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Nuclear Physics

Nuclear Physics. Rutherford’s Scattering Experiment. The Structure of the Atom. 4. He. 2. Neutron = Proton = Alpha = Hydrogen =. The Structure of the Atom. 4. He. 2. Neutron = 1 0 n Proton = 1 1 p Alpha = 4 2 α

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Nuclear Physics

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  1. Nuclear Physics

  2. Rutherford’s Scattering Experiment

  3. The Structure of the Atom 4 He 2 Neutron = Proton = Alpha = Hydrogen =

  4. The Structure of the Atom 4 He 2 Neutron = 10n Proton = 11p Alpha = 42α Hydrogen = 11H

  5. Isotopes 12 C 13 14 C C 6 6 6 An isotope is an atom with a different number of neutrons: Adding neutrons to small nuclei can make then unstable. Carbon 14 is a radio-isotope and is used in carbon dating. However…. adding neutrons to large nuclei can make them more stable.

  6. Protons in the nucleus exert an electrostatic repulsion on each other. • The strong nuclear force counteracts this repulsion, holding the nucleus together. • This strong force only acts over very small distances (10-14 m) meaning that large nuclei are held together less tightly. • Extra neutrons in large nuclei help keep the protons apart. • When the no. of protons > 83 adding neutrons is not enough and all elements become less stable.

  7. N-Z Graph Line of Stability N = Z

  8. What is the evidence for the strong nuclear force?(4 marks) • Protons in the nucleus exert an electrostatic repulsion on each other. • Nulceons in the nucleus exert a gravitational attraction on each other. • The electrostatic repulsion is much greater than the gravitational attraction. • There must be another force counteracting this repulsion, holding the nucleus together.

  9. Mass Defect Constituent parts of an nucleus Nucleus

  10. Binding Energy • The binding energy of a nucleus is the energy required to completely separate the nucleons. It is due to the strong force which holds protons and neutrons together, working against the electrostatic repulsion forced between the protons. Therefore, when a nucleus is formed there is a net release of energy, and so energy must be supplied to pull a nucleus apart again. The energy released is proportional to the loss in mass as the nucleus forms and can be calculated using Einstein’s equation E = mc2. In order to calculate the binding energy you need to know the precise masses of the individual protons and neutrons, and the mass of the entire nucleus in its bound state.

  11. 1. Use the data below to calculate the binding energy in MeV of a nucleus of oxygen. Data: mass of proton = 1.007 276 u mass of neutron = 1.008 665 u mass of oxygen nucleus = 15.990 527 u 1u = 1.6605 x 10-27 kg Binding energy = ............................................ MeV Calculate the binding energy per nucleon of 168O. Binding energy per nucleon = ..................................

  12. 2. Particle energies are often quoted in units of mega-electronvolts (MeV). Show that the base units of the electronvolt can be expressed as kg m2 s–2. Calculate the theoretical energy released when a U nucleus is formed from individual protons and neutrons. Give your answer in MeV. Data (masses): U = 238.0003 u proton = 1.0073 u neutron = 1.0087 u Name the two main forces acting in the nucleus of an atom. State what each of these forces acts upon in the nucleus and indicate their ranges. Force 1: ............. Force 2: ………..

  13. 5626Fe = largest BE / nucleon = most stable The final BE is greater than the original value, increasing the stability. The final BE is greater than the original value, increasing the stability

  14. A graph of binding energy per nucleon shows that the most stable element is iron. For elements lower than iron in the periodic table, becoming more stable requires them to increase the size of their nucleus by undergoing fusion. For elements higher up becoming more stable requires a decrease in the size of the nucleus by undergoing fission. The higher the binding energy of a nucleus, the more stable it will be.

  15. What is meant by the term binding energy? • On the axes below sketch a graph of binding energy per nucleon against nucleon number. • The binding energy of 168O is 123.45 MeV and the binding energy of 178O is 126.43 MeV.Which of these two isotopes of oxygen would you expect to be more stable? Explain your answer. • Iron has the highest binding energy per nucleon of any nucleus. What does this tell you about an iron nucleus?

  16. Nuclear Fusion + 11H + 21H 32 He deuterium Often, the result is two or more particles: 11H + 21H 31 He + ? 32He + 32He 42 He + ? + ?

  17. Nuclear Fusion + 11H + 21H 32 He deuterium Often, the result is two or more particles: 11H + 21H 31 He + 11H 32He + 32He 42 He + 2 11H

  18. Nuclear Fusion + Total mass of separate nuclei > Mass of new nuclei Mass appears to have been lost. Actually, mass has been turned into energy: ∆ E = ∆ m c2 If you pull a nucleus apart, work is done on the particles and the energy transferred to them is turned into mass. When a new nucleus is formed from separate nuclei, the excess mass will disappear and the energy is released. The total amount of “mass-energy” must remain constant.

  19. Binding Energy • BE = The energy required to pull a nucleus apart. • The energy is transferred to the separate nuclei as extra mass. • If you add nuclei together = the excess mass disappears and the energy is released

  20. Nuclear Fission More neutrons Neutron Unstable nucleus Unstable U-235 nucleus New nuclei (Ba and Kr)

  21. Chain reactions Each fission reaction releases neutrons that are used in further reactions.

  22. Little Boy - The First Atomic Bomb

  23. Hiroshima Mushroom Cloud

  24. Hiroshima

  25. Hiroshima Building

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