  We present experimental results of $\mu$--atomic and $\mu$--molecular
processes induced by negative muons in pure helium and helium--deuterium
mixtures. The experiment was performed at the Paul Scherrer Institute
(Switzerland). We measured muonic x--ray $K$ series transitions relative
intensities in $(\mu{}^{3,4}\mathrm{He})^*$ atoms in pure helium as well as in
helium--deuterium mixture. The muon stopping powers ratio between helium and
deuterium atoms and the $d \mu{}^3 \mathrm{He}$ radiative decay probability of
for two different helium densities in $\mathrm{D}_2 + {}^3\mathrm{He}$ mixture
were also determined. Finally, the $\mathrm{q}_{1s}^{\mathrm{He}}$ probability
for a $d\mu$ atom formed in an excited state to reach the ground state was
measured and compared with theoretical calculations using a simple cascade
model.
