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Nuclear Reactions

Nuclear Reactions. Fission and Fusion. History:. Hahn & Strassman (1939). Bombarded Uranium-235 samples with neutrons expecting the Uranium-235 to capture neutrons. Meitner & Frisch. Explained Hahn & Strassman results. Instead of heavier Uranium, it had split into smaller elements =.

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Nuclear Reactions

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  1. Nuclear Reactions Fission and Fusion

  2. History: • Hahn & Strassman (1939) • Bombarded Uranium-235 samples with neutrons expecting the Uranium-235 to capture neutrons

  3. Meitner & Frisch • Explained Hahn & Strassman results. • Instead of heavier Uranium, it had split into smaller elements = Nuclear Fission

  4. Nuclear Forces • Electric repulsion – ________ charge particles repel each other same • Strong Nuclear Force – causes protons and neutrons to ________ each other attract • Stable Nuclei = strong nuclear force is ________ than repulsion force greater • Unstable Nuclei = strong nuclear force is ________ than repulsion force less

  5. Fission When atoms are bombarded with neutrons, their nuclei splits into 2 parts which are roughly equal in size. Nuclear fission in the process whereby a nucleus, with a high mass number, splits into 2 nuclei which have roughly equal smaller mass numbers. During nuclear fission, neutrons are released.

  6. Nuclear Fission There are 2 types of fission that exist: 1. Spontaneous Fission 2. Induced Fission

  7. Spontaneous Fission Some radioisotopes contain nuclei which are highly unstable and decay spontaneously by splitting into 2 smaller nuclei. Such spontaneous decays are accompanied by the release of neutrons.

  8. Induced Fission Nuclear fission can be induced by bombarding atoms with neutrons. The nuclei of the atoms then split into 2 equal parts. Induced fission decays are also accompanied by the release of neutrons.

  9. 235 1 U n 92 0 The Fission Process A neutron travels at high speed towards a uranium-235 nucleus.

  10. 235 1 U n 92 0 The Fission Process A neutron travels at high speed towards a uranium-235 nucleus.

  11. 235 1 U n 92 0 The Fission Process A neutron travels at high speed towards a uranium-235 nucleus.

  12. 235 1 U n 92 0 The Fission Process The neutron strikes the nucleus which then captures the neutron.

  13. 236 U 92 The Fission Process The nucleus changes from being uranium-235 to uranium-236 as it has captured a neutron.

  14. The Fission Process The uranium-236 nucleus formed is very unstable. It transforms into an elongated shape for a short time.

  15. The Fission Process The uranium-236 nucleus formed is very unstable. It transforms into an elongated shape for a short time.

  16. The Fission Process The uranium-236 nucleus formed is very unstable. It transforms into an elongated shape for a short time.

  17. 1 1 1 n n n 0 0 0 92 141 Ba Kr 36 56 The Fission Process It then splits into 2 fission fragments and releases neutrons.

  18. 1 1 1 n n n 0 0 0 92 141 Ba Kr 36 56 The Fission Process It then splits into 2 fission fragments and releases neutrons.

  19. 1 1 1 n n n 0 0 0 92 141 Ba Kr 36 56 The Fission Process It then splits into 2 fission fragments and releases neutrons.

  20. 1 1 1 n n n 0 0 0 92 141 Ba Kr 36 56 The Fission Process It then splits into 2 fission fragments and releases neutrons.

  21. 235 235 141 96 92 138 U U Cs Kr Ba Rb 2 3 + + + + + + 92 92 55 36 37 56 1 1 1 1 n n n n 0 0 0 0 Nuclear Fission Examples

  22. Energy from Fission Both the fission fragments and neutrons travel at high speed. The kinetic energy of the products of fission are far greater than that of the bombarding neutron and target atom. EK before fission << EK after fission Energy is being released as a result of the fission reaction.

  23. + + + 235 138 96 U Cs Rb 2 92 37 55 1 1 n n 0 0 Energy from Fission

  24. Energy from Fission Calculate the total mass before and after fission takes place. The total mass before fission (LHS of the equation): 3.9014 x 10-25 + 1.6750 x 10-27 = 3.91815 x 10-25 kg The total mass after fission (RHS of the equation): 2.2895 x 10-25 + 1.5925 x 10-25 + (2 x 1.6750 x 10-27) = 3.9155 x 10-25 kg

  25. Energy from Fission The total mass before fission = 3.91815 x 10-25 kg 3.91550 x 10-25 kg The total mass after fission = total mass before fission > total mass after fission

  26. Energy from Fission mass difference, m = total mass before fission – total mass after fission m = 3.91815 x 10-25 – 3.91550 x 10-25 m = 2.65 x 10-28 kg This reduction in mass results in the release of energy.

  27. E c2 m Energy Released The energy released can be calculated using the equation: E = mc2 Where: E = energy released (J) m = mass difference (kg) c = speed of light in a vacuum (3 x 108 ms-1)

  28. + + + 235 96 138 U Cs Rb 2 92 37 55 1 1 n n 0 0 Energy from Fission Calculate the energy released from the following fission reaction: m = 2.65 x 10-28 kg E = mc2 E = 2.65 x 10-28 x (3 x 108)2 c = 3 x 108 ms-1 E = 2.385 x 10-11 J E = E

  29. Energy from Fission The energy released from this fission reaction does not seem a lot. This is because it is produced from the fission of a single nucleus. Large amounts of energy are released when a large number of nuclei undergo fission reactions.

  30. Energy from Fission Each uranium-235 atom has a mass of 3.9014 x 10-25 kg. The total number of atoms in 1 kg of uranium-235 can be found as follows: No. of atoms in 1 kg of uranium-235 = 1/3.9014 x 10-25 No. of atoms in 1 kg of uranium-235 = 2.56 x 1024 atoms

  31. Energy from Fission If one uranium-235 atom undergoes a fission reaction and releases 2.385 x 10-11 J of energy, then the amount of energy released by 1 kg of uranium-235 can be calculated as follows: total energy = energy per fission x number of atoms total energy = 2.385 x 10-11 x 2.56 x 1024 total energy = 6.1056 x 1013 J

  32. 2 4 H He 1 2 Energy + + + 1 3 n H 0 1 Nuclear Fusion In nuclear fusion, two nuclei with low mass numbers combine to produce a single nucleus with a higher mass number.

  33. 2 3 H H 1 1 The Fusion Process

  34. 2 3 H H 1 1 The Fusion Process

  35. 2 3 H H 1 1 The Fusion Process

  36. 2 3 H H 1 1 The Fusion Process

  37. The Fusion Process

  38. The Fusion Process

  39. The Fusion Process

  40. The Fusion Process

  41. 4 He 2 1 n 0 The Fusion Process ENERGY

  42. 4 He 2 1 n 0 The Fusion Process ENERGY

  43. 4 He 2 1 n 0 The Fusion Process ENERGY

  44. 4 He 2 1 n 0 The Fusion Process ENERGY

  45. 2 4 H He 1 2 Energy + + + 1 3 n H 0 1 Energy from Fusion

  46. Energy from Fusion Calculate the following: • The mass difference. • The energy released per fusion.

  47. 2 4 H He 1 2 Energy + + + 3 1 n H 0 1 Energy from Fusion The total mass before fusion (LHS of the equation): 3.345 x 10-27 + 5.008 x 10-27 = 8.353 x 10-27 kg The total mass after fission (RHS of the equation): 6.647 x 10-27 + 1.675 x 10-27 = 8.322 x 10-27 kg

  48. Energy from Fusion m = total mass before fission – total mass after fission m = 8.353 x 10-27 – 8.322 x 10-27 m = 3.1 x 10-29 kg

  49. 2 4 H He 1 2 Energy + + + 1 3 H n 1 0 Energy from Fusion m = 3.1 x 10-29 kg E = mc2 E = 3.1 x 10-29 x (3 x 108)2 c = 3 x 108 ms-1 E = 2.79 x 10-12 J E = E The energy released per fusion is 2.79 x 10-12 J.

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