What type of radiation can be stopped by a piece of paper?

Alpha particles are positively charged particles consisting of two protons and two neutrons, essentially making them helium nuclei. They are relatively heavy compared to other forms of radiation and have a very low penetration power. A primary characteristic of alpha particles is that they can be easily stopped by materials that are quite thin, such as a single sheet of paper or even the outer layer of human skin.

This high level of interaction with matter and low penetration capability is due to their charge and mass, which causes them to lose energy quickly as they collide with atoms in the materials they encounter. When alpha particles encounter a barrier such as paper, they are absorbed, and their energy is dissipated, preventing them from passing through.

In contrast, beta particles, gamma rays, and X-rays have much greater penetration capabilities. Beta particles, which are high-energy electrons or positrons, can penetrate plastic or glass but are typically stopped by a few millimeters of aluminum. Gamma rays and X-rays, being forms of electromagnetic radiation, have much greater penetration capabilities and require dense materials such as lead or thick concrete to effectively shield against them.