PHYS 3330 Module 6 Self Assessment Practice Problems

Module 6 Self Assessment Practice Problems

6.1
A beam of photons has a linear attenuation coefficient of 0.03 cm^-1. Calculate the fraction transmitted through layers of material 5 mm, 1.5 cm, and 20 cm thick.
Answer: 0.985, 0.956, 0.549

6.2
The linear attenuation coefficient for 2.0-MeV gamma rays in a solid material is 0.23 cm^-1. If the intensity of a beam of 2.0-MeV gamma rays is 1500 photons/s•cm² at the surface of the solid material, what will its intensity be after passing through 3.0 cm of the material?
Answer: 752 photons/s•cm²

6.3
The mass attenuation coefficient for an x-ray beam 0.003 m²/kg and the material has density of 3000 kg/m³. Calculate the percentage transmitted through layers of 1 mm, 0.5 cm, and 5 cm thickness.
Answer: 0.991, 0.956, 0.638

6.4
Find the HVL of 100 keV photons in aluminum, copper, lead, and water.
Answer: 1.507 cm, 0.169 cm, 0.011 cm, 4.061 cm

6.5
A linear accelerator (LINAC) produces a spectrum of radiation with photons from 0 to 24 MeV. Assuming this is equivalent to photons at 8 MeV, find the thickness of lead required to reduce the intensity by a factor of 12 million.
Answer: 30.7 cm

6.6
What thickness of water would cause the intensity of a 0.25-MeV x-ray beam to be reduced by a factor of 10?
Answer: 16.8 cm

6.7
You are building an x-ray facility that produces x-rays with a maximum energy of 150 keV. You need to install lead shielding on the walls to reduce the intensity of x-rays passing through the walls. What would be the transmitted fraction of 150-keV x-rays if you lined the walls with a sheet of lead that was 3.0-mm thick? Would you expect lower energy x-rays to be attenuated more or less than the 150-keV x-rays? Explain.
Answer: 0.001

6.7

You are building an x-ray facility that produces x-rays with a maximum energy of 150 keV. You need to install lead shielding on the walls to reduce the intensity of x-rays passing through the walls. What would be the transmitted fraction of 150-keV x-rays if you lined the walls with a sheet of lead that was 3.0-mm thick? Would you expect lower energy x-rays to be attenuated more or less than the 150-keV x-rays? Explain.

Answer: 0.001

6.8
5 mm of aluminum (𝜌 = 2.7 g/cm³) transmits 30% of a beam of 30 keV photons. What is the mass attenuation coefficient of aluminum for these photons?
Answer: 0.891 cm²/g

6.9
A linear attenuation coefficient of 0.001 cm−1 means that 0.1% of the photons in the beam are attenuated per cm of absorber. Does this mean that 1000 cm of absorber will attenuate all the photons in the beam? How do you justify your answer?
Answer:

6.10
What would have to occur for the homogeneity coefficient to be greater than unity? Under what circumstances might this be possible?
Answer: