Pixel and Microdot Detectors

This chapter describes pixel, microdot, and micropixel detectors. Their invention was inspired by A. Oed's work on MSGCs. In these detectors avalanche multiplication occurs near small anode dots/pixels instead of near anode strips. This naturally segments the detector area into independent active cells, or pixels, which can be attractive in some applications. For two-dimensional position measurements, each anode and cathode row is connected to the readout line. These readout lines are placed perpendicular to the anode/cathode rows. If necessary, each pixel can be connected to its own preamplifier. One of the advantages with this pixel geometry is that it allows gas gains that are ten times higher than what is achievable with MSGCs. This is due to that the electric field lines near the anode dots are radial, which is favorable for quenching surface streamers. Although up to now the microdot and micropin detectors remain in a stage of laboratory prototypes, this interesting concept recently gained new momentum after the development of microdot detectors with resistive electrodes. These innovative detectors satisfy the requirements of some application such as noble liquid Time Projection Chambers.