  Muon spin rotation ($\mu^+$SR) experiments have been carried out in the heavy
fermion compound UBe$_{13}$ in the temperature range from 0.025 K to 300 K and
in magnetic fields up to 7 T, supported by resistivity and magnetization
measurements. The $\mu^+$SR spectra are characteristic of formation of a spin
polaron which persists to the lowest temperature. A gap in the spin excitation
spectrum of f-electrons opens up at about 180 K, consistent with anomalies
discovered in resistivity, heat capacity, NMR and optical conductivity
measurements of UBe$_{13}$.
