UNIT 3 PHYSICS

• Radioactive decay


  Radioactive nuclei emit radiation RANDOMLY to become more stable

  
• What can a nucleus emit?


  • Alpha particle
  • Beta particle
  • Gamma wave
  • Neutron

  
• Alpha particle emission


  A particle made of 2 protons and 2 neutrons (42He) is emitted
• Beta particle emission


  A neutron splits into a proton and an electron, and the electron is emitted
• Gamma wave emission


  The nucleus emits a gamma wave
• Neutron emission


  The nucleus emits a neutron
• Alpha particle emission


  Mass number decreases by 4
• Beta particle emission


  Atomic number increases by 1 (the nucleus has an extra proton)
• Gamma wave emission


  No change in mass number or atomic number
• Neutron emission


  Mass number decreases by 1
• What can block/absorb this radiation?


  • Paper, skin, a few mm of air
  • Thin metal foil, a few m of air
  • Thick lead/concrete
  • N/A
• Half-life


  The time it takes for the number of radioactive nuclei in the sample to halve

  
• Calculating half-life from a graph


  1. Choose a value on the y axis, move along to the curve and then down to the x-axis

  2. Choose the y axis value that is HALF the one you chose, move along to the curve and down to the x-axis

  3. The difference between the 2 times is the half-life
• Count rate


  The number of radioactive decays in a given time
• Geiger-Muller tube is used to measure count rate
• Contamination


  Unwanted presence of a radioactive source inside or on the surface of an object; it makes the object emit radiation
• Irradiation


  The process of exposing an objective to radiation from an outside source; the object does not become radioactive, and can be protected from irradiation by screening
• Ionising radiation


  • Alpha
  • Beta
  • Gamma
  • X-rays
  • UV
• Ionising radiation


  • Turns atoms into ions
  • Breaks up molecules
  • Changes DNA
  • Causes gene mutations
  • Can lead to cancer
• High-energy gamma rays


  Can destroy cancer cells
• Radiation dose


  The risk of harm caused by radiation, measured in Sieverts
• Benign tumour


  Stays in the same place and stops growing when it isn't too larger
• Malignant tumour


  Spreads to other parts of the body in the blood, and grows in other parts of the body
• Effects of radiation on atoms

  1. When targeted at cancer cells, high-energy gamma rays can destroy cancer cells

  2. When an atom is exposed to radiation, some electrons can jump up to higher energy levels (shells)

  3. The electron will jump back down to its original level, and gives out radiation when it does this
• Radiation emission


  • Neon and sodium give out visible light when their electrons drop back down
  • Mercury gives out UV light when its electrons drop back down