Electron Spin Resonance of F Centers in Magnesium Oxide; Confirmation of the Spin of Magnesium-25

An electron spin resonance (ESR) spectrum induced in magnesium oxide crystals by pile irradiation has been interpreted as arising from F centers. After an oxide ion is displaced from its normal position by neutrons, an electron donated by ever-present divalent impurities may become trapped at the vacancy. Those centers having only Mg²⁴ and Mg²⁶ neighbors give a single ESR line with $g=2.0023$, while those with one or more Mg²⁵ neighbors give hyperfine patterns corresponding to the nuclear spin value of 5/2. The magnitudes of the isotropic and anisotropic parts of the hyperfine interaction show strong localization of the electron in the vacancy.