Question

Among the following which is used to control the rate of reaction in nuclear fission
A). Water
B). Heavy water
C). Cadmium
D). Graphite

Answer 1

This question is related to nuclear reactors. So, you must have knowledge about nuclear reactors. In these reactors, the neutron is fired at an atom which causes it to disintegrate into small, excited states which emit neutrons, protons, and other subatomic particles. A control rod is used to control the rate of these reactions which are made up of neutron-absorbing elements. Elements with high neutron capture cross-sections are used for this purpose. Some rare-earth elements are also used for controlling the rate of reaction in nuclear fission.

Complete step-by-step solution
Nuclear reactors are the tractor driver by nuclear fission. During these fission processes, the temperature has to be controlled to slow down or fasten the speed of reactions. This is done with the help of control rods. Control rods are made up of neutron-absorbing elements. These neutron-absorbing elements include silver, boron, cadmium, etc. Alloys or compounds of these elements can also be used. Examples of these can be a silver-indium-cadmium alloy, boron carbide, etc. These elements absorb the neutrons and thus maintain and control the nuclear reactions.
Hence, among the given options, cadmium is used to control the rate of reaction in nuclear fission
So, the correct answer is option C i.e. Cadmium.

Note: Students must remember that these neutron-absorbing elements absorb the neutrons but do not fission themselves. These elements have different cross-sections to absorb the neutron of various energies. Example: Breeder reactors operate with fast neutrons while heavy water reactors and heavy water reactors operate on thermal neutrons. Each reactor design uses different control rod materials according to the energy spectrum of neutrons.