Progress in AMS Target Production of Sub-Milligram Samples at the NERC Radiocarbon Laboratory

Abstract

Recent progress in graphite target production for sub-milligram environmental samples in our facility is presented. We describe an optimized hydrolysis procedure now routinely used for the preparation of CO2 from inorganic samples, a new high-vacuum line dedicated to small sample processing (combining sample distillation and graphitization units), as well as a modified graphitization procedure. Although measurements of graphite targets as small as 35 micrograms C have been achieved, system background and measurement uncertainties increase significantly below 150 micrograms C. As target lifetime can become critically short for targets <150 micrograms C, the facility currently only processes inorganic samples down to 150 micrograms C. All radiocarbon measurements are made at the Scottish Universities Environmental Research Centre (SUERC) accelerator mass spectrometry (AMS) facility. Sample processing and analysis are labor-intensive, taking approximately 3 times longer than samples greater than or equal to 500 micrograms C. The technical details of the new system, graphitization yield, fractionation introduced during the process, and the system blank are discussed in detail.