Q11.

(a) A teacher used a Geiger-Muller tube and counter to measure the number of counts in 60 seconds for a radioactive rock.

The counter recorded 819 counts in 60 seconds.

The background radiation count rate was 0.30 counts per second.

Calculate the count rate for the rock in counts per second.

[3 marks]

(b) A householder is worried about the radiation emitted by the granite worktop in his kitchen.

1 kg of granite has an activity of 1250 Bq.

The kitchen worktop has a mass of 180 kg.

Calculate the activity of the kitchen worktop in Bq.

[2 marks]

The average total radiation dose per year in the UK is 2.0 millisieverts.

The table below shows the effects of radiation dose on the human body.

 Radiation dose in millisieverts per year Effects 10 000 Immediate illness; death within a few weeks 1000 Radiation sickness; unlikely to cause death 100 Lowest dose with evidence of causing cancer

The average radiation dose from the granite worktop is 0.003 millisieverts per day.

Explain why the householder should not be concerned about his yearly radiation dose from the granite worktop. (One year is 365 days).

[2 marks]

(c) Bananas are a source of background radiation.

Some people think that the unit of radiation dose should be changed from 'sieverts' to 'Banana Equivalent Dose'.

Suggest one reason why the Banana Equivalent Dose may help the public be more aware of radiation risks.

[1 mark]

[Total: 8 marks]