Uses of Radiation (Cambridge O Level Physics)

• Radiation is used in a number of different ways, for example:
  1. Medical procedures (including diagnosis and treatment of cancer)
  2. Sterilising food (irradiating food to kill bacteria)
  3. Sterilising medical equipment (using gamma rays)
  4. Determining the age of ancient artefacts
  5. Measuring and controlling the thickness of materials
  6. Household fire (smoke) detectors

• The properties of the different types of radiation determine which one is used in a particular application

Smoke Detectors

• Alpha particles are used in smoke detectors
• The alpha radiation will normally ionise the air within the detector, creating a current
• The alpha emitter is blocked when smoke enters the detector
• The alarm is triggered by a microchip when the sensor no longer detects alpha

Smoke Detector in Normal Operation

How is smoke detected in a smoke alarm?

When alpha particles are stopped by the smoke, this prevents the flow of current and triggers the alarm

Measuring the Thickness of Materials

• Radiation can be used for tracing and gauging thickness
  • Beta particles are most commonly used for this

• As the material moves along a belt above a beta source, the particles that are able to penetrate it can be monitored using a detector on the other side
• If the material gets thicker, more particles will be absorbed by the material, meaning less will arrive at the detector
  • If the material gets thinner, more particles will arrive at the detector

• This allows the machine to make adjustments to keep the thickness of the material constant

Measuring the Thickness of Aluminium using Beta Radiation

Beta particles can be used to measure the thickness of thin materials such as paper, cardboard or aluminium foil

• Beta radiation is used because it will be partially absorbed by the material
  • If alpha particles were used all of them would be absorbed and none would get through
  • If gamma were used almost all of it would get through and the detector would not be able to sense any difference if the thickness were to change

Diagnosis and Treatment of Cancer

• Radiotherapy is the name given to the treatment of cancer using radiation
  • Whereas, chemotherapy is the treatment of cancer using chemicals

• Although radiation can cause cancer, it is also highly effective at treating it
• Radiation can kill living cells
  • Some cells, such as bacteria and cancer cells, are more susceptible to radiation than others

• Beams of gamma rays are directed at the cancerous tumour
  • Gamma rays are used because they are able to penetrate the body, reaching the tumour
  • The beams are moved around to minimise harm to healthy tissue whilst still being aimed at the tumour

• A tracer is a radioactive isotope that can be used to track the movement of substances, like blood, around the body
  • A PET scan can detect the emissions from a tracer to diagnose cancer and determine the location of a tumour

Radiation Therapy for Cancer Treatment

Radiation therapy to remove a tumour

Sterilising Food & Medical Equipment

• Gamma radiation is widely used to sterilise medical equipment
• Gamma is most suited to this because:
  • It is the most penetrating out of all the types of radiation
  • It is penetrating enough to irradiate all sides of the instruments
  • Instruments can be sterilised without removing the packaging

• Food can be irradiated in order to kill any microorganisms that are present in it
• This makes the food last longer and reduces the risk of food-borne infections

The Radura Symbol

Food that has been irradiated carries this symbol, called the Radura. Different countries allow different foods to be irradiated