  There is considerable experimental effort dedicated to the directional
detection of particle dark matter. Gaseous mu-TPC detectors present the
privileged features of being able to reconstruct the track and the energy of
the recoil nucleus following the interaction. A precise measurement of the
recoil energy is a key point for the directional search strategy. Quenching has
to be taken into account, i.e. only a certain fraction of the recoil energy is
deposited in the ionization channel. Measurements of the ionization quenching
factor for different gas mixture at room temperature have been made with a
dedicated ion beam facility at the LPSC of Grenoble.
