Origin and properties of X-rays MCQs With Answer

Origin and properties of X-rays MCQs With Answer

X‑rays are high‑energy electromagnetic photons produced when energetic electrons decelerate at a metal target (Bremsstrahlung) or when inner‑shell electron vacancies are filled (characteristic X‑rays). Understanding X‑ray production, spectrum, wavelength, photon energy, and interactions with matter—photoelectric effect, Compton scattering, attenuation and absorption edges—is essential for B.Pharm students working in radiopharmacy, diagnostic imaging and radiation safety. Key practical parameters include tube voltage (kVp), tube current (mA), filtration, target material Z, linear attenuation coefficient, half‑value layer (HVL), and biological effects such as ionization and dose. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary physical process responsible for the continuous X‑ray spectrum produced in an X‑ray tube?

• Characteristic electron transitions
• Bremsstrahlung (braking radiation)
• Pair production
• Compton scattering

Correct Answer: Bremsstrahlung (braking radiation)

Q2. Characteristic X‑rays are produced when:

• Electrons are decelerated by the nuclear field
• Inner‑shell vacancies are filled by outer electrons
• Photons scatter off free electrons
• Positrons annihilate with electrons

Correct Answer: Inner‑shell vacancies are filled by outer electrons

Q3. Which parameter in an X‑ray tube primarily determines the maximum photon energy (cut‑off energy) of the spectrum?

• Tube current (mA)
• Tube voltage (kVp)
• Target atomic number (Z)
• Filtration thickness

Correct Answer: Tube voltage (kVp)

Q4. The minimum wavelength (λmin) of X‑rays in an X‑ray tube is inversely proportional to:

• Tube current (mA)
• Tube voltage (kVp)
• Target atomic number (Z)
• Filtration material

Correct Answer: Tube voltage (kVp)

Q5. Which interaction dominates X‑ray absorption in high‑Z materials at low diagnostic energies?

• Compton scattering
• Pair production
• Photoelectric effect
• Rayleigh scattering

Correct Answer: Photoelectric effect

Q6. At typical diagnostic X‑ray energies (30–150 keV), the most significant scattering process in soft tissues is:

• Photoelectric absorption
• Compton scattering
• Pair production
• Thomson scattering

Correct Answer: Compton scattering

Q7. The exponential attenuation law for X‑rays in matter is I = I0 e^(-μx). The parameter μ represents:

• Half‑value layer
• Linear attenuation coefficient
• Mass energy transfer coefficient
• Relative transmission

Correct Answer: Linear attenuation coefficient

Q8. Half‑value layer (HVL) is defined as the thickness of material required to:

• Reduce beam energy by half
• Reduce photon number to half of its original value
• Absorb all X‑rays
• Double the photon intensity

Correct Answer: Reduce photon number to half of its original value

Q9. Increasing the tube current (mA) in an X‑ray tube primarily affects:

• Maximum photon energy
• Photon number (intensity)
• Photon wavelength
• Characteristic line energies

Correct Answer: Photon number (intensity)

Q10. Which change increases the mean energy (quality) of an X‑ray beam?

• Decreasing kVp
• Increasing filtration
• Decreasing mA
• Using a lower Z target material

Correct Answer: Increasing filtration

Q11. Characteristic Kα and Kβ lines are associated with transitions to which shell?

• M‑shell
• L‑shell
• K‑shell
• Outer valence shell

Correct Answer: K‑shell

Q12. Moseley’s law links characteristic X‑ray frequencies to which atomic property?

• Atomic mass
• Atomic number (Z)
• Electron affinity
• Neutron number

Correct Answer: Atomic number (Z)

Q13. Which material is commonly used as an anode target in diagnostic X‑ray tubes because of its high Z and thermal conductivity?

• Aluminum
• Tungsten
• Carbon
• Lead

Correct Answer: Tungsten

Q14. The primary biological effect of X‑ray interaction with tissue is due to:

• Heating of tissue
• Ionization and free radical formation
• Elastic scattering without energy transfer
• Magnetic resonance effects

Correct Answer: Ionization and free radical formation

Q15. Which unit measures absorbed dose (energy deposited per unit mass) in tissue?

• Sievert (Sv)
• Curie (Ci)
• Gray (Gy)
• Roentgen (R)

Correct Answer: Gray (Gy)

Q16. The radiobiological quantity that accounts for differing biological effects of radiation types is measured in:

• Gray (Gy)
• Sievert (Sv)
• Becquerel (Bq)
• Oersted (Oe)

Correct Answer: Sievert (Sv)

Q17. Added filtration in an X‑ray tube serves mainly to:

• Increase low‑energy photons to improve contrast
• Remove low‑energy photons to reduce patient dose
• Change characteristic line energies
• Decrease tube voltage

Correct Answer: Remove low‑energy photons to reduce patient dose

Q18. Which of the following is a direct consequence of increasing the target atomic number (Z) in an X‑ray tube?

• Lower characteristic X‑ray energies
• Higher efficiency of X‑ray production
• Decreased Bremsstrahlung yield
• Reduced heat capacity of the target

Correct Answer: Higher efficiency of X‑ray production

Q19. The photoelectric absorption probability is approximately proportional to:

• Z^3 / E^3
• Z / E
• Z^2 / E
• E^2 / Z

Correct Answer: Z^3 / E^3

Q20. Compton scattering energy transfer to recoil electrons increases when incident photon energy:

• Decreases significantly
• Is near binding energy of K‑shell
• Increases
• Equals zero

Correct Answer: Increases

Q21. An X‑ray spectrum showing sharp peaks superimposed on a continuous background indicates:

• Only Bremsstrahlung production
• Characteristic lines plus Bremsstrahlung
• Pure thermal radiation
• Pair production dominance

Correct Answer: Characteristic lines plus Bremsstrahlung

Q22. The X‑ray tube cathode contains a filament that when heated emits electrons by:

• Photoelectric emission
• Thermionic emission
• Field emission due to high voltage only
• Pair production

Correct Answer: Thermionic emission

Q23. Beam hardening refers to:

• Increasing the number of low‑energy photons
• Removal of low‑energy photons so mean energy increases
• Softening the beam to improve contrast
• Cooling the X‑ray tube anode

Correct Answer: Removal of low‑energy photons so mean energy increases

Q24. In diagnostic radiology, which interaction is most useful for producing image contrast between bone and soft tissue?

• Pair production differences
• Differences in photoelectric absorption due to high Z of bone
• Elastic Rayleigh scattering predominance
• Differences in Compton scattering only

Correct Answer: Differences in photoelectric absorption due to high Z of bone

Q25. The term “attenuation coefficient” depends on:

• Only the material composition
• Material composition and photon energy
• Only photon flux
• Only target temperature

Correct Answer: Material composition and photon energy

Q26. Which statement about characteristic X‑ray energies is correct?

• They decrease as target Z increases
• They are independent of target material
• They correspond to discrete electron shell energy differences
• They form a smooth continuous spectrum

Correct Answer: They correspond to discrete electron shell energy differences

Q27. The primary factor that determines spatial resolution in conventional X‑ray imaging is:

• Tube voltage (kVp)
• Focal spot size
• Added filtration material
• Patient dose only

Correct Answer: Focal spot size

Q28. Which protective material is most effective for shielding diagnostic X‑rays?

• Aluminum
• Lead
• Plastic
• Wood

Correct Answer: Lead

Q29. The clinical principle ALARA stands for:

• As Low As Reasonably Achievable
• All Levels Are Radiologically Acceptable
• As Long As Radiation Allowed
• Atomic Level Assessment of Radiation Activity

Correct Answer: As Low As Reasonably Achievable

Q30. Which parameter should be increased to reduce motion blur in radiographic imaging while maintaining image receptor exposure using higher mA and shorter exposure time?

• Decrease kVp markedly
• Increase mA and decrease exposure time
• Decrease mA and increase exposure time
• Remove all filtration

Correct Answer: Increase mA and decrease exposure time

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