As the ceramic window of the waveguide transmission system of a medical electron accelerator cracked and F 12 ; gas leaked into its vacuum system

some verdigris was found to contaminate the internal surface of the accelerating tube The X ray diffraction analysis indicates that the verdigris consists of CuCl·3[Cu（OH） 2 ] predominately and CuCl The causes of forming verdigris are discussed It seems that any kinds of isolation gas leaked into the vacuum system can be ionized and then corrode the copper surface Various possible reasons for causing cracks on the ceramic window are cited and some preventive measures are suggested