radioactivity

• Particles found in the atom

  • Proton
  • Neutron
  • Electron
• Particles found in the nucleus

  • Proton
  • Neutron
• 14

  C

  6

  Protons: 6

  Neutrons: 8

  Electrons: 6
• Mass number


  14
• Atomic number


  6
• Isotope


  A nuclide with the same number of protons and electrons but a different number of neutrons
• Atoms of different elements have different numbers of

  • Protons
• Different isotopes of the same element have

  • The same number of protons and electrons but a different number of neutrons
• Types of radioactivity


  • Alpha
  • Beta
  • Gamma
• Radioactivity


  A random process
• Radiation does to neutral atoms

  It ionises them (knocks electrons off, makes them charged)
• Why some atoms emit radioactivity
• What stops alpha radiation


  • A few millimetres of metal such as aluminium
• What stops beta radiation

  • A few centimetres of air
  • A thin sheet of paper
• Material that can stop gamma radiation

  • Many centimetres of lead or many metres of concrete can reduce the amount
• Beta particle


  An electron
• Alpha particle


  A helium nucleus
• Gamma ray


  A high frequency electromagnetic wave
• What happens to the mass number and atomic number of a nucleus that emits an alpha particle

  Mass number - no change, Atomic number - rises by 1
• What happens to the mass number and atomic number of a nucleus that emits a beta particle

  Mass number - falls by 4, Atomic number - falls by 2
• What happens to the mass number and atomic number of a nucleus that emits a gamma ray

  Mass number - no change, Atomic number - no change
• Equation:

  241

  95

  Am→ Np+


  4

  2

  237

  93

  241

  95

  +

  →

  Np

  Am
• Equation:

  90

  39

  Sr→ Y+


  0

  1

  90

  39

  90

  38

  Sr→ Y+−
• What happens to photographic film when exposed to radiation
• Charge on proton, electron, neutron


  Proton +1, Electron -1, Neutron 0
• Radiation detector that uses a tube

  Geiger counter or Geiger-Müller tube and counter
• Background radiation


  Radiation that is all around us
• Effect of ionising radiation on cells
• Sources of background radiation

  • Rocks
  • Radon gas
  • Cosmic rays from space
  • Food
  • Medical radiation
  • Nuclear power stations
  • 1950s nuclear weapons tests
• Half-life


  The time taken for the number of radioactive nuclei in a sample to halve or the time taken for the count rate of a sample to halve
• Calculating half-lives


  200 ÷ 2 = 100

  100 ÷ 2 = 50

  50 ÷ 2 = 25, which is what we want

  We needed to ÷2 three times, so three half-lives have passed.
• Calculating remaining atoms after 4 half-lives

  Four half-lives pass, so we must ÷2 four times.

  800 ÷ 2 = 400

  400 ÷ 2 = 200

  200 ÷ 2 = 100

  100 ÷ 2 = 50
• Activity of radioactive material

  It reduces as time passes
• Radioactivity produced by medical tracers

  Gamma, as it is the least ionising and can pass out of the body to be detected
• Uses of radioactivity


  • Medical tracers
  • Non-medical tracers
  • Radiotherapy
  • Radioactive dating of archaeological specimens
  • Radioactive dating of rocks
• Nuclear fission


  A neutron is absorbed by a Uranium-235 nucleus. The nucleus splits into two smaller nuclei. Neutrons are released which can carry on the process.
• Moderator in nuclear reactor

  It slows down the fast neutrons released from fissions so that they are more likely to cause further fissions. It helps keep the reaction going.
• Fuel for most nuclear fission reactors

  Uranium-235
• Control rods in nuclear reactor


  They absorb neutrons so that the chain reaction cannot continue
• Common waste products of Uranium fission reactions

  • They can be two of many different isotopes, all of which are very radioactive and have long half-lives. The exam board like to mention Krypton and Barium.