Among the common types of radioactive radiation, which ray has the least penetrating power when passing through matter such as paper, metal, or human tissue?

Introduction / Context:

Radioactive substances emit different types of radiation, mainly alpha, beta, and gamma rays. Each type interacts with matter in a different way and has different penetrating power. This question checks whether you can identify which radiation is least able to pass through materials and is therefore easiest to stop.

Given Data / Assumptions:

• The options include alpha rays, beta rays, gamma rays, and X rays.
• We compare only their penetrating powers in ordinary matter.
• We assume typical energies as encountered in basic nuclear physics.

Concept / Approach:

Alpha particles are relatively heavy and carry a double positive charge. Because of this, they interact very strongly with matter and lose energy quickly. Beta particles are fast moving electrons or positrons and interact less strongly than alpha particles. Gamma rays and X rays are high energy electromagnetic waves that can penetrate deep into materials. Thus, to find the least penetrating radiation, we look for the radiation that is most easily absorbed or stopped by a thin barrier.

Step-by-Step Solution:

Verification / Alternative check:

Many safety charts show typical shielding materials. Alpha radiation is blocked by paper, beta by thin metal, and gamma by thick dense shielding. This order confirms that alpha radiation is the easiest to stop and thus the least penetrating.

Why Other Options Are Wrong:

Option A: Gamma rays have very high penetrating power and are used in medical imaging and industrial inspection because they pass through many materials.

Option B: Beta rays penetrate more than alpha rays and can pass through paper, so they cannot be the least penetrating.

Option D: X rays are similar to gamma rays in nature and are also highly penetrating.

Common Pitfalls:

Students sometimes confuse ionising power with penetrating power. Alpha particles have very high ionising power but low penetrating power. Gamma rays are the opposite, with low ionising power per unit path but high penetration. Keeping these two ideas distinct helps to avoid confusion in exam questions.

Final Answer:

The least penetrating radiation among the options is alpha rays.