Diffusion and trapping of positive muons in niobium

Abstract

Using zero- and longitudinal-field muon spin relaxation, the conventional interpretation of the "double-humped" behavior of the ${\mu }^{+}$-depolarization rate in Nb has been established unambiguously. Thus the ${\mu }^{+}$ mobility is shown to increase monotonically with temperature. The widths of the magnetic field distributions (due to the Nb nuclear moments) and the rates for finding or escaping from traps have been measured at several temperatures. In addition, equations are presented which govern the time evolution of the ${\mu }^{+}$ polarization, when the muons are finding traps, escaping from traps, or both, for zero, longitudinal, and transverse external magnetic fields. A method for including the effect of more than one kind of trap acting at a particular temperature is given.