Cadmium rods are used to absorb neutrons in nuclear reactors, because cadmium is neutron absorber.

Thermonuclear fusion?is a way to achieve?nuclear fusion?by using extremely high temperatures. There are two forms of thermonuclear fusion:?uncontrolled, in which the resulting energy is released in an uncontrolled manner, as it is in?thermonuclear weapons?such as the hydrogen bomb, and?controlled, where the fusion reactions take place in an environment allowing some of the resulting energy to be harnessed for constructive purposes. This article focuses on the latter.

The?neutron?is a subatomic particle, symbol n or n0, with no net electric charge and a mass slightly larger than that of a proton. Protons and?neutrons, each with mass approximately one atomic mass unit, constitute the nucleus of an atom, and they are collectively referred to as nucleons.

If at least one neutron from U-235 fission strikes another nucleus and causes it to fission, then the chain reaction will continue. If the reaction will sustain itself, it is said to be critical, and the mass of U-235 required to produce the critical condition is said to be a critical mass. A critical chain reaction can be achieved at low concentrations of U-235 if the neutrons from fission are moderated to lower their speed, since the probability for fission with slow neutrons is greater. A fission chain reaction produces intermediate mass fragments which are highly radioactive and produce further energy by their radioactive decay. Some of them produce neutrons, called delayed neutrons, which contribute to the fission chain reaction. In nuclear reactors, the reaction is slowed down by the addition of control rods which are made of elements such as boron, cadmium, and hafnium which can absorb a large number of neutrons. In nuclear bombs, the reaction is uncontrolled and the large amount of energy released creates a nuclear explosion.Theory based question