CylinderPaalmanPingsCorrection v2¶

CylinderPaalmanPingsCorrection dialog.

Table of Contents

Summary
Properties
Description
- Restrictions on the input workspace
- Energy transfer modes
Usage
Related Algorithms
Source

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	Mandatory	Sample chemical formula
SampleDensityType	Input	string	Mass Density	Use of Mass density or Number density. Allowed values: [‘Mass Density’, ‘Number Density’]
SampleDensity	Input	number	0.1	Mass density (g/cm^3) or Number density (atoms/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
CanDensityType	Input	string	Mass Density	Use of Mass density or Number density. Allowed values: [‘Mass Density’, ‘Number Density’]
CanDensity	Input	number	0.1	Mass density (g/cm^3) or Number density (atoms/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).

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: %s' % (', '.join(corr.getNames()))

Output:

Correction workspaces: corr_ass, corr_assc, corr_acsc, corr_acc

Source ¶

Python: CylinderPaalmanPingsCorrection2.py