(These questions need rewriting!)

1. For 140 keV gamma-rays the mass attenuation coefficients for hydrogen and oxygen are 0.26 and 0.14 cm2/g respectively. What is the mean free path in water at this energy:

3.85 cm
4.55 cm
7.14 cm

 2. Consider the graph of absorption vs energy for three types of absorber material. If the initial energy was 10 MeV, what thickness  would the three absorbers have to be to decrease the intensity by half, given that no buildup occurs and hence all gamma-rays leaving the absorber are detected: 0.01 cm,   0.46 cm,  1.52 cm 1.50 cm,   6.32 cm,  9.92 cm 0.81 cm,   2.50 cm,  6.93 cm No, this is not correct. No, this is not correct. Yes, this is correct.

3. Using the graph above, what will be the energy remaining in an initial beam of 5 MeV gamma-rays after passing through 1.0 cm of copper:

0.5 MeV
3.52 MeV
5.0 MeV

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