T02_P01

RESEARCH ON MORTAR RADIOCARBON DATING IN FLORENCE: STATE OF THE ART AND FUTURE PERSPECTIVES

Barone S^1,2,  Fedi M¹, Liccioli L¹, Calandra S³, Cantisani E⁴, Salvadori B⁴, Garzonio C⁵

¹INFN - Sezione di Firenze, Sesto Fiorentino (FI), Italy, ²Università degli Studi di Firenze, Department of Physics and Astronomy, Sesto Fiorentino (FI), Italy, ³Università degli Studi di Firenze, Department Of Chemistry "Ugo Schiff", Sesto Fiorentino (Fi), Italy, ⁴ISPC - CNR, Sesto Fiorentino (Fi), Italy, ⁵Università degli Studi di Firenze, Department of Earth Science, Firenze, Italy

As many studies have so far pointed out, despite the easiness of the principle, radiocarbon dating of mortars may present many issues in its application. Such issues are ascribable to the vast heterogeneity of mortars: anthropogenic calcite, which is the carbon fraction to be isolated for dating, is typically mixed with aggregates of several different compositions, even carbonaceous, and of different grain sizes; rest of geogenic calcite, as well as areas of uncomplete carbonation may be present; recrystallization phenomena may alter the original carbon content. The research during these years has highlighted that characterization of the mortar prior to dating is mandatory to identify the most efficient procedure to remove the possible contaminations in our mortar samples.

In the last few years, thanks to the multidisciplinary collaboration between INFN and ISPC-CNR in Florence, a procedure for the selection and treatment of mortars to be dated by radiocarbon was developed. The procedure includes a preliminary in-depth characterization of mortars, by means of different analyses such as XRD and FTIR-ATR, and the extraction of CO₂ from the datable isolated fraction through acidification, thanks to a new set-up that allows us to select different aliquots of CO₂ while the acidification reaction takes place. This set-up is coupled with the graphitization line specifically optimized for microsamples, allowing us to analyze small amounts of mortar calcite or one lump at a time. 

In this poster we describe our procedure, the new experimental set-up installed at our laboratories and the results of the first tests. 

T02_P02

Preliminary studies on tracing the source of carbon in organic matter and carbonate in coral and aquatic snail by ¹⁴C

Cheng P¹,  Du H¹, Lu X¹

¹Institute of Earth Environment,CAS, Xi'an, China

The variation of ¹⁴C concentrations in organic matter and inorganic carbonates in coral and aquatic snail shells may reflect how carbon is used by these organisms. However, there are few studies on the source of organic matter in coral and snail shells. The main reasons are as follows:1) there is less organic matter in shells and coral; 2) there are few reliable methods for extracting organic matter. In order to verify the reliability of our extracted method, four water-soluble substances with known ¹⁴C ages (50,000 to modern) were oxidized by sodium persulfate oxidation method. The results show there is no obvious old or young carbon contamination during the oxidation process. Further analysis of the samples showed that the ¹⁴C age of the organic matter of the coral was older than the ¹⁴C age of the carbonate, to a maximum of 670 years and to a minimum of 80 years, the organic matter of the snails in the lake had a ¹⁴C age 90 years older than the carbonates. The differences of ¹⁴C ages of organic matter and carbonate indicate that corals and aquatic snail have different carbon utilization and carbon source during growth. The change of carbon source is reasonable to trace the changes of water environment.

T02_P03

Optimisation of phosphoric acid digestion for cremated bones: ultrasonication and extension of collection time

Giannì M¹,  Chivall D¹, Griffiths S²

¹Oxford Radiocarbon Accelerator Unit (ORAU), School of Archaeology, University of Oxford, Oxford, OX1 3QY, United Kingdom, ²Department of History, Politics and Philosophy, Manchester Metropolitan University, Manchester, M15 6LL, United Kingdom

Cremated bone pretreatment for radiocarbon dating at ORAU consists of acetic acid predigestion, to remove residual organic carbon, followed by phosphoric acid digestion to liberate endogenous carbonates as carbon dioxide. The phosphoric acid digestion follows a general protocol common to other materials including shells, foraminifera and other calcified material.

The phosphoric acid digestion is currently performed at 50°C for 2 to 3 hours. Afterwards, CO₂ is transferred, via a -65°C water trap (for 45 seconds), into vials using liquid nitrogen (for 15 seconds). The transfer is repeated three times taking a total of 3 minutes per sample.

Unlike shells and foraminifera, cremated bone takes 3.5 to 4.5 hours to turn in a dense liquid opaque mixture. Bubbles of trapped gas are clearly visible on the surface even after 3 minutes of CO₂ collection.

The ability of ultrasonication to provide higher yield by releasing trapped gas was tested on cremated bone fragments by comparing non-ultrasonicated samples with duplicates that were ultrasonicated. Separately, another round of 3-minute collection was performed for which the yield and radiocarbon age were determined. Finally, dates were compared for consistency between all duplicates.

Both ultrasonication and double-time collection increase the yield with minimal impact on date consistency, allowing for small samples (less than 500mg) to be accurately dated.

We therefore suggest a protocol modification that introduces a 5-minute ultrasonication step following digestion, before CO₂ collection, and an extension of the collection time from 3 to up to 6 minutes.

T02_P04

The impact of leaching on foraminifera radiocarbon ages

Grotheer H^1,2,  Mollenhauer G^1,2

¹Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany, ²University Bremen, MARUM, Bremen, Germany

Reliable radiocarbon ages of foraminifera are a prerequisite to generate robust high-resolution age-depth models or to obtain precise understanding of past carbon cycle dynamics. With the advance of small-scale radiocarbon measurements instrumental precision and levels of contamination become increasingly important to consider as with decreasing sample size the precision becomes progressively poorer, and the effect of contamination increases proportionally. To reduce the effect of carbon contamination, an attempt can be made to remove it by chemical pretreatment. An alternative might be mathematical corrections based on processing blanks of the same sample material and assuming constant contamination.

Here we report on radiocarbon analyses of monospecific foraminifera samples compared between different blank corrections and sample treatments I) to examine whether chemical pre-treatment and mathematical blank correction are comparable, and II) to determine limitations hindering reliable radiocarbon dating with ever smaller sample sizes. The data show that chemical pre-treatment does remove surface contamination and that the same effect on data reliability can be achieved by mathematically correcting for blank values determined from sample size-matched blank foraminifera. Theoretical considerations show that chemical pretreatment only has a beneficial effect where the isotopic difference between chemically untreated and pre-treated samples exceed the analytical precision

T02_P05

Radiocarbon dating of small snail shells in loess-paleosol sequence at Mangshan, central China

Gu Y^1,2,  Lu H¹, Hajdas I², Haghipour N², Zhang H¹, Wu J¹, Shao K¹

¹Laboratory of AMS Dating and the Environment, School of Geography and Ocean Science, Nanjing University, Nanjing, China, ²Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland

Radiocarbon age obtained on small snail shells show that the limestone effect is smaller than for the large shells, providing great potential to constrain accurate ages of late Quaternary loess deposits. In the Chinese Loess Plateau (CLP), snail shells are often the only radiocarbon dating material available for building chronology. However, the reliability of different small snail shells for radiocarbon dating remains an open question. Here, we collected different small snail shells from a loess-paleosol sequence located at south-east CLP to test their availability. Both solid graphite target AMS measurement and gas AMS measurement were performed to evaluate the reliability and possible contamination of different sizes of small shells for radiocarbon dating. ¹⁴C ages of graphitized samples are generally consistent with corresponding OSL ages, indicating the reliability of small snails ¹⁴C dating at CLP. Ages of the surface fraction of small snails are close to the ages of the interior part and the contamination after chemical treatment is limited, indicating fossil snail shells behave as a close system during burial. In addition, gas measurement results further demonstrate the different degrees of reliability among various snail species. For minute taxa, such as Vallonia and Pupilla, their shells can mainly reveal reliable ¹⁴C ages. While for larger taxa, such as Cathaica and Metodontia, much attention should be paid to selecting the appropriate shells. Large individuals and snail hatchlings may contain considerable old carbon and only small shells larger than newly incubation (<10 mm and > 2 mg) can provide reliable ¹⁴C ages.

T02_P06

Testing Protocols for Removing a Commercial Wood Stabilizer from Dry Wood for Radiocarbon Dating

Hadden C¹,  Sheng H¹, Carmody D¹, Cherkinsky A¹

¹Center For Applied Isotope Studies, Athens, United States

Conservation treatments such as wood stabilizers pose challenges for radiocarbon dating because they contain carbon of a different age than the object of study and must be removed completely in order to achieve an accurate radiocarbon age. Wood Juice© is a commercially available wood stabilizer with a proprietary formula that includes petroleum-based ingredients. It has been used recently by museum conservators in the United States to stabilize Native American dugout canoes and other logboats. The purpose of this study was to test whether Wood Juice can be effectively removed from dry wood to achieve reliable radiocarbon dates. For the experiment we intentionally contaminated with Wood Juice (25% by dry weight) a sample of a single-year tree ring from a pre-Columbian dugout canoe with a radiocarbon age of 459 ± 10 ¹⁴C yr. We tested the effectiveness of several common chemical pretreatment protocols for removing the Wood Juice, including a standard acid/base/acid (ABA) protocol, α-cellulose extraction, and a variety of organic solvents. We determined that ABA and α-cellulose protocols easily and effectively removed 100% of the contaminating carbon, without the need for an organic solvent. The results of this study will be of interest to radiocarbon researchers, archaeologists, and museum conservators working with canoes, logboats, and other wooden artifacts.

T02_P07

Samples screening and treatment for accurate radiocarbon dating

Hajdas I¹,  Guidobaldi G¹, Haghipour N^1,2, Wyss K¹

¹Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland, ²Earth Sciences Department, ETH Zurich, Zurich, Switzerland

Only carbon inherent to the material in quest of dating contains the original ¹⁴C signal from the time of formation or deposition. Apart from reservoir effects and calibration issues that must be considered, the major challenge in radiocarbon dating is the extraction of autogenic carbon. Various prescreening and purity checkups of sample material are vital to the choice of sample treatment. At the ¹⁴C prep laboratory ETH Zurich, the FTIR analysis supports the binocular investigations, which provides information on the sample's composition. Significantly, any anthropogenic conservation substances can be detected and identified, allowing for proper choice of treatment steps. Bulk sediments are cross-checked for carbonates or dolomite. Also, the treated samples are checked for purity before the final combustion. Occasionally, contaminated fractions are analyzed using a gas ion source to support evaluation.

Preservation of sample material is a crucial factor and assessing it helps choose an appropriate laboratory procedure. Currently, we estimate the N% and C/N ratio of the original bone sample to predict the success of collagen separation, although the use of FTIR analysis would simplify this step as the sample does not require weighing. On the other hand, the N% and C% of the original samples can be directly stored in the database after combustion in the elemental analyzer. Evaluation of procedures and their modifications is vital for an efficiently working laboratory. This paper will present an overview of methods applied to evaluate and treat various materials and samples.

T02_P08

Tree-ring-radiocarbon dating paraffin conserved charcoal: An experimental and archaeological case study

Kessler N¹

¹University Of Arizona, Tucson, United States

For wood and charcoal in museum collections, past conservation practices can be a challenge for high precision ¹⁴C-based chronometry. For example, in the United States, the treatment of archaeological charcoal with paraffin consolidant was a widespread practice. This complicates ¹⁴C dating of tree-ring segments in wiggle-matches as trace amounts of dead carbon can induce significant offsets. This poster presents experimental evidence for the efficacy of a solvent pretreatment protocol for known age and archaeological charcoal conserved with paraffin. FTIR and ¹⁴C analysis confirm that a chloroform pretreatment is very effective at removing paraffin from laboratory contaminated known-age charcoal as well as historically contaminated archaeological charcoal. Using the pretreatment protocol, new wiggle-matched dates were obtained from a large platform mound (Mound 10) at the Kincaid Site, a Mississippian center in southern Illinois U.S.A. Wiggle-matched cutting dates from the final construction episodes on Mound 10 at Kincaid, indicate that the mound was used in the late 1300s with the construction of a unique building on the apex occurring in the 1390s, just one or two generations prior to the depopulation of the site. This study demonstrates the potential for museum collections of archaeological charcoal to contribute high resolution chronological information through wiggle-matching despite past conservation practices that complicate ¹⁴C dating.

T02_P09

Squeaky clean cellulose for different applications

Khumalo W¹,  Svarva H¹, Zurbach D¹, Nadeau M¹

¹The National Laboratory for Age Determination, Trondheim, Norway

This project aims to determine the most time effective method of extracting cellulose “clean” enough for applications in ¹⁴C dating and stable isotope analysis, namely δ¹⁸O, for both young and old wood samples. We compare classic, commonly used, methods for the extraction of cellulose to more recent, simpler approaches.

α-Cellulose is considered the best component to extract for high precision ¹⁴C dating of younger wood samples. However, these methods are often too destructive on old wood samples resulting in sample yields too small for ¹⁴C dating. Vigorous cellulose extraction methods needed for ¹⁴C dating may not be necessary to produce accurate δ¹⁸O results. Therefore, we also consider more crude cleaning methods. Specifically, the use of di-glyme and other organic compounds to pretreat wood samples in a much shorter time.

We analyse the purity of cellulose, determined by Fourier Transform Infrared Spectroscopy (FTIR), in relation to the ¹⁴C and δ¹⁸O results as well as pretreatment yields for modern and old samples. The goal of this being to determine how “clean” a sample must be to produce accurate results while avoiding un-necessary cleaning steps while producing a high enough yield for analysis. This project investigates if different approaches for wood pretreatment are needed depending on application and the preservation of the wood.

T02_P10

System for graphitization of CO₂ samples - development status.

Kłosok K^1,2,  Rakowski A¹, Kolarczyk A², Miłosz S², Tudyka K¹

¹Silesian University Of Technology, Gliwice, Poland, ²miDose Solutions, Zabrze, Poland

The accelerator mass spectrometry (AMS) technique is widely used in radiocarbon dating and biocomponent determination due to the possible measurement of small samples with a carbon content of about 1 mg.

The design of a line for graphitisation of carbon dioxide samples for radiocarbon dating, along with the results of acceptance tests, have been presented in scientific articles (Krąpiec et al. 2018, Wiktorowski et al. 2020). Currently, within the Innovation Incubator 4.0 project, a prototype of an automatic line for graphitisation of samples, is being developed, which will allow to significantly reduce the time needed to prepare samples for measurement. The result of this project is expected to be a commercial device for automatic graphitisation of samples.

T02_P11

The Development of an Organic Solvent Pretreatment Based on Thermodynamic Insights for the Accurate Radiocarbon Dating of Conserved Samples

Lacey T¹,  Tate A¹

¹DirectAMS, Bothell, United States

Conserved archaeological samples, while the subject of high academic interest, are challenging for radiocarbon dating laboratories because the conservation substance is usually unknown and may be chemically complex. Furthermore, the samples are typically poorly preserved, available in limited quantity, and require additional pretreatment with organic solvents to remove the applied carbon. To date, such solvent protocols have been presented with limited discussion of the underlying science of dissolution required to efficiently target the widest possible chemistries of conservation chemicals.   A novel organic solvent protocol informed by the by Hansen Solubility Parameter model is discussed and its efficacy is assessed against a diverse set of polymeric conservation chemicals.

T02_P12

Funny and tricky sample wrappings – Challenging your radiocarbon laboratory

Lindauer S¹,  Friedrich R¹

¹Curt-Engelhorn-Centre Archaeometry, Mannheim, Germany

Radiocarbon samples can be wrapped in all sorts of bag and materials to make sure the samples arrive safe and sound. Over the years  variety of possible and impossible samples arrived at our lab, causing problems occassionally but often being the highlight of the day cheering up the people involved.

When someone is in the field, sometimes an important samples needs to be taken when the person is totally unprepared. Then things like cigarette packets, or former office packets can become important to help out. But sometimes samples are taken, wrapped in aluminium foil and forgotten in the desks. See on our poster what happened to these.

This poster is meant to cheer you up, not to blame anybody. But also with a little warning here and there.

T02_P13

A short note on temperature influence of the acid step in bone sample preparation

Lindauer S¹,  Friedrich R¹

¹Curt-Engelhorn-Centre Archaeometry, Mannheim, Germany

Several sample preparation protocols are known which deal with the trial to extract as much collagen of a bone sample in reliable quality as possible. In addition, care must be taken to conserve the isotope ratio if further investigations such as stable isotopes are planned. Often these protocols are compared by modifying several parameters at once so that the real effects of the different components cannot be compared very well. We concentrated our test on the temperature influence of the first acid step. This step serves to demineralize the sample. We compare sample preparation at room temperature with two acid strength concentrations and at 4°C with the same acid concentrations. Our results imply that the acid concentration is not the key influence on the collagen yield, but the temperature is.

T02_P14

An Approach to Dating Poorly Preserved Bones

Eugenia M¹,  Regev L¹, Boaretto E¹

¹Weizmann Institute of Science, Rehovot, Israel

When analyzing bones found in arid regions such as Near East for radiocarbon dating, we are very often faced with low insoluble collagen contents (<1%) or  the absence of insoluble collagen. We therefore try to find alternative solutions. We tested the suitability of dating the acid soluble fraction (ASF) recovered during the standard procedure of hydroxyapatite demineralization. This fraction is  normally  discarded during the extraction of collagen. For such samples, we propose a tailored approach that involves the separation of  biological materials present in the ASF. This includes reassembled  collagen and non-collagenous protein (NCP). Based on recent studies in the field of proteomic analysis, this fraction (NCP) is rich in biomolecular material. The problem of using ASF for radiocarbon dating, lies in the difficulty of removing exogenous carbon from the mixed material. In this study, we attempt to characterize the ASF from fossil bones, followed by isolation and dating of BGP (bone Gla protein) from the NCP.

T02_P15

Novel sample preparation approach to investigate

¹⁴C from iron material

Baráth B¹,  Jull A¹, Molnar M¹

¹INTERACT Laboratory, Debrecen, Hungary

In this study, we present a novel approach for ¹⁴C analyses of iron material. Artefacts made from wrought iron, could  incorporate some C content from the applied heating material (charcoal, wood), which deliver a measurable ¹⁴C content into the iron. This C and ¹⁴C might allow the ¹⁴C based dating of the production of the iron tool. Neutron flux could also produce significant amount of ¹⁴C atoms inside the iron based construction elements (vessel wall, tubes, etc) of nuclear reactors. 

For all the above listed applications, we need a good sample preparation method, to extract the C from the iron. As the typical concentration is maximum a few percent C in the iron (m/m%), a complete combustion/oxidation of 0.1 - 1 g iron for this purpose is necessary. We present an elegant way of this preparation, using a LECO C744 type iron – C analyser. The exhaust gas of this automatized oxidizer is applied for trapping the produced CO2, for further isotope analyses. About 1g of iron is completely oxidized within 1 minute by the C744 unit, and the exhaust gas is collected. C yield, and reproducibility of this preparation method is investigated by AMS ¹⁴C analyses of known age iron artefacts, and several ¹⁴C reference materials.

This method could play an important role, when nuclear power plants are decommissioned and significant amount of iron waste has to be classified according their ¹⁴C isotope content.

T02_P16

A semi-automated graphitization system

Olsen J¹

¹Aarhus University, Aarhus, Denmark

Presented here is a semi-automated graphitization system. The design of the system is inspired by semi-automated graphitization system in use at the A.E. Lalonde Accelerator Mass Spectrometry (AMS) Laboratory. The system is made from stainless steel with VCR fittings and orbital welded joints and consists of 20 graphitization units connected to a common vacuum system. The graphitization ovens are made with quick-fit joint to ease operation. Further the ovens are well insolated having an outer surface temperature of c. 30 °C when operated at core temperature of 550 °C. The system is controlled by a National Instruments real-time computer. This ensures continues monitoring of the system as well as ensuring a high degree of safety in terms on oven and vacuum interlocks. A gas inlet system with three channels for H₂, Ar and O₂ enables the introduction of H₂ for CO₂ reduction and Ar for venting tube-crackers and reactors. O₂ is at present not installed on system but will enable pre-combustion of reactors for improved ¹⁴C backgrounds. The real-time FPGA unit ensures fast (ns) measurements of gas inlet flow rates and pressure to ensure quick shutdown of gasses in case of malfunctioning. The user interface (UI) is made using LabView and runs on a separate PC which can lock-on to the real-time system. The UI is build with database access and with a user friendly look to ensure safe and easy operation.

T02_P17

Predicting the collagen yield of unknown samples

Olsen J¹,  Schrøder T¹, Philippsen B¹, Kanstrup M¹

¹Aarhus University, Aarhus, Denmark

Bone samples for radiocarbon analysis are difficult and time consuming. Often the bone preservation is unknown and frequently the bone collagen yield is underestimated resulting in small samples. If the collagen can be predicting some of these problems can avoided. At Aarhus AMS Centre we have collected FTIR spectra, %C and %N of raw bone samples of more than 200 samples. Further, we extracted collagen and conducted FTIR analysis as well as elemental and stable isotope analysis. Presented here are modelling results from which the collagen yield is predicted from measurements of raw bones. Different types of models (correlation models, neural networks, machine learning) and their performance will be presented and discussed.

T02_P18

Radiocarbon dating of fossil wood - verification of the effectiveness of various preparation methods

Michczyńska D¹, Jędrzejowski M¹, Kłusek M¹, Michczyński A¹,  Pawełczyk F¹, Piotrowska N¹, Wyss K², Hajdas I²

¹Institute of Physics - CSE, Silesian University of Technology, Gliwice, Poland, ²Laboratory of Ion Beam Physics, ETHZ, Zurich, Switzerland

A comparison of a few various preparation methods was carried out on sub-samples of fossil wood from Szczerców near Bełchatów (Central Poland). The tests were performed for both large and small samples - for LSC and AMS dating, respectively, and all preparation methods were performed two ways: with and without solvent washes in the Soxhlet apparatus. We compared the usefulness and effectiveness of individual methods based on the results of FTIR analysis and ¹⁴C measurements. Our aim was also to check whether the long, multi-stage preparation of large samples, with ¹⁴C concentration value close to the range of radiocarbon method, leads to significant absorption of CO₂. The conducted research and multi-criteria analysis, considering: cost, efficiency, repeatability and work- and time consumption, allowed to select the most effective method of fossil wood preparation.

T02_P19

Collagen extraction and amino acid purification for radiocarbon dating of a Late Neolithic mass grave

Philippsen B^1,2, Olsen J²,  Nørkjær Johannsen N³

¹Museum Lolland-Falster, Nykøbing F, Denmark, ²Aarhus AMS Centre, Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark, ³School of Culture and Society - Department of Archeology and Heritage Studies, Aarhus University, Højbjerg, Denmark

The purpose of this paper is to improve the preparation of bone samples for radiocarbon dating. As a test case, we use the Late Neolithic mass grave of Koszyce, Poland.

DNA analysis of the individuals from the mass grave has demonstrated that they had been a large extended family. This supports the archaeological observation that the individuals were buried there in one single event. The mass grave thus contains bone samples of the same age and can be used to test radiocarbon sample preparation methods.

For an earlier study, we have extracted and radiocarbon dated bone collagen of fifteen human individuals and one sheep bone from the mass grave. With the traditional collagen extraction methods usually utilized at the Aarhus AMS Centre, only the sheep and three human bones yielded sufficient collagen for radiocarbon dating. We therefore modified the pretreatment procedure by using weaker reagents at lower temperatures. This enabled us to extract sufficient collagen from the remaining twelve human bone samples. However, the radiocarbon ages showed considerable spread, and several outliers had to be removed from the dataset. We therefore suspected that we had not been successful in removing all contaminants from the bone collagen and tested an alternative approach, purification of the collagen hydrolysate with an ion exchange resin.

T02_P20

Implementation of Fe/Zn graphitization method in Dendrochronological laboratory at AGH University of Science and Technology , Krakow, Poland 

Krąpiec M¹, Rakowski A²,  Molnar M³, Pawlyta J¹, Huels M⁴

¹AGH, Kraków, Poland, ²SUT, Gliwice, Poland, ³ATOMKI, Debrecen, Hungary, ⁴Uni Kiel, Kiel, Germany

Accelerator mass spectrometry (AMS) is the most common measuring technique used in the radiocarbon dating. The procedure of age determination with this technique is divided into two parts: sample preparation and measurement. Sample preparation includes mechanical and chemical processes of cleaning, combustion, graphitization and pressing into sample holder to form a perfect cathode.  Fe/Zn method for preparation of graphite targets for AMS measurements of radiocarbon concentration has been tested in the Dendrochronological Laboratory at AGH University of Science and Technology, Kraków. Performance of the method was tested with samples of NIST Ox-II, IAEA standards (IAEA C3, C5, C6, and C8), and blank samples. The test confirms good reproducibility of results obtained for the samples prepared using this method. 

T02_P21

¹⁴C ramp-pyrolysis and FTIR analysis of Trondheim CaCO₃ precipitates of atmospheric CO₂ samples: further investigations and insights

Santos G¹,  Leong C¹, Seiler M², Grootes P², Svarva H², Nadeau M²

¹University of California, Irvine, Irvine,, United States, ²The National Laboratory for Age Determination, NTNU University Museum, Trondheim, Norway

An archive of atmospheric CO₂ samples collected by the Trondheim Radiocarbon Laboratory (NTNU) since early 1960s, and precipitated as CaCO₃, has been evaluated by radiocarbon (¹⁴C) analysis for its reliability (Seiler et al. 2022). Results indicated the presence of a contaminant that was not removed by different chemical cleansing procedures. Here, we present a follow up investigation using a subset of the samples shown in Seiler et al. (2022). The selected CaCO₃ samples and several reference materials of carbonate and mixed matrix origins were subjected to ramp-pyrolysis at < 285ºC. Upon 24 hours, CaCO₃ samples as well as reference materials were transferred still hot to the vacuum line, flame torch sealed, combusted, and then brought through graphitization using standard protocols. Radiocarbon measurements of CaCO₃ samples performed at Keck Carbon Cycle Accelerator Mass Spectrometer match with those recently attained by NTNU. To determine the performance of heat treatment, Fourier-transform infrared (FTIR) spectroscopy were performed on ramp-pyrolysis treated and untreated CaCO₃ samples. While FTIR confirmed that water and chains of carbohydrates have been removed upon heating, their absence did not improve the ¹⁴C results of CaCO₃ powders. Maximum ¹⁴C depletion was still 11‰. This may indicate that the elusive contaminant is of carbonate origin, possibly due to reactivation of carbonation by moisture and changes in temperature during decades of poor storage conditions. These findings will be discussed.

Seiler et al. 2022. Radiocarbon. Accepted.

T02_P22

Assessing a one-for-all alpha-cellulose procedure for ¹⁴C analysis of fossil to post-bomb ages

Santos G¹,  Komatsu A¹, Renteria J¹, Brandes A², Leong C¹, Collado S³, De Pol-Holz R³

¹University of California, Irvine, Irvine,, United States, ²Universidade Federal Fluminense, Niterói,, Brazil, ³Universidad de Magallanes, Punta Arenas, Chile

Cellulose is an important component in plants’ cell walls and is often separated from other compounds, such as hemicelluloses, lignin and extractives by chemical steps in order to be utilized in isotopic studies. In ¹⁴C analysis, reliable ages are fundamental, including those at the extremes of the ¹⁴C age array, i.e., post-bomb 1950 AD and ¹⁴C limit (beyond 50 kyrs). Finding a one-for-all procedure that can accurately provide results that satisfy the large ¹⁴C age spectrum can be challenging. Therefore, any procedure and/or procedures that whereby can make wood cleaning or cellulose-rich residual fraction extractions easier, faster and reliable for the full ¹⁴C age spectrum are preferable. Here, we describe a simple and fast manual procedure that can be easily scaled up or down as desired, as well as modified on demand (depending on samples requirements). Same-day or three-days are needed to extract chipped wood to alpha-cellulose homogenized fibers from batches of ≤ 10 to 40 samples, respectively. Procedure setup (e.g., reagents, laboratory instrumentation and consumables) are relatively simple, as they are all off-the-shelf items that are commercially available. High levels of precision and accuracy was attained from replicates ranging from post-bomb 1950 AD to ¹⁴C limit by using woody reference materials as well as samples from pantropical regions (post-bomb, subfossil and fossil). Results were in the order of 0.3% or better, regardless of the age group studied. Details about this protocol will be shared and discussed.

T02_P23

Experimental Conditions for ¹⁴C graphite preparation at GXNU lab, China

Shen H^1,2,  Wang L¹, Tang J¹,  Li Z¹, Shi S¹,  Zhang G¹, Chen  D¹,  Qi  L,  Wang N^1,2

¹Guangxi Normal University, Guilin, China, ²Guangxi key laboratory of nuclear physics and nuclear technology, Guilin, China

As a vital sample preparation method for ¹⁴C graphite, the Zn-Fe reduction method has been widely used in various laboratories. However, there are still few studies on the experimental conditions for the preparation of ¹⁴C graphite with this method. In this work, ¹⁴C graphite samples were prepared based on the Zn-Fe method, and the experimented key parameters such as the reduction reaction temperature, reaction time, reagent dosage, Fe powder activation, and other factors were investigated and determined. The results provide important instructions for the preparation line of ¹⁴C graphite at GXNU lab.

T02_P24

Preparation method of foraminifera radiocarbon sample and its age determination at GXNU-AMS

Qi L¹, Tang J¹, Shi S¹, Wang L¹, Zhang G¹, Chen D¹, Shen H^1,2

¹Guangxi Normal University, Guilin, China, ²Guangxi key laboratory of nuclear physics and nuclear technology, Guilin, China

Foraminifera radiocarbon (¹⁴C) measurements allow absolute geological dating with high accuracy. However, the reliable and accurate measurement of foraminiferal radiocarbon is challenging due to the small sample size and the sample preparation procedure. A series of foraminifera and shell samples from the Pearl River Estuary of China were prepared and performed radiocarbon measurements with a campact accelerator mass spectrometer (GXNU-AMS) at Guangxi Normal University. The results showed that the recovery rate of the samples was more than 80%, and the formation time of foraminifera was between 525 yrBP and 37500yrBP.

Keywords: Foraminifera; GXNU-AMS; ¹⁴C

T02_P25

New developments in the radiocarbon-based source apportionment for the water-soluble organic carbon fraction of airborne particulate matter

Strähl J¹,  Lechleitner F¹, Laemmel T¹, Geissbühler D¹, Salazar G¹, Szidat S¹

¹Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Air pollution is known for its adverse effects on human health (Burnett et al., 2014) and causes annually more than 6 million premature deaths (Gakidou et al., 2017). This demonstrates the exigency for effective mitigation strategies. Water-soluble organic carbon (WSOC) poses a large fraction of airborne particulate matter (Pöschl, 2005), and its source apportionment is crucial to understand the origin of pollution. The analysis of ¹⁴C is a powerful tool for source apportionment as it allows to discriminate between fossil and non-fossil emissions (Szidat, 2009). WSOC is extracted from samples using a wet oxidation procedure, with the advantage of low blank contamination and rapid sample processing times (Rauber et al., in prep.). The CO₂ generated from the wet oxidation can be analysed for its ¹⁴C content using an accelerator mass spectrometer equipped with a gas ion source (Ruff et al., 2007).

Here we present an optimized setup for the preparation and treatment of WSOC samples for ¹⁴C analysis that addresses concerns regarding sample recovery and blank contamination. A newly developed sintered needle minimizes losses of CO₂ during the sampling from the headspace of closed vials, while circumventing issues arising from the use of carbon-based glues. This allows the measurement of smaller sample amounts and simplifies the previous setup as no high-capacity water traps are needed anymore. A recently incorporated non-dispersive infrared CO₂ detector increases the accuracy of sample amount quantification. Finally, a detailed blank assessment on the new setup enables to detect possible remaining contamination sources and minimize their contribution.

T02_P26

Using XAD resin to remove synthetic contamination from archaeological bone prior to radiocarbon dating

van der Sluis L^1,2,  Zazzo A¹, Thil F³, Pétillon J⁴

¹Archéozoologie, Archéobotanique, Sociétés, Pratiques et Environnements (AASPE) UMR 7209, Muséum national d’Histoire naturelle, CNRS, Paris, France, ²Department Of Evolutionary Anthrpology, University of Vienna, Vienna, Austria, ³Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL UMR 8212, CEA-CNRS-UVSQ, Université Paris Saclay, F-91198 , Gif-sur-Yvette, France, ⁴Travaux et Recherche Archéologiques sur les Cultures, les Espaces et les Sociétés (TRACES) UMR 5608, Toulouse,  France

Extraction protocols for radiocarbon dating bone collagen samples are continuously being tested and improved. Contamination can originate from the burial environment as well as post-excavation treatments, involving conservation treatments using synthetic consolidants. While most contamination can be removed using the ABA method, this is not the case for cross-linked contamination. The most suitable method to remove contamination from especially small bone samples seems to be the XAD method.

The XAD protocol was implemented at the MNHN radiocarbon laboratory and tested using known age bone samples and a Palaeolithic bone sample that had been consolidated and produced an anomalous peak in the FTIR-ATR spectra at 1725 cm^-1.

To test the functionality of the XAD resin, samples of known age were consolidated with shellac or Paraloid and artificially aged in a climate chamber for a month. Samples were then treated with or without the XAD resin and radiocarbon dated. The Hollis bone blank showed that XAD resin was able to remove young carbon from shellac, which was not the case for the ABA-only method. Results from VIRI I were more variable and VIRI F was possibly too young to show the effects of the consolidants. Four radiocarbon dates on the Palaeolithic bone after XAD treatment are statistically the same, while a sample without XAD treatment was significantly older, suggesting that the contaminant was not fully removed by the classical ABA treatment. This study demonstrates the interest of the XAD treatment to clean heritage bone samples stored in museums prior to geochemical analyses.

T02_P27

Preliminary study to reduce the amount of sampling

for ¹⁴C dating of non-buried ivory

Wojcieszak M¹, Ligovich G, Van den Brande T, Boudin M

¹Royal Institute for Cultural Heritage (KIK/IRPA), Brussels, Belgium

According to European law and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), worked ivory and raw tusks acquired before 1947 can be traded in the EU. Radiocarbon dating is an effective method to recognise ivory formed after 1947 since during 1950s and 1960s atomic bomb testing created a large increase in atmospheric radiocarbon content. Prior to dating the ivory, the common pre-treatment method is the same as the one used for bone and consists of extracting the collagen. Depending on the age and state of the ivory sample, the collagen content varies between ~10 and 20 % by weight. To obtain enough collagen for dating, around 100 mg of sample is needed and around 3.5 mg of collagen is combusted and graphitised. In this study we compared the ¹⁴C dates of samples prepared with the traditional collagen extraction, and samples directly combusted without any treatment. The preliminary tests show almost no differences between the dates obtained with the two methods. Around 10 mg of sample were used for the direct combustion method, which reduces the amount of sample needed by 10 times. This would be significant in the case of small ivory objects. However, this procedure can only be performed with non-buried materials since a pre-treatment is necessary in the case of buried ones.

T02_P28

The impact of micro-CT scanning on radiocarbon dating of fossil material: a cautionary note

Wood R¹,  Martín-Francés L², Duval M³

¹University Of Oxford, Oxford, United Kingdom, ²Centro de Evolución y Comportamiento Humanos (UCM-ISCIII), Madrid, Spain, ³Centro Nacional de Investigación sobre la Evolución Humana, Burgos, Spain

It is imperative that damage to rare and valuable remains is minimised in palaeoanthropological research. Micro-computerized tomography (mCT) scanning of fossils is now routinely used to record a high resolution three-dimensional reconstruction of samples prior to destructive analyses such as radiocarbon dating. It is therefore crucial to establish whether the method has a negative impact on the associated analysis, and to determine how this impact can be reduced. We examine whether a range of mCT acquisition parameters could influence collagen yield of a well preserved woolly rhino bone. Whilst mCT had no significant impact on the radiocarbon age obtained, we find that collagen yield is reduced from around 7% to 4.5%, suggesting protein is damaged during the scanning process. This does not seem to be strongly correlated to the x-ray intensity. In this bone, collagen yield remained well above the minimum cut-offs of 0.5 or 1%  typically used in radiocarbon laboratories. However, it does imply that a larger sample may be required from bones that have undergone previous scanning. This might become an issue for highly valuable fossils like in palaeoanthropology. Additionally, samples with low collagen yield might also result unsuitable for ¹⁴C dating after mCT. This is the second study showing that mCT scanning of fossils may have a non-negligible impact on dating results, after a similar work focused on Electron Spin Resonance (ESR) dating. It might be worth reconsidering the systematic and unlimited use of mCT scanning in palaeoanthropology in the light of these results.