radioactivity

• an atom consists of:

  • a positively charge nucleus made of positive protons and neutral neutrons
  • it is surrounded by negatively charged electrons which orbit the nucleus
• isotopes

  • same number of protons
  • different number of neutrons
• radioactive decay

  • spontaneous transformation of unstable nucleus into more stable one by release of radiation
  • random process
• alpha particles

  • highly ionising
  • weakly penetrating
  • stopped by a sheet of paper
  • two protons & two neutrons - identical to helium nucleus
• beta particles

  • identical to electron
  • moderately ionising
  • moderately penetrating
  • stopped by thin sheet of aluminium
• gamma particles

  • form of electromagnetic radiation
  • lowly ionising
  • highly penetrating
  • stopped by many centimetres of lead
• gm tube

  • geiger-muller tube detects radiation
  • produces clicking sound upon detection of radiation
  • greater frequency of clicks means more radiation is present
• background radiation

  • cosmic rays
  • bananas, brazil nuts
  • radon gas
• radioactivity

  • activity is the number of decays per unit time
  • measured in becquerels (Bq) where 1Bq is equal to 1 decay per second
  • activity of a radioactive source decreases over time
• half-life

  • time taken for the activity to halve
  • different for different isotopes
• contamination

  • when a radioactive source has been introduced into or onto an object
• irradiation

  • when an object is exposed to a radioactive source but doesn't come into contact with it
• dangers of radiation

  • exposure to it can destroy living cell membranes by ionisation, causing the cells to die
  • or damage dna causing mutations that lead to cancer
• safety measures

  • minimising time of exposure to radiation
  • keep a large distance from source
  • use shielding (e.g protective clothing)
• radioactive waste

  • must be disposed of carefully
  • burying it in sealed drums deep underground & remotely handling it after it has been thoroughly cooled
• fission

  • neutron absorbed by uranium nucleus
  • uranium nucleus splits
  • produces 2 daughter nuclei
  • extra neutrons released
  • kinetic energy released