Module Sample-Environment

# VITESS Module Sample-Environment

The module sample_environ simulates coherent and incoherent elastic scattering in material around the sample. This sample environment is supposed to have the form of a hollow cylinder centered around the sample. As the beam has to pass through it twice, it also has to be added twice to the list of components in the instrument. For more than one sample environment, all have to appear twice in the order in which the neutrons pass through them. In each case, a parameter has to be set defining if it is before or after the sample. The modules before the sample have to be marked as direction 'in', those after the sample as direction 'out'. So the order of modules for 2 sample environments around a sample would be:
...
outer_environment (in)
inner_environment (in)
sample
inner_environment (out)
outer_environment (out)
...
Coherent as well as incoherent scattering is treated. Therefore, data about the properties of each sample environment have to be given in a parameter file: size, scattering coefficients, structure factor file and the unit cell volume. The first sample environment defines the center position of the sample and all sample environments. The sample and all following sample enviroment modules have to give (0,0,0) as sample (environment) position to express that they are all concentric.
Passing through the sample environment creates new trajectories: For each trajectory entering a transmitted, an isotropically scattered and N Bragg scattered trajectories are created. (N is the number of d-spacings in the structure factor file that fulfill the Bragg condition.) All these trajectories are then scattered in the sample and in the same way in all following sample environment modules. The colour marking the coherently scattered neutrons can be set. The incoherently scattered neutrons are marked by a number that is 1 higher than the coherently scattered neutrons. The neutrons scattered at the sample can also be marked by a colour. In this way, scattering from all parts of sample and sample environment can be distinguished and separated later on.

### Parameters for module 'eval_sans'

Parameter Unit | Description | Range or Values | Command Option
parameter file | The parameter file describes the geometry and compositions of the sample environment | - | -F
x y z [cm] | x-, y and z-position of the centre of the sample environment (usually the sample position) in the frame of the previous module | any | -x -y -z
colour | The trajectories will be marked by a so-called 'colour' to show that they are scattering in this sample environment the given colour is used for coherent scattering, the incoherent scattering is marked with (colour+1) | >=0 | -c
direction | in : sample environment before sample out: sample environment after sample | in out | -r

### File Input Parameters

Parameter Unit | Description | Range or Values
structure factor file | The spectrum file: it contains the d-spacing values | -
thickness [cm] | thickness of the hollow cylinder surrounding the sample | >0
diameter [cm] | outer diameter of the hollow cylinder | >0
height [cm] | outer height of the cylinder | >0
incoherent scattering [1/cm] | macroscopic incoherent scattering cross-section | >=0
total scattering [1/cm] | macroscopic total scattering cross-section | >=0
absorption [1/cm] | macroscopic absorption cross-section (with respect to a wavelength of 1.798 A) | >=0
unit cell volume [Å^3] | Unit cell volume (this is necessary for normalisation of the scattering probability) | > 0

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Last modified: Tue May 8 17:08:06 MET DST 2001