What is the difference betwen Nuclar fission and Nuclear fusion reaction?

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ndnordic's profile pic

ndnordic | High School Teacher | (Level 2) Associate Educator

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Fission means the splitting or breaking down of large elements into smaller elements. In nuclear fission reactions the large element used is most often uranium.  Uranium is naturally radioactive, meaning it will split by itself, at a certain rate.  However, to increase that rate, neutrons are used to split additional uranium atoms. When a uranium atom splits, several things happen.  One, a certain amount of energy is released which can be used to generate electric energy.  Second, two or more smaller elements are formed.  Third, several additional neutrons are released which can then split more uranium atoms, continuing the process.  In a nuclear fission reactor, the rate at which the uranium atoms are split is carefully controlled to generate the useful energy.

Fusion is a process in which small elements are forced together to form larger elements. The most common fusion reaction is to join two hydrogen atoms to form helium.  This is the process believed to fuel the energy release on the sun. It takes very high temperatures and extreme pressures to take place. This is because the nucleus of each atom is positive and positive charges repel. To force the nuclei together this very high repulsion force must be overcome.

Scientists have been trying for decades to recreate this process on earth  as an alternate source of energy to produce electric energy but have so far been unsuccessful.

kumarvaibhav123's profile pic

kumarvaibhav123 | Student, Grade 11 | (Level 1) Salutatorian

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Fission refers to the breaking or spliting into two or more parts. In a Fission reaction nuclei of a heavy weight element splits into two or more medium weight elements when bombarded with slow moving electron,e.g- in nuclear power plant when a uranium-235 atom is bombarded with slow moving electron it breaks into two another atoms { barium-139  and  krypton-94} with the emission of three neutrons and produces very large amount of energy,{ here energy produced is calculated by the equation  E=mc^2}.


fusion means joining or combining two or more things. In a fusion reaction two or atom join together to form a atom with a weight more than the previous atom which fuse together. Fusion usually produces much more energy than fission. It naturally takes place inside the stars. e.g- inside the sun four hydrogen atoms fuse together to form helium and with the emission of one positron and produce a very large amount of energy given by{e=mc^2}.


Hydrogen bomb works on fusion of hydroden isotopes.

Fusion reaction requires a large amount of pressure and temperature to take place. since  we know that nuclei of two atom are positively charged so they repel each other, so when the atom are heated to high temperature under very high pressure nuclei of atoma starts moving quickly and cannot repel each other due to the pressure exerted and when come close to each other they fuse together when they collide.

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mukundbj | Student, Grade 9 | (Level 1) eNoter

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Fission is the splitting of a large atom into two or more smaller ones. It takes place when a high speed neutron is directed towards a highly unstable radio active atom(eg. Uranium). This results in the creation of photons in the form of gamma rays, free neutrons, and other subatomic particles. It takes very little energy to take place. This reaction is used in nuclear reactors as well as in uclear bombs. It does not take place naturally.


Fusion is the fusing of two or more lighter atoms(eg. hydrogen) into a larger one(eg. helium). High density, high temperature environment is required for it to take place. Extremely high energy is required to bring two or more protons close enough that nuclear forces overcome their electrostatic repulsion. It occurs naturaly in the stars but humans have not found an efficiant way of harnessing this energy.

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