Uses of Radiation (Cambridge (CIE) IGCSE Physics)

Uses of radiation

Extended tier only

• The type of radiation emitted and the half-life of an isotope determine which isotope is used for the following applications:
  

  • household fire (smoke) alarms

  • irradiating food to kill bacteria

  • sterilisation of equipment using gamma rays

  • measuring and controlling thicknesses of materials with the choice of radiations used linked to penetration and absorption

  • diagnosis and treatment of cancer using gamma rays

Household fire alarms are a use of alpha radiation

• Alpha particles are used in smoke detectors

• The alpha radiation ionises 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 the alpha particles

• An isotope of alpha radiation with a long half-life is used for smoke detectors so they don't need replacing often

Uses of alpha radiation: household fire alarms

In the diagram at the bottom, alpha particles are stopped by the smoke, preventing the flow of current and triggering the alarm

Sterilisation of equipment using gamma rays

• 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

• The source of gamma radiation used for sterilisation has a half-life of around 5 years

  • This means the sterilisation equipment does not need to be replaced often

Irradiating food to kill bacteria using gamma rays

• Food can be irradiated to kill any microorganisms that are present on it

• This makes the food last longer and reduces the risk of food-borne infections

Uses of gamma radiation: killing bacteria

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

Measuring the thickness of materials using different radiation

• Beta radiation is most commonly used to measure the thickness of materials because it will be partially absorbed by most materials

  • Alpha particles are used for thinner materials because they have a lower penetrating power and are absorbed by a thin sheet of aluminium 

  • Gamma radiation can be used for very thick materials because they have a higher penetrating power and are mostly absorbed by thick pieces of lead.

• A material moves across a radiation source

  • The particles that penetrate it are monitored using a detector above

• The thickness of the material is monitored

  • If the material gets thicker, more particles will be absorbed by the material, meaning that less will get through and be detected by the detector

  • If the material gets thinner the opposite happens

• The machine makes adjustments to keep the thickness of the material constant

• Radiation used to measure the thickness of materials has a half-life of many years (10-20 years) so that the count rate remains relatively constant each day

Uses of radiation: monitoring material thickness

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

Diagnosis and treatment of cancer using gamma rays

• Radiotherapy is the name given to the treatment of cancer using radiation

  • Chemotherapy is treatment using chemicals

• 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 can penetrate the body, reaching the tumour

  • The beams are moved around to minimise harm to healthy tissue whilst still being aimed at the tumour

• Gamma radiation used in radiotherapy has a half-life of around 5 years

  • This means that it does not need to be replaced often within the machine that uses it

Uses of gamma radiation: treatment of cancer

Radiation therapy to remove a 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

• The half-life of a tracer is several hours

  • This provides time for a scan to be conducted and then the radiation to leave the body quickly