4 Gaseous Detectors
119
Fig. 4.15 Examples of deposits on 20 μm anode wires after strong irradiation [56]
reasons for ageing in particular circumstances have been elucidated and the studies
permit to establish some general rules on how for improving the chances for a longer
lifetime:
• Many materials have to be avoided, in the gas system, in the detector and during
the construction: Si compounds, e.g. in bubbler oils, adhesives, vacuum grease
or protection foils, PVC tubing, soft plastics in general, certain glues and many
more. The workshop proceedings and reviews mentioned present details, also on
materials found acceptable.
• For the highest radiation loads, up to a few C/cm, gas components most frequently used in the past, namely hydrocarbons like Methane, Ethane, etc., should
be avoided. Indeed, the LHC experiments make use of them only exceptionally.
There remains only a very restricted choice of acceptable gases: mixtures of rare
gases and CO 2 and possibly N 2 , CF 4 or DME. CF 4 is offering high electron drift
119
Fig. 4.15 Examples of deposits on 20 μm anode wires after strong irradiation [56]
reasons for ageing in particular circumstances have been elucidated and the studies
permit to establish some general rules on how for improving the chances for a longer
lifetime:
• Many materials have to be avoided, in the gas system, in the detector and during
the construction: Si compounds, e.g. in bubbler oils, adhesives, vacuum grease
or protection foils, PVC tubing, soft plastics in general, certain glues and many
more. The workshop proceedings and reviews mentioned present details, also on
materials found acceptable.
• For the highest radiation loads, up to a few C/cm, gas components most frequently used in the past, namely hydrocarbons like Methane, Ethane, etc., should
be avoided. Indeed, the LHC experiments make use of them only exceptionally.
There remains only a very restricted choice of acceptable gases: mixtures of rare
gases and CO 2 and possibly N 2 , CF 4 or DME. CF 4 is offering high electron drift