Which component of the x-ray tube becomes negatively charged during an x-ray exposure?

• A. Anode target
• B. Vacuum envelope
• C. Cathode filament
• D. Tube housing

Answer: (C)

During an x-ray exposure, the cathode assembly, specifically the filament, sits at the negative side of the high-voltage supply. The filament is heated to emit electrons (thermionic emission), and the anode is held at a high positive voltage to attract those electrons. Because electrons carry negative charge, the filament region becomes negatively charged relative to the anode as the exposure proceeds. The other parts—the vacuum envelope and the tube housing—aren’t meant to carry a sustained negative charge in normal operation; they’re either neutral or held at ground potential, while the anode target is kept positive to attract the electrons.