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, and then irradiated again. This process is repeated for a number of cycles, and the spectra from each counting are summed together to give one 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 is the cyclic neutron activation analysis (CNAA) by irradiation with the thermal, epithermal, and fast neutrons produced from nuclear reactor, accelerator, and isotopic neutron source. The nuclear reactor can supply a much high neutron flux and is most often used for this purpose. At least 20 elements produced short‐lived nuclides (half‐life <100 s) by thermal neutron bombardment, and more than 10 elements produced nuclides with half‐life of 100–600 s. These can be determined by thermal and epithermal neutron CAA. This technique has been widely applied in biological, environmental, geological, and industrial studies, and 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 improvement in the detection limit, analytical precision, and accuracy for the elements by using short‐lived nuclides; short experimental time and increased analytical number of samples per unit time; capability of estimation or confirmation of the half‐life of the short‐lived nuclide; and determination of the degree of homogeneity of a sample. 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 pileup are serious problems in CAA and must be corrected. The principle, selection of optimal experiment conditions, detection limit, analytical precision of CAA, as well as the dead time and pileup corrections are discussed in this article. Some applications of this method are highlighted.

Determination of selenium in biological materials by short-time neutron activation analysis using ⁷⁷ᵐSe at the Dalat research reactor

“…At a 95% confidence level, a signal is said to be detected above the background signal (B), the interfering radionuclides, if LOD > 3√B. Therefore, the concentration at which an element becomes detectable expressed as sensitivity = 3√B/(P/m) (µg) according to Hou [13], in which P is the net area counts of 161.9 keV peak of the 77m Se and m is the mass of selenium. The detection limits for Se could be high in the samples with the presence of large amounts of Al, Na, Cl and Br.…”