An intense paramagnetic EPR signal generated from x-ray-irradiated, powdered YCOB crystals was observed at the liquid nitrogen temperature for the first time. Five peaks, located at the positions where the effective 9factor equals to 1.992, 1.986, 1.980, 1.974 and 1.965, labeled as A, B, C, D and E respectively, were observed. It is believed that the peaks A, B, C and D generated from the BO2-F+ center which is a single electron trapped in an oxygen vacancy which was originally occupied by an O2- ion bonded to a (BO3)3- anion group. The peak E is thought of coming from Y2+ ions that are formed by the Y3+ ions trapping electrons. The mechanism for the formation of the radiation-induced defects in the YCOB crystals is suggested.
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