NRRPT Internal Dosimetry and Bioassay 2 — Questions and Answers
Question 1: Which analytical technique is commonly used for indirect bioassay of uranium in urine samples?
- Gamma spectroscopy
- Fluorometric analysis or ICP-MS (Correct answer)
- Liquid scintillation counting only
- Geiger-Müller counting
Correct answer: Fluorometric analysis or ICP-MS
Uranium is detected in urine via fluorometric analysis or inductively coupled plasma mass spectrometry (ICP-MS) because natural uranium emits very weak radiation.
Question 2: What ICRP lung model parameter describes how quickly an inhaled material is cleared from the respiratory tract?
- Absorption type (F, M, or S) (Correct answer)
- Dose conversion factor
- Effective half-life
- Lung retention fraction
Correct answer: Absorption type (F, M, or S)
The ICRP Human Respiratory Tract Model classifies inhaled materials as Fast (F), Moderate (M), or Slow (S) based on their rate of absorption into blood.
Question 3: A whole-body counter (WBC) is most sensitive for detecting which type of emitter inside the body?
- Pure alpha emitters
- Pure beta emitters
- Gamma emitters (Correct answer)
- Neutron emitters
Correct answer: Gamma emitters
WBCs detect gamma photons penetrating the body using NaI or HPGe detectors, making them most useful for gamma-emitting radionuclides.
Question 4: Which organ is the critical organ for dosimetry purposes when a worker inhales tritium (H-3) as HTO?
- Lungs
- Thyroid
- Whole body (uniform distribution) (Correct answer)
- Bone marrow
Correct answer: Whole body (uniform distribution)
Tritiated water (HTO) rapidly distributes uniformly throughout body water, so the whole body is used as the reference tissue for dose calculations.
Question 5: What is the effective half-life (T_eff) of a radionuclide in the body?
- The physical half-life of the radionuclide
- The biological half-life of the element
- The combined half-life accounting for both physical decay and biological elimination (Correct answer)
- The time for dose rate to fall to 1/10 of initial value
Correct answer: The combined half-life accounting for both physical decay and biological elimination
T_eff = (T_physical × T_biological) / (T_physical + T_biological), combining radioactive decay with the body's elimination rate.
Question 6: What trigger level typically initiates a formal internal dosimetry investigation under NRC guidance?
- Any detectable activity in a bioassay sample
- Intake exceeding 10% of the ALI (Correct answer)
- Intake exceeding 1% of the ALI
- Any positive urine sample result
Correct answer: Intake exceeding 10% of the ALI
NRC and most internal dosimetry programs initiate formal dose assessment investigations when estimated intake exceeds 10% of the ALI.
NRRPT Internal Dosimetry and Bioassay 2
Which analytical technique is commonly used for indirect bioassay of uranium in urine samples?