Positive muons in sodium fluoride: A simple spin system

Abstract We report on the relaxation of positive muons stopped in a single crystal of sodium fluoride. The observed time dependence of the μ + spin polarization is found to deviate from the familiar Kubo-Toyabe form at late times, exhibiting hyperfine oscillations in the long time tail. Quantitative analysis indicates that most of the time dependence can be explained by including only first shell (i.e., two fluorine and two sodium nuclei) interactions and suggests strongly that the muon occupies a site along the 〈110〉 axis, midway between two fluorine nuclei.