GCSEPhysics: Combined ScienceOCR GatewayExam Questions6. Radioactivity6.1 Radioactive Emissions

Radioactive Emissions (OCR Gateway GCSE Physics: Combined Science)

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6.1 Radioactive Emissions

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6.1 Radioactive Emissions

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1a3 marks
a)
Some isotopes of cobalt are radioactive.

The isotope cobalt‐60 (Co‐60) has the symbol:

Co presubscript 27 presuperscript 60

The isotope cobalt‐57 (Co‐57) has the symbol:

Co presubscript 27 presuperscript 57

i)
State the number of protons in a nucleus of Co‐60.

Number of protons = .......................................................... [1]

 

ii)
Give one similarity and one difference between the nucleus of Co‐57 and the nucleus of Co‐60.

Similarity ............................................................................................

Difference ...........................................................................................

[2]

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1b4 marks
b)
A teacher measures the radiation emitted by Co‐60.

She uses this equipment:

q18b-paper2-oct-nov2020-ocr-gcse-physics

The teacher’s results are shown in Table 18.1.

  Count-rate (counts per minute)
Measurement 1 191
Measurement 2 224
Measurement 3 212

Table 18.1

i)
Explain why the teacher’s three measurements are not the same.

[1]



ii)
Use the teacher’s results in Table 18.1 to calculate the mean count‐rate for Co‐60.

Count‐rate = ............................ counts per minute [2]

 

iii)
Co‐60 emits gamma radiation.

The teacher puts thin aluminium foil between Co‐60 and the detector.

State what happens to the count‐rate.

 [1]

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1c4 marks
c)
i)
Explain what is meant by the half‐life of a radioactive isotope.


 [1]

ii)
The half‐life of Co‐60 is 5 years.

The count‐rate of a sample of Co‐60 is 160 counts per minute.

Calculate the count‐rate of the Co‐60 after 10 years.


Count‐rate = ............................ counts per minute [3]

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2a2 marks

Atoms can absorb and emit electromagnetic radiation.

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

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

2 ....................................................................................................................
[2]

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2b2 marks
b)
Alpha radiation is not emitted in the processes in part (a).

Explain why.

[2]

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3a1 mark
a)
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 [1]

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3b9 marks
b)
This is a graph showing the radiation emitted from samples of three different isotopes A, B and C.

q23b-paper2-june2098-ocr-gcse-physics

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

[1]

Tick (✓) one box.
A square
B square
C square
ii)
Two scientists discuss the isotopes in the graph.

Scientist 1 Scientist 2

‘I think isotope A is more hazardous than
B.

A has a higher activity than B.’

‘I think isotope B is more hazardous than
A.

B has a longer half-life than A.’

 

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]

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3c4 marks
c)
This is a diagram to show a nuclear fusion reaction:

q23c-paper2-june2098-ocr-gcse-physics

i)
Explain why this is nuclear fusion.

[1]

ii)
It is difficult for nuclear fusion reactions to occur on Earth.

Explain why nuclear fusion reactions occur in the Sun.

[2]

iii)
What will happen to our Sun when it runs out of hydrogen?

[1]

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3d1 mark
d)
Some scientists say nuclear fission is renewable. Other scientists say it is non-renewable.

Suggest why the scientists disagree.

[1]

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4a2 marks

A teacher measures the activity of different radioactive isotopes.

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

fig-23-1-paper4-june2098-ocr-gcse-physics

Fig. 23.1

a)
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 [2]

How did you do?

4b2 marks
b)
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.

Time (minutes) Activity (counts per minute)
0  
10  
20 84
30 64
40 52
50 40
60 32
70 25
80 20
90 16

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 [2]

How did you do?

4c2 marks
c)
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-paper4-june2098-ocr-gcse-physics

Fig. 23.2

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

Conclusion 1:

I think the results are very inaccurate.
The isotope stops being radioactive and then gets more radioactive again.
Conclusion 2: I do not think the isotope has a half-life.

Is the student correct?

Evaluate each conclusion and explain your answer.

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

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

[2]

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5a1 mark

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.

q17-paper2-june2018-ocr-gcse-physics

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

1 .............................................................................................................................
2 ............................................................................................................................. 

[2]

How did you do?

5b6 marks
b)
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.

Source Count rate using different barriers
Paper Aluminium Lead No barrier
A 113 112 22 112
B 20 21 20 182
C 162 23 21 164
D 282 78 24 280

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]

How did you do?

5c2 marks
c)
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. ............................................................................................................................

[2]

How did you do?

5d2 marks
d)
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.
[2]

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1a2 marks

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.

q24-paper4-specimen-ocr-gcse-physics

The table shows the results.

Distance between source and detector (cm)

 Count rate
(counts per minute)
10 1024
20 256
40 64
80 16

a)
Describe, using these results, how the count rate changes as the detector is moved away from the source.
[2]

How did you do?

1b3 marks
b)
The student takes two further readings at 160 and 320 cm.

He adds these further readings to his table.

Distance between source and detector (cm)

 Count rate
(counts per minute)
10 1024
20 256
40 64
80 16
160 6
320 0

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.
[3]

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2a2 marks

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

a)
This is the symbol for americium-241:

begin mathsize 26px style Am presubscript 95 presuperscript 241 end style

Describe the structure of an americium-241 nucleus.
[2]

How did you do?

2b3 marks
b)
Americium-241 decays by emitting alpha radiation to form neptunium (Np).

Complete the balanced symbol equation for the decay.
q20b-paper4-oct-nov2020-ocr-gcse-physics
[3]

How did you do?

2c1 mark
c)
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.

[1]

How did you do?

2d4 marks
d)
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.

Source Half-life (years) Radiation emitted
Americium-241 (Am-241) 432 Alpha
Thorium-228 (Th-228) 2 Alpha


Both sources start with the same number of radioactive nuclei.

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

 [2]

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