CHAPTER 13 -- SCATTERING AND INTERACTION TYPES
When particles or waves encounter matter, they can be scattered or absorbed.
13.1 ELASTIC SCATTERING
In elastic scattering, the kinetic energy of the system is conserved. The incident particle changes direction but does not lose energy to the internal states of the target.
- Rayleigh Scattering: Scattering of light by particles much smaller than the wavelength (e.g., blue sky caused by air molecules). Scattering intensity is proportional to 1 / lambda^4.
- Thomson Scattering: Low-energy photon scattering off a free electron.
13.2 INELASTIC SCATTERING
In inelastic scattering, kinetic energy is not conserved. Energy is transferred between the incident particle and the internal energy of the target.
- Compton Scattering: A photon collides with an electron, transferring energy to it. The scattered photon has a longer wavelength.
Delta_lambda = (h / m_e * c) * (1 - cos(theta))
- Raman Scattering: Scattering of photons by molecules where the photon gains or loses energy corresponding to vibrational/rotational transitions.
13.3 ENERGY TRANSFER MECHANISMS
- Photoelectric Effect: A photon is completely absorbed by an atom, ejecting an electron. Dominant at low photon energies.
- Pair Production: A high-energy photon (> 1.022 MeV) interacts with a nucleus and converts into an electron-positron pair.
13.4 RADAR REFLECTION VS ABSORPTION
In radar systems:
- Reflection: Conductive surfaces (metals) reflect EM waves efficiently. The skin depth is small, so the wave essentially bounces off.
- Absorption: Stealth technology uses materials (Radar Absorbent Material - RAM) that absorb the incoming wave energy (via dielectric or magnetic loss) rather than reflecting it back to the source.
- Scattering Geometry: Shape also matters. Faceted surfaces deflect waves away from the receiver.
