1. 1
   A geologist is carrying out a radiation survey across several field sites as part of research into local rock formations, and needs to distinguish background radiation readings from any additional radiation coming from a specific rock sample.

   (a)

   A geologist takes a Geiger-Muller counter reading in an open field, away from any known radioactive sources, and records a small but non-zero count rate. What is the most likely explanation for this reading?

   [1 mark]

   • AA fault in the Geiger-Muller tube that always gives a positive reading
   • BBackground radiation from sources such as rocks, soil and cosmic rays
   • CRadiation leaking from a nearby hospital
   • DRadiation created by the detector itself with no external source

   (b)

   The geologist finds that a granite rock sample she is examining gives a count rate noticeably higher than the background reading, and that this count rate is decreasing over several weeks. What does this decrease in count rate over time indicate about the radioactive isotopes in the sample?

   [1 mark]

   • AThe Geiger-Muller tube is wearing out and detecting less radiation
   • BThe isotopes are becoming more radioactive as time passes
   • CThe activity of the isotopes is decreasing as unstable nuclei decay over time
   • DThe rock sample is absorbing radiation from the surrounding air

   (c)

   Explain what is meant by the term 'half-life' of a radioactive isotope, and state why different isotopes found in rock samples have different half-lives.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hospital's nuclear medicine department is using a short-lived radioactive tracer, injected into a patient, to obtain diagnostic images of internal organs, and doctors must carefully consider the timing of the scan and the safety of both patient and staff.

   (a)

   A hospital uses a radioactive tracer with a half-life of 6 hours to carry out a diagnostic scan on a patient. If the initial activity injected is 80 MBq, what will the activity be after 18 hours?

   [1 mark]

   • A10 MBq
   • B20 MBq
   • C40 MBq
   • D60 MBq

   (b)

   A radiographer who prepares and injects the tracer stands close to the radioactive source many times each working day. Which of these is a correct description of the difference between contamination and irradiation in this context?

   [1 mark]

   • AContamination is exposure to background radiation, while irradiation is exposure to a hospital source
   • BContamination and irradiation both mean radioactive material has entered the body
   • CIrradiation only occurs with alpha sources, while contamination only occurs with gamma sources
   • DContamination is radioactive material getting onto or into a person or object, while irradiation is exposure to radiation from a source without the material being present on the person

   (c)

   Explain why a tracer with a short half-life, rather than a long half-life, is chosen for this diagnostic medical procedure, and describe one danger to the radiographer from repeated exposure to ionising radiation.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An industrial engineer at a metal processing plant is responsible for maintaining consistent thickness in rolled aluminium sheeting, using a radioactive source and detector system, and must also manage the radioactive waste this process eventually produces.

   (a)

   An industrial engineer uses a radioactive source to check the thickness of aluminium sheeting as it passes continuously between the source and a detector on a production line. Describe how this thickness-gauging system works, including how the detector's reading is used to control the rollers producing the sheet.

   [3 marks]

   (b)

   Explain why a beta source, rather than an alpha or gamma source, is normally chosen for this thickness gauge when measuring aluminium sheet of a few millimetres thickness, and describe how the associated radioactive waste from decommissioned sources should be managed to reduce risk.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A regulatory body is reviewing safety guidance for a university research laboratory that stores several sealed radioactive sources with widely differing half-lives, used for equipment calibration and undergraduate teaching demonstrations.

   (a)

   A regulatory body is reviewing safety guidance for a research laboratory that stores several sealed radioactive sources with different half-lives, ranging from a few hours to many thousands of years, used for calibration and teaching purposes. Explain the sources of background radiation that staff in the laboratory are exposed to even without handling the sealed sources.

   [6 marks]

   (b)

   Discuss how the half-life of each stored source affects how it should be stored, monitored and eventually disposed of, comparing a source with a half-life of thousands of years to one with a half-life of only a few hours.

   [6 marks]

   Total for question 4: 12 marks

End of questions