Which type of radiation is stopped by a few centimeters of air or a thin sheet of paper?

Alpha radiation is composed of alpha particles, which consist of two protons and two neutrons. Due to their relatively large mass and positive charge, alpha particles have limited penetration power. They can be stopped by just a few centimeters of air or even a thin sheet of paper. This weakness in penetration is largely due to their heavier mass and strong interaction with matter, which causes them to lose energy quickly as they collide with other atoms.

In contrast, beta radiation, which consists of fast-moving electrons or positrons, has greater penetration capabilities and can pass through paper but is still affected by materials like plastic or aluminum. Gamma and X-ray radiation, on the other hand, are forms of electromagnetic radiation with much higher energy and can penetrate materials to a much greater extent, generally requiring dense materials such as lead or several centimeters of concrete to stop them. Thus, the specific properties of alpha particles account for their inability to penetrate beyond very light materials.