NRRPT Physics and Interactions 2 — Questions and Answers
Question 1: What is the primary interaction mechanism of alpha particles with matter?
- Coulombic interactions with orbital electrons (Correct answer)
- Photoelectric absorption
- Pair production
- Compton scattering
Correct answer: Coulombic interactions with orbital electrons
Alpha particles lose energy primarily through Coulombic (electrostatic) interactions with the orbital electrons of atoms in the absorbing material.
Question 2: The linear energy transfer (LET) of a radiation type is best described as:
- Energy deposited per unit path length in an absorber (Correct answer)
- Total energy of the radiation beam
- Ratio of scattered to absorbed photons
- Energy lost due to bremsstrahlung only
Correct answer: Energy deposited per unit path length in an absorber
LET is defined as the energy deposited per unit path length (keV/μm) and characterizes how densely ionizing a radiation type is.
Question 3: Which process is responsible for the production of characteristic X-rays?
- Bremsstrahlung
- Electron capture
- Photoelectric effect (Correct answer)
- Compton scattering
Correct answer: Photoelectric effect
The photoelectric effect ejects an inner-shell electron; when an outer-shell electron fills the vacancy, a characteristic X-ray is emitted with energy equal to the difference in binding energies.
Question 4: The Q-value of a nuclear reaction is defined as:
- The kinetic energy of the incident particle
- The difference in rest-mass energies between reactants and products (Correct answer)
- The binding energy per nucleon of the target nucleus
- The threshold energy for pair production
Correct answer: The difference in rest-mass energies between reactants and products
The Q-value equals (sum of reactant rest masses minus sum of product rest masses) × c², representing the energy released (positive Q) or absorbed (negative Q) in the reaction.
Question 5: Pair production requires a minimum photon energy of approximately:
- 0.511 MeV
- 1.022 MeV (Correct answer)
- 1.25 MeV
- 2.044 MeV
Correct answer: 1.022 MeV
Pair production creates an electron-positron pair, each with rest mass energy of 0.511 MeV, so the threshold is 2 × 0.511 = 1.022 MeV.
Question 6: Which nuclear decay mode results in no change in atomic mass number (A) but increases atomic number (Z) by one?
- Alpha decay
- Beta-minus decay (Correct answer)
- Neutron emission
- Isomeric transition
Correct answer: Beta-minus decay
Beta-minus decay converts a neutron to a proton (Z increases by 1) while emitting a beta particle and antineutrino; A remains unchanged.
Question 7: The cross section for neutron capture (n,γ) in most nuclides generally varies with neutron energy as:
- Proportional to neutron velocity (1/v law at low energies) (Correct answer)
- Proportional to the square of neutron velocity
- Independent of neutron energy
- Inversely proportional to the square of neutron energy
Correct answer: Proportional to neutron velocity (1/v law at low energies)
At thermal energies, neutron capture cross sections follow the 1/v law, meaning they are inversely proportional to neutron velocity (and thus increase at lower energies).
NRRPT Physics and Interactions 2
What is the primary interaction mechanism of alpha particles with matter?