Table of Contents
NUCLEAR FUSION
Nuclear fusion is the process by which two light atomic nuclei fuse together to form one heavier one while releasing a tremendous amount of energy. Fusion reactions occur in a state of matter known as plasma, which is a hot, charged gas that differs from solids, liquids, and gases in that it is composed of free-moving electrons and positive ions. Stars, such as our sun, are powered by nuclear fusion. This fusion reaction takes place under extreme temperatures and pressures, allowing hydrogen isotopes to combine to form helium, as well as light and heat energy. Fusion is a promising alternative to traditional energy sources because it generates minimal radioactive waste and has an abundant fuel supply from isotopes like deuterium and tritium.
WHAT IS NUCLEAR FUSION?
Definition: The phenomenon of several light nuclei joining together to form a relatively large nucleus is called nuclear fusion.
Nuclear fusion is the opposite of nuclear fission.
Example: The probability of fusion between two hydrogen nuclei, i.e. two protons, is very low. The simplest example of nuclear fusion is the fusion of two deuterons; incidentally, the nucleus of heavy hydrogen i.e. deuterium is called deuteron, its symbol is 1H2.
1H2 + 1H2 → 2H3 + 0n1 ……….(1)
Also, the probability of deuteron fusion with the nucleus of another isotope of hydrogen, tritium (1H3), i.e. triton, is also very high.
1H3 + 1H2 → 2He4 + 0n1 ………..(2)
ENERGY RELEASED IN NUCLEAR FUSION
The loss of mass in nuclear fusion is converted into energy according to the mass-energy principle. For addition as shown in equation (1) above,
Initial mass = Mass of 2 deuterons = 2 X 2.015 = 4.030u
Final mass = combined mass of He3 and neutron = 3.017 + 1.009 = 4.026u
So, mass-loss = 4.030 – 4.026 = 0.004u
Since the equivalent energy of 1u mass is about 931 MeV, the free energy in this fusion = 0.004 X 931 = 3.7 MeV (approx.)
If all the nuclei of just 1g of deuterium could be combined, the free energy would be about 9 X 10¹⁰ J. This energy will be much higher, about 30 X 10¹⁰ J, in case of addition as shown in equation no. (2). Thus, the amount of energy released by nuclear fission of U-235 is greater than the amount of energy released by nuclear fusion of the relatively readily available deuterium or tritium. Moreover, more nuclei participate in fusion than in fission. That is why nuclear fusion releases about 10 times more energy than nuclear fission. Hydrogen bombs are made based on this fusion reaction.
CONDITIONS OF NUCLEAR FUSION
- Light Element: Bringing multiple positively charged nuclei into contact with each other for fusion must work against the static-electric repulsive force. For this reason, it is advantageous to take a light element like hydrogen, because in that case the amount of positive charge on the nucleus is less, so the mutual repulsive force is also less.
- Very High Temperature: For nuclear fusion, hydrogen isotopes must be heated to hundreds of millions of degrees Celsius, below which fusion cannot occur. That is why nuclear fusion is actually a thermo-nuclear reaction. The most effective way to generate such high temperatures is through uncontrolled nuclear fission, i.e. in effect the explosion of a nuclear bomb. So, it can be said that in order to get energy from nuclear fusion, nuclear fission is necessary first.
ENERGY OF THE SUN AND THE STARS
Energy is generated through thermo-nuclear reactions within the Sun and various stars. The temperature of several million degrees Celsius in their central regions is very favorable for such nuclear fusion.
The currently accepted theory is: a cycle of thermo-nuclear reactions is completed in several steps inside the Sun; A helium nucleus and two positrons are formed by the addition of essentially four protons per cycle.
1H1 + 1H1 + 1H1 + 1H1 (four protons) → 2He4 (Helium) + 1e0 + 1e0 (Two positrons)
Mass loss in this reaction = mass of 4 protons – combined mass of 2He4 and 2 positrons
= 4 X 1.008 -(4.003 + 2 X 0.00055) = 0.0279u
Equivalent power = 0.0279 X 931 = 26 Mev (approx.)
The Sun contains large amounts of hydrogen; only about 1 in 10¹¹ of this hydrogen is converted into energy each year. Nevertheless, the rate of energy production from nuclear fusion inside the Sun is very high, with a value of about 4 X 10²⁶ W. Even at this rate of energy production, the vast amount of hydrogen fuel in the Sun will continue to generate this energy for billions of years
DIFFERENCES BETWEEN NUCLEAR FISSION AND NUCLEAR FUSION
| NUCLEAR FISSION | NUCLEAR FUSION |
|---|---|
1. In this process heavy nucleus is divided into two fragments along with few neutrons. | 1. In this process lighter nuclei will join together to produce heavy nucleus. |
2. This reaction will take place even at room temperature. | 2. This reaction will take place at very high temperature, such as 10⁷ K. |
3. To start fission at least one thermal neutron from outside is compulsory. | 3. No necessary of external neutrons. |
4. Energy released per unit of mass of participants is less. | 4. Energy released per unit mass of participants is high. Nearly seven times more than fission reaction. |
5. In this process neutrons are liberated. | 5. In this process positrons are liberated. |
6. This reaction can be controlled. Ex - nuclear reactor. | 6. There is no control on fusion reaction. |
7. Atom bomb works on principle of fission reaction. | 7. Hydrogen bomb works on the principle of fusion reaction. |
8. The energy released in fission can be used for peaceful purpose. Ex - nuclear reactor and atomic power stations. | 8. The energy released in fusion cannot be used for peaceful purpose. |
CONCLUSION
Nuclear fusion, which fuels stars such as our Sun, occurs when atomic nuclei combine to generate heavier atoms, releasing massive amounts of energy. Hydrogen atoms fuse in stars to form helium, which provides heat and light required for life on Earth. Unlike nuclear fission, fusion produces less radioactive waste and poses fewer environmental risks. It has the potential to provide practically limitless, clean energy. However, recreating and sustaining controlled fusion reactions on Earth remains a big scientific problem, necessitating technological improvements to make it a viable and dependable energy alternative for the future.
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