Tsing Hua Univ, Dept Engn Phys, Beijing 100084, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
; PLA, Inst Chem Def, Beijing 102205, Peoples R China
GEM gas detector is a type of Micro-pattern gas detectors, which has a wide potential in particle physics experiment and lower energy X-ray imaging system. In this paper a tri-GEM gas detector was developed, and the gas gain, energy resolution and charge transfer efficiency of the tri-GEM detector were studied with source of Fe-55. The results of the test indicate that more than 105 effective gain and about 24% energy resolution of 5.9keV X ray of the tri-GEM detector can be reached. The results also show that when the electric field in transfer region is more than 3kV/(cm-atm), the best,energy resolution of the tri-GEM detector can be obtained.