14C Background Levels in an Accelerator Mass Spectrometry System

Abstract

The levels and sources of the measurement background in an AMS 14C 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 14C concentrations in samples of anthracite coal ranging in size from 15 micrograms 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 100 micrograms of carbon can yield useful 14C dates throughout the Holocene, 200 to 500 micrograms 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 100 micrograms of carbon would be sufficient for dating most materials.