Final answer:
Aluminum in an X-ray tube serves as a filter to absorb lower energy X-rays, enhancing the quality of the resulting X-ray beam by improving image contrast and reducing radiation dose.
Step-by-step explanation:
Aluminum in an X-ray tube predominantly serves as a filter. In an X-ray tube, a filament voltage carries a large current through the electron source, which ejects electrons. These electrons are then accelerated towards the target material, typically tungsten due to its high melting point, by a strong electric field. When electrons strike the tungsten target, two types of X-rays are produced: bremsstrahlung, or braking radiation, and characteristic X-rays which are typical of the anode material. Aluminum acts as a filter by absorbing some of the lower energy X-rays that would otherwise contribute to a softer X-ray spectrum, leaving a beam of X-rays that have more uniformly high energy levels. This filtration enhances the quality of the X-ray images by improving their contrast and reducing the dose of radiation to the patient or object being imaged.