Edexcel IGCSE Physics 复习笔记 7.2.3 Uses of Radioactivity

• Radiation is used in a number of different ways:
  • Medical procedures including diagnosis and treatment of cancer
  • Sterilising food (irradiating food)
  • Sterilising medical equipment
  • Determining the age of ancient artefacts
  • Checking the thickness of materials
  • Smoke detectors (alarms)

   

• 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

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

Measuring the Thickness of Materials

• As a material moves above a beta source, the particles that are able to penetrate it can be monitored using a detector
• If the material gets thicker more particles will be absorbed, meaning that less will get through
• If the material gets thinner the opposite happens
• This allows the machine 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 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(Chemotherapy is treatment 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 to remove a tumour

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

• • Consider the different properties of alpha, beta and gamma:
    • Alpha is the most weakly penetrating and strongest ioniser
    • Beta and gamma have stronger penetrating power and weaker ionising power

     

  • If beta or gamma radiation were used in this situation then they would pass straight through the smoke and the alarm would not go off
  • Therefore, since alpha is absorbed by smoke, and beta and gamma are not, this makes it most suitable for use in a smoke detector