radioactivity

• The half-life is the time it takes for one-half of the atoms to decay.
• Radioactive elements are unstable because they have too many or too few neutrons, which causes them to emit radiation until they reach stability.
• Alpha particles consist of two protons and two neutrons bound together as a helium nucleus (He2+).
• Atom


  Smallest part of an element
• Element


  Every type of atom
• Proton


  • Positive charge
• Neutron


  • No charge (neutral)
• Electron


  • Negative charge
• Ionisation


  When an atom loses or gains an electron, the charges are no longer balanced and the charged atom is called an ion
• Excitation


  When an atom absorbs electromagnetic radiation, an electron moves further from the nucleus
• Emission


  When an electron moves closer to the nucleus, electromagnetic radiation is emitted
• Atomic number


  Number of protons in an atom
• Atomic mass


  Number of protons and neutrons in an atom
• Types of radiation


  • Alpha (α)
  • Beta (β)
  • Gamma (γ)
• Alpha radiation


  • Helium nucleus, penetrated by paper or thin layer of air
• Beta radiation


  • High energy electron emitted from the nucleus, penetrated by thin layer of aluminium
• Gamma radiation


  • High energy electromagnetic radiation, penetrated by thick layer of lead or concrete
• Radioactivity occurs when an unstable nucleus decays to become more stable, releasing energy</b>
• Radioactive decay happens randomly and spontaneously, the time of decay for individual atoms is unknown
• Half-life


  Time taken for half of a sample of unstable nuclei to decay
• Unit of radioactivity is Becquerel (Bq), one atom decaying per second
• Alpha decay


  Nucleus emits 2 protons and 2 neutrons to form a helium nucleus
• Beta decay


  Neutron in nucleus converts to a proton, electron and antineutrino are emitted
• Gamma decay


  Nucleus emits high energy electromagnetic radiation without changing atomic number or mass
• Radioactive materials can cause ionisation of molecules in living cells, leading to damage and mutation
• Alpha radiation is least penetrating but most dangerous if inhaled or ingested
• Beta radiation is slightly more penetrating, gamma radiation is most penetrating and dangerous
• Exposure to radiation can be reduced by increasing distance from source, limiting time, and using shielding
• Film badges are used to monitor radiation exposure of workers
• Activity of carbon-14 after 11,200 years is 600 Bq
• The two fusing nuclei will both be positively charged due their protons, so strongly repel each other.

  A high temperature and pressure is required to overcome this electrostatic repulsion.
• No, nuclear fusion does not produce radioactive waste.
• Steps of nuclear fission?

  1. A neutron is fired at an unstable nucleus (e.g. uranium-235), causing it to split apart.
  2. The unstable nucleus splits into 2 daughter nuclei and 2 or 3 neutrons. It also emits a large amount of energy as gamma radiation.
  3. The 2 or 3 neutrons that were released are then absorbed by other unstable nuclei and this repeats the process from the previous step.
  4. This process then occurs over and over again in what we call a chain reaction.
• Walls of nuclear reactor have to be very thick to stop the gamma radiation from passing out of the reactor, where it could harm the workers
• Advantages of nuclear power:

  1. Nuclear power plants can reliably produce large amounts of electricity.
  2. Nuclear power does not produce any greenhouse gas.
  3. Although not renewable, there are very large quantities of the uranium and plutonium fuel.
• Spontaneous fission is when the fission is unforced, and the  by itself.This is very rare.
• Control rods can be lowered into the nuclear reactor to absorb neutrons and slow the chain reaction.
• Nuclear fusion occurs in stars
• Main type of nuclear fusion that takes place in stars is the fusion of two hydrogen nuclei
• The energy released during nuclear fusion comes from converting mass into energy (E=mc^2)