NUCLEAR FISSION AND NUCLEAR FUSION by sujith kp

well detail on nuclear fission and nuclear fusion of nuclear chemistry

1. NUCLEAR FISSION AND NUCLEAR FUSION Presented by , SUJITH K P MSC CHEMISTRY KARUNYA UNIVERSITY COIMBATORE , TAMILNADU INDIA

2. CONTENTS …. NUCLEAR FISSION MECHANISM OF NUCLEAR FISSION USES OF NUCLEAR FISSION ADVANTAGES AND DISADVANTAGES NUCLEAR FUSION REQUIREMENTS OF FUSION REACTION USES OF NUCLEAR FUSION ADVANTAGES AND DISADVANTAGES Presented By , SUJITH K P

3. FISSION The nuclear reaction in which one heavier nucleus is split up into two lighter nuclei of almost equal size with the release of a huge amount of energy is called nuclear fission or atomic fission

4. HISTORY Nuclear fission was first discovered on December 17,1938 by German Otto Hahn Explained theoretically in January 1939 by lise Meitner and her nephew otto Robert Frisch

5. The splitting of nucleus cause to the formation of different smaller fragments These fragments are about equal to half the original mass Two or three neutrons and large amount of energy also released It is responsible for all type of power generations like in nuclear power plants and nuclear weapons Uranium is the most common element used in nuclear fission U-235 is the most commonly used isotopes of uranium for nuclear energy production

6. What happens when a neutron is bombarded to U-235 ? An unstable nucleus of U-236 forms and undergoes fission (splits) Smaller nuclei are produced such as Kr-92 and Ba-141 (fission products ) Three neutrons (secondary neutrons ) are released to bombard more U-235 . The number of neutrons relased determine the success of chain reaction In addition to that huge amount of energy (fission energy) released

7. Fission is exothermic The amount of energy released in nuclear fission can be calculated by mass defect method In fission reaction , the total mass of the product is always less than the mass of the reacting nuclei (parent nuclei ) This decrease in mass is called mass defect which is converted into energy According to mass-energy relationship (Einstein’s equation), E = mc² Thus for the nuclear fission of the type :

8. Mechanism of nuclear fission- liquid drop model Suggested by Bohr-wheeler Since an atomic nucleus has many similarities with a liquid drops A liquid drop has a spherical shape due to its surface tension If sufficient energy is applied on the drop to overcome the Force of surface tension , the drop may change its spherical Shape into elliptical shape. If the external force is large, the Elliptical shape may changes into dumb-bell shape and break Into two portions of spherical shape. Here , spherical shape : uranium external force : neutrons The energy absorbed by uranium nucleus to change from Spherical shape to critical shape is called threshold energy. Since two parts of critical shape have + ve charge, they repel From each other and separated from each other forming two Spherical shape of same size + +

9. USES OF NUCLEAR FISSION The enormous energy liberated in nuclear fission and the occurrence of chain reaction have been used in atomic bomb. ATOMIC BOMB ( FISSION BOMB ) Each U-235 liberates three neutrons called secondary neutrons. Each neutrons will strikes on to the another fresh U-235 nucleus and cause further reactions Some of the neutrons will escape into the air cause no reactions and explosion The size of U-235 nucleus which is smaller than critical size is called super-critical size . If it is in this condition , the large number of neutrons were captured by U-235 nucleus and cause large explosion and chain reaction The atomic bomb consist of thousands of pieces of U-235 in sub-critical size. At the time of explosion, these are driven together , and these sub-critical size of U-235 will combined together and will form one large piece of super critical size Now neutrons from other source will strike on this large piece of U-235 and cause a rapid chain reaction This reaction cause a violent explosion with releasing of vast amount of energy.

10. Advantages It helps minimize environmental pollution This means they can provide heat, electricity, and power to consumers without producing lots of carbon dioxide emissions. It helps reduce global warming. nuclear fission, there would be less greenhouse gases (e.g. carbon dioxide and methane) in the atmosphere. As a result, the greenhouse effect would be felt less and global warming would be stopped or at least reduced. It can keep up with energy demands . nuclear plants can produce high amounts of nuclear fission energy. This can be a good thing in today’s modern times, wherein the demand for energy is steadily rising as more and more people drive cars, build houses, use electronic devices, and do other energy-intensive activities

11. Disadvantages It can be dangerous for employees. Radiation, which is one of the by-products of nuclear fission, can be harmful to people if they’re exposed to it at large amounts . It can be dangerous for communities. waste by-products pollute the environment but will also endanger the lives of the people who live near the disposal sites. Nuclear plants are also highly volatile; if an accident occurs, they can explode and affect the surrounding areas and communities It has high initial expenses. Nuclear plants need specialized equipment and machinery before they can become fully functional and therefore require millions of dollars to be built. The plants also need to put safety measures in place to protect their workers and the surrounding areas, and these measures can cost a significant amount of money.

12. Fusion Nuclear fusion is the process by which multiple nuclei joined together to form an heavier nucleus It is accomplished by the release or absorption of energy depending on the mass of the nuclei involved It is also called thermonuclear reactions

13. Requirements for Fusion Reaction Plasma Temperature:100-200 million Kelvin : A plasma is a macroscopically neutral collection of charged particles . Needed to overcome natural positive repulsive forces of plasma ions Energy Confinement Time: 4-6 seconds : The Energy Confinement Time is a measure of how long the energy in the plasma is retained before being lost. Central Density in Plasma:1-2 x 10 20 particles m -3 : Large density needed because number of fusion reactions per unit volume is roughly proportional to the square of the density

14. USES OF NUCLEAR FUSION HYDROGEN BOMB The principle of nuclear fusion is used in hydrogen bomb. The temperature required for the purpose of fusion is produced by fission reactions. The explosion of an atom bomb produces temperature of the order of 50 million degree Celsius. A suitable assembly of deuteron and triton is arranged at the sight of the explosion of the atom bomb. Favorable temperature initiates the fusion of light nuclei in an uncontrolled manner. This releases enormous amount of heat energy . The fusion reaction in hydrogen bomb is : 1 H 3  +  1 H 2   -- -- >  2 He 4  +  n 1  + energy

15. Advantages Nuclear fusion doesn’t create harmful waste nuclear fusion only has the creation of helium as a byproduct. Helium is non-toxic, safe, and won’t create the same environmental damage that the burning of fossil fuels creates. It is incredibly inexpensive to create.  The estimated cost of providing energy through nuclear fusion is just $0.03 per kilowatt hour. This makes it one of the cheapest forms of energy that humans have ever discovered . There is an infinite amount of fuel for nuclear fusion.  The main ingredient of nuclear fusion, which is deuterium, is distilled from ocean water. Every other component of the process is either easily found or easily made. The end result is an infinite amount of fuel that can be used to create energy resources for the entire planet.

16. Disadvantages It requires almost as much energy to create nuclear fusion  To fuse two atoms together, high levels of heat are required. In order to create this heat, a large energy investment must be made . This industry still requires innovation.  The high levels of heat that are required to create nuclear fusion mean that we need materials available that can withstand those temperatures to create energy. With our current technology, we have no knowledge of a specific material that can withstand the heat necessary to create fusion . There may be unanticipated consequences to using nuclear fusion.  The fact is that we don’t really know much about this form of energy creation. What would happen to the planet in 50 years with an increased level of helium in the atmosphere? Are there health dangers that we simply do not know yet and cannot predict?