What type of radiation can be stopped by paper or skin?

Alpha particles are heavy, positively charged particles consisting of two protons and two neutrons, which are emitted from the decay of heavy elements such as uranium or radium. Due to their relatively large mass and charge, alpha particles have a very short range in matter and can be easily stopped by minimal barriers.

Paper, skin, or even the outer layer of human tissue can effectively block alpha particles, making them less penetrating than beta particles, gamma rays, or X-rays. This characteristic means that alpha radiation poses a greater risk when alpha-emitting materials are ingested or inhaled, as internal exposure can have significant biological effects, while external exposure to alpha particles is generally not harmful. Understanding the properties of alpha particles is crucial in radiation safety and protection measures, particularly in environments where these particles may be present.