Accelerator Mass Spectrometry Laboratory Research Articles

Indigenous artefacts and oral stories

This article presents the results of studies conducted by Canadian academics in collaboration with Sturgeon Lake and Pelican Narrows First Nations communities (Saskatchewan, Canada). The objectives of the project were: (1) developing a research ethics protocol for collecting, studying, and preserving indigenous artefacts; (2) measurements of chemical compositions of artefacts; (3) collecting oral stories of Elders. Within the project, two workshops were organized in Pelican Narrows and Sturgeon Lake. Post-secondary students were trained to work on the project. The laboratory measurements of chemical compositions of artefacts were conducted at the Scanning Electron Microscope Laboratory (University of Alberta), and the Saskatchewan Isotope Laboratory (University of Saskatchewan). The carbon-dating measurements were carried out at André E. Lalonde Accelerator Mass Spectrometry Laboratory (University of Ottawa). The statistical analysis of chemical compositions was conducted in order to test the provenance similarities of artefacts. The project was supported by the Department of Canadian Heritage.

SAFE PREPARATION AND DELIVERY OF GRAPHITE TARGETS FOR 14C ANALYSIS: PROCEDURES OF BRAVHO LAB AT BOLOGNA UNIVERSITY

ABSTRACT Nowadays, most radiocarbon (14C) laboratories can reliably avoid and remove any possible sample contamination during the pretreatment of organic samples (e.g., bones, charcoal, or trees) thanks to a series of methods commonly used by the radiocarbon community. However, what about the final step, the storage of graphite? Rarely do the laboratories produce their graphite and ship it as pressed targets to accelerator mass spectrometry (AMS) facilities for measurement. Pressed graphite in aluminum targets are vulnerable to contamination, and during shipment or storage, exogenous carbon can be introduced again. Here we report a test on various archaeological sample materials from different environments and different periods (from the past three millennia to the Middle Paleolithic period). We transformed them into graphite, pressed the graphite into targets and sent them to two different AMS laboratories to be dated. We observe that packing details of the targets, extended shipment and storage time may lead to contamination which can be avoided by appropriate packaging in tight metal cans and sealed in vacuum bags. Close cooperation and coordination between our chemistry laboratory and the AMS facilities, high standards in contamination removal, and efficient measurement planning enabled us to obtain reliable 14C ages within a short time.

Status report of the first AMS laboratory in the Czech Republic at the Nuclear Physics Institute, Řež

The first accelerator mass spectrometry (AMS) laboratory in the Czech Republic has been established and put into routine operation in February 2022. Here we briefly describe the facilities available, namely a 300 kV multi-isotope low-energy AMS system (MILEA) capable of determination 10Be, 14C, 26Al, 41Ca, 129I, isotopes of U, especially 236U, Pu and other actinoids, and accessories for 14C measurements, which include a gas interface system, a preparative gas chromatography system for compound-specific radiocarbon dating analysis, and an isotope-ratio mass spectrometer. The first results achieved for separation and measurement of the above radionuclides (except for 41Ca) are also reported, with the main focus on 14C measurements. A specimen breakdown of 729 graphitised samples analysed for 14C so far is presented, as well as a proof of measurement stability of the MILEA system obtained by analysis of radiocarbon standards and analytical blanks. For the other radionuclides, well proven or novel procedures for sample preparation and measurement are presented.

Studies of Physical Parameters of Indigenous Artifacts. Collecting and Preserving the Relating Oral Stories

The project, supported by the Department of Canadian Heritage, was conducted by scholars from First Nations University of Canada (FNUniv), University of Regina (U of R) and Royal Saskatchewan Museum (RSM) in 2018 - 2020, in collaboration with Sturgeon Lake and Pelican Narrows First Nations communities. More than forty people, including Elders and students, participated in this project. The research Ethics review was done by U of R. We also consulted with Elders regarding the research Ethics protocols during the individual meetings, ceremonies and workshops in Pelican Narrows and Sturgeon Lake. Research assistants (Indigenous students) were trained (Indigenous studies and the basics of archaeology) for working in First Nations communities and at the RSM. We interviewed Elders and Knowledge Keepers from Pelican Narrows and Sturgeon Lake and recorded their oral stories; collected Indigenous artifacts in these communities and selected samples from RSM collections for physical measurements at the Scanning Electron Microscope Laboratory of the University of Alberta, Saskatchewan Isotope Laboratory of the University of Saskatchewan and André E. Lalonde Accelerator Mass Spectrometry Laboratory of the University of Ottawa. Then we carried out the statistical analysis of the obtained data. The preliminary results of the project were presented to community members.

INTERCOMPARISON EXERCISE ON FUEL SAMPLES FOR DETERMINATION OF BIOCONTENT RATIO BY 14C ACCELERATOR MASS SPECTROMETRY

ABSTRACTThe method of determining the biobased carbon content in liquid fuel samples is standardized, but different laboratories use different protocols during sample preparation and perform the measurements using different machines. The accelerator mass spectrometry (AMS) laboratories use different combustion, preparation, and graphitization methods for the graphite production for the spectrometric measurements. As a result, the intercomparison between the laboratories is inevitable to prove precision and accuracy and to demonstrate that the results are comparable. In this study, we present the results of an intercomparison campaign involving three 14C accelerator mass spectrometry laboratories. Five samples were used in the measurement campaign, including two biocomponents (fatty acid methyl ester, hydrotreated vegetable oil), one fossil component (fossil diesel), and two blends (mixtures of fossil and biocomponent with 90–10% mixing ratio) in the laboratories of CEDAD (Italy), ETH (Switzerland), and INTERACT (Hungary). The results presented by the laboratories are comparable, and all three laboratories could determine the biobased carbon content of the samples within 1% relative uncertainty, which is acceptable in the scientific, economic, and industrial fields for biocomponent determination.

Principles and Applications of Accelerator Mass Spectrometry

Accelerator mass spectrometry (AMS) represents an ultrasensitive analytical method for measurement of long-lived radionuclides, namely 14C, 10Be, 26Al, 41Ca, 129I, and 236U. It provides information about isotopic ratios up to 10–16 in samples of mass from several miligrams to tens of micrograms. The first AMS laboratory in the Czech Republic was built in Nuclear Physics Institute, Řež, in collaboration with Archaeological Institute, Prague (both Czech Academy of Sciences) and Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, and equipped with AMS MIELA (Ionplus AG, Switzerland). This review summarizes history, principles, and use of this unique analytical method.

Preparation of new 10Be and 26Al AMS standard reference materials

Accelerator Mass Spectrometry (AMS) measurements require reliable standards for calibration. Beryllium-10, 26Al, 36Cl, and 41Ca AMS standards that were prepared by the author are used as primary normalization standards in most AMS laboratories worldwide. The expansion of applications and AMS facilities, accordingly an increase in sample measurements, over the last three decades has largely depleted the available stock of 10Be and 26Al standards that were prepared in 2001 as a series known as the “2001 or 01 dilution”. We have undertaken the task of making a new series of 10Be and 26Al AMS Standard Reference Materials (SRM) (“2014 or 14” series) that were prepared from the same parent solution used to produce the 2001 standards. Seven different concentrations of 10Be AMS standards were prepared from a stock solution 2001-4 by sequential dilution with (∼10 kg of) 36.5 mg Be/g carrier solution. The 10Be/Be ratios of the new standards are 1.01 × 10−13, 5.02 × 10−13, 2.507 × 10−12, 2.508 × 10−12, 7.523 × 10−12, 1.504 × 10−11, and 2.502 × 10−11. Six different concentrations of 26Al AMS standards were prepared from a stock solution 2001-3 by sequential dilution with a 35.7 mg Al/g carrier solution. The 26Al/Al ratios of the new standards are 1.51 × 10−13, 5.01 × 10−13, 2.501 × 10−12, 7.501 × 10−12, 1.500 × 10−11 and 5.000 × 10−11. Both 10Be/Be and 26Al/Al ratios of the new 2014 SRM were measured by five AMS laboratories; excellent linearity as well as agreement with the 2001 standard were observed. New 2014 10Be and 26Al SRM are available for the AMS community and are being distributed in the same way as the 36Cl and 41Ca SRM.

Characterization of the isobar separator for anions integrated into the A. E. Lalonde laboratory’s 3 MV AMS system

Accelerator Mass Spectrometry (AMS) of isotopes with abundant negative ion-forming isobars often requires the use of large accelerators to achieve high sensitivity measurements. The Isobar Separator for Anions (ISA) is a radio frequency quadrupole (RFQ) reaction cell system that can provide selective isobar suppression in the low energy system, prior to injection into an accelerator. A commercial version from Isobarex Corp. has been installed in a second injection line of the 3 MV tandem accelerator system at the A. E. Lalonde AMS Laboratory, University of Ottawa. Here, we present the characterization of the ISA for its optimization of S– suppression and Cl– transmission. He gas was selected as a cooling buffer gas, as it provided the best Cl– transmission of ∼50 % through the ISA column. These tests use NO2 as a reaction gas due to its well-known exothermic reaction with S– but endothermic reaction with Cl–. More than six orders of magnitude reduction of S to Cl has been observed.

RADIOCARBON IN MEXICO: FROM PROPORTIONAL COUNTERS TO AMS

ABSTRACTAugusto Moreno is credited with establishing the first radiocarbon (14C) laboratory in Mexico in the 1950s, however, 14C measurement with the accelerator mass spectrometry (AMS) technique was not achieved in our country until 2003. Douglas Donahue from the University of Arizona, a pioneer in using AMS for 14C dating, participated in that experiment; then, the idea of establishing a 14C AMS laboratory evolved into a feasible project. This was finally reached in 2013, thanks to the technological developments in AMS and sample preparation with automated equipment, and the backing and support of the National Autonomous University of Mexico and the National Council for Science and Technology. The Mexican AMS Laboratory, LEMA, with a compact 1 MV system from High Voltage Engineering Europa, and its sample preparation laboratories with IonPlus automated graphitization equipment, is now a reality.

14C-AMS IN MEXICO AND PRE-COLUMBIAN ARCHAEOLOGY

ABSTRACTThe complex geographical scenario of Mexico allowed the cultural diversification and development of multiple cultures such as Tolteca, Teotihuacan, Mexica, and Maya, among others. Despite this rich cultural heritage, radiometric dating of Mexican cultural samples with radiocarbon (14C) began only in the 1980s and with accelerator mass spectrometry (AMS) in 2013. Analysis of 14C with AMS is the most widely used technique to date archaeological objects and cultural heritage. Since 2013, the Accelerator Mass Spectrometry Laboratory (LEMA) facility of the Institute of Physics at UNAM (IF-UNAM) has supported archaeological research in Mexico, but also investigation in other areas such as geology, physics, chemistry, and environmental sciences through the analysis of 14C, 10Be, 26Al, 129I, and Pu. The absolute dating with 14C continues to be the core of LEMA’s work, where different geographical scenarios of the country and climatic conditions present very diverse analytical challenges. This work presents a basic description of the AMS system of the LEMA laboratory and describes some applications that are currently being developed.

RADIOCARBON DATING APPLIED TO PREHISPANIC TERRITORIAL DYNAMICS AT EL MAYE, IXMIQUILPAN, HIDALGO, MEXICO

ABSTRACTEl Maye is a community located in the municipality of Ixmiquilpan, Hidalgo, in the central region of Mexico. During the late Postclassic period (1350–1521 AD), the Aztecs controlled the area through the establishment of a dual-headed system, one part belonging to the Aztec government and the other to the local government. El Maye was the local government center for the Ixmiquilpan territory under the Aztec domain. The residential units of El Maye archaeological site were constructed in 6 different occupational phases, with the presence of large rooms, stucco floors and walls, offerings, and a variety of ceramics belonging to the late Aztec III ceramic period (1400–1520 AD). The Axis Project of the Mezquital Valley (PEVM-ENAH) and the Accelerator Mass Spectrometry Laboratory (LEMA-UNAM) have undertaken a collaborative study of the El Maye site by performing absolute radiocarbon accelerator mass spectrometry (14C AMS) dating. For a better understanding of the emergence and development of El Maye, a series of AMS 14C dates of charcoal and bone samples recovered from different stratigraphic levels, was performed. This allowed us to locate the occupation of the site between 1320 and 1625 cal AD.

Analysis of 14C concentration in teeth to estimate the year of birth in the Mexican population

The 14C analysis of permanent teeth employing nuclear techniques has a direct application in Forensic Sciences since teeth are the hardest part of the human body and can survive natural decay or extreme conditions. After the first Accelerator Mass Spectrometry Laboratory AMS-LEMA at UNAM, our research group is interested in reproducing 14C analysis on teeth as other countries to estimate age in the Mexican population samples. One of the main goals of this exploratory study is to know the best methodology considering relevant biological factors based on differences in tissues (enamel and dentin) that allows us to know the year of birth through the 14C concentration comparing the yield between 14C analyses from carbonate in enamel and collagen in dentin. In this study, Accelerator Mass Spectrometry (AMS) has been performed in 22 contemporary teeth samples (each one donated from 1 different adult), participating 22 individuals by informed consent to enable a new tool and improve forensic practices in Mexico. Carbon is extracted, converted to graphite, and pressed into a cathode. The sample is taken to an AMS system, where carbon isotopes are separated, counted, and the 14C/12C and 13C/12C ratios determined. Our results for standards and teeth samples from Mexican people are in good agreement with the expected values; they are also useful to set up the best conditions for studies in dentin and enamel. However, this is a destructive technique for dental organs; it is not suitable for individuals born previous 1950. New challenges in sample preparation processes are to be solved to take advantage of the nuclear techniques developed in the last 50 years and make new contributions to society.

Findings from an in-Depth Annual Tree-Ring Radiocarbon Intercomparison

ABSTRACTThe radiocarbon (14C) calibration curve so far contains annually resolved data only for a short period of time. With accelerator mass spectrometry (AMS) matching the precision of decay counting, it is now possible to efficiently produce large datasets of annual resolution for calibration purposes using small amounts of wood. The radiocarbon intercomparison on single-year tree-ring samples presented here is the first to investigate specifically possible offsets between AMS laboratories at high precision. The results show that AMS laboratories are capable of measuring samples of Holocene age with an accuracy and precision that is comparable or even goes beyond what is possible with decay counting, even though they require a thousand times less wood. It also shows that not all AMS laboratories always produce results that are consistent with their stated uncertainties. The long-term benefits of studies of this kind are more accurate radiocarbon measurements with, in the future, better quantified uncertainties.

Meteoric 10Be concentrations in the center of Mexico

The 1MV AMS system installed at National Accelerator Mass Spectrometry Laboratory (LEMA) has been used to determine the meteoric 10Be concentrations from particulate matter at the center of Mexico during 2012. The meteoric 10Be concentration range between (1.1 ± 14%, and 5.1 ± 12%) × 104 atoms m−3. In this work, we presented the first data of concentrations of meteoric 10Be found in this kind of samples by using AMS technique in Mexico.

First AMS measurements of 60Fe/Fe isotopic ratios at the Cologne 10 MV tandem accelerator

The measurement capabilities of the new accelerator mass spectrometry (AMS) system at the 10 MV FN tandem accelerator of CologneAMS has been extended with AMS measurements of 60Fe/Fe in the range of 10-8, 10-10 and 10-12. The measurements were conducted combining a 135° gas-filled magnet and a subsequent energy loss measurement in a 5 anode gas ionization chamber. This technique allows a good separation of the stable isobar 60Ni resulting in a suppression by a factor of 107 for the high energy mass spectrometer. With this a limit for the background level of 7·10-14 was achieved. The calculation of the error normalized sensitivity allowed a first comparison to other AMS laboratories.

Status Report on the Sample Preparation Laboratory for Radiocarbon Dating at the New Bucharest Roams Center

ABSTRACTThe accelerator mass spectrometry (AMS) center at Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Bucharest, is based on the latest-generation 1 MV Tandetron® accelerator, produced by High Voltage Engineering Europa (HVEE), The Netherlands. The AMS center became fully functional at the start of 2013, and at the end of 2015 the laboratory established the RoAMS international code and it was added to the list of AMS laboratories maintained by Radiocarbon journal. An important aspect in the establishment of a new AMS laboratory is the declaration and documentation of the adopted protocols and to demonstrate the reliability and reproducibility of the measurements in comparison to internationally recognized reference materials. In this paper, we present the dating results on the Sixth International Radiocarbon Intercomparison (SIRI) samples that were pretreated, graphitized, and measured in our laboratory. The newly developed sample preparation laboratory can handle sample materials as (1) organic materials, (2) wood, (3) bones, and (4) carbonates. The results of our measurements are in very good agreement with the SIRI consensus values and confirm the reliability of our sample preparation laboratory and also the good performance of the HVEE AMS system. The blank levels for the SIRI materials are 0.277±0.045/0.333±0.046 percent modern carbon (pMC) for wood samples, 0.441±0.038 pMC for bone collagen, and 0.239±0.030 pMC for carbonate materials, considering an average mass of 1 mg sample graphite.

BIOBASED CONTENTS OF MODEL RUBBER COMPOUNDS BASED ON ISO 19984 SERIES

ABSTRACT The percent modern carbon (pMC) values of natural rubbers from certain global areas as biomass resources and foods in Japan were confirmed by accelerator mass spectrometry (AMS). The pMC value of biomass harvested in 2014 and 2015 was determined to be 101%. The optimal conditions for AMS pretreatment procedures were examined. Eleven model rubber compounds were prepared to determine biobased contents. The biobased contents of the model rubber compounds were calculated using their formulations and measured by carbon-14 concentration (equivalent to percent modern carbon) using AMS. The biobased carbon contents of the rubber compounds were estimated based on ISO 19984-1 by the ratio of biobased carbon mass to total carbon mass in the sample material and measured based on ISO 19984-2 using AMS for the sample itself. Their biobased mass contents were calculated based on ISO 19984-1 as the ratio of biobased ingredient mass to total sample mass and measured based on ISO 19984-3 by chemical analysis and AMS for separated samples of rubber, solvent extract, and inorganics including carbon black. The reproducibility of the biobased contents was determined by round robin test (RRT) in the ISO technical committee 45 “Rubber and Rubber Products” during preparation, documentation, and discussion of the ISO 19984 series. Nine AMS laboratories and one chemical evaluation laboratory, located in four countries, participated in this RRT. These methods for determining biobased contents were confirmed to have high reproducibility. The biobased carbon content and the biobased mass content of commercial rubber products, such as tire parts, were successfully measured based on ISO 19984-2 and 3.

Compatibility of Atmospheric 14CO2 Measurements: Comparing the Heidelberg Low-Level Counting Facility to International Accelerator Mass Spectrometry (AMS) Laboratories

AbstractCombining atmospheric Δ14CO2 data sets from different networks or laboratories requires secure knowledge on their compatibility. In the present study, we compare Δ14CO2 results from the Heidelberg low-level counting (LLC) laboratory to 12 international accelerator mass spectrometry (AMS) laboratories using distributed aliquots of five pure CO2 samples. The averaged result of the LLC laboratory has a measurement bias of –0.3±0.5‰ with respect to the consensus value of the AMS laboratories for the investigated atmospheric Δ14C range of 9.6 to 40.4‰. Thus, the LLC measurements on average are not significantly different from the AMS laboratories, and the most likely measurement bias is smaller than the World Meteorological Organization (WMO) interlaboratory compatibility goal for Δ14CO2 of 0.5‰. The number of intercomparison samples was, however, too small to determine whether the measurement biases of the individual AMS laboratories fulfilled the WMO goal.

Semi-Automated Equipment for CO2 Purification and Graphitization at the A.E. Lalonde AMS Laboratory (Ottawa, Canada)

AbstractNew computer-controlled, semi-automatic systems were designed and built for CO2 purification and graphitization at the A.E. Lalonde Accelerator Mass Spectrometry (AMS) Laboratory with consideration for user friendliness and high throughput. The stainless steel vacuum lines are orbitally welded to ensure clean seams with low memory. The insulated graphitization ovens with plug-in electrodes provide a hazard-free environment for operators. The closed-loop cooling system circulating low-viscosity Dynalene at –40°C provides highly efficient water trapping. The LabVIEWTM software features (1) pressure and temperature recording for QA/QC; (2) safety interlocks to preclude operator errors resulting in sample loss, cross-contamination, or damaging a vacuum pump; and (3) automation for leak checking, iron conditioning, and running samples. Results from the first year of routinely measured standards, reference, and background materials are reproducible and within acceptance values. In the first year of operation (commissioned in spring 2014), over 1000 targets (~60% unknowns) were produced. With new tube sealing and CO2 purification lines, and two more graphitization lines now operational, the Lalonde AMS Laboratory is able to provide routine radiocarbon analysis (>200 µg carbon) at a capacity of more than 7000 targets per year. Most importantly, the equipment is safe and intuitive, making it ideal for education and training students to run their own samples.

He stripping for AMS of 236U and other actinides using a 3 MV tandem accelerator

Interest in the long-lived radioisotope 236U (t1/2=23.4 million years) has significantly increased recently, due to the emergence of environmental and earth science applications. Presently, only a few (AMS) accelerator mass spectrometry instruments are suited for this measurement. One major limitation is the relatively low total detection efficiency (on the order of 10−4), which is partly caused by a low stripping yield of the positive ion charge state selected after the tandem accelerator. It has been shown that high yield can be achieved using helium as stripper gas for uranium ion energies below 0.35MeV. Here we investigate the potential of He stripping of U at the 3-MV tandem accelerator VERA. Phenomenological charge state distributions for U and Th are presented for terminal voltages from 1.0 to 1.7MV. These terminal voltages provide better background rejection than possible below 1MeV, and are suited to the widely used 1–3MV workhorses of many accelerator mass spectrometry laboratories. The methods can be applied to other actinides also.