Which particle both begins and is produced by a nuclear chain reaction ?

Options

A. positron
B. alpha particle
C. neutron
D. beta particle

Explanation

To solve the question "Which particle both begins and is produced by a nuclear chain reaction?", we will analyze the options provided and understand the role of each particle in a nuclear chain reaction.

### Step-by-Step Solution:

1. **Understanding Nuclear Chain Reactions**:
- A nuclear chain reaction occurs when a single nuclear reaction causes a series of further reactions. This is commonly seen in nuclear fission processes.

2. **Identifying the Options**:
- The options given are:
- A) Positron
- B) Alpha particle
- C) Neutron
- D) Beta particle

3. **Analyzing Each Option**:
- **A) Positron**: A positron is the antimatter counterpart of an electron and is not involved in initiating or sustaining a nuclear chain reaction.
- **B) Alpha particle**: An alpha particle consists of two protons and two neutrons. While it can be emitted during some nuclear reactions, it does not initiate a chain reaction.
- **C) Neutron**: Neutrons are neutral particles that can initiate a nuclear chain reaction by colliding with a fissile nucleus (like Uranium-235). They are also produced during the fission process when the nucleus splits.
- **D) Beta particle**: A beta particle is an electron or positron emitted during radioactive decay. It does not initiate or sustain a nuclear chain reaction.

4. **Conclusion**:
- From the analysis, we find that the neutron is the only particle that both initiates and is produced in a nuclear chain reaction. When a neutron collides with a fissile nucleus, it can cause the nucleus to split, releasing more neutrons and continuing the chain reaction.

5. **Final Answer**:
- The particle that both begins and is produced by a nuclear chain reaction is **C) Neutron**.