Applications of statistical quality control to isotope measurements made by accelerator mass spectrometr

Radiocarbon Dating has been recognised as one of the greatest discoveries of the 20th century. The age of any organic organism can be estimated using this technique and the invention of Accelerator Mass Spectrometry (AMS) empowered the already wide applications of this technique to smaller and smaller samples. This technique is able to measure samples of a size of less than 1 mg of radiocarbon (14C) and to reach very high precision. Quality Assurance procedures are essential where measurements need to be precise and failures have to be quickly identified. In fact, AMS data acquisition is highly automated and produces a large volume of data in a relatively short period of time. Unexpected failures in the sample preparation or in the measurement would produce low quality data, which together with homogeneity and variation need to be monitored. Statistical Process Control charts were here used for this purpose. The aim of this piece of work was to assess whether a long series of repeated measurements can be used to assess the quality of routinely produced measurements and to monitor statistical control. The usefulness of some of the most common control charts has been evaluated, and Homogeneity and Equivalence testing applied to the data for the first time. The first one is the procedure used to determine if any of the determinations can be taken as representative of the all data set in which case it would be considered homogenous, while the latter one is used to determine if determinations are equivalent, or in other words not different enough to be considered otherwise. Results were given based on the Schuirmann's test of equivalence and on the Ward and Wilson's test of homogeneity. Uncertainty and accuracy of the radiocarbon measurements were assessed by using Radial Plots as proposed by Galbraith R F in 1988. Again, it is the first time that these techniques are applied to such data.