Radioactive Emissions (OCR GCSE Combined Science A (Gateway): Physics)

Atoms can absorb and emit electromagnetic radiation.

Describe two possible effects on an electron in an atom when it absorbs electromagnetic radiation.

1 .......................................................................................................

2 .......................................................................................................

Alpha radiation is not emitted in the processes in part (a).

Explain why.

A radioactive isotope has a half-life of 6 hours.

50 g of the isotope are put in a container.

What mass of the isotope is left after 6 hours?

Mass = ................................ g

This is a graph showing the radiation emitted from samples of three different isotopes A, B and C.

i) Which isotope, A, B or C, takes the longest time to decay?

Tick (✓) one box.

[1]

ii) Two scientists discuss the isotopes in the graph.

Do you agree with the views of scientist 1 and scientist 2?

Use the graph and ideas about radioactivity and half-life to explain your answer.

Scientist 1 ......................................................................................

Scientist 2 ......................................................................................

[4]

iii) Scientist 1 wants to identify the type of radiation emitted by isotope A.

This is a list of equipment Scientist 1 has in his laboratory:

•   radiation detector    

•   piece of thick lead    

•   piece of cardboard    

•   piece of aluminium.

Describe how Scientist 1 does the experiment and explain how they can work out the type of radiation emitted.

You may include a diagram in your answer.

[4]

Higher Tier Only

A teacher measures the activity of different radioactive isotopes.

Fig. 23.1 is a graph of her results for isotope A.

Fig. 23.1

Use Fig. 23.1 to calculate the half-life of isotope A.

Show your working on the graph in Fig. 23.1.

Half-life = ................................ minutes

The teacher measures the activity of isotope B.

She starts taking activity measurements after 20 minutes.

Table 23.1 shows her results for isotope B.

Table 23.1

Predict the activity of isotope B at 0 minutes.

Use the information in Table 23.1 to help you.

Activity = ............................ counts per minute

The teacher measures the activity of isotope C.

Fig. 23.2 is a graph which shows how activity varies with time for isotope C.

Fig. 23.2

A student makes two conclusions from the graph in Fig. 23.2:

Is the student correct?

Evaluate each conclusion and explain your answer.

Conclusion 1 ....................................................................................

Conclusion 2 ...................................................................................

A teacher demonstrates an experiment about radioactivity. He demonstrates how different types of radiation can be absorbed.

He puts different barriers between the source and the Geiger-Müller tube. He uses four different radioactive sources A, B, C and D.

Suggest two safety precautions that the teacher should use when demonstrating this experiment.

1 ........................................................................................................

2 ......................................................................................................

The teacher chooses source A and uses the Geiger-Müller tube to measure the count rate (counts per minute) for different barriers. He repeats the experiment with source B, source C and then source D.

Look at his results.

He also finds that the average count rate with no sources and no barriers is 20.

i) Which source A, B, C or D emits gamma radiation only?

Explain your answer.

Source ............... because ............................................ [2]

ii) Which source A, B, C or D emits alpha radiation only?

Explain your answer.

Source ............... because ............................................ [2]

iii) Which source A, B, C or D could emit both beta and gamma radiation?

Explain your answer.

Source ............... because ............................................ [2]

The teacher notices that the count rate behind the lead barrier ranges from 20 to 24.

Give two reasons why there are a wide range of results around 22 counts per minute.

1. .....................................................................................................

2. ......................................................................................................

The teacher decides to repeat the experiment.

This time he records the number of counts for a much longer time interval for each source.

Explain why this is an improvement to the experiment.

A student does an experiment with radioactive materials.

• He investigates how the activity of radiation changes with distance.

• The radiation moves from the radioactive source to a detector.

• He measures the counts per minute at the detector.

The table shows the results.

Describe, using these results, how the count rate changes as the detector is moved away from the source.

The student takes two further readings at 160 and 320 cm.

He adds these further readings to his table.

As the distance is increased to 160 and 320 cm, the results do not follow the same pattern as the other results.

Predict what these last two results should have been and explain the anomalies in the last two results.

Americium-241 is a radioactive source that is used in smoke detectors.

This is the symbol for americium-241:

Describe the structure of an americium-241 nucleus.

Americium-241 decays by emitting alpha radiation to form neptunium (Np).

Complete the balanced symbol equation for the decay.

When smoke enters a detector:

• The smoke particles absorb the emitted alpha radiation.

• The alarm sounds.

Explain why beta and gamma sources are not suitable for use in a smoke detector.

The half-life of americium-241 is 432 years.

i) Explain what is meant by half-life.

 [1]

ii) Explain why the half-life of americium-241 is suitable for a smoke detector.

 [1]

iii) The table shows some data for two radioactive sources.

Both sources start with the same number of radioactive nuclei.

Which source is a greater health risk? Explain your answer.

 [2]