Nuclear Energy Class 10 Notes
Nuclear energy
Definition :
Energy released, when some changes take place in the nucleus of an atom of a substance, is called nuclear energy.
Nature :
It is partly renewable and partly non-renewable.
Nuclear fusion is renewable because hydrogen needed for this process is available in plenty in nature.
Nuclear fission is non-renewable because uranium needed for this process has only limited existence.
Modern atomic structure
Introduction :
According to modern theory of atomic structure atom of every substance consists of a central core called nucleus. This nucleus is made up of protons (positively charged heavy particles) and neutrons (uncharged heavy particles). Nucleus contains almost whole of the mass of the atom. Protons and Neutrons are together known as Nucleons.
Outside the nucleus but inside the atom, there are electrons (negatively charged light particles) which surround the nucleus and revolve around it in orbits (shells) of different radii.
The charge on an electron is –1.6 × 10–19 C.
The number of electron surrounding the nucleus is equal to the number of protons inside the nucleus. Thus, atom as a whole is electrically neutral.
Nucleus has a diameter of 10–15 m, whereas atom has diameter of about 10–10 m.
Table : Characteristics of Neutron, Proton and Electron (Elementary Particles)
Identity of an element (atomic number and mass number)
Definition
A substance having all the atoms having same number of Protons, is called an element.
An element is distinguished from another by the number of protons in them.
Atomic Number
The number of protons present in the nucleus of an atom of an element, is called its atomic number (or charge number) of the element.
It is represented by the symbol Z.
As a neutral atom has as many electron outside the nucleus and as the number of protons inside the nucleus. So we can say that :
Atomic number (Z) = Number of Protons = Number of Electrons
Mass Number
The total number of protons and neutrons present in the nucleus of an atom of an element, is called the mass number of that element. It is represented by the symbol A.
Hence,
Mass number (A) = Number of protons + Number of neutrons
= Number of nucleons
(Nucleons is the common name of protons and neutrons)
Number of neutrons present in the nucleus of the atom, is called neutron number.
It is represented by the symbol N.
Hence, We can write symbolically, A = Z + N
Isotopes, isobars and isotones of an element
Isotopes
(i) Definition :
Atoms of an element having same atomic number but different mass number, are called isotopes of that element.
Isotopes have equal number of protons.
(ii) Example :
The three isotopes of hydrogen are :
(a) 
H (protium)
(b) 
H (deuterium or heavy hydrogen)
(c) 
H (tritium).
Isobars
Atoms of different elements (which have different atomic number) , having same mass number, are called isobars. They have equal number of nucleons.
For example, 
C and 
N
Isotones
Atoms of different elements (which have different atomic number), having same number of neutrons, are called isotones.
For example, N and 
O
Symbols of some important particles
Before we study radioactivity and nuclear reactions, it is very important to know the symbols of alpha particle, beta particle, gamma ray, neutron, proton, deutron, triton, positron and neutrino, which we will be using again and again in these topics. These are given below :
(i) The alpha particle is a helium nucleus
The symbol of an alpha particle (∝-particle) is 
He.
The atomic number of ∝-particle is 2 .
The mass number of ∝-particle is 4 .
(ii) The beta particle is an electron (emitted by the nucleus of an atom)
The symbol of a beta particle 
β-particle .
Here –1 denotes that ‘β’ particle has Negative elementary charge and ‘0’ denotes that it has 0 mass number.
Please note that a nucleus does not contain a beta particle (or electron) in it. It is during nuclear reactions that a beta particle (or electron) is formed by the conversion of a neutron into a proton in the nucleus :
(iii) Gamma ray is an electromagnetic radiation of very short wavelength
The symbol of gamma ray is 
ϒ.
The charge on a gamma ray is 0.
The mass number of a gamma ray is also 0.
(iv) Neutron is a neutral particle having 1 unit mass
The symbol of a neutron is 
n.
The charge on a neutron is 0.
The mass number of a neutron is 1.
In those cases where there is no need to show the charge and mass, a neutron is represented by the letter n (small n).
(v) Proton is the nucleus of ordinary hydrogen atom
The symbol of a proton is H
The charge on a proton is 1
The mass number of a proton is also 1
A proton is also represented by the letter p (small p).
(vi) Deutron is the nucleus of heavy hydrogen called deuterium
The symbol of a deutron is H
The atomic number of deutron is 1
The mass number of deutron is 2
A deutron is also represented by the letter D (capital D).
(vii) Triton is the nucleus of very heavy hydrogen called tritium.
The symbol of triton is H
The atomic number of triton is 1.
The mass number of triton is 3.
A triton is also represented by the letter T (capital T)
(viii) Positron is a positively charged particle having 1 unit positive charge but a negligible mass equal to that of an electron. It is also called a positive electron.
The symbol of a positron is 
e
The charge on a positron is + 1 or just 1
The mass number of a positron is 0
Just like a beta particle (or electron), a positron does not exist in the nucleus of an atom. A positron is formed by the conversion of a proton into a neutron during nuclear reaction :
Positron is also represented by the symbol β+ or e+.
(ix) Neutrino is a nuclear particle having no mass and no charge.
The symbol of a neutrino is ν (pronounce it as nu)
The charge on a neutrino is 0
The mass number of a neutrino is also 0.
Keeping these particles in mind, we will first describe the phenomenon of radioactivity and then the nuclear reactions of fission and fusion.
Stability and unstability of nuclei
A nucleus contains a number of protons and neutrons. Protons are positively charged particles and repel each other due to electric forces. But, the nucleus does not break up because of this. This means, there must be attractive force acting inside the nucleus, which balance the electric repulsion and thus keep the nucleons together. This attractive force is called nuclear force, and it operates between two protons, between two neutrons, and between a proton and a neutron.
Nuclear force is the force acting between nucleons, other than gravitational and electric forces.
Nuclear force is effective only if the nucleons are very close to each other.If two protons are kept at a distance of 1cm, theattractive nuclear force between them will be almost zero, whereas the repulsive electric force will have a considerable magnitude. So, the protons will fly apart. However, the separation between the protons inside a nucleus is only about 10–13 cm. At this distance, the attractive nuclear force between two protons is much larger than the repulsive electric force. As the nuclear force is effective only for small separations, we say that nuclear force is short-ranged.
Thus, we see that electric forces as well as nuclear forces operate inside a nucleus. The gravitational force between nucleons of a nucleus is negligible as compared to the electric and nuclear forces, and therefore, has no significance in a nuclear process. Electric forces try to break the nucleus apart and nuclear forces try to keep it bound. Therefore, there is a balance between the two kinds of forces, and the nucleus remains.
Radioactivity
Definition :
The spontaneous disintegration of the nucleus of certain heavy atoms with the emission of alpha particles or beta particles and gamma rays is called radioactivity.
All combinations of different number of neutrons and protons do not form stable nuclei.
The ratio N/Z plays an important role in determining the stability of a nucleus, and it is different for nuclei of different mass. For the stability of lighter nuclei, it is required that the proton number Z and the neutron number N be equal or differ only slightly, so that N/Z ≈1. For heavier nuclei, N is considerably larger than Z. For example, in{^{235}_{92}} U, Z = 92, N = 143. The N/Z ratio of U-235 is more than 1.5, and it is quite stable. But a light or middleweight nucleus will not be stable for this value of N/Z.
Substances with unstable nuclei are called radioactive substances. Their nuclei spontaneously transform (decay / disintegrate) to form a more stable nuclei. An unstable nucleus can transform itself to a more stable nucleus.
Any radioactive substance emit three type of radiation
α-decay : In this mode of radiation, radioactive element amits α-particles (Helium nucleus). Its penetrating power is very less.
Example :
β-decay : In this mode of radiation, radioactive element emits β-particles (An electron). Its penetrating power is greater than a particle.
Example :
ϒ-radiation : In this mode of radiation, radioactive element emits ϒ-radiation. Its penetrating power is the greatest among all three radiation. Nucleus structure doesn’t change in this radiation. Only electronic transition takes place.
Chemical Reactions
In chemical reactions, only the outermost electrons of the atoms take part, the nuclei of the atoms remain unaffected. Only a rearrangement of atoms takes place in a chemical reaction but no new atoms (or new elements) can be produced in a chemical reaction. Moreover, usually a small amount of energy (in the form of heat, light etc.) is released during a chemical reaction, and this energy is called chemical energy. For example, when charcoal (carbon) is burned in the oxygen of air, a chemical reaction takes place to form carbon dioxide gas, and a lot of heat is released in this chemical reaction. This can be written as :
In this chemical reaction, the reactants contain carbon and oxygen elements, and the product carbon dioxide also contains the carbon and oxygen elements. So, no new element has been produced in this chemical reaction. We will now describe nuclear reactions in which new elements can be produced, and an extremely large amount of energy is released.
Nuclear Reactions
In nuclear reactions, the nucleus of an atom undergoes a change forming new atoms and releasing a tremendous amount of energy. New atoms (or new elements) can be produced in a nuclear reaction, which is not possible in the case of a chemical reaction. Thus, a nuclear reaction can convert one element into another element. Some of the nuclear reactions take place in nature on their own in order to attain stability. This process is called as Radioactivity. However nuclear reactions can also be invoked artificially to obtain large amounts of energy.
Such reactions are of two types :
(i) Nuclear fission (ii) Nuclear fusion
Binding Energy
The paritcles present in the nucleus (protons and neutrons) are called nucleons. The sum of the individual mass of various particles in the nucleus must be equal to the nuclear mass. But this is not so. The nuclear mass is somewhat less than the sum of the individual masses of various nuclear particles. The difference between the actual nuclear mass and the expected nuclear mass (sum of the individual masses of nuclear particles) is referred to as mass defect. The mass defect can be converted into equivalent energy by means of Einstein equation (E = mc2) .
The energy equivalent to mass defect is responsible for holding the nucleons together and is called binding energy of the nucleus.
The binding energy per nucleon is a measure of the stability of nucleus. Binding energy may also be considered as the energy required to separate the individual particles of the nucleus.
Mass defect Δm in amu can be directly obtained by using the following formula.
Δm = [Zmp + (A – Z) mn] – mN
where z is atomic number
A is mass number mp is mass of proton
mn is mass of neutron mN is mass of nucleus.
Nuclear Fission
Definition :
A nuclear fission reaction may be defined as the reaction in which a heavy nucleus breaks into two or more nuclei of nearly comparable masses.
It is accompanied with the release of a large amount of energy.
Explanation :
When a heavy nucleus splits into two or more moderate nuclei, some mass is converted into energy. Hence a large amount of energy is released.
Example :
In 1938, German scientists Otto Hahn and Strassmann found that when Uranium is bombarded with slow neutrons, the product of disintegration flew apart with tremendous speed. The products of disintegration were the isotopes of Barium and Krypton which are lighter than Uranium and large energy is released.
23592U Can be disintegrated by capture of a slow neutron according to the following nuclear reaction.
01n + 23592U → 23692U → 14156Ba + 9236Kr + 3 01n + Q (200 MeV)
The 200 MeV energy released (Q) comes to be about 0.9 MeV per nucleon. (It is equal to the difference of average binding energy of 8.5 MeV per nucleon of the moderate nuclei formed and average binding energy of 7.6 MeV per nucleon of uranium nucleus). The energy is mostly in the form of K.E. of fission fragments.
The neutrons produced after fission are called secondary neutrons.
[Another fissionable element is Pu-239 (Plutonium-239), but it does not exist in nature. It can be prepared artificially by bombarding U-238 with neutrons. (U–238, though found in abundance, is not self fissionable.)
Chain Reaction
A reaction in which the particle which initiates (starts) the reaction, is also produced during the reaction to carry on the reaction further and further, is called a chain reaction. Once started, a chain reaction will go on propagating by itself, until one of the reactants is all used up. Thus, a chain reaction is a self-sustaining process or self-propagating process. The fission of uranium-235 by means of slow moving neutrons is an example of chain reaction. (See figure)
Figure : Chain Reaction
Nuclear Fusion
Definition :
A nuclear fusion reaction may be defined as the reaction in which two or more lighter nuclei combine (fuse) together to form a heavier nucleus.
It is accompanied with the release of a large amount of energy.
Explanation :
Light nuclei have less average binding energy per nucleon. The heavier nucleus formed by fusion has more average binding energy per nucleon.
When light nuclei are fused to form a heavier nucleus, some mass is converted into energy. Hence a large amount of energy is released.
Example :
Two deuterium nuclei fused together to form a single helium nucleus, and emit energy of the order of MeV. The nuclear reaction can be represented as follows :
21H + 21H → 42He + Q (26.7 MeV)
Figure : Two deuterium nuclei fuse to give one helium nucleus (42He).
Conditions :
(i) For fusion, the nuclei must have K.E. of the order of 0.1 MeV or more.
On small scale in laboratory such high energy particles can be produced by accelerating low atomic number nuclei in a particle accelerator. These high energy projectiles are made to strike target nuclei.
On large scale, energy of such high value is obtained by sufficient rise in temperature of nuclei. A nuclei with kinetic energy of 0.1 MeV needs a temperature of 107 K. Such extreme conditions cannot be easily arranged in laboratory. They exist in the interior of the Sun.
(ii) Nuclear fusion occurs at a very high temperature and is so called thermonuclear reaction. (It is an uncontrolled nuclear- reaction.)
Nuclear fusion as source of solar energy
The sun is a huge mass of hydrogen gas and the temperature in it is extremely high. The sun may be considered a big thermonuclear furnace where hydrogen atoms are continuously being fused into helium atoms. Mass is being lost during these fusion reactions and energy is being produced. Thus, the sun which gives us heat and light, derives its energy from the fusion of hydrogen nuclei into helium nuclei, which is going on inside it, all the time.
Nuclear fusion reaction taking place in the sun releases a tremendous amount of energy. Fusion of 4 hydrogen atom nuclei fuses to form a bigger nucleus of helium atom, as
The total energy produced by fusion of hydrogen into helium is tremendous. All this energy is released in the form of heat and light. Thus, nuclear fusion reaction of hydrogen are the source of sun’s energy. Please note that just like the sun, other stars also obtain their energy from the fusion reactions of hydrogen. Thus, the energy emitted by the sun and other stars is produced by a sequence of thermonuclear reactions (nuclear fusion) of hydrogen.
Hydrogen Bomb
Principle :
It works on the principle of nuclear fusion (which is an uncontrolled nuclear reaction).
Construction :
It consists of an arrangement for nuclear fission at the centre of a mixture of deuterium (21H) and lithium (63Li) at the centre, which increases the temperature. This temperature is used to produce fusion reaction of deuterium and tritium with liberation of enormous amount of energy.
Working :
The nuclear fission provides heat and neutrons.
Fission (in the centre) → Neutrons + Heat … (1)
Neutrons are used in converting lithium into tritium (31H) and heat is liberated.
… (2)
This heat liberated raises the temperture of deuterium and tritium to 107 ºC. Heat liberated starts fusion between 21H and 31H and liberates large amount of energy
21H + 31H → 42He + 10n + energy … (3)
Deuterium
31H + 31H → 42He + 2 10n + energy … (4)
21H + 21H → 42He + energy (MeV)
Tritium has to be produced within the hydrogen bomb because being unstable is not found in nature.
Amount of energy produced :
In formation of a single helium nucleus, four nucleons (2 21H) take part and 26.7 MeV of energy is produced.
Hence energy released per nucleon = \frac{{{\rm{26}}{\rm{.7}}}}{{\rm{4}}} = 6.675 MeV.
It is about 8 times more than in fission. This fact makes hydrogen bomb 8 times more dangerous than atom bomb which is a fission bomb.
Table : Differences between nuclear fission and nuclear fusion
| Fission | Fusion |
| 1. In a fission reaction, a heavy nucleus breaks up to form two lighter nuclei. | 1. In a fusion reaction, two light nuclei combine to form a heavy nucleus. |
| 2. Nuclear fission is a chain reaction. | 2. Nuclear fusion is not a chain reaction. |
| 3. Fission reactions are carried out by bombarding the heavy nuclei with neutrons. | 3. Fusion reactions are carried out by using a particle accelerator or by heating the light atoms to an extremely high temperature. |
| 4. Nuclear fission reaction have been controlled to generate electricity. | 4. Nuclear fusion reactions have not been controlled so far. |
| 5. Nuclear fission produces a large amount of energy. | 5. The energy produced in a nuclear fusion reaction is much more than that produced during fission. |
Table : Differences between nuclear fission energy and fossil fuel energy
| Nuclear Fission Energy | Fossil Fuel Energy |
| Advantages (Merits) | Advantages (Merits) |
| 1. Even a small amount of fuel produces tremendous amount of energy. 1 gram U-235 can give 9.0 × 1010 joules of energy. | 1. A large amount of fuel is required. 1 gram coal gives only about 3.5 × 104 joules of energy. |
| 2. U-235 once fed in a nuclear power plant will last for two to three years. | 2. Coal or natural gas have to be fed regularly in thermal power plants. |
| 3. It is cheap in long run. | 3. It is costly throughout. |
| 4. It does not produce smoke. | 4. It produces smoke. |
| Disadvantages (Demerits) | Disadvantages (Demerits) |
| 1. Its production is dangerous. | 1. Its production is more safe. |
| 2. Leakage from power plants is dangerous. Example of accidents : First in March 1979 at Three Mile island in U.S.A. Second in April 1986 at Chernobyl in Soviet Union. | 2. Leakage from power plant is not so dangerous. |
| 3. It emits extermely harmful radiations. Exposure of them can cause cancer and leukaemia. | 3. It emits smoke which can be controlled by using chimneys. |
| 4. There is large amount of nuclear waste from nuclear reactors. They emit harmful radiations. Their disposal is an international problem. | 4. The waste is not much in quantity and is less harmful. |
Atom Bomb (A fission bomb)
Principle :
It works on the principle of nuclear fission.
It makes use of the uncontrolled nuclear fission chain reaction.
Construction :
It consists of two or more thin polythene bags each containing fissionable material U-235 or Pu-239. The mass of material in each bag is less than the critical mass.
By a pin action, the bags are pierced and the mass brought together, to make the material have mass more than critical mass. Then any stray neutron starts the fission reaction which releases large amount of energy which causes a violent explosion then the atom bomb is said to have been exploded. The atom bombs dropped on the cities of Hiroshima and Nagasaki in Japan during the second world war were based upon the uncontrolled chain reaction of fission of U-235 and Pu-239.
The first nuclear bomb dropped on Hiroshima (Japan) on August 6, 1945 used uranium (235U) as fuel. The other bomb was dropped on Nagasaki (Japan) on August 9, 1945 which used plutonium (239Pu) as fuel. Both of these produced horrifying death of 1.54 lakh human lives and devastation of property.
Nuclear tests of India :
Indian scientists and technologists have successfully exploded fission devices at Pokhran (Rajasthan) earlier on May 18, 1974 and recently on May 11 and 13, 1998.
Nuclear Reactor
Principle :
A nuclear reactor or an atomic reactor is a device in which nuclear fission can be maintained as a self-sustained yet controlled chain reaction. The energy released in a controlled manner can be used for industrial and other peaceful purposes. The fission reaction is :
Uses :
(i) A nuclear reactor is used for producing radio isotopes which are used in biological research, medicine, agriculture, industry and in pure and applied research.
(ii) It produces plutonium for explosive purpose.
(iii) It produces high velocity, high intensity neutron beam for bombarding nuclei of elements and causing artificial transmutation.
(iv) It can generate power for propulsion of ships, submarines and aircraft.
Cross sectional view of nuclear reactor :
(It is shown in Fig.)
Figure : Nuclear Reactor
Atomic Energy Plants (Nuclear Reactors) In India
Aim :
In India, as in the entire world atomic energy has been put for peaceful uses like generation of electricity. Another important peaceful use of atomic energy is in cancer treatment. Further, in our country, atomic energy is also being used for the improvement in industry and agriculture.
Locations :
(i) Major Research Centres. Bhabha Atomic Research Centre (BARC) at Bombay (Mumbai) is the major centre for research and development of atomic energy.
Besides there are good nuclear research laboratories at Gulmarg (Srinagar) and Calcutta (Kolkata) (West Bengal).
(ii) Atomic Energy Plants. There are four nuclear power plants (stations) in India.
(a) Tarapur Atomic Power station at Tarapur in Maharashtra. It is the first atomic power station in India which started functioning in 1969.
(b) Rajasthan Atomic Power station, at Rana Pratap Sagar near Kota in Rajasthan.
(c) Madras (Chennai) Atomic Power station at Kalpakkam in Tamil Nadu.
(d) Narora Atomic Power station in Uttar Pradesh.
All these power plants produce about 3% of the total energy being produced in India.
Industrialised countries like Belgium, Finland, France, Germany, Hungary, Japan, Spain, Swedan, Switzerland and Taiwan generate more than 30% of their total electrical energy by using a variety of nuclear reactors.
Fuel supply centres :
(i) Uranium ore is mined from Jaduguda mines in Jharkhand.
(ii) Uranium ore is processed and enriched at the Nuclear Fuel complex at Hyderabad in Andhra Pradesh.
Heavy water, which is used as moderator and coolant in nuclear reactors is produced at Nangal in Punjab. Four more plants for producing heavy water are under construction at Baroda, Kota, Talchi and Tuticorln.
Pollution caused by nuclear reaction (hazards of using nuclear energy)
Introduction :
It has been observed that pollutants from nuclear reactions are much more harmful and dangerous as compared to other pollutants. Slight leakage of nuclear radiations (α, β or γ-rays) can cause irrepairable damage to our body cells.
Nuclear radiations may cause
(i) Genetic defects by damaging genes and chromosomes.
(ii) Serious diseases such as leukemia (blood cancer) or cancer.
(iii) Damage to cell membranes, tissues, blood corpuscles causing irreversible damage to human body.
Causes for Pollution :
(i) Leakage from nuclear reactors : The leakage may occur due to earthquake or faulty design of the reactor.
(ii) Disposal of Nuclear waste material : Nuclear fuel like 23592U and 23994Pu and the products of fission are highly radioactive. The harmful waste substances produced during the various steps of nuclear cycle and capable of emitting nuclear radiations are called nuclear waste. The discharge of these radioactive waste in sewage system may cause many problems, so for disposing nuclear wastes we use the following methods :
(a) Sealing the nuclear wastes in strong containers and storing in deep mines which are not in use.
(b) Enclosing the nuclear wastes in containers made of concrete and then dumping them in the sea.
(c) Fusing the nuclear wastes into glass and then sealing them deep inside hard-rock formations.
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