Which type of radiation can be stopped by paper?

Alpha particles are composed of two protons and two neutrons, essentially forming a helium nucleus. Their relatively large mass and positive charge lead to a limited range of penetration. Due to their size and charge, alpha particles interact strongly with matter. When they encounter materials, they lose energy quickly and can easily be stopped by very thin barriers, such as a sheet of paper or even the outer layer of human skin.

This characteristic makes alpha radiation less hazardous when the radioactive material is outside the body, as it cannot penetrate the skin. However, if alpha-emitting materials are ingested or inhaled, they can pose a significant health risk due to the high energy they can deliver to localized tissues.

In contrast, beta particles, gamma rays, and X-rays have much greater penetration capabilities and require denser materials—like plastic, glass, or lead—to effectively block or shield against them. Therefore, paper's ability to stop alpha particles demonstrates the unique properties of different types of radiation and their interactions with matter.