Radionuclides fissile nuclides

The first photonuclear activation for analytical purposes was performed with radionuclides as the activating radiation source. These applications were reported in the early 1950s, although apparently the first beryllium determinations by photodisintegration were performed in the late 1930s in the Soviet Union. The analytical detection power of photon activation analysis using radionuclide sources is poor and restricted to the analysis of deuterium, beryllium, several fissile nuclides, and a few nuclides that have low-lying isomeric states. Nonetheless, nuclide excitation is still in use. 

Fissile material is defined in 49 CFR 173.403 as plutonium , plutonium, uranium uranium , or any combination of these radionuclides. The term does not apply to material containing fissile nuclides, nonirradiated natural uranium, and nonirradiated depleted uranium, or to natural uranium or depleted uranium that has been irradiated in thermal reactors only. 

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