Article
Article
Sum rules
Article By:
Bertsch, George F. Department of Physics, Michigan State University, East Lansing, Michigan.
Last reviewed:January 2021
DOI:https://doi.org/10.1036/1097-8542.667260
Formulas in quantum mechanics for transitions between energy levels, in which the sum of the transition strengths is expressed in a simple form. Sum rules are used to describe the properties of many physical systems, including solids, atoms, atomic nuclei, and nuclear constituents such as protons and neutrons. The sum rules are derived from quite general principles, and are useful in situations where the behavior of individual energy levels is too complex to describe by a precise quantum-mechanical theory. See also: Energy level (quantum mechanics)
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