What does it mean if a tube is described as evacuated?

When a tube is described as evacuated, it means that it has been vacuum sealed. In the context of X-ray tubes, the evacuation process involves removing air and other gases from inside the tube to create a vacuum environment. This is critical because the presence of air can lead to the scattering of X-rays and decrease the efficiency of the tube. A vacuum allows for better performance by facilitating the movement of electrons and improving image quality.

The vacuum environment also helps prevent the oxidation of the filament and ensures that the X-rays produced are more directed and efficient, resulting in clearer images during diagnostic procedures. This process is a fundamental aspect of the design of X-ray tubes and contributes significantly to their functionality in medical imaging and diagnostics.