The rate at which unstable nuclei in a radioactive source decay , measured in becquerels (Bq) .

Define the becquerel .

The unit of activity ; 1 Bq is equal to one nucleus decaying per second in a source.

Why does the activity of a radioactive source decrease over time?

Each decay event reduces the number of radioactive nuclei remaining in the source, so fewer nuclei are left to decay in each following second.

What do the fluctuations seen when count rate is plotted against time provide evidence for?

The randomness of radioactive decay.

A source with an activity of 2000 Bq means that ______ nuclei decay every second.

A source with an activity of 2000 Bq means that 2000 nuclei decay every second.

True or False? Activity and count rate mean the same thing.

False. Activity is the rate at which unstable nuclei decay ; count rate is the rate at which radioactive emissions are detected (e.g. by a GM tube).

The time taken for the number of nuclei of a radioactive isotope in a sample to decrease by half (equivalently, the time for the sample's activity to fall to half its original value).

Describe how the half-life of a sample can be determined experimentally.

Measure the initial activity , A ~ 0 ~, of the sample, then measure how the activity changes with time . The half-life is the time taken for the activity to fall to half its original value.

What percentage of a sample remains after two half-lives have passed?

25% (a quarter) of the original amount remains.

With each half-life that passes, the amount of a radioactive isotope remaining ______ .

With each half-life that passes, the amount of a radioactive isotope remaining decreases by half .

A sample has an initial activity of 880 Bq. After one year, the activity has fallen to 220 Bq. What is the half-life of this sample?

220 Bq is a quarter of 880 Bq, so two half-lives have passed in one year. Therefore the half-life of the sample is 6 months .

True or False? The half-life of a given isotope changes over time.

False. The half-life is constant for a particular isotope — the time to fall from 100% to 50% activity is the same as the time to fall from 50% to 25%.

Define radiotherapy .

The treatment of cancer using ionising radiation (beams of gamma rays directed at a tumour), which is different from chemotherapy (a drug-based treatment).

Why is alpha radiation used in smoke detectors, rather than beta or gamma?

Alpha is the most ionising and least penetrating type of radiation, so it is readily absorbed by smoke entering the detector, blocking the ionising current and triggering the alarm. Beta and gamma would mostly pass straight through the smoke without being absorbed.

Why is beta radiation , rather than alpha or gamma, used to monitor the thickness of thin materials such as aluminium foil?

Beta radiation is only partially absorbed , so the count rate detected changes with thickness. Alpha would be fully absorbed regardless of thickness, and gamma would nearly all be detected regardless of thickness, so neither can be used to track changes in thickness.

Why is gamma radiation used to sterilise medical equipment?

Gamma is the most penetrating type of radiation, so it can irradiate all sides of the instruments and sterilise them without removing the packaging .

A ______ is a radioactive isotope used to track the movement of a substance, such as blood, around the body.

A tracer is a radioactive isotope used to track the movement of a substance, such as blood, around the body.

True or False? Increasing the thickness of a material being monitored with a beta source increases the count rate detected.

False. A thicker material absorbs more beta particles , so the count rate detected decreases .

State three uses of radioactivity.

Any three from: smoke detectors , monitoring the thickness of materials , diagnosis and treatment of cancer , sterilising food , sterilising medical equipment , determining the age of ancient artefacts.

Define contamination (in radioactivity).

The accidental transfer of a radioactive substance onto or into a material, which causes that material to become radioactive .

The process of exposing a material to ionising radiation . Irradiation does not make the material radioactive.

How can irradiation be prevented?

By using shielding , such as a lead-lined suit , which absorbs radiation before it reaches the person.

How can contamination be prevented?

By wearing an airtight suit , which prevents radioactive atoms getting onto or into the person.

Why does a source with a longer half-life pose a greater contamination risk than one with a shorter half-life?

A longer half-life means the source remains radioactive for longer , so it needs to be controlled, shielded and stored for longer to prevent it spreading.

A source with a ______ half-life has a higher activity, so poses a greater irradiation risk.

A source with a shorter half-life has a higher activity, so poses a greater irradiation risk.

True or False? An object that has been irradiated becomes radioactive.

False. Irradiation does not make an object radioactive; only contamination (the transfer of radioactive material onto or into it) does.

Why are alpha sources more dangerous than gamma sources if they get inside the body?

Alpha is the most ionising type of radiation (gamma is around 20 times less ionising ), so alpha causes the most damage to living cells when the source is inside the body.

Why are gamma sources more dangerous than alpha sources if they are outside the body?

Gamma is the most penetrating type of radiation, so it can pass through skin and reach living cells inside the body. Alpha is the least penetrating and is absorbed by air before it even reaches the skin.

A device (also called a radiation badge ) that measures the amount of radiation a person has been exposed to; it is often worn by radiographers or anyone working with radiation.

Give three ways of handling a radioactive source safely to minimise the risk of contamination.

Any three from: keeping the source in a shielded container (e.g. a lead-lined box) when not in use, using tongs or gloves rather than handling it directly, wearing protective clothing , and limiting the time the source is out of its container.

______ -emitting nuclear waste requires storage inside lead-lined, thick concrete silos.

Gamma -emitting nuclear waste requires storage inside lead-lined, thick concrete silos.

True or False? Radioactive waste with a long half-life can be safely stored above ground in ordinary containers.

False. Long half-life waste stays dangerous for a very long time, so it must be buried underground in secure, geologically stable sites, in strong, corrosion-resistant containers.

What effect can ionising radiation have on the DNA within a living cell?

It can damage DNA . The cell may repair the damage successfully, but an incorrect repair can cause a mutation , which can lead to cancer .

IGCSEPhysicsEdexcelPhysics (Modular)Unit 2Flashcards8. Radioactivity & ParticlesRadioactivity, Uses & Dangers

Radioactivity, Uses & Dangers (Edexcel IGCSE Physics (Modular): Unit 2): Flashcards

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FrontActivity & Decay
Define activity.

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Cards in this collection (35)

Define activity.
The rate at which unstable nuclei in a radioactive source decay, measured in becquerels (Bq).
Define the becquerel.
The unit of activity; 1 Bq is equal to one nucleus decaying per second in a source.
Why does the activity of a radioactive source decrease over time?
Each decay event reduces the number of radioactive nuclei remaining in the source, so fewer nuclei are left to decay in each following second.
Which piece of apparatus is used to measure the count rate of a radioactive source?
A Geiger-Muller (GM) tube.
What do the fluctuations seen when count rate is plotted against time provide evidence for?
The randomness of radioactive decay.
A source with an activity of 2000 Bq means that ______ nuclei decay every second.
A source with an activity of 2000 Bq means that 2000 nuclei decay every second.
True or False?
Activity and count rate mean the same thing.
False.
Activity is the rate at which unstable nuclei decay; count rate is the rate at which radioactive emissions are detected (e.g. by a GM tube).
Define half-life.
The time taken for the number of nuclei of a radioactive isotope in a sample to decrease by half (equivalently, the time for the sample's activity to fall to half its original value).
Describe how the half-life of a sample can be determined experimentally.
Measure the initial activity, A~0~, of the sample, then measure how the activity changes with time. The half-life is the time taken for the activity to fall to half its original value.
What is the half-life of carbon-14?
5700 years.
What percentage of a sample remains after two half-lives have passed?
25% (a quarter) of the original amount remains.
With each half-life that passes, the amount of a radioactive isotope remaining ______.
With each half-life that passes, the amount of a radioactive isotope remaining decreases by half.
A sample has an initial activity of 880 Bq. After one year, the activity has fallen to 220 Bq. What is the half-life of this sample?
220 Bq is a quarter of 880 Bq, so two half-lives have passed in one year. Therefore the half-life of the sample is 6 months.
True or False?
The half-life of a given isotope changes over time.
False.
The half-life is constant for a particular isotope — the time to fall from 100% to 50% activity is the same as the time to fall from 50% to 25%.
Define radiotherapy.
The treatment of cancer using ionising radiation (beams of gamma rays directed at a tumour), which is different from chemotherapy (a drug-based treatment).
Why is alpha radiation used in smoke detectors, rather than beta or gamma?
Alpha is the most ionising and least penetrating type of radiation, so it is readily absorbed by smoke entering the detector, blocking the ionising current and triggering the alarm. Beta and gamma would mostly pass straight through the smoke without being absorbed.
Why is beta radiation, rather than alpha or gamma, used to monitor the thickness of thin materials such as aluminium foil?
Beta radiation is only partially absorbed, so the count rate detected changes with thickness. Alpha would be fully absorbed regardless of thickness, and gamma would nearly all be detected regardless of thickness, so neither can be used to track changes in thickness.
Why is gamma radiation used to sterilise medical equipment?
Gamma is the most penetrating type of radiation, so it can irradiate all sides of the instruments and sterilise them without removing the packaging.
A ______ is a radioactive isotope used to track the movement of a substance, such as blood, around the body.
A tracer is a radioactive isotope used to track the movement of a substance, such as blood, around the body.
True or False?
Increasing the thickness of a material being monitored with a beta source increases the count rate detected.
False.
A thicker material absorbs more beta particles, so the count rate detected decreases.
State three uses of radioactivity.
Any three from: smoke detectors, monitoring the thickness of materials, diagnosis and treatment of cancer, sterilising food, sterilising medical equipment, determining the age of ancient artefacts.
Define contamination (in radioactivity).
The accidental transfer of a radioactive substance onto or into a material, which causes that material to become radioactive.
Define irradiation.
The process of exposing a material to ionising radiation. Irradiation does not make the material radioactive.
How can irradiation be prevented?
By using shielding, such as a lead-lined suit, which absorbs radiation before it reaches the person.
How can contamination be prevented?
By wearing an airtight suit, which prevents radioactive atoms getting onto or into the person.
Why does a source with a longer half-life pose a greater contamination risk than one with a shorter half-life?
A longer half-life means the source remains radioactive for longer, so it needs to be controlled, shielded and stored for longer to prevent it spreading.
A source with a ______ half-life has a higher activity, so poses a greater irradiation risk.
A source with a shorter half-life has a higher activity, so poses a greater irradiation risk.
True or False?
An object that has been irradiated becomes radioactive.
False.
Irradiation does not make an object radioactive; only contamination (the transfer of radioactive material onto or into it) does.
Why are alpha sources more dangerous than gamma sources if they get inside the body?
Alpha is the most ionising type of radiation (gamma is around 20 times less ionising), so alpha causes the most damage to living cells when the source is inside the body.
Why are gamma sources more dangerous than alpha sources if they are outside the body?
Gamma is the most penetrating type of radiation, so it can pass through skin and reach living cells inside the body. Alpha is the least penetrating and is absorbed by air before it even reaches the skin.
Define dosemeter.
A device (also called a radiation badge) that measures the amount of radiation a person has been exposed to; it is often worn by radiographers or anyone working with radiation.
Give three ways of handling a radioactive source safely to minimise the risk of contamination.
Any three from: keeping the source in a shielded container (e.g. a lead-lined box) when not in use, using tongs or gloves rather than handling it directly, wearing protective clothing, and limiting the time the source is out of its container.
______-emitting nuclear waste requires storage inside lead-lined, thick concrete silos.
Gamma-emitting nuclear waste requires storage inside lead-lined, thick concrete silos.
True or False?
Radioactive waste with a long half-life can be safely stored above ground in ordinary containers.
False.
Long half-life waste stays dangerous for a very long time, so it must be buried underground in secure, geologically stable sites, in strong, corrosion-resistant containers.
What effect can ionising radiation have on the DNA within a living cell?
It can damage DNA. The cell may repair the damage successfully, but an incorrect repair can cause a mutation, which can lead to cancer.

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