Activation analysis

Activation analysis is an exclusively elemental analytical method. It involves irradiating the sample to be analyzed with a stream of suitable particles, neutrons, charged particles, etc., and then, after irradiation, identifying the radioactive isotopes created from the elements to be measured. The very principle of this method makes it unique among analytical methods: excitation is directed at the atom's nucleus, and measurements are taken on the artificial radioactive isotopes thus created. The result is a number of advantages: not only is the analysis multi-elemental and highly sensitive (detection limits of up to 10 ^-12 g and sometimes less), but its response is independent of the element's chemical form. Sample mass can vary widely, from a few milligrams to several grams, and sample preparation is generally straightforward.

Most of the risks of error (losses and pollution) that threaten conventional methods can be avoided or, failing that, controlled. After irradiation, surface contamination is removed by stripping, and any contamination introduced during chemical separations can neither distort results nor degrade detection limits. Radioactivity measurements enable highly selective identification of each of the atoms present, and quantification of their number. Calibration is generally obtained either from the element itself, or from a flux monitor, irradiated simultaneously or under comparable conditions. For trace analysis, this method is one of the few to routinely and reliably reach its theoretical detection limits.

Lastly, it can be analyzed in situ with portable irradiation equipment, and in some cases it is possible to analyze the distribution of elements at depth.

On the other hand, in most cases, activation analysis requires heavy irradiation and handling of radioactive substances. What's more, its response times are dependent on the decay period of the radioisotopes used, and can reach several days.

The method can be applied without major modification to a wide range of materials (metals, semiconductors, archaeological, biological and geological samples, etc.) whose shape and mass can vary widely. The same applies to the quantities measured, which can vary from picograms to grams, and sometimes even to kilograms, with an accuracy generally in the order of a few percent, whatever the content, except in the vicinity of the detection limit.

Today, the method is mainly used for trace and ultratrace analysis, either on its own, or to calibrate and verify results obtained by other methods, which are generally more accessible and faster, but which do not always have the reliability of activation analysis. The ability to simultaneously...