Which of the following is used in a nuclear reactor to slow down fast-moving neutrons?
Answer Details
In a nuclear reactor, a chain reaction is sustained by the collision of neutrons with atomic nuclei, which leads to the release of more neutrons and a large amount of energy. However, not all neutrons are capable of causing this chain reaction, as only neutrons with sufficient energy (known as fast neutrons) can interact with the nuclei to cause the chain reaction.
To increase the efficiency of the chain reaction, it is desirable to slow down these fast-moving neutrons so that they are more likely to interact with atomic nuclei and cause the chain reaction to continue. This is achieved by using a material known as a moderator, which is placed in the reactor core to slow down the fast neutrons.
Of the options given, the material commonly used as a moderator in nuclear reactors is graphite rods. Graphite is made of carbon atoms and has a layered structure that allows it to efficiently slow down fast neutrons. Other materials such as heavy water and beryllium can also be used as moderators, but graphite is the most commonly used.
Therefore, the correct answer to the question is "Graphite rods".