¹⁴C Background Levels in An Accelerator Mass Spectrometry System

TLDR

The study quantified background contributions in an AMS 14C system by measuring carbon concentrations in anthracite coal samples ranging from 15 µg to 20 mg across combustion, graphitization, storage, handling, and accelerator stages. The results show that background uncertainty dominates over measurement precision for very old or small samples, that 100 µg of carbon suffices for Holocene dates but 200–500 µg is needed for late Pleistocene, and that eliminating contamination sources can reduce the background enough to allow 100 µg samples for most dating applications.

Abstract

The levels and sources of the measurement background in an AMS 14 C dating system have been studied in detail. The relative contributions to the total background from combustion, graphitization, storage, handling, and from the accelerator were determined by measuring the C concentrations in samples of anthracite coal ranging in size from 15μg to 20mg. The results show that, for the present system, the uncertainty in the background is greater than that due to measurement precision alone for very old or for very small samples. While samples containing 100μg of carbon can yield useful 14 C dates throughout the Holocene, 200 to 500μg are required for dating late Pleistocene materials. With the identification of the procedures that introduce contamination, the level and uncertainty of the total system background should both be reducible to the point that 100μg of carbon would be sufficient for dating most materials.