\(\renewcommand\AA{\unicode{x212B}}\)

FlatPlatePaalmanPingsCorrection v1¶

../_images/ImageNotFound.png — Enable screenshots using DOCS_SCREENSHOTS in CMake¶

Summary ¶

Calculates absorption corrections for a flat plate 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).
SampleThickness	Input	number	0	Sample thickness in cm
SampleAngle	Input	number	0	Angle between incident beam and normal to flat plate surface
CanWorkspace	Input	MatrixWorkspace		Name for the input container workspace
CanChemicalFormula	Input	string		Container 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).
CanFrontThickness	Input	number	0	Container front thickness in cm
CanBackThickness	Input	number	0	Container back thickness in cm
NumberWavelengths	Input	long	10	Number of wavelengths for calculation
Interpolate	Input	boolean	True	Interpolate the correction workspaces to match the sample workspace
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 only in Efixed energy transfer mode.
OutputWorkspace	Output	WorkspaceGroup	Mandatory	The output corrections workspace group

Calculates absorption corrections for an infinite flat plate sample giving output in the Paalman and Pings absorption factors: \(A_{s,s}\) (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).

Details of the analytical method used to calculate the correction factors is available in RAL Technical Report 74-103.

Restrictions on the input workspace ¶

The input workspaces must have a fully defined instrument.
In the energy transfer modes other than Efixed they have to have X axis units of wavelength.

Efixed mode ¶

In Efixed mode, the correction will be computed for a single wavelength number derived from the analyser or monochromator energy, which by default will be attempted to be read from the instrument parameters (named Efixed), but can also be overridden in the Efixed input property. In this case, the NumberWavelengths and Interpolate options will be ignored.

Workflow ¶

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 = FlatPlatePaalmanPingsCorrection(SampleWorkspace=sample,
                                       SampleChemicalFormula='H2-O',
                                       SampleThickness=0.1,
                                       SampleAngle=45,
                                       CanWorkspace=can,
                                       CanChemicalFormula='V',
                                       CanFrontThickness=0.01,
                                       CanBackThickness=0.01,
                                       Emode='Indirect',
                                       Efixed=1.845)

print('Correction workspaces: %s' % (', '.join(corr.getNames())))

Output:

Correction workspaces: corr_ass, corr_assc, corr_acsc, corr_acc

Source ¶

Python: FlatPlatePaalmanPingsCorrection.py