CC2404 Applied Physics and Instrumentation in Health Care Unit 12 Problems 1.
An x-ray tube has a tube voltage of 50 kV. Calculate the maximum frequency of the x-ray photons (in Hz) from this x-ray tube.
E = eV = 50000 ⋅1.6 ⋅10 −19 J = 8 ⋅10 −15 J
E 8.5 ×10 −15 f = = = 1.28 ×10 19 Hz −34 h 6.63 ×10
2. An x-ray tube has a tube voltage of 45 kV and the tube current is 40mA. The efficiency of the x-ray tube is 1%. a. Calculate the power of x-ray tube. P = IV = 45 kV × 40 mA = 1800 W
b. Calculate the power of x-ray beam. P = 1800 W × 0.01 = 18W
3. Explain why the mechanism of photoelectric effect is useful in the production of an xray imaging while Compton scatter is not useful for this purpose?
The attenuation coefficient is Z
3
dependent, so medium of different Z number will results in very different attenuation of x-ray. A good contrast can be created between tissues of different Z-numbers. Example of bone and soft tissue
For Compton scatter, the attenuation coefficient is independent of Z number, bone and soft tissue attenuated equally x-rays, so this mechanism does not contribute to the contrast between bone and soft tissue. 4.
Explain why Compton scatter is a preferable mechanism for x-ray therapy while not the photoelectric effect? In Compton scattering, attenuation is independent of the Z-number of the absorbing medium, so bone and soft tissue attenuate equally the x-ray. No preferable attenuation by bone
In photoelectric effect, bone has higher Z-number and will absorb more energy than surrounding tissue, so more damage is made to bone instead of cancerous cells.