In typical NAA, stable nuclides (^AZ, the target nucleus) in the sample undergo neutron capture reactions in a flux of (incident) neutrons. The radioactive nuclides (^A+1Z, the compound nucleus) produced in this activation process will, in most cases, decay through the emission of a beta particle (ß^-) and gamma ray(s) with a unique half-life. A high-resolution gamma-ray spectrometer is used to detect these "delayed" gamma rays from the artificially induced radioactivity in the sample for both qualitative and quantitative analysis.

Sequence of events that occur during the most common type
of nuclear reaction used for activation analysis

An example of the gamma-ray spectrum from the activation of a human nail used as a biological monitor of trace-element status is shown below. [Visit SeLevel Testing Services to learn how you can test for your own selenium level.]