Difference Between Fission and Fusion

Edited by Diffzy | Updated on: May 13, 2023


Difference Between Fission and Fusion

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Fission and Fusion are types of Nuclear Reactions. A Nuclear Reaction is a process in which one or more nuclides get created from the collisions between one atomic nucleus or two atomic nuclei and a subatomic particle. The sum of the individual masses of each subatomic particle that constitutes an atomic nucleus is always more than the mass of an atomic nucleus. A Nuclear reaction must cause a conversion of a minimum of one nuclide to another. Natural nuclear reactions happen in the interaction between matter and cosmic rays. These reactions can be employed to acquire nuclear energy at an adjustable rate. Natural nuclear reactions happen in the interaction between matter and cosmic rays. Kinetic energy can either be emitted during a reaction known as an exothermic reaction, or kinetic energy may have to be provided for the procedure to happen known as an endothermic reaction.

Nuclear Fusion and Nuclear Fission are two distinct categories of reactions that emit energy due to the occurrence of high-powered atomic bonds amongst particles found within a nucleus.

Fission vs Fusion

Fission and Fusion are two types of Nuclear reactions and they are very different from each other. Fission is the process of the splitting of a nucleus into two or more smaller atoms. In Fission, very less energy is required to split an atom. Fusion is a nuclear reaction in which two or more nuclei atoms combine to form a larger nucleus. In Fusion, extremely high amount of energy is required to bring two or more atoms to combine with each other. The primary fuel used during Fission in power plants is Uranium. The primary fuel used is Hydrogen isotope. Fission takes place when a large and unstable isotope is barraged by high-speed particles. On the contrary, fusion takes place when two low-mass isotopes combine under high temperature and pressure.

Difference Between Fission and Fusion in Tabular Form

Parameters of ComparisonFissionFusion
DefinitionFission is the process of the splitting of a nucleus into two or more smaller atoms.Fusion is a nuclear reaction in which two or more nuclei atoms combine to form a larger nucleus.
By-productsHighly radioactive particles get generated in large amounts during Fission.Very few radioactive particles are generated after Nuclear Fusion.
Energy RequirementIn Fission, very less energy is required to split an atom.In Fusion, extremely high amount of energy is required to bring two or more atoms to combine with each other.
Energy ReleasedThe energy released is a million times greater than that released in other chemical reactions.Energy released during Fusion is 4-5 times greater than that released in Fission.
ConditionsFission requires high-speed neutrons and the critical mass of the substance.Nuclear Fusion requires high temperatures and high density.
Fuel usedThe primary fuel used during Fission in power plants is Uranium.The primary fuel used is Hydrogen isotope.Deuterium atoms + Tritium atoms = Hydrogen atom
Nuclear weaponFission bomb or atom bomb is a class of nuclear weapon.Hydrogen bomb is a nuclear bomb that uses fission to trigger fusion.
Type of ProcessFission is an exothermic process. Energy gets emitted out during the reaction.Fusion is an endothermic process. It results in the absorption of energy.

What is Fission?

In Fission or Nuclear Fission, the nucleus of an atom splits apart into two or more nuclei. When a large nuclei fissions, it results in the release of energy. So much energy gets emitted that there is a measurable decrease in mass, from the mass-energy equivalency. In 1934, Enrico Fermi split the uranium nuclei. He assumed that some elements could generate by bombarding uranium with neutrons. He anticipated the new nuclei to have bigger atomic numbers than the original uranium, but he found that the developed ones were radioisotopes of lighter elements. Usually, in a nuclear fission reaction, more than one neutron is released by each separating nucleus.

Nuclear fission contradicts significantly other types of nuclear reactions. It can get amplified and sometimes controlled through a nuclear chain reaction.  In this type of reaction, free neutrons are emitted by each fission occurrence which in turn release more neutrons, causing more Fission.

Discovery of Fission

Fission was discovered in 1938 in the building of the Kaiser Wilhelm Society for Chemistry. It took over four decades of labour on the science of radioactivity and the expansion of new nuclear physics that explained the components of atoms. 

In 1911, a model of the atom in which a very small, dense and positively charged nucleus of protons was surrounded by orbiting, negatively charged electrons, was proposed by Ernest Rutherford. Niels Bohr worked on this further in 1913, by negotiating the quantum behaviour of electrons. The model was named the Bohr model. 

Works by Marie Curie, Henri Becquerel, Pierre Curie, and Rutherford explained that the nucleus, even though tightly bound, could experience different forms of radioactive deterioration, and thereby transmute into other elements.

In 1939, a Columbia University team the first nuclear fission experiment in the United States was performed and the experiment was conducted in the basement of Pupin Hall. The experiment consisted of placing uranium oxide inside an ionization chamber, illuminating it with neutrons, and measuring the energy thus released.

Important terms related to Fission

  • Nuclear Chain reaction- Chain reaction refers to a procedure in which neutrons emitted in fission create extra Fission in at least one additional nucleus and this nucleus produces neutrons. 
  • Critical Mass- The point where the chain reaction can become self-sustaining is known as critical mass. Two to three neutrons are produced for each fission but not all neutrons are functional for persisting the fission reaction. The amount of a fissionable material's critical mass relies on- its composition and density, the shape of the material, and the amount of purity. 
  • Spontaneous Nuclear Fission- It is the possibility that a given atom will fission spontaneously, without any external intervention. Scientists assessed the spontaneous fission rate of each material while developing nuclear weapons.
  • A fission reactor- The most common type of nuclear reactor is a Critical Fission reactor. Neutrons produced by the fission of fuel atoms are helpful in generating more fission, to maintain a controllable quantity of energy release. Devices that create contrived but non-self-sustaining fission reactions are subcritical fission reactors. Such devices use radioactive corrosion or particle accelerators to trigger fissions.
  • Fission Bombs- It is a fission reactor developed to release as much energy and as rapidly as practicable, before the radiated energy causes the reactor to burst. The first fission bombs were thousand times more explosive than a relative mass of chemical explosives. Modern nuclear weapons are a hundred times more animated than the first pure-fission atomic bombs. 

What is Fusion?

A nuclear reaction in which two or more atomic nuclei are merged to form one or more atomic nuclei and subatomic particles is known as Fusion (Nuclear Fusion). The disparity in mass between the reactants and products is possible by exemplifying the discharge or absorption of energy. Usually, atomic nuclei repel each other because of having the same charge. Therefore, high temperature or pressure is necessary to overpower this repulsion. A study states that on Earth, temperatures in nuclear fusion reactors get nearly six times than those found in the sun's core. A considerable energy barrier of electrostatic forces must be overcome prior to fusion. Nuclear fusion is the phenomenon that powers main-sequence stars and high-magnitude stars, where large amounts of energy are released. The galaxy is full of illustrations of nuclear fusion reactions. Every star employs it to create power.

Discovery related to Fusion

Arthur Eddington, in 1920, suggested that helium-hydrogen fusion can be a primary origin of stellar energy. In 1927, Quantum Tunneling was invented by Friedrich Hund. Soon after, Fritz Houtermans and Robert Atkinson demonstrated that large amounts of energy could be emitted by the fusion of small nuclei. The hypothesis of the main cycle of nuclear fusion in stars was performed by Hans Bethe. The first self-sustaining nuclear fusion was worked on in 1952 in the Ivy Mike hydrogen bomb test. 

Sustained fusion is required for it to be an applicable and controlled energy resource, despite being discovered in the operation of the hydrogen bomb.

By the 1970s it became clear that it would not be easy to generate energy using fusion and would require a collaborative effort for its production. In 1973, European countries came together and began the design work and it was given approval in 1977. The notion of a cooperative international project for developing fusion energy for peaceful resolutions got suggested by General Secretary Gorbachev of the former Soviet Union to US President Reagan.

Important terms related to Fusion

  • Thermonuclear fusion- It is the process of the fusion of atomic nuclei using high temperatures to drive them close to each other. These temperatures cause the matter to become plasma and cause fusion reactions to occur because of clashes with the intense thermal kinetic energies of the particles. The measurement of the average kinetic energy of the particle is Temperature, heating the material will gain energy.
  • Deuterium-Tritium fusion- Deuterium atom fusion with Tritium atom to obtain a Helium atom is the most promising fusion at present time. It requires temperatures of approximately 72 million degrees Fahrenheit and generates 17.6 million electron volts of energy. 
  • Muon-catalyzed fusion- This fusion occurs at ordinary temperatures. In the 1980s, Steve Jones studied it in particular. The high energy required to create muons makes it impossible to generate net energy.

Main Differences Between Fission and Fusion (In Points)

  • Fission is the process of splitting a large and unstable nucleus into two lighter nuclei, and Fusion is the process where two light nuclei merge emitting vast quantities of energy. 
  • The energy released during Fission heats water into steam in nuclear power reactors. The steam is useful in spinning a turbine to generate carbon-free electricity. Nuclear fusion is the process that powers the sun and produces enormous amounts of energy- several times grander than Fission. 
  • During Fission, highly radioactive particles get generated in large amounts. On the other hand, very few radioactive particles get generated after Nuclear Fusion.
  • The energy released during Fission is a million times greater than that discharged in other chemical reactions. It is an exothermic process. The energy emitted during Fusion is 4-5 times greater than that released in Fission. It is an endothermic process.
  • Fission requires high-speed neutrons and the critical mass of the substance. Nuclear Fusion needs high temperatures and high density to occur.
  • Fission is applicable in nuclear power plants. The primary fuel employed during Fission in power plants is Uranium. Fusion is helpful in the generation of energy.
  • Fission is used in nuclear power reactors since it can be controlled, but fusion is not yet utilized to produce power. It is costly to create the required conditions for a fusion reaction. Fusion reactions are not efficiently controlled.


Nuclear Fission and Fusion are the two fundamental types of Nuclear reactions. Nuclear Fusion is a reaction in which two or more light nuclei fuse to form a heavier nucleus. The Nuclear Fusion procedure happens in components having a low atomic number. Nuclear Fusion is the opposite of Nuclear Fission reaction, in which substantial elements split and develop lighter elements. When neutrons split unstable isotopes, fission chain reactions occur. This kind of impact and disperse process is challenging to control, but the initial requirements are relatively easy to achieve. Fusion chain reaction, on the other hand, creates or materialises only under extreme pressure and temperature conditions. The conditions are kept steady by the energy released during the fusion process. Both Fusion and Fission create a massive amount of energy.

This article has tried to explain the concept of Fission and Fusion and clear the air concerning the differences between them. Where one works to split the atom, the other combines two or more atoms. They both have different and significant uses therefore, scientists have given their all to bring out the best in these reactions. After several years of hard work, collaborations, and inventions, they have successfully achieved using Fission and Fusion processes for the betterment of the world and its people.


  • https://en.wikipedia.org/wiki/Nuclear_reaction#Notable_types
  • https://energyeducation.ca/encyclopedia/Nuclear_fission
  • https://en.wikipedia.org/wiki/Nuclear_fusion#Thermonuclear_fusion


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"Difference Between Fission and Fusion." Diffzy.com, 2023. Wed. 07 Jun. 2023. <https://www.diffzy.com/article/difference-between-fission-and-fusion-1324>.

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