Everything You Need To Know About Nuclear Fission simplified

Nuclear Fission

Fission just like binary fission in Biology means splitting. 

It is the process in which a heavy atom splits into two or more lighter atoms that are more stable than the heavy atom. Here by the term heavy nucleus I mean an atom that has a pretty large mass number, say 92 (Uranium).

Just remember, anything that can undergo fission or split is called fissile.

Splitting of heavy atoms provides us with a large amount of energy which is used in nuclear power plants to generate electricity, in nuclear submarines or even bombs!

Let's consider the example of Uranium 235.

Uranium 235 is quite unstable. What we do is, we bombard the nucleus of U235 with a neutron. Understand bombarding like smacking. When we do this, the neutron becomes part of the nucleus of the U235 atom and hence increases its mass number by 1. (mass no. = no of protons + neutrons).

∴ U236 is formed. Observe that there is no change in its atomic number and hence we have created an isotope of Uranium.

This U236 is highly unstable. Much more unstable than U235. It is infact so unstable that it immediately wants to become lighter and hence immediately splits into two new atoms creating Krypton(Kr) and Barium(Ba) and 3 little neutrons.

Something very important happens now. The 3 little neutrons go and collide into another U235 atom each converts itself into U236 which splits into 3 new neutrons along with Kr and Ba. Hence creating 9 new neutrons. These 9 neutrons repeat the same process. This is called a chain reaction.

Projectile: It is the particle which is used to bombard the nucleus of atoms for causing the atom to split is called a projectile. In the example of U235, a neutron was the projectile.

Chain Reaction: It is a process in which the particle used to start the reaction gets produced over and over and is responsible for the carrying forward of the reaction.

Every time U236 splits, it releases a little amount of energy. But when so many atoms of U236 split because of the chain reaction, the net energy is a lot.

In the fissioning of uranium some mass of uranium disappears(is lost). This mass gets converted into energy. Einstein gave the equation E=mc ²      

where E= energy 

m= mass

c= speed of light in vacuum (3×10⁸ m/s)

∴ There is conservation of mass and charge in nuclear fission.

Uranium is the only element that is capable of undergoing nuclear fission. Most of the heavy elements (90-100) are capable of this.

Plutonium was the fissile element used in the bomb dropped in Nagasaki in 1945.

Even though a small amount of mass gets converted into energy notice that the speed of light is squared. So even a small amount of mass is capable of producing a huge amount of energy.

Elements that occur in nature are quite stable, so the probability of them undergoing nuclear fission on their own is pretty small. So nuclear fission is carried out by bombarding the heavy nucleus with a slow moving particle such as a neutron.

Another way to understand how nuclear fission works is by the Liquid Drop Model.

Liquid Drop Model

It states that fission works in the same way as the splitting of a drop of water when another drop of water is added to it. Take a drop of water. From the top, drop another drop of water over it. You will notice that the drop elongates and splits into two water droplets smaller in size.

In nuclear fission, the original drop of water is the heavy unstable atom and the second drop of water is the projectile. When the projectile bombards the heavy water drop, it becomes unstable first, then elongates and finally splits into two smaller water droplets.