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Nuclear Fusion

Nuclear reactions are the characteristics reaction of an atomic nucleus. These reactions are induced by the bombardment of an energetic particle. The bombarding particles are alpha particle, a neutron, a gamma photon, or an iron, or a proton. For bombardment of particles, the particles must possess enough amount of energy. The reaction can be completed between a heavy nucleus and a light particle. The first nuclear reaction was observed by Ernest Rutherford in 1919 when he bombarded nitrogen particles on alpha particles and observed the emitted light particles of protons and the nuclei of oxygen. The first artificial nuclear reaction was produced J.D. Cockcroft and E.T.S. Walton in 1932. They bombarded lithium with protons and observed the generation of helium or alpha particles. The nuclear reactions are classified in two categories that are nuclear fission and nuclear fusion.

Here, we are discussing all about the nuclear fusion and difference in both the nuclear reaction. These are the reaction in which two light weight nuclei are reacted to form big nucleus. Fusion reaction takes place between sun and stars.

 

What is Nuclear Fusion?

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Nuclear Fusion is the type of nuclear reaction in which two atoms combines under influence of large amount of heat and energy. The result of this fusion is tremendous amount of energy and heat.

The example of nuclear fusion is shown in figure below:

Nuclear Fusion
Here two isotopes of hydrogen (tritium and deuterium) are fused together, under high pressure and temperature, to form a more stable atom of helium. The fusion process also results in release of a neutron and hence in turn releases a large amount of energy.

A physical reaction which involves changes in the nucleus of an atom is called a nuclear reaction. The energy released during a nuclear reaction is called Nuclear Energy. This energy can also be produced by the use of the radioactive elements. For producing the energy by the use of radioactive material there are two different methods:

Nuclear Fission:
This is the easiest reaction which yields energy. In fission the unstable atom is disintegrated into two stable atoms. In the fission reaction a neutron is added to the atom of a radioactive element making it unstable and hence it disintegrates into two stable atoms releasing energy.Example:            92U235 + 0n1 --------> 56Ba141 + 36Kr92 + 3 0n1 + Q.

Nuclear Fusion:
It is reverse of the nuclear fission. In fusion reaction, nuclei of two atoms fuse together to form a heavier nucleus. The fusion reaction is usually accomplished by the release of large energy. Example:                  1H3 + 1H2 --------> 2He4 + 0n1 + energy

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History of Nuclear Fusion

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The Nuclear Fusion is the most prominent and ancient of the nuclear reaction of the two (nuclear fission and nuclear fusion). It is the source of energy of all of the star, universe and galaxies.

Why is the Nuclear fusion energy source for sun and other stars?
Nuclear fusion occurs at very high temperatures i.e., 107 K because only under such conditions that protons come close together against their mutual repulsion. Further, high density is also desirable for such collisions to occur. These conditions are found in the Sun. Thus, the source of Sun's energy is nuclear fusion.We started to understand the nuclear fusion since 1940’s. In the late 40’s of the twentieth century various scientist from both USSR (now Russia) and USA began experimenting to understand the energy source of our Sun and other star in our Milky Way. By these experiments we understand that other than nuclear fission there exists another type of nuclear energy which can be produced by the Nuclear Fusion.

Since then various organizations in the world started experimenting to understand this new type of Nuclear Energy which is more efficient and produces clean energy.

The main disadvantage of fusion reaction is that it needs Very high temperature for the reaction to take place. So till now we have not been able to build a nuclear reactor which produces Nuclear Energy based on Nuclear Fusion reaction.

Nuclear Fission and Fusion

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Nuclear Fusion Nuclear fission
Here disintegration of an unstable atom into two different atom and thereby releasing large energy. Here the integration of two atom takes place to produce one atom and thereby releasing tremendous amount of energy.
Energy released is less compared to energy given to start the reaction. Energy released is comparatively more.
It is a clean reaction where the bi-product produced of the the fusion reaction is a stable atom. It is not a clean reaction as the bi-product of this reaction is radioactive.
The disadvantage here is to start is that the fusion reaction requires large amount of energy to start the reaction and then more energy to keep the reaction going. Here energy can be easily acquired in the controlled manner by fission reaction.

Nuclear Fusion in the Sun

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Our Sun is the best nuclear fusion in the universe. It has plenty of protons which is the essential requirement of fusion reaction. The nuclear reaction of the Sun produces tremendous energy which is the prime source of life on the earth.

1H + 1H ----> 2H + e+ + $\nu$
2H + 1H ----> 2H + e+ + $\nu$
2H + 1H ----> 3He + $\gamma$
3He + 3He -----> 4He + 1H + 1H.

                                      Nuclear Fusion Reaction

The fusion reaction happening in the Sun can be understood by these reactions:
  1. Two protons are combined to form an isotope of hydrogen, deuterium, atom (hydrogen atom with one neutron and one proton), a positron and a neutrino.
  2. A deuterium atom and a proton combine to form a helium-3 (He-3) atom and a gamma ray. The He-3 atom has two protons and one neutron.
  3. Two helium-3 (He-3) atoms then combine to form a helium-4 (He-4) atom and two protons. The He-4 has two protons and two neutrons.
The result of these reactions is the release of tremendous energy. These reactions contribute 85% to 90% of the sun’s energy. There are several different reactions going on Sun’s surface. The amount of energy is such that the sun’s temperature reaches many million degrees Kelvin.

Nuclear Fusion Reactor

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The Nuclear fusion Reactor would produce energy by the use of fusion reaction, which offers less radiation and less nuclear waste than the fission reaction. The Nuclear Fusion Reactor which produces energy by the sustainable nuclear fusion reaction is very difficult to produce. The Fusion Reactor is based on the nuclear fusion reaction in which two atoms combine to form a new atom and in this process lots of energy is released.

Nuclear Fusion Reactor

The Magnetic and Electrostatic nuclear fusion reactors have come but they have their own limitations. Currently there are few experimental reactor available but the working reactor is still miles ahead.

Nuclear Fusion Equation

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Following are the Nuclear Fusion Equation :
2p+ ---> 2H1 + 1e+ + 1ne
2H1 + 2p+ ---> 3He1 + $\gamma$
2 3He1 ---> 4He1 + 2p+ + Energy.
The first reaction is the collision of proton with each other which produces one deuterium atom, one neutron and one positron (antimatter particle). This collision begins the proton-proton cycle.

In the second reaction the deuterium (formed from the first equation) and proton combined to form He-3 and releases gamma radiation.

In the third equation two He-3 (formed from the second equation) are combined to form He-4, two protons and tremendous energy.

Nuclear Fusion in Stars

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The Nuclear fusion is the most prominent energy source of the intergalactic & celestial bodies. At the center of star tremendous pressure and heat energy the atoms collide and fuse together to release even larger energy and this energy fuel the next stage of more atom. This process continues and the star gets energy and makes it hot and bright, like our Sun.

The smaller stars convert hydrogen into helium. The medium and large sized stars convert helium in oxygen and carbon and other complex and heavier elements to continue the fusion reaction. When the stars gets depleted they spew these elements into space.

Nuclear Fusion reactions in small stars :


The main overall nuclear fusion reaction is the fusion of four hydrogen atom nuclei to form a bigger nucleus of a helium atom i.e.
4 1H1 $\rightarrow$ 4He2 + 2 0e+1+ energyi.e., 4 Hydrogen nuclei -----> Helium nucleus + 2 positrons + energy.

The conversion of hydrogen nuclei in the stars can take place in a number of different ways. The most probable series of steps that can be envisaged for this conversion of hydrogen nuclei (or protons) into helium nuclei are the following three steps:

Step 1 :
Two protons (or hydrogen nuclei) fuse together to form a deuteron (hydrogen isotope having mass number as two) with the emission of a positron and a neutrino :
p + p -----------> D + e+ + $\nu$i.e., proton + proton -----------> deuteron + positron + neutrino

Step 2 :
In the second step , the deuteron formed in step 1 fuses with another proton to form a helium – 3 isotope, with the emission of gamma rays :
D + p ------------> 3He + $\gamma$ i.e., Deuteron + proton ---------> Helium – 3 + Gamma ray

Step 3 :
In the third step, two helium-3 nuclei fuse together to form a helium-4 nucleus and two protons.
3 He + 3 He --------------> 4 He + 2p
i.e., Helium-3 + Helium - 3 --------> Helium- 4 + 2 protons.

Combining all the above three equations suitably will eventually result in the main overall nuclear fusion reaction as discussed in the beginning. The tremendous energy produced by the fusion of hydrogen into helium is released in the form of heat and light.

It is this energy which makes all the stars in the sky twinkle like diamonds in the sky !

Fusion Energy

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We know that the Sun is theoretically an infinite source of heat and energy. It is a renewable source of energy. The Sun gets its energy by the nuclear fusion reaction. The fusion energy has the potential of becoming the major source of energy for the decades to come with very less raw material.

The Nuclear fusion power has several advantages:
  1. No carbon emissions,
  2. Highly energy efficient system,
  3. Abundant fuel,
  4. Very less radioactive waste as compared to the fission reaction.

Examples of Nuclear Fusion

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The best examples of the nuclear fusion is the energy of our sun. The sun is composed of lots of hydrogen and by the fusion of two isotopes of the hydrogen, helium is produced and in turn energy is released.
1H2 + 1H2 ----> 2He + 24 Mev
1
H2 + 1H4 ----> 2H4 + 0n1 + 12.6 Mev
1
H2 + 1H2 ----> 2H3 + 0n1 + 3.35 Mev.

Nuclear Fusion Power

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Due to the nuclear fusion reaction the power produced is very high as compared to the power applied to initiate it. The nuclear fusion power is a viable and more clean fuel as compared to nuclear fission power since its by product is water and not the radioactive material as in the case of the nuclear fission.
The Nuclear Fusion Power is the future fuel of the mankind and several research is going on this fuel to make it sustainable and useful for our day to day energy needs.
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