NRRPT Radiation Fundamentals & Detection 2 — Questions and Answers
Question 1: Which interaction mechanism is responsible for most of the ionization produced by alpha particles in tissue?
- Photoelectric effect
- Coulombic interactions with orbital electrons (Correct answer)
- Nuclear collisions
- Pair production
Correct answer: Coulombic interactions with orbital electrons
Alpha particles lose energy primarily through coulombic (electrostatic) interactions with orbital electrons, causing excitation and ionization along their path.
Question 2: A Geiger-Müller tube operating in the Geiger region produces output pulses that are:
- Proportional to the initial ion pairs created
- Independent of the energy of the incident radiation (Correct answer)
- Larger for alpha particles than for beta particles
- Dependent on the applied voltage within the plateau
Correct answer: Independent of the energy of the incident radiation
In the Geiger region, avalanche discharge saturates the detector so all pulses are the same size regardless of incident radiation energy.
Question 3: The Q-value of a nuclear reaction is defined as:
- The total kinetic energy of the products minus that of the reactants (Correct answer)
- The binding energy per nucleon of the product nucleus
- The difference in atomic mass numbers between reactants and products
- The threshold energy required to initiate the reaction
Correct answer: The total kinetic energy of the products minus that of the reactants
The Q-value equals the kinetic energy of products minus that of reactants, which corresponds to the mass-energy difference (Q = Δmc²).
Question 4: Which property of a scintillation detector makes it superior to a GM tube for gamma spectroscopy?
- Higher operating voltage
- Pulse amplitude proportional to photon energy (Correct answer)
- Ability to detect alpha particles
- Insensitivity to neutrons
Correct answer: Pulse amplitude proportional to photon energy
Scintillation detectors produce light output proportional to the deposited energy, enabling energy discrimination and spectroscopy.
Question 5: Thermoluminescent dosimeters (TLDs) measure dose by:
- Counting ion pairs produced in a gas cavity
- Reading the optical density of darkened crystals
- Measuring charge released when heated crystals luminesce (Correct answer)
- Detecting current flow through a semiconductor junction
Correct answer: Measuring charge released when heated crystals luminesce
TLDs trap electrons in crystal defects; when heated, electrons release energy as light proportional to absorbed dose.
Question 6: The specific ionization of a charged particle in matter generally increases as the particle:
- Gains kinetic energy
- Slows down near the end of its range (Correct answer)
- Increases in mass at constant velocity
- Moves from high-density to low-density material
Correct answer: Slows down near the end of its range
Specific ionization increases sharply near the end of a charged particle's range, forming the Bragg peak as the particle slows.
Question 7: Which of the following nuclides undergoes electron capture (EC) decay?
- Carbon-14
- Strontium-90
- Iron-55 (Correct answer)
- Cobalt-60
Correct answer: Iron-55
Iron-55 decays by electron capture to Manganese-55, emitting characteristic X-rays rather than a beta particle.
NRRPT Radiation Fundamentals & Detection 2
Which interaction mechanism is responsible for most of the ionization produced by alpha particles in tissue?