Alpha particles are blocked by which material?

Alpha particles are relatively heavy and carry a positive charge, which makes them interact strongly with matter. Because of their mass and charge, they have a very limited range in air and can be stopped by quite thin barriers.

The dead layer of skin, which consists of keratinized cells, effectively absorbs alpha particles. When alpha particles come into contact with this outer layer, they do not possess enough energy to penetrate beyond it. Thus, the skin provides a sufficient barrier, preventing alpha radiation from causing harm to the underlying tissues.

In contrast, other materials like lead, plastic, and concrete are not specifically effective against alpha particles in the way that skin is because alpha particles can be blocked by much lighter materials. These materials are more relevant for stopping beta and gamma radiation, which require denser substances to provide adequate shielding. Understanding the interaction of different types of radiation with various materials is crucial for safety in radiological environments, highlighting the importance of recognizing that alpha particles can be stopped by very accessible and lighter barriers like skin.