3.9

ReflectometryReductionOne v2

../_images/ReflectometryReductionOne-v2_dlg.png

ReflectometryReductionOne dialog.

Summary

Reduces a single TOF/Lambda reflectometry run into a mod Q vs I/I0 workspace. Performs monitor normalization and transmission corrections.

Properties

Name Direction Type Default Description
InputWorkspace Input MatrixWorkspace Mandatory Run to reduce.
ProcessingInstructions Input string Mandatory Grouping pattern on workspace indexes to yield only the detectors of interest. See GroupDetectors for details.
WavelengthMin Input number Mandatory Wavelength minimum in angstroms
WavelengthMax Input number Mandatory Wavelength maximum in angstroms
RegionOfDirectBeam Input int list   Indices of the spectra a pair (lower, upper) that mark the ranges that correspond to the direct beam in multi-detector mode.
I0MonitorIndex Input number Optional I0 monitor workspace index
MonitorBackgroundWavelengthMin Input number Optional Wavelength minimum for monitor background subtraction in angstroms.
MonitorBackgroundWavelengthMax Input number Optional Wavelength maximum for monitor background subtraction in angstroms.
MonitorIntegrationWavelengthMin Input number Optional Wavelength minimum for integration in angstroms.
MonitorIntegrationWavelengthMax Input number Optional Wavelength maximum for integration in angstroms.
NormalizeByIntegratedMonitors Input boolean True Normalize by dividing by the integrated monitors.
FirstTransmissionRun Input MatrixWorkspace   First transmission run, or the low wavelength transmission run if SecondTransmissionRun is also provided.
SecondTransmissionRun Input MatrixWorkspace   Second, high wavelength transmission run. Optional. Causes the FirstTransmissionRun to be treated as the low wavelength transmission run.
Params Input dbl list   A comma separated list of first bin boundary, width, last bin boundary. These parameters are used for stitching together transmission runs. Values are in wavelength (angstroms). This input is only needed if a SecondTransmission run is provided.
StartOverlap Input number Optional Start wavelength for stitching transmission runs together. Only used if a second transmission run is provided.
EndOverlap Input number Optional End wavelength (angstroms) for stitching transmission runs together. Only used if a second transmission run is provided.
StrictSpectrumChecking Input boolean True Enforces spectrum number checking prior to normalization by transmission workspace. Applies to input workspace and transmission workspace.
CorrectionAlgorithm Input string None The type of correction to perform. Allowed values: [‘None’, ‘PolynomialCorrection’, ‘ExponentialCorrection’]
Polynomial Input dbl list   Coefficients to be passed to the PolynomialCorrection algorithm.
C0 Input number 0 C0 value to be passed to the ExponentialCorrection algorithm.
C1 Input number 0 C1 value to be passed to the ExponentialCorrection algorithm.
OutputWorkspace Output MatrixWorkspace Mandatory Output Workspace IvsQ.
OutputWorkspaceWavelength Output MatrixWorkspace   Output Workspace IvsLam. Intermediate workspace.

Description

This algorithm is not meant to be used directly by users. Please see ReflectometryReductionOneAuto v2 which is a facade over this algorithm.

This algorithm reduces a single reflectometry run into a mod Q vs I/I0 workspace. The mandatory input properties, WavelengthMin, WavelengthMax and ProcessingInstructions, must be manually set by the user. In addition, for the algorithm to be able to convert from wavelength to momentum transfer correctly, instrument components, specially detectors, must be located at the correct positions. The expected experimental setup for the algorithm to produce correct results is shown below, where the angle between the beam direction and the sample-to-detector vector must be 2\theta.

../_images/ReflectometryReductionOneDetectorPositions.png

The figure below displays a high-level workflow diagram illustrating the main steps taking place in the reduction.

../_images/ReflectometryReductionOne_HighLvl-v2_wkflw.png

Conversion to Wavelength

First, the algorithm checks the X units of the input workspace. If the input workspace is already in wavelength, normalization by monitors and direct beam are not performed, as it is considered that the input run was already reduced using this algorithm. If the input workspace is in TOF, monitors, detectors of interest and region of direct beam are extracted by running GroupDetectors v2 with ProcessingInstructions as input, GroupDetectors v2 with RegionOfDirectBeam as input, and CropWorkspace v1 with I0MonitorIndex as input respectively, and each of the resulting workspaces is converted to wavelength (note that AlignBins is set to True in all the three cases). Note that the normalization by a direct beam is optional, and only happens if RegionOfDirectBeam is provided. In the same way, monitor normalization is also optional, and only takes place if I0MonitorIndex, MonitorBackgroundWavelengthMin and MonitorBackgroundWavelengthMax are all specified. Detectors can be normalized by integrated monitors by setting NormalizeByIntegratedMonitors to true, in which case MonitorIntegrationWavelengthMin and MonitorIntegrationWavelengthMax are used as the integration range. If monitors are not integrated, detectors are rebinned to monitors using RebinToWorkspace v1 so that the normalization by monitors can take place. Finally, the resulting workspace is cropped in wavelength according to WavelengthMin and WavelengthMax, which are both mandatory properties. A summary of the steps is shown in the workflow diagram below. For the sake of clarity, all possible steps are illustrated, even if some of them are optional.

../_images/ReflectometryReductionOne_ConvertToWavelength-v2_wkflw.png

Transmission Correction

Transmission corrections can be optionally applied to the workspace resulting from the previous step. Transmission corrections can be either specified via transmission runs or specific correction algorithms.

../_images/ReflectometryReductionOne_TransmissionCorrection-v2_wkflw.png

When normalizing by transmission runs, i.e. when one or two transmission runs are given, the spectrum numbers in the transmission workspaces must be the same as those in the input run workspace. If spectrum numbers do not match, the algorithm will throw and exception and execution of the algorithm will be stopped. This behaviour can be optionally switched off by setting StrictSpectrumChecking to false, in which case a warning message will be shown instead.

When normalizing by transmission run, this algorithm will run CreateTransmissionWorkspace v2 as a child algorithm, with properties WavelengthMin, WavelengthMax, I0MonitorIndex, MonitorBackgroundWavelengthMin, MonitorBackgroundWavelengthMax, MonitorIntegrationWavelengthMin, MonitorIntegrationWavelengthMax, and ProcessingInstructions. In addition, when both FirstTransmissionRun and SecondTransmissionRun are provided the stitching parameters Params, as well as StartOverlap and EndOverlap will be used by CreateTransmissionWorkspace v2 to create the transmission workspace that will be used for the normalization.

If no transmission runs are provided, then algorithmic corrections can be performed instead by setting CorrectionAlgorithm to either PolynomialCorrection or ExponentialCorrection, the two possible types of corrections at the moment. If PolynomialCorrection, is selected, PolynomialCorrection v1 algorithm will be run, with this algorithm’s Polynomial property used as its Coefficients property. If the CorrectionAlgorithm property is set to ExponentialCorrection, then the ExponentialCorrection v1 algorithm is used, with C0 and C1 taken from the C0 and C1 properties.

Conversion to Momentum Transfer (Q)

Finally, the output workspace in wavelength is converted to momentum transfer (Q) using ConvertUnits v1. Note that the output workspace in Q is therefore a workspace with native binning, and no rebin step is applied to it.

../_images/ReflectometryReductionOne_ConvertToMomentum-v2_wkflw.png

If you wish to obtain a rebinned workspace in Q you should consider using algorithm ReflectometryReductionOneAuto v2 instead, which is a facade over this algorithm and has two extra steps (Rebin v1 and Scale v1) to produce an additional workspace in Q with specified binning and scale factor. Please refer to ReflectometryReductionOneAuto v2 for more information.

Previous Versions

This is version 2 of the algorithm. For version 1, please see here.

Usage

Example - Reduce a run

run = Load(Filename='INTER00013460.nxs')
# Basic reduction with no transmission run
IvsQ, IvsLam = ReflectometryReductionOne(InputWorkspace=run,
                                         WavelengthMin=1.0,
                                         WavelengthMax=17.0,
                                         ProcessingInstructions='3:4',
                                         I0MonitorIndex=2,
                                         MonitorBackgroundWavelengthMin=15.0,
                                         MonitorBackgroundWavelengthMax=17.0,
                                         MonitorIntegrationWavelengthMin=4.0,
                                         MonitorIntegrationWavelengthMax=10.0)

print "%.4f" % (IvsLam.readY(0)[533])
print "%.4f" % (IvsLam.readY(0)[534])
print "%.4f" % (IvsQ.readY(0)[327])
print "%.4f" % (IvsQ.readY(0)[328])

Output:

0.0003
0.0003
0.0003
0.0003

Example - Reduce a run and normalize by transmission workspace

run = Load(Filename='INTER00013460.nxs')
trans1 = Load(Filename='INTER00013463.nxs')
trans2 = Load(Filename='INTER00013464.nxs')
# Basic reduction with two transmission runs
IvsQ, IvsLam = ReflectometryReductionOne(InputWorkspace=run,
                                         WavelengthMin=1.0,
                                         WavelengthMax=17.0,
                                         ProcessingInstructions='3-4',
                                         I0MonitorIndex=2,
                                         MonitorBackgroundWavelengthMin=15.0,
                                         MonitorBackgroundWavelengthMax=17.0,
                                         MonitorIntegrationWavelengthMin=4.0,
                                         MonitorIntegrationWavelengthMax=10.0,
                                         FirstTransmissionRun=trans1,
                                         SecondTransmissionRun=trans2)

print "%.4f" % (IvsLam.readY(0)[480])
print "%.4f" % (IvsLam.readY(0)[481])
print "%.4f" % (IvsQ.readY(0)[107])
print "%.4f" % (IvsQ.readY(0)[108])

Output:

0.4588
0.4655
0.7336
1.0156

Categories: Algorithms | Reflectometry