The Drift Region

The ejectiles leave behind a track of ion pairs in the concentric electric field inside the drift region. The time the ejectiles need to travel through the chamber is small compared to the drift time of the electrons. After some amplification in the GEM, the electron current is detected in the anode pads. The radial position of each point of the track can be derived from the time difference of the pulses. Additionally, the charge contained in each pulse is a measure for the energy loss of the particles.