| Date | May 2016 | Marks available | 2 | Reference code | 16M.3.HL.TZ0.15 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 0 |
| Command term | Discuss | Question number | 15 | Adapted from | N/A |
Question
In medical imaging, X-rays can be passed through aluminium before reaching the body. The graph shows the variation of the linear absorption coefficient of aluminium for different photon energies.
X-rays are incident on an aluminium sheet of thickness 8.0 cm. Calculate the fraction of the incident X-ray intensity that emerges from this sheet for photon energies of
(i) 9.0 MeV.
(ii) 3.0×10−3 MeV.
With reference to your answers to (a)(i) and (a)(ii), discuss the advantages of using the aluminium sheet.
Markscheme
(i) \(\mu = 2.7 \times {10^{ - 3}}\left( { \pm 0.3 \times {{10}^{ - 3}}} \right)\)
So \(\frac{I}{{{I_{\rm{O}}}}} = \ll {e^{ - \mu x}} = {e^{ - \left( {2.7 \times {{10}^{ - 3}} \times 8 \times {{10}^{ - 2}}} \right)}} \gg = 0.9999 \approx 1.0\)
(ii) \( \ll \mu = 50{\rm{to give}} \gg \frac{I}{{{I_{\rm{O}}}}} = 1.8 \times {10^{ - 2}}\)
low energy radiation removed but not high energy radiation
radiation has narrower range of energies
only necessary radiation reaches the patient making it safer
