Radiography Exam Radiation Protection and Safety 2 — Questions and Answers
Question 1: Protective lead shielding should be placed between the radiation source and a fertile woman's gonads when the gonadal dose would exceed:
- 5 mGy (0.5 rad) during the entire pregnancy (Correct answer)
- 50 mGy (5 rad) per month
- 1 mGy (0.1 rad) per procedure
- 100 mGy (10 rad) per year
Correct answer: 5 mGy (0.5 rad) during the entire pregnancy
Gonadal shielding should be used when the gonads are within 5 cm of the primary beam or when the gonadal dose would exceed 5 mGy (0.5 rad) during the gestation period.
Per NCRP guidelines, gonadal shielding is indicated when the gonads are within 5 cm of the collimated beam or when the gonadal dose could exceed 5 mGy during the pregnancy. The monthly limit for declared pregnant radiation workers is 0.5 mSv. Proper shielding placement requires not obscuring relevant anatomy.
Question 2: The declared pregnant radiation worker has a monthly dose equivalent limit of:
- 0.5 mSv (0.05 rem) (Correct answer)
- 5 mSv (0.5 rem)
- 50 mSv (5 rem)
- 1 mSv (0.1 rem)
Correct answer: 0.5 mSv (0.05 rem)
NCRP recommends a monthly dose limit of 0.5 mSv (50 mrem) for the embryo/fetus of a declared pregnant radiation worker.
Once a worker formally declares her pregnancy in writing, the monthly embryo/fetus dose limit drops to 0.5 mSv (0.05 rem) per NCRP Report No. 116. The total gestational limit is 5 mSv (0.5 rem). Employers must take reasonable steps to ensure compliance, often reassigning the worker to lower-exposure areas.
Question 3: Which device provides an immediate, real-time readout of radiation dose during a procedure?
- Pocket ionization dosimeter (Correct answer)
- Film badge
- TLD badge
- OSL dosimeter
Correct answer: Pocket ionization dosimeter
Pocket ionization dosimeters (pocket dosimeters) provide an immediate readout of accumulated dose during a procedure.
Pocket ionization dosimeters (pencil dosimeters) are air-filled ionization chambers that allow direct reading of accumulated dose at any time during a procedure. They must be charged before use and read after each procedure. Unlike TLD or film badges, they provide immediate feedback but are less accurate for permanent record-keeping.
Question 4: What is the recommended practice for wearing a radiation monitoring badge during fluoroscopy when wearing a lead apron?
- Wear one badge at collar level outside the apron
- Wear the badge under the apron at waist level
- Wear two badges: one outside at collar, one under apron at waist (Correct answer)
- Wear the badge on the wrist closest to the beam
Correct answer: Wear two badges: one outside at collar, one under apron at waist
During fluoroscopy, two badges are recommended: one at collar level outside the apron and one under the apron at waist level to accurately estimate effective dose.
When wearing a lead apron during fluoroscopy, two dosimeters are recommended. The collar badge (outside the apron) monitors the unshielded head and neck region. The waist badge (under the apron) monitors the dose to the shielded trunk. Using an algorithm (e.g., the NCRP method), effective dose is calculated from both readings. This two-badge method is more accurate than a single badge.
Question 5: Primary radiation barriers must attenuate the useful beam to what level?
- The primary barrier must reduce transmission to 1 mSv/week (Correct answer)
- The primary barrier must reduce transmission to 5 mSv/week
- The primary barrier must reduce transmission to 0.1 mSv/week
- The primary barrier must reduce transmission to 10 mSv/week
Correct answer: The primary barrier must reduce transmission to 1 mSv/week
Primary barriers are designed to reduce the transmitted primary beam to an acceptable level, typically 1 mSv (0.1 rem) per week for controlled areas.
Per NCRP Report No. 151, primary barriers must reduce the primary beam to ≤1 mSv (100 mrem) per week in controlled areas (where occupational workers are present). For uncontrolled areas (where the public may be), the limit is 0.1 mSv/week (1/10 mSv). Primary barriers are typically constructed of lead or concrete and cover floors, walls in the beam's path.
Question 6: Coherent (classical) scattering differs from Compton scattering in that coherent scattering:
- Produces no ionization and the scattered photon has the same energy as the incident photon (Correct answer)
- Produces ionization and the photon loses energy
- Ejects an inner-shell electron from the atom
- Converts a photon entirely to kinetic energy
Correct answer: Produces no ionization and the scattered photon has the same energy as the incident photon
In coherent (classical) scattering, the photon is redirected without ionization; the scattered photon retains the same energy as the incident photon.
Coherent scattering (Thomson or Rayleigh) occurs when a low-energy photon interacts with an atom, causing its electrons to oscillate and re-emit a photon of the same wavelength/energy in a slightly different direction. No ionization occurs and no energy is transferred to the atom. This interaction predominates at very low photon energies (below ~10 keV) and contributes minimally to diagnostic imaging or radiation hazard.
Radiography Exam Radiation Protection and Safety 2
Protective lead shielding should be placed between the radiation source and a fertile woman's gonads when the gonadal dose would exceed: