Final answer:
Tungsten is chosen for the anode in X-ray tubes because of its high atomic number, which allows for the emission of high-energy X-rays, and its high melting point, which enables it to sustain the high temperatures encountered during X-ray generation.
Step-by-step explanation:
Tungsten is used as the target material on the tube's anode because it has a high atomic number and a high melting point. The high atomic number (Z) contributes to the production of X-rays with large photon energies, as these energies increase approximately as Z². Tungsten's high melting point is crucial for withstanding the high temperatures generated as the material absorbs the energy of the impinging electrons during the X-ray creation process. These properties make tungsten an ideal choice for the role of the anode in X-ray tubes.