Radioactive Emissions (OCR Gateway GCSE Physics)

Topic Questions

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

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

[2]

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1b3 marks

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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1c4 marks

Gamma radiation is used to irradiate cancers in the brain.

Treatment is given for 15 minutes every 4 days.

Each patient receives a certain dose of radiation. q24c-paper4-specimen-ocr-gcse-physics

Explain how this treatment reduces damage to healthy cells.

[4]

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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]

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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]

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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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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]

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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]

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

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

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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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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.

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