Radioactive Emissions (OCR Gateway GCSE Physics)

Exam Questions

1 hour22 questions

1a3 marks

Some isotopes of cobalt are radioactive.

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

${}_{27}^{60}{Co}$

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

${}_{27}^{57}{Co}$

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

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

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

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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1d5 marks

A radioactive isotope can be used as a tracer in a patient’s body. It is monitored by a radiation detector outside the body.

Four possible radioactive isotopes are shown in Table 18.2.

Radioactive isotope	Type of radiation emitted	Half-life
Radon‐222	Alpha	4 days
Iodine‐131	Gamma	8 days
Cobalt‐60	Gamma	5 years
Plutonium‐238	Alpha	88 years

Table 18.2

Doctors wear a lead apron when they use radioactive isotopes.

Explain why.

[2]

ii)

Which radioactive isotope from Table 18.2 is best to use as a radioactive tracer in a patient’s body?

Tick (✓) one box.

Radon-222	$□$
Iodine-131	$□$
Cobalt-60	$□$
Plutonium-238	$□$

Explain your answer.

[3]

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3a1 mark

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

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3b9 marks

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

q23b-paper2-june2098-ocr-gcse-physics

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

[1]

Tick (✓) one box.

A	$□$
B	$□$
C	$□$

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]

How did you do?

3c4 marks

This is a diagram to show a nuclear fusion reaction:

q23c-paper2-june2098-ocr-gcse-physics

Explain why this is nuclear fusion.

[1]

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]

How did you do?

3d1 mark

Some scientists say nuclear fission is renewable. Other scientists say it is non-renewable.

Suggest why the scientists disagree.

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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

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

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

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

How did you do?

5b6 marks

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
Source	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.

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]

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5c2 marks

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. .................................................................................................................

How did you do?

5d2 marks

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.

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2a2 marks

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

This is the symbol for americium-241:

{}_{95}^{241}{Am}

Describe the structure of an americium-241 nucleus.

[2]

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2b3 marks

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

q20b-paper4-oct-nov2020-ocr-gcse-physics

[3]

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2c1 mark

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

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

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]

How did you do?

2e2 marks

Read the information below about smoke detectors.

In smoke detectors, fine particles of americium-241 are rolled into a metallic foil. The americium-241 cannot be inhaled or move around.

The amount of radiation emitted is very small compared with the natural radioactivity in 1 m³of soil.

Americium-241 also emits a small amount of gamma rays.

A scientist says, ‘There is no risk from the disposal of smoke detectors in household waste.’

Do you agree with this statement? Give two reasons for your answer.

Yes	$□$
No	$□$

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

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

[2]

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

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.

Distance between source and detector (cm)	Count rate (counts per minute)
10	1024
20	256
40	64
80	16
160	6
320	0