Radioactivity, Uses & Dangers (Edexcel IGCSE Physics)
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What is the activity of a radioactive source?
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What is the activity of a radioactive source?
The activity of a radioactive source is the rate at which the unstable nuclei decay.
What is 1 becquerel (Bq)?
1 becquerel (Bq) is equivalent to 1 nucleus in a radioactive source decaying in 1 second.
How does the activity of a radioactive source change over time?
The activity of a radioactive source decreases over time.
What is the difference between activity and count rate?
Activity is the rate at which radiation is emitted, whereas count rate is the rate at which radiation is detected.
How can the randomness of radioactive decay be observed?
The randomness of radioactive decay can be observed by
measuring the count rate of a source using a GM tube
plotting a graph of count rate against time
Define the term half-life.
Half-life is the time taken for half the nuclei of a particular isotope in any sample to decay.
True or False?
The half-life for a particular isotope is always the same.
True.
Half-life is constant for any particular isotope.
How is the activity of a radioactive sample affected after one half-life?
The activity of a radioactive sample will have halved after one half-life
True or False?
Half-life is different for different isotopes.
True.
Half-life is different for different isotopes.
What is the value of the activity of a radioactive sample after two half-lives?
The value of the activity of a radioactive sample after two half-lives is
of its original value.How do you determine the half-life of an isotope on a graph of activity against time?
To determine the half-life of an isotope on a graph of activity over time:
identify the point at which the activity has halved and draw a line to the curve
track that point down to the time axis
What proportion of original nuclei in a radioactive sample will remain after three half-lives?
After three half-lives, the proportion of original nuclei remaining in the sample will be
.Which type of nuclear radiation is used in smoke detectors?
Alpha radiation is used in smoke detectors.
Which type of nuclear radiation is used for measuring and controlling the thickness of materials?
Beta radiation is used in measuring and controlling the thickness of materials.
Which type of nuclear radiation is used for irradiating food to kill bacteria?
Gamma radiation is used for irradiating food to kill bacteria.
Which type of nuclear radiation is used for sterilising equipment?
Gamma radiation is used for sterilising equipment.
How does a smoke alarm work?
A smoke alarm works as follows:
alpha particles ionise the air inside the detector creating a current
the alpha emitter is blocked by the presence of smoke particles
the alarm is triggered when the sensor no longer detects alpha particles
Why are alpha particles not used to detect the thickness of materials?
Alpha particles are stopped by paper, so they would not penetrate the material to reach the detector.
Why is gamma radiation used in the sterilisation of food and equipment?
Gamma radiation can penetrate packaging and objects so all surfaces of the food or equipment can be irradiated. Gamma radiation is ionising enough to kill any microorganism, therefore it is used for sterilisation.
Why are beta particles used to detect the thickness of materials?
Beta particles can penetrate materials such as paper and aluminium foil, so the number of beta particles detected by a sensor can be used to measure and control the thickness of the substance.
How is gamma radiation used in the treatment of cancer?
Gamma radiation is used in the treatment of cancer in the process of radiotherapy. Gamma radiation can damage cells and tissues so this can be used to target cancer cells. Gamma rays can penetrate the body to reach the cancer cells, but the beams must be emitted from different angles to reduce the damage to healthy tissues.
Define contamination.
Contamination is the accidental transfer of a radioactive substance onto or into a material.
Define irradiation.
Irradiation is the process of exposing a material to ionising radiation.
True or False?
A substance becomes radioactive when it is irradiated.
False.
A substance can only become radioactive by contamination.
What is the main difference between irradiation and contamination?
The main difference between irradiation and contamination is that contamination makes an object radioactive whereas irradiation does not.
True or False?
Surgical equipment is sterilised by irradiation.
True.
Surgical equipment is sterilised by irradiation.
How can the risk of irradiation be reduced?
The risk of irradiation can be reduced by using shielding made from materials such as lead or by increasing distance from the source.
How can the risk of contamination be reduced?
The risk of contamination can be reduced by
handling radioactive sources safely
wearing appropriate clothing, such as gloves or an airtight suit
True or False?
Contamination poses a greater risk to health than irradiation.
True.
Contamination poses a greater risk to health than irradiation, especially if the radioactive material gets inside the body.
What effects does ionising radiation have on living organisms?
The effects of ionising radiation on living organisms are:
cell death (and therefore tissue damage)
mutations
cancer
How does ionising radiation cause cell mutations?
Ionising radiation can remove electrons from the atoms that make up DNA and therefore change the structure of the molecule. A structural change in DNA can lead to mutated cells. Mutated cells usually either die or get destroyed by the immune system, but some mutations can cause cells to replicate uncontrollably and lead to cancer.
How is radioactive waste disposed of?
Radioactive waste is disposed of by:
containing it in marked containers
burying it underground
leaving it undisturbed for thousands of years
How can radioactive samples be handled safely?
Radioactive samples can be handled safely by:
storing the sample encased in lead
using gloves and tongues to move the sample
wearing protective clothing
keeping the sample at a distance from the body
minimising the exposure time
washing hands after to avoid contamination
How do people working with radiation monitor exposure?
People working with radiation monitor their exposure by wearing a badge containing photographic film (dosemeter). The photographic film darkens when exposed to radiation.