atomic structure

• radioactivity

  • the nuclei of some elements are not stable
  • to become more stable, radioactivity is emitted from the nucleus
  • the three types of radioactivity are alpha, beta and gamma
• alpha radiation

  • particle - helium nucleus with a 2+ charge
  • low range
  • low penetration ability
  • high ionisation powers
  • can be blocked with card
• beta radiation

  • particle - electron with 1- charge
  • medium range
  • medium penetration ability
  • medium ionisation powers
  • can be blocked with 3mm aluminium
• gamma radiation

  • wave
  • high range
  • high penetration ability
  • low ionisation powers
  • blocked with 5cm+ of lead
• radioactivity is dangerous because it is ionising. this means is can knock electrons out of atoms, damaging cells which can lead to radiation burns and sickness, and cause mutations to the DNA which can lead to cancer.
• contamination is when the radioactivity is on your skin or inside your body.
• irradiation is when the radioactivity is in the environment around you.
• dosimetry badges are used to measure the amount of different types of radiation a person has been exposed to.

  
• nuclear decay and decay equations

  • when alpha or beta decay occurs, the nucleus changes and becomes a different element as there is a different number of protons
  • during alpha decay, a particle of 2 electrons and 2 neutrons is emitted
  • during beta decay, a neutron decays to a proton and emits an electron

  
• half life

  • radioactivity is random and spontaneous - we don't know which atom will decay next, or how long it takes them all to decay
  • the activity of a radioisotope is the rate of decay
  • activity is measured in Becquerel (Bq)
  • the activity decreases over time as less atoms are left to decay
  • the half life is the time taken for the activity or number of radioactive atoms to drop to half of the original level
  • the half life of a given isotope is constant, irrespective of how many atoms there are
• uses of radioactivity - sterilising food and surgical equipment

  • food or equipment is sealed in packaging, then irradiated for the desired time with a gamma source to kill microorganisms on the food/equipment
  • once removed from the chamber it is safe as it is not contaminated
  • gamma isotopes are used as companies will want to use sources with a suitably long half life that they don't have to regularly pay to replace
• uses of radioactivity - medical uses

  • radiotherapy - can kills off cancer cells completely and stop them dividing or reproducing
  • medical tracer - the person is injected with, or ingests, a radioactive source, the isotope moves around the body and can be checked to see if body is functioning properly. gamma is used as it is least ionising so less risk to patient, and has high penetration so can pass through body to be detected
• uses of radioactivity - smoke alarms

  • the smoke blocks the particles which stops the current and causing the siren to sound
  • alpha radioactivity is used as it has low penetration so cannot get through smoke, but high ionising so can effectively ionise air particles

  
• background radiation

  • the radiation that is all around us all the time, from natural and artificial sources
  • average annual dose to the UK population - 50% from radon, 9.5% from food and drink (both natural background radiation, 15% medical (artificial background radiation)