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Why is a vacuum used inside an X-ray tube?
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X-ray
The relationship of X-rays to other electromagnetic radiation within the electromagnetic spectrum.
An X-ray tube is an evacuated electron tube designed to produce X-rays by accelerating electrons to high velocities and colliding them with a target anode.1
A vacuum is used inside the tube to ensure that the electrons emitted from the cathode can travel to the anode without colliding with gas molecules. If air or other gases were present, these molecules would obstruct the path of the electrons, scattering them and preventing them from reaching the high velocities necessary to generate X-rays upon impact with the target material. Furthermore, the presence of residual gases can lead to the degradation of the cathode's properties, which would impair the tube's performance and longevity.213