At low temperatures and high magnetic fields, the electron in a muonium or radical state may be polarised if it has an opportunity to reach thermal equilibrium. Such a polarisation is seen in transverse field muSR of the shallow donor states in II-VI semiconductors although it is found to be sample-dependent. This experiment will perform RF-muSR to complement the existing transverse field data. It may reveal the mechanism, and timescale, for formation and thermal ionisation of the state and the spin-exchange processes leading to polarisation.