA while 25% of the original CsF2 current was transmitted into the accelerator. 135Cs was measured without any interference from 133Cs to an abundance sensitivity of 1.3 × 10–10. The abundances of four stable Ba isotopes (masses 133, 134, 135 and 137) were measured and no isotope-dependent bias was detected using the ISA in vacuum. CONCLUSIONS: The results demonstrate the feasibility of measuring long-lived Cs isotopes without Ba interference by AMS with on-line isobar separation and the ability to use shorter lived Cs isotopes for yield tracing. Copyright © 2014 John Wiley & Sons, Ltd.
The usefulness of 134Cs and 137Cs isotope measurements has been well established in radiation protection, age dating, environmental analysis, and reactor diagnostics.[1–3] 134Cs and 137Cs, however, have relatively short half-lives (2.06a and 30a, respectively) which means that the majority of 137 Cs that was created during nuclear weapons testing has decayed, making it increasingly difficult to measure radiometrically. 134C is not created in weapons fallout and any that was released into the environment from the Chernobyl reactor accident has all decayed. In 2011, the Fukushima incident released a large amount of 134Cs; however, this will all also decay away soon. 135Cs is created with nearly the same fission yield as 137Cs (6–7%) and has a half-life of 2.3 million years,[4] making it a possible candidate for long-term analysis. In addition, the 137Cs/135Cs ratio is a useful diagnostic tool.[2] The ability to measure both 135Cs and 137Cs can provide an estimate of the age and source of Cs isotopes in an environmental sample. Traditional methods of decay counting of 135Cs are impractical so measurement by mass spectrometry is potentially more sensitive. Thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICPMS) have been used to measure 135Cs.[1,2] However, neither technique has the
Rapid Commun. Mass Spectrom. 2015, 29, 115–118
EXPERIMENTAL The largest challenge in measuring Cs isotopes by AMS is the isobaric interference from Ba. Although Ba contamination can be greatly reduced by sample preparation techniques, these techniques alone are often insufficient when it comes to the detection of rare long-lived 135Cs at its natural levels.[1,9] Previous ISA configurations have proved effective at
Copyright © 2014 John Wiley & Sons, Ltd.
115
* Correspondence to: C. MacDonald, Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, ON, K1N 6N5, Canada. E-mail: [email protected]
ability of AMS to eliminate isobaric and abundance sensitivity interferences in low level samples (135Cs/133Cs
Revised: 21 October 2014
Accepted: 22 October 2014
Published online in Wiley Online Library
Rapid Commun. Mass Spectrom. 2015, 29, 115–118 (wileyonlinelibrary.com) DOI: 10.1002/rcm.7083
Detection of
135Cs
by accelerator mass spectrometry
C. MacDonald1*, C. R. J. Charles1, R. J. Cornett2, X. L. Zhao1, W. E. Kieser1 and A. E. Litherland3 1
Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, ON, K1N 6N5, Canada Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, ON, K1N 6 N5, Canada 3 IsoTrace Laboratory, University of Toronto, 60 St. George St., Toronto, ON, M5S 1A7, Canada 2
RATIONALE: The ability to measure both 135Cs and 137Cs can provide an estimate of the age and source of Cs isotopes in
an environmental sample. Accelerator mass spectrometry (AMS) consistently reports lower abundance sensitivities than other techniques and, with the addition of an on-line reaction cell, simpler isobaric suppression. Therefore, an AMS methodology was developed to measure Cs isotopes using CsF2 as the initial anion. METHODS: The ion beam is passed through the Isobar Separator for Anions (ISA) where it is captured by radiofrequency quadrupoles in a gas cell before injection into the tandem accelerator. In the ISA, the beam reacts with O2 gas, selectively removing the BaF2 and leaving the Cs analyte to be reaccelerated and sent through the remainder of the AMS system. RESULTS: The BaF2 signal was attenuated by a factor of 105 in the ISA while 25% of the original CsF2 current was transmitted into the accelerator. 135Cs was measured without any interference from 133Cs to an abundance sensitivity of 1.3 × 10–10. The abundances of four stable Ba isotopes (masses 133, 134, 135 and 137) were measured and no isotope-dependent bias was detected using the ISA in vacuum. CONCLUSIONS: The results demonstrate the feasibility of measuring long-lived Cs isotopes without Ba interference by AMS with on-line isobar separation and the ability to use shorter lived Cs isotopes for yield tracing. Copyright © 2014 John Wiley & Sons, Ltd.
The usefulness of 134Cs and 137Cs isotope measurements has been well established in radiation protection, age dating, environmental analysis, and reactor diagnostics.[1–3] 134Cs and 137Cs, however, have relatively short half-lives (2.06a and 30a, respectively) which means that the majority of 137 Cs that was created during nuclear weapons testing has decayed, making it increasingly difficult to measure radiometrically. 134C is not created in weapons fallout and any that was released into the environment from the Chernobyl reactor accident has all decayed. In 2011, the Fukushima incident released a large amount of 134Cs; however, this will all also decay away soon. 135Cs is created with nearly the same fission yield as 137Cs (6–7%) and has a half-life of 2.3 million years,[4] making it a possible candidate for long-term analysis. In addition, the 137Cs/135Cs ratio is a useful diagnostic tool.[2] The ability to measure both 135Cs and 137Cs can provide an estimate of the age and source of Cs isotopes in an environmental sample. Traditional methods of decay counting of 135Cs are impractical so measurement by mass spectrometry is potentially more sensitive. Thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICPMS) have been used to measure 135Cs.[1,2] However, neither technique has the
Rapid Commun. Mass Spectrom. 2015, 29, 115–118
EXPERIMENTAL The largest challenge in measuring Cs isotopes by AMS is the isobaric interference from Ba. Although Ba contamination can be greatly reduced by sample preparation techniques, these techniques alone are often insufficient when it comes to the detection of rare long-lived 135Cs at its natural levels.[1,9] Previous ISA configurations have proved effective at
Copyright © 2014 John Wiley & Sons, Ltd.
115
* Correspondence to: C. MacDonald, Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, ON, K1N 6N5, Canada. E-mail: [email protected]
ability of AMS to eliminate isobaric and abundance sensitivity interferences in low level samples (135Cs/133Cs
