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FlatPlateAbsorption v1¶
Summary¶
Calculates binbybin correction factors for attenuation due to absorption and scattering in a sample of ‘flat plate’ geometry.
See Also¶
Properties¶
Name 
Direction 
Type 
Default 
Description 

InputWorkspace 
Input 
Mandatory 
The X values for the input workspace must be in units of wavelength 

OutputWorkspace 
Output 
Mandatory 
Output workspace name 

ScatterFrom 
Input 
string 
Sample 
The component to calculate the absorption for (default: Sample). Allowed values: [‘Sample’, ‘Container’, ‘Environment’] 
AttenuationXSection 
Input 
number 
Optional 
The ABSORPTION crosssection, at 1.8 Angstroms, for the sample material in barns. Column 8 of a table generated from http://www.ncnr.nist.gov/resources/nlengths/. 
ScatteringXSection 
Input 
number 
Optional 
The (coherent + incoherent) scattering crosssection for the sample material in barns. Column 7 of a table generated from http://www.ncnr.nist.gov/resources/nlengths/. 
SampleNumberDensity 
Input 
number 
Optional 
The number density of the sample in number of atoms per cubic angstrom if not set with SetSampleMaterial 
NumberOfWavelengthPoints 
Input 
number 
Optional 
The number of wavelength points for which the numerical integral is calculated (default: all points) 
ExpMethod 
Input 
string 
Normal 
Select the method to use to calculate exponentials, normal or a fast approximation (default: Normal). Allowed values: [‘Normal’, ‘FastApprox’] 
EMode 
Input 
string 
Elastic 
The energy mode (default: elastic). Allowed values: [‘Elastic’, ‘Direct’, ‘Indirect’] 
EFixed 
Input 
number 
0 
The value of the initial or final energy, as appropriate, in meV. Will be taken from the instrument definition file, if available. 
SampleHeight 
Input 
number 
Mandatory 
The height of the plate in cm 
SampleWidth 
Input 
number 
Mandatory 
The width of the plate in cm 
SampleThickness 
Input 
number 
Mandatory 
The thickness of the plate in cm 
ElementSize 
Input 
number 
1 
The size of one side of an integration element cube in mm 
Description¶
This algorithm uses a numerical integration method to calculate attenuation factors resulting from absorption and single scattering in a flat plate (slab) sample with the dimensions and material properties given. Factors are calculated for each spectrum (i.e. detector position) and wavelength point, as defined by the input workspace. The sample is divided up into cuboids having sides of as close to the size given in the ElementSize property as the sample dimensions will allow. Thus the calculation speed depends linearly on the total number of bins in the workspace and goes as \(\rm{ElementSize}^{3}\).
Path lengths through the sample are then calculated for the centrepoint of each element and a numerical integration is carried out using these path lengths over the volume elements.
Restrictions on the input workspace¶
The input workspace must have units of wavelength. The instrument associated with the workspace must be fully defined because detector, source & sample position are needed.
Usage¶
Example:
ws = CreateSampleWorkspace("Histogram",NumBanks=1,BankPixelWidth=2)
ws = ConvertUnits(ws,"Wavelength")
SetSampleMaterial(ws,ChemicalFormula="V")
wsOut = FlatPlateAbsorption(ws, SampleHeight=1, SampleWidth=0.5, SampleThickness=0.5)
print("The created workspace has one entry for each spectra: %i" % wsOut.getNumberHistograms())
Output:
The created workspace has one entry for each spectra: 4
Categories: AlgorithmIndex  CorrectionFunctions\AbsorptionCorrections
Source¶
C++ header: FlatPlateAbsorption.h
C++ source: FlatPlateAbsorption.cpp