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Nuclear Physics

Presented by Samuel Wang

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The Nucleus

  • Made up of protons and neutrons
  • Protons have +1 charge and neutrons have 0 charge�
  • Example: Helium-4 Nucleus has 2 protons (red) and 2 neutrons (black)

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Atomic & Mass Number

Atomic number: Number of protons in the nucleus

Mass number: Number of protons and neutrons in the nucleus

Example: The atomic number of helium is 2.� The mass number is 4.

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Radioactive Decay

  • Some nuclei are unstable and “decays” by releasing radiation
  • There are three (main) types of radioactive decay, two of which are caused by the weak force:
    • : There are too many protons, the atom emits a helium nucleus
    • : There are too many neutrons
      • decay: A neutron turns into a proton, the atom emits an electron and an electron antineutrino
      • decay: The atom emits a positron and an electron neutrino
    • : The atom is overexcited, it emits gamma ray photons

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Nuclear Fission

  • Nuclear fission is the process of an atom splitting into two smaller nuclei
  • It was discovered by Otto Hahn and Lise Meitner, the latter of which became the name for element 109
  • Every time atoms undergo fission, a large amount of energy is released, which can be used to make nuclear bombs. The uranium bomb was the one dropped on Hiroshima
  • You can also control the splitting of atoms to get nuclear power and nuclear energy
  • Example: Uranium-235 undergoes fission

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Nuclear Fission (cont.)

  • From left to right and top to bottom:
    • Fission of Uranium-235
    • How the chain reaction happens in any nuclear fission process
    • A nuclear power plant in the Czech Republic

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Nuclear Fusion

  • Nuclear fusion is the process of combining two nuclei together
  • Unlike fission, fusion was theorised by Arthur Eddington to occur in the Sun, but was only proven once Hans Bethe found a way for hydrogen to turn into helium
  • Although fission has been done on Earth already, our only example of fusion so far is the stars
  • Scientists are currently working on ways to make a fusion reactor
    • The International Thermonuclear Experimental Reactor is currently trying to maintain temperatures high enough to sustain fusion for practically “infinite” energy.
    • The fusion temperatures must be 6 to 7 times higher than the sun because the Earth has less gravity
    • So far, we’re still working on it…

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The Joint European Torus and the ITER

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Fusion in the stars

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Nuclear Binding Energy

  • NBE is the amount of energy you need to completely take apart a nucleus (using the strong force)
  • The energy required is less if the mass of the nucleus is less

Useful graph:

  • Nuclei larger than Iron-58 undergo fission
  • Nuclei smaller than Iron-58 undergo fusion