  Mechanisms of charging-up and charging-down of Gas Electron Multiplier (GEM)
have been studied. Experimental investigations have been carried out on both
dielectric polarization and radiation charging of GEMs. Environmental
parameters, such as pressure and temperature have been monitored to normalize
their effects on the charging-up and charging-down measurements. Variation in
gain due to the combined, as well as individual, effects of the mentioned
parameters has been illustrated.
