/Multiple Scattering

Group 1

Concerning slide where we define "nomenclature" 

Distorted Wave Born Approximation, is some sort of multiple scattering, because incoming bam is split into reflected and refracted beams

Joachim: reflection from interface can be described as scattering, in Sinha paper,m thye discuss scattering from inginite volume and then describe reflection. Known way tod eal with reflection and refraction, this gives DWBA. scattering is not by interfaces, they are taken into account by DWBA.

Henrich: Parratt algorithm is a dynamic approach. it takes into account multiple reflections. Do not know how it can get more precise.

reflection and refraction should be excluded from multiple scattering

if we calculate all transmission and reflection coefficients, we are left with 16 rflection and transmission combination terms. some have different momentum transfers. this is shown like reflection/refraction, reflection/reflection. should we call this multiple scattering.

Ammat: Multiple scattering: Born approximation is single scattering event. Multile scattering comes with further scatterign events, is not included in DWBA. magnetic interactions. when they are important, we cannot reply on Born approximation, but use multiple scattering in solid state. when first scattering event happens, system responds. this process continues. is a dynamical process, not single kinematical process.

"Dynamic" term different than dynamic (meaning energy transfer)

Boris: full solution, we have to consider changes in the sample. even i first order scattring calculations,

Philipp (question to Boris): have you ever confused the term dynamic scattering with inelastic scattering? Boris: with ToF is feasible. 100 neV (depends on wavelengths), to see this you need reasonable resolution in pulse. perfect for SNS, here at ILL we have rather broad pulse.

experiment from Sascha Frank on standing/moving waves. if it is standing waves, density gives periodic structure and same stripes. alternatively, if we have one magnon / phonon, we have one branch (stokes/antistokes). the excitations produce the harmonic.

Philipp: we consider higher orders of BA as multiple scattering? Boris: object, because Born series valid for amplitudes and valid within the transverse coherence lengths, that all interfaces produce one plane wave in same direction if we have lateral homogeneity and interfere with each other. but, multiple scattering when events in sequence but incoherent in between of them. it could be multiple specular reflection, but gap should be greater than transverse coherence length (where particles reflct multiply within 1 cm gap). may look like a semantic differenc.e you take interference between ecvents or not? multiple scattering requires than path length is much greater than mean free path (1/Sigma_total*density of the particles).

when BA is valid, or,

Joachim: multiple scattering (in book of Sears) is treated in terms of transport theory. need to have a distance to avoid interference