Sample Preparation Methods Used at the Australian National University Radiocarbon Facility

Abstract

The Single Stage AMS radiocarbon facility at the Australian National University has operated for the past 14 years. This paper presents the pretreatment methods used for the major sample types dated and reflects on whether quality assurance protocols can adequately detect altered materials. The majority of fossil samples dated by the facility are from tropical and arid environments where diagenesis of both organic samples and carbonates is often severe. A large proportion of the samples submitted cannot be dated, and screening and quality assurance methods are crucial. Based on analysis of 250 measurements on bone collagen, quality assurance indicators for bone are revised. From May 2021, the laboratory has accepted dates on collagen where yield >0.5%, %C is in the range of 39.7–46.9, and the C:N ratio is between 3.00 and 3.30.

Abrupt onset of intensive human occupation 44,000 years ago on the threshold of Sahul

“…Pretreatment of charcoal at the ANU Radiocarbon Centre 53 consisted of physical cleaning with a scalpel followed by Acid-Base-Acid (ABA) chemical treatment: The samples were washed in hot HCl, rinsed and treated with multiple hot NaOH washes, then the NaOH insoluble fraction was treated with hot HCl, filtered, rinsed, and dried. After each treatment samples were rinsed in ultrapure water at least three times or until the water remains colourless.…”

The Size Inherited Age Effect on Radiocarbon Dates of Alluvial Deposits: Redating Charcoal Fragments in a Sand-Bed Stream, Macdonald River, Nsw, Australia

“…2 mm using a scalpel, prior to reaction in HCl (1 M, 30 min, 70 o C), NaOH (1M, 30 min, 70 o C, solution changed until it remained colorless) and HCl (1 M, 30 min, 70 o C). Between each treatment, the sample was rinsed 3 times in ultrapure water, or until it remained colorless (Wood et al 2023). After freeze-drying the charcoal was combusted in a sealed quartz tube in the presence of CuO wire and Ag foil.…”

“…To assess the cleanliness of the charcoal, the %C was measured volumetrically during collection of the CO 2 gas. Except where the charring temperature is very low, charcoal normally contains >50 %C (Ascough et al 2011;Wood et al 2023). If much lower than this, substantial amounts of clay may be present in the dated sample, potentially affecting the date obtained.…”