Introduction to Neutron Activation Analysis
Written and developed by Prof. Tor Bjørnstad (IFE/UiO)
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Neutron activation analysis (NAA) is a sensitive analytical technique for performing both qualitative and quantitative multi-element analysis of major, minor and trace elements in samples of almost every conceivable field of scientific or technical interest. For many elements and applications, NAA offers sensitivities that are superior to those attainable by other methods. In addition, because of its accuracy and reliability, NAA is generally recognized, as the "referee method" of choice when new procedures are being developed or when other methods yield results that do not agree. NAA is widespread worldwide at most nuclear reactor installations.
Neutron activation analysis was discovered in 1936 when Hevesy and Levi found that samples containing certain rare earth elements became highly radioactive after exposure to a source of neutrons. From this observation, they quickly recognized the potential of employing nuclear reactions on samples followed by measurement of the induced radioactivity to facilitate both qualitative and quantitative identification of the elements present in the samples.
The basic essentials required to carry out an analysis of samples by NAA are a source of neutrons, instrumentation suitable for detecting gamma rays, and a detailed knowledge of the reactions that occur when neutrons interact with target nuclei. Brief descriptions of the NAA method, reactor neutron sources, and gamma-ray detection are given below.