NDT Radiographic Testing Safety 4 — Questions and Answers
Question 1: What is the primary biological target of ionizing radiation that leads to long-term cancer risk?
- Cell membrane lipids
- Mitochondrial proteins
- DNA in the cell nucleus (Correct answer)
- Cytoplasmic ribosomes
Correct answer: DNA in the cell nucleus
Ionizing radiation's primary long-term risk comes from DNA damage in the cell nucleus, which can cause mutations leading to cancer.
Question 2: A 'direct reading dosimeter' (DRD) is required during field radiography in addition to a passive dosimeter because it:
- Provides a legal cumulative dose record
- Gives the radiographer real-time dose rate feedback (Correct answer)
- Measures neutron dose more accurately
- Functions as backup shielding for the torso
Correct answer: Gives the radiographer real-time dose rate feedback
DRDs provide immediate, real-time dose rate information so radiographers can take protective action during a shoot.
Question 3: The 'controlled area' boundary during a radiographic exposure is typically established where the dose rate does not exceed:
- 0.005 mSv/hr (0.5 mrem/hr)
- 0.02 mSv/hr (2 mrem/hr)
- 2 mSv/hr (200 mrem/hr) (Correct answer)
- 5 mSv/hr (500 mrem/hr)
Correct answer: 2 mSv/hr (200 mrem/hr)
In practice, the controlled (restricted) area boundary is placed where dose rates reach or exceed 2 mSv/hr (200 mrem/hr), limiting access to radiation workers.
Question 4: A radiation survey meter reads 'off-scale high' when pointed at the source container. This most likely indicates:
- The meter battery is low and needs replacement
- The meter is malfunctioning due to high humidity
- The source has failed to retract into its shielded position (Correct answer)
- Background radiation has temporarily spiked
Correct answer: The source has failed to retract into its shielded position
An off-scale high reading near the source container strongly suggests the source is exposed or partially retracted, requiring immediate evacuation.
Question 5: Scatter radiation during industrial radiography primarily originates from:
- The radioactive source container walls
- Interaction of the primary beam with the work piece and surroundings (Correct answer)
- Reflection off the film cassette back to the source
- Background cosmic radiation enhanced by the source
Correct answer: Interaction of the primary beam with the work piece and surroundings
Scatter radiation is produced when the primary beam interacts with the test object, nearby structures, and the ground, radiating in all directions.
Question 6: Which of the following correctly states the concept of 'stochastic' radiation effects?
- Effects that occur only above a specific threshold dose
- Effects whose severity increases with dose but probability does not
- Effects whose probability increases with dose but severity does not (Correct answer)
- Effects that are immediate and predictable for any dose level
Correct answer: Effects whose probability increases with dose but severity does not
Stochastic effects like cancer have a probability proportional to dose but the severity (e.g., tumor type) is independent of how much dose caused it.
Question 7: A 'lost or stolen' radioactive source must be reported to the NRC within:
- 4 hours of discovery (Correct answer)
- 24 hours of discovery
- 72 hours of discovery
- 30 days in the annual report only
Correct answer: 4 hours of discovery
A lost or stolen licensed radioactive material must be reported immediately (within 4 hours) to the NRC Operations Center and local authorities.
NDT Radiographic Testing Safety 4
What is the primary biological target of ionizing radiation that leads to long-term cancer risk?