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CHAPTER 27: Nuclear reaction (3 Hours)

NUCLEAR REACTION. CHAPTER 27: Nuclear reaction (3 Hours). 27.1 Nuclear reaction 27.2 Nuclear fission and fusion. Learning Outcome:. 27.1 Nuclear reaction ( 1 hour). At the end of this chapter, students should be able to:

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CHAPTER 27: Nuclear reaction (3 Hours)

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  1. NUCLEAR REACTION CHAPTER 27: Nuclear reaction(3 Hours) 27.1 Nuclear reaction 27.2 Nuclear fission and fusion

  2. Learning Outcome: 27.1 Nuclear reaction (1 hour) At the end of this chapter, students should be able to: • Statethe conservation of charge (Z) and nucleon number (A) in a nuclear reaction. • Write and completethe equation of nuclear reaction. • Calculatethe energy liberated in the process of nuclear reaction

  3. a) Radioactive decay. c) Nuclear fission. d) Nuclear fusion. 27.1 Nuclear reaction Examples: b) Induced nuclear reaction (particle bombardment).

  4. 27.1 Nuclear reaction • In any nuclear reaction, several conservation laws • must be obeyed, primaryly conservation of • charge and conservation of nucleons. Conservation of charge (atomic number Z) Conservation of mass number A (nucleon)

  5. Reaction energy Q • Reaction energy is the energy released (absorbed) • in a nuclear reaction in the form of kinetic energy • of the particle emitted, the kinetic energy of the • daughter nucleus and the energy of the gamma- • ray photon that may accompany the reaction. Reaction energy ,

  6. Note: Δm = mi - mf a) If Δm or Q> 0 (positive value) - exothermic (exoergic) reaction. - energy is released. b) If Δm or Q< 0 (negative value) - endothermic (endoergic) reaction. - energy is required/absorbed in the form of kinetic energy of the bombardment particle. Other reference : Δm = mf – mi Δm →negative (energy is released) Δm →positive (energy is absorbed)

  7. Example 27.1 Complete and state the type of reaction in the following nuclear reactions. Natural/decaying Fusion Fission

  8. Example 27.2 When lithium 7Li is bombarded by a proton, two alpha 4He particles are produced. Calculate the reaction energy. Given

  9. c2 or

  10. Example 27.3 A deuterium bombards a 136C nuclide and produces 147 N nuclide. a) Write an equation for the nuclear reaction. b) Calculate the kinetic energy (in MeV) that is released in the reaction.

  11. Solution 27.3 a) b) Kinetic energy is released

  12. Example 27.4 Q= 15.67 MeV A nuclear reaction can be written as . Calculate the energy involved in the reaction and state whether it is absorbed or released.

  13. emitted particle new nucleus (daughter nucleus) Target nucleus (parent nucleus) bombarding particle

  14. Learning Outcome: 27.2 Nuclear fission and fusion (2 hour) At the end of this chapter, students should be able to: • Distinguishthe processes of nuclear fission and fusion. • Explainthe occurrence of fission and fusion using the graph of binding energy per nucleon. • Explainchain reaction in nuclear fission of a nuclear reactor. • Describethe process of nuclear fusion in the sun.

  15. 27.2 Nuclear fission and fusion • Nuclear fission is the process by which heavy • nuclei are split into two lighter nuclei. • Energy is released by the process because the • average binding energy per nucleon of the • fission products is greater than that of the parent. • The energy released is in the form of increased • kinetic energy of the product particles • (neutrons) and any radiation emitted (gamma ray).

  16. 27.2 Nuclear fission and fusion • Nuclear fission can be divided into two ways • of processes : • spontaneous fission -very rarely occur • (take very long time) • ii) induced fission – heavy nucleus is bombarded by a particle : proton, alpha particle and neutron (slow neutrons or thermal neutrons of low energy (about 10-2 eV).

  17. 27.2 Nuclear fission and fusion • Example : is bombarded by a slow neutron. Nucleus in the excited state. (unstable) (10-12 s)

  18. 27.2 Nuclear fission and fusion • Other possible reactions are: • Figure X is a graph of the distribution of fission • fragments (daughter nuclei) from the fission of • uranium-235 versus mass number A. • Most of the fission fragments (daughter nuclei) • of the uranium-235 have mass numbers from 90 • to 100 and from 135 to 145.

  19. Figure X

  20. Greatest stability Binding energy per nucleon (MeV/nucleon) Mass number A Binding energy per nucleon as a function of mass number,A daughter nuclei parent nuclei fission Moving toward more stable nuclei Figure Y

  21. An estimate of the energy released in a fission • reaction can be obtained by considering the graph in • Figure Y. • From the Figure Y, the binding energy per nucleon • for uranium is about 7.6 MeV/nucleon, but for • fission fragment (Z~100), the average binding • energy per nucleon is about 8.5 MeV/nucleon. • Since the fission fragments are tightly bound, they • have less mass. • The difference in mass (or energy) between the • original uranium nucleus and the fission fragments • is about 8.5 -7.6 = 0.9 MeV per nucleon. Since there • are 236 nucleons involved in each fission, the total • energy released is

  22. Example 27.5 Calculate the energy released (MeV) in the following fission reaction :

  23. Example 27.6 Calculate the energy released when 10 kg of uranium-235 undergoes fission according to Given:

  24. Solution 27.6 The energy released for one atom.

  25. Solution 27.6 235x10-3 kg of 235U contains 6.02 x 1023 atoms. 10 kg of urainum-235 contains ; The energy released for 10 kg 235U ,

  26. Chain Reaction

  27. Chain Reaction

  28. Chain Reaction in nuclear fission of a nuclear reactor. • Chain reaction is a series of nuclear fissions • whereby some of the neutrons produced by • each fission cause additional fissions. • Conditions to achieve chain reaction in a nuclear • reactor : • a) Slow neutrons are better at causing fission. • b) The fissile/fission material must more than a • critical size/mass (a few kg). • The critical size/mass is defined as the minimum • mass of fissile/fission material required to • produce a sustained chain reaction.

  29. B A n n n n A : If the amount of uranium is less than critical mass, most neutrons escape before additional fissions occur, and the chain reaction is not sustained. B : If the amount of uranium exceeds the critical mass, a sustained chain reaction is possible.

  30. Chain Reaction in nuclear fission of a nuclear reactor. • A nuclear reactor is a device in which energy is • generated by a controlled fission chain reaction. • Apart from being used to obtain energy from the • reaction of fission, a reactor is widely applied, for • example to generate : • - radioactive elements, • - new fissile materials, such as 233U or 239Pu, • - neutrons for scientific research.

  31. A nuclear reactor

  32. movable Moderator (water)

  33. A nuclear reactor consists of fuel rods (fission • material), movable control rods and a moderator • (water). • Fission reactors use a combination of 235U and • 238U (3-5% 235 U). • The 235U will fission, while the 238U(more stable) • merely absorbs neutrons (slow neutrons). • Firstly, neutron is bombarded to the 235U and other • neutrons are emitted during fission. • Then the emitting neutrons with high energy are • slowed down by collisions with nuclei in the • surrounding material, called moderator, so that they • can cause further fissions and produce more • energy.

  34. In order to release energy at a steady rate, the rate • of the reaction is controlled by inserting or • withdrawing control rods made of elements (often • cadmium) whose nuclei absorb neutrons without • undergoing any additional reaction. • To have a self-sustaining chain reaction, the mass of • fission material must be sufficiently large (> critical • mass) so that on the average at least one neutron • produced in each fission must go on to produce • another fission.

  35. Nuclear Fusion • Nuclear fusion is the process in which nuclei of • light elements combine to form nuclei of heavier • elements. • The energy released in this reaction is called • thermonuclear energy. • Examples ; • The amount of energy released by this process • can be estimated by using the binding energy per • nucleon curve (Figure Y).

  36. Greatest stability Binding energy per nucleon (MeV/nucleon) Mass number A Binding energy per nucleon as a function of mass number,A Moving toward more stable nuclei fusion Figure Y

  37. From Figure Y, the binding energy per nucleon for • the lighter nuclei (2H) is small compared to the • heavier nuclei. • The energy released per nucleon • in the fusion process is given by the difference • between two values of binding energy per nucleon. • And it is found that the energy released per nucleon • by this process is greater than the energy released • per nucleon by fission process.

  38. Example 27.7

  39. Example 27.8 A fusion reaction occur as follows : • If 2 kg 2H is used, determine • Total mass loss after fusion • Energy released per helium nucleus obtained. • Total energy produced. • Given : mass of 21H = 2.014 u, • mass of 42 He = 4.002 u

  40. Solution 27.8 Δm = mbefore –mafter Δm = 2(2.014)-4.002 Δm = 0.026 u a) The mass loss after fusion for 2 2H nuclei is 0.026 u. Number of nucleus for 2 kg 2H is, Total mass loss after fusion

  41. Solution 27.8 b) Energy released per helium nucleus obtained, Q = 3.88 x10-12 J c) Total energy produced, Q= Δmc2 =(0.013)(3x108)2 =1.17x1015 J

  42. For two nuclei to undergo fusion, they must come • together to within the range of the nuclear force, • typically of the order of 2 x 10-15 m. • To do this, they must overcome the electrical • repulsion of their positive charges. • For two protons at this distance, the corresponding • potential energy is about 1.2 x 10-13 J or 0.7 MeV; • this represents the total initial kinetic energy that • the fusion nuclei must have, for example, 0.6 x 10-13J • each in head-on collision. • Atoms have this much energy only at extremely • high temperature (108 K).

  43. The lower border of the fusion temperature is 107 K. • Reactions that required such extremely high • temperature are called thermonuclear reactions. • The most important thermonuclear reactions • occurs in stars, such as our own sun.

  44. Nuclear Fusion in the Sun • Nuclear fusion occurs in the interior of the sun • because the temperature of the sun is very high • (approximately 1.5 x 107K). • The energy radiated by the sun comes from deep • within its core, where the temperature is high • enough to initiate the fusion process. • One group of reactions thought to occur in the sun is • the proton-proton cycle, which is a series of • reactions whereby 6 protons form one helium • nucleus, 2 positrons, 2 gamma-rays, 2 protons • and 2 neutrinos.

  45. The sequence of fusion reactions are shown below ; neutrino i) Positron (beta plus) ii) Gamma-ray iii) • The net result is the combination of 4 protons • to form a helium nucleus, two positrons and • two neutrinos. (consumes 6 protons but gives two • back) • The energy released by the proton-proton cycle is • about 26.7 MeV.

  46. Comparison between nuclear Fission and nuclear Fusion Differences

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