The Keck Carbon Cycle AMS Laboratory, University of California, Irvine: Initial Operation and a Background Surprise

Abstract

ABSTRACT.A new radiocarbon accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5MV AMS system was installed in mid-2002 and has operated routinely since October of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported 14 C AMS background: charge exchange tails from 14 N beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator.

Modifying a sealed tube zinc reduction method for preparation of AMS graphite targets: Reducing background and attaining high precision

“…Graphite is hammered into the central 1 mm diameter hole in the aluminum target holder [11]. The graphite targets are analyzed for 14 C at Keck Carbon Cycle AMS facility at UC Irvine [12,13].…”

“…Fractionation of carbon isotopes does occur during graphitization and depends on the graphitization yield, which can be affected by the amounts of reagents used and other conditions. The d 13 C of our zinc-reduced graphite is usually lighter by 2-3& than the CO 2 from which it is made, but this is corrected for in our system by simultaneous measurement of 13 C/ 12 C along with 14 C/ 12 C by the spectrometer. This method is suitable for 14 C enriched samples, as well as natural abundance 14 C samples, especially those with modern 14 C contents.…”

Sources and transport of Δ<sup>14</sup>C in CO<sub>2</sub> within the Mexico City Basin and vicinity

“…Measurements of 14 C content in samples of CO 2 from selected air samples were made following previously described methods (Southon et al, 2003). Briefly, CO 2 gas is graphitized to pure carbon in the presence of H 2 and hot zinc metal.…”

Daily variability of dissolved inorganic radiocarbon at three sites in the surface ocean

“…Seawater samples for isotopic, [DIC] and alkalinity analyses were poisoned with saturated HgCl 2 solution to prevent biological remineralization of organic matter. Water samples were processed for DIC Δ 14 C analysis using conventional counting (Alcyone, Eve and Hydros cruises) (Griffin and Druffel, 1985) and accelerator mass spectrometry (AMS) (SOce, Avon and SarC cruises) (McNichol et al, 1994;Southon et al, 2004). Radiocarbon measurements are reported as Δ 14 C in per mil (Stuiver and Polach, 1977).…”