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Fusion Power

We know that chemical reactions involve the conversion of reactant molecules to product molecules. Here some chemical bonds of reactant molecules are broken and some of the new bonds are formed with different arrangement of atoms in the molecule. This results the formation of new compound. In a chemical reaction, the valence electrons of an atom take part. Electrons which are located in the outermost shell of an atom are called as valence electrons.

So we can say that chemical reactions involve transfer or sharing of valence electrons of atoms which provide them stability. All chemical reaction can be represented with the help of chemical equation in which reactants and products are represented with their chemical formulae. The reactant molecules must be on left side and products are on right side of equation which is separated by an arrow.

Unlike chemical reactions, nuclear reactions involve nuclei of atoms. Can we say that there is no role of electrons in nuclear reactions? We know that an atom is composed of certain sub-atomic particles; electrons, neutrons and protons. In these particles, protons are positively charged particles; neutrons are neutral whereas electrons are negatively charged particles. Protons and neutrons are placed at the center of atom that is called nucleus. Since neutrons are neutral particles, so nucleus has positive charge and negatively charged electrons are placed in certain energy levels called as orbitals.

Nuclear reactions are chemical reactions in which nuclei of two different or same element react together to form new nuclei with emission of some nuclear particles or radiations. In other words, nuclear reactions involve the transformation of one nuclide to another with addition or removal of certain small particles like alpha particles, beta particles, positrons, gamma rays etc. If the interaction of one nuclide with another nuclide does not change the nature of any nuclide, it is called as nuclear scattering. It is not a nuclear reaction.

Like chemical equation, the nuclear reactions represent with nuclear notations in which the atomic symbols of elements are used with mass number as superscript and atomic number as sub-script must be written. For example neutron capture of B-10 forms Li-7 and He-4 with release of some energy. The nuclear equation can be written as below.

$_{5} ^{10}B + _{0} ^{1}N + _{3} ^{7}Li + _{2} ^{4}He + 2.8 Mev$

The particles involve in nuclear reactions are abbreviated as;
• p $\rightarrow$ Proton,
• n $\rightarrow$ Neutron
• d $\rightarrow$ Deuteron
• $\alpha$ $\rightarrow$  Alpha particles or helium-4
• $\beta$ $\rightarrow$ Beta particle or electron
• $\gamma$  $\rightarrow$ Gamma rays
Nuclear reactions can be classified on the basis of types of particles emitted during the reactions. Elastic scattering- Such nuclear reactions do not involve any energy transfer between the parent nucleus and the daughter nuclei.

$^{208}Pb + _{0}n^{1} \rightarrow _{0}n^{1} + _{208}Pb$

Inelastic scattering- Some energy transferred between parent and daughter nuclei during these processes therefore difference of kinetic energies is saved in excited nuclide.

$_{40}Ca + \alpha particle \rightarrow \alphaâ€™ particle + ^{40}Ca$

Capture reactions- Nuclei can capture both charged and neutral particles and form new nuclei.  For example, neutron capture reaction forms radioactive nuclides and this process is called as induced radioactivity.

$^{238}U + _{0}n^{1} \rightarrow _{239}U$

Radioactive decay- The nuclear decay of unstable atom loses energy with emission of ionizing radiation. It is a random process that is impossible to predict. On the basis of emitted particles, radioactive decay can be classified as;
1. Alpha decay- Alpha particles are helium nuclei with two protons and two neutrons. Due to large mass and charge, these particles can ionize material easily and has a very short range. Alpha decay forms nuclei with atomic number less by 2 and mass number less by 4.
2. Beta decay- These are high-energy, high-speed electrons or positrons. They have greater range of penetration power and ionizing radiation.  The emission of beta particle increases the atomic number but mass number remains same for daughter nuclei.
3. Gamma decay- Gamma radiations are neutral radiations very high frequency and high energy. The gamma decay from parent nuclei reduces the energy level of daughter nuclei.
4. Neutron emission- Like alpha and beta decay, neutron emission usually occurs with those nuclei which have excess of neutrons.
5. It is one of the most important reactions in nuclear reactors.

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Fusion Power Definition

Another classification of nuclear reaction is on the basis of nuclear reaction between two or more nuclei. Nuclear reactions can be classified as;
• Nuclear fission
• Nuclear fusion
Nuclear fissions are nuclear reactions in which heavy nuclei reacts with some energetic particles like neutrons to form two or more small light weight daughter nuclei. One of the best examples of nuclear fission is fission of Uranium-236 to Kr-92 and Ba-141 with 3 neutrons and large amount of energy.

Another type of nuclear reaction is nuclear fusion reactions. As name suggested, these are the reactions in which small nuclei combine together to form large heavy nuclei. These reactions produce more energy than nuclear fission reactions. The nuclear fusion reactions of light elements like deuterium and tritium is the energy production reaction of stars and the Sun. The interactions between cosmic rays and matter are also nuclear reactions. Fusion power can be defined as the energy released during any nuclear fusion reaction. In such reactions two or more atomic nuclei collide at a very high speed and combine or fuse to form new nuclei.

How Does Nuclear Fusion Power the Sun?

Our Earth is the only place in the Solar System where life is known to be able to live. The Earth lies within our Sunâ€™s Habitable Zone therefore it is in right spot to receive the abundant solar energy; light and heat which are essential for all the chemical reactions in living organisms.

The nuclear fusion reaction releases an incredible amount of energy in the form of light and heat that causes high temperature at the Sun. The core of the Sun is rich in hydrogen gas that gets squeeze together so tightly that results the fusion of four hydrogen nuclei to form one helium atom. In this fusion some of the mass of the hydrogen atoms is converted into energy in the form of light.

So we can say that the most common nuclear fusion occurs in the core of the sun at 10-15 million Â°C which converts hydrogen to helium and release an ample amount of energy called solar energy. This solar energy is responsible for life on the Earth. The fusion of deuterium and tritium also forms He-4 nuclei with a neutron and releases large amount of energy.

$^{2} _{1}Deuterium + ^{3} _{1}Tritium \rightarrow ^{4}_{2}He + ^{1}_{0}n + 17.6 MeV$.

Today we know a large number of energy sources which are useful in some field of our everyday life. We cannot create or destroy energy but can convert it from one form to another. No energy source is perfect, there are always some pros and cones with all energy sources.

Nuclear energy is the most important energy source as it provides enormous amount of energy compare to other energy sources like coal, petroleum etc. Nuclear reactions like nuclear fusion and fission both are good source of energy although they are based on different types of nuclear reactions. Some common differences between these two reactions are listed below.

 Nuclear Fission Nuclear Fusion 1. It can be defined as the fission or splitting of large nuclei to two or more smaller ones. It involves the fusion of two or more lighter atoms into a larger one. 2. Such reactions do not occur normally occur in nature. These are most common reactions in stars, such as the sun. 3. Many highly radioactive particles are formed a byproducts of nuclear fission reactions. Only few radioactive particles are produced as byproduct by fusion reaction. 4. The main reactions conditions are critical mass of the substance and high-speed neutrons for nuclear fission reactions. Critical reaction conditions such as high density, high temperature environment are required for nuclear fusion. 5. The reaction can be initiated by little energy to split two atoms. Unlike fission processes, extremely high energy is required to bring two or more nuclei close enough to overcome the nuclear forces. 6. Compare to normal chemical reactions, the energy released by fission is a million times greater but lower than nuclear fusion. The energy released is 3-4 times greater than the energy of nuclear fission. 7. Used in fission bomb or atomic bomb or atom bomb. Used in hydrogen bomb 8. Also used in nuclear power plants It is an experimental technology for producing power. 9. Uranium is used as fuel. Hydrogen isotopes such as Deuterium and Tritium are used as fuel.

Nuclear fusion is major source of energy in the universe as it empowers the sun and all of the stars. It involves fusion of two atoms of the same lightweight element such as isotopes of hydrogen, to form helium-4.

The uncontrolled nuclear fusion reaction is used in hydrogen bomb in which all the tremendous energy is released at once in a highly destructive manner. If this energy could be released gradually in a controlled manner like it occurs in the sun, it could become the ultimate source of energy. A controlled fusion reaction has proven very difficult because fusion of two hydrogen atoms is a difficult process as they have the same charge and will electrically repel each other.

At Sun the temperature is around 12 million degrees C that accelerates the fusion of nuclei to overcome the electrical repulsion between them. Producing this temperature and critical conditions is a great engineering challenge. When elements are heated until they reach a plasma state, no material could withstand without melting.

At the same time the reacting elements must be suspended without touching the walls in the vessel means they must be at great gravity, inertia, or magnetism. These all reaction conditions are very challenging to create and control for continuous reaction. Today all the experimental nuclear fusion reactors are using deuterium and tritium as the parent nuclei for fusion process.

At the same time, there are many limitations of nuclear fusion reaction.  On industrial scale, it is difficult or impossible till at least 2050.  The nuclear fusion power plants would be extremely expensive to build and maintain due to requirement of extremely high temperatures. Hence disadvantages of nuclear fusion can be summarized as;
• Energy input VS energy output- The energy input is more than output so nuclear fusion energy is truly not plausible.
• Construction costs- The maintenance of nuclear fusion plant are immensely expensive.
• Little Understood- It is a new form of energy so yet full scope of dangers and effects of nuclear fusion energy isn’t understood.
• No perfect fuel- For nuclear fusion no known material is known which can sustain at extremely high temperature.