Alpha particles are a byproduct of nuclear decay that cannot pass through the skin.

• A. Alpha particles
• B. Beta particles
• C. Gamma rays
• D. Neutrons

Answer: (A)

Different types of nuclear radiation have very different abilities to penetrate matter. Alpha particles are helium nuclei, heavy and highly charged, so they interact strongly with matter and lose energy quickly. Their range is very short: in air they go only a few centimeters, and in tissue they’re stopped almost immediately by the outer layer of skin. That’s why external exposure to alpha emitters isn’t dangerous beyond being on the skin, but if such material is inhaled or ingested it can cause serious internal damage because the particles deposit most of their energy locally.

In contrast, beta particles are lighter charged particles that can penetrate the skin to some depth and are stopped by a few millimeters of material like aluminum. Gamma rays are electromagnetic radiation with much higher penetrating power and require dense shielding such as lead. Neutrons, being uncharged, can penetrate quite far and are slowed by certain materials like water or concrete.

So the statement is true: alpha particles cannot pass through the skin.