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CylinderPaalmanPingsCorrection v2¶

Summary ¶

Calculates absorption corrections for a cylindrical or annular sample using Paalman & Pings format.

Properties ¶

Name	Direction	Type	Default	Description
SampleWorkspace	Input	MatrixWorkspace	Mandatory	Name for the input Sample workspace.
SampleChemicalFormula	Input	string		Sample chemical formula
SampleCoherentXSection	Input	number	0	The coherent cross-section for the sample material in barns. To be used instead of Chemical Formula.
SampleIncoherentXSection	Input	number	0	The incoherent cross-section for the sample material in barns. To be used instead of Chemical Formula.
SampleAttenuationXSection	Input	number	0	The absorption cross-section for the sample material in barns. To be used instead of Chemical Formula.
SampleDensityType	Input	string	Mass Density	Use of Mass density or Number density for the sample. Allowed values: [‘Mass Density’, ‘Number Density’]
SampleNumberDensityUnit	Input	string	Atoms	Choose which units SampleDensity refers to. Allowed values: [Atoms, Formula Units]. Allowed values: [‘Atoms’, ‘Formula Units’]
SampleDensity	Input	number	0.1	The value for the sample Mass density (g/cm^3) or Number density (1/Angstrom^3).
SampleInnerRadius	Input	number	0.05	Sample inner radius
SampleOuterRadius	Input	number	0.1	Sample outer radius
CanWorkspace	Input	MatrixWorkspace		Name for the input Can workspace.
CanChemicalFormula	Input	string		Can chemical formula
CanCoherentXSection	Input	number	0	The coherent cross-section for the can material in barns. To be used instead of Chemical Formula.
CanIncoherentXSection	Input	number	0	The incoherent cross-section for the can material in barns. To be used instead of Chemical Formula.
CanAttenuationXSection	Input	number	0	The absorption cross-section for the can material in barns. To be used instead of Chemical Formula.
CanDensityType	Input	string	Mass Density	Use of Mass density or Number density for the can. Allowed values: [‘Mass Density’, ‘Number Density’]
CanNumberDensityUnit	Input	string	Atoms	Choose which units CanDensity refers to. Allowed values: [Atoms, Formula Units]. Allowed values: [‘Atoms’, ‘Formula Units’]
CanDensity	Input	number	0.1	The value for the can Mass density (g/cm^3) or Number density (1/Angstrom^3).
CanOuterRadius	Input	number	0.15	Can outer radius
BeamHeight	Input	number	3	Beam height
BeamWidth	Input	number	2	Beam width
StepSize	Input	number	0.002	Step size
Interpolate	Input	boolean	True	Interpolate the correction workspaces to match the sample workspace
NumberWavelengths	Input	number	10	Number of wavelengths for calculation
Emode	Input	string	Elastic	Energy transfer mode. Allowed values: [‘Elastic’, ‘Indirect’, ‘Direct’, ‘Efixed’]
Efixed	Input	number	0	Analyser energy (mev). By default will be read from the instrument parameters. Specify manually to override. This is used in energy transfer modes other than Elastic.
OutputWorkspace	Output	WorkspaceGroup	Mandatory	The output corrections workspace group

Calculates absorption corrections for a cylindrical or annular sample giving output in the Paalman and Pings absorption factors: \(A_{s,s}\) (correction factor for scattering and absorption in sample), \(A_{s,sc}\) (scattering in sample and absorption in sample and container), \(A_{c,sc}\) (scattering in container and absorption in sample and container) and \(A_{c,c}\) (scattering and absorption in container). This uses the equations from Kendig Pings 1965 which account for partially illuminated samples.

Restrictions on the input workspace ¶

The input workspace must have a fully defined instrument.

Energy transfer modes ¶

The algorithm operates in different energy transfer modes, where the incident (\(\lambda_1\)) and the final (\(\lambda_2\)) wavelengths are defined as follows:

Elastic : \(\lambda_1 = \lambda_2 = \lambda_{step}\)
Direct : \(\lambda_1 = \lambda_{fixed}, \lambda_2 = \lambda_{step}\)
Indirect : \(\lambda_1 = \lambda_{step}, \lambda_2 = \lambda_{fixed}\)
Efixed : \(\lambda_1 = \lambda_2 = \lambda_{fixed}\),

where \(\lambda_{fixed}\) is computed from the Efixed value corresponding to the monochromator or the analyser, and \(\lambda_{step}\) iterates equidistantly over the wavelength points in the input workspace x-axis, controlled by NumberWavelengths property.

Therefore, in all the modes except Efixed, the input workspaces must have the x-axis unit of Wavelength. In all the modes except Elastic, Efixed value is needed. By default it will be attempted to be read from the instrument parameters, but can be overridden by the homonym property. In the Efixed mode the NumberWavelengths and Interpolate options will be ignored.

Usage ¶

Example:

# Create a sample workspace
sample = CreateSampleWorkspace(NumBanks=1, BankPixelWidth=1,
                               XUnit='Wavelength',
                               XMin=6.8, XMax=7.9,
                               BinWidth=0.1)

# Copy and scale it to make a can workspace
can = CloneWorkspace(InputWorkspace=sample)
can = Scale(InputWorkspace=can, Factor=1.2)

# Calculate absorption corrections
corr = CylinderPaalmanPingsCorrection(SampleWorkspace=sample,
                                      SampleChemicalFormula='H2-O',
                                      SampleInnerRadius=0.05,
                                      SampleOuterRadius=0.1,
                                      CanWorkspace=can,
                                      CanChemicalFormula='V',
                                      CanOuterRadius=0.15,
                                      BeamHeight=0.1,
                                      BeamWidth=0.1,
                                      StepSize=0.002,
                                      Emode='Indirect',
                                      Efixed=1.845)

print('Correction workspaces: {}'.format((', '.join(corr.getNames()))))

Output:

Correction workspaces: corr_ass, corr_assc, corr_acsc, corr_acc

References ¶

Kendig, A. P., and C. J. Pings. X‐Ray Absorption Factors for Cylindrical Samples in Annular Sample Cells Exposed to Incident Beams of Limited Width. Journal of Applied Physics 36.5 (1965): 1692-1698 doi: 10.1063/1.1703111

Source ¶

Python: CylinderPaalmanPingsCorrection2.py