7.2.1-7.2.5 - Radioactivity, Uses and Danger Flashcards
What are objects called that contain radioactive nuclei?
Objects containing radioactive nuclei are called sources of radiation
What is the activity which radiation decays at defined as?
The rate at which the unstable nuclei from a source of radiation decays
What is radiation measured in?
Activity is measured in Becquerels the symbol is BQ.1 Becquerel is equal to 1 nucleus in the source decaying in 1 second
How does the activity of a source decrease?
The activity of a source decreases with time
This is because each decay event reduces the overall number of radioactive particles in the source
The nature of radioactive decay can be demonstrated by observing the count rate of a source using a Geiger-Muller (GM) tube, and then plotting these results against time
These fluctuations in count rate on the GM tube also provide evidence for the randomness of radioactive decay
What is half life?
The time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half
How is half life measured?
Measure the initial activity, A0, of the sample
Determine the half-life of this original activity
Measure how the activity changes with time
The time taken for the activity to decrease to half its original value is the half-life
What are the many ways that radiation can be used?
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)
How is Alpha used in smoke detectors?
Alpha particles 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
How is Beta used in 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
Why couldn’t an alpha source or a gamma source measure the thickness of materials?
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
How are Gamma rays used in Diagnosis and treatment of cancer?
Radiotherapy is the name given to the treatment of cancer using radiation
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
How is Gamma used in 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 infection
What are the properties of the three sources of radiation?
Alpha is the most weakly penetrating and strongest ioniser
Beta and gamma have stronger penetrating power and weaker ionising power
What is contamination?
The unwanted presence of materials containing radioactive atoms and other materials.
What make a substance radioactive?
A substance is only radioactive if it contains radioactive atoms that emit radiation. Contamination occours when a radioactive isotope gets onto a material where it should not be often called a leak.