The velocity of neutrons in nuclear is slowed down by

Options

A. Heavy water
B. Ordinary water
C. Zinc rod
D. Fused caustic soda

Answer

To solve the question regarding what slows down the velocity of neutrons in nuclear reactions, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Role of Neutrons in Nuclear Reactions**:
- Neutrons play a crucial role in sustaining nuclear reactions, especially in fission processes. Their speed can affect the likelihood of further reactions.

2. **Identify the Need for Slowing Down Neutrons**:
- In many nuclear reactors, particularly thermal reactors, it is important to slow down fast neutrons to increase the probability of them causing further fission reactions.

3. **Define a Moderator**:
- A moderator is a substance that slows down fast neutrons. It is essential in nuclear reactors to enhance the efficiency of the fission process.

4. **Evaluate the Options Given**:
- The options provided are:
- A) Heavy water (D2O)
- B) Ordinary water (H2O)
- C) Zinc rod
- D) Fused caustic soda

5. **Analyze Each Option**:
- **Heavy Water (D2O)**: This is commonly used as a moderator in nuclear reactors. It effectively slows down neutrons due to its molecular structure.
- **Ordinary Water (H2O)**: While it can also act as a moderator, it is not as effective as heavy water in certain types of reactors.
- **Zinc Rod**: Zinc is not used as a moderator; it is often used as a neutron absorber.
- **Fused Caustic Soda**: This is not used as a neutron moderator.

6. **Select the Correct Answer**:
- Based on the analysis, the best choice for slowing down neutrons in nuclear reactions is **Heavy Water (D2O)**.

### Final Answer:
The velocity of neutrons in nuclear reactions is slowed down by **Heavy Water (D2O)**.

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