ISIS muons for materials and molecular science studies

This article marks the first 25 years of muon production at ISIS and the creation in that time of a facility dedicated to the use of these elementary particles as unique microscopic probes in condensed matter and molecular science. It introduces the basic techniques of muon spin rotation, relaxation and resonance, collectively known as μSR, that were already in use by specialist groups at other accelerator labs by the mid-1980s. It describes how these techniques have been implemented and made available at ISIS, beginning in 1987, and how they have evolved and improved since then. Ever widening applications are illustrated with highlights from magnetism, superconductivity, interstitial diffusion and charge transport, semiconductors and dielectrics, chemical physics and radical chemistry. Over these first 25 years, a fully supported User Facility has been established, open to all academic or industrial users. It presently comprises 4 scheduled instruments, optimised for different types of measurement, together with auxiliary equipment for radiofrequency or microwave spin manipulation and future plans for pump-probe laser excitation.