ARRT Radiation Physics and Radiobiology 5 — Questions and Answers
Question 1: Auger electrons are emitted following which process?
- Beta-minus decay
- Pair production
- Electron capture or internal conversion (Correct answer)
- Compton scattering
Correct answer: Electron capture or internal conversion
Auger electrons are emitted when an inner-shell vacancy (created by electron capture or internal conversion) is filled and the released energy ejects an outer-shell electron instead of producing a characteristic x-ray.
Question 2: Which statement correctly describes the four R's of radiobiology?
- Repair, Redistribution, Repopulation, Reoxygenation (Correct answer)
- Resistance, Repair, Recovery, Redistribution
- Reoxygenation, Resistance, Repopulation, Response
- Redistribution, Resistance, Reaction, Repair
Correct answer: Repair, Redistribution, Repopulation, Reoxygenation
The four R's of radiobiology are Repair of sublethal damage, Redistribution of cells through the cell cycle, Repopulation of surviving cells, and Reoxygenation of hypoxic tumor cells.
Question 3: What is the primary purpose of added filtration in a diagnostic x-ray tube?
- To increase the maximum photon energy
- To remove low-energy photons that would only contribute dose without imaging benefit (Correct answer)
- To focus the x-ray beam toward the detector
- To reduce the tube current
Correct answer: To remove low-energy photons that would only contribute dose without imaging benefit
Added filtration absorbs low-energy photons that would be absorbed by the patient without contributing to the image, thereby reducing patient dose while maintaining image quality.
Question 4: Radioactive equilibrium in which the daughter's activity equals the parent's activity is called:
- Secular equilibrium (Correct answer)
- Transient equilibrium
- Dynamic equilibrium
- Isotopic equilibrium
Correct answer: Secular equilibrium
Secular equilibrium occurs when the parent's half-life is much longer than the daughter's, resulting in equal activities after many daughter half-lives have elapsed.
Question 5: The LD50/60 for humans exposed to whole-body radiation refers to:
- The dose lethal to 50% of an exposed population within 60 days (Correct answer)
- The dose causing 50% cell survival at 60 seconds
- The dose reducing tissue volume by 50% in 60 weeks
- The dose at which 60% of cells show DNA damage after 50 Gy
Correct answer: The dose lethal to 50% of an exposed population within 60 days
LD50/60 is the whole-body radiation dose that is lethal to 50% of an exposed population within 60 days, typically estimated at 3–4 Gy for humans without medical support.
Question 6: Which of the following best describes coherent (Rayleigh) scattering?
- The photon ejects an inner-shell electron and is absorbed
- The photon is scattered with no energy loss or ionization (Correct answer)
- The photon creates an electron-positron pair
- The photon transfers partial energy to a free electron
Correct answer: The photon is scattered with no energy loss or ionization
In coherent (Rayleigh) scattering, the photon interacts with an atom as a whole and is deflected with essentially no energy loss and no ionization produced.
Question 7: A radiograph taken with a higher kVp and lower mAs compared to a standard technique will result in:
- Increased patient dose and higher contrast
- Decreased patient dose and lower contrast (Correct answer)
- Increased patient dose and lower contrast
- Decreased patient dose and higher contrast
Correct answer: Decreased patient dose and lower contrast
Increasing kVp while reducing mAs to maintain film density lowers patient dose (more penetrating beam, less absorption) but also reduces contrast because more Compton scattering occurs.
ARRT Radiation Physics and Radiobiology 5
Auger electrons are emitted following which process?