13 Nuclear Fusion Process:Explanations And Facts


In this article the nuclear fusion process is going to be illustrated step by step with explanations and facts related to it.

Before starting the detailed facts related to nuclear fusion process we should have a basic idea regarding nuclear fusion reaction and how it is different from the nuclear fission reaction. Nuclear fusion is just the opposite reaction of nuclear fission.

We all know that when a heavy nucleus of uranium 235 breaks into two fragments of two different lighter nuclei of barium and krypton accompanied by 3 faster neutrons then this reaction is known as nuclear fission. In case of fusion two lighter nuclei combine to form a heavier nucleus.

Let’s come to the core of this concept i.e, the bindinding energy per nucleon.

According to the binding energy curve, comparatively lighter nuclei that are placed on the steep portion of the curve have lesser values of binding energy per nucleon than the binding energy per nucleon of the nuclei of intermediate mass numbers.

Nuclear binding energy curve from wikipedia

This is the reason if two lighter nuclei get fused together to form a heavy nucleus then the binding energy would have a greater value and the nuclear mass would decrease consequently. A positive Q value is the result obtained from it that signifies a release of energy.

The nuclear reaction that is mentioned above is termed as nuclear fusion.

Nuclear fusion process
Nuclear fusion from wikipedia

It has been shown by a scientist Eddington in 1920 that four hydrogen can be fused together to form a helium atom. It would release 7 MeV/nucleon or a total of 28 MeV for all the four atoms.

Equation of nuclear fusion reaction is written below:

1H1 + 1H1 1H2 + 1e0 + 𝜈 + Q                              Q= 0.42 MeV                       

1H2 + 1H2  → 2He3 + 0n1 + Q                                Q= 3.3 MeV

Q denotes the value of released energy.

The factors on which nuclear fusion process depends upon are:

(i) The collisions must be between two very energetic nuclei

(ii) There is a requirement to re-arrange the nucleus subsequently

(iii) The released energy should be the kinetic energy and excitation energy of the product nuclei

Both the colliding nuclei are charged positively. Hence a strong electrostatic repulsion force acts between them that tries to separate them from each other. Therefore the kinetic energy of these colliding nuclei must be very high so that it can overcome the electrostatic coulomb repulsion force.

It must be a self sustaining reaction so that the energy released is greater than the energy absorbed in initiating the reaction.

As the value of kinetic energy increases,temperature also increases. So that a sufficient amount of energy is delivered to the secondary nuclei. This is why nuclear fusion reactions are also termed as thermonuclear reactions.

The obtained high temperature in a nuclear fusion process is as high as  10⁹ degree Celsius. As the atomic numbers become high the temperature rise is also high. Mainly three isotopes of hydrogen(1H1,1H2,1H3) are used in nuclear fusion process,especially deuterium(1H2).

Nuclear fusion from wikipedia

The steps of nuclear fusion process are stated below:

Step 1:

At first two lighter nuclei specially two deuterium atoms are brought close to each other.

Step 2:

After that these two nuclei are heated at a very high temperature of 10⁹ degree Celsius.

Step 3:

The atoms should collide at a very high speed to overcome the electrostatic coulomb repulsion force acting between them( this force of repulsion is acting as both of them are positively charged).

Step 4:

Then these two atoms are fused to each other.

                1H1 + 1H1 1H2 + 1e0 + 𝜈 + Q                              Q= 0.42 MeV

                1H2 + 1H2  → 2He3 + 0n1 + Q                                Q= 3.3 MeV

Step 5:

After the reaction occurs,neutrons are formed and a huge amount of energy is released.

Step 6:

All of us are quite familiar with Einstein’s mass-energy relation. That is, E=mc² where E= energy,m= mass and c= velocity of light. Now the mass of the product atom is less than the mass of the two reacting atoms.

This excess mass is not lost during the reaction,it only gets transformed into energy according to the above mass energy relation.

From this whole process it can be observed that we need a very small quantity of mass to generate a huge amount of energy.

13+ nuclear fusion process with detailed illustrations are stated below:

Nuclear fusion process in the stars

Stars mostly contain densely packed hydrogen and helium atoms. As they are very closely packed with each other they create huge pressure at the core of the stars. Due to this high pressure and temperature around  10⁹ degree Celsius nuclear fusion occurs here.

Two lighter atoms fuse together in the nuclear fusion reaction. Two hydrogen atoms combine together to form a helium atom in the core of the stars. Though it takes a lot of energy to initiate nuclear fusion,once it gets started it produces a huge amount of energy.

Nuclear fusion process occurs continuously in the stars. At first two hydrogen combine to form helium,after that beryllium etc. As there is one proton in a hydrogen atom, hence the fusion of hydrogen atoms in stars is also known as proton-proton fusion.

Nuclear fusion process in the sun

Nuclear fusion also takes place in the sun. Here also hydrogen atoms combine to form helium atoms. Four hydrogen atoms get fused to each other to form each helium atom.  Some mass of the products get transformed into energy during this nuclear fusion process.

Stellar reactions

All elements belonging to this universe were hydrogen in previous situations. Protons and neutrons that belong to some lighter nuclei are combined together to form new elements within the stars. The process through which this occurs is known as stellar nucleosynthesis.

Stellar nucleosynthesis from wikipedia

Hydrogen is changed to helium,heat energy and radiant energy through the nuclear fusion process. So basically new nuclei are formed from the pre existing nuclei in the stars through these reactions.

In primordial nucleosynthesis H,He and Li-7 are produced in the hot early universe. Today stellar nucleosynthesis takes place through thermonuclear reactions in the stellar environment and neutron captures in the stellar environment.

Nuclear fusion process occurrence inside the earth’s core

The source from which nuclear fusion process occurs inside the inner core of the earth is yet yet to be found. Hence it is assumed by the scientists that decay of radioactive elements can be one of the sources of nuclear fusion here.

Here this nuclear fusion that occurs from the deuterons increases the rate of the reaction at a very high pressure of 364 GPa and a very high temperature of 5700 K. the required equation of the reaction is:

2D + 2D + 2D → 2 1H1 + 2He4 + 20.85 MeV

The rate at which heat is produced is 8.12 X 10¹² J/m3

Uncontrolled nuclear fusion process

In a hydrogen incendiary device both nuclear fission and fusion reactions occur. The fission part within it contains uranium 235 and plutonium 239. An atmosphere of deuterium and tritium has surrounded them. This fission part plays the role of an igniting fuse at first and provides a high temperature of 107-108 degree Celsius.

This extremely hot ambience helps in initiating the process of nuclear fusion. This temperature is then maintained so that the process can keep running.

Thermonuclear munition from wikipedia

Controlled nuclear fusion process

We know that nuclear fusion can not be obtained in a laboratory as it requires a very high temperature to start. Hence to solve this problem the process of using particles having high kinetic energies has been initiated.

Another approach to solve this problem is to convert the nuclear fusion fuel into plasma.

Nuclear fusion reactors

Nuclear fusion reactor is an application of controlled fusion reaction. In this type of reactor basically nuclear energy gets transformed into electrical energy. Its mechanism is similar to the normal nuclear  fusion reaction.

An insignificant amount of mass is converted into an enormous amount of energy according to Einstein’s mass-energy relation,E=mc².

Nuclear fusion reactor from wikipedia

Proton – proton cycle

This is basically a type of stellar reaction. In this reaction protons are fused to produce helium nuclei. Stellar energy is also liberated in this reaction. The equations of proton-proton cycle are-

                                                     1H1 + 1H11H2 +1e0 + v + 0.42 MeV

                                                    1H2 + 1H12He3 + γ + 5.5 MeV

                                                    2He3 + 2He32He4 + 2 1H1 + 12.8 MeV

Carbon – nitrogen cycle

This is another type of stellar reaction. It is used in the stars as an alternative to the proton-proton cycle. The energy released in it is also the same as the previous cycle.

The overall equation for this is:

4 1H12He4 + 2 1e0 + 2v+ 3γ  + 26.72 MeV

Thermonuclear fusion

This type of nuclear fusion is used in thermonuclear munitions. At a very high temperature the atoms go to the plasma state in this type of reaction. Extremely high kinetic energies help the particles to collide. Hence fusion occurs.

Inertial electrostatic confinement nuclear fusion process

In these devices an electric field is used to heat the ions which in turn helps in occurrence of a nuclear fusion reaction. This concept is used in a fusor.

Inertial confinement nuclear fusion process

Here a fuel target is heated and compressed so that fusion energy can be liberated. The fuel target contains a pellet of deuterium and tritium.

Beam-target nuclear fusion process

In this method accelerators are used in achieving high kinetic energies to occur light-ion fusion reactions.

Ankita Biswas

I am Ankita. I have done my B.Sc in physics honours and my M.Sc in Electronics. Currently I am working as physics teacher in a Higher Secondary School. I am very enthusiastic about high energy physics field. I love to write complicated physics concepts in understandable and simple words.

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