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PowderReduceP2D v1¶

Summary ¶

The algorithm used to process the results of powder diffraction experiments and create a ‘.p2d’ file for multidimensional Rietveld refinement.

Properties ¶

Name	Direction	Type	Default	Description
SampleData	Input	string		Datafile that should be used.
DoIntensityCorrection	Input	boolean	False	If set to True you have to declare a vanadium measurement for intensity correction.
VanaData	Input	string		Vanadium measurement for intensity correction.
DoBackgroundCorrection	Input	boolean	False	If set to True you have to declare an empty can measurement for background correction.
EmptyData	Input	string		Empty measurement of the can for background correction.
CalFile	Input	string		Calibration file.
DoEdgebinning	Input	boolean	False	If set to True you have to declare a BinEdges file.
BinEdgesFile	Input	string		BinEdges file used for edgebinning.
OutputFile	Input	string	Mandatory	Output File for p2d Data.
SystemTest	Input	boolean	False	Set to True if running a system test. Greatly decreases the amount of data used.
TwoThetaMin	Input	number	50	Minimum value for 2 Theta. Everything smaller gets removed.
TwoThetaMax	Input	number	120	Maximum value for 2 Theta. Everything bigger gets removed.
WavelengthCenter	Input	number	0.7	Center Wavelength is used to calculate automatic values for lambdaMin and lambdaMax if they are not specified.
LambdaMin	Input	number	0.3	Minimum value for lambda. Everything smaller gets removed. If zero it is not used and values get calculated from center wavelength.
LambdaMax	Input	number	1.1	Maximum value for lambda. Everything bigger gets removed. If zero it is not used and values get calculated from center wavelength.
DMin	Input	number	0.11	Minimum value for d. Everything smaller gets removed. If zero it is not used and values get calculated from 2 theta and lambda.
DMax	Input	number	1.37	Maximum value for d. Everything bigger gets removed. If zero it is not used and values get calculated from 2 theta and lambda.
DpMin	Input	number	0.48	Minimum value for dp. Everything smaller gets removed. If zero it is not used and values get calculated from 2 theta and lambda.
DpMax	Input	number	1.76	Maximum value for dp. Everything bigger gets removed. If zero it is not used and values get calculated from 2 theta and lambda.
ReturnLinearRanges	Input	boolean	False	if set to true, the algorithm would return linear detector’s ranges (dx,dy) rather then angular ranges (dAzimuthal,dPolar)
ParFile	Input	string	not_used.par	An optional file that contains of the list of angular parameters for the detectors and detectors groups; If specified, will use data from file instead of the data, calculated from the instument description. Allowed extensions: [‘.par’, ‘.phx’]
OutputParTable	Input	string	Detec	If not empty, a name of a table workspace which will contain the calculated par or phx values for the detectors.
LowerCutoff	Input	number	99.998	The percentage of the average to use as the lower bound.
Width	Input	number	150	The width of the time of flight (in microseconds) to remove from the data.
Frequency	Input	number	Optional	The frequency of the source (in Hz) used to calculate the minimum time of flight to filter.
WorkspaceName	Input	string	POWTEX	The base of the output workspace names. Names will have _group, _cal, _mask appended to them.
InstrumentName	Input	string		Optional: Name of the instrument to base the GroupingWorkspace on which to base the GroupingWorkspace.
InstrumentFilename	Input	string		Optional: Path to the instrument definition file on which to base the GroupingWorkspace. Allowed extensions: [‘.xml’]
MakeGroupingWorkspace	Input	boolean	True	Set to true to create a GroupingWorkspace with called WorkspaceName_group.
MakeCalWorkspace	Input	boolean	True	Set to true to create a CalibrationWorkspace with called WorkspaceName_cal.
MakeMaskWorkspace	Input	boolean	True	Set to true to create a MaskWorkspace with called WorkspaceName_mask.
TofMin	Input	number	0	Minimum for TOF axis. Defaults to 0.
TofMax	Input	number	Optional	Maximum for TOF axis. Defaults to Unused.
FixConversionIssues	Input	boolean	True	Set DIFA and TZERO to zero if there is an error and the pixel is masked
MaskedWorkspace	Input	string	POWTEX_mask	If given but not as a SpecialWorkspace2D, the masking from this workspace will be copied. If given as a SpecialWorkspace2D, the masking is read from its Y values.
SpectraList	Input	int list		A list of spectra to mask
DetectorList	Input	int list		A list of detector ID’s to mask
WorkspaceIndexList	Input	unsigned int list		A list of the workspace indices to mask
ForceInstrumentMasking	Input	boolean	False	Works when ‘MaskedWorkspace’ is provided and forces to use spectra-detector mapping even in case when number of spectra in ‘Workspace’ and ‘MaskedWorkspace’ are equal
StartWorkspaceIndex	Input	number	0	If other masks fields are provided, it’s the first index of the target workspace to be allowed to be masked from by these masks, if not, its the first index of the target workspace to mask. Default value is 0 if other masking is present or ignored if not.
EndWorkspaceIndex	Input	number	Optional	If other masks are provided, it’s the last index of the target workspace allowed to be masked to by these masks, if not, its the last index of the target workspace to mask. Default is number of histograms in target workspace if other masks are present or ignored if not.
ComponentList	Input	str list		A list names of components to mask
AttenuationXSection	Input	number	5.08	The ABSORPTION cross-section, at 1.8 Angstroms, for the sample material in barns. Column 8 of a table generated from http://www.ncnr.nist.gov/resources/n-lengths/.
ScatteringXSection	Input	number	5.1	The (coherent + incoherent) scattering cross-section for the sample material in barns. Column 7 of a table generated from http://www.ncnr.nist.gov/resources/n-lengths/.
SampleNumberDensity	Input	number	0.07192	The number density of the sample in number of atoms per cubic angstrom if not set with SetSampleMaterial.
CylinderSampleHeight	Input	number	4	The height of the cylindrical sample in centimetres.
CylinderSampleRadius	Input	number	0.4	The radius of the cylindrical sample in centimetres.
NumberOfSlices	Input	number	10	The number of slices into which the cylinder is divided for the calculation.
NumberOfAnnuli	Input	number	10	The number of annuli into which each slice is divided for the calculation.
ScatterFrom	Input	string	Sample	The component to calculate the absorption for (default: Sample). Allowed values: [‘Sample’, ‘Container’, ‘Environment’]
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.
CylinderAxis	Input	dbl list	0,1,0	A 3D vector specifying the cylindrical sample’s orientation
dSpaceBinning	Input	dbl list		A comma separated list of first bin boundary, width, last bin boundary. Optionally this can be followed by a comma and more widths and last boundary pairs. Negative width values indicate logarithmic binning.
dPerpendicularBinning	Input	dbl list		A comma separated list of first bin boundary, width, last bin boundary. Optionally this can be followed by a comma and more widths and last boundary pairs. Negative width values indicate logarithmic binning.
NormalizeByBinArea	Input	boolean	False	Normalize the binned workspace by the bin area.
FWHM	Input	number	2	The number of points covered, on average, by the fwhm of a peak. Passed through to FindPeaks. Default 7.
Tolerance	Input	number	2	A measure of the strictness desired in meeting the condition on peak candidates. Passed through to FindPeaks. Default 4.
PeakPositionTolerance	Input	number	0.05	Tolerance on the found peaks positions against the input peak positions. A non-positive value turns this option off.
BackgroundType	Input	string	Quadratic	The type of background of the histogram. Present choices include Linear and Quadratic. Allowed values: [Linear, Quadratic]
HighBackground	Input	boolean	True	Flag to indicate that the peaks are relatively weak comparing to background.
WorkspaceIndex	Input	number	Optional	If set, will remove peaks only in the given spectrum of the workspace. Otherwise, all spectra will be searched.
Filter	Input	string	Butterworth	The type of the applied filter. Allowed values: [Zeroing, Butterworth]
Params	Input	string	20,2	The filter parameters: For Zeroing, 1 parameter: n - an integer greater than 1 meaning that the Fourier coefficients with frequencies outside the 1/n of the original range will be set to zero. For Butterworth, 2 parameters: n and order, giving the 1/n truncation and the smoothing order.
IgnoreXBins	Input	boolean	True	Ignores the requirement that X bins be linear and of the same size. Set this to true if you are using log binning. The output X axis will be the same as the input either way.
AllSpectra	Input	boolean	True	Smooth all spectra.
WorkspaceIndexSmooth	Input	number	0	Workspace index for smoothing
AddMinimum	Input	boolean	True	If set to True, adds the most negative intensity to all intensities.
ResetValue	Input	number	0	Set negative intensities to the specified value (default=0).
AddMinimumVana	Input	boolean	True	If set to True, adds the most negative intensity to all intensities.
ResetValueVana	Input	number	1	Set negative intensities to the specified value (default=1).

This algorithm can be used for one run of sample data. For correction and background reduction additional measurements of Vanadium(VanaData) and an empty can(EmptyData) can be specified but are not necessary. If an empty measurement is specified, it is substracted from the sample measurement. If a Vanadium measurement is specified, the sample measurement is divided by the vanadium measurement. If either or both are not specified these steps are skipped. It is highly recommended to specify both.

Calibration, Grouping, Masking ¶

The calibration is done using the Calibration File(CalFile). Additionally three implicit workspaces (<instrument>_group, <instrument>_cal, <instrument>_mask) are created during the algorithms execution if they do not exist already.

Binning ¶

The recommended binning (edgebinning) requires an edgebinning file to be specified. If no edgebinning file is specified, logarithmic binning (standard values: x1=-0.008, x2=0.01) is used.

Manipulating data with constants ¶

The reduced data are checked for negative intensities. If any are found, they are removed either by adding the most negative valueor by setting the intensity to a specified value. This is done, because negative values cannot be processed in multidimensional Rietveld refinement.

Output ¶

The output of this Workflow algorithm is a p2d file. The p2d file contains values for 2Theta and lambda (columns 1 and 2) as well as d and dperp (columns 3 and 4). Column 5 contains the intensity data.

Workflow ¶

../_images/PowderReduceP2D_ProcessSampleRun.svg

../_images/PowderReduceP2D_ProcessCanRun.svg

../_images/PowderReduceP2D_ProcessVanadiumRun.svg

Usage ¶

This is a workflow algorithm to process the results of powder diffraction experiments and create a p2d file for multidimensional Rietveld refinement. The algorithm is currently tested for the Instruments PG3 (POWGEN) and PTXatPG3 (POWTEX detector at POWGEN instrument).

Categories: AlgorithmIndex | Diffraction\Reduction

Source ¶

Python: PowderReduceP2D.py