Which penetrates further, X-rays or gamma rays?

• A. X-rays
• B. Gamma rays
• C. Alpha particles
• D. Beta particles

Answer: (B)

Penetration depth depends on how the radiation interacts with matter. X-rays and gamma rays are both photons, but gamma rays are usually emitted from the nucleus with higher energy than most X-rays used in imaging. That higher energy, combined with having no charge, means gamma rays pass through more material before being absorbed or scattered. Alpha particles are heavy and charged, so they lose energy quickly and are stopped by a sheet of paper or skin. Beta particles are lighter and carry charge, so they penetrate farther than alpha but are still attenuated by a few millimeters of material like aluminum. In short, gamma rays go through more material than X-rays, so they penetrate further.