A-Level AQA Physics Magnetic Fields: Figure 1 shows a sealed radioact

Question

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

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

2. A sealed source contains radium-226 ($^{226}	ext{Ra}$). The sealed source emits $\alpha$ and $\beta$ particles to produce $^{206}	ext{Pb}$ which is stable.

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

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

4. Identify which of the nuclei A to M are common to all the possible ways that $^{226}	ext{Ra}$ decays into $^{206}	ext{Pb}$.

5. The sealed source emits $\gamma$ radiation in addition to $\alpha$ and $\beta$ particles. A student uses the sealed source to investigate the inverse-square law for $\gamma$ radiation. The student begins by making measurements to find the count rate $A_b$ for background radiation.

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

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

The sealed source emits:
- $\alpha$ particles with energy $E_{\alpha}$ between 3.8 MeV and 7 MeV
- $\beta$ particles with energy $E_{\beta}$ between zero and 5.5 MeV.

Figure 4 shows how the energy $E_k$ of $\beta$ particles in aluminium depends on their range.

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

Ionisation takes place inside the detector. The effective distance travelled by $\gamma$ radiation from the source is $(d + \epsilon)$, where $\epsilon$ is the thickness of a lead (cast) casing behind the detector.

From the inverse-square law for $\gamma$ radiation, it can be shown that:

$$A = \dfrac{A_b}{\sqrt{d + \epsilon}}$$

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

The student plots the graph of $d$ against $\sqrt{\dfrac{1}{A}}$ shown in Figure 6.

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

Determine $\epsilon$ 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 $^{226}\text{Ra}$ decays into $^{206}\text{Pb}$.

State and explain procedures to eliminate systematic error in the measurements used to find $A_b$.

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 $\epsilon$ using Figure 6.

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