2.7 physics

• Nuclear model


  Atoms consisting of a central nucleus of protons and neutrons and surrounding shells of orbiting electrons
• Sub-atomic particles


  • Protons
  • Neutrons
  • Electrons
• Proton


  Relative charge: +1, Relative mass: 1
• Neutron


  Relative charge: 0, Relative mass: 1
• Electron


  Relative charge: -1, Relative mass: 1/1840 (negligible)
• Atomic number (Z)


  Number of protons in the nucleus
• Mass number (A)


  Sum of protons and neutrons in the nucleus
• Isotopes


  Alternative forms of the same element with the same atomic number but different mass numbers
• Ions


  Atoms with a net charge due to gaining or losing electrons
• Chemical symbols


  Represent elements and can include atomic number and mass number
• Calculating sub-atomic particles in an isotope

  1. Atomic number = Protons

  2. Mass number = Protons + Neutrons

  3. Neutrons = Mass number - Atomic number
• Radioactivity


  Unstable atomic nuclei emitting ionising radiation through radioactive decay to become more stable
• Alpha radiation


  • Slow moving, strongly ionising, low penetrating power, range ~5 cm, stopped by thin paper
• Beta radiation


  • Faster moving, less strongly ionising, higher penetrating power, range ~1 m, stopped by thin metal
• Gamma radiation


  • Travels at speed of light, weakly ionising, highly penetrating, range >1 m, stopped by thick lead
• Half-life


  Time taken for the number of radioactive nuclei to halve
• Radioactive decay is random in nature
• Sources of background radiation

  • Cosmic rays
  • Rocks
  • Living things
  • X-rays
  • Nuclear power stations
  • Nuclear weapons
• Low level nuclear waste


  Protective clothing, equipment or material that is contaminated, disposed of in landfill surrounded by concrete
• Intermediate level nuclear waste

  Radioactive sources from smaller medical settings and components from nuclear reactors, disposed of by mixing with concrete in steel drums and burying in purpose-built stores
• High level nuclear waste


  Chemicals from nuclear reactors and nuclear fuels, stored in underwater pools in casks for over 20 years to allow decay, takes thousands of years to decay to safer levels