| Date | May 2015 | Marks available | 3 | Reference code | 15M.3.HL.TZ1.20 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 20 | Adapted from | N/A |
Question
This question is about X-rays.
Two parallel beams of monochromatic X-rays of the same intensity are incident on equal thicknesses of bone and fat in a patient.
The attenuation coefficient for fat is 180m−1 and the attenuation coefficient for bone is 345m−1. The thickness of both materials is 0.0150m.
Calculate \(\frac{{{I_b}}}{{{I_f}}}\) where \({I_b}\) is the intensity of the beam leaving the bone and \({I_f}\) is the intensity of the beam leaving the fat.
Explain how fluorescent emitters are used to enhance the image formed on a photographic X-ray plate.
Markscheme
\(\frac{{{I_b}}}{{{I_f}}} = \frac{{{e^{ - {\mu _b}x}}}}{{{e^{ - {\mu _f}x}}}}\);
=e-0.0150×165;
0.0842;
Award [3] for a bald correct answer.
fluorescent emitters are placed each side of the photographic plate;
X-rays cause emission of (visible) light from the fluorescent material that causes (additional) plate exposure;
better contrast because many X-rays pass through plate without interaction / photographic plate is more sensitive to visible light than to X-rays;
