Level-crossing resonances are observed for spin-polarized ⁸Li in copper at 200 K. The positions of the resonances as a function of magnetic field and crystal orientation are a precise measure of the induced quadrupolar interaction on the nearest-neighbor Cu spins and provide unambiguous evidence that ⁸Li occupies a substitutional site. The resonances are detected as enhancements in the ⁸Li spin relaxation rate and are much broader than predicted from a static spin Hamiltonian. A strong collision model is used to extract a decoherence time as a result of the dipolar coupling of the ⁸Li-Cu subsystem to the surrounding nuclear spin bath.