Which type of radiation can be most effectively stopped by a sheet of paper?

Alpha particles are relatively large and carry a positive charge, making them heavily ionizing but low in penetration ability. Because of their larger mass and charge, they interact quickly and strongly with matter. A sheet of paper can easily stop alpha particles because they can only travel a few centimeters through the air before they lose energy and come to a halt. In practical terms, this means that alpha radiation poses little risk when outside the body, as the outer layer of skin or even a piece of paper can act as a sufficient barrier.

In contrast, gamma rays, beta particles, and X-rays possess significantly greater penetrating power due to their differing physical properties. Gamma rays and X-rays, being electromagnetic radiation, require denser materials—like lead or several centimeters of concrete—to attenuate effectively. Beta particles, which are electrons, can penetrate further than alpha particles but are still relatively low in penetration compared to gamma radiation; a few millimeters of plastic or glass can stop them, but they are not as easily blocked as alpha particles by a simple sheet of paper. Understanding these characteristics is crucial in radiological safety and protection.