  Q13. The bar chart below shows the total radiation dose that the average person in the UK gets from natural background radiation sources in one year. (a)

(i) Calculate the percentage of the total radiation dose the average person in the UK receives from cosmic rays.

[2 marks]

(ii) Over one year, a person may get a higher than average dose of radiation from cosmic rays. Suggest one reason why.

[1 mark]

[1 mark]

(b) The diagram shows the apparatus a teacher used to investigate the radiation emitted by a source. (i) Before using the radioactive source the teacher measured the background radiation in her laboratory. She did this three times. The measurements were taken correctly but all three measurements were different.

Why were the three background measurements different?

[1 mark]

(ii) Here are the results of her experiment

 Thickness of aluminium / mm Counts in one minute 2 350 4 68 6 20

The teacher changed the thickness of the aluminium between the source and the Geiger-Müller (GM) tube and recorded number of counts for each thickness.

The mean background measurement was 20 counts in one minute.

A student concluded that the radioactive source emits beta radiation. Explain how the results support this conclusion.

[2 marks]

(iii) The teacher said that the source also emits alpha radiation. Describe how the investigation could be changed in order to show that the source emits alpha radiation.

[2 marks]

(Total 9 marks) 