Topic 6

• Types of nuclear radiation


  • Alpha particles
  • Beta particles
  • Gamma rays
  • Neutrons
• Background radiation


  • Radiation that is always present
  • It is in very small amounts and so not harmful
• Sources of background radiation


  • Rocks
  • Cosmic rays from space
  • Nuclear weapon testing
  • Nuclear accidents
• Measuring and detecting background radiation

  1. Photographic film

  2. Geiger-Muller counter
• Photographic film used to measure radiation


  A photographic film turns dark when it absorbs radiation. This is useful for people who work on radiation as the more radiation they are exposed to, the darker the film becomes. Therefore the workers know when they have been exposed to too much radiation.
• Geiger-Muller tubes used to measure radiation

  When the Geiger-Muller tube absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation. The frequency of the pulse depends on how much radiation is present. A high frequency would mean the tube is absorbing a large amount of radiation.
• Alpha particle


  • Two protons and two neutrons
  • It is the same as a helium nucleus
• Range of alpha particle through air

  A few centimetres (normally in the range of 2-10cm)
• What blocks beta radiation


  • A thin sheet of aluminium
  • Several metres of air
• What blocks gamma radiation


  • Several centimetres of lead
  • A few metres of concrete
• Most ionising radiation


  Alpha radiation
• Least ionising radiation


  Gamma radiation
• Effect of gamma emission on mass/charge of atom


  Both mass and charge remain unchanged
• Plum-pudding model of the atom

  A sphere of positive charge, with the negatively charged electrons distributed evenly throughout it
• Prior to the discovery of the electron, the atom was believed to be indivisible
• Experiment that led to the plum-pudding model being discarded


  Rutherford's alpha-Scattering experiment
• Currently accepted model of the atom

  The Bohr model
• Rutherford's experiment


  1. Alpha particles (charge +2) were fired at a thin sheet of gold foil

  2. Most particles went straight through

  3. Some particles were deflected by small angles (< 90º)

  4. A few particles were deflected by large angles (> 90º)
• Conclusions of Rutherford's experiment


  • Most of an atom is empty space
  • The nucleus has a positive charge
  • Most of the mass is concentrated in the nucleus
• Beta plus decay


  A proton turns into a neutron and a positron (in order to conserve charge)
• Beta minus decay


  A neutron changes into a proton and an electron
• Effect of alpha decay on atomic number and mass number


  • The atomic number decreases by 2
  • The mass number decreases by 4
  • A new element is made since the atomic number has changed
• Effect of beta minus decay on mass number and atomic number


  • The mass number stays the same as the total number of neutrons and protons hasn't changed (one has just turned in the other)
  • The atomic number increases since there is one more proton
• 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 is in the alarm which 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
• How beta radiation is used to determine thickness


  1. A beta source is placed above the material and a detector is placed below it

  2. If there is an increase in radiation detected by the detector, too much radiation is passing through the material, and so it is too thin

  3. If there is a decrease in radiation is detected, then the material blocks too much radiation, and so it is too thick
• Why ionising radiation is dangerous


  • It can damage tissue and kill cells
  • It can cause cell mutations
• Precautions when using ionising radiation


  • Avoid handling the source directly (use tongs)
  • Wear radiation protective clothing
  • Keep the radiation in lead containers to reduce the amount of radiation that can escape
  • Keep exposure time to a minimum
• Long half life vs short half life

  If it has a long half life then it would remain highly radioactive for longer therefore making it more dangerous
• Precautions for doctors and patients using ionising radiation


  • Only a small dose is given to the patient so they are not exposed to too much
  • The radiation used has a short half life so it won't remain highly radioactive for long. This reduces the risk to the doctors using it as well as the patient
  • Doctors and patients (when applicable) wear protective clothing
• Radioactive contamination


  The presence of unwanted radioactive nuclei on other materials
• Irradiation


  • The process of exposing a material to nuclear radiation
  • The material does not become radioactive
• How a radioactive tracer is used in medicine

  1. The tracer is placed inside the body (it can be in a drink, eaten or injected)

  2. The tracer releases gamma radiation which is detected by a detector which moves around the body

  3. This can then be used to produce a picture of the patient's body
• How a PET scanner works


  1. PET (positron emission tomography) uses a tracer, which is injected into the patient's body

  2. The scanner detects the gamma rays which are released by the trace

  3. Multiple images are taken and this is used to form a 3D image of the patient's body
• Isotopes are used in PET scanners. They must be produced near the hospital because the isotopes used have a short half life so must be used soon after production.