Difference Between Fusion and Fission (With Table)

The terms fusion and fission are related to the world of science and are associated with nuclear reactions that release or produce energy. Fusion and fission are two such processes where chemical reactions between different atomic bodies produce a great amount of energy. Though both of these scientific methods create nuclear energy, the processes are exactly opposite to each other.

Fusion vs Fission

The main difference between fusion and fission is that while in fusion, a larger atom is separated into two small atoms, in fission, two or more small atoms come together to make a larger one. Since the former process, the atomic nucleus is split into many atoms, it releases a lot of energy as compared to the process of fission.

Fusion is a chemical process where two or more nucleons merge together to create a more powerful, larger atom. Thus, the term can be defined as simply the combination or merging of two or more nuclei. It is a scientific process combining lighter atoms together and basically releasing a lot of nuclear energy in the process.

Fission, on the other hand, is completely a different nuclear process. In a nuclear reaction, when a larger atom is divided into smaller atoms, the process is called nuclear fission. As opposed to fusion, fission breaks an atom into many smaller atoms and neutrons. The energy released in this process is also not as enormous as produced in fusion.

Comparison Table Between Fusion and Fission

Parameters of Comparison




In fusion, two or more atoms combine.

In fission, a larger atom is split into smaller atoms.


It releases an enormous amount of energy.

In fission, the energy is lower in scale as compared to fusion.


Fusion is not harmful as it is natural.

Fission can be too dangerous.


To make a fusion reaction, a high temperature and proper environment are needed.

For a fission reaction, less energy is utilised.

Chain reaction

It does not involve any chain reaction.

Fission has a chain reaction.

What is Fusion?

Recent scientific developments have solidified this fact, and mass can be converted into energy and vice versa. A nuclear fusion is an example of that fact. In a nuclear fusion reaction, two or smaller atoms are joined together to make a larger atom. Thus, the number of atoms and neutrons increases after the completion of the reaction.

The greatest example of a fusion reaction is the sun. At the beginning of the twentieth century, questions started to arise on how the sun has managed to produce that amount of heat as well as light continuously. Then various theories have been made, and different experiments continue to seek the answer.

In 1926, when it was found that the sun is made up of hydrogen and helium, a theory was proposed that it is possible only because of the process of fusion. The other instance of fusion that we can find on Earth is the fusing of deuterium and tritium.

To make a nuclear fusion reaction possible, a high amount of energy and a suitable environment is required. As a result, an enormous amount of energy is also get released. The biggest advantage of this nuclear reaction is that it does not produce any harmful greenhouse gas or waste that could do any damage to nature or our world.

What is Fission?

As the name indicates, fission is linked with the breaking of a bigger thing into smaller or lighter ones. Similarly, in a nuclear fission reaction, a larger atom is divided into smaller atoms. Before the splitting, the larger atom remains unstable and heavier, but after the process, the atoms created in the process are stable and lighter.

In this method, a neutron is bombarded onto the heavier and larger atom, the nuclei of that neutron split into two or more nuclei. A huge amount of energy is released, and the atoms also become stable. Since this process involves the breaking of a heavy nucleus into two nuclei, it is termed a nuclear fusion.

The energy released in this is ten times powerful than many chemical reactions, but it is less than the energy produced in fusion reactions. Unlike a fusion reaction, it does not require a lot of temperatures to initiate the process. The nuclear reaction used in making an atom bomb is fission.

Fission reactions need an artificial environment to happen. So it is not natural. These reactions can be used to harm and cause damage to anyone. Thus, it is very vital to know the consequences of these reactions beforehand. Unlike fission, this process produces a lot of radioactive waste and pollution that are lethal for our survival.

Main Differences Between Fusion and Fission

  1.  Nuclear fusion starts with creating a huge temperature, whereas fission begins when a neutron is bombarded onto the larger atom. 
  2. In fusion, two light atoms combine to make a heavy one. In fission, a heavy nucleus is broken down into medium-sized nuclei. 
  3. Nuclear fusion does not involve any chain reaction, but fission has a chain reaction. 
  4. Fusion is a safe nuclear reaction that does not produce any harmful radiation. But fission is quite harmful to our environment. 
  5. It is impossible to create a controlled fusion reaction as they happen naturally. Since fission reaction is unnatural, it can be controlled.


These two energy-producing processes, fusion and fission, are often confused as both of them create a lot of energy. But the methods are absolutely the opposite of each other. Where fusion combines atoms, fission breaks them down. So, one process can be called the reverse of the other. Apart from this difference, fusion reactions cannot be controlled as they naturally happen, but fission can be manually controlled as it is created unnaturally. Fusion never leaves any harmful effect on nature but fission, as it creates a lot of waste, is dangerous for the environment. The latter is also used to make atomic bombs that can destroy life on Earth easily. 


  1. https://ui.adsabs.harvard.edu/abs/1980mit..book…..M/abstract
  2. https://www.sciencedirect.com/science/article/pii/S0920379610005119