A large ${\mu }^{-}$ polarization was achieved in muonic Bi atoms with the help of the strong hyperfine field in a polarized nuclear target. Using ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ nuclei polarized to (59 ± 9)% in ferromagnetic BiMn, we observed a $\mu -e$ decay asymmetry of (13.1 ± 3.9)%, which gives ${\mu }^{-}$ polarization per nuclear polarization equal to -1.07 ± 0.35. This value is almost consistent with -0.792 calculated for nuclei with spin $I=\frac{9}{2}$ and a positive magnetic moment under the assumption that the hyperfine interaction becomes effective in the lowest muonic states.

• Received 28 April 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.1847