Backscattering occurs in quite different physical situations. The incoming waves or particles can be deflected from their original direction by quite different mechanisms:
Rayleigh scattering of electromagnetic waves from small particles, diffuse reflection from large particles, or Mie scattering in the intermediate case, causing alpenglow and gegenschein, and showing up in weather radar;
inelastic collisions between electromagnetic waves and the transmitting medium (Brillouin scattering and Raman scattering, important in fiber optics, see below;
inelastic collisions between accelerated ions and a sample (Rutherford backscattering)
Bragg diffraction from crystals, used in inelastic scattering experiments (neutron backscattering, X-ray backscattering spectroscopy);
Compton scattering, used in Backscatter X-ray imaging.
Thanks, Huntsville! Definately looks like the technology improves security. Would take a backscatter over a pat-down anyday.