waves

• unstable nuclei can become stable through emitting radiation called radioactive decay
• alpha waves can be stopped by paper, beta waves can be stopped by aluminium and gamma waves can be stopped by lead
• to investigate radiation, use geiger muller detector, and when not using a source, keep it in a lead lined container
• • When the alpha particle is emitted from the unstable nucleus, the mass number and atomic number of the nucleus changes
  • The mass number decreases by 4
  • The atomic number decreases by 2
• Activity (Bq) × Time period (s) = decay
• Gamma rays are used for radiotherapy, sterelise medical equipment since it is the most penetrating and weak ionising power
• Irradiation can be used as a method of sterilisation:

  • Surgical equipment is irradiated before being used in order to kill any micro-organisms on it before surgery
• Shielding is used to absorb radiation

  • Lead lined suits are used to reduce irradiation for people working with radioactive materials
• • Radioactive sources should be kept in a shielded container when not in use, for example, a lead-lined box
  • Radioactive materials should only be handled when wearing gloves, and with tongs to increase the distance from them
  • It may be appropriate to wear protective clothing to prevent the body becoming contaminated
• Radioactive waste with a long half-life is buried underground to prevent it from being released into the environment
• • purpose of a control rod: To absorb neutrons
  • purpose of moderator: to slow down neutrons, ensuring that it reacts efficiently with uranium fuel
  • The purpose of shielding is to absorb hazardous radiation
  • The daughter nuclei formed during fission, and the neutrons emitted, are radioactive
• • The higher the frequency, the higher the energy of the radiation
  • Radiation with higher energy is:
  • Highly ionising
  • Harmful to cells and tissues causing cancer (e.g. UV, X-rays, Gamma rays)
  • Radiation with lower energy is:
  • Useful for communications
  • Less harmful to humans
• electromagnetic waves become more dangerous the shorter their wavelength
• • Transverse waves are defined as:

  Waves that vibrate or oscillate perpendicular to the direction of energy transfer

  • Longitudinal waves are defined as:

  Waves where the points along its length vibrate parallel to the direction of energy transfer
• • From less dense to more dense (e.g air to glass), light bends towards the normal
  • From more dense to less dense (e.g. glass to air), light bends away from the normal
  • When passing along the normal (perpendicular) the light does not bend at all
• (plotting) compass used; multiple compasses or repeated use of single compass; joining up of dots/idea of compasses forming continuous line; OR iron filings used; sprinkled
• Violet has the shortest wavelength and red has the longest wavelength
• Sterilisation


  Used to kill bacteria or parasites on equipment so it is safe for operations
• Protective packaging


  Eliminates the risk of contamination
• Diagnosis and treatment


  • Short half-life gamma emitters such as technetium-99m are used as tracers in medicine as they concentrate in certain parts of the body
  • The half-life must be long enough for diagnostic procedures to be performed, but short enough to not remain radioactive for too long
• Gamma emitters


  • Cobalt-60 can be used to destroy tumours with a high dose of radiation
• Contamination


  • Occurs when a radioactive source has been introduced into or onto an object
  • The contaminated object will be radioactive for as long as the source is in or on it
• Irradiation


  • Occurs when an object is exposed to a radioactive source which is outside the object
  • The irradiated object does not become radioactive
• Exposure to radiation

  • Can destroy living cell membranes by ionisation, causing the cells to die
  • Can damage DNA which causes mutations that could lead to cancer
• Safety measures


  1. Minimising the time of exposure to radiation

  2. Keeping as big a distance from the radioactive source as possible

  3. Using shielding against radiation (such as protective clothing made from dense materials such as lead)
• Radioactive waste from nuclear reactors

  • Must be disposed of carefully, usually by burying it in sealed drums deep underground and remotely handling it after it has been thoroughly cooled
• Nuclear fission


  The process of splitting a nucleus
• A thermal (slow-moving) neutron splits the nucleus