  For its ease manufacturing, flexible geometry, and cheap manufacturing cost,
the gas electron multiplier (GEM) detector can be used as an x-ray image
sensor. For this purpose, we acquired relative detection efficiencies and
suggested a method to increase the detection efficiency in order to study the
possibility of GEM detector as an x-ray image sensor. The GEM detector system
is composed of GEM foils, the instrument system, the gas system, and the
negative power supply. The instrument system consists of the A225 charge
sensitive preamp, A206 discriminator, and MCA8000D multichannel analyzer. For
the gas system, Argon gas was mixed with CO2 to the ratio of 8:2, and for the
negative 2,000 volts, the 3106D power supply was used. The CsI-coated GEM foil
was used to increase the detection efficiency. Fe-55 was used as an x-ray
source and the relative efficiency was acquired by using the ratio of GEM
detector to the CdTe detector. The total count method and the energy spectrum
method were used to calculate the relative efficiency. The relative detection
efficiency of GEM detector for Fe-55 by using total count method was 32 % and
by using energy spectrum method, the relative efficiencies were 5, 43, 33, 37,
35, and 36 % respectively according to the energy spectrum of 2, 3, 4, 5, 6,
and 7 KeV. In conclusion, we found that the detection efficiency of the two
layered GEM detector is insufficient for the x-ray image sensor, so we
suggested a CsI coated GEM foil to increase the efficiency rate and the result
value was increased to 41 %.
