Question

In the nuclear reactor cadmium rods are used. This is because the cadmium
A. Control the chain reaction
B. Speeds up the neutrons
C. Emits neutrons
D. Slows down the neutrons.

Answer 1

Hint: Cadmium is a material that is capable of absorbing neutrons without fissioning themselves. It has a neutron-capture cross section for neutrons of various energies. The material of the rod varies in accordance with the energy spectrum of the neutron.

Complete step by step answer:
In a nuclear reactor, all the reactions take place in the main chamber and it is protected by a reflective wall. The neutrons might get generated rapidly during the reaction and this is to be controlled. This is done by neutron absorption and it is done by the cadmium rods which are otherwise known as control rods.
When we insert these rods into our nuclear reactor, it absorbs the extra nucleons. It helps in maintaining the nuclear reaction ratio of 1:1 . These rods ensure stability of the reaction and also, due to the high thermal neutron absorption cross section of this element, cadmium rods easily absorb neutrons, thereby making them unavailable to cause fission.

The fission of uranium is carried out by bombarding a slow moving neutron on uranium which leads to the emission of 3 more neutrons along with its byproducts. Hence, cadmium rods are used to absorb these extra neutrons so that we gain a controlled chain reaction.

So, the correct answer is Option A .

Note:
Boron is also used as a control rod in nuclear reactors. Control rods highly influence the reactivity of the nuclear reactor as it is dependent on the number of rods inserted as well as the distance to which they are inserted.