  We report on the systematic study of a single-gas-electron-multiplication
(GEM) loaded gaseous detector developed for precision measurements of
high-energy particle beams and dose-verification measurements. In the present
study, a 256-channel prototype detector with an active area of 16$\times$16
cm$^{2}$, operated in a continuous current-integration-mode signal-processing
method, was manufactured and tested with x rays emitted from a 70-kV x-ray
generator and 43-MeV protons provided by the MC50 proton cyclotron at the Korea
Institute of Radiological and Medical Science (KIRAMS). The amplified detector
response was measured for the x rays with an intensity of about
5$\times$10$^{6}$ Hz cm$^{-2}$. The linearity of the detector response to the
particle flux was examined and validated by using 43-MeV proton beams. The
non-uniform development of the amplification for the gas electrons in space was
corrected by applying proper calibration to the channel responses of the
measured beam-profile data. We concluded from the radiation tests that the
detector developed in the present study will allow us to perform quality
measurements of various high-energy particle beams and to apply the technology
to dose verification measurements in particle therapy.
