Some modern applications of activation analysis

Abstract

Applications of neutron-activation analysis have considerably increased in importance since the advent of high-resolution germanium (lithium) detectors. Complex spectra can indeed be analysed without the need for lengthy chemical separations. Obviously, applications are still mainly orientated towards the determination of minor or trace constituents in a number of fields.

An area of application that has been increasingly used is the determination of the inorganic composition of aerosols. By varying the different parameters, such as irradiation time, decay time, thermal or epithermal neutron activation, over forty elements were quantitatively determined, down to the nanogram level. From comparative inter-laboratory tests on standards it appeared that neutron activation was not only superior as far as sensitivity is concerned, but also in regard to accuracy of the results, compared with other instrumental methods.

Neutron activation has also been a powerful aid in archaeology, especially in the determination of potsherds. Chemical analysis can provide information about the origin of the pottery, for instance to determine if it is of local or imported origin. Obviously an answer can only be found from the determination of minor and trace elements, as they possibly allow one to distinguish between samples of different origins or to link those with a common origin. The neutron-activation technique applied to potsherds is similar to that used for geological material. A combination of a large and low-energy photon germanium (lithium) detector allows the determination of about twenty-five minor and trace constituents. From the large amount of data obtained a classification must of course be obtained, leading to a conclusion of similarity or dissimilarity of origin. Procedures based on statistical or cluster analyses have been developed for this purpose, which lead to consistent conclusions.

Considerable progress was also achieved in activation analysis with 14 MeV neutrons, in which the most important application is still the oxygen determination, either as a major constituent, for instance in rocks, or as a trace element in metals. By taking into account all the parameters that can cause systematic errors absolute standardisation procedures have been developed leading to a precision and accuracy of approximately 1 per cent. relative.

Development of relatively inexpensive isotopic neutron sources as californium-252 and actinium-227-beryllium has increased the interest in the determination of major constituents. The advantages offered for a number of elements such as fluorine, manganese, aluminium, silicon and silver are either due to high speed, and/or precision of the analysis compared with other instrumental methods.