What particle is needed to begin a nuclear chain reaction?

Explanation

To answer the question "What particle is needed to begin a nuclear chain reaction?", we can follow these steps:

### Step 1: Understand Nuclear Chain Reactions
A nuclear chain reaction occurs when a single nuclear reaction causes a series of subsequent reactions. This is commonly seen in nuclear fission, where the nucleus of an atom splits into smaller parts.

**Hint:** Think about how one event can trigger a series of events in a chain reaction.

### Step 2: Identify the Key Particle
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