NANTeL Radiation Protection and ALARA 3 — Questions and Answers
Question 1: Which radiological survey instrument is best suited for detecting low-energy beta contamination on surfaces?
- Geiger-Mueller (GM) pancake probe (Correct answer)
- Ion chamber
- Neutron rem meter
- Thermoluminescent dosimeter (TLD)
Correct answer: Geiger-Mueller (GM) pancake probe
A GM pancake probe has a thin window that allows low-energy beta particles to enter and be detected, making it ideal for surface contamination surveys.
Question 2: At nuclear power plants, what is the primary source of airborne radioactivity that workers in the reactor coolant system area may encounter?
- Tritium from fuel pellets
- Noble gas fission products and radioiodines from fuel defects (Correct answer)
- Activation products from stainless steel
- Radon from concrete structures
Correct answer: Noble gas fission products and radioiodines from fuel defects
Fuel defects allow fission product noble gases and radioiodines to escape into the reactor coolant, making them the primary airborne concern.
Question 3: What is the committed effective dose equivalent (CEDE) used to account for?
- The dose received from a single high-exposure event
- The long-term dose from an internally deposited radionuclide over 50 years (Correct answer)
- The cumulative external dose over a worker's career
- The dose rate at the surface of a radioactive source
Correct answer: The long-term dose from an internally deposited radionuclide over 50 years
CEDE represents the total effective dose that will be received over 50 years as a result of a single intake of radioactive material.
Question 4: When using a self-reading pocket dosimeter (SRPD), a reading that has gone off-scale should prompt the worker to do what?
- Continue work and report the reading at the end of shift
- Immediately exit the area and notify radiation protection personnel (Correct answer)
- Recharge the dosimeter and continue
- Assume the dosimeter is malfunctioning and ignore it
Correct answer: Immediately exit the area and notify radiation protection personnel
An off-scale SRPD indicates the worker may have received a significant dose and requires immediate exit and RP evaluation to protect health and meet regulatory requirements.
Question 5: Which of the following best describes 'as low as reasonably achievable' (ALARA) in regulatory context?
- Maintaining doses at exactly the regulatory limit
- Keeping radiation doses as far below regulatory limits as practicable (Correct answer)
- Reducing dose only when it costs less than $100 per person-rem averted
- Applying dose limits only to workers under age 18
Correct answer: Keeping radiation doses as far below regulatory limits as practicable
ALARA requires active effort to keep doses well below regulatory limits using reasonable means, not merely complying with those limits.
Question 6: What type of dosimeter provides a legal record of occupational radiation dose that can be read only after processing in a laboratory?
- Self-reading pocket dosimeter
- Electronic personal dosimeter (EPD)
- Thermoluminescent dosimeter (TLD) (Correct answer)
- Ion chamber survey meter
Correct answer: Thermoluminescent dosimeter (TLD)
TLDs store energy from radiation exposure in crystalline material and are processed in a lab to provide an official, legally defensible dose record.
Question 7: Which shielding material is most appropriate for reducing neutron dose in a nuclear reactor environment?
- Lead
- Aluminum
- Polyethylene or water (Correct answer)
- Copper
Correct answer: Polyethylene or water
Hydrogenous materials like polyethylene and water efficiently moderate (slow) and absorb neutrons through hydrogen scattering and capture reactions.
NANTeL Radiation Protection and ALARA 3
Which radiological survey instrument is best suited for detecting low-energy beta contamination on surfaces?