Which of the following characteristics applies to alpha particles?

• A. They travel only short distances in the air.
• B. They can penetrate through the skin.
• C. A thick lead sheet is needed to protect the body from alpha particles.
• D. They are not produced by radioactive decay.

Answer: (A)

Alpha particles have limited penetration in matter because they are heavy, positively charged helium nuclei. This makes them interact strongly with atoms and lose energy quickly as they travel. In air, that rapid energy loss means they can only cover a short distance before stopping—typically a few centimeters. That short range is the core characteristic being tested.

They are not capable of penetrating the skin; a thin barrier like a sheet of paper or even the outer dead layer of skin stops them, so external exposure is minimal. Because of their limited range, shielding does not require thick materials like lead; a very thin barrier is sufficient. And alpha particles are indeed produced by radioactive decay, specifically alpha decay, so the statement that they’re not produced by radioactive decay is incorrect.