NRRPT Physics and Interactions 5 — Questions and Answers
Question 1: Internal conversion (IC) electrons are emitted with energies equal to:
- The gamma-ray energy minus the electron's atomic binding energy (Correct answer)
- The full gamma-ray energy
- The sum of the gamma-ray energy and the binding energy
- Half the gamma-ray energy
Correct answer: The gamma-ray energy minus the electron's atomic binding energy
In internal conversion, the nuclear excitation energy is transferred directly to an orbital electron; the electron is ejected with energy equal to the gamma-ray energy minus its atomic binding energy.
Question 2: Which interaction dominates for low-energy photons (<100 keV) in high-Z materials?
- Compton scattering
- Pair production
- Photoelectric effect (Correct answer)
- Rayleigh (coherent) scattering only
Correct answer: Photoelectric effect
The photoelectric effect dominates at low photon energies and is proportional to Z⁴–Z⁵, making it dominant in high-Z materials at energies below ~100 keV.
Question 3: The specific ionization of a charged particle in air generally increases as the particle slows down near the end of its range, forming a region known as the:
- Bragg peak (Correct answer)
- Compton plateau
- Auger maximum
- Raman edge
Correct answer: Bragg peak
As heavy charged particles slow near the end of their range, the interaction cross section increases, producing a sharp maximum in ionization density called the Bragg peak.
Question 4: A radionuclide decays by beta-minus emission. Which statement about the emitted beta particle energy spectrum is correct?
- It is a discrete line spectrum at a single energy
- It is a continuous spectrum with a maximum energy (Emax) (Correct answer)
- It has two discrete energy peaks
- Energy is always equally shared between the beta particle and gamma ray
Correct answer: It is a continuous spectrum with a maximum energy (Emax)
Beta particles are emitted with a continuous spectrum from near zero up to Emax because the available decay energy is shared between the beta particle and the antineutrino.
Question 5: The nuclear binding energy per nucleon is greatest for nuclides near which mass number?
- A ≈ 4 (helium)
- A ≈ 56 (iron) (Correct answer)
- A ≈ 120 (tin)
- A ≈ 238 (uranium)
Correct answer: A ≈ 56 (iron)
The binding energy per nucleon curve peaks around A = 56 (iron-56), which is why fusion of light elements and fission of heavy elements both release energy.
Question 6: Coherent (Rayleigh) scattering of photons differs from Compton scattering in that it:
- Transfers significant energy to the recoil electron
- Scatters the photon with no energy transfer to the atom (Correct answer)
- Produces secondary characteristic X-rays
- Requires photon energies above 1.022 MeV
Correct answer: Scatters the photon with no energy transfer to the atom
In Rayleigh scattering, the photon is deflected by the atom as a whole with essentially no energy transfer; the wavelength (and energy) of the photon remains unchanged.
Question 7: The dose equivalent (H) is calculated as:
- H = D × Q, where D is absorbed dose and Q is radiation quality factor (Correct answer)
- H = D / Q
- H = D + Q
- H = D × LET only, without a quality factor
Correct answer: H = D × Q, where D is absorbed dose and Q is radiation quality factor
Dose equivalent H = D × Q (in older ICRP terminology), where D is absorbed dose in gray and Q is the quality factor reflecting the relative biological effectiveness of the radiation type.
NRRPT Physics and Interactions 5
Internal conversion (IC) electrons are emitted with energies equal to: