RSO Dosimetry and Personal Exposure Assessment 2 — Questions and Answers
Question 1: The shallow dose equivalent (SDE) on a personnel dosimeter measures dose at a tissue depth of:
- 0.007 cm (70 µm) (Correct answer)
- 0.3 cm
- 1.0 cm
- 10.0 cm
Correct answer: 0.007 cm (70 µm)
Shallow dose equivalent represents the dose at 0.007 cm (70 micrometers) depth in tissue, representing the basal layer of skin and used to assess skin dose from beta and low-energy photon radiation.
Question 2: A personnel dosimeter reading must be investigated when it exceeds what percentage of the applicable dose limit according to NRC guidance?
- 10%
- 25% (Correct answer)
- 50%
- 75%
Correct answer: 25%
NRC guidance recommends that doses exceeding 25% of the applicable dose limit trigger investigation to determine the cause and ensure limits are not exceeded.
Question 3: To estimate effective dose when using two dosimeters (collar outside apron, waist under apron) during fluoroscopy, the NCRP formula uses:
- Average of the two readings
- 0.5 × collar + 0.5 × waist
- 0.025 × collar + 0.5 × waist (or similar weighting formula) (Correct answer)
- Maximum of the two readings only
Correct answer: 0.025 × collar + 0.5 × waist (or similar weighting formula)
Weighted formulas such as E = 0.025 × H_collar + 0.5 × H_waist are used to estimate effective dose from two dosimeter readings during fluoroscopic procedures with lead aprons.
Question 4: A radiation worker's finger ring dosimeter shows 1,500 mrem for the month. The NRC quarterly limit for extremity dose is:
- 1,250 mrem
- 3,750 mrem (part of 50,000 mrem/year)
- 12,500 mrem (part of 50 rem/year extremity limit) (Correct answer)
- 5,000 mrem
Correct answer: 12,500 mrem (part of 50 rem/year extremity limit)
The NRC annual extremity dose limit is 50 rem (500 mSv); divided equally over four quarters, the quarterly limit is approximately 12,500 mrem (12.5 rem).
Question 5: Internal dose assessment via bioassay is required when a worker's intake of radioactive material could result in a committed effective dose exceeding:
- 0.1 mSv (10 mrem)
- 1 mSv (100 mrem)
- 10 mSv (1 rem) (Correct answer)
- 5 mSv (500 mrem)
Correct answer: 10 mSv (1 rem)
NRC regulations (10 CFR 20.1502) require monitoring internal exposure when an individual is likely to receive an annual intake resulting in a committed effective dose exceeding 10% of the annual limit, which is 10% of 50 mSv = 5 mSv; however, many RSOs use 10 mSv (1 rem) as a practical investigation threshold.
Question 6: Which type of dosimeter provides real-time dose-rate information that passive dosimeters cannot?
- Film badge
- TLD
- Electronic personal dosimeter (EPD) (Correct answer)
- OSL dosimeter
Correct answer: Electronic personal dosimeter (EPD)
Electronic personal dosimeters (EPDs) provide real-time digital readout of dose rate and accumulated dose with audible alarms, unlike passive integrating dosimeters.
RSO Dosimetry and Personal Exposure Assessment 2
The shallow dose equivalent (SDE) on a personnel dosimeter measures dose at a tissue depth of: