Radiation

• Activity is the rate at which an unstable nucleus decays. The activity of a radioactive source reduces over time.
• Alpha particles are:

  • Positively charged
  • Has two protons and two neutrons
  • Highly ionising
  • Can be stopped by a few cm of air or paper
• Background radiation is radiation that is all around us and found in small quantities. It originates from natural sources such as rocks and cosmic rays as well as man made sources such as nuclear testing and accidents.
• Becquerel is the unit of radioactive activity
• Irradiation is the process of an object being exposed to radiation without the object itself becoming radioactive.
• Beta particles are:

  • A high speed electron
  • Nucleus emits when a neutron converts into a proton
  • Ionising (moderate)
  • Can be stopped by a thin sheet (5mm) of aluminium
• Gamma Rays are:

  • Electromagnetic radiation emitted from a nucleus
  • High penetrating power
  • Several cm of lead to be stopped/ absorbed
• An isotope is atoms o the same element that has the same amount of neutrons how different number of neutrons.
• Relative masses of:

  Neutron - 1 unit

  Proton - 1 unit

  Electron - 1/1850 unit
• All types of radiation are emitted from unstable nuclei: Gamma, Neutron, Alpha and Beta.
• Another device that can also be used to detect radioactivity is photographic film.
• Neutron radiation is:

  • When a neutron is ejected such as in neutron rich nuclides and nuclear fission
• The addition part of a neutron radiation equation is (the atomic element - 1 neutron) +1n
• Radioactivity in Industry:

  Smoke detectors -

  1. Uses Long half-life alpha emitters
  2. Alpha particles cause a current in the alarm
  3. If the smoke enters the detector, some of the alpha particles are absorbed and the current drops, triggering the alarm.
• Radioactivity in industry:

  Thickness monitoring (metal sheet) -

  1. Uses long half-life beta emitters
  2. A source and receiver are placed on either side of the sheet during it's production
  3. If there is a drop or rise in the number of beta particles detected then the thickness of the sheet has changed and needs to be adjusted
• Radiation in Medicine:

  Sterilisation of equipment -

  Gamma emitters are used to kill bacteria or parasites on equipment so it's safe for operation
• Radiation in Medicine:

  Diagnosis and treatment -

  Short half-life gamma emitters such as technetium-99m are used as tracers in medicine.

  The half-life must be long enough for diagnostic procedures to be performed but short enough to not remain radioactive for too long.

  Other gamma emitters such as cobalt-60 can be used to destroy tumours with a high does 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
• Exposure to radiation can destroy living cell membranes by ionisation, causing the cells to die or damage DNA which causes mutations that could potentially lead to cancer
• Safety Measures:

  • Minimise time of radiation exposure
  • Stay far away from the source
  • Use shielding against radiation
  • Radioactive waste from nuclear reactors must be disposed of carefully
  • Remotely handle it after it has been thoroughly cooled
• There are three types of ionising radiation: Alpha, Beta and Gamma. (neutron radiation isn't ionising due to it's lack of charge)
• The Geiger-Muller tube is a device that can be used to detect ionising radiation.
• Half-life is the amount of time it takes for the number of unstable nuclei of an isotope to halve

  or

  the time it takes for the initial count rate of a sample of the isotope to halve.