Epithermal neutron activation analysis ENAA

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). 

FIGURE 4.5 Gammaray spectrum after excitation by epithermal neutron activation analysis (ENAA) for determination of the uranium content in Nigerian food products. Comparison of the gamma ray spectrum of uranium in normal mode and with Compton suppression. (From Kapsimalis, R. et al., Appl. Radiat. hot., 67, 2097, 2009. With permission.)... 

ENAA Epithermal neutron activation analysis HPGe High-purity germanium... 

ENAA epithermal neutron activation analysis FNAA fast-neutron activation analysis FWHM full width at half maximum I beam intensity... 

The term PCNAA is used when preconcentration precedes the neutron activation while if epithermal neutrons are used to excite the sample the acronym given is ENAA. The monitoring of the delayed neutrons emitted after excitation is termed DNAA. All these NAA procedures are nondestructive techniques used for characterizing solid (and in some cases also liquid) samples. However, a neutron source and a suitable detector are required and the sample can become quite radioactive after irradiation. The sensitivity of NAA techniques varies widely among different elements and sample preparation and post-irradiation methods employed. Several specific examples of NAA application for analysis of uranium in different matrices will be presented in the appropriate chapters. 

---