Approximately 3000 nuclides have been discovered thus far, and most are unstable. Unstable nuclei decay by spontaneous fission, α-particle, β-particle, or γ-ray emission, or electron capture in order to achieve stability. The stability of a nuclide is governed by the structural arrangement and binding energy of the nucleons in the nucleus. One criterion of stability is the neutron-to-proton ratio (N/Z) of the stable nuclides; the radionuclides decay to achieve the N/Z of the nearest possible stable nuclide. Radioactive decay by particle emission or electron capture changes the atomic number of the radionuclide, whereas decay by γ-ray emission does not.
KeywordsDisintegration Rate Electron Capture Shell Electron Particle Emission Internal Conversion
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