Which type of radiation cannot penetrate human skin?

Alpha particles are composed of two protons and two neutrons, essentially making them helium nuclei. Due to their relatively large mass and positive charge, alpha particles possess low penetration power. When alpha particles are emitted, they can only travel a short distance in air and are unable to penetrate the outer layer of human skin. In fact, they can be stopped by just a few centimeters of air or a piece of paper, which clearly demonstrates their limited ability to penetrate materials.

This characteristic makes alpha radiation less harmful when outside the body but significantly more hazardous if alpha-emitting materials are ingested or inhaled. Understanding the properties of different types of radiation, including their penetration abilities, is crucial in radiation safety and protection.