Radiation Processes in Astroparticle Physics

Vocabulary flashcards detailing radiation processes, photon and charged particle interactions, and hadronic decay chains based on astroparticle physics lecture notes.

Radiation processes

The mechanisms describing how particles and photons interact with matter and how they lose, transfer, or convert energy.

Photoelectric absorption

A process where a photon is completely absorbed by an atom, using its energy to overcome the electron's binding energy and eject the electron with kinetic energy $E_e = E_\text{gamma} - E_{\text{binding}}$.

Photoelectric cross section

The probability of interaction which scales approximately as $\sigma \propto \frac{Z^\alpha}{E^3}$ where $Z$ is the atomic number and $\alpha \approx 4-5$, dominating at low energies.

Compton scattering

The collision between a photon and an electron where the photon transfers part of its energy and survives but changes direction.

Thomson cross section

The classical low-energy limit of photon-electron scattering where $E_\gamma \ll m_e c^2$, resulting in a constant cross section $\sigma_T = \frac{8 \pi r_e^2}{3}$.

Klein-Nishina cross section

The description of Compton scattering at relativistic photon energies ($E_\gamma \gg m_e c^2$) where the cross section decreases with energy as $\sigma_{KN} = \frac{3 \sigma_T}{8} \frac{\ln(2E)}{E}$.

Pair production

The process where a photon converts into matter, creating an electron and a positron ($\gamma \rightarrow e^- + e^+$) in the presence of a nucleus's electric field.

Energy threshold for pair production

The minimum energy a photon must provide to create a pair, calculated as $2m_e c^2 \approx 1.02\,\text{MeV}$, below which the process is impossible.

Ionization

An interaction where a charged particle transfers enough energy via Coulomb forces to remove an electron from an atom, producing a free electron and a positive ion.

Stopping power

A quantity denoted as $- \frac{dE}{dx}$ that describes the average rate at which a particle loses energy while traversing matter.

Bethe formula

The fundamental equation in detector physics that describes the average energy loss due to ionization as a function of particle velocity, charge, and material properties.

Minimum ionizing particle (MIP)

A particle, such as a cosmic-ray muon, moving at relativistic velocities whose ionization energy loss is close to the minimum of the Bethe curve.

Bremsstrahlung

Meaning "braking radiation," it is the emission of a photon by a charged particle as it is accelerated or slowed down in the electric field of a nucleus.

Bremsstrahlung mass dependence

The emitted radiation scales approximately as $\frac{1}{m^2}$, making the process significantly more important for electrons than for heavier particles like protons.

Radiation length ($X_0$)

A characteristic property of a material describing how quickly high-energy electrons lose energy through Bremsstrahlung and how likely photons satisfy pair production.

Cherenkov radiation

Emission occurring when a charged particle moves through a medium faster than the local speed of light ($v > \frac{c}{n}$), resulting in a characteristic cone of light.

Cherenkov angle ($\theta_c$)

The angle at which light is emitted relative to the particle's direction, defined by $\cos(\theta_c) = \frac{1}{n\beta}$.

Transition radiation

Emission produced when a relativistic charged particle crosses the boundary between two media with different dielectric properties.

Hadronic interactions

Inelastic nuclear collisions involving particles affected by the strong nuclear force, such as protons and neutrons, which produce particle cascades.

Pions

The lightest hadrons, produced commonly in hadronic interactions, consisting as charged ($\pi^{\pm}$) or neutral ($\pi^0$) varieties.

Neutral pion decay

An electromagnetic decay channel ($\pi^0 \rightarrow \gamma + \gamma$) that produces high-energy photons and initiates electromagnetic cascades.

Charged pion decay

A weak interaction decay occurring primary as $\pi^+ \rightarrow \mu^+ + \nu_\mu$ or $\pi^- \rightarrow \mu^- + \bar{\nu}_\mu$, producing muons and neutrinos.