6.4.2.1
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The radioactive decay of an unstable element.
Activity is measured in Becquerel (Bq).
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Some atomic nuclei are unstable. The nucleus gives out ionising radiation as it changes to become more stable. This is a random process called radioactive decay.
Activity is the rate at which a source of unstable nuclei decays and is measured in Becquerel.
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0.4
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Why are some atoms radioactive?
Where does the radiation come from?
Describe radioactive decay as a process by which an unstable atom releases radiation.
How does activity change with time?
Research how nuclear radiation was discovered and who discovered it.
State that the part of the atom, which releases the radiation, is the nucleus.
Describe how the emission of radiation from a radioactive atom is a random process, but over time the amount of decay can be predicted.
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Investigate the random nature of radioactive decay by throwing dice or coins. Is it possible to predict which dice will land on a six (or coins on a head)?
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BBC Bitesize – Radioactive decay
Pass My Exams – Stable and Unstable Nuclei
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6.4.2.1
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The nature of different types of nuclear radiation.
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The nuclear radiation emitted may be:
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an alpha particle (α) – this consists of two neutrons and two protons, it is identical to a helium nucleus
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a beta particle (β) – a high speed electron ejected from the nucleus as a neutron turns into a proton
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a gamma ray (γ) – electromagnetic radiation from the nucleus.
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a neutron (n)
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0.4
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Are all radioactive sources the same?
Describe the composition of each type of radiation and where relevant, give the particle that the type of radiation is identical to, eg an alpha particle is a helium nucleus.
Research how with beta decay an electron happens to be in the nucleus.
Describe how in beta emission a neutron decays into a proton and an electron, with the electron then being ejected from the nucleus at high speed.
Describe gamma rays as being part of the electromagnetic spectrum as well as a type of nuclear radiation.
Describe how a neutron can be emitted from a nucleus.
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Model alpha, beta, gamma and neutron decay using plasticine and/or stop frame animation. Models should show the atom before and after decay as well as the radiation emitted.
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Nuffield Foundation | Nature of ionising radiations
Cyberphysics – Radioactivity Index
Pass My Exams – Alpha, Beta and Gamma Rays
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6.4.2.1
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The penetration of alpha, beta and gamma radiation through different materials.
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Properties of alpha particles, beta particles and gamma rays limited to their penetration through materials and their range in air.
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0.4
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Which type of radiation is the most dangerous?
Where do radioactive sources come from?
Draw a diagram to illustrate the penetration of the different types of nuclear radiation.
Evaluate the use of different shielding materials for use when handling radioactive sources when supplied with relevant data.
Explain why gamma sources are usually the most harmful when outside the body and alpha are the most dangerous when inside the body in terms of penetration of the radiation.
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Demonstrate the penetration of alpha, beta and gamma radiation. Link the penetration of each type of radiation to the nature of the radiation and the uses of the radioactive sources.
Plan an experiment to determine the type of radiation emitted by an unknown radioactive source. Produce a risk assessment for this experiment.
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BBC Bitesize – Penetrating properties of radiation
Cyberphysics – Ionizing Power and Penetrating Power
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6.4.2.2
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Nuclear decay equations
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Nuclear equations are used to represent radioactive decay.
In a nuclear equation an alpha particle may be represented by the symbol:
and a beta particle by the symbol:
The emission of the different types of ionising radiation may cause a change in the mass and/or the charge of the nucleus. For example:
Alpha decay causes both the mass and charge of the nucleus to decrease.
Beta decay does not cause the mass of the nucleus to change, but it does cause the charge of the nucleus to increase.
The emission of a gamma ray does not cause the mass or the charge of the nucleus to change.
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0.5
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How do atoms change when they undergo radioactive decay?
Describe what happens to an atom when it undergoes alpha, beta and gamma emission.
Calculate how the mass number, the proton number and the number of neutrons in an atom change when it undergoes alpha, beta and gamma emission.
State the composition of alpha and beta particles and be able to recall that an alpha particle can be represented as:
and a beta particle can be represented as:
Complete nuclear decay calculations for alpha and beta decay. The calculations may be in the form of an equation or a table of results showing the same data.
Describe in words how the nucleus of an atom changes when it undergoes alpha and beta decay.
Describe how the charge of a nucleus changes as it undergoes alpha and beta decay.
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Model the radioactive decay of alpha and beta sources. Use the model to construct decay equations for alpha and beta decay. Critically analyse the limitations of the models produced by the class.
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ChemTeam – Writing Alpha and Beta Equations
BBC Bitesize – Nuclear equations – Higher tier
Cyberphysics – Alpha Particle Emission
Cyberphysics – Beta Particle Emission
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6.4.2.3
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The randomness of radioactive decay.
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Radioactive decay is random so it is not possible to predict which individual nucleus will decay next. But with a large enough number of nuclei it is possible to predict how many will decay in a certain amount of time.
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0.5
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How does the activity of a radioactive substance change with time?
Can you predict, with accuracy, which atoms in a radioactive substance will decay first?
Describe the process of radioactive decay as being a random event analogous to flipping lots of coins – not knowing which coins will fall on heads but knowing about half of them will on any given throw.
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Demonstrate the randomness of the decay of a radioactive substance by throwing six dice and getting a prediction of the number of dice that will land on a six. Alternatively, drop 20 coins and get students to predict the number that will land on a head.
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BBC Bitesize – Properties of radiation
Cyberphysics – Decay Animations
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6.4.2.3
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Determination of half-life using calculations and graphical methods.
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The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half of its initial level.
Students should be able to calculate the net decline, expressed as a ratio, in a radioactive emission after a given number of half-lives. HT only.
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0.6
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Define the term half-life.
Calculate the half-life of a radioactive source from a decay curve of the radioactive element.
Calculate the mass of a radioactive substance remaining after a given time when given the half-life of the substance and the initial mass of the radioactive source.
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Investigate half-life by throwing a large number of Tillich bricks. Any that land on the side with the odd colour get removed and the number remaining is recorded. Plot a graph of the number of throws against number of cubes remaining. Determine the half-life of the cubes (the number of throws needed to get the number of cubes to reduce by half).
This experiment can also be carried out using coins. Is it possible to predict which cubes or coins will land on a certain side?
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S-cool, the revision website – Half life
Cyberphysics – Half Life and Rate of Decay
Pass My Exams – Radioactive Half Life
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6.4.2.4
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How to handle radioactive sources safely to avoid contamination.
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Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials. The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard.
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0.7
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Describe how radioactive contamination can occur.
If radiation is dangerous, why is it used in schools?
How would a person become contaminated by radiation?
Explain how the procedure followed by people dealing with radioactive sources reduces the risk of contamination.
If a person gets contaminated by radiation how are they decontaminated?
Research decontamination techniques for workers exposed to radioactive sources.
Describe how decontamination would take place if a person’s clothes or skin have been contaminated by a radioactive source.
Explain why contamination by a highly active alpha source may be a lot more damaging than a low activity gamma source.
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Compare precautions taken by a teacher handling radioactive sources with those used by, say, in a nuclear power station.
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BBC Bitesize – Handling radioactive materials
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6.4.2.4
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The process and uses of irradiation.
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Irradiation is the process of exposing an object to ionising radiation. The irradiated object does not become radioactive.
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0.5
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Explain how fruit is irradiated before sending on a long trip.
If radiation is harmful, why is food irradiated using radiation?
When irradiating food, does it become radioactive?
Find out the advantages and disadvantages of irradiating food.
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Evaluate the use of irradiating fruit in terms of cost of goods and potential risk due to the exposure of workers and consumers of the irradiation process.
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Video clip
YouTube: Food irradiation: Is it safe?
Cyberphysics – Radioactivity and Food
Pass My Exams – Uses of Radioactivity, Gamma Rays in Sterilisation
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6.4.2.4
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Safety precautions taken when dealing with radioactive sources.
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Suitable precautions must be taken to protect against any hazard the radioactive source used in the process of irradiation may present.
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0.5
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Describe and explain how radioactive sources are used safely within a science lab, looking in terms of reducing the risk of contamination and reducing the exposure to the radiation itself.
Explain the safety requirements needed in a work place that deals with radioactive sources.
Research the types of food irradiated at the sources of radiation used in this process. Find out the safety precautions taken in the food industry when dealing with radioactive sources and how this differs from the use of radioactive sources in schools.
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Justify the use of radioactive sources in school in terms of risk-benefit analysis to the students in the class.
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BBC Bitesize – Hazards from radioactive materials
Cyberphysics – Radioactivity – safety
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