1. Describe the relationship between scatter and beam energy. Discuss how the different types of photon interactions govern this relationship.
2. You expose a patient phantom with x-rays and perform a preliminary measurement of the scatter onto the image receptor. The measurement that includes the transmitted beam and scatter yields 10,000 photons in 1 second. Covering off the scatter and measuring only the transmitted beam, you obtain 9,500 photons in 1 second. How large is the error of the scatter portion based on these measurements? You would like to increase your confidence in the scatter portion of the measurement and obtain this value with a precision of 3%. How long do you need to measure the beam with scatter and the beam without scatter, assuming that you will allocate equal measurement time for each?
3. Derivation of the equation you used to calculate the linear attenuation coefficient of the penny material. Be sure to clearly define your variables.
4. You have two 1 cm attenuating plates (Al and Cu), but you don't know which one's which, so you use your handy-dandy x-ray machine to figure it out.
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Aluminum (cm2/g)
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Copper (cm2/g)
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(μ/ρ) 5kev
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1.93E+02
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1.90E+02
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(μ /ρ) 80kev
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2.02E-01
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7.63E-01
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You measure the density of the two plates as (and as trivial as it is, pretend you don't have Google or a chemistry book to tell you the density of aluminum and copper):
ρ1 =3.0 g/cm3
ρ2 =9.0 g/cm3
Exp A: Set voltage to 10 kVp and measure at 5 keV:
ln(I/Io) 1= -5.15 x 102
ln(I/Io) 2= -1.71 x 103
Exp B: Set voltage to 110 kVp and measure at 80 keV:
ln(I/Io)1 = -0.55
ln(I/Io)2 = -6.85
Was first test set-up sufficient for differentiating plates? If not, show that test 2 is better.