  The advancement of Micro Pattern Gaseous Detector technology offers us
different kinds of detectors with good spatial resolution and high rate
capability and the Gas Electron Multiplier (GEM) detector is one of them.
Typically GEM is made up of a thin polyimide foil having a thickness of 50
micrometers with 5 micrometers copper cladding on top and bottom sides. The
presence of polyimide changes the gain of the detector under the influence of
external radiation and the phenomenon is referred to as the charging up effect.
The charging up effect is investigated with a double mask triple GEM detector
prototype with Ar/CO$_2$ gas mixture in 70/30 ratio under continuous
irradiation from a strong Fe$^{55}$ X-ray source. The detailed method of
measurements and the test results are presented in this article.
