X-rays originate from which process?

• A. Nuclear decay
• B. Acceleration of electrons near nuclei
• C. Fusion of hydrogen
• D. Cooling of electrons

Answer: (B)

X-rays in this context come from fast electrons interacting with the nuclei in the target material. As these high-energy electrons are accelerated toward and pass near a nucleus, they are suddenly slowed (decelerated) by the strong electric field. This slowdown causes the electrons to emit photons in the X-ray range—a process known as bremsstrahlung. In practice, X-ray tubes use this mechanism to generate X-rays, and there can also be characteristic X-rays when inner-shell electrons are ejected and the atom relaxes, but the fundamental origin is the interaction of rapid electrons with nuclei, i.e., the acceleration/deceleration of electrons near nuclei.

Nuclear decay would emit radiation from changes in the nucleus itself, not from electrons slowing in a target. Fusion of hydrogen is a nuclear fusion process, not how X-rays are produced in typical XRF instruments. Cooling of electrons would release lower-energy radiation (often infrared or visible), not X-rays.