Radioactivity

• Give an approximation for the radius of an atom
• Radius of an atom

  1x10-10 metres
• Subatomic constituents of an atom

  • Proton
  • Neutron
  • Electron
• Most of the mass of an atom is concentrated in the nucleus
• Arrangement of protons, neutrons and electrons in an atom


  • Protons and neutrons are found in the atom's nucleus
  • Electrons are found in discrete energy levels around the nucleus
• Charge of the nucleus

  • Positive charge
  • The nucleus contains protons and neutrons
  • Protons have a positive charge
  • Neutrons have no charge
• Ways an atom's electron arrangement can be changed

  • Absorbing electromagnetic radiation
  • Emitting electromagnetic radiation
• How an atom's electron arrangement changes when it absorbs EM radiation

  1. Electrons move to higher energy levels

  2. They move away from the nucleus
• How an atom's electron arrangement changes when it emits EM radiation

  1. Electrons move to a lower energy level

  2. They move towards the nucleus
• Reason atoms have no overall charge

  • The number of protons is equal to the number of electrons
  • Protons and electrons have equal and opposite charges, so charge cancels
• All forms of the same element have the same number of protons
• Number of protons in an atom

  Atomic Number
• Mass number of an atom

  The total number of protons and neutrons in the atom
• Isotope of an atom

  An atom of an element that has a different number of neutrons, but the same number of protons
• Difference between isotopes of an element

  The mass of the atom
• How atoms turn into positive ions


  1. They lose one or more of their outer electrons

  2. Electrons are negatively charged, so the resultant charge of the atom is positive
• Relative masses of a proton, neutron and electron

  • 1 - proton
  • 1 - neutron
  • 1/1850 - electron
• Relative charge of a proton

  + 1
• Relative charge of an electron

  • 1
• Advantages of nuclear power for generating electricity

  • Nuclear fuels do not produce carbon dioxide
  • The fuel is readily available, so would reduce strain on the fossil fuel supplies
  • Less nuclear fuel has to be used to produce the same amount of energy as burning fossil fuel
  • Does not contribute to global warming
• Disadvantages of using nuclear power to generate electricity

  • Unpopular - the public perceive nuclear power as very dangerous
  • Security risks as the radioactive substances can be useful for terrorists
  • Expensive to commission and decommission the stations - which may be bad for a country's economy
  • The radioactive waste can be difficult to dispose of and will remain radioactive for many years - which can be dangerous to humans and the environment
  • Risk of nuclear accidents
• Nuclear fission


  The splitting of large, unstable nuclei to form smaller more stable nuclei (+ the emission of spare neutrons)
• What usually needs to happen to induce fission

  1. The unstable nuclei must absorb a neutron

  2. Spontaneous fission (where no neutron absorption occurs) is rare
• What is emitted in a fission reaction

  • Two or three neutrons
  • Gamma rays
  • Energy
• Main components of the core of a nuclear reactor

  • Fuel rods
  • Control rods
  • Moderator
• What takes place during a chain reaction in a nuclear reactor

  1. An unstable nucleus absorbs a neutron

  2. The nucleus undergoes fission and releases 2 or 3 further neutrons

  3. These induce more fission, which results in a chain reaction
• Consequence of an uncontrolled chain reaction

  • The rate of fission events becomes to high and results in the production of too much energy
  • This can lead to a nuclear explosion
• How the chain reaction in a fission reactor is kept under control

  1. Control rods are positioned in between the fuel rods

  2. The rate of fission is controlled by moving these rods up and down

  3. The lower the rods are inserted, the slower the rate of fission
• Role of the moderator in a nuclear reactor

  To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission
• How electricity is produced in a nuclear power station

  1. The reactions release thermal energy

  2. The thermal energy is used to boil water and then produce steam

  3. This steam is then used to turn a turbine which starts the generator
• Nuclear fusion


  When two light nuclei join to produce a heavier nucleus and release energy
• Isotopes of hydrogen commonly used in nuclear fusion

  • Deuterium
  • Tritium
• Which releases more energy, nuclear fission or nuclear fusion

  Nuclear fusion
• Difficulty of generating energy through nuclear fusion

  Fusion requires very high temperatures which in itself requires large quantities of energy. Currently, the production of fusion results in a net loss of energy
• Where fusion occurs


  • In the sun - stars use fusion as their energy source
• Why nuclear fusion requires so much energy

  This is because both nuclei are positive therefore a lot of energy is required to overcome the electrostatic repulsion between the two nuclei
• Uses of radioactivity


  • Household fire alarms (smoke)
  • Irradiating food
  • Sterilisation of equipment
  • Tracing and gauging thicknesses of materials
  • Diagnosis and treatment of cancer
• How smoke alarms work

  1. A radioactive substance emits alpha radiation

  2. The emitted alpha particle ionises the air in the detector and causes a current to flow between the plates

  3. When smoke interferes with the radiation, the air is no longer ionised and so no current can flow

  4. This reduction in current flow triggers the alarm
• Uses of nuclear radiation in medicine

  • Examining of internal organs
  • Radiotherapy in the treatment of cancer
• Role of beta radiation in tracers

  • The tracer is inserted in your body, and targets a specific part of the body
  • The radioactive substance in the tracer releases beta radiation which can be detected by external machines