Radioactivity

• Relative mass and charge of Proton Neutron Electron

  Proton - 1 , +1

  Neutron - 1, 0

  Electron - 0.0005, -1
• What is an isotope

  Isotope - Same number of protons different number of neutrons
• What is the mass number

  (proton number determines the element)

  Mass number - Number of protons and neutrons
• What is the atomic number

  Atomic number - Number of neutrons
• Radioactive decay

  The spontaneous transformation of an unstable nucleus into a more stable nucleus through the release of radiation

  Random process meaning wont know when it will decay and what will decay
• Alpha

  Alpha - Heavy nucleus emits alpha particles

  Is a helium 4 nucleus no electrons 4/2

  Most ionising but least penetrating and is stopped by a few cm of air or thin paper
• Beta

  Beta - Neutron turns into a proton and emits beta particle

  High energy electron 0/-1

  Moderately ionising and penetrating stopped by thin aluminium
• Gamma

  Gamma - After previous decay nucleus with excess energy emits gamma particle

  High energy EM wave 0/0

  Has no mass or charge

  weakly ionising highly penetrating stopped by thick lead
• Neutron radiation

  neutron rich nucleoids emit one or more neutrons also happens during fission

  Creates nucleus of new element
• Photographic film :

  White film becomes darker the more radiation that is emitted

  They are worn by people who work with radiation and lets them know how much exposure they have had
• Geiger muller tube:

  Can detect radiation

  Each time it detects radiation it sends an electrical pulse to the machine which produces a clicking sound

  Greater the frequency of clicks heard the more radiation is present
• Background radiation

  What is it

  Sources

  It is weak radiation coming from an external source

  • Cosmic rays - high energy particles penetrating the atmosphere
  • Radioactive food and drink
  • Radioactive rocks ( give of radon gas)
  • Fallout of nuclear weapon testing
  • MRI scanners and x-rays
  • Nuclear power plants which produce nuclear waste
• Activity of Radio active sources

  What is it measured in and how

  How does the activity of radioactive sources change over time

  What is half life

  Number of decays which occur per unit time and measured in Becquerels

  Activity decreases over time

  The half life is the time taken for half of the nuclei do decay

  Half life is constant and background radiation has to be subtracted when performing half life calculations
• Thickness monitoring

  Thickness monitoring -Long half life beta emitters used for metal sheets ,if drop or rise in particles detected can be adjusted
• Smoke detectors

  Smoke detectors- Long half life alpha emitters used to cause a current in the alarm , if smoke enters the detector then some particles absorbed triggering the alarm as the current drops
• Medicine - sterilising equipment

  Gamma emitters used to kill bacteria through the protective packaging from equipment to limit contamination
• Diagnosis and treatment

  Short half life gamma emitter used as tracers in the body as they concentrate on certain parts have to be long enough for procedure but short enough so not to much exposure

  Destroy tumours with high dose of radiation
• Contamination

  Irradiation

  When a radioactive source has been introduced to a an object will become radioactive until removed

  When an object comes into exposure to radioactive substance but does not become radio active
• Effects of exposure to radiation

  Ionisation leads to the destroying of cell living membranes

  causes cells to die

  or to damage DNA leads to mutations
• Safety measures (2)

  • Minimising time of exposure
  • Increasing distance
  • ShieldingRadio active waste must be disposed of carefully by:
  • Burying sealed drums dee underground
  • remotely handling it after it has been thoroughly cooled
• Nuclear Fission

  Definition

  Common fissionable materials

  Splitting of a nucleus into 2 daughter nuclei and 2 or 3 neutrons

  Uranium 235. Plutonium 239
• Nuclear Fission


  1. Slow moving Neutrons absorbed by Uranium

  2. Unstable nucleus splits into 2 SDN and 2 or 3 high speed neutrons

  3. Energy released in process
• Moderator


  • Used to slow down neutrons so can be absorbed by Uranium 235
• Control rods (Boron)


  • Lowered to absorb excess neutrons to control the chain reaction
• Coolant (water)


  • Used to cool fuel rods preventing overheating
• Electricity generation


  1. Energy stored by fuel rods transferred into heat exchanger

  2. Produces steam

  3. Steam drives turbine

  4. Produces electricity

  5. Steam cools and is put back through system
• Nuclear Fusion

  Definition -

  Process of combining two smaller nuclei into one large nucleus
• Why does it require high temperatures and pressure

  Small loss of mass after fusion as some mass is converted into energy

  Large amounts of energy released as Em radiation and

  Requires high temperatures and high pressure to overcome electrostatic repulsion

  sun has pressure from strong gravitational field causing the positively charged atoms which repel each other to be forced together

  High temperature nuclei move faster store more energy
• Nuclear Fission Negatives

  Positive

  • Can't be harnessed on earth
  • Requires lots of energy to fuse two nuclei
  • More energy produced per kg of fuel than fission