Which type of radiation can be stopped by paper?

Alpha radiation can be effectively stopped by a sheet of paper due to its relatively large mass and positive charge. Alpha particles are essentially helium nuclei (two protons and two neutrons) and, because of their size, they have a very limited penetration capability. When alpha particles interact with matter, they lose energy rapidly and can be stopped by even a thin barrier, such as paper or the outer layer of human skin. This means that while alpha radiation can be a hazard if ingested or inhaled, it does not pose a risk of external exposure in most situations.

In contrast, other types of radiation like beta and gamma radiation have different properties that allow them to penetrate materials to a greater extent. Beta particles, which are electrons or positrons, can penetrate skin but are generally stopped by plastics or thin metals. Gamma radiation, being electromagnetic radiation with no mass, requires denser materials such as lead or concrete to be effectively shielded. Understanding these differences in radiation properties is crucial in radiation safety and protection measures.