Radioactivity

• Alpha decay occurs in heavy elements that have too many protons to be stable, so an alpha particle is released.
• What is an alpha particle?


  It is like the nucleus of a helium atom, made up of two protons and two neutrons.
• Alpha decay equation:

  Z A X —> Z-2 A-4 Y + 2 4 He

  Where X is the original element.

  Where Y is the element after decay.

  Where Z is the number of protons.

  Where A is the atomic mass.
• Beta decay occurs in a nucleus with too many neutrons. A neutron will spontaneously turn into a proton and then a high speed electron will be emitted.
• Beta decay equation:

  Z A X —> Z+1 A Y + -1 0 e

  Where X is original element, Y is the element after decay, e is the electron, Z is the number of protons and A is the atomic mass.
• Alpha decay is positively charged (+2) and is highly ionising. It can be stopped through paper and is very slow in the air. It has a range of 5cm in the air.
• Beta decay is negatively charged (-1) and is somewhat ionising. It can be stopped with aluminium and moves at a high speed. It has a range of 20cm in the air.
• Gamma emissions occur when a nucleus has too much energy. The energy is emitted as an electromagnetic wave of high energy.
• Gamma emissions are neutral and are barely ionising. It is stopped or slightly absorbed by lead and is very quick (the speed of light). It has an infinite range.
• A half-life is the time taken for half of the unstable nuclei to decay to a stable isotope.
• What does a tracer do?

  Use a detector (radiation camera) to track the progress of an injected or ingested radioactive isotope. Beta is most commonly used, but alpha is never used.
• What is radiotherapy?


  The treatment of cancer using ionising radiation. A high doe of radiation will destroy cells, healthy and cancerous. It is directed carefully and accurately to try to minimise the damage to the healthy cells. Gamma radiation is most commonly used.
• How is radiation used for antiseptic cleaning?

  Radiation can destroy bacteria on medical instruments and make them cleaner than any cleaning fluid could.
• What is nuclear fission?

  A type of nuclear reaction used to release energy from large, unstable atoms by splitting them into smaller atoms. This happens in a nuclear reactor.
• How does nuclear fission work?

  • A uranium-235 nucleus absorbs a neutron
  • The nucleus splits into two and creates two lighter elements
  • Two or three neutrons are also released
  • Energy and gamma radiation are released
  • The neutrons can then go onto cause more nuclei to split. This is called a chain reaction
• A nuclear reactor controls fission to get heat and to generate electricity.
• In a fission reactor, one neutron goes on to cause another atom to split. The other neutrons are absorbed by control rods. Raising the rods increase the number of neutrons and therefore more energy is released.
• What is nuclear fusion?

  The joining of two or more atoms. It is the opposite of nuclear fission. It occurs naturally in stars with very high temperatures and pressures.
• How does nuclear fusion work?

  • Two light nuclei collide at high speeds to create a heavier nucleus
  • Some of the mass of the small nuclei is converted to energy
  • Light nuclei are easier to speed up and have a lower charge to overcome
• Nuclear fusion example:

  1 2 H + 1 1 H —> 2 3 He + energy

  2 3 He is produced because 1 proton from each hydrogen element makes two protons. 2 electrons from the first hydrogen element and 1 electron from the other make 3 electrons. The element with 2 protons and 3 electrons is helium.
• Fusion reactors could supply huge amounts of energy. However, there are many reasons why we can’t use them yet:

  • would need to be at 100 million degrees celsius
  • high cost
• Why are radioactive materials dangerous?

  They emit ionising radiation that can damage living cells. It can damage DNA but this rarely leads to cancer because DNA can repair itself. However, radiation damaged DNA in a sperm or egg cell can produce genetic defects.
• What is irradiation?


  Objects that are near a radioactive source are irradiated by it. This exposure can be harmful but it does not make the objects radioactive.
• How can we prevent irradiation?

  We can limit exposure time, further the distance and use protective screens (lead).
• Contamination is when unwanted radioactive atoms get onto or into a material. Sometimes these contaminated atoms decay and release radiation. For example, handling radioactive sources without gloves can lead to skin contamination.
• How can we reduce contamination?

  We can use disposable gloves, wear a mask or protective suit, check for breakages or leakages and use tongs.