Article

Speed Dating: A Rapid Way to Determine the Radiocarbon Age of Wood by EA-AMS

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Abstract

Radiocarbon measurements in tree rings can be used to estimate atmospheric 14 C concentration and thereby used to create a 14 C calibration curve. When wood is discovered in construction sites, rivers, buildings, and lake sediments, it is unclear if the wood could fill gaps in the 14 C calibration curve or if the wood is of historical interest until the age is determined by dendrochronology or 14 C dating. However, dendrochronological dating is subjected to many requirements and 14 C dating is costly and time consuming, both of which can be frivolous endeavors if the samples are not in the age range of interest. A simplified 14 C dating technique, called Speed Dating, was thus developed. It can be used to quickly obtain 14 C ages as wood samples are neither chemically treated nor graphitized. Instead, wood is combusted in an elemental analyzer (EA) and the CO 2 produced is carried into an accelerator mass spectrometer (AMS) with a gas ion source. Within a day, 75 samples can be measured with uncertainties between 0.5–2% depending on the age, preservation, and contaminants on the material and Speed Dating costs about one-third of conventional AMS dates.

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... While all samples agree within a 1 σ interval, smaller samples bear larger uncertainties that are due to counting statistics. AMS measurements rely on direct counting of 14 C atoms present in the sample, which for samples > 200 μg C allows precision down to 2‰ error [62], whereas samples below 100 μg C typically yield uncertainties ranging between 0.5 to 2% [63,64]. These errors increase further from constant contamination because of error propagation (Additional file 1: Table S6). ...
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Article
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... (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) 2013; Sookdeo et al., 2017), and traditional high-precision radiocarbon dating methods (Longworth et al., 2015) at the National Ocean Sciences Accelerator Mass Spectrometer (NOSAMS) facility at Woods Hole Oceanographic Institution. The reconnaissance analysis was performed after initial sample collection in order to obtain approximate estimates of age. ...
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... Process blanks, reference material and samples were chemically treated to extract cellulose. Cellulose is a component of wood that has remained unchanged over time and can be used for an accurate 14 C-date (Hoper et al. 1998;Brock et al. 2010;Sookdeo et al. 2017). Cellulose was extracted in batches of 56 (2 TK121, 2 BK, 2 KB and 50 samples) using a modified base-acid-base-acid-bleaching method outlined by Němec et al. (2010). ...
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... Recently, a method using an elemental analyzer combined with the AGE (EA-AGE method) has been applied to some types of samples (e.g. cellulose, bone collagen) (Cersoy et al. 2017;Sookdeo et al. 2017;Fewlass et al. 2018). ...
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... The methods of chemical pretreatment of wood for 14 C dating, including high accuracy dating, were examined and described by numerous authors (e.g. Hoper et al. 1998;Bird et al. 1999;Santos et al. 2001;Anchukaitis et al. 2008;Nemec et al. 2010;Southon and Magana 2010;Santos and Ormsby 2013;Staff et al. 2014, Wacker et al. 2014Hajdas et al. 2016;Sookdeo et al. 2016). Also, the authors of this article had decided to conduct their own tests, carried out in three Polish laboratories (Gliwice, Kraków, and Poznań). ...
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... The choice of wood preparation method for high resolution 14 C measurements is often a compromise between minimizing material loss and separation of the least-mobile wood component which best reflects the initial state (content of 14 C isotope) at the moment of ring formation. A number of studies have been carried out on wood preparation for 14 C measurements (Anchukaitis et al., 2008;Bird et al., 1999;Hajdas et al., 2016;Hoper et al., 1998; et al., 2001;Santos and Ormsby, 2013;Sookdeo et al., 2016;Southon and Magana, 2010). In this study the authors decided to test different types of wood preparation methods. ...
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An analysis was performed on samples from a series of well-preserved tree trunks and in situ stumps of Allerød/Younger Dryas age found in Koźmin and Kwiatków, Kolska Basin, Central Poland. Five different types of wood preparation methods were investigated in three Polish radiocarbon laboratories (Gliwice, Poznań and Krakow) in order to find the most stable, repeatable and reliable procedure. Their effect was tested on the stable carbon isotope ratio (δ¹³C) and ¹⁴C age. Additionally, FTIR spectroscopy was used as a simple technique for obtaining rapid information on the structure of wood constituents and chemical changes taking place in wood due to various chemical treatments. The results of AMS measurements did not show statistically significant differences in radiocarbon ages of samples prepared according to the tested methods. On the other hand, δ¹³C measurements showed that the smallest scattering results gave α-cellulose obtained by the method BABA + Bleaching (with NaClO2 and HCl) + strong base. Moreover, the mean δ¹³C values for holo-cellulose samples are higher than those for α-cellulose samples. Studies evidenced that the methods of preparation leading to holo- or α-cellulose gave the same FTIR spectra, while the standard method of the chemical pretreatment of samples for ¹⁴C measurements (ABA) preceded by mercerization is insufficient for removing compounds containing aromatic rings.
... Performed at the Laboratory of Ion Beam Physics, ETH-Zurich, both the well-established high-precision 14 C Accelerator Mass Spectrometer (AMS) dating (Synal et al., 2007;Wacker et al., 2014Wacker et al., , 2010, as well as the novel 'Speed Dating' (Sookdeo et al., 2016), were used for radiocarbon dating (Güttler et al., 2015(Güttler et al., , 2013N emec et al., 2010). While high-resolution AMS-dating ( ±20e25-year 1sigma) can reveal accurate tree ages along the IntCal13 calibration curve , the simplified 'Speed Dating' technique provides rough estimates of the expected age range. ...
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... It should be noted in this regard that the Lake Gerber sampling site in the Spanish central Pyrenees still provides some potential to extend the composite chronology further back in time. There still remain ample subfossil trunks preserved in several smaller and larger lakes between 2100 and 2400 m MSL although to recover them will be costly, calling for professional diving campaigns, as well as numerous high-precision 14 C dates in addition to conventional tree-ring dating (Sookdeo et al. 2017). ...
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An on-line measurement system was installed at the MICADAS in Zurich, using an elemental analyzer (EA) as a combustion unit to enable direct radiocarbon measurement of samples containing carbon in the range of 5-100 μg possible with minimum effort. The samples are combusted in small capsules and the gaseous combustion products are separated by the EA. The carbon dioxide leaving the EA in a high helium flow is concentrated on a small external trap containing X13 zeolite adsorber material. This new concept, avoiding a cryogenic trapping for the enrichment step, allows the construction of a very compact system able to work even with the smallest samples. Concentrated on the external trap, the carbon dioxide is flushed into the gas-tight syringe of our gas inlet system using a low helium stream. The gas mixture is measured with the MICADAS gas ion source. Several different sample capsules were analyzed to minimize the major blank contribution coming from the sample vessel. The best results were achieved with 25-μL tin capsules, which contained only 0.34 ± 0.13 μg carbon at 65 pMC. This work describes the development of the on-line system and the protocol for measurement runs. Results are presented for on-line measurements of reference materials and a comparison is performed with typical dating samples measured previously as graphite targets. Finally, relevance and limitations of on-line measurements are discussed. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.
Article
The reaction conditions for the graphitization of CO2 with hydrogen were optimized for a fast production of high-quality carbon samples for accelerator mass spectrometry (AMS) measurement. The iron catalyst in use is first oxidized by heating with air to remove possible carbon and other impurities and then after evacuation reduced back to iron with hydrogen in several flushing steps to remove any iron oxide. The optimum conditions for a fast graphitization reaction were experimentally determined by changing the reaction temperatures and the H-2/CO2 ratio. The resulting graphite samples were measured by AMS to find the smallest isotopic changes (delta C-13) at a minimum of molecular fragment formation ((CH)-C-13 current). The improvements are based on thermodynamic data and are explained with Baur-Glaessner diagrams.
Article
For more than 4 years, gaseous samples of 1–50 μg carbon have been routinely measured with the gas ion source of the small AMS (Accelerator Mass Spectrometer) facility MICADAS (MIni CArbon DAting System) at ETH Zurich. The applied measurement technique offers a simple and fast way of 14C measurements without the need of sample graphitization. A major drawback of gaseous 14C measurements, however, is the relatively low negative ion current, which results in longer measurement times and lower precision compared to graphitized samples. In December 2009, a new, improved Cs sputter ion source was installed at MICADAS and we began to optimize conditions for the measurement of gaseous samples. 12C− currents from the new ion source were improved from initially 3 to 12–15 μA for routine measurements and the negative ion yield was increased by a factor of 2, reaching 8% on average during routine operation. Moreover, the new measurement settings enable a doubled CO2 flow, thus substantially reducing measurement times. The achieved performance allows closing the sample size gap between gaseous and solid samples and makes the gas ion source a promising tool for dating with a measurement precision of 5‰ on samples as small as 50 μg carbon.
Article
Here we present the entire range of Lateglacial tree-ring chronologies from Switzerland, Germany, France, covering the Lateglacial north and west of the Alps without interruption as well as finds from northern Italy, complemented by a 14C data set of the Swiss chronologies. Geographical expansion of cross-matched European Lateglacial chronologies, limits and prospects of teleconnection between remote sites and extension of the absolute tree-ring chronology are discussed. High frequency signals and long-term fluctuations are revealed by the ring-width data sets of the newly constructed Swiss Late-glacial Master Chronology (SWILM) as well as the Central European Lateglacial Master Chronology (CELM) spanning 1606 years. They agree well with the characteristics of Boelling/Alleroed (GI-1) and the transition into Younger Dryas (GS-1). The regional chronologies of Central Europe may provide improved interconnection to other terrestrial or marine high-resolution archives. Nevertheless the breakthrough to a continuous absolute chronology back to Boelling (GI-1e) has not yet been achieved. A gap remains, even though it is covered by several floating chronologies from France and Switzerland.
Article
A method for interfacing an automated combustion unit to a gas ion source for 14C analysis is described. This method makes use of an actively controlled transfer line which accommodates the relatively fast flow of the output He carrier gas and short time duration during which the CO2 is released from the combustion unit, and provides a constant ratio of CO2 to He carrier gas to the ion source. Details of the active control system are presented and results from the testing of this control are provided.
Article
This paper reports on the performance of a new method of sample injection using the High Voltage Engineering Europa (HVEE) SO-110 ion source jointly developed between HVEE and Oxford. In order to use this source, we have devel- oped a new gas handling system which works on the direct injection of carbon dioxide mixed into a continuous flow of helium. Preliminary work has also been carried out on online gas chromatography-accelerator mass spectrometry (GC-AMS). In this application, a GC is directly coupled to the AMS system using a GC-IRMS combustion interface and Nafion™ drier. We show here results for the measurement of natural abundance in separated compounds with good peak separation and pre- cisions of about 10%. This type of system should be ideal for source apportionment studies, biomedical, and other similar work where high precision is not required but where sample sizes are very low.
Article
A data evaluation program was developed at ETH Zurich to meet the requirements of the new compact AMS systems MICADAS and TANDY in addition to the large EN-Tandem accelerator. The program, called “BATS”, is designed to automatically calculate standard and blank corrected results for measured samples. After almost one year of routine operation with the MICADAS C-14 system BATS has proven to be an easy to use data reduction tool that requires minimal user input. Here we present the fundamental principle and the algorithms used in BATS for standard-sized radiocarbon measurements.
Article
The sealed tube zinc reduction method for converting CO 2 to graphite for AMS 14 C measurements was originally developed for rapid production of graphite in biomedical tracer experiments. The method was usually thought to have low precision and a high background. We have modified the zinc reduction method originally outlined in Vogel [J.S. Vogel, Radiocarbon 34 (3) (1992) 344] by carefully con-trolling the amounts of reagents (zinc, titanium hydride and Co or Fe catalyst) and now routinely obtain a precision of 2–3& and a relatively low background of $50,000 14 C years when analyzing for 14 C at the Keck Carbon Cycle AMS facility at UC Irvine. Fraction-ation of carbon isotopes does occur during graphitization and depends on the graphitization yield, which can be affected by the amounts of reagents used and other conditions. The d 13 C of our zinc-reduced graphite is usually lighter by 2–3& than the CO 2 from which it is made, but this is corrected for in our system by simultaneous measurement of 13 C/ 12 C along with 14 C/ 12 C by the spectrometer. This method is suitable for 14 C enriched samples, as well as natural abundance 14 C samples, especially those with modern 14 C contents. With improved precision and background, we believe that many disciplines can benefit from this technique because of its low cost and rapid production of graphite.
Article
The state of the art in accelerator mass spectrometry (AMS) is reviewed. The review is divided in two parts. The first covers the general methodology, followed by its specific elaborations for the commonly measured long-lived isotopes such as 10Be, 14C, 26Al, 36Cl and 129I, as well as other isotopes with emerging applications. The second part considers the very wide spectrum of applications that now employ AMS, and groups these according to research area rather than isotope. The period up until late 1998 is covered, with an emphasis on post-1990 developments and literature.
Conference Paper
A novel tabletop AMS system with overall dimensions of only 2.5 x 3 m(2) has been built and tested. The mini radiocarbon dating System (MICADAS) is based on a vacuum insulated acceleration unit that uses a commercially available 200 kV power supply to generate acceleration fields in a tandem configuration. At the high-energy end, ions in charge state 1(+) are selected and interfering molecules of mass 14 amu are destroyed in multiple collisions. The new system is now fully operational. It is the prototype of a new generation of radiocarbon spectrometers which fulfill the requirements for radiocarbon dating applications as well as for the less demanding C-14/C-12 isotopic ratio measurements as needed, e.g. in biomedical applications. A detailed description of the system is given and results of performance tests are discussed. (c) 2007 Elsevier B.V. All rights reserved.
Article
Two catalytic processes have been explored for the preparation of suitable samples for use in 14C measurements on an accelerator mass spectrometer. A heavy hydrocarbon was condensed from C2H2 using AlBr3 as a catalyst. This process had low isotopic fractionation, and the carbon ion beam obtainable was 60–70% that from graphite. In the second process, iron powder was used to produce graphite directly from CO2 and H2 at 600 °C. A sample preparation system using this reaction has been built. The carbon product produces exceptionally intense, long-lived ion beams. The process introduces little 14C background, and has no observed memory effects.
Article
A new graphitisation system, directly coupled to an elemental analyser, has been developed for convenient, fast and efficient sample preparations for radiocarbon measurement by means of accelerator mass spectrometry. We demonstrate an alternative to the cryogenic transport of CO2 into the graphitisation reactors with liquid nitrogen, which is used by others. Instead, the CO2 coming from an EA is absorbed on a single column filled with zeolite. The CO2 can then be easily released by heating the zeolite trap and transferred to the reactor by gas expansion. The system is simple and fully automated for sample combustion and graphitisation.
Article
Radiocarbon accelerator mass spectrometry (AMS) is a high-sensitivity analysis technique which is nowadays widely used in many research fields such as archaeology, geology, environmental and earth sciences. We report on the features of the new high throughput accelerator mass spectrometer at the University of Lecce, Italy. The experimental apparatus is described and its general characteristics are reported in terms of measurement precision, accuracy and achievable background.
Article
A number of operationally defined methods exist for pretreating plant tissues in order to measure C, N, and O isotopes. Because these isotope measurements are used to infer information about environmental conditions that existed at the time of tissue growth, it is important that these pretreatments remove compounds that may have exchanged isotopes or have been synthesized after the original formation of these tissues. In stable isotope studies, many pretreatment methods focus on isolating "cellulose" from the bulk tissue sample because cellulose does not exchange C and O isotopes after original synthesis. We investigated the efficacy of three commonly applied pretreatment methods, the Brendel method and two variants of the Brendel method, the Jayme-Wise method and successive acid/base/acid washes, for use on three tissue types (wood, leaves, roots). We then compared the effect of each method on C and O isotope composition (13C, 14C, 18O), C and N content, and chemical composition of the residue produced (using 13C nuclear magnetic resonance (NMR)). Our results raised concerns over use of the Brendel method as published, as it both added C and N to the sample and left a residue that contains remnant lipids and waxes. Furthermore, this method resulted in 18O values that are enriched relative to the other methods. Modifying the Brendel method by adding a NaOH step (wash) solved many of these problems. We also found that processed residues vary by tissue type. For wood and root tissues, the 13C NMR spectra and the 18O and 13C data showed only small differences between residues for the Jayme-Wise and modified Brendel methods. However, for leaf tissue, 13C NMR data showed that Jayme-Wise pretreatments produced residues that are more chemically similar to cellulose than the other methods. The acid/base/acid washing method generated 13C NMR spectra with incomplete removal of lignin for all tissues tested and both isotopic, and 13C NMR results confirmed that this method should not be used if purified cellulose is desired.
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