Unit 12 Problems Solution

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

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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.