'A' Level Medical Option Questions - X-Rays
Q2.
![](dIAGRAM2ANS.png)
(a) The diagram shows a rotating-anode X-ray tube. Complete the labelling of the three numbered arrows in the diagram.
See diagram ![](../../../../graphics/symbols/nuclides/ticksmall.png)
![](../../../../graphics/symbols/nuclides/ticksmall.png)
![](../../../../graphics/symbols/nuclides/ticksmall.png)
(3 marks)
(b) Explain why the anode
(i) is rotated,
The anode is rotated so that the heat produced is spread over a greater volume/area/section
This allows more energetic X-rays to be produced [or allows X-rays to be generated for longer]
without risk of melting the anode.
(ii) has a bevelled edge.
The bevelled edge gives larger target area for the electrons![](../../../../graphics/symbols/nuclides/ticksmall.png)
but a smaller source area from which the X-rays are produced.
This gives a sharper image beam of X-rays and produces a sharper image.
(3 marks)
(c) Define for a material,
(i) the linear attenuation coefficient, ![](../../../../graphics/symbols/mu.gif)
The linear attenuation coefficient,
is the fraction of X-rays removed per unit thickness of the material. ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(ii) the half-value thickness.
The thickness of the material which will reduce the intensity to half its original level for a specified energy of the X-rays ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(2 marks)
(d) A monochromatic X-ray beam of intensity 6.0 W m–2 is incident on an aluminium sheet of thickness 2.0 mm. For these X-rays, the half-value thickness of aluminium is 3.2 mm. Calculate the intensity of the transmitted beam.
= ln2/3.2
= 0.217 mm-1 ![](../../../../graphics/symbols/nuclides/ticksmall.png)
I = Io e-
x
I = 6.0 x e-0.217x 2 ![](../../../../graphics/symbols/nuclides/ticksmall.png)
intensity = 3.9 W m-2 ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(3 marks)
(Total 11 marks)