DRC Radiologic Physics & Safety 3 — Questions and Answers
Question 1: When the kilovoltage peak (kVp) is increased in dental X-ray equipment, the resulting radiation beam has:
- Lower energy and longer wavelength
- Higher energy and shorter wavelength (Correct answer)
- Higher energy and longer wavelength
- Lower energy and shorter wavelength
Correct answer: Higher energy and shorter wavelength
Increasing kVp accelerates electrons to higher speeds, producing X-rays with greater energy and correspondingly shorter wavelengths.
Question 2: The inverse square law states that X-ray intensity is inversely proportional to:
- The square of the distance from the source (Correct answer)
- The milliamperage setting
- The exposure time
- The thickness of the target material
Correct answer: The square of the distance from the source
The inverse square law states that radiation intensity decreases with the square of the distance from the source, so doubling distance reduces intensity to one-quarter.
Question 3: Which material is most commonly used as the target (anode) in dental X-ray tubes?
- Copper
- Molybdenum
- Tungsten (Correct answer)
- Lead
Correct answer: Tungsten
Tungsten is used as the target material because of its high atomic number, high melting point, and efficiency in X-ray production.
Question 4: Filtration in dental X-ray equipment is used primarily to:
- Increase the exposure time required
- Remove long-wavelength low-energy photons from the beam (Correct answer)
- Increase patient image contrast
- Collimate the X-ray beam to a smaller size
Correct answer: Remove long-wavelength low-energy photons from the beam
Filtration absorbs soft, low-energy X-rays that would not contribute to the image but would increase patient skin dose.
Question 5: In radiation physics, the term 'half-value layer' (HVL) refers to:
- Half the thickness of lead shielding required
- The thickness of material that reduces beam intensity by 50% (Correct answer)
- Half the value of the kVp setting
- The depth at which dose is halved in tissue
Correct answer: The thickness of material that reduces beam intensity by 50%
The half-value layer is the thickness of an absorber that reduces X-ray beam intensity to half its original value.
Question 6: The minimum total filtration required for dental X-ray equipment operating above 70 kVp is:
- 1.0 mm aluminum equivalent
- 1.5 mm aluminum equivalent
- 2.5 mm aluminum equivalent (Correct answer)
- 3.0 mm aluminum equivalent
Correct answer: 2.5 mm aluminum equivalent
For X-ray equipment operating above 70 kVp, the minimum required total filtration is 2.5 mm aluminum equivalent per NCRP guidelines.
Question 7: Which type of scattered radiation contributes most to occupational exposure in dental radiography?
- Coherent scatter
- Compton scatter (Correct answer)
- Pair production scatter
- Rayleigh scatter
Correct answer: Compton scatter
Compton scatter, in which a photon ejects an outer-shell electron and travels in a new direction, is the primary source of occupational scatter radiation.
DRC Radiologic Physics & Safety 3
When the kilovoltage peak (kVp) is increased in dental X-ray equipment, the resulting radiation beam has: