T01_01

Real-world ¹⁴C quantification by Saturated-absorption CAvity Ring-down (SCAR) spectroscopy

Carcione F^1,3, Delli Santi M⁷, Insero G^2,5, Cancio P^2,6, Galli I^2,6, Giusfredi G⁶, De Natale P^2,8, Mazzotti D^2,6, Defeo G⁴, Bartalini S^1,2,6

¹ppqSense Srl., Sesto Fiorentino, Italia, ²European Laboratory for Nonlinear Spectroscopy (LENS), Sesto Fiorentino, Italy, ³Università di Firenze, Dipartimento di Ingegneria, Firenze, Italy, ⁴Ars Tinctoria Srl., Santa Croce sull'Arno, Italy, ⁵Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy, ⁶Istituto Nazionale di Ottica (INO-CNR), Sesto Fiorentino, Italy, ⁷Istituto Nazionale di Ottica (INO-CNR), Pozzuoli, Italy, ⁸Istituto Nazionale di Ottica (INO-CNR), Firenze, Italy

Saturated-absorption cavity ring-down (SCAR) spectroscopy has pushed molecular detection to an unprecedented sensitivity of a few parts-per-quadrillion (ppq), thus allowing precise quantification of ¹⁴CO₂. Technology has been progressing since its first demonstration in 2011 and has taken to a portable instrument which is being deployed worldwide. Recently, our instrument has been applied for addressing specific problems in very different areas of science and humanities. Results will be shown for SCAR application to: discrimination of biogenic vs. fossil content in materials and fuels; radiological assessment of waste coming from decommissioning of a nuclear power plant; dating of archeological samples from a 4500 years old Sumerian site.

Next applications aim to ¹⁴C precise measurements in atmospheric samples, since distinguishing and measuring fossil vs. biogenic CO₂ in the atmosphere is the key to quantify the anthropogenic contribution to climate change. Aspects of the above applications, and many others that will come in the future, are in line with the European Green Deal, aiming to adopt a set of proposals to make the EU's climate, energy, transport and taxation policies fit for reducing net greenhouse gas emissions by at least 55% within 2030. In this perspective a cheap, compact, fast and clean technique for biogenic carbon analysis, like SCAR, will provide a crucial tool for implementing many of the European Green Deal strategies. We will also touch upon progress towards a biological SCAR instrument where dynamic range, throughput, and sample size are of the utmost importance.

T01_02

NIR-imaging and Radiocarbon dating together for making the invisible visible. A non-destructive visualization of collagen before attempting a radiocarbon date

Catelli E¹,  Malegori C², Sciutto G¹, Oliveri P², Prati S¹, Benazzi S³, Cercatillo  S⁴, Paleček D⁴, Mazzeo R¹, Talamo S^4,5

¹University of Bologna, Department of Chemistry “G. Ciamician”, Ravenna Campus, Via Guaccimanni, 42, 48121, Ravenna, Italy, ²University of Genova, Department of Pharmacy, Viale Cembrano 4, I-16148, Genova, Italy, ³University of Bologna, Department of Cultural Heritage, Ravenna Campus, Via Degli Ariani, 1, 48121, Ravenna, Italy, ⁴University of Bologna, Department of Chemistry “G. Ciamician”, Via Selmi, 2, 40126, Bologna, Italy, ⁵Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany

Many archaeological rarest bones (human remains and precious bone objects) from Prehistory are enormously precious and are considered a cultural and historical patrimony. Radiocarbon dating is a well-established technique that estimates the age of bones by analyzing the collagen content. However, it is a destructive method and must be limited. In this study, we use imaging technology to visualize the presence of collagen on bone samples in a non-destructive way, hence minimizing the destruction of precious samples submitted to radiocarbon dating. The technique is near-infrared hyperspectral imaging (NIR-HSI).

NIR-HSI was used with a chemometric model to create chemical images of collagen distribution in ancient bones. The model also quantifies the collagen at every pixel and thus answering the questions: what, how much, and where.

Sixty archaeological samples (from the modern age to >50,000 years ago) have been used for developing the predictive model for quantifying collagen, based on partial least squares (PLS) regression. The amount of collagen in the selected bones was previously determined through the pretreatment of bone for the extraction of collagen for radiocarbon analysis. The model was validated using Cross-Validation (CV) and an independent test set of NIR-HSI bone images. The method represents a sustainable pre-screening approach for identifying sampling points for subsequent specific analyses, such as ¹⁴C dating.

Since the cultural heritage represents the testimony of past civilizations, our result will provide a significant advance not only for the study of human evolution but also for protecting and enhancing European cultural heritage.

T01_03

Radiocarbon AMS below 100 keV

Maxeiner S¹,  Synal H², De Maria D², Wacker L², Müller A², Fahrni S¹, Suter M²

¹Ionplus AG, Dietikon, Switzerland, ²Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland

New technologies such as He-stripping have enabled the miniaturization and simplification of compact accelerator mass spectrometry (AMS) systems over the last two decades. As one of the most compact AMS systems, the MICADAS was optimized for stripping energies of around 240 keV and provides precise and efficient radiocarbon measurements for more than 15 years. In a collaboration between ETH Zurich and Ionplus AG, a new ultra-compact radiocarbon AMS system has been developed. It is based on many of the principles of MICADAS and operates near or at the physical limits of efficient radiocarbon AMS with stripping energies of around 100 keV. Measurements performed with an early prototype system showed that, despite the much lower beam energies, highly efficient, sensitive, and precise measurements comparable to MICADAS are possible. The technical challenges at such low voltages and the measurement results with different prototype configurations will be discussed and a new commercial product will be presented: the Low Energy Accelerator (“LEA”). With a footprint of 2.6 m x 1.8 m and with a tandem acceleration voltage of 50 kV, LEA is expected to perform similarly to the MICADAS at less than half its energy.

T01_04

Testing the measurement of small (<50 ug C) graphite samples on the ORAU MICADAS

Becerra-Valdivia L¹,  Cameron J¹, Spindler L¹, Gianni M¹, Chivall D¹, Bronk Ramsey C¹, Wood R¹

¹Oxford Radiocarbon Acceleration Unit, Oxford, United Kingdom

The Oxford Radiocarbon Accelerator Unit (ORAU) has processed about 5,000 samples for research and commercial purposes since the installation of a Mini Carbon Dating System AMS (MICADAS; Ionplus AG, CH) in 2019. Very few of the measurements produced, however, have been on graphite samples of less than 100 ug C. Given the need to reduce sample size in order to adequately address research questions across disciplines, a study was aimed at testing our ability to reliably measure very small graphite samples (<50 ug C) as an alternative to gas measurement by reassessing our current graphitisation (iron-catalysed hydrogen reduction), combustion and cleaning procedures. This included decreasing reaction vessel volume, increasing the mass of iron powder used, and decreasing graphitisation temperature to assess isotopic fractionation and AMS current behaviour. Throughout these experiments, efforts were made to efficiently and minimally adjust our current equipment set-up for simplicity. Here we present the preliminary results of this study and discuss archaeological and paleoecological applications.

T01_05

Rapid DIC extraction-to-graphite hybrid system at NOSAMS

Gospodinova K¹,  Gagnon A¹, Wilson J², Hansman R¹, Elder K¹, Burton J¹, Lang S¹, Kurz M¹

¹Woods Hole Oceanographic Institution, Woods Hole, United States, ²AEON Laboratories, Tucson, United States

The Rapid Extraction of Dissolved Inorganic Carbon System (REDICS) is used to provide precise stable isotope and radiocarbon measurements of dissolved inorganic carbon (DIC) at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility. For the past year REDICS has primarily been used to provide oceanic radiocarbon measurements for the GO-SHIP program. REDICS automatically extracts sample DIC in the form of CO₂ using a membrane contactor and stores the extracted gas into a glass manifold for subsequent analysis on one of NOSAMS graphitization systems.

NOSAMS recently purchased a carbon extraction and graphitization system (CEGS) from AEON Laboratories, which was customized to automatically process and graphitize ten samples while obtaining sample splits for stable isotope δ¹³C analysis. The system is compact, easily transportable, and, unlike other graphitization systems at NOSAMS, the sample graphitization begins immediately post-sample transfer to the reactor. These characteristics make it ideal for connecting to other CO₂ extraction systems.

Here we present our work on linking the REDICS and CEGS systems to create a hybrid system for rapidly processing DIC from seawater and groundwater samples. The analysis time from extraction to beginning of graphitization is on the order of 35 min, with current output designed for ten samples each day. Linking the two systems not only streamlines the process but shortens it from a two-day analysis to one, further increasing overall sample throughput at the facility.

T01_06

Simultaneous ¹⁴C and ¹³C measurements for any source of CO²

Wertnik M¹,  Wacker L¹, Haghipour N¹, Bernasconi S¹, Synal H¹, Eglinton T¹, Welte C¹

¹ETH Zurich, Zürich, Switzerland

Carbon isotopes are an important source of information for a broad range of research fields related to carbon cycle studies and beyond. In this context, radiocarbon can be used to study temporal and partitioning effects, while the stable isotope (¹³C) gives information about the source of the carbon (e.g. terrestrial or marine). Recently, an approach enabling the simultaneous analysis of all naturally occurring carbon isotopes in organic combustible materials has been introduced[1].

Here, we present a novel and very flexible method for simultaneous ¹⁴C and ¹³C measurements that can be combined with any CO₂-feeding interface. The CO₂ from the sample is captured on a zeolite trap and subsequently transferred into a syringe, where it is diluted with Helium to a concentration of around 4%. The syringe allows constant feeding of the gas for simultaneous measurement with a split of 85% of gas to the accelerator mass spectrometer (AMS) and 15% to the isotope ratio mass spectrometer (IRMS). For carbonate samples, we can measure samples from 8 – 200 μg of Carbon to a precision of 0.1‰.

[1]         C. P. McIntyre et al., ‘Online ¹³C and ¹⁴C Gas Measurements by EA-IRMS-AMS at ETH Zürich’, Radiocarbon, vol. 59, no. 3, pp. 893–903, Oct. 2016

T01_07

An automated processing line for the extraction of dissolved inorganic carbon from water for radiocarbon dating

Yang B¹,  Williams A², Nguyen T¹, Freeman P¹, Jacobsen G¹, Smith A¹

¹Australian Nuclear Science & Technology Organization (ansto), Lucas Heights, Australia, ²Deceased. , ,

At ANSTO, radiocarbon analyses of dissolved inorganic carbon (DIC) in groundwaters are in high demand for water resource sustainability research. A grant from the NSW Research Attraction and Acceleration Program enabled the development of an automated DIC extraction line for unattended processing of 10 samples.  This line operates at ambient pressure with helium (He) gas as carrier. CO₂ gas is extracted from 50 mL of water in a 250 mL reaction vessel by adding 5 mL of phosphoric acid. The He gas is sparged through the water sample and then passed through two water traps at -100°C to remove water; and two CO₂ traps at -165°C to collect CO₂ gas. Complete recovery of CO₂ is determined by passing the He flow through a CO₂ analyser before releasing to waste to verify the absence of any residual CO₂. The CO₂ gas is then cryogenically transferred into one of 10 storage vessels until all queued samples on the system are processed. Between samples, the water traps and CO₂ traps are cleaned by evacuation to a pressure <5/10³ mbar. The water loop is flushed by He gas, followed by Milli-Q® water and a portion of the next sample, so eliminating sample memory. The line is controlled by a Python program running on a PC through serial connections, and several important parameters are logged to check that the system is working properly. After processing 10 samples, CO₂ sample is manually transferred to glass break seals for purification and conversion to graphite for AMS measurement.

T01_08

Direct Radiocarbon Analysis of Methane by Positive Ion Mass Spectrometry

Mcintyre C¹,  Shanks R¹, Gulliver P¹, Dolan M², Freeman S¹

¹SUERC, East Kilbride, UK, ²GENeco, Avonmouth, UK

After carbon dioxide (CO₂), methane is the second most abundant anthropogenic atmospheric green house gas and it has a warming potential 25 times that of CO₂. Radiocarbon (¹⁴C) is useful for tracking the source, fate and quantity of methane within the atmosphere however, current techniques for its analysis are lengthy and use multiple preparative steps for concentration, combustion and purification.

Positive ion mass spectrometry (PIMS) can directly analyse the ¹⁴C content of gases without the need for graphitization. It uses a plasma-based ion source to produce a positively charged carbon beam and a simple reaction cell to supress ¹⁴C interferences. This plasma-based ion source typically operates on carbon dioxide  but initial experiments have shown that methane analysis is also possible. Initial data from analysis of contemporary and fossil methane using PIMS will be presented and the performance compared with CO₂ PIMS and conventional AMS will be discussed. This new method opens up new areas of application, such as rapid biogas analysis.

In addition, the current status of the integration of automatic sample introduction to the PIMS system and its performance will be presented.

T01_P01

Double Trap Interface: A novel gas handling system for high throughput AMS analysis

De Maria D¹,  Fahrni S², Wacker L¹, Synal H¹

¹ETH Zurich, Zurich, Switzerland, ²Ionplus AG, Dietikon, Switzerland

Over the last decade, the interest in a combustion based AMS technology has increased due to significant progresses made towards compact AMS systems and the development of hybrid ion sources, allowing the analysis of samples in gaseous form.

To address the requirements of higher samples throughput and level of automation, a novel gas handling system, the Double Trap Interface (DTI), was developed. The instrument couples an elemental analyzer (EA) to the ion source of a MICADAS (Micro Carbon Dating System) AMS system. The DTI features two external traps filled with a zeolite molecular sieve, which collect the sample material in form of CO₂ after combustion with EA. Subsequently, the gaseous sample is released by thermal desorption and injected into the ion source. The alternating use of the traps allows a quasi continuous analysis, as the loading and measurement procedures are now decoupled and run in parallel on the two traps. The analysis of a sample requires less than 5 minutes, corresponding to a throughput of 12 to 13 samples per hour. To speed up further the measurement routine, we implemented an option allowing multiple analyses on a single cathode.

The main target are biomedical companies conducting metabolism and pharmacokinetic studies using radiocarbon as tracer during the validation of new pharmaceutical compounds. However, the EA-DTI system is not limited to biomedical studies only. The methodology has a huge potential for all applications requiring an increased throughput but less precision, as for example environmental tracer studies or the analysis of organic sediments.

T01_P02

The progress of AMS ¹⁴C analysis for small samples down to ultra-microscale size (μg level) at Xi’an AMS Center

Du H^1,2,  Fu Y^1,2, Yang B³, Zhou W^1,2

¹ State Key Laboratory of Loess and Quaternary Geology，Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China, ² Shaanxi Key Laboratory of Accelerator Mass Spectrometry Technology and Application, Xi’an AMS Center，, Xi'an, China, ³Australian Nuclear Science and Technology Organisation, Sydney,  Australia

As the urgent requirement at Xi’an AMS Center for Chronological Research and Tracer applications to radiocarbon (¹⁴C) analyze samples smaller than 0.1 mg carbon (mgC), a compact microgram carbon sample graphitization system has been  applied. The system include two small-volume graphitization reaction units connected quartz manifold and a stainless steel cold finger which can be used as a transfer line for measuring carbon mass and effective trapping of water vapour during the reaction. In a 1.2 mL graphitization reactors we can prepare samples containing 10–600μgC using an iron catalyst with an excess of hydrogen,and even a few micrograms graphite(<10μg) can be obtained. We detailed the effect of the chemical reaction rates with different brand iron catalysts and the morphology analysis of microscale graphite,compared the conventional closed-tube combustion method with the combustion and purification system based on an elemental analyzer (EA) connected to cryogenic traps, especially for the preparation performance of microscale sample. Futhermore, we made some case studies of chronological research on several foraminiferal samples from marine sediment core，and got a series of microgram graphites which have been performed well by our upgrade 3MV Xi’an AMS facility.This is mainly a report of our current capability with the preparation and measurement of micro-sample ¹⁴C-AMS and in the future we will expand the application of microgram carbon sample ¹⁴C-AMS analysis to archaeological bone samples, the microgram carbon graphitisation system will provide the technological opportunities to develop some challenging research.

T01_P04

Radiocarbon analysis of methane

Gentz T¹,  Höhn M¹, Grotheer H¹, Kattein L¹, Mollenhauer G¹

¹AWI-Bremerhaven, Bremerhaven, Germany

Methane (CH₄) is the most abundant organic compound in the atmosphere and its influence on the global climate is subject to widespread and ongoing scientific discussion. Two sources of atmospheric methane are the release of methane from the ocean seafloor, as well as from thawing permafrost.

In recent years the origin, sediment and water column processes and subsequent pathways of methane have received growing interest in the scientific community. ^13C/¹²C ratio measurements can be used to determine the methane source (biogenic or thermogenic), but potential formation/alteration processes by microbes are not yet fully understood.

Radiocarbon analysis can help to understand these carbon cycling processes. The presented method is a novel approach for the radiocarbon age determination of methane. A modified PreConn is used to separate methane from other gases such as CO₂ in a gaseous sample. Afterwards, the purified methane is transferred to a furnace and oxidized to CO₂. Subsequently, produced CO₂ is concentrated on a custom-made zeolite trap, which can be connected to a novel sampling unit implemented into the GIS system (by Ionplus AG) for direct CO₂ measurements on a MICADAS. The zeolite trap has ¼“ quick-fit connectors (Swagelok) that allow to detach the trap from the oxidation unit and to re-attach it in the GIS. Initial testing showed minimal blank carbon incorporation associated with sample storage, transfer and handling of the custom-build zeolite trap.

Here we will present the setup of the method, first results of the blank determination as well as precision of common standard gases.

T01_P05

DETERMINATION OF CARBON-14 SPECIFIC ACTIVITY IN SOIL AND SEDIMENTS BY TUBE COMBUSTION AND LIQUID SCINTILLATION COUNTING METHOD

Krishnan K A¹,  S B¹, N K¹

¹Centre for Advanced Research in Environmental radioactivity (CARER), Mangalore, India

Carbon-14 (¹⁴C) is a pure beta emitter and occurs naturally in the environment due to cosmic ray induced production in the atmosphere. ¹⁴C is also released into the atmosphere by nuclear fuel cycle facilities and gaseous discharges from all types of nuclear power plants (NPPs).  Oxidation of the samples in a combustion system, trapping the produced CO₂ in an amine-based absorber, and subsequent liquid scintillation analysis (LSA) is a proven method for samples with high carbon content, such as terrestrial plants. However, for soil and sediment matrices, which are considered poor carbon pools, improved methods are to be adopted for combustion since a large mass of these samples is to be combusted to produce sufficient CO₂ for saturation of the absorber.

This paper reports an improved method in which the conventional tube furnace system is used for combusting soil and sediment samples collected from the clean air region and from the vicinity of a NPP. The produced CO₂ was absorbed in NaOH, precipitated as BaCO₃, and CO₂ was regenerated by acid hydrolysis of BaCO₃ in a specially designed regeneration setup and trapped in an amine-based absorber, mixed with a liquid scintillator, and subjected to LSA. Validation of the method was performed by combusting IAEA C3 reference material. The method is capable of yielding accurate results with a deviation of <2.2 % from the target value.Upon validation, the suitability of the method for the determination of small excess ¹⁴C activity in the vicinity of a nuclear power plant was demonstrated.

T01_P06

Absolute dating with ¹⁴C and ⁴¹Ca - is it feasible?

Kutschera W¹,   Paul M²

¹University of Vienna, Vienna, Austria, ²The Hebrew University of Jerusalem, Jerusalem, Israel

It is well-known that ‘wiggles‘ and ‘plateaus‘ of the ¹⁴C calibration curve often limit the precision of age determinations. In principle this problem could be avoided by absolute dating [1]. This requires to measure the ‘mother/daughter‘ abundance ratio ¹⁴C/¹⁴N* which is independent of the initial ¹⁴C abundance and only depends on the half-life and the age. Whereas ¹⁴C dating in the ‘classical‘ way is well established – although with the limitations mentioned above – dating with ⁴¹Ca (half-life = 100,000 years) would require absolute dating because a global calibration curve for ⁴¹Ca does not exist. In this case, the abundance ratio of ⁴¹Ca/⁴¹K* has to be measured. In both cases the ubiquitous existence of stable nitrogen or potassium on Earth makes the detection of the feeble radiogenic signals of ¹⁴N* and ⁴¹K* extremely challenging.

It was noted by Szabo et al. [1] that the kinematics of the ¹⁴C beta decay leads to ¹⁴N* recoil energies < 6.9 eV comparable to binding energies of atoms in molecules. Due to the pure electron-capture decay of ⁴¹Ca, the recoil energy of ⁴¹K* is even lower: <2.2 eV: Thus, there exist a certain retention probability for the decay products to stay in the original molecule or change their chemical character. Possible detection methods of ¹⁴N* and ⁴¹K* and their potential applications in archaeology will be discussed.      

[1]  J. Szabo, I. Carmi, D. Segal, E. Mintz, “An attempt at absolute ¹⁴C dating,“ Radiocarbon

      40/1 (1998) 77-83. 

T01_P07

A new setup for CH₄ analysis at CologneAMS

Melchert J¹, Rethemeyer J¹, Gierga M¹, Gwozdz M²,

¹University Of Cologne - Institute for Geology and Mineralogy, Cologne, Germany, ²University Of Cologne - Institute for Nuclear Physics, Cologne, Germany

The radiocarbon analysis of CH₄ required the development of a new sample handling routine and the establishment of a new vacuum system that converts CH₄ to CO₂ for direct measurement with the gas injection system of the AMS at the CologneAMS facility. First tests with multiple series of ₁₄C-free and modern standards, as well with a biogas mixture with sample sizes ranging from 20 to 50 μg C resulted in a CH₄ to CO₂ conversion efficiency of 94 – 97%. Processed standards were further evaluated for contamination with extraneous carbon. With this new set up blank values achieved 0.006 ± 0.003 F¹⁴C, which is comparable to blank values achieved with our routinely used CO2 vacuum system. With the processed standard series, we were able to quantify a low contribution of 0.26 ± 0.13 μg modern and 0.33 ± 0.12 μg dead exogenous carbon, respectively, for the new system. Both sources of contamination resulted in 0.58 ± 0.18 μg of extraneous C, introduced during sample handling and pre-treatment, with a corresponding F14C of 0.447 ± 0.245. First tests with a near modern CH₄:CO₂ biogas mixture delivered reproducible results with a ¹⁴C content of 0.978 – 1.010 F¹⁴C, after applying the correction for extraneously introduced carbon.

T01_P08

LEA – A novel Low Energy Accelerator for Radiocarbon Dating under a long-term Performance Test

Ramsperger U¹,  De Maria D¹, Gautschi P¹, Maxeiner S², Müller A¹, Synal H¹, Wacker L¹

¹ETH Zurich, Zurich, Switzerland, ²ionplus, Dietikon, Switzerland

Based on MICADAS (Mini Carbon Dating System) technology the acceleration voltage at the gas stripper unit, where charge exchange of the negative ions takes place and interfering isobar molecules are dissociated, is further reduced from 200 kV for MICADAS to 50 kV for LEA (Low Energy Accelerator) system. By using He stripper gas at a local areal density of ≈ 0.5 μg/cm² molecular interferences can be destroyed at a particle energy of less than 100 keV without excessive beam losses that would impede reproducible measurements conditions. Detailed optimization of the acceleration stage hosting the stripper gas volume where necessary to balance molecule dissociation power and optical beam losses to enable measurement conditions suitable for routine high performance radiocarbon dating measurements. Basic elements such as the ion source, injection magnet, and the fast beam bouncing system are copies of the MICADAS design, whereas the mass spectrometer following the acceleration stage had been modified according to the reduced ion energy. After an initial testing phase of the LEA system it has been installed at ETHZ in a configuration suitable for routine radiocarbon dating measurements. Here, we present data of long-term measurements over several days with the LEA system and compare the results with data of the well-established MICADAS system, with an emphasis on stability and accuracy.

T01_P09

Assessing radiocarbon blanks associated with solid phase extraction of dissolved organic carbon from sea water

Schlagenhauff S¹,  Grotheer H¹, Niggemann J², Dittmar T², Mollenhauer G^1,3

¹Alfred Wegener Institute, Bremerhaven, Germany, ²Institute for Chemistry and Biology of the Marine Environment, Oldenburg, Germany, ³Marum Center for Marine Environmental Research and Department of Geosciences, Bremen, Germany

Radiocarbon analysis of marine dissolved organic carbon (DOC) gives insight into mixing timescales and C-storage, but technical challenges make obtaining samples for radiocarbon analysis costly and time consuming. Solid phase extraction (SPE) is a common technique to access not only the radiocarbon age of the SPE-DOC pool but also its molecular composition. The combination of SPE and low mass radiocarbon analysis using the MICADAS is a promising path to increase sample resolution but care must be taken to ensure confidence in the results. The aim of this work is to determine the amount and F¹⁴C value of extraneous carbon (Cex) in solid phase extracted samples to be analyzed on the MICADAS.  The Cex of modified styrene divinyl benzene polymer (PPL) cartridges was investigated indirectly by measuring a ¹⁴C free fossil standard, a modern standard (F¹⁴C =1), as well as fresh water (Suwannee River 2R101N) and marine (NELHA) DOC reference materials. These standards were compared systematically across PPL cartridge sizes and lots. The Cex mass contribution from the SPE ranged from 5.5-17µgC while the F¹⁴C value of the blank was unique to each cartridge lot. Interestingly, no correlation was found between the size of the cartridge used and the amount of Cex introduced into the samples. Since it is not possible to predict or influence the F¹⁴C of blanks in each cartridge lot, when working with low mass SPE samples, it is necessary to incorporate thorough blank assessment procedure.

T01_P10

HVE design of a gas interface for routine ¹⁴C sample AMS measurement

Scognamiglio G¹,  Klein M¹, Stolz A², Mous D¹

¹High Voltage Engineering Europa B.V., Amersfoort, Netherlands, ²Institute of Nuclear Physics, University of Cologne, Cologne, Germany

The ¹⁴C AMS measurement of CO₂ gas samples has two main advantages compared to solid: (i) the time-consuming graphitization process is not required and (ii) small sample masses are sufficient for the measurement (below 150 µg carbon), while graphitized samples need few mg carbon. These advantages make the AMS measurement of gas samples a recognized tool in both biomedical and dating applications.

The gas measurement requires a gas interface between the CO₂ source and the AMS system that collects, dilutes with helium and transfers the sample gas with a specific flow and timing.

In this contribution, we present the HVE design of a gas interface for the measurement of carbon samples combusted in an elemental analyzer. The CO₂ resulting from the combustion is collected in a zeolite trap and then transferred to a motor-driven syringe, which ensures the gas transfer to the AMS ion source in a controlled manner. The dead time is minimized by the implementation of two syringes and two zeolite traps. The gas interface is fully automated and can handle sample masses down to a few µg carbon. In combination with the elemental analyzer and the AMS, it supports a throughput of more than 10 samples per hour.

T01_P11

Experimental study on charge exchange cross sections of low energy Carbon ions in helium at GXNU

Zhang G¹, Zhao Z¹, Shi S¹, Tang J¹, Wang L¹, Chen D¹, Qi L¹, Shen H¹,2

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

Compared with nitrogen and argon, helium is lighter and can better reduce the beam loss caused by angular scattering during beam transmission, and the molecular dissociation cross-section in helium at low energy is high and stable, which makes the helium the prevalent stripping gas at low energy AMS. For the further study of the stripping behavior of ¹⁴C ions in helium at low energy, the charge state distributions of ion beams of carbon ions with -1, +1, +2, +3, and +4  charge states were measured at the energies of 40-220 keV with a compact 14C-AMS at Guangxi Normal University(GXNU).  Based on the experimental data, the stripping characteristics of C-He in the energy range of 40-220keV were analyzed, and the new charge state yields and exchange cross-sections in C-He at the energies of 40-220keV were obtained. 

Keywords：AMS;  state yield;   cross section;

T01_P12

Results of MODIS2 mortar dating intercomparison for the Zagreb Radiocarbon Laboratory, Croatia

Sironić A¹,  Cherkinsky A², Borković D¹, Barešić J¹, Krajcar Bronić I¹

¹Ruđer Bošković Institute, Zagreb, Croatia, ²Center for Applied Isotope Studies, University of Georgia, Athens, United States of America

The second international Mortar Dating Intercomparison Study (MODIS2) conducted in 2020. Three mortar samples have been distributed among interested radiocarbon laboratories in form of 1 g particle size fraction smaller than 150 µm and 2-5 g bulk mortar.

Our approach to dating MODIS2 mortars at the Zagreb Radiocarbon Laboratory, Croatia, was to separate 32 – 63 µm particle size fraction and to collect CO₂ by sequential dissolution with 85 % H3PO4 after 3 s, 15 s and until the end of reaction. The first fraction was regarded as date of the mortar, while the following fractions pointed to increase in dead carbon amount. The reported dates were: for sample #1 640 ± 20 BP, for sample #2 665 ± 20 BP and for sample #3 1750 ± 20 BP. In general, all the samples fit the expected ages, but bordering on upper limit age, implying still incomplete dead carbon removal.

Here we will also present dates obtained by data extrapolation, which we found can eliminate dead carbon contamination, and we will discuss the differences between the two approaches.

T01_P13

Source Term Analysis and Experimental Measurement Design of Carbon-14 in High-Temperature Gas-Cooled Reactor Pebble-Bed Module

Wang Y¹,  Guo J¹, Cao J¹, Xie F¹, Tong J¹, Dong Y¹, Zhang Z¹

¹Tsinghua University, Beijing, China

As carbon-14 (¹⁴C) plays an important role in the public radiation dose, increasing attention has been paid to the environmental impact assessment of nuclear power plants. Based on the experience and technology of the 10 MW high temperature gas-cooled reactor (HTR-10) and Arbeitsgemeinschaft Versuchsreaktor (AVR), the high-temperature gas-cooled reactor pebble-bed module (HTR-PM) has been designed and is currently under construction in China. In this article, the source terms of ¹⁴C in the reactor core and primary loop of HTR-PM are presented along with a complete theoretical model. The production mechanism, distribution characteristics, reduction route, and release type of ¹⁴C are illustrated. The average activity amount of ¹⁴C per year in the core of HTR-PM was computed as 2.22 × 10¹²Bq, and the activity concentration of ¹⁴C in the primary loop at operating equilibrium was calculated as 2.51 × 10⁴ Bq/m³ (STP). The calculation results indicated the dominant source of ¹⁴C in both the reactor core and the primary coolant is the activation reaction of ¹⁴N in the fuel elements. The ¹⁴C sampling system in the helium purification system (HPS) of HTR-PM has been designed and illustrated, which can generate reliable activity concentration values of ¹⁴C in the primary loop.