What is an effective shield for alpha particles?

What is an effective shield for alpha particles?

• A. A piece of paper.
• B. Lead plate.
• C. A few meters of concrete.
• D. A vacuum.

Answer: (A)

Alpha particles have very low penetration depth; they lose energy quickly as they collide with atoms in matter. Because of that, only a tiny amount of shielding is needed to stop them. A simple sheet of paper provides enough material to absorb their energy and halt them, making it an effective shield in practice. Thicker shielding like a lead plate or several meters of concrete would certainly stop alpha radiation too, but it’s more than what’s needed for safety and adds unnecessary bulk. A vacuum isn’t shielding at all—without any material to interact with, the alpha particle would travel freely until it hits something, so it doesn’t serve as a shield.

Alpha particles have very low penetration depth; they lose energy quickly as they collide with atoms in matter. Because of that, only a tiny amount of shielding is needed to stop them. A simple sheet of paper provides enough material to absorb their energy and halt them, making it an effective shield in practice.

Thicker shielding like a lead plate or several meters of concrete would certainly stop alpha radiation too, but it’s more than what’s needed for safety and adds unnecessary bulk. A vacuum isn’t shielding at all—without any material to interact with, the alpha particle would travel freely until it hits something, so it doesn’t serve as a shield.