MYP Physics · 17 · extended response
Select an isotope for diagnostic imaging
Atomic and nuclear physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 8
- Topics
- 2
- Answer
- Complete
A hospital needs a tracer that can be detected outside the body during a scan completed within two hours. Consider the simplified candidates below.
| Isotope | Main radiation | Half-life | Other information |
|---|---|---|---|
| P | gamma | 6 h | available from a nearby supplier |
| Q | gamma | 8 d | easy to store |
| R | alpha | 3 min | strongly ionising over a short range |
- a
Select Select the most suitable isotope and justify your choice using two properties.
3 marks - b
Explain Explain why isotope R is unsuitable even though its half-life is short.
2 marks - c
Evaluate Evaluate two practical controls that should accompany the use of isotope P.
3 marks
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a
Select Select the most suitable isotope and justify your choice using two properties.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Selects isotope P as the most suitable tracer for the two-hour diagnostic scan.
- 2
Explains that gamma radiation can leave the body and be detected externally.
- 3
Explains that 6 h is long enough for preparation and scanning but much shorter than 8 d, reducing prolonged exposure and waste activity.
b
Explain Explain why isotope R is unsuitable even though its half-life is short.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Alpha radiation is poorly penetrating and is unlikely to escape the body for external imaging.
- 2
Its 3 min half-life may be too short for transport, preparation, administration, and the scan.
c
Evaluate Evaluate two practical controls that should accompany the use of isotope P.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Identifies a valid control such as minimising activity and time, maximising distance, shielding, secure handling, monitoring, or planned waste storage.
- 2
Explains how one named control reduces dose or prevents contamination.
- 3
Explains a second control or links decisions to patient benefit, staff exposure, and responsible waste management.
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