NRRPT - National Registry of Radiation Protection Technicians Dosimetry and Exposure Control Questions and Answers — Questions and Answers
Question 1: A radiation worker needs to perform a task in a high radiation area with a dose rate of 150 mrem/hr. The administrative dose limit for this task is 100 mrem. What is the maximum stay time permitted for the worker to complete the task without exceeding the administrative limit?
- 20 minutes
- 30 minutes
- 40 minutes (Correct answer)
- 60 minutes
Correct answer: 40 minutes
Stay time is calculated by dividing the allowed dose by the dose rate. In this case, Stay Time = 100 mrem / 150 mrem/hr = 0.667 hours. To convert this to minutes, multiply by 60: 0.667 hours * 60 minutes/hour = 40 minutes.
Question 2: Which of the following personal dosimeters uses a crystalline solid that, when heated after exposure to ionizing radiation, emits light proportional to the dose received?
- Film Badge
- Thermoluminescent Dosimeter (TLD) (Correct answer)
- Pocket Ionization Chamber
- Optically Stimulated Luminescence (OSL) Dosimeter
Correct answer: Thermoluminescent Dosimeter (TLD)
A Thermoluminescent Dosimeter (TLD) contains a crystalline material (like Lithium Fluoride) that traps energy from ionizing radiation. When heated, this stored energy is released as visible light, and the amount of light is proportional to the radiation dose absorbed by the crystal.
Question 3: A technician measures a dose rate of 400 mR/hr at a distance of 2 feet from a point source. If the technician moves to a distance of 8 feet from the source, what will the new dose rate be, according to the inverse square law?
- 100 mR/hr
- 50 mR/hr
- 25 mR/hr (Correct answer)
- 12.5 mR/hr
Correct answer: 25 mR/hr
The inverse square law states that radiation intensity is inversely proportional to the square of the distance from the source (I₁d₁² = I₂d₂²). The distance increased by a factor of 4 (from 2 ft to 8 ft). Therefore, the dose rate will decrease by a factor of 4², which is 16. The new dose rate is 400 mR/hr / 16 = 25 mR/hr.
Question 4: The fundamental principle of ALARA (As Low As Reasonably Achievable) in radiation protection means that:
- All radiation exposure must be eliminated completely.
- Exposures must be kept below the annual regulatory limits, with no other considerations.
- Radiation exposures should be maintained as far below the dose limits as is practical, taking into account social and economic factors. (Correct answer)
- Only acute, high-level exposures need to be managed and controlled.
Correct answer: Radiation exposures should be maintained as far below the dose limits as is practical, taking into account social and economic factors.
ALARA is a cornerstone of radiation safety philosophy. It doesn't just mean staying below regulatory limits, but making every reasonable effort to reduce doses further, balancing the benefits of the reduction against the costs (both economic and social).
Question 5: What is the primary operational difference between an Optically Stimulated Luminescence (OSL) dosimeter and a Thermoluminescent Dosimeter (TLD)?
- OSL dosimeters are stimulated with heat, while TLDs are stimulated with light.
- OSL dosimeters can be re-read multiple times, while the signal from a TLD is typically erased upon reading. (Correct answer)
- TLDs are more sensitive to low doses of radiation than OSL dosimeters.
- OSL dosimeters measure dose in real-time, whereas TLDs provide an integrated dose over time.
Correct answer: OSL dosimeters can be re-read multiple times, while the signal from a TLD is typically erased upon reading.
The key difference is the stimulation method. OSLs use light (typically from a laser) to stimulate the detector material, which does not deplete the stored signal, allowing for multiple readouts. TLDs use heat, which releases all the stored energy at once, zeroing out the dosimeter.
Question 6: An administrative control level is established by a licensee for radiation workers. What is the primary purpose of this level in an exposure control program?
- To replace the federal regulatory dose limits with a less strict standard.
- To serve as a threshold that, if reached, triggers an investigation or requires specific authorization for further exposure. (Correct answer)
- To define the absolute maximum dose a worker can legally receive in one year.
- To measure the average background radiation in a specific work area.
Correct answer: To serve as a threshold that, if reached, triggers an investigation or requires specific authorization for further exposure.
Administrative control levels are set by the licensee at a fraction of the regulatory limits (e.g., NRC limits). They act as an internal trigger point to ensure that regulatory limits are not approached or exceeded, prompting a review or requiring management approval before the worker can receive additional exposure. This is a key tool in implementing ALARA.
