  Gas Electron Multiplier (GEM) detector, one of the advanced members of the
Micro Pattern Gas Detector (MPGD) group, is widely used in High Energy Physics
(HEP) experiments. The high rate handling capability and spatial resolution
make it a desired tracking detector for high rate HEP experiments.
Investigation of the long-term stability is an essential criterion for any
tracking device used in HEP experiments. To investigate the long-term stability
of a Single Mask~(SM) triple GEM detector prototype, it is irradiated
continuously using a $^{55}$Fe X-ray source of energy 5.9 keV. The chamber is
operated with Ar/CO$_2$ gas mixture in continuous flow mode. The gain and
energy resolution of the chamber are calculated from the 5.9 keV X-ray peak and
studied as a function of time. The applied voltage, divider current and also
the environmental parameters (ambient temperature, pressure and relative
humidity) are recorded continuously. It is observed that at a fixed applied
voltage, the divider current of the detector is changing with time and as a
result, the gain of the detector also changes. A systematic investigation is
carried out to understand the probable reasons behind the observed variation in
divider current and also to find its possible remedies. The details of the
experimental setup, methodology and results are discussed in this article.
