Which material can stop alpha particles?

Which material can stop alpha particles?

• A. A sheet of paper
• B. A block of concrete
• C. A sheet of lead
• D. A vacuum

Answer: (A)

Alpha particles are heavy, positively charged helium nuclei that interact strongly with matter and lose energy quickly as they pass through material. Because of this strong interaction and their relatively high charge, they have a very short range in any substance. A thin barrier is enough to stop them—think of a sheet of paper. The atoms in paper provide numerous collisions that rapidly absorb the alpha particle’s energy, bringing it to a halt in a tiny thickness of material. A vacuum doesn’t stop alpha particles because there is no material to cause those collisions; the particles would continue moving until they hit something. Other materials, like concrete or lead, would also stop alphas, but they’re much more than needed to illustrate the point. The key idea is that alpha radiation can be stopped by a very small amount of matter, such as a sheet of paper.

Alpha particles are heavy, positively charged helium nuclei that interact strongly with matter and lose energy quickly as they pass through material. Because of this strong interaction and their relatively high charge, they have a very short range in any substance. A thin barrier is enough to stop them—think of a sheet of paper. The atoms in paper provide numerous collisions that rapidly absorb the alpha particle’s energy, bringing it to a halt in a tiny thickness of material.

A vacuum doesn’t stop alpha particles because there is no material to cause those collisions; the particles would continue moving until they hit something. Other materials, like concrete or lead, would also stop alphas, but they’re much more than needed to illustrate the point. The key idea is that alpha radiation can be stopped by a very small amount of matter, such as a sheet of paper.