Epithermal and Fast Neutron Activation Analysis

The NAA technique makes use of the slow neutrons. However, the epithermal and fast neutrons may also be used for the activation. An NAA technique that employs only epithermal neutrons to induce (n, y) reactions by irradiating the samples being analyzed inside either cadmium or boron shields is called epithermal neutron activation analysis (ENAA). An NAA technique that employs nuclear reactions induced by fast neutrons is called fast neutron activation analysis (FNAA). 

The sample matrix plus standards for the elements of interest are irradiated for a select period of time in the neutron flux of a research reactor. After irradiation and appropriate radioactive decay, the y energy spectrum is measured by counting the sample with a high resolution (to separate various y-transitions of close-by energies) y-detection system. The NAA technique provides highly resolved analysis of elemental composition by the identification of characteristic y-ray energies associated with different isotopes. Quantitative analysis is provided by element-to-element comparison of the number of y-rays emitted per unit time by the unknown sample to the number of y-rays emitted per unit time by the calibration standards. 

The technique of NAA can be applied to most sample matrices without any pre-treatment of the sample. This includes (a) solids such as coal. 

The procedure of NAA can be divided into three steps preparing and irradiating the samples, performing Measurements and Interpreting the results. 

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