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Atomic structure

Megan Leek Physics GCSE English

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Atomic structure

Isotopes
- Different numbers of neutrons
- Not stable
  - Emitting radiation from nuclei
    - Some more radiation per second
History of the atom
- matter is made of atoms
  - Democritus 400BC
- Atoms of the same element are identical
  - Dalton 1803
- Plum Pudding model
  - Thomson 1904
    - Discovered electron
- Nuclear model
  - Alpha scattering
  - Discovers the nucleus
  - Rutherford 1911
- Bohr's model
  - Bohr 1913
  - electrons only orbit in specific energy levels
    - energy is quantised
  - When they absorb energy, it can jump to a higher energy state
  - Electromagnetic energy is emitted if an electron jumps from an excited level to one closer to the nucleus
- Chadwick discovered neutron
Radioactive substances
- Alpha radiation
  - 2 neutrons
  - 2 protons
  - Big an heavy
  - Strongly ionising
  - Few cm in air
  - Uses
    - Smoke detector
- Beta radiation
  - Electron ejected
  - Nucleus => Proton
  - Small + fast
  - Moderately ionising
  - Thin sheet of aluminium (5mm)
  - Uses
    - Tests thickness
- Gamma radiation
  - Weakly ionising
  - Thick sheets of lead
  - Metres of concrete
- Neutron
Half Life
- Used to measure a materials age
- Time taken for half to decay
- Activity
  - numver of emissions detected per second
Radiation in medicine
- Radioactive tracers
  - Trace the flow of a substance through an organ
  - Gamma
    - Short half life
- Gamma Cameras
  - Image internal organs
  - Crystal scintellator
    - Light when wave hits it
  - Photomultiplier
    - Light => Electrical signal
- Gama radiotherapy
  - Irridation
  - Cancer cells are exposed to radiation from several signs
    - Narrow beams
  - Gamma knife
    - 200 weak beams
    - Target brain tumours
- Radioactive implants
  - Beta
  - Advantage
    - Localised
    - Less time in hospital
  - Disadvantage
    - Small risk of exposure to others
    - Only early tumours
Nuclear fission
- Splitting nucleus
  - Uranium - 235
  - Plutonium - 239
- Releases heat energy
  - Boils water
    - Steam
      - Turns turbine
  - Small number per reaction
    - Billions of reactions
- Baron control rods
  - Absorb neutrons
    - Become radioactive
  - Control rate of reaction
- Radioactive waste
Nuclear fusion
- Powers the sun
- Hydrogen => Helium + 1N
  - Deuterium (D) 1N
  - Tritium (T) 2N
  - Fuse togethor
- Plasma state
- Advantages
  - Abundant fuels
    - Deuterium
      - Extracted from water
    - Lithium
      - Earth's crust
  - Tritium is a by product
    - Originally bred from Lithium
  - Safe
  - No greenhouse gases
  - No radioactive waste
Background Radiation