Uses of Radiation (Cambridge (CIE) IGCSE Physics)
Revision Note
Written by: Ashika
Reviewed by: Caroline Carroll
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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
Worked Example
Use the diagram to explain why alpha radiation is used in smoke detectors, and beta or gamma radiation is not.
Answer:
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
Examiner Tips and Tricks
If you are presented with an unfamiliar situation in your exam don’t panic! Just apply your understanding of the properties of alpha, beta and gamma radiation. Mainly think about the range (how far it can travel) and ionising power of the radiation to help understand which radiation is used in which situation.
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