GCSE Questions: Medical Physics

- scanning and therapy


(a) A radiation detector and counter were used to detect and measure the radiation emitted from a weak source. The graph shows how the number of counts recorded in one minute changed with time.

(i) Even though the readings from the counter were accurately recorded, not all the points fit the smooth curve.

What does this tell us about the process of radioactive decay?

(1 mark)

(ii) After ten minutes the number of counts recorded each minute is almost constant.

Explain why.

(2 marks)

(b) The radioactive isotope sodium-24 injected into the bloodstream can be used to trace blood flow to the heart. Sodium-24 emits both beta particles and gamma rays.

(i) What is a beta particle?

(1 mark)

(ii) What is a gamma ray?

(1 mark)

(iii) The count rate from a solution containing sodium-24 decreases from 584 counts per minute to 73 counts per minute in 45 hours.

Calculate the half-life of sodium-24.

Show clearly how you work out your answer.

(3 marks)

(iv) Give one advantage of using sodium-24 to trace blood flow compared to using an isotope with a half-life of:

[A] ten years

(1 mark)

[B] ten seconds

(1 mark)

(Total 10 marks)