The spinning target of a general-purpose x-ray tube is primarily composed of which element?

• A. Aluminum
• B. Lead
• C. Gadolinium
• D. Tungsten

Answer: (D)

When producing X-rays, you want a material that both yields a strong X-ray signal and can survive the intense heat from the electron beam. The spinning (rotating) anode helps by spreading that heat over a larger area, but the target itself still has to withstand extreme temperatures while efficiently generating X-rays. Tungsten fits these needs best: it has a very high atomic number, which boosts X-ray production efficiency and gives useful characteristic X-ray energies, and it has an exceptionally high melting point, so it won’t melt under the bombardment. In practice, the tungsten focal surface is often backed by copper to pull heat away quickly, and the assembly is designed to rotate to minimize local overheating. Aluminum or lead wouldn’t provide the same combination of high X-ray yield and heat tolerance, and gadolinium doesn’t offer the practical thermal and mechanical properties needed for a durable X-ray target.