Which material is commonly used as the target material in diagnostic X-ray tubes because of its high atomic number and high melting point?

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

Answer: (D)

When selecting a target material for diagnostic X-ray tubes, you balance X-ray production efficiency with the ability to withstand extreme heat. A high atomic number (Z) increases the likelihood of X-ray production, especially bremsstrahlung and characteristic X-rays, while a very high melting point and good thermal properties let the target survive the intense heat from the electron beam. Tungsten fits both needs: its high Z (74) boosts X-ray yield, and its exceptionally high melting point (about 3422°C) plus solid thermal performance let it endure the heat. That’s why tungsten is the standard target material, often in a rotated or alloyed form to further spread heat. Copper, aluminum, and lead don’t meet both requirements as well—copper and aluminum have lower Z and melt at far lower temperatures, and lead, despite a high Z, cannot tolerate the heat due to its low melting point.