Physics and Interactions Flashcards

What is the primary interaction mechanism of alpha particles with matter?

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.

The linear energy transfer (LET) of a radiation type is best described as:

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.

Which process is responsible for the production of characteristic X-rays?

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.

The Q-value of a nuclear reaction is defined as:

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.

Pair production requires a minimum photon energy of approximately:

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.

Which nuclear decay mode results in no change in atomic mass number (A) but increases atomic number (Z) by one?

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.

The cross section for neutron capture (n,γ) in most nuclides generally varies with neutron energy as:

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).