Semi-insulating SI GaAs samples from a zone refined crystal were irradiated with high energy protons (24 GeV/c, fluences up to 1.64x10(14) p/cm(2)). Optical spectra in transmittance and reflectance were accurately measured in the energy range of 0.6-1.4 eV to determine, through the absorption coefficient, the concentrations of both neutral and ionized EL2 defects as a function of the proton fluence. Both these concentrations have been shown to increase linearly with the proton fluence; this behavior well explains the remarkable decrease of the charge collection efficiency observed in proton irradiated GaAs detectors at doses associated with high luminosity beams at a new particle collider accelerator (e.g., the LHC at the CERN laboratory)
