1. 1
   A domestic smoke alarm contains a small sealed source of americium-241 mounted a few millimetres from two metal electrodes inside a small ionisation chamber. In normal operation, radiation from the source ionises the air between the electrodes, allowing a tiny, steady electric current to flow. The alarm circuit continuously monitors this current.

   (a)

   Which type of nuclear radiation is used in this kind of smoke alarm?

   [1 mark]

   • AAlpha radiation
   • BBeta radiation
   • CGamma radiation
   • DNeutron radiation

   (b)

   When smoke enters the ionisation chamber described above, the smoke particles absorb some of the radiation before it can ionise the air. What happens to the current between the electrodes, and how does this trigger the alarm?

   [1 mark]

   • AThe current stops completely and instantly, which is what sounds the alarm in every case
   • BThe current increases, and the circuit detects this rise and sounds the alarm
   • CThe current stays the same, but the voltage across the chamber increases and sounds the alarm
   • DThe current decreases, and the circuit detects this drop and sounds the alarm

   (c)

   Even in a house with no smoke alarm fitted, people are constantly exposed to a low level of background radiation. State two different sources of background radiation and briefly describe where each one comes from.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hospital operates a PET scanner to produce detailed images of a patient's brain activity. A radioactive tracer is injected into the patient's bloodstream a short time before the scan begins. The tracer isotope is manufactured on-site, at a small cyclotron inside the hospital, only shortly before each patient's appointment.

   (a)

   A hospital uses a PET (positron emission tomography) scanner to image a patient's brain. A radioactive tracer that emits positrons is injected into the patient shortly before the scan, and the tracer is manufactured at a cyclotron located inside the hospital building itself, rather than being delivered from a distant factory. Why must the tracer be produced so close to where it is used?

   [1 mark]

   • AThe tracer must be kept below room temperature or it stops being radioactive
   • BThe tracer emits alpha radiation, which cannot travel through the walls of a transport container
   • CThe tracer has a very short half-life, so its activity would fall too low before it could be transported and used
   • DHospitals are not permitted by law to transport any radioactive materials by road

   (b)

   Inside the patient's body, the tracer emits positrons. Each positron almost immediately collides with a nearby electron, and the pair annihilate, converting their mass into radiation that travels out of the body and is detected by sensors surrounding the patient. What type of radiation is detected by the PET scanner's sensors?

   [1 mark]

   • AAlpha radiation
   • BGamma radiation
   • CBeta-minus radiation
   • DNeutron radiation

   (c)

   Explain why choosing a tracer isotope with a short half-life is beneficial both for producing a clear scan image and for the patient's safety.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A food processing factory irradiates fresh strawberries with gamma radiation from a heavily shielded source, in order to kill bacteria and extend shelf life; the strawberries pass close to the source on a conveyor belt but never touch it directly, and leave the factory carrying no radioactive material of their own. In a separate incident at a research laboratory, a technician is accidentally exposed when radioactive dust from an open sample container settles on his hands and clothing.

   (a)

   Explain the difference between irradiation and contamination, using these two situations to illustrate your answer, and explain why contamination is generally the more hazardous of the two in the longer term.

   [3 marks]

   (b)

   Describe four precautions that should be used to protect the workers who operate the gamma irradiation equipment at the strawberry factory from receiving a harmful radiation dose.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital is treating two patients. The first patient has an overactive thyroid gland and will be given a drink containing a radioactive iodine isotope, which is naturally absorbed and concentrated by the thyroid tissue (an internal treatment). The second patient has a tumour deep inside a different organ, which the medical team plans to treat using repeated sessions of an external beam of gamma radiation aimed at the tumour from a machine outside the body.

   (a)

   A patient has been diagnosed with an overactive thyroid gland and, separately, a patient in the same hospital has a tumour in a different organ that cannot be reached easily by swallowing or injecting a substance. The medical team treating the thyroid patient plans to give her a drink containing a radioactive iodine isotope, which becomes concentrated in the thyroid gland (internal/sealed-source-free treatment). The medical team treating the second patient instead plans to aim a external beam of gamma radiation from a machine outside the body directly at the tumour on repeated visits. Compare and contrast these two treatment approaches, explaining at least two advantages and two disadvantages of each method.

   [6 marks]

   (b)

   The isotope chosen for the thyroid patient's internal treatment has a half-life of about eight days, whereas an isotope with a half-life of many years would not be considered safe for this use. Explain how the half-life of a radioactive isotope affects how dangerous it is to use for treatment inside the body, and describe the precautions that must still be taken by medical staff and family members while the thyroid patient's body remains radioactive.

   [6 marks]

   Total for question 4: 12 marks

End of questions