· Web viewKey Stage 4 – Too hot to handleNotes for teachers At a glanc e One of the many engineering problems faced by scientists working on nuclear fusion is how to create materials

Key Stage 4 – Too hot to handle

Notes for teachers

At a glance

One of the many engineering problems faced by scientists working on nuclear fusion is how to create materials that are able to cope with being bombarded with highly energetic neutrons created by the fusion process. In order to discover more about how neutrons damage materials, scientists at the University of Oxford placed samples of metal inside a nuclear reactor. Once the samples were removed from the reactor, they were too radioactive to work on safely, so the samples had to be safely stored for seven years before the scientists could work on them.

This lesson looks at how we measure radioactivity and how to calculate the half-life of radioactive materials.

Learning Outcomes

Students will be able to name a Geiger counter as an instrument used to measure the radioactivity of a source.

Students will be able to describe what is meant by a half life Students will be able to solve simple half life problems using graphs

Each student will need

Student Worksheet Graph paper

Possible Lesson Activities

www.oxfordsparks.ox.ac.uk/content/materials-nuclear-fusion-how-do-you-confine-sun-box

1. Starter activity Show the Oxford Sparks, ‘Materials for Nuclear Fusion’ animation to the students. Remind the students that the samples were placed in the reactor for 200 days and then the

scientists had to wait for seven years before they could work on them. Ask the students in pairs/small groups to discuss:

Why they were too dangerous to work with immediately. The nuclei of radioactive elements are unstable. They spontaneously decay by

emitting radiation and turn into other elements (or isotopes) which are more stable (although they may still be radioactive).

The radiation created by this process can damage living cells so is potentially dangerous.

Why they would be safer after seven years. The amount of radiation emitted by the sample depends on the number of

radioactive nuclei inside it. The more radioactive nuclei inside the sample the greater the amount of radiation produced.

Over time some of the nuclei decay to form more stable nuclei and become less radioactive.

Eventually enough time has passed that the samples are safe enough to work with.

2. Main activity: Measuring radioactivity and half-life

Explain that in order to know whether the sample is safe enough to work with we need a way to measure its radioactivity.

Ask the students to read the page of the student worksheet on measuring radioactivity and background radiation and answer the questions.

Explain that the scientists were able to work with the samples after 7 years because they had become less radioactive over time. How fast the radioactive sample becomes safe to work with depends on its half-life.

Ask the students to read the page of the student worksheet on half-life and answer the questions.

3. Plenary: Carbon Dating Explain that the most common form of Carbon has 6 protons and 6 neutrons. Remind the

students that this is written as 126C this is often known as Carbon-12. However there is a

radioactive form of Carbon with two extra neutrons 146C known as Carbon-14. This is

constantly being created in the atmosphere by cosmic rays. The proportion of Carbon-14 in the atmosphere is tiny (about a trillionth of other Carbon isotopes).

Explain that all living (organic) things contain carbon and due to the carbon cycle the relative amounts of Carbon-12 and Carbon-14 are the same as in our atmosphere.

However, once a living thing dies, the Carbon 14 contained inside it decays slowly so that the amount of Carbon-14 decreases as a proportion of the carbon present over time.


So an object that is 2000 years old will have less Carbon-14 than one which is only 100 years old. By looking at the relative proportions of Carbon-12 and Carbon-14 scientists can work out how old objects that contain organic matter are. This is known as carbon dating.

Ask the students to discuss in small groups how carbon dating could be used to tell whether a recently discovered parchment (made of animal skin) is really 2000 years old or a clever fake.

Ask the students to write a short news article explaining how scientists have uncovered the fake.

Answers to questions on student sheets

Measuring Radioactivity

A is the more radioactive source (as it would produce 7200 counts in an hour).

2880cpm. The count due to background radiation is 120cpm, the count due to the radiation source and background radiation is 3000cpm].

Half-Life questions1) Half- life = 30 hours (this can be seen most easily by looking at the count rate at 0, 30 and 60

hours).2) Half-life= 1.5 hours (Although the half-life can be determined by drawing the graph and reading off

the value for time when the count rate is 3000, some students may spot that the count after three hours is ¼ of the initial count rate and work out that two half-lives must have passed in those three hours).

Weblinks Oxford Sparks ‘Materials for Nuclear Fusion’ animation and background info page


Information on carbon dating

https://www.glam.ox.ac.uk/article/carbon-dating-finds-bakhshali-manuscript-contains-oldest-recorded-origins-symbol-zero




http://www.oxfordsparks.ox.ac.uk/content/materials-nuclear-fusion-how-do-you-confine-sun-box

· Web viewKey Stage 4 – Too hot to handleNotes for teachers At a glanc e One of the many engineering problems faced by scientists working on nuclear fusion is how to create materials

Documents