Neutron Activation Analysis of Inhomogeneous Large Samples; An Explorative Study

Neutron activation analysis is a powerful technique for the determination of trace-element concentrations. Since both neutrons that are used for activation and gamma rays that are detected have a high penetrating power, the technique can be applied for relatively large samples (up to 13 L), as demonstrated by Overwater. This technique resulted only in average results for the element concentration, which led to the following problems. Firstly, the result for a (simple) single sample doesnât give information about the representativity of the sample related to the population it was sampled from. Secondly, evaluation by Overwater of the impact of element distributions on the correctness of results indicated large errors, up to 100%, without being noticed by the analyst if no extra measures were taken. A method that provides information as to the spatial element distribution may overcome these problems in a reverse order. Firstly, if the element distribution is known, then the total amount of the element in the sample can be determined more accurately. Secondly, the element distribution gives information about the inhomogeneity of the sample; if the sample is a composition of subsamples the results also provide information about the representativity of the sample and the inhomogeneity of the population. A third advantage is that such a method would provide information about the structure of the sample. This may be of interest for e.g. geological samples. Therefore the study underlying this thesis was started. It explores methods for determination of element distributions in large samples using the principles of Neutron Activation Analysis (NAA)