The sturdy ceramic structure of the channel electron multipliers series KBL cannot disguise the fact that the black lead glass surface must be protected from damages and contamination. It is well known that hydrocarbons (caused by backstreaming of oil diffusion pumps, for example) in the residual gas atmosphere dramatically decreases the CEM lifetime. Never use plastic or any other material containing hydrocarbons in the vacuum chamber! The gain degradation will take place so quickly that you will be able to watch it.

!	Never use material containing hydrocarbons in the vacuum chamber together with the CEMs.

A source of dark pulses could be particles that have entered into the funnel during assembly or due to a malfunction. It must therefore be pointed out here that the metalization near the funnel should not be damaged during installation of the channel electron multiplier, as this may result in particles entering the funnel, which then cause dark pulses due to field electron emissions.

Looking into the CEM funnel through a microscope shows if there are particles. If this is the case, then the particles can be removed with tweezers if they are large enough, such as lint. If there are many small particles, use a ultra-sonic bath filled with isopropyl-alcohol for a few seconds in order to clean the CEM surface.