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SNSPowderReduction v1¶

Summary ¶

The algorithm used for reduction of powder diffraction data obtained on SNS instruments (e.g. PG3)

Properties ¶

Name	Direction	Type	Default	Description
Filename	Input	list of str lists	Mandatory	Files to combine in reduction. Allowed extensions: [‘_event.nxs’, ‘.nxs.h5’]
PreserveEvents	Input	boolean	True	If the InputWorkspace is an EventWorkspace, this will preserve the full event list (warning: this will use much more memory!).
DMin	Input	dbl list		Minimum for Dspace axis. (Default 0.)
DMax	Input	dbl list		Maximum for Dspace axis. (Default 0.)
DeltaRagged	Input	dbl list		Step parameter for rebin
Sum	Input	boolean	False	Sum the runs. Does nothing for characterization runs
PushDataPositive	Input	string	None	Add a constant to the data that makes it positive over the whole range. Allowed values: [‘None’, ‘ResetToZero’, ‘AddMinimum’]
BackgroundNumber	Input	long list	0	If specified overrides value in CharacterizationRunsFile If -1 turns off correction.
VanadiumNumber	Input	long list	0	If specified overrides value in CharacterizationRunsFile. If -1 turns off correction.
VanadiumBackgroundNumber	Input	long list	0	If specified overrides value in CharacterizationRunsFile. If -1 turns off correction.
CalibrationFile	Input	string		Allowed extensions: [‘.h5’, ‘.hd5’, ‘.hdf’, ‘.cal’]
GroupingFile	Input	string		Overrides grouping from CalibrationFile. Allowed extensions: [‘.xml’]
CharacterizationRunsFile	Input	list of str lists		File with characterization runs denoted. Allowed values: [‘txt’]
ExpIniFilename	Input	string		Allowed extensions: [‘.ini’]
LorentzCorrection	Input	boolean	False	Multiply each spectrum by sin(theta) where theta is half of the Bragg angle
UnwrapRef	Input	number	0	Reference total flight path for frame unwrapping. Zero skips the correction
LowResRef	Input	number	0	Reference DIFC for resolution removal. Zero skips the correction
CropWavelengthMin	Input	number	0	Crop the data at this minimum wavelength. Overrides LowResRef.
CropWavelengthMax	Input	number	Optional	Crop the data at this maximum wavelength. Forces use of CropWavelengthMin.
RemovePromptPulseWidth	Input	number	0	Width of events (in microseconds) near the prompt pulse to remove. 0 disables
MaxChunkSize	Input	number	0	Specify maximum Gbytes of file to read in one chunk. Default is whole file.
Binning	Input	dbl list	0,0,0	Positive is linear bins, negative is logorithmic
ResampleX	Input	number	0	Number of bins in x-axis. Non-zero value overrides “Params” property. Negative value means logarithmic binning.
BinInDspace	Input	boolean	True	If all three bin parameters a specified, whether they are in dspace (true) or time-of-flight (false)
StripVanadiumPeaks	Input	boolean	True	Subtract fitted vanadium peaks from the known positions.
VanadiumFWHM	Input	number	7	Default=7
VanadiumPeakTol	Input	number	0.05	How far from the ideal position a vanadium peak can be during StripVanadiumPeaks. Default=0.05, negative turns off
VanadiumSmoothParams	Input	string	20,2	Default=20,2
VanadiumRadius	Input	number	0.3175	Radius for CarpenterSampleCorrection
BackgroundSmoothParams	Input	string		Default=off, suggested 20,2
FilterBadPulses	Input	number	95	Filter out events measured while proton charge is more than 5% below average
ScaleData	Input	number	1	Constant to multiply the data before writing out. This does not apply to PDFgetN files.
OffsetData	Input	number	0	Constant to add to the data before writing out. This does not apply to PDFgetN files.
SaveAs	Input	string	gsas	List of all output file types. Allowed values are ‘fullprof’, ‘gsas’, ‘nexus’, ‘pdfgetn’, and ‘topas’
OutputFilePrefix	Input	string		Overrides the default filename for the output file (Optional).
OutputDirectory	Input	string	Mandatory
CacheDir	Input	string		comma-delimited ascii string representation of a list of candidate cache directories
CleanCache	Input	boolean	False	Remove all cache files within CacheDir
FinalDataUnits	Input	string	dSpacing	Allowed values: [‘dSpacing’, ‘MomentumTransfer’]
TypeOfCorrection	Input	string	None	Specifies the Absorption Correction terms to calculate, if any. Allowed values: [‘None’, ‘SampleOnly’, ‘SampleAndContainer’, ‘FullPaalmanPings’]
SampleFormula	Input	string		Chemical formula of the sample
SampleGeometry	Input	Dictionary	null	A dictionary of geometry parameters for the sample.
MeasuredMassDensity	Input	number	0.1	Measured mass density of sample in g/cc
SampleNumberDensity	Input	number	Optional	Number density of the sample in number of atoms per cubic Angstrom will be used instead of calculated
ContainerShape	Input	string	PAC06	Defines the container geometry
ContainerScaleFactor	Input	number	1	Factor to scale the container data
ElementSize	Input	number	1	The size of one side of an integration element cube in mm
NumWavelengthBins	Input	number	1000	Number of wavelength bin to calculate the for absorption correction
SplittersWorkspace	Input	Workspace		Splitters workspace for split event workspace.
SplitInformationWorkspace	Input	TableWorkspace		Name of table workspace containing information for splitters.
LowResolutionSpectraOffset	Input	number	-1	If larger and equal to 0, then process low resolution TOF and offset is the spectra number. Otherwise, ignored.
NormalizeByCurrent	Input	boolean	True	Normalize by current
CompressTOFTolerance	Input	number	0.01	Tolerance to compress events in TOF.
FrequencyLogNames	Input	str list	SpeedRequest1,Speed1,frequency,skf1.speed	Candidate log names for frequency
WaveLengthLogNames	Input	str list	LambdaRequest,lambda,skf12.lambda,BL1B:Det:TH:BL:Lambda,freq	Candidate log names for wave length

There are three properties which will modify the data after it is reduced: PushDataPositive, ScaleData, OffsetData. These options are all performed on the data after all other operations. They will be done as

\[wksp = ScaleData * wksp + OffsetData\]

followed by ResetNegatives with AddMinimum being True if PushDataPositive='AddMinimum'. ResetNegatives is not run when PushDataPositive='None'.

About Filter Wall ¶

Filter wall is enabled by setting FilterCharacterizations property to true. Then the _getTimeFilterWall routine is used to build the filter wall from the data defined by SplitInformationWorkspace and SplittersWorkspace properties. Time filter wall is used in _loadData to load data in a certain range of time. Here is how the filter is used:

There is NO filter if filter wall is NONE
There is NO lower boundary of the filter wall if wall[0] is ZERO
There is NO upper boundary of the filter wall if wall[1] is ZERO

More information is found in Event Filtering.

Calibration, grouping, and masking ¶

There are two properties related to calibration (CalibrationFile and GroupingFile) and three implicit workspace dependencies (<instrument>_mask, <instrument>_group, and <instrument>_cal). If the workspaces do not exist, they will be created during the algorithm’s execution.

If specified, the CalibrationFile is loaded using LoadDiffCal v1. If the GroupingFile is specified, the grouping it specifies takes precedence over the one that is in the CalibrationFile. LoadDetectorsGroupingFile v1 performs the loading. The order of preference in which to use is (first found wins):

Calibration: <instrument>_cal, then CalibrationFile
Grouping: <instrument>_group workspace, then GroupingFile, then CalibrationFile
Masking: <instrument>_mask, then CalibrationFile

AlignAndFocusPowder v1 does the actual resolution of which information to use.

Characterization runs ¶

The CharacterizationRunsFile, ExpIniFilename, BackgroundNumber, VanadiumNumber, VanadiumBackgroundNumber all contribute to determine which runs to use for background subtraction and normalization. Specifying the various *Number properties as 0, indicates using the values found in the files. Specifying -1 indicates to not do the corrections at all. The files are loaded using PDLoadCharacterizations v1 which also contains the focus positions. Which runs to used are determined by PDDetermineCharacterizations v1.

Caching ¶

The result of time-consuming tasks that need not be repeated, such as calculating the absorption correction of a sample for every value of the temperature in a heating experiment, can be stored as cache files in a cache directory. These cache files will be loaded if property CacheDir is set. User can clean the cache files by setting property CleanCache to reclaim drive space or to prevent accidental misuse, such as reducing with an instrument of a different geometry and/or calibration. Cleaning the cache takes place immediately before reduction.