Characterization and ongoing development of the ANSTO AMS radiocarbon small mass H2/Fe graphitization lines

Williams, A; Varley, S

Characterization and ongoing development of the ANSTO AMS radiocarbon small mass H2/Fe graphitization lines

Date

2009-06-01

Authors

Williams, A

Varley, S

Publisher

20th International Radiocarbon Conference

Abstract

The ANSTO AMS radiocarbon graphitization laboratory was originally established with a set of 8 graphitization lines, using Zn/Fe and having volumes around 10 to 13 mL. As the demand for smaller sample masses increased, 12 smaller volume (~3.5 mL) H2/Fe graphitization lines were developed. These lines proved to be versatile, as the operating volume could be varied by changing the volume of a removable cold finger, allowing small mass samples of <100 μg C up to ~3 mg C to be graphitized reliably. Following the success of these lines, the original Zn/Fe lines were replaced in 2004 with a second set of 12 H2/Fe lines. In 2006, following the serial failure of the original gauges used for the 3.5-mL lines we had the opportunity to decrease the reaction volume further and thus reduce the graphitization mass limit. This poster will describe the smaller volume (~2.5 mL) versions, of the original H2/Fe graphitization lines; these new lines were developed using stainless steel diaphragm pressure sensors. This development was successful in extending our lower working mass limit down to ~10 μg C at ~50% graphitization efficiency, while still retaining the flexibility to graphitize up to ~3 mg C reliably. We will present the efficiency data and the characterization tests that these lines underwent, following their rebuilding as ~2.5-mL lines. In addition, we will present the development of new graphitization lines, which are in the process of construction. These comprise 3 very small volume (~0.9 mL) H2/Fe graphitization lines (using ceramic diaphragm pressure sensors), with the primary objective of minimizing, and stabilizing, the absolute mass of added extraneous carbon and stabilizing its pMC value. To assist in this objective, we are also developing revised methods for our sample combustion and transfer procedures, and the development of a modified transfer line. Preliminary results from this work will be presented.

Keywords

ANSTO, Graphitization, Stainless steels, Carbon, Mass spectroscopy, Isotope dating

Citation

Williams, A., & Varley, S. (2009). Characterization and ongoing development of the ANSTO AMS radiocarbon small mass H2/Fe graphitization lines. Poster presented to the 20th International Radiocarbon Conference, 31st May - 5th June 2009, Big Island, Hawaii: Kailua-Kona.