Question

Which of the following has the highest penetrating power?

• A. \(\alpha\)-rays
• B. \(\beta\)-rays
• C. \(\gamma\)-rays
• D. Cathode rays

Hint:

A simple way to remember the order of penetrating power is: \(\gamma>\beta>\alpha\). The opposite is true for ionizing power: \(\alpha>\beta>\gamma\). The more ionizing a particle is, the less penetrating it is.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Penetrating power is the ability of a form of radiation to pass through matter. The more a particle or ray interacts with the atoms of the material it passes through, the more quickly it loses its energy and the lower its penetrating power.
Step 2: Detailed Explanation:
Let's compare the penetrating power of the given radiations:
(A) \(\alpha\)-rays (Alpha particles): These are helium nuclei (\(^{4}_{2}\text{He}\)). They have a large mass and a double positive charge (+2e). Due to their strong charge and large size, they interact very strongly with matter through ionization. They lose their energy over a very short distance and have the \textit{lowest} penetrating power. They can be stopped by a sheet of paper or even the outer layer of skin.
(B) \(\beta\)-rays (Beta particles): These are high-speed electrons or positrons. They are much lighter than alpha particles and have a single charge (-e or +e). They interact less strongly with matter than alpha particles, so they can penetrate further. They have a \textit{medium} penetrating power and can be stopped by a few millimeters of aluminum.
(C) \(\gamma\)-rays (Gamma rays): These are high-energy photons (electromagnetic radiation). They have no mass and no charge. Because they are uncharged, they do not interact strongly via electrostatic forces and penetrate deeply into matter. They have the \textit{highest} penetrating power and require thick layers of dense materials like lead or concrete to be significantly attenuated.
(D) Cathode rays: These are streams of electrons, essentially the same as beta particles but typically with lower energies found in cathode ray tubes. Their penetrating power is less than that of gamma rays and is comparable to beta particles.
Step 3: Final Answer:
Comparing the four options, gamma rays have the least interaction with matter due to their lack of charge and mass, giving them the highest penetrating power. Therefore, option (C) is correct.