Perhaps the two most blatant omissions from the preceding chapters on μSR are background theory and solid-state applications. Justification for the dearth of theoretical derivations of the equations used in the text is offered on the grounds that each facet of μSR theory, from quantum electrodynamics to free radical hyperfine tensors, has already been dealt with elsewhere, better than could be accomplished here. Particularly commendable from the chemists' point of view are the treatments of Hughes (1966), Ivanter & Smilga (1968), Brewer, Crowe, Gygax & Schenck (1975), Schenck (1976), Percival & Fischer (1976), Brewer & Crowe (1978), Fleming et al. (1979), Garner (1979) and Roduner & Fischer (1981).

On the second major omission, it must be acknowledged that solid-state physics constitutes at least three-quarters of the total μSR research effort (Brewer & Crowe, 1978). This reflects the great value of the muon's unique magnetic moment, and its spin polarization, as a probe of structure and dynamics. The solid state encompasses more diversification than one should try to enumerate. Chemical compositions range from pure elements, through compounds and complex minerals, to an inexhaustible selection of ‘doped’ materials. Their magnetic properties include diamagnetics, paramagnetics, ferromagnetics and antiferromagnetics; electrical properties range from metals through semi-conductors to insulators; structures embrace ionic crystals, molecular crystals, amorphous phases and glassy media; and many of these properties change drastically with temperature, which is readily altered from several hundred degrees to almost zero. Mu and μ+ (and μ−) probe the local magnetic, nuclear and electronic structures, and they can mimic H and p+ as inter st it ials.