Nuclear isomerism

Article By:

Batchelder, Jon C. Joint Institute for Heavy Ion Research/Oak Ridge National Laboratory, Oak Ridge Associated Universities, Oak Ridge, Tennessee.

Last reviewed:June 2020

DOI:https://doi.org/10.1036/1097-8542.458900

The existence of nuclear isomers. A nuclear isomer is an excited metastable energy state with a half-life significantly longer than most other excited energy levels. A metastable state of a given isomer is designated with an m next to the mass number of the isotope, or in the case of an isotope with more than one isomer, m1, m2, and so forth. (For example, silver-116 has two metastable states in addition to the ground state, so the three states would be written as ¹¹⁶Ag, ^116m1Ag, and ^116m2Ag.) All excited nuclear states have quantized energy (E), spin (J), parity (π), and a half-life associated with that level. The spin and parity of a given state are determined by the orbitals that the valence protons and neutrons occupy, and the interactions between the particles. The half-lives of most (nonisomer) states are in the range of tens of picoseconds (10⁻¹¹ s) or less. See also: Excited state; Parity (quantum mechanics); Spin (quantum mechanics)

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