Radiation damage on X-ray CCDs and restoration technique for space astronomy

We studied the proton damage effects of the X-ray CCD, and searched for a possible restoration technique in orbit. We measured the X-ray CCD performances after irradiation at energies of 2 and 9.5 MeV, and confirmed a clear degradation of the charge transfer efficiency (CTE) and the energy resolution. To restore the degraded CTE and energy resolution, we tried a charge injection technique, and found the improvement in the CTI (= 1 - CTE) and energy resolution to be 1/4 and 1/3, respectively. We also estimated the energy level of the deep trap, which causes a quantization of the dark current from the radiation-damaged pixels. The trap energy level was about 0.57 eV, or near to the center of forbidden band.