Which of the following has the maximum penetrating power?

Options

A. `alpha`-particle
B. Proton
C. `gamma`-particle
D. Positron

Answer

To determine which of the given particles has the maximum penetrating power, we need to analyze the properties of each particle mentioned: alpha particles, protons, positrons, and gamma rays.

### Step-by-Step Solution:

1. **Understanding the Types of Particles:**
- **Alpha Particles:** These are positively charged particles consisting of 2 protons and 2 neutrons (essentially a helium nucleus). They have a relatively large mass and charge.
- **Protons:** These are positively charged subatomic particles found in the nucleus of an atom. They are similar to alpha particles in that they are also charged and have a significant mass.
- **Positrons:** These are the antimatter counterparts of electrons, carrying a positive charge. They are much lighter than alpha particles and protons.
- **Gamma Rays:** These are high-energy electromagnetic waves (not particles) that have no charge and no mass.

2. **Comparing Penetrating Power:**
- **Alpha Particles:** Due to their large mass and positive charge, alpha particles have low penetrating power. They can be stopped by a sheet of paper or a few centimeters of air.
- **Protons:** Protons have greater penetrating power than alpha particles but are still limited in their ability to penetrate materials compared to gamma rays.
- **Positrons:** Positrons have a similar penetrating ability to electrons, which is greater than alpha particles but less than gamma rays.
- **Gamma Rays:** Gamma rays have the highest penetrating power among these particles. They can penetrate through most materials, including human tissue, and require dense materials like lead or several centimeters of concrete to be effectively blocked.

3. **Conclusion:**
- Based on the properties and penetrating abilities of the particles, gamma rays have the maximum penetrating power compared to alpha particles, protons, and positrons.

### Final Answer:
**Gamma rays have the maximum penetrating power.**