X-Ray Certification Radiation Physics and Protection 3 — Questions and Answers
Question 1: What happens to X-ray beam intensity as the distance from the source doubles?
- It doubles
- It remains the same
- It decreases to one-quarter (Correct answer)
- It decreases by half
Correct answer: It decreases to one-quarter
According to the inverse square law, doubling the distance reduces intensity to one-quarter (1/distance²) of the original value.
Question 2: Which type of ionizing radiation consists of two protons and two neutrons?
- Beta particle
- Alpha particle (Correct answer)
- Gamma ray
- X-ray photon
Correct answer: Alpha particle
An alpha particle is identical to a helium-4 nucleus, consisting of two protons and two neutrons.
Question 3: Lead aprons used in radiography protect against radiation primarily by which interaction?
- Compton scattering
- Photoelectric effect (Correct answer)
- Pair production
- Coherent scattering
Correct answer: Photoelectric effect
The high atomic number of lead promotes the photoelectric effect, completely absorbing low-energy scattered X-rays used in diagnostic imaging.
Question 4: What is bremsstrahlung radiation?
- Radiation emitted when nuclei undergo radioactive decay
- X-rays produced when electrons are decelerated near a nucleus (Correct answer)
- Scatter radiation from Compton interactions
- Characteristic radiation from inner-shell electron transitions
Correct answer: X-rays produced when electrons are decelerated near a nucleus
Bremsstrahlung (braking radiation) is produced when high-speed electrons are slowed and deflected by the nucleus of a target atom.
Question 5: What is the annual occupational whole-body effective dose limit recommended by NCRP?
- 10 mSv
- 50 mSv (Correct answer)
- 100 mSv
- 150 mSv
Correct answer: 50 mSv
NCRP recommends an annual occupational effective dose limit of 50 mSv (5 rem) for radiation workers.
Question 6: Which property of X-rays allows them to penetrate soft tissue but be attenuated by bone?
- X-rays travel at the speed of light
- X-ray attenuation increases with tissue atomic number and density (Correct answer)
- X-rays have no charge
- X-rays are part of the electromagnetic spectrum
Correct answer: X-ray attenuation increases with tissue atomic number and density
Attenuation of X-rays is directly related to the atomic number and density of the material, which is why dense bone absorbs more than soft tissue.
Question 7: A dosimeter reading of 2 mGy represents which of the following?
- 2 millijoules of energy per gram of tissue
- 2 millijoules of energy per kilogram of tissue (Correct answer)
- 2 joules of energy per gram of tissue
- 2 joules of energy per kilogram of tissue
Correct answer: 2 millijoules of energy per kilogram of tissue
The Gray (Gy) is defined as 1 joule of energy absorbed per kilogram of matter, so 2 mGy = 2 millijoules per kilogram.
X-Ray Certification Radiation Physics and Protection 3
What happens to X-ray beam intensity as the distance from the source doubles?