atomic structure

• Gold Foil Experiment

  Most 𝛼𝛼 particles went straight through - So most of atom is empty space

  Some 𝛼𝛼 particles were slightly deflected - So nucleus must be charged deflecting positive 𝛼𝛼

  Few 𝛼𝛼 particles were deflected by >90° - So nucleus contained most of the mass
• Alpha


  highly ionising , weakly penetrating , lowest range in air
• beta 


  medium ionizing , medium penetration , medium range in air
• gamma


  low ionising , highest penetration ,highest range in air
• A short half-life

  • o The source presents less of a risk, as it does not remain strongly radioactive
  • o This means initially it is very radioactive, but quickly dies down
  • o So presents less of a long-term risk
• The half-life of an isotope is the time taken for half the nuclei in a sample to decay or the time taken for the activity or count rate of a sample to decay by half.
• • It cannot be predicted when any one nucleus will decay, but the half-life is a constant that enables the activity of a very large number of nuclei to be predicted during the decay.
• long half life

  activity falls more slowly as most of the nuclei dont decay for a long time - source just suits there , releasing small amounts of radiation for a long time

  dangerous - nearby areas are exposed to radiation for many years
• • Contamination
  • Lasts for a long period of time
  • The source of the radiation is transferred to an object
  • Radioactive contamination is the unwanted presence of radioactive atoms on other materials – the hazard is the decaying of the contaminated atoms releasing radiation
• irradiation

  lasts for a short period of time , source emits radiation , which reaches the object , exposing an object to nuclear radiation bur does no make it radioactive .medical items are irradiated sometimes to kill bacteria on its surface, but not to make the medical tools themsleves radioactive.
• Background radiation

  cosmic rays , radiation from underground rocks , nuclear fallout , medical rays
• process of nuclear fission

  -When the unstable nuclei absorbs a neutron it splits into two smaller nuclei, roughly equal in size and it then emits two or three neutrons and gamma rays.

  • Energy is released by the fission reaction.

  - This neutron may collide with another radioactive nucleus.

  • This nucleus absorbs the neutron and becomes unstable
  • This nucleus splits, releasing another neutron and produces more energy
  • This is a chain reaction, as energy is being released and one ‘split’ causes another to occur
• nuclear fusion

  2 light nuclei collide at high speed + fuse to create a large, heavier nucleus

  fusion releases a lot of energy