To generate x-rays efficiently, the target must be a _____ atomic number material.

• A. Low
• B. High
• C. Medium
• D. Very high

Answer: (B)

The main idea is that X-ray production efficiency grows with the atomic number of the target material. When fast electrons hit the target, x-rays are produced mainly through bremsstrahlung and through inner-shell ionization that leads to characteristic x-rays. The probability and energy of these processes are higher for atoms with a larger nuclear charge, so a high-Z target yields more x-ray photons per unit of electron current. That’s why materials with high atomic numbers, like tungsten, are preferred for efficient x-ray generation. Using a very low or medium Z would produce far fewer x-rays for the same electron beam, and while very high Z can add heat management considerations, the essential requirement for efficiency is a high atomic number.