ARRT Radiography Practice Test
ARRT Radiation Physics & Radiobiology Practice Questions
Radiation Physics & Radiobiology makes up 5 of every 50 questions on a Tigertest ARRT practice test. Here are 10 of the 20 questions on it, each with the answer and the reason.
Updated by the Tigertest team. Based on the ARRT Radiography Examination Content Specifications. Original questions; 50 per test, weighted like the real exam. Not affiliated with ARRT.
1. Where are the electrons that produce x-rays released in the x-ray tube?
- A.At the tube window
- B.At the cathode filament
- C.At the anode target
- D.At the anode rotor
Answer: B. Heating the tungsten filament on the cathode releases electrons by thermionic emission. They are then accelerated across the tube to the anode.
2. About how much of the energy of the electrons striking the anode becomes x-rays?
- A.About 50%
- B.More than 90%
- C.About 25%
- D.Less than 1%
Answer: D. Over 99% of the electrons' kinetic energy becomes heat at the target; under 1% becomes x-ray photons, which is why tube heat limits matter.
3. Which target interaction produces most of the photons in a diagnostic x-ray beam?
- A.Bremsstrahlung
- B.Coherent scatter
- C.Characteristic
- D.Photoelectric
Answer: A. Most of the beam comes from bremsstrahlung (braking) radiation as electrons slow near tungsten nuclei. Characteristic photons are a small share.
4. Which factor sets the highest photon energy in the x-ray beam?
- A.Exposure time
- B.Focal spot size
- C.kVp
- D.mA
Answer: C. The maximum photon energy in keV equals the kVp. mA and time change the number of photons, not their maximum energy.
5. Raising the mAs while keeping kVp the same changes the beam's:
- A.Maximum energy
- B.Wavelength range
- C.Quantity
- D.Quality
Answer: C. mAs controls how many photons are produced (quantity). kVp and filtration control penetrating ability (quality).
6. As x-ray photon energy increases, its wavelength:
- A.Decreases
- B.Stays the same
- C.Doubles
- D.Increases
Answer: A. Energy and wavelength are inversely related: higher energy photons have shorter wavelengths and higher frequency.
7. Which photon interaction completely absorbs the photon and adds most to patient dose?
- A.Pair production
- B.Compton scatter
- C.Coherent scatter
- D.Photoelectric
Answer: D. In photoelectric absorption the photon gives all its energy to an inner-shell electron and disappears, depositing dose and creating image contrast.
8. Which interaction is the main source of scatter reaching the radiographer?
- A.Bremsstrahlung
- B.Compton scatter
- C.Photoelectric absorption
- D.Coherent scatter
Answer: B. Compton interactions eject an outer-shell electron and send a lower-energy photon off at an angle. The patient becomes the main source of occupational exposure.
9. The chance of photoelectric absorption rises sharply when tissue has a higher:
- A.Temperature
- B.Atomic number
- C.Water content
- D.Air content
Answer: B. Photoelectric probability rises with about the cube of the atomic number, so bone and iodine absorb far more than soft tissue.
10. An exposure rate is 40 mGy per hour at 40 cm from a source. What is it at 80 cm?
- A.80 mGy per hour
- B.5 mGy per hour
- C.20 mGy per hour
- D.10 mGy per hour
Answer: D. By the inverse square law, doubling distance cuts intensity to one quarter: 40 x (40/80) squared = 10 mGy per hour. 20 is the mistake of halving.
Practice all 20 radiation physics & radiobiology questions, and the rest of the 200-question bank, in the free ARRT training sets. Questions you miss come back until you have mastered them.
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