radiationinteraction

Radiation interaction is the set of physical processes by which radiation interacts with matter. It encompasses electromagnetic radiation such as X-rays and gamma rays, as well as charged particles and, for neutrons, nuclear processes. The outcome may be energy transfer to the material, scattering of the radiation, or production of secondary particles. Interaction likelihood is described by cross sections and depends on radiation type, energy, and material composition.

Photons interact predominantly through three processes in ordinary materials: the photoelectric effect, Compton scattering, and pair production. The photoelectric effect dominates at low photon energies and high atomic number materials, leading to absorption and ejection of an electron. Compton scattering prevails at intermediate energies, transferring part of the photon energy to an electron and changing the photon's direction. Above 1.022 MeV, pair production can occur in the nuclear field, producing an electron-positron pair.

Charged particles interact mainly by ionizing and exciting atoms, losing energy as they traverse matter. For electrons and positrons, ionization and excitation dominate at moderate energies, with Bremsstrahlung radiation becoming significant at higher energies, especially in high-Z materials. Heavy charged particles such as alphas lose energy almost entirely to ionization over short ranges. These processes determine the stopping power and particle range.

Neutrons interact through the strong nuclear force rather than electric charge. They cause elastic and inelastic scattering, absorption (capture), and, for fissile materials, fission. The probability of these interactions varies strongly with neutron energy and with material composition, making neutron shielding and moderation a specialized task.

In practice, radiation interaction data underpin shielding design, dosimetry, medical imaging, and radiation therapy. Quantitative treatment relies on cross sections, attenuation coefficients, stopping powers, and transport simulations, often using Monte Carlo methods to model the stochastic nature of individual interactions and to predict dose distributions and material responses.