A-Level AQA Physics Classification of Particles: Figure 1 shows a sealed radioact

Question

Figure 1 shows a sealed radioactive source used in schools and colleges.

1.1 State two safety procedures to reduce risk when using this type of source.

1.2 A sealed source contains radium-226 (226Ra).
226Ra decays by emitting α and β- particles to produce 206Pb which is stable.

Figure 2 is a graph of neutron number N against proton number Z, showing the different ways that 226Ra can decay into 206Pb.

Points A to M represent all the unstable nuclei that may be formed as 226Ra decays into 206Pb.

1.3 Determine the number of routes by which B can change into K.

1.4 Identify which of the nuclei A to M are common to all the possible ways that 226Ra decays into 206Pb.

1.5 The sealed source emits γ radiation in addition to α and β particles.
A student uses the sealed source to investigate the inverse-square law for γ radiation.
The student begins by making measurements to find the count rate A0 for background radiation.

State and explain procedures to eliminate systematic error in the measurements used to find A0, to reduce the percentage uncertainty in A0.

1.6 Figure 3 shows an aluminium absorber placed between the sealed source and a radiation detector.
This is to make sure that only γ radiation from the source reaches the detector.

The sealed source emits:
α particles with energy Eα between 3.8 MeV and 7.8 MeV
β particles with energy Eβ between zero and 5.5 MeV.

Figure 4 shows how the range of β particles in aluminium depends on Eβ.

Deduce the minimum thickness of the aluminium absorber that should be used in the experiment.

1.7 Ionisation takes place inside the detector. The effective distance travelled by γ radiation from the source is (d + ε).
The distance ε, shown in Figure 5, cannot be measured directly.

Figure 5

From the inverse-square law for γ radiation, it can be shown that:
A is the count rate, corrected for background radiation k is a constant.

The student plots the graph of d / A against 1 / A0.5 shown in Figure 6.

1.8 Deduce ε using Figure 6.
Explain your reasoning.
Give a suitable unit for your result.

Figure 1 shows a sealed radioactive source used in schools and colleges - AQA - A-Level Physics - Question 1 - 2019 - Paper 3

Worked Solution & Example Answer:Figure 1 shows a sealed radioactive source used in schools and colleges - AQA - A-Level Physics - Question 1 - 2019 - Paper 3

1.1 State two safety procedures to reduce risk when using this type of source.

1.2 A sealed source contains radium-226 (226Ra). Determine the number of routes by which B can change into K.

1.3 Identify which of the nuclei A to M are common to all the possible ways that 226Ra decays into 206Pb.

1.4 State and explain procedures to eliminate systematic error in the measurements used to find A0.

1.5 Deduce the minimum thickness of the aluminium absorber that should be used in the experiment.

1.6 Deduce ε using Figure 6. Explain your reasoning. Give a suitable unit for your result.

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