Accelerator mass spectrometry ¹⁴C determination in CO₂ produced from laser decomposition of aragonite

Abstract

Determination of 14 C in aragonite (CaCO3) decomposed thermally to CO2 using an yttrium-aluminum-garnet doped neodymium laser is reported. Laser decomposition accelerator mass spectrometer (LD-AMS) measurements reproduce AMS determinations of 14 C from conventional reaction of aragonite with concentrated phosphoric acid. The lack of significant differences between these sets of measurements indicate that LD-AMS radiocarbon dating can overcome the significant fractionation that has been observed during stable isotope (C and O) laser decomposition analysis of different carbonate minerals. The laser regularly converted nearly 30% of material removed to CO2 despite being optimized for ablation, where laser energy breaks material apart rather than chemically altering it. These results illustrate promise for using laser decomposition on the front-end of AMS systems that directly measure CO2 gas. The feasibility of such measurements depends on 1. the improvement of material removal and/or CO2 generation efficiency of the laser decomposition system and 2. the ionization efficiency of AMS systems measuring continuously flowing CO2.

Direct coupling of a laser ablation cell to an AMS

“…The pressure was measured directly at the gas inlet of the cell with a miniature piezoresistive pressure transducer (Keller AG, Switzerland). Using this value, the known volume of the ablation cell and the amount of carbonate removed from the sample specimen, a maximum CO 2 yield of about 70% was calculated, which is significantly higher than observed in the previous study [30]. It is also more than estimated from the previous LA-ICPMS measurements.…”

“…In that pilot study CO 2 was produced using a commercial 213 nm LA system, flushed onto a CO 2 trap, graphitized and subsequently measured as a conventional solid AMS target. Although the study demonstrated the principal applicability of LA sampling for radiocarbon analyses of carbonates, the suggested method could not benefit from the latest developments of online injection of CO 2 into an AMS gas ion source [30]. A pulsed laser system offers the possibility to produce CO 2 from carbonates at a rate that allows direct feeding of the CO 2 into an AMS gas ion source.…”

Development of a commercial Automated Laser Gas Interface (ALGI) for AMS

“…Loaded into the titanium plate are stainless steel mesh wells, each containing a bed of 20 mg of CuO powder, which serves as an oxidizing reactor to convert sample carbon to CO 2 . After the wells are packed with CuO, the plate is heated in an oven at $750°C for several hours with a continuous flow of O 2 through the oven to oxidize any organic material contaminating the CuO and maximize the amount of adsorbed O 2 [4]. The baked plates are then stored in argon to avoid atmospheric contamination.…”

Laser ablation–accelerator mass spectrometry reveals complete bomb 14C signal in an otolith with confirmation of 60-year longevity for red snapper (Lutjanus campechanus)

“…The first otolith analysed (RS07) was sampled beyond the initial milled core 14 C measurement and into the growth zone sequence using the micromill. This series of samples was analysed by gas AMS (Rosenheim et al 2008;Wacker et al 2013). In this timeefficient online approach, the carbonate samples are placed in septum-sealed vials under a helium atmosphere.…”