Regarding Prompt neutrons

Options

A. They are highly energetic
B. They constitute 99%
C. Cannot initiate chain reaction
D. 1,2,3 are correct

Answer

### Step-by-Step Solution:

1. **Understanding Prompt Neutrons**:
- Prompt neutrons are the neutrons that are emitted almost immediately during a nuclear fission reaction. They are produced as a result of the splitting of heavy nuclei, such as uranium or plutonium.

**Hint**: Remember that prompt neutrons are associated with the immediate aftermath of fission.

2. **Properties of Prompt Neutrons**:
- These neutrons are characterized by their high energy levels. The energy of prompt neutrons typically ranges from 0.1 MeV to 10 MeV.

**Hint**: Focus on the energy range to understand their energetic nature.

3. **Proportion of Prompt Neutrons**:
- In a typical fission reaction, approximately 99% of the neutrons emitted are prompt neutrons. The remaining neutrons are known as delayed neutrons, which are emitted after a short delay.

**Hint**: Consider the significance of the 99% figure in relation to the total number of neutrons emitted during fission.

4. **Chain Reaction Initiation**:
- The statement that prompt neutrons cannot initiate a chain reaction is incorrect. In fact, prompt neutrons are crucial for sustaining a chain reaction in a nuclear reactor or an atomic bomb.

**Hint**: Think about the role of neutrons in sustaining nuclear reactions.

5. **Conclusion**:
- Based on the analysis:
- Statement 1: Correct (Prompt neutrons are highly energetic).
- Statement 2: Correct (They constitute about 99% of the emitted neutrons).
- Statement 3: Incorrect (They can initiate a chain reaction).
- Therefore, the correct option is that statements 1 and 2 are correct, while statement 3 is incorrect.

### Final Answer:
The correct option is that statements 1 and 2 are correct, while statement 3 is incorrect.