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Note the format of the parameter notation SXYab, where "S" stands for scattering parameter or S-parameter, "X" is the response mode (differential or common), "Y" is the stimulus mode (differential or common), "a" is the response (output) port and b is the stimulus (input) port. This is the typical nomenclature for scattering parameters.
Modeling photon propagation with Monte Carlo methods is a flexible yet rigorous approach to simulate photon transport. In the method, local rules of photon transport are expressed as probability distributions which describe the step size of photon movement between sites of photon-matter interaction and the angles of deflection in a photon's trajectory when a scattering event occurs.
In radiotherapy, a percentage depth dose curve (PDD) (sometimes percent depth dose curve) relates the absorbed dose deposited by a radiation beam into a medium as it varies with depth along the axis of the beam.
It relates the scattered wave function with the interaction that produces the scattering (the scattering potential) and therefore allows calculation of the relevant experimental parameters (scattering amplitude and cross sections). The most fundamental equation to describe any quantum phenomenon, including scattering, is the Schrödinger equation.
Porod's law is concerned with wave numbers q that are small compared to the scale of usual Bragg diffraction; typically .In this range, the sample must not be described at an atomistic level; one rather uses a continuum description in terms of an electron density or a neutron scattering length density.
Consider the scattering of a beam of wavelength by an assembly of particles or atoms stationary at positions , =, …,.Assume that the scattering is weak, so that the amplitude of the incident beam is constant throughout the sample volume (Born approximation), and absorption, refraction and multiple scattering can be neglected (kinematic diffraction).
where G, R g, and B are constants related to the scattering contrast, structural volume, surface area, and radius of gyration. q is the magnitude of the scattering vector which is related to the Bragg spacing, d, q = 2π/d = 4π/λ sin(θ/2). λ is the wavelength and θ is the scattering angle (2θ in diffraction).
Multiple-scattering effects of light scattering by particles are treated by radiative transfer techniques (see, e.g. atmospheric radiative transfer codes). The relative size of a scattering particle is defined by its size parameter x, which is the ratio of its characteristic dimension to its wavelength: