Calcium rods are used in nuclear reactors to slow down the neutrons taking part in the fission process

Answer

### Step-by-Step Solution:

1. **Understanding the Role of Moderators**: In a nuclear reactor, the primary function of a moderator is to slow down fast neutrons produced during fission reactions. This is crucial because slow (thermal) neutrons are more likely to induce further fission in fissile materials like Uranium-235 or Plutonium-239.

2. **Identifying Common Moderators**: Common materials used as moderators include water (H2O), heavy water (D2O), and graphite. These substances effectively slow down neutrons through elastic collisions.

3. **Analyzing the Given Statement**: The statement claims that calcium rods are used in nuclear reactors to slow down neutrons. We need to verify if calcium is indeed used as a moderator.

4. **Researching Calcium's Role**: Upon investigation, it becomes clear that calcium is not used as a moderator in nuclear reactors. Instead, materials like water and graphite are commonly employed for this purpose.

5. **Conclusion**: The statement that calcium rods are used in nuclear reactors to slow down neutrons is false. Calcium does not serve as a neutron moderator.

### Final Answer:
Calcium rods are not used in nuclear reactors to slow down neutrons; instead, materials like water and graphite are used as moderators.

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