MultipleScatteringCylinderAbsorption dialog.
Table of Contents
Multiple scattering absorption correction, originally used to correct vanadium spectrum at IPNS.
| Name | Direction | Type | Default | Description |
|---|---|---|---|---|
| InputWorkspace | Input | MatrixWorkspace | Mandatory | The name of the input workspace. |
| OutputWorkspace | Output | MatrixWorkspace | Mandatory | The name of the output workspace. |
| AttenuationXSection | Input | number | 2.8 | Coefficient 1, absorption cross section / 1.81 if not set with SetSampleMaterial |
| ScatteringXSection | Input | number | 5.1 | Coefficient 3, total scattering cross section if not set with SetSampleMaterial |
| SampleNumberDensity | Input | number | 0.0721 | Coefficient 2, density if not set with SetSampleMaterial |
| CylinderSampleRadius | Input | number | 0.3175 | Sample radius, in cm |
This algorithm is a port to C++ of a multiple scattering absorption correction, used to correct the vanadium spectrum for the GPPD instrument at the IPNS. The correction calculation was originally worked out by Jack Carpenter and Asfia Huq and implemented in Java by Alok Chatterjee. The java code was translated to C++ in Mantid by Dennis Mikkelson.
In [1]__ we see that the calculation of the attenuation factor F involves
an integral over the sample cylinder. By expanding the integrands as a power series,
we can factor out any dependence on scattering cross section and radius.
These integral terms are denoted by 
and so we may write:
where 
is the inverse scattering length.
The functions 
are written in terms of Chebyshev
expansion coefficients:
where the Chebyshev coefficients 
up to m + n
5 have been tabulated and are stored as an array by the algorithm.
Example: A simple cylindrical sample
ws = CreateSampleWorkspace("Histogram",NumBanks=1,BankPixelWidth=1)
ws = ConvertUnits(ws,"Wavelength")
ws = Rebin(ws,Params=[1])
SetSampleMaterial(ws,ChemicalFormula="V")
#restrict the number of wavelength points to speed up the example
wsOut = MultipleScatteringCylinderAbsorption(ws,CylinderSampleRadius=0.2)
print "Output: ", wsOut.readY(0)
Output:
Output: [ 6.1210107 6.57502041 19.47638255 7.58160094 8.13860778
2.33885171]
| [1] | J.M. Carpenter Attenuation Correction Factor for Scattering from Cylindrical Targets Review of Scientific Instruments 40.4 (1969): 555. doi: 10.1063/1.1684003 |
| [2] | D.F.R. Mildner, J.M. Carpenter, and C.A. Pelizzari Generalized Attenuation Correction Factor for Scattering from Cylindrical Targets Review of Scientific Instruments 45.4 (1974): 572. doi: 10.1063/1.1686687 |
| [3] | D.F.R. Mildner and J.M.Carpenter Improvements to the Chebyshev Expansion of Attenuation Correction Factors for Cylindrical Samples. J Appl Crystallogr 23.5 (1990): 378–386 doi: 10.1107/S0021889890005258 |
See also
Algorithm MayersSampleCorrection v1
Categories: Algorithms | CorrectionFunctions\AbsorptionCorrections
C++ source: MultipleScatteringCylinderAbsorption.cpp
C++ header: MultipleScatteringCylinderAbsorption.h