Uses of Radioactivity (Edexcel IGCSE Physics: Double Science)

• Radioactivity has many uses, such as:
  • Smoke detectors (alarms)
  • Monitoring the thickness of materials
  • Medical procedures including diagnosis and treatment of cancer
  • Sterilising food (irradiating food)
  • Sterilising medical equipment
  • Determining the age of ancient artefacts

• 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

When no smoke is present, alpha particles ionise the air and cause a current to flow. When smoke is present, alpha particles are absorbed and current is prevented from flowing which triggers the alarm

Measuring the thickness of materials

• When a material, such as aluminium foil, moves above a beta source, some beta particles will be absorbed, but most will penetrate
  • The amount of beta particles passing through the material can be monitored using a detector

• If the material gets thicker, more particles will be absorbed, and the count rate will decrease
• If the material gets thinner, fewer particles will be absorbed, and the count rate will increase
• This allows the manufacturer to make adjustments to keep the thickness of the material constant

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

• Beta radiation is used because the material will only partially absorb it
  • If an alpha source were used, all alpha particles would be absorbed regardless of material thickness
  • If a gamma source were used, almost all gamma rays would be detected regardless of material thickness

Diagnosis and treatment of cancer

• Radiotherapy is the name given to the treatment of cancer using radiation
  • Note: this is different to chemotherapy which is a drug treatment for cancer

• Although radiation can cause cancer, it is also highly effective at treating it
• Ionising 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 as they can penetrate the body and reach 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 is a type of cancer treatment which targets the tumour with ionising radiation

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

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