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.