A-LevelPhysicsMedical physics9702/41 · Oct/Nov 2021 · Q117 Marks
State, for an X-ray image, what is meant by: sharpness
- (a)(i)State, for an X-ray image, what is meant by: sharpness[1]
- (a)(ii)contrast.[1]
- (b)A parallel X-ray beam passes through a thickness of 2.3 cm of soft body tissue. The intensity of the emerging beam is 12% of the intensity of the incident beam. Calculate the linear attenuation (absorption) coefficient μ of the soft body tissue. Give a unit with your answer.[3]
- (c)In medical diagnosis, X-rays may be used to produce a single X-ray image or may be used in computed tomography (CT scanning). Suggest an advantage and a disadvantage of CT scanning compared with single X-ray imaging for diagnosis.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.
- [B1] ease with which edges can be distinguished
- [B1] difference in degrees of blackening
- [C1] I = I₀ exp (-μx)
- [C1] 0.12 = exp (-μ× 2.3)
- [A1] μ = 0.92 cm⁻¹
- [B1] advantage: produces 3-dimensional image
- [B1] disadvantage: (much) greater exposure to radiation
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