A-Level AQA Physics Alpha, Beta & Gamma Radiation: 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 and 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 E₁ between 3.8 MeV and 7.8 MeV
- β particles with energy E₂ between zero and 5.5 MeV.

Figure 4 shows how the range of β particles in aluminium depends on E₁.

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 + e). The distance e, shown in Figure 5, cannot be measured directly.

From the inverse-square law for γ radiation, it can be shown that

A = k rac {A₀}{d + e} = k rac {A₀}{	ext{constant}}

where A is the count rate, corrected for background radiation k is a constant.

The student plots the graph of d against rac {1}{	ext{A}} shown in Figure 6.

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

1.8 Determine e using Figure 6.

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

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

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

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

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

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

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

Determine e using Figure 6.

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