For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisons in response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990; Rozanski et al. 1992; Guiliksen and Scott 1995; Scott et al. 1997).&lt;br/&gt; In this report, we provide an update on the current C-14 laboratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those resulting from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating of small samples (milligram size)

Bryant, C.,

Carmi, I.,

Cook, G.T.,

Gulliksen, S.,

Harkness, D.D.,

Heinemeier, J.,

McGee, E.,

Naysmith, P.,

Plicht, J. van der,

Possnert, G.,

Scott, E.M.,

Strydonck, M. van,

English

Bryant, C.

Carmi, I.

Cook, G.T.

Gulliksen, S.

Harkness, D.D.

Heinemeier, J.

Mcgee, E.

Naysmith, P.

Possnert, G.

Scott, E.M.

van Strydonck, M.

Enlighten: Publications

Is comparability of C-14 dates an issue?: A status report on the fourth international radiocarbon intercomparison

McGee, E.

Plicht, J. van der

Strydonck, M. van

University of Groningen Research Database

  
 University of Groningen
Is Comparability of 14C Dates an Issue?: A Status Report on the Fourth International
Radiocarbon Intercomparison
Bryant, C.; Carmi, I.; Cook, G.T.; Gulliksen, S.; Harkness, D.D.; Heinemeier, J.; McGee, E.;
Naysmith, P.; Possnert, G.; Scott, E.M.
Published in:
Radiocarbon
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from
it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date:
2001
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Bryant, C., Carmi, I., Cook, G. T., Gulliksen, S., Harkness, D. D., Heinemeier, J., ... Strydonck, M. V.
(2001). Is Comparability of 14C Dates an Issue?: A Status Report on the Fourth International Radiocarbon
Intercomparison. Radiocarbon, 43(2A), 321-324.
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© 2001 by the Arizona Board of Regents on behalf of the University of Arizona
RADIOCARBON, Vol 43, Nr 2A, 2001, p 321–324
Proceedings of the 17th International 14C Conference, edited by I Carmi and E Boaretto 321
IS COMPARABILITY OF 14C DATES AN ISSUE?: A STATUS REPORT ON THE 
FOURTH INTERNATIONAL RADIOCARBON INTERCOMPARISON
C Bryant1  I Carmi2  G T Cook3  S Gulliksen4  D D Harkness5  J Heinemeier6  E McGee7 
P Naysmith3  G Possnert8  E M Scott5,9  J van der Plicht10  M van Strydonck11 
ABSTRACT. For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisons
in response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990;
Rozanski et al. 1992; Gulliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current 14C lab-
oratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those result-
ing from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating of
small samples (milligram size).
INTRODUCTION
Comparability of radiocarbon age measurements has long been seen by laboratories and users as an
important issue. As the availability of routine accelerator mass spectrometry dating has become
more widespread, questions and doubts have been raised concerning the comparability and reliabil-
ity of radiometric dating and accelerator mass spectrometry (AMS). Occasionally, and in some cir-
cumstances, significant differences have been observed between the radiometric and AMS measure-
ments. 
The 14C community has been involved in an extensive program of intercomparisons with the most
recent example (FIRI) having the objectives of:
 Demonstration of the comparability of routine analyses by both AMS and radiometric labs;
 Quantification of the extent of, and sources of, any variation;
 Investigation of the effects of sample size, pretreatment and precision requirements on the
results.
The issues of comparability and reliability go beyond the basic metrological principle, and must con-
front the differing sample size requirements of AMS and radiometric methods. In the following sec-
tions, we describe the current laboratory intercomparison and explore how it tackles comparability.
The Current Intercomparison (FIRI)
As in previous intercomparisons (Gulliksen and Scott 1995), FIRI has focused on the use of natural
materials, and has also implemented a two-stage design, with a set of core samples and a set of
optional samples. In addition, two samples were identified for sample size and precision investiga-
tions.
1NERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East Kilbride, Scotland
2Centre for Archaeological Science, Weizmann Institute, Rehovot, Israel
3SUERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East Kilbride, Scotland
4National 14C Laboratory, NUST, Trondheim, Norway
5Department of Statistics, University of Glasgow, Scotland
6AMS laboratory, Institute of Physics and Astronomy, University of Aarhus, Aarhus, Denmark
7Department of Experimental Physics, University College, Dublin, Eire
8Tandem Accelerator Laboratory, University of Uppsala, Uppsala, Sweden
9Corresponding author. Email: marian@stats.gla.ac.uk.
10CIO, University of Groningen, Groningen, the Netherlands
11Koninklijk Institut voor Kunstpatrimonium, Brussels, Belgium
322 C Bryant et al.
The core samples comprised a total of 10 samples of 5 materials; wood, barley, humic acid, cellulose
and turbidite. 
Wood samples
Approximately 10 kg and 12 kg of dendro-dated wood (comprising 20 and 40 rings, respectively)
were cut to appropriate sizes (at least 40 g for radiometric and at least 4 g for AMS) before being
labeled and bagged. Other wood samples were subdivided to appropriate sample sizes (approxi-
mately 50 g and 5 g, respectively for radiometric and AMS labs). 
Two cellulose samples were also prepared from dendro-dated wood (16 kg and 10 kg, respectively)
using an acid/alkali/acid procedure followed by bleaching using sodium chlorite. The extract was
then washed, dried at 40 °C, physically mixed and then packaged into samples of 10 g and 1 g,
respectively for radiometric and AMS laboratories.
Other Materials
Turbidite carbonate (mainly coccolith calcite) was taken from a single distal turbidite, derived
from the middle ungraded deposit. The sample was immediately oven dried (approximately 50 °C),
ground and fully homogenized before being bagged (sample size approximately 100 g and 10 g,
respectively) and labeled. 
A humic acid sample from a coastal cliff deposit at St Bees Head in Cumbria, northwest England
which has been exposed by erosion was also prepared. A large peat sample was digested in 2% KOH
at 80 °C. The alkali extracts were filtered and combined into a large container until over 150 L of
solution were obtained. The bulk aqueous solution was then thoroughly mixed and the humic acid
precipitated by adjusting the pH to 3 by the stirred addition of 2M H2SO4. The solid precipitate was
then recovered by filtration and given a preliminary wash with cold distilled water. It was then re-
dissolved, re-precipitated and dried. After drying to a constant weight, the crystalline humic acid
was washed free of sulfate inclusions with hot distilled water. The sample was then re-dried and
ground to obtain a relatively standard size of crystal. Samples for radiometric and AMS measure-
ment are approximately 10 g and 1 g, respectively.
Barley mash is produced as a by-product of whisky manufacture. A sample (approximately 15 kg)
from the current year was force dried and physically mixed. Samples are of approximately 50 g and
5 g, respectively, for radiometric and AMS laboratories.
Optional Samples
The optional samples included two wood samples (one dendro-dated), a whole peat sample (linked
to the humic acid core sample) for both AMS and radiometric analysis and three separate mammoth
tusks spanning the 14C age range, leather and fabric from a scythian burial and parchment for AMS
analysis only. 
Homogeneity Testing
The key sample requirement in an intercomparison is that of homogeneity, which simply means that
any sub-sample, taken randomly from the bulk material is representative of that material and that
when dealing with trace element assay, that the trace element is uniformly distributed throughout the
bulk material. 
Comparability of 14C Dates 323
Each material (with the exception of the dendro-dated wood) was independently tested in two labo-
ratories (where possible a radiometric and an AMS laboratory). A minimum of eight analyses was
required for homogeneity testing of each core material. Homogeneity testing for the barley mash
was carried out by radiometric analysis at the SUERC 14C laboratory, East Kilbride and 14C labora-
tory, University College Dublin, for the first of the cellulose samples, homogeneity testing was car-
ried out by radiometric analysis at the SUERC 14C laboratory, East Kilbride, and at the 14C labora-
tory of the Weizmann Institute. 
For the turbidite, homogeneity testing was carried out by radiometric and AMS analysis at the
National 14C laboratory, NUST, Trondheim and Tandem accelerator laboratory, University of Upp-
sala. For the second cellulose sample, homogeneity testing was carried out by radiometric analysis
at the KIK 14C laboratory, Brussels and by AMS at the 14C laboratory, University of Groningen. For
the humic acid sample, homogeneity testing was carried out by radiometric and AMS analysis at the
NERC 14C laboratory, East Kilbride and AMS laboratory, University of Aarhus. 
The results of the homogeneity testing were satisfactory and are being reported separately.
Current Status of FIRI
All core samples were distributed in September 1999, the deadline for results being August 2000.
Currently over 80 sets of results have been returned and their analysis is underway. The full analysis
was presented and discussed at an FIRI workshop in March 2001.
Optional samples are currently being distributed to participating laboratories.
Future Needs
There is still a need in routine dating for regular checks which can be satisfied by materials such as
the IAEA reference materials and by programmes such as TIRI and FIRI which are directed more at
large sample dating, but there is clearly also a need for further exploration of comparability and vari-
ation at the limits of the technique (very small or very old samples).
The issue of sample homogeneity becomes more and more important, indeed the definition of a sam-
ple becomes critical as smaller and smaller (compound specific) samples are dated. There are diffi-
culties in taking a representative sub-sample from the bulk material. Indeed how do we know it is
representative? Do we fully know the potential scale of natural 14C variation in sample matrices?
Continuation in this work is important, the linkage to previous work provides an invaluable continu-
ity (e.g. IAEA and other reference materials are still available and should be used), but in addition,
further new materials should be sought, and these should include known age material. For the con-
ventional laboratory, the typical sample requirement might be 5 g C with sample age ranges from <1
to approximately 7–8 half-lives. However, for the AMS labs and for those conventional labs where
small samples are dated, we need to explore the natural variation in reportedly single event samples
(deposits of charcoal, grain from a single growing season, single insects from a well defined stra-
tum). This information is not just important for the laboratory, but is also of fundamental importance
for the sample submitter who must select samples referring to the event of interest. Future inter-com-
parisons therefore will see some shift in emphasis to reflect these challenging issues. 
CONCLUSIONS
In general, past intercomparisons have shown direct comparability of the AMS and radiometric lab-
oratories but have also emphasized the potential variation that can be observed as a result of the sam-
324 C Bryant et al.
ple heterogeneity, a feature which gains increasing prominence as the sample size requirement
decreases. In the current laboratory intercomparison, comparability still remains the major issue, but
the emphasis has shifted from comparability of the measurement to the more difficult issue of com-
parability of the samples and sampling. A full report on FIRI will be available by the end of 2001
and a special issue of this journal will appear in 2002.
ACKNOWLEDGMENTS
This work has been supported by NERC (GR9/03389) and the European Commission (SMT4-
CT98-2265). 
We also wish to express our gratitude to the sample providers, Mike Baillie, Marco Spurk, Roy Swit-
sur, Glengoyne Distilleries, Ganna Zaitseva, Kh Arslanov, Steinar Gulliksen, Mark van Strydonck,
John Thomson, Israel Carmi, and Alan Hogg.
REFERENCES
Scott EM, Aitchison TC, Harkness DD, Cook GT, Baxter
MS. 1990. An overview of all three stages of the inter-
national radiocarbon intercomparison. Radiocarbon
32(2):303–19.
Rozanski K, Stichler W, Gonfiantini R, Scott E M, Beu-
kens R P, Kromer B, van der Plicht J. 1992.  The IAEA
14C intercomparison exercise 1990. Radiocarbon
34(3):506–19.
Gulliksen S, Scott EM. 1995. TIRI report. Radiocarbon
37(2):820–1.
Scott EM, Harkness DD, Cook GT. 1997. Analytical pro-
tocol and quality assurance for 14C analyses: proposal
for a further intercomparison. Radiocarbon 39(3):
347–51.


Is Comparability of 14C Dates an Issue?: A Status Report on the Fourth International Radiocarbon Intercomparison

For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisons in response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990; Rozanski et al. 1992; Guiliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current C-14 laboratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those resulting from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating of small samples (milligram size).</p

ARTS repository - University of Groningen

   University of GroningenIs Comparability of 14C Dates an Issue?: A Status Report on the Fourth InternationalRadiocarbon IntercomparisonBryant, C.; Carmi, I.; Cook, G.T.; Gulliksen, S.; Harkness, D.D.; Heinemeier, J.; McGee, E.;Naysmith, P.; Possnert, G.; Scott, E.M.Published in:RadiocarbonIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2001Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Bryant, C., Carmi, I., Cook, G. T., Gulliksen, S., Harkness, D. D., Heinemeier, J., McGee, E., Naysmith, P.,Possnert, G., Scott, E. M., Plicht, J. V. D., & Strydonck, M. V. (2001). Is Comparability of 14C Dates anIssue?: A Status Report on the Fourth International Radiocarbon Intercomparison. Radiocarbon, 43(2A),321-324.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.© 2001 by the Arizona Board of Regents on behalf of the University of ArizonaRADIOCARBON, Vol 43, Nr 2A, 2001, p 321–324Proceedings of the 17th International 14C Conference, edited by I Carmi and E Boaretto 321IS COMPARABILITY OF 14C DATES AN ISSUE?: A STATUS REPORT ON THE FOURTH INTERNATIONAL RADIOCARBON INTERCOMPARISONC Bryant1  I Carmi2  G T Cook3  S Gulliksen4  D D Harkness5  J Heinemeier6  E McGee7 P Naysmith3  G Possnert8  E M Scott5,9  J van der Plicht10  M van Strydonck11 ABSTRACT. For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisonsin response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990;Rozanski et al. 1992; Gulliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current 14C lab-oratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those result-ing from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating ofsmall samples (milligram size).INTRODUCTIONComparability of radiocarbon age measurements has long been seen by laboratories and users as animportant issue. As the availability of routine accelerator mass spectrometry dating has becomemore widespread, questions and doubts have been raised concerning the comparability and reliabil-ity of radiometric dating and accelerator mass spectrometry (AMS). Occasionally, and in some cir-cumstances, significant differences have been observed between the radiometric and AMS measure-ments. The 14C community has been involved in an extensive program of intercomparisons with the mostrecent example (FIRI) having the objectives of: Demonstration of the comparability of routine analyses by both AMS and radiometric labs; Quantification of the extent of, and sources of, any variation; Investigation of the effects of sample size, pretreatment and precision requirements on theresults.The issues of comparability and reliability go beyond the basic metrological principle, and must con-front the differing sample size requirements of AMS and radiometric methods. In the following sec-tions, we describe the current laboratory intercomparison and explore how it tackles comparability.The Current Intercomparison (FIRI)As in previous intercomparisons (Gulliksen and Scott 1995), FIRI has focused on the use of naturalmaterials, and has also implemented a two-stage design, with a set of core samples and a set ofoptional samples. In addition, two samples were identified for sample size and precision investiga-tions.1NERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East Kilbride, Scotland2Centre for Archaeological Science, Weizmann Institute, Rehovot, Israel3SUERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East Kilbride, Scotland4National 14C Laboratory, NUST, Trondheim, Norway5Department of Statistics, University of Glasgow, Scotland6AMS laboratory, Institute of Physics and Astronomy, University of Aarhus, Aarhus, Denmark7Department of Experimental Physics, University College, Dublin, Eire8Tandem Accelerator Laboratory, University of Uppsala, Uppsala, Sweden9Corresponding author. Email: marian@stats.gla.ac.uk.10CIO, University of Groningen, Groningen, the Netherlands11Koninklijk Institut voor Kunstpatrimonium, Brussels, Belgium322 C Bryant et al.The core samples comprised a total of 10 samples of 5 materials; wood, barley, humic acid, celluloseand turbidite. Wood samplesApproximately 10 kg and 12 kg of dendro-dated wood (comprising 20 and 40 rings, respectively)were cut to appropriate sizes (at least 40 g for radiometric and at least 4 g for AMS) before beinglabeled and bagged. Other wood samples were subdivided to appropriate sample sizes (approxi-mately 50 g and 5 g, respectively for radiometric and AMS labs). Two cellulose samples were also prepared from dendro-dated wood (16 kg and 10 kg, respectively)using an acid/alkali/acid procedure followed by bleaching using sodium chlorite. The extract wasthen washed, dried at 40 °C, physically mixed and then packaged into samples of 10 g and 1 g,respectively for radiometric and AMS laboratories.Other MaterialsTurbidite carbonate (mainly coccolith calcite) was taken from a single distal turbidite, derivedfrom the middle ungraded deposit. The sample was immediately oven dried (approximately 50 °C),ground and fully homogenized before being bagged (sample size approximately 100 g and 10 g,respectively) and labeled. A humic acid sample from a coastal cliff deposit at St Bees Head in Cumbria, northwest Englandwhich has been exposed by erosion was also prepared. A large peat sample was digested in 2% KOHat 80 °C. The alkali extracts were filtered and combined into a large container until over 150 L ofsolution were obtained. The bulk aqueous solution was then thoroughly mixed and the humic acidprecipitated by adjusting the pH to 3 by the stirred addition of 2M H2SO4. The solid precipitate wasthen recovered by filtration and given a preliminary wash with cold distilled water. It was then re-dissolved, re-precipitated and dried. After drying to a constant weight, the crystalline humic acidwas washed free of sulfate inclusions with hot distilled water. The sample was then re-dried andground to obtain a relatively standard size of crystal. Samples for radiometric and AMS measure-ment are approximately 10 g and 1 g, respectively.Barley mash is produced as a by-product of whisky manufacture. A sample (approximately 15 kg)from the current year was force dried and physically mixed. Samples are of approximately 50 g and5 g, respectively, for radiometric and AMS laboratories.Optional SamplesThe optional samples included two wood samples (one dendro-dated), a whole peat sample (linkedto the humic acid core sample) for both AMS and radiometric analysis and three separate mammothtusks spanning the 14C age range, leather and fabric from a scythian burial and parchment for AMSanalysis only. Homogeneity TestingThe key sample requirement in an intercomparison is that of homogeneity, which simply means thatany sub-sample, taken randomly from the bulk material is representative of that material and thatwhen dealing with trace element assay, that the trace element is uniformly distributed throughout thebulk material. Comparability of 14C Dates 323Each material (with the exception of the dendro-dated wood) was independently tested in two labo-ratories (where possible a radiometric and an AMS laboratory). A minimum of eight analyses wasrequired for homogeneity testing of each core material. Homogeneity testing for the barley mashwas carried out by radiometric analysis at the SUERC 14C laboratory, East Kilbride and 14C labora-tory, University College Dublin, for the first of the cellulose samples, homogeneity testing was car-ried out by radiometric analysis at the SUERC 14C laboratory, East Kilbride, and at the 14C labora-tory of the Weizmann Institute. For the turbidite, homogeneity testing was carried out by radiometric and AMS analysis at theNational 14C laboratory, NUST, Trondheim and Tandem accelerator laboratory, University of Upp-sala. For the second cellulose sample, homogeneity testing was carried out by radiometric analysisat the KIK 14C laboratory, Brussels and by AMS at the 14C laboratory, University of Groningen. Forthe humic acid sample, homogeneity testing was carried out by radiometric and AMS analysis at theNERC 14C laboratory, East Kilbride and AMS laboratory, University of Aarhus. The results of the homogeneity testing were satisfactory and are being reported separately.Current Status of FIRIAll core samples were distributed in September 1999, the deadline for results being August 2000.Currently over 80 sets of results have been returned and their analysis is underway. The full analysiswas presented and discussed at an FIRI workshop in March 2001.Optional samples are currently being distributed to participating laboratories.Future NeedsThere is still a need in routine dating for regular checks which can be satisfied by materials such asthe IAEA reference materials and by programmes such as TIRI and FIRI which are directed more atlarge sample dating, but there is clearly also a need for further exploration of comparability and vari-ation at the limits of the technique (very small or very old samples).The issue of sample homogeneity becomes more and more important, indeed the definition of a sam-ple becomes critical as smaller and smaller (compound specific) samples are dated. There are diffi-culties in taking a representative sub-sample from the bulk material. Indeed how do we know it isrepresentative? Do we fully know the potential scale of natural 14C variation in sample matrices?Continuation in this work is important, the linkage to previous work provides an invaluable continu-ity (e.g. IAEA and other reference materials are still available and should be used), but in addition,further new materials should be sought, and these should include known age material. For the con-ventional laboratory, the typical sample requirement might be 5 g C with sample age ranges from <1to approximately 7–8 half-lives. However, for the AMS labs and for those conventional labs wheresmall samples are dated, we need to explore the natural variation in reportedly single event samples(deposits of charcoal, grain from a single growing season, single insects from a well defined stra-tum). This information is not just important for the laboratory, but is also of fundamental importancefor the sample submitter who must select samples referring to the event of interest. Future inter-com-parisons therefore will see some shift in emphasis to reflect these challenging issues. CONCLUSIONSIn general, past intercomparisons have shown direct comparability of the AMS and radiometric lab-oratories but have also emphasized the potential variation that can be observed as a result of the sam-324 C Bryant et al.ple heterogeneity, a feature which gains increasing prominence as the sample size requirementdecreases. In the current laboratory intercomparison, comparability still remains the major issue, butthe emphasis has shifted from comparability of the measurement to the more difficult issue of com-parability of the samples and sampling. A full report on FIRI will be available by the end of 2001and a special issue of this journal will appear in 2002.ACKNOWLEDGMENTSThis work has been supported by NERC (GR9/03389) and the European Commission (SMT4-CT98-2265). We also wish to express our gratitude to the sample providers, Mike Baillie, Marco Spurk, Roy Swit-sur, Glengoyne Distilleries, Ganna Zaitseva, Kh Arslanov, Steinar Gulliksen, Mark van Strydonck,John Thomson, Israel Carmi, and Alan Hogg.REFERENCESScott EM, Aitchison TC, Harkness DD, Cook GT, BaxterMS. 1990. An overview of all three stages of the inter-national radiocarbon intercomparison. Radiocarbon32(2):303–19.Rozanski K, Stichler W, Gonfiantini R, Scott E M, Beu-kens R P, Kromer B, van der Plicht J. 1992.  The IAEA14C intercomparison exercise 1990. Radiocarbon34(3):506–19.Gulliksen S, Scott EM. 1995. TIRI report. Radiocarbon37(2):820–1.Scott EM, Harkness DD, Cook GT. 1997. Analytical pro-tocol and quality assurance for 14C analyses: proposalfor a further intercomparison. Radiocarbon 39(3):347–51.

Enlighten

© 2001 by the Arizona Board of Regents on behalf of the University of ArizonaRADIOCARBON, Vol 43, Nr 2A, 2001, p 321–324Proceedings of the 17th International 14C Conference, edited by I Carmi and E Boaretto 321IS COMPARABILITY OF 14C DATES AN ISSUE?: A STATUS REPORT ON THE FOURTH INTERNATIONAL RADIOCARBON INTERCOMPARISONC Bryant1  I Carmi2  G T Cook3  S Gulliksen4  D D Harkness5  J Heinemeier6  E McGee7 P Naysmith3  G Possnert8  E M Scott5,9  J van der Plicht10  M van Strydonck11 ABSTRACT. For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisonsin response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990;Rozanski et al. 1992; Gulliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current 14C lab-oratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those result-ing from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating ofsmall samples (milligram size).INTRODUCTIONComparability of radiocarbon age measurements has long been seen by laboratories and users as animportant issue. As the availability of routine accelerator mass spectrometry dating has becomemore widespread, questions and doubts have been raised concerning the comparability and reliabil-ity of radiometric dating and accelerator mass spectrometry (AMS). Occasionally, and in some cir-cumstances, significant differences have been observed between the radiometric and AMS measure-ments. The 14C community has been involved in an extensive program of intercomparisons with the mostrecent example (FIRI) having the objectives of: Demonstration of the comparability of routine analyses by both AMS and radiometric labs; Quantification of the extent of, and sources of, any variation; Investigation of the effects of sample size, pretreatment and precision requirements on theresults.The issues of comparability and reliability go beyond the basic metrological principle, and must con-front the differing sample size requirements of AMS and radiometric methods. In the following sec-tions, we describe the current laboratory intercomparison and explore how it tackles comparability.The Current Intercomparison (FIRI)As in previous intercomparisons (Gulliksen and Scott 1995), FIRI has focused on the use of naturalmaterials, and has also implemented a two-stage design, with a set of core samples and a set ofoptional samples. In addition, two samples were identified for sample size and precision investiga-tions.1NERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East Kilbride, Scotland2Centre for Archaeological Science, Weizmann Institute, Rehovot, Israel3SUERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East Kilbride, Scotland4National 14C Laboratory, NUST, Trondheim, Norway5Department of Statistics, University of Glasgow, Scotland6AMS laboratory, Institute of Physics and Astronomy, University of Aarhus, Aarhus, Denmark7Department of Experimental Physics, University College, Dublin, Eire8Tandem Accelerator Laboratory, University of Uppsala, Uppsala, Sweden9Corresponding author. Email: marian@stats.gla.ac.uk.10CIO, University of Groningen, Groningen, the Netherlands11Koninklijk Institut voor Kunstpatrimonium, Brussels, Belgium322 C Bryant et al.The core samples comprised a total of 10 samples of 5 materials; wood, barley, humic acid, celluloseand turbidite. Wood samplesApproximately 10 kg and 12 kg of dendro-dated wood (comprising 20 and 40 rings, respectively)were cut to appropriate sizes (at least 40 g for radiometric and at least 4 g for AMS) before beinglabeled and bagged. Other wood samples were subdivided to appropriate sample sizes (approxi-mately 50 g and 5 g, respectively for radiometric and AMS labs). Two cellulose samples were also prepared from dendro-dated wood (16 kg and 10 kg, respectively)using an acid/alkali/acid procedure followed by bleaching using sodium chlorite. The extract wasthen washed, dried at 40 °C, physically mixed and then packaged into samples of 10 g and 1 g,respectively for radiometric and AMS laboratories.Other MaterialsTurbidite carbonate (mainly coccolith calcite) was taken from a single distal turbidite, derivedfrom the middle ungraded deposit. The sample was immediately oven dried (approximately 50 °C),ground and fully homogenized before being bagged (sample size approximately 100 g and 10 g,respectively) and labeled. A humic acid sample from a coastal cliff deposit at St Bees Head in Cumbria, northwest Englandwhich has been exposed by erosion was also prepared. A large peat sample was digested in 2% KOHat 80 °C. The alkali extracts were filtered and combined into a large container until over 150 L ofsolution were obtained. The bulk aqueous solution was then thoroughly mixed and the humic acidprecipitated by adjusting the pH to 3 by the stirred addition of 2M H2SO4. The solid precipitate wasthen recovered by filtration and given a preliminary wash with cold distilled water. It was then re-dissolved, re-precipitated and dried. After drying to a constant weight, the crystalline humic acidwas washed free of sulfate inclusions with hot distilled water. The sample was then re-dried andground to obtain a relatively standard size of crystal. Samples for radiometric and AMS measure-ment are approximately 10 g and 1 g, respectively.Barley mash is produced as a by-product of whisky manufacture. A sample (approximately 15 kg)from the current year was force dried and physically mixed. Samples are of approximately 50 g and5 g, respectively, for radiometric and AMS laboratories.Optional SamplesThe optional samples included two wood samples (one dendro-dated), a whole peat sample (linkedto the humic acid core sample) for both AMS and radiometric analysis and three separate mammothtusks spanning the 14C age range, leather and fabric from a scythian burial and parchment for AMSanalysis only. Homogeneity TestingThe key sample requirement in an intercomparison is that of homogeneity, which simply means thatany sub-sample, taken randomly from the bulk material is representative of that material and thatwhen dealing with trace element assay, that the trace element is uniformly distributed throughout thebulk material. Comparability of 14C Dates 323Each material (with the exception of the dendro-dated wood) was independently tested in two labo-ratories (where possible a radiometric and an AMS laboratory). A minimum of eight analyses wasrequired for homogeneity testing of each core material. Homogeneity testing for the barley mashwas carried out by radiometric analysis at the SUERC 14C laboratory, East Kilbride and 14C labora-tory, University College Dublin, for the first of the cellulose samples, homogeneity testing was car-ried out by radiometric analysis at the SUERC 14C laboratory, East Kilbride, and at the 14C labora-tory of the Weizmann Institute. For the turbidite, homogeneity testing was carried out by radiometric and AMS analysis at theNational 14C laboratory, NUST, Trondheim and Tandem accelerator laboratory, University of Upp-sala. For the second cellulose sample, homogeneity testing was carried out by radiometric analysisat the KIK 14C laboratory, Brussels and by AMS at the 14C laboratory, University of Groningen. Forthe humic acid sample, homogeneity testing was carried out by radiometric and AMS analysis at theNERC 14C laboratory, East Kilbride and AMS laboratory, University of Aarhus. The results of the homogeneity testing were satisfactory and are being reported separately.Current Status of FIRIAll core samples were distributed in September 1999, the deadline for results being August 2000.Currently over 80 sets of results have been returned and their analysis is underway. The full analysiswas presented and discussed at an FIRI workshop in March 2001.Optional samples are currently being distributed to participating laboratories.Future NeedsThere is still a need in routine dating for regular checks which can be satisfied by materials such asthe IAEA reference materials and by programmes such as TIRI and FIRI which are directed more atlarge sample dating, but there is clearly also a need for further exploration of comparability and vari-ation at the limits of the technique (very small or very old samples).The issue of sample homogeneity becomes more and more important, indeed the definition of a sam-ple becomes critical as smaller and smaller (compound specific) samples are dated. There are diffi-culties in taking a representative sub-sample from the bulk material. Indeed how do we know it isrepresentative? Do we fully know the potential scale of natural 14C variation in sample matrices?Continuation in this work is important, the linkage to previous work provides an invaluable continu-ity (e.g. IAEA and other reference materials are still available and should be used), but in addition,further new materials should be sought, and these should include known age material. For the con-ventional laboratory, the typical sample requirement might be 5 g C with sample age ranges from <1to approximately 7–8 half-lives. However, for the AMS labs and for those conventional labs wheresmall samples are dated, we need to explore the natural variation in reportedly single event samples(deposits of charcoal, grain from a single growing season, single insects from a well defined stra-tum). This information is not just important for the laboratory, but is also of fundamental importancefor the sample submitter who must select samples referring to the event of interest. Future inter-com-parisons therefore will see some shift in emphasis to reflect these challenging issues. CONCLUSIONSIn general, past intercomparisons have shown direct comparability of the AMS and radiometric lab-oratories but have also emphasized the potential variation that can be observed as a result of the sam-324 C Bryant et al.ple heterogeneity, a feature which gains increasing prominence as the sample size requirementdecreases. In the current laboratory intercomparison, comparability still remains the major issue, butthe emphasis has shifted from comparability of the measurement to the more difficult issue of com-parability of the samples and sampling. A full report on FIRI will be available by the end of 2001and a special issue of this journal will appear in 2002.ACKNOWLEDGMENTSThis work has been supported by NERC (GR9/03389) and the European Commission (SMT4-CT98-2265). We also wish to express our gratitude to the sample providers, Mike Baillie, Marco Spurk, Roy Swit-sur, Glengoyne Distilleries, Ganna Zaitseva, Kh Arslanov, Steinar Gulliksen, Mark van Strydonck,John Thomson, Israel Carmi, and Alan Hogg.REFERENCESScott EM, Aitchison TC, Harkness DD, Cook GT, BaxterMS. 1990. An overview of all three stages of the inter-national radiocarbon intercomparison. Radiocarbon32(2):303–19.Rozanski K, Stichler W, Gonfiantini R, Scott E M, Beu-kens R P, Kromer B, van der Plicht J. 1992.  The IAEA14C intercomparison exercise 1990. Radiocarbon34(3):506–19.Gulliksen S, Scott EM. 1995. TIRI report. Radiocarbon37(2):820–1.Scott EM, Harkness DD, Cook GT. 1997. Analytical pro-tocol and quality assurance for 14C analyses: proposalfor a further intercomparison. Radiocarbon 39(3):347–51.

An overview of all three stages of the international radiocarbon intercomparison.

Analytical protocol and quality assurance for 14C analyses: proposal for a further intercomparison.

University of Groningen

   University of GroningenIs Comparability of 14C Dates an Issue?: A Status Report on the Fourth InternationalRadiocarbon IntercomparisonBryant, C.; Carmi, I.; Cook, G.T.; Gulliksen, S.; Harkness, D.D.; Heinemeier, J.; McGee, E.;Naysmith, P.; Possnert, G.; Scott, E.M.Published in:RadiocarbonIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2001Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Bryant, C., Carmi, I., Cook, G. T., Gulliksen, S., Harkness, D. D., Heinemeier, J., ... Strydonck, M. V.(2001). Is Comparability of 14C Dates an Issue?: A Status Report on the Fourth International RadiocarbonIntercomparison. Radiocarbon, 43(2A), 321-324.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019© 2001 by the Arizona Board of Regents on behalf of the University of ArizonaRADIOCARBON, Vol 43, Nr 2A, 2001, p 321–324Proceedings of the 17th International 14C Conference, edited by I Carmi and E Boaretto 321IS COMPARABILITY OF 14C DATES AN ISSUE?: A STATUS REPORT ON THE FOURTH INTERNATIONAL RADIOCARBON INTERCOMPARISONC Bryant1  I Carmi2  G T Cook3  S Gulliksen4  D D Harkness5  J Heinemeier6  E McGee7 P Naysmith3  G Possnert8  E M Scott5,9  J van der Plicht10  M van Strydonck11 ABSTRACT. For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisonsin response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990;Rozanski et al. 1992; Gulliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current 14C lab-oratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those result-ing from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating ofsmall samples (milligram size).INTRODUCTIONComparability of radiocarbon age measurements has long been seen by laboratories and users as animportant issue. As the availability of routine accelerator mass spectrometry dating has becomemore widespread, questions and doubts have been raised concerning the comparability and reliabil-ity of radiometric dating and accelerator mass spectrometry (AMS). Occasionally, and in some cir-cumstances, significant differences have been observed between the radiometric and AMS measure-ments. The 14C community has been involved in an extensive program of intercomparisons with the mostrecent example (FIRI) having the objectives of: Demonstration of the comparability of routine analyses by both AMS and radiometric labs; Quantification of the extent of, and sources of, any variation; Investigation of the effects of sample size, pretreatment and precision requirements on theresults.The issues of comparability and reliability go beyond the basic metrological principle, and must con-front the differing sample size requirements of AMS and radiometric methods. In the following sec-tions, we describe the current laboratory intercomparison and explore how it tackles comparability.The Current Intercomparison (FIRI)As in previous intercomparisons (Gulliksen and Scott 1995), FIRI has focused on the use of naturalmaterials, and has also implemented a two-stage design, with a set of core samples and a set ofoptional samples. In addition, two samples were identified for sample size and precision investiga-tions.1NERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East Kilbride, Scotland2Centre for Archaeological Science, Weizmann Institute, Rehovot, Israel3SUERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East Kilbride, Scotland4National 14C Laboratory, NUST, Trondheim, Norway5Department of Statistics, University of Glasgow, Scotland6AMS laboratory, Institute of Physics and Astronomy, University of Aarhus, Aarhus, Denmark7Department of Experimental Physics, University College, Dublin, Eire8Tandem Accelerator Laboratory, University of Uppsala, Uppsala, Sweden9Corresponding author. Email: marian@stats.gla.ac.uk.10CIO, University of Groningen, Groningen, the Netherlands11Koninklijk Institut voor Kunstpatrimonium, Brussels, Belgium322 C Bryant et al.The core samples comprised a total of 10 samples of 5 materials; wood, barley, humic acid, celluloseand turbidite. Wood samplesApproximately 10 kg and 12 kg of dendro-dated wood (comprising 20 and 40 rings, respectively)were cut to appropriate sizes (at least 40 g for radiometric and at least 4 g for AMS) before beinglabeled and bagged. Other wood samples were subdivided to appropriate sample sizes (approxi-mately 50 g and 5 g, respectively for radiometric and AMS labs). Two cellulose samples were also prepared from dendro-dated wood (16 kg and 10 kg, respectively)using an acid/alkali/acid procedure followed by bleaching using sodium chlorite. The extract wasthen washed, dried at 40 °C, physically mixed and then packaged into samples of 10 g and 1 g,respectively for radiometric and AMS laboratories.Other MaterialsTurbidite carbonate (mainly coccolith calcite) was taken from a single distal turbidite, derivedfrom the middle ungraded deposit. The sample was immediately oven dried (approximately 50 °C),ground and fully homogenized before being bagged (sample size approximately 100 g and 10 g,respectively) and labeled. A humic acid sample from a coastal cliff deposit at St Bees Head in Cumbria, northwest Englandwhich has been exposed by erosion was also prepared. A large peat sample was digested in 2% KOHat 80 °C. The alkali extracts were filtered and combined into a large container until over 150 L ofsolution were obtained. The bulk aqueous solution was then thoroughly mixed and the humic acidprecipitated by adjusting the pH to 3 by the stirred addition of 2M H2SO4. The solid precipitate wasthen recovered by filtration and given a preliminary wash with cold distilled water. It was then re-dissolved, re-precipitated and dried. After drying to a constant weight, the crystalline humic acidwas washed free of sulfate inclusions with hot distilled water. The sample was then re-dried andground to obtain a relatively standard size of crystal. Samples for radiometric and AMS measure-ment are approximately 10 g and 1 g, respectively.Barley mash is produced as a by-product of whisky manufacture. A sample (approximately 15 kg)from the current year was force dried and physically mixed. Samples are of approximately 50 g and5 g, respectively, for radiometric and AMS laboratories.Optional SamplesThe optional samples included two wood samples (one dendro-dated), a whole peat sample (linkedto the humic acid core sample) for both AMS and radiometric analysis and three separate mammothtusks spanning the 14C age range, leather and fabric from a scythian burial and parchment for AMSanalysis only. Homogeneity TestingThe key sample requirement in an intercomparison is that of homogeneity, which simply means thatany sub-sample, taken randomly from the bulk material is representative of that material and thatwhen dealing with trace element assay, that the trace element is uniformly distributed throughout thebulk material. Comparability of 14C Dates 323Each material (with the exception of the dendro-dated wood) was independently tested in two labo-ratories (where possible a radiometric and an AMS laboratory). A minimum of eight analyses wasrequired for homogeneity testing of each core material. Homogeneity testing for the barley mashwas carried out by radiometric analysis at the SUERC 14C laboratory, East Kilbride and 14C labora-tory, University College Dublin, for the first of the cellulose samples, homogeneity testing was car-ried out by radiometric analysis at the SUERC 14C laboratory, East Kilbride, and at the 14C labora-tory of the Weizmann Institute. For the turbidite, homogeneity testing was carried out by radiometric and AMS analysis at theNational 14C laboratory, NUST, Trondheim and Tandem accelerator laboratory, University of Upp-sala. For the second cellulose sample, homogeneity testing was carried out by radiometric analysisat the KIK 14C laboratory, Brussels and by AMS at the 14C laboratory, University of Groningen. Forthe humic acid sample, homogeneity testing was carried out by radiometric and AMS analysis at theNERC 14C laboratory, East Kilbride and AMS laboratory, University of Aarhus. The results of the homogeneity testing were satisfactory and are being reported separately.Current Status of FIRIAll core samples were distributed in September 1999, the deadline for results being August 2000.Currently over 80 sets of results have been returned and their analysis is underway. The full analysiswas presented and discussed at an FIRI workshop in March 2001.Optional samples are currently being distributed to participating laboratories.Future NeedsThere is still a need in routine dating for regular checks which can be satisfied by materials such asthe IAEA reference materials and by programmes such as TIRI and FIRI which are directed more atlarge sample dating, but there is clearly also a need for further exploration of comparability and vari-ation at the limits of the technique (very small or very old samples).The issue of sample homogeneity becomes more and more important, indeed the definition of a sam-ple becomes critical as smaller and smaller (compound specific) samples are dated. There are diffi-culties in taking a representative sub-sample from the bulk material. Indeed how do we know it isrepresentative? Do we fully know the potential scale of natural 14C variation in sample matrices?Continuation in this work is important, the linkage to previous work provides an invaluable continu-ity (e.g. IAEA and other reference materials are still available and should be used), but in addition,further new materials should be sought, and these should include known age material. For the con-ventional laboratory, the typical sample requirement might be 5 g C with sample age ranges from <1to approximately 7–8 half-lives. However, for the AMS labs and for those conventional labs wheresmall samples are dated, we need to explore the natural variation in reportedly single event samples(deposits of charcoal, grain from a single growing season, single insects from a well defined stra-tum). This information is not just important for the laboratory, but is also of fundamental importancefor the sample submitter who must select samples referring to the event of interest. Future inter-com-parisons therefore will see some shift in emphasis to reflect these challenging issues. CONCLUSIONSIn general, past intercomparisons have shown direct comparability of the AMS and radiometric lab-oratories but have also emphasized the potential variation that can be observed as a result of the sam-324 C Bryant et al.ple heterogeneity, a feature which gains increasing prominence as the sample size requirementdecreases. In the current laboratory intercomparison, comparability still remains the major issue, butthe emphasis has shifted from comparability of the measurement to the more difficult issue of com-parability of the samples and sampling. A full report on FIRI will be available by the end of 2001and a special issue of this journal will appear in 2002.ACKNOWLEDGMENTSThis work has been supported by NERC (GR9/03389) and the European Commission (SMT4-CT98-2265). We also wish to express our gratitude to the sample providers, Mike Baillie, Marco Spurk, Roy Swit-sur, Glengoyne Distilleries, Ganna Zaitseva, Kh Arslanov, Steinar Gulliksen, Mark van Strydonck,John Thomson, Israel Carmi, and Alan Hogg.REFERENCESScott EM, Aitchison TC, Harkness DD, Cook GT, BaxterMS. 1990. An overview of all three stages of the inter-national radiocarbon intercomparison. Radiocarbon32(2):303–19.Rozanski K, Stichler W, Gonfiantini R, Scott E M, Beu-kens R P, Kromer B, van der Plicht J. 1992.  The IAEA14C intercomparison exercise 1990. Radiocarbon34(3):506–19.Gulliksen S, Scott EM. 1995. TIRI report. Radiocarbon37(2):820–1.Scott EM, Harkness DD, Cook GT. 1997. Analytical pro-tocol and quality assurance for 14C analyses: proposalfor a further intercomparison. Radiocarbon 39(3):347–51.

For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisons in response to the issue of comparability of measurements as perceived within the wider user communities. In this report, we provide an update on the current 14C laboratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those resulting from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating of small samples (milligram size).

University of Groningen Digital Archive

ABSTRACT. For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisons in response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990; Rozanski et al. 1992; Gulliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current 14C lab-oratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those result-ing from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating of small samples (milligram size)

C Bryant

I Carmi

G T Cook

S Gulliksen

D D Harkness

J Heinemeier

E Mcgee

P Naysmith

G Possnert

E M Scott

CiteSeerX

Is comparability of 14C dates an issue?: A status report on the Fourth International Radiocarbon Intercomparison. Radiocarbon 43(2A):321–4

For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisons in response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990; Rozanski et al. 1992; Gulliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current 14C laboratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those resulting from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating of small samples (milligram size).</jats:p

E McGee

J van der Plicht

M van Strydonck

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Radiocarbon

Is Comparability of <sup>14</sup>C Dates an Issue?: A Status Report on the Fourth International Radiocarbon Intercomparison

For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisons in response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990; Rozanski et al. 1992; Guiliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current C-14 laboratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those resulting from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating of small samples (milligram size)

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Is comparability of C-14 dates an issue?: A status report on the fourth international radiocarbon intercomparison

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