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Difference Between Nuclear Fission and Nuclear Fusion

Last updated date: 28th Feb 2024
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The process of nuclear fusion is as opposed to that of nuclear fission. By considering the following scenario, we can distinguish between nuclear fission and nuclear fusion.

When two highly active atoms collide and fuse to form a larger atom due to the strong inter-atomic force of attraction, this is referred to as nuclear fusion. Similarly, when a source of energy (light) splits into quanta or photons, this is referred to as the nuclear fission process.

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What is the Distinction between Nuclear Fission and Nuclear Fusion?

Nuclear Fission

The term "fission" clearly denotes the splitting or breaking of something into smaller pieces. In this context, nuclear fission refers to the breaking or splitting of a large or parent atom into smaller ones, or two or more daughter atoms. These small atoms are technically light in their weight.

When the nuclear fission process breaks, a large amount of energy is released, indicating that the nuclear fission process is exothermic.

Nuclear Fusion

The term "fuse" refers to the joining of two or more objects. The term 'nuclear fusion' refers to the process by which two or more atoms combine to form a larger atom. The nuclear fusion process is endothermic because it requires absorbing energy to fuse two atoms. Consider two train bogies joining or fusing via a magnet.

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The Distinction between Nuclear Fission and Nuclear Fusion in Tabular form:


Nuclear Fission

Nuclear Fusion


Nuclear Fission refers to the splitting of one atom into two or more daughter atoms (lighter atoms)

Nuclear fusion is the combination of two or lighter atoms to form a larger one

The process of natural occurrence

This cannot be observed in nature as fission does not occur naturally

The process of fusion can be observed in stars such as the sun

By-products formed after the reaction takes place

A lot many highly radioactive particles are generated after fission

A very few radioactive particles are produced in the process of nuclear fusion, however, when the “trigger” fission is used then the formation of radioactive particles take place

Critical conditions

It is necessary to have a critical mass of the substance with high-speed neutrons for a nuclear fission process to occur

A higher density with an environment of high temperature is necessary for the process of nuclear fusion

The energy requirement

It takes a little energy to split an atom

Extremely high energy is required to bring two or more protons in close approach with each other

The release of an energy

The energy released by fission is a million times greater than that released in chemical reactions. This process is exothermic

The energy released in the process of fusion is 3-4 times higher than that of what is released by fission. This process is endothermic

The formation of a nuclear bomb

One class of nuclear weapons is a fission bomb to which we call an atomic bomb. 

One class nuclear weapon is the H2 bomb that uses a fission reaction to activate a fusion reaction

The production of energy

Nuclear fission has an application in nuclear power plants

Fusion is the technology for experimentation that is used for the generation of energy

The fuel usage

Uranium is the significant fuel used in nuclear power plants primarily

Hydrogen isotopes, Deuterium and Tritium are the primary fuels, which are used in fusion power plants experimentation 

What are Nuclear Fission and Nuclear Fusion in Physics?

Atoms are held together by two fundamental natural forces: weak and strong nuclear bonds. The binding energy is the total amount of energy held within the atomic bonds. The greater the amount of binding energy held within the bonds, the more stable the atom. Furthermore, atoms attempt to become more stable by increasing their binding energy.

Nuclear Fusion versus Nuclear Fission

Nuclear fission and nuclear fusion reactions are both chain reactions, which means that one nuclear event causes at least one other nuclear reaction, and the chain reaction typically continues. As a result, an ever-increasing cycle of reactions emerges, which can quickly become uncontrollable. A nuclear reaction of this type can have multiple splits of heavy isotopes such as Uranium 235U or the combining of light isotopes such as 2H and 3H).

Only when neutrons break unstable isotopes do fission chain reactions occur. This type of impact and scatter process is difficult to control/bear, but the initial conditions are relatively easy to achieve.

The fusion chain reaction, on the other hand, develops or occurs only under extreme pressure and temperature conditions that are kept stable by the energy released during the fusion process. We also discovered that the initial conditions and stabilising fields are extremely difficult to implement with our current technology, implying that Physics requires extremely advanced technology to carry out this extreme process.

Use of Nuclear Fission and Nuclear Fusion

It is well known that the basic unit of matter such as atoms themselves consist of electrons, protons and neutrons. Neutrons and protons are present at the centre of the atom and the electrons are arranged around it in their valence shells. The number of neutrons and protons in an atom decides the chemical characteristic of the atom or the properties of the element they are identified with.

All these atomic particles are held with a strong nuclear force that acts at a very close distance. When electrons change the valence shells then the change in the energy contained in the atom is observed. When an electron transfers from outer valence shells to inner valence shells then it does so by absorption of energy. Inversely, when an electron transfers from the inner shell to the outer shell then it does so by releasing energy. By general concept, the energy released is very vast compared to other forms of energy that we use in every other activity. After the discovery of this fact, many scientists have developed the method of extracting and utilising this immense amount of energy obtained from this method.

Isotopes of an element are a form of that atom having the same number of neutrons but different numbers of protons and electrons. In these types of atoms, it is relatively easy to detach the electrons and protons along with the energy holding them. This method of obtaining energy by splitting an atom into two parts is known as Nuclear fission. Contrastingly it is when two atoms merge giving release to energy. This method of obtaining energy is called nuclear fusion. This method of releasing energy occurs in the Sun and other stars. In these luminous celestial bodies, two hydrogen atoms merge to form a helium atom.

FAQs on Difference Between Nuclear Fission and Nuclear Fusion

1. Can nuclear fission be controlled by nuclear fusion?

During the process of nuclear fission an enormous amount of energy is liberated during the ongoing reaction. However, this liberation or release is 3-4 times lesser than the energy liberated during the nuclear fusion process.

Nuclear fission can be controlled via varying scientific processes while nuclear fusion is impossible to control.

2. What is the difference between nuclear fusion and nuclear fusion?

Nuclear fusion and nuclear fission are two different types of reactions that release energy because of the presence of high-powered atomic bonds between particles residing in the nucleus. In fission, an atom splits into two or more tiny, lighter atoms. Fusion, on the other hand, occurs when two or more light-weighted atoms fuse together, producing a larger and heavier atom.

The process of nuclear fusion is more expensive than the process of nuclear fission.Nuclear fission confines to reside in a lighter nuclei, while nuclear fusion tends to confine in a large nuclei.

3. Is nuclear fusion possible naturally?

Yes. We can see this process in stars like the Sun but this is possible only when there is extremely high temperature, pressure, and density.

4. What are chain reactions?

Nuclear reactions such as fission and fusion are chain reactions, which means that one nuclear event causes at least one other nuclear reaction, if not more. As a result, an increasing cycle of reactions occurs, which can quickly become uncontrollable. This type of nuclear reaction can consist of multiple splits of heavy isotopes (for example, 235 U) or the merging of light isotopes (e.g. 2H and 3H).

5. What are nuclear bombs?

As the energy released by nuclear fission is so immense that it can be used  Uranium, Thorium isotopes can be used to get this energy. If this energy is released without control and containment then it can be devastating in nature and can cause great destruction in its surroundings. This is what know as a nuclear bomb. Many countries have developed technology to use this method to use against the enemy countries by dropping it in their territory. The best example of such an incident is the nuclear explosion in Hiroshima and Nagasaki of Japan by the United States of America during World War 2.

6. What is the actual mechanism of nuclear fission and fusion ?

Nuclear energy can be derived from the isotopes of Uranium, Thorium and other other heavy elements in a very controlled environment. This unconventional source of energy is currently obtained in the nuclear reactors built by many countries. An isotope of hydrogen known as deuterium is used to absorb the extra atoms produced during the chain reaction occurring in the reactors. To know more about the actual mechanism of this process students can refer to the other articles provided in the Vedantu website. They access these resources by registering themselves on the portal which is free of cost.