What is the only difference between Gamma rays and X-rays?

The distinction between gamma rays and X-rays primarily lies in their origin. Gamma rays are produced from the radioactive decay of atomic nuclei, while X-rays are generated by electronic transitions in atoms or in deceleration of fast-moving electrons when they interact with matter. This fundamental difference in origin is what categorizes them distinctly within the electromagnetic spectrum despite other characteristics such as energy, frequency, and wavelength being similar or overlapping.

Gamma rays typically have higher energy than X-rays, but both can exist across a range of energies. Frequency and wavelength are also closely related attributes that can vary across both types of radiation, but these variations do not serve as the defining difference between them. Thus, understanding that gamma rays come from nuclear reactions and X-rays originate from electronic events in materials clarifies why the origin is regarded as the critical distinguishing feature.