The spinning target of a general purpose x-ray tube is primarily composed of_________.

• A. aluminum
• B. lead
• C. gadolinium
• D. tungsten

Answer: (D)

The main idea is that the spinning target (anode) must withstand extreme heat while efficiently producing x-rays. Tungsten fits this role because it has a very high atomic number, which makes x-ray production more efficient, and an exceptionally high melting point, so it won’t melt or deform under the intense heat of the electron beam. In a rotating anode, the focal track is spread over a larger area, and tungsten is typically backed by copper to quickly transfer heat away. Other materials like aluminum have too low a melting point and lower efficiency for x-ray production; lead is great for shielding but not suitable as a heat-dissipating focal target; gadolinium isn’t used for this purpose. Tungsten provides the best combination of heat tolerance and x-ray efficiency, so the spinning target is primarily composed of tungsten.