Method of the activation analysis

The Gamma-ray spectrum of the cobalt isotope

METHOD OF THE ACTIVATION ANALYSIS (EN: method of the activation analysis; DE: Aktivierungsanalyse; FR: methode de l'analyse par activation; ES: metode de analisis por activacion; RU: активационного анализа метод) is the qualitative and quantitative determination of the composition of the substance, which is based on the measurement of the energy of the radiation and of the half-life (T1/2) of the radioactive isotopes, which are forming in the researched substance during the irradiation of it by the neutrons, protons, alpha particles, gamma rays, and others. The hungarian chemists George Charles de Hevesy and Hilde Levi (1936) and the soviet physicist G.A.Greenberg (1940) have used the method of the activation analysis for the first time.

The instantaneous radiation of the nuclear reactions is used for the analysis of the material composition of the mineral raw materials and of the products of its processing. The low Coulomb barrier of the nuclei of the light elements permits to perform the nuclear reactions due to the action of the charged particles of the small energy. They use for the analytical purposes the nuclear reactions with the alpha particles of the radioisotope sources, and with the alpha particles, deuterons and protons, which are produced in the accelerators of the particles. They determine the Be, B, F, Li elements with the neutrons and gamma quanta, which are emerging in the nuclear reactions. The reaction with the slow neutrons (n, a), which is accompanied by the emission of the alpha particles, is used for the determination of the B and Li elements. They use the reactions with the fast neutrons, which are accompanied by the emission of the gamma rays (n, n) of the inelastic scattering, and (n, g) of the radiative capture (see the Neutron gamma method article), and also the reaction (g, n) (see the Photon-neutron analysis article), for the determination of the elements in the samples of the large volume.

The nuclear reactions are also causing the induced radioactivity, the level of which serves as the measure of the content of the analysed element. The recording devices are the scintillation or semiconductor detectors (the corresponding spectrum of the gamma radiation of the rock sample, which has been activated by the neutrons, is shown on the Figure).

The difference of the cross section of the activation, of the energy spectrum of the emitted radiation, and of the period of the half-life of the induced activity, is used for the selective determination of the analyzed elements. They also use various activating flows and the analysis with the charged particles. The charged particles with the low energies activate the elements with the small atomic number. They determine the B and Al elements in the ores and the products of the benefication with the help of the alpha particles of the (210Po, 238Pu, and others) radioisotope sources with the 10B (a, n) to 13N (T1/2 = 10 minutes) and 27Al (a, n) to 30R (T1/2 = 2.5 minutes) reactions. The accelerators permit to obtain the high sensitivity at the low energies: they determine the content of the carbon for the energies of above 0.5 MeV with the 12C (p, g) 13N and 12C (d, n) 13N reactions, and the content of the B, Na, Mg, Al, P elements with the reactions with the deuterons of the low energies. With the increase of the energy of the charged particles, the quantity of the activated elements increases.

The special accelerators have been created for the method of the activation analysis with the charged particles. If the determination of the analized element is not possible with the help of the instrumental (non-destructive) analysis, then they use the radiochemical methods of the isolation of the activated elements (see the Radiochemical analysis article).

The high selectivity and sensitivity of the method of the activation analysis, the simplicity of the operations of the determination, which is associated with the registration of the radiation, and the rapidity, permit to widely use the method of the activation analysis for the analysis of the mineral raw materials and of the products of its processing. The high penetrating ability of the primary and secondary radiation for the neutron and gamma activation analysis permits to use these methods not only for the control of the analytical samples, but also for the non-prepared samples and for the continuous control in the transport streams. The usage of the method of the activation analysis is also promising in the geochemistry of the rare and trace elements.