Physics:Radiation damage in gaseous detectors

The main effect of prolonged operation of wire or microstrip gas chambers with many charged particles passing in the sensitive area, are deposits on the anode (e.g. sense wires), occasionaly also on the cathodes. Other effects concern walls and edges, and alterations in the gas composition, e.g. by outgasing from the chamber materials into the active gas. These ageing effects are highly dependent on the chamber geometry and on the operating conditions (mostly gas mixture and high voltage); they manifest themselves as films or protrusions (sometimes called ``whiskers), occasionally also as liquid depositions. The practical effect is loss of amplification (``gain) and the stretching of signals in time or other modifications of the signal shape; eventually, complete electrical breakdown (short circuit) is possible. Being due to polymerization, curing of damaged chambers a posteriori is difficult or impossible. Permanent gas circulation, as sometimes done in wire chambers, largely prevents radiation damage.

Microstrip gas chambers are affected by ageing in a similar way to wire chambers: outgasing and polymerization have the same effect.

A fairly complete review of wire chamber ageing can be found in Kadyk91; also Va'vra92. For the ageing of MSGCs, see Geijsberts92.