1. 1
   A science technician sets up a sealed sample of the unstable isotope radon-220 gas in a laboratory. A Geiger–Müller tube connected to a counter is placed close to the sample to detect emissions. The technician records that the count rate is high at the start of the investigation and decreases steadily as time passes. The isotope is known to decay by emitting alpha particles.

   (a)

   Which of these best describes the alpha particle emitted by the radon-220 sample?

   [1 mark]

   • AA high-energy electron ejected from the nucleus
   • BTwo protons and two neutrons bound together, equivalent to a helium nucleus
   • CA packet of electromagnetic radiation with no mass or charge
   • DA free neutron ejected from an unstable nucleus

   (b)

   Which statement correctly describes the penetrating power of the alpha radiation emitted by the radon-220 sample?

   [1 mark]

   • AIt can pass through several centimetres of lead
   • BIt can travel several metres through air before being absorbed
   • CIt is stopped by a few centimetres of air or a thin sheet of paper
   • DIt can only be stopped by a thick sheet of lead or several metres of concrete

   (c)

   The technician notices that the count rate detected by the Geiger–Müller tube falls steadily as time passes, even though no undecayed nuclei are added to or removed from the sample. Explain, in terms of the random nature of radioactive decay, why the count rate decreases over time.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hospital physicist is using a radioactive tracer to diagnose a patient with a PET scanner. The tracer nuclide decays by beta-plus (positron) emission. Meanwhile, in a research laboratory, a different unstable nuclide decays by beta-minus emission, in which a neutron inside the nucleus changes into a proton and an electron.

   (a)

   In the research laboratory, the unstable nuclide decays by beta-minus (β−) emission. What happens to the proton (atomic) number of the nucleus as a result of this decay?

   [1 mark]

   • AIt increases by 1
   • BIt stays the same
   • CIt decreases by 1
   • DIt decreases by 2

   (b)

   The tracer used in the hospital's PET scanner decays by beta-plus (β+) emission. What happens to the proton (atomic) number of the tracer nucleus as a result of this decay?

   [1 mark]

   • AIt increases by 1
   • BIt stays the same
   • CIt decreases by 2
   • DIt decreases by 1

   (c)

   Describe, in terms of the particles inside the nucleus, what happens during beta-minus (β−) decay.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A sample of thorium-232 is monitored in a laboratory. A second, short-lived radioactive sample is also being studied: its activity is measured as 800 Bq at the start of the investigation, and it has a known half-life of 8 hours.

   (a)

   A sample of thorium-232 (mass number 232, proton number 90) undergoes alpha decay to form a daughter nucleus. Write a balanced nuclear equation for this decay, stating the mass number and proton number of the daughter nucleus and identifying it, given that a proton number of 88 corresponds to the element radium (Ra).

   [3 marks]

   (b)

   The second, short-lived sample has an activity of 800 Bq at the start of the investigation and a half-life of 8 hours. Calculate the activity of this sample after 24 hours have passed. Show your working.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A national energy company is considering building a new nuclear fission power station to replace an ageing coal power station. Local residents have raised concerns about safety, radioactive waste disposal and public perception, while the company highlights the reduced carbon dioxide emissions of nuclear power compared with burning coal.

   (a)

   Evaluate the advantages and disadvantages of the energy company's proposal to replace the coal power station with a nuclear fission power station, referring to carbon dioxide emissions, safety, radioactive waste disposal and public perception.

   [6 marks]

   (b)

   Explain how ionising radiation released from radioactive waste could damage human tissue and cause mutations, and describe the precautions that should be taken to protect medical personnel and members of the public who may be exposed to radiation from the waste.

   [6 marks]

   Total for question 4: 12 marks

End of questions