ASNT Neutron Radiography 2 — Questions and Answers
Question 1: What is the approximate kinetic energy range for thermal neutrons used in neutron radiography?
- Below 0.5 eV (Correct answer)
- 1 keV to 10 keV
- 0.1 MeV to 1 MeV
- Above 10 MeV
Correct answer: Below 0.5 eV
Thermal neutrons have energies approximately equal to room-temperature kinetic energy, typically below 0.5 eV (around 0.025 eV at room temperature), which gives them high interaction cross-sections with many nuclides.
Question 2: In the transfer (indirect) neutron radiography method, what is the purpose of using an activation foil?
- To amplify the neutron beam intensity
- To become radioactive during exposure and later expose film away from the neutron source (Correct answer)
- To filter fast neutrons from the beam
- To calibrate the neutron fluence rate
Correct answer: To become radioactive during exposure and later expose film away from the neutron source
In the transfer method, a foil (commonly indium or dysprosium) is activated by neutron bombardment alongside the specimen; the foil is then placed against film in a low-background area to produce the radiographic image.
Question 3: What major radiation safety hazard is unique to neutron radiography compared to conventional X-radiography?
- Induced radioactivity in inspected components and equipment (Correct answer)
- Infrared heat emission from the beam port
- Ultraviolet skin burns from scattered radiation
- Static charge buildup on film cassettes
Correct answer: Induced radioactivity in inspected components and equipment
Neutron bombardment can induce radioactivity in the specimen and surrounding structural materials through neutron activation, requiring careful handling and decay waiting periods after inspection.
Question 4: Which isotope produces prompt gamma radiation with a large thermal neutron cross-section and is sometimes used in real-time neutron imaging scintillator screens?
- Boron-10 (Correct answer)
- Carbon-12
- Oxygen-16
- Nitrogen-14
Correct answer: Boron-10
Boron-10 has a very large thermal neutron capture cross-section (~3,840 barns) and produces detectable charged particles; boron-loaded scintillators exploit this reaction for real-time neutron imaging.
Question 5: What is the term for the image quality indicator (IQI) used to verify sensitivity and resolution in neutron radiography?
- Penetrameter (Correct answer)
- Beam quality indicator
- Neutron sensitivity coupon
- Beam purity indicator
Correct answer: Penetrameter
A penetrameter (also called an image quality indicator or IQI) is placed on the source side of the object to verify that the radiograph meets minimum sensitivity requirements, as described in ASTM E748.
Question 6: Fast neutron radiography differs from thermal neutron radiography primarily in that fast neutrons:
- Require no moderator and penetrate more deeply into high-density materials (Correct answer)
- Interact more strongly with hydrogen than thermal neutrons do
- Cannot penetrate metallic materials
- Always require a reactor source
Correct answer: Require no moderator and penetrate more deeply into high-density materials
Fast neutrons (energies above ~0.1 MeV) are less thermalized and can penetrate thick, high-density metallic components more readily than thermal neutrons, though they lose some contrast sensitivity for light elements.
Question 7: What property of water makes it an effective neutron moderator AND a neutron shield in reactor-based neutron radiography facilities?
- Its high atomic number and electron density
- Its high hydrogen content, which thermalizes and absorbs neutrons effectively (Correct answer)
- Its high melting point and thermal conductivity
- Its ability to reflect neutrons via total internal reflection
Correct answer: Its high hydrogen content, which thermalizes and absorbs neutrons effectively
Water contains abundant hydrogen atoms, which are nearly equal in mass to neutrons; elastic collisions with hydrogen nuclei efficiently slow (moderate) and eventually absorb neutrons, serving dual moderation and shielding functions.
ASNT Neutron Radiography 2
What is the approximate kinetic energy range for thermal neutrons used in neutron radiography?