What type of radiation is most effectively stopped by a sheet of paper?

The type of radiation that is most effectively stopped by a sheet of paper is alpha particles. Alpha particles consist of two protons and two neutrons, making them relatively heavy and positively charged. Due to their larger mass and charge, they have low penetration power and cannot travel very far through materials; in fact, they can be stopped by the outer layer of human skin or a simple sheet of paper. This characteristic makes alpha radiation relatively easy to shield against. In practical terms, if alpha-emitting materials are handled properly and shielded with something as thin as paper, they pose little risk of penetrating the skin or causing internal exposure.

In contrast, beta particles, gamma rays, and X-rays have greater penetration capabilities. Beta particles can penetrate paper but are typically stopped by materials like plastic or aluminum. Gamma rays and X-rays are highly penetrating electromagnetic radiation that requires more substantial shielding, such as lead or several centimeters of concrete, to significantly attenuate their intensity. Thus, the unique properties of alpha particles make them the radiation type that is most effectively stopped by something as simple as a sheet of paper.