Atomic structure

Atomic structure

1. Isotopes

   • Different numbers of neutrons
   • Not stable
     • Emitting radiation from nuclei
       • Some more radiation per second

2. 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

3. 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

4. Half Life

   • Used to measure a materials age
   • Time taken for half to decay
   • Activity
     • numver of emissions detected per second

5. 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

6. 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

7. 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

8. Background Radiation

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