# Chain Reaction and Thermonuclear Reaction

Chain reaction: Uranium breaks to give krypton and Barium along with three neutrons and energy. Thus formed three neutrons further collides three other uranium atoms and another fission reaction occurs forming nine other neutrons. Similarly the reaction goes on multiplying until the whole uranium available is used up. Such reaction is called PP(proton proton) chain reaction.

0n1 + 92U235 → 36Kr92 + 56Ba141 + 30n1 + energy

Chain reaction

Chain reactions are of two types:

a. Controlled chain reaction: If the fission chain reaction is performed and energy of desired amount is produced in a nuclear reactor plant then such type of chain reaction is called controlled chain reaction. Such produced energy is used for various useful purposes in daily life which is one of the major energy sources in different parts of the world.

b. Uncontrolled chain reaction: If the chain reaction is performed and large amount of energy is released in a short time then such type of chain reaction is called uncontrolled chain reaction. In such reaction the large amount of energy produced may bring destruction to the place where the reaction is taking place. This type of reaction is carried out in an atomic bomb.

Multiplication factor: The ratio of number of neutrons produced in any generation to the number of neutrons present in the previous generation in a chain reaction is known as multiplication factor. It is denoted by k.

$$i.e., \text{Multliplication Factor}= \frac{\text{number of neutrons in any generation}}{\text{number of neutrons in previous generation}}$$

Conditions:

If the multiplication factor (k) is greater than 1 i.e. k >1 then the nuclear reaction is building up and the condition is called super-critical.

If the multiplication factor (k) is equal to 1 i.e. k =1 then the nuclear reaction is just sustained and the condition is called critical.

If the multiplication factor (k) is less than 1 i.e. k <1 then the nuclear reaction is decreasing and will eventually stop. This condition is called super-critical.

Thermonuclear reaction:

The reactions that take place in very high temperature of about 107Kelvin are called thermonuclear reaction.

1H2 + 1H2 → 2He4 + energy

At this high temperature all the materials become completely ionized. Such ionized mass is called as 4th state of matter and is named plasma state.

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