NDT Radiographic Testing Safety 5 — Questions and Answers
Question 1: What is the purpose of a 'source activity decay chart' kept on an Ir-192 camera?
- To track film sensitivity changes over time
- To calculate current source activity for proper exposure times (Correct answer)
- To log cumulative radiation dose to all users
- To record the number of exposures made per shift
Correct answer: To calculate current source activity for proper exposure times
Because Ir-192 decays continuously, the decay chart lets radiographers calculate current activity so they can set correct exposure times and maintain image quality.
Question 2: Which area classification applies to a location where dose rate could exceed 0.02 mSv (2 mrem) in any one hour but is unrestricted to the public?
- Exclusion zone
- Unrestricted area (Correct answer)
- Restricted area
- High radiation area
Correct answer: Unrestricted area
An unrestricted area under 10 CFR Part 20 is one where individual doses stay below 0.02 mSv (2 mrem) per hour and access is not controlled for radiation protection.
Question 3: A 'two-man rule' in radiographic testing requires that:
- Two separate film readers must evaluate every radiograph
- A radiographer and a trainee must always work together during source exposure
- At least two qualified individuals must be present during source exposure operations (Correct answer)
- Two dosimeters must be worn simultaneously at all times
Correct answer: At least two qualified individuals must be present during source exposure operations
The two-man rule ensures that at least two qualified radiographers are present during any exposure, providing a safety check and emergency response capability.
Question 4: Se-75 is preferred over Ir-192 for imaging thin materials primarily because:
- Se-75 has a much longer half-life, reducing source change frequency
- Se-75 emits lower-energy gamma rays that provide better contrast in thin sections (Correct answer)
- Se-75 is less expensive and easier to handle
- Se-75 requires no radiation shielding in the camera
Correct answer: Se-75 emits lower-energy gamma rays that provide better contrast in thin sections
Se-75's lower energy gamma rays (~66–401 keV) are better suited for thin materials and small-diameter pipe welds, providing superior contrast compared to Ir-192.
Question 5: After completing a radiographic exposure, a radiographer must perform a 'post-exposure survey' to verify:
- The film has been properly developed and fixed
- The source has returned to its fully shielded position in the camera (Correct answer)
- The exclusion zone barriers have been removed
- The client's representative has signed the exposure log
Correct answer: The source has returned to its fully shielded position in the camera
A post-exposure survey with a calibrated radiation survey meter confirms the source is fully retracted and dose rates have returned to background levels.
Question 6: Which of the following is a deterministic (non-stochastic) radiation effect?
- Leukemia induced 5 years after exposure
- Radiation-induced cataracts from a threshold dose (Correct answer)
- Hereditary genetic mutations in offspring
- Solid tumor formation 20 years post-exposure
Correct answer: Radiation-induced cataracts from a threshold dose
Radiation-induced cataracts are a deterministic effect: they occur only above a dose threshold (~500 mGy) and their severity increases with dose above that threshold.
Question 7: Iridium-192 cameras used in field radiography must be surveyed for radiation levels and integrity after each use. This is required under:
- ASTM E94 radiographic testing standards
- NRC regulations under 10 CFR Part 34 (Correct answer)
- OSHA 29 CFR 1910.1096 general industry standards
- ANSI/ASNT CP-189 qualification requirements
Correct answer: NRC regulations under 10 CFR Part 34
10 CFR Part 34 specifically governs the use of sealed sources in industrial radiography, including required post-exposure surveys and equipment inspections.
NDT Radiographic Testing Safety 5
What is the purpose of a 'source activity decay chart' kept on an Ir-192 camera?