What is the purpose of the sealed glass envelope in radiation equipment?

• A. It cools the x-ray tube.
• B. Made of leaded glass and filters out lower energy photons.
• C. It shields the operator from all radiation.
• D. It accelerates electrons toward the anode.

Answer: (B)

The sealed glass envelope primarily serves to keep a high vacuum around the tube so electrons can travel from the filament to the target with minimal scattering, while also providing electrical insulation and structural support. When the envelope is made of leaded glass, it adds inherent filtration by absorbing a portion of the low-energy (soft) photons produced during x-ray generation. This helps reduce patient dose and improve beam quality by removing photons that contribute little to imaging but increase exposure. Cooling is accomplished by the oil and cooling system around the tube, shielding the operator cannot be achieved by the envelope alone, and accelerating electrons is driven by the tube’s high voltage between cathode and anode, not the envelope.