First Observation of Signals Due to KAERI's 10 MeV Electron Beam by Using GEM Detectors

Abstract
Performance tests of a single channel double Gas Electron multiplier (GEM) detector constructed by the Radiation Detector Development Group of Changwon National University (CNU) and a multi-channel double GEM chamber constructed by the High Energy Physics Group of the University of Texas at Arlington was carried out at the Korea Atomic Energy Research Institute (KAERI's) RF accelerator by using 10-MeV electron beams during May 20 - 26, 2006. In this experiment, we observed signals by both 10-MeV beam electrons and X-ray photons in the CNU single-channel double GEM chamber and in the UTA chamber by using an oscilloscope and photographed waveforms. By analyzing the chamber output signals on the oscilloscope, computing the number of X-rays photons produced by bremsstrahlung of the beam electrons in a 2-mm lead plate, calculating the angular distribution of beam electrons caused by multiple scatterings in the lead plate, and estimating the interaction probabilities of X-ray photons in the lead plate, the Ar/CO$_2$ gases fill in the GEM chamber, and the cathode copper layer of the chamber, we were able to determine the time profile of the KAERI's 10-MeV electron beam bunches. In addition, we were able to derive the spatial electron number density distribution with the time profile determined using the data from this experiment. This experiment is a significant accomplishment because it is the first time the time and the spatial profiles of the KAERI 10-MeV electron beam have been determined using particle detectors. Finally, we also were able to estimate the effective gain of the CNU GEM-007 chamber by analyzing the output currents measured in the chamber.
Keywords: GEM detector, KAERI's 10-MeV RF accelerator, Lissajous curve, Electron beam signal, Electron beam profile, Spatial electron number density distribution, Braking radiation, X-ray, Multiple scattering, Mass attenuation coefficient

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