GXMO Radiation Physics and Safety 2 — Questions and Answers
Question 1: Which unit is used to measure the absorbed dose of radiation in tissue?
- Roentgen
- Gray (Correct answer)
- Sievert
- Becquerel
Correct answer: Gray
The Gray (Gy) is the SI unit of absorbed dose, defined as 1 joule of energy deposited per kilogram of tissue.
Question 2: What is the term for radiation that can remove electrons from atoms it interacts with?
- Non-ionizing radiation
- Ionizing radiation (Correct answer)
- Thermal radiation
- Background radiation
Correct answer: Ionizing radiation
Ionizing radiation carries enough energy to eject electrons from atoms, creating ion pairs that can damage biological tissue.
Question 3: The half-value layer (HVL) of a material is defined as the thickness that reduces beam intensity by what fraction?
- One-quarter
- One-third
- One-half (Correct answer)
- Two-thirds
Correct answer: One-half
The HVL is the thickness of a specified material required to reduce the primary radiation beam intensity to 50% of its original value.
Question 4: What type of interaction causes an x-ray photon to be completely absorbed while ejecting an inner-shell electron from an atom?
- Compton scatter
- Pair production
- Coherent scatter
- Photoelectric effect (Correct answer)
Correct answer: Photoelectric effect
In the photoelectric effect, the x-ray photon is totally absorbed and its energy is used to eject a bound inner-shell electron called a photoelectron.
Question 5: Which of the following best describes the ALARA principle?
- Always Limit All Radiation Annually
- As Low As Reasonably Achievable (Correct answer)
- Avoid Limiting Allowed Radiation Areas
- As Large As Radiation Allows
Correct answer: As Low As Reasonably Achievable
ALARA stands for As Low As Reasonably Achievable, guiding radiation workers to minimize exposure while still accomplishing the diagnostic task.
Question 6: A patient's gonads should be shielded when the gonads are within what distance of the primary x-ray field?
- 1 cm
- 3 cm
- 5 cm (Correct answer)
- 10 cm
Correct answer: 5 cm
Lead gonadal shields should be used when the gonads are within 5 cm of the primary x-ray beam to reduce genetic dose.
Question 7: What is the primary purpose of added filtration in an x-ray beam?
- Increase patient dose
- Remove high-energy photons
- Remove low-energy photons that cannot penetrate to the image receptor (Correct answer)
- Increase beam intensity
Correct answer: Remove low-energy photons that cannot penetrate to the image receptor
Added filtration removes low-energy (soft) photons that would be absorbed by the patient without contributing useful diagnostic information, reducing skin dose.
GXMO Radiation Physics and Safety 2
Which unit is used to measure the absorbed dose of radiation in tissue?