A FRAMEWORK FOR TRANSDISCIPLINARY RADIOCARBON RESEARCH: USE OF NATURAL-LEVEL AND ELEVATED-LEVEL 14C IN ANTARCTIC FIELD RESEARCH

ABSTRACT Radiocarbon (14C) is an isotopic tracer used to address a wide range of scientific research questions. However, contamination by elevated levels of 14C is deleterious to natural-level laboratory workspaces and accelerator mass spectrometer facilities designed to precisely measure small amounts of 14C. The risk of contaminating materials and facilities intended for natural-level 14C with elevated-level 14C-labeled materials has dictated near complete separation of research groups practicing profoundly different measurements. Such separation can hinder transdisciplinary research initiatives, especially in remote and isolated field locations where both natural-level and elevated-level radiocarbon applications may be useful. This paper outlines the successful collaboration between researchers making natural-level 14C measurements and researchers using 14C-labeled materials during a subglacial drilling project in West Antarctica (SALSA 2018–2019). Our strict operating protocol allowed us to successfully carry out 14C labeling experiments within close quarters at our remote field camp without contaminating samples of sediment and water intended for natural level 14C measurements. Here we present our collaborative protocol for maintaining natural level 14C cleanliness as a framework for future transdisciplinary radiocarbon collaborations.

RADIOCARBON PROTOCOLS AND FIRST INTERCOMPARISON RESULTS FROM THE CHRONOS 14CARBON-CYCLE FACILITY, UNIVERSITY OF NEW SOUTH WALES, SYDNEY, AUSTRALIA

ABSTRACT The Chronos 14Carbon-Cycle Facility is a new radiocarbon laboratory at the University of New South Wales, Australia. Built around an Ionplus 200 kV MIni-CArbon DAting System (MICADAS) Accelerator Mass Spectrometer (AMS) installed in October 2019, the facility was established to address major challenges in the Earth, Environmental and Archaeological sciences. Here we report an overview of the Chronos facility, the pretreatment methods currently employed (bones, carbonates, peat, pollen, charcoal, and wood) and results of radiocarbon and stable isotope measurements undertaken on a wide range of sample types. Measurements on international standards, known-age and blank samples demonstrate the facility is capable of measuring 14C samples from the Anthropocene back to nearly 50,000 years ago. Future work will focus on improving our understanding of the Earth system and managing resources in a future warmer world.

GAS ION SOURCE PERFORMANCE OF THE ENVIRONMICADAS AT HEKAL LABORATORY, DEBRECEN, HUNGARY

ABSTRACTA coupled accelerator mass spectrometer–gas interface system has been successfully operating at the Hertelendi Laboratory of Environmental Studies, Debrecen, Hungary, since 2013. Over the last 6 years more than 500 gas targets were measured below 100 µg carbon content for carbon isotopic composition. The system was tested with blanks, OxII, IAEA-C1, IAEA-C2, and IAEA-C7 standards. The performance of our instrumentation shows good agreement with other published gas-interface system data and also shows a quite good agreement with the nominal value of international standard samples. There is a measurable but quite small memory effect after modern samples, but this does not significantly affect the final results. Typical ion currents at the low energy side were between 10–15 µA with a 5% CO2 in He mixing ratio. The relative errors average ±6% for samples greater than or equal to 10 µgC sample with mean count rates of 300 counts per microgram C for OxII. The blank is comparable with other systems, which is 0.0050 ± 0.0018 F14C or 34,000–47,000 yr BP, which allows for the routine measurement of both of small environmental and archeological samples.

Status of the AMS graphitization system in the dendrochronological laboratory at AGH-UST, Kraków

A new system for the preparation of graphite samples for radiocarbon (14C) measurement using an accelerator mass spectrometer (AMS) has been built in the Dendrochronological Laboratory at AGH-UST, Kraków. This system consists of three independent components. The first is the equipment for mechanical and chemical sample pre-treatment. The second is the vacuum line for sample sealing and the purification of CO2. The third and central part of this system is a graphitization line, where graphite is produced from CO2. In the first stage, chemical sample preparation was carried out to remove impurities. IAEA and NIST OxII standard materials were converted to CO2 without pre-treatment. In the next step, samples were combusted to CO2. The resulting CO2 was released under vacuum and cryogenically purified for subsequent graphitization. The performance of the system was tested with NIST OxII, IAEA standards (IAEA C5, C6 and C7) and background samples. The test confirms good reproducibility of results obtained for the samples prepared using this system. The results of the 49 samples of NIST Ox-II, IAEA standards and blank samples were presented in this article.

The paleoecology and extinction of endemic tortoises in the Bahamian Archipelago

No native species of tortoises ( Chelonoidis spp.) live today in the Bahamian (Lucayan) Archipelago (= The Bahamas + The Turks and Caicos Islands), although a number of species inhabited these islands at the first human contact in the late-Holocene. Until their extinction, tortoises were the largest terrestrial herbivores in the island group. We report 16 accelerator mass spectrometer (AMS) radiocarbon (14C) dates determined directly on individual bones of indigenous, extinct tortoises from the six Bahamian islands (Abaco, Eleuthera, Flamingo Cay, Crooked, Middle Caicos, Grand Turk) on five different carbonate banks. These 16 specimens probably represent six or seven species of tortoises, although only one ( Chelonoidis alburyorum on Abaco) has been described thus far. Tortoises seem to have survived on most Bahamian islands for only one or two centuries after initial human settlement, which took place no earlier than AD ~700–1000. The exception is Grand Turk, where we have evidence from the Coralie archeological site that tortoises survived for approximately three centuries after human arrival, based on stratigraphically associated 14C dates from both tortoise bones and wood charcoal. The stable isotope values of carbon (σ13C) and nitrogen (σ15N) of dated tortoise fossils show a NW-to-SE trend in the archipelago that may reflect increasing aridity and more consumption of cactus.

Measurement of the 13C(n,$\gamma$) thermal cross section via neutron irradiation and AMS

Ampoules of amorphous 99.5% enriched 13C were irradiated at the PF1b neutron beam line at the high-flux ILL research reactor in order to produce 14C atoms. The precise ratio of 14C/13C was subsequently measured at the VERA Accelerator Mass Spectrometer, allowing the 13C(n,$ \gamma$γ)14C thermal cross section to be accurately determined. This is the first measurement of this cross section at sub-eV energies via this technique and the result of $ 1.52 \pm 0.07$1.52±0.07 mb for the thermal cross section is in good agreement with other recent measurements which were performed via Prompt Gamma-ray Activation Analysis.

Radiocarbon Dating at Groningen: New and Updated Chemical Pretreatment Procedures

ABSTRACTThe Centre for Isotope Research (CIO) at the University of Groningen has operated a radiocarbon (14C) dating laboratory for almost 70 years. In 2017, the CIO received a major upgrade, which involved the relocation of the laboratory to new purpose-built premises, and the installation of a MICADAS accelerator mass spectrometer. This period of transition provides an opportunity to update the laboratory’s routine procedures. This article addresses all of the processes and quality checks the CIO has in place for registering, tracking and pretreating samples for radiocarbon dating. Complementary updates relating to radioisotope measurement and uncertainty propagation will be provided in other forthcoming publications. Here, the intention is to relay all the practical information regarding the chemical preparation of samples, and to provide a concise explanation as to why each step is deemed necessary.

Radiocarbon Characterization study of Atmospheric PM2.5 in Beijing during the 2014 APEC Summit

ABSTRACTRadiocarbon (14C) has become a unique and powerful tracer in source apportionment of atmospheric carbonaceous particles. In this study, the Asia Pacific Economic Cooperation summit (APEC) held in Beijing in 2014 was used as a demonstration to research the source apportionment of atmosphere PM2.5. We used a 200 kV single stage accelerator mass spectrometer recently completed at China Institute of Atomic Energy (CIAE). The PM2.5 samples related to above case were collected, and the characteristics of radiocarbon in organic carbon (OC) and elemental carbon (EC) in samples were analyzed using the AMS. The results show that the Before-APEC pollution emission mode is different from the During-APEC and After-APEC pollution emission modes. For Before-APEC, During-APEC and After-APEC, the average values of fossil carbon fraction of OC are 0.463, 0.431 and 0.615, respectively, and those of EC are 0.644, 0.561 and 0.687. The fossil source contributions of traffic activities using fossil fuels to OC and EC are 15.8 % and 21.9 %, respectively. The fossil source contributions of industrial activities to OC and EC are 38.0 % and 8.2 %, respectively. It is about 7–10 days that is needed to take to regenerate the PM2.5 pollution caused by human activities.