Cyclic Activation Analysis

Abstract

Cyclic activation analysis (CAA) is a method of activation analysis for elemental analysis in which a sample is irradiated, decayed, counted, then irradiated again, and this process is repeated for a number of cycles, the spectra from each counting being summed to give a final total spectrum. By this process, the counts of a short‐lived nuclide of interest are considerably increased and the analytical sensitivity of elements is significantly improved. The most commonly used CAA method is cyclic neutron activation analysis (CNAA) by irradiation with thermal, epithermal, and fast neutrons produced from a nuclear reactor, accelerator, or isotopic neutron source. A nuclear reactor can supply a very high neutron flux and is most often used for this purpose. At least 20 elements which produce short‐lived nuclides (half‐life less than 100 s) by thermal neutron bombardment, and also more than 10 elements which produce nuclides with half‐lives of 100–600 s can be determined by thermal and epithermal neutron CAA. This technique has been widely applied in biological, environmental, geological, and industrial studies, and the most often measured elements include Se, F, Pb, Hf, Sc, O, Ag, and Rh. The advantages of CAA, as compared with conventional activation analysis, include significant improvements of the detection limits, analytical precision, and accuracy for the elements by using short‐lived nuclides, short experimental time, increased number of samples per unit time, a capability for the estimation or confirmation of the half‐lives of short‐lived nuclides and determination of the degree of homogeneity of samples. However, the application of CAA is limited by the number of elements determined, because only some of the elements determined by conventional activation analysis can be determined by this method. In addition, dead time and pile‐up are serious problems in CAA and must be corrected. The principle, selection of optimum experimental conditions, detection limit, and analytical precision of CAA, and also the dead time and pile‐up corrections, are discussed in this article.