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ReflectometryILLSumForeground v1¶

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

Summary ¶

Sums foreground pixels in selected summation mode, optionally converting to reflectivity.

Properties ¶

Name	Direction	Type	Default	Description
InputWorkspace	Input	MatrixWorkspace	Mandatory	A reflected beam workspace (units wavelength).
OutputWorkspace	Output	MatrixWorkspace	Mandatory	The summed foreground workspace.
SubalgorithmLogging	Input	string	Logging OFF	Enable or disable child algorithm logging. Allowed values: [‘Logging OFF’, ‘Logging ON’]
Cleanup	Input	string	Cleanup ON	Enable or disable intermediate workspace cleanup. Allowed values: [‘Cleanup ON’, ‘Cleanup OFF’]
SummationType	Input	string	SumInLambda	Type of summation to perform. Allowed values: [‘SumInLambda’, ‘SumInQ’]
DirectForegroundWorkspace	Input	MatrixWorkspace		Summed direct beam workspace (units wavelength).
Foreground	Input	long list	2147483647,2147483647,2147483647	A three element array of foreground start, centre and end workspace indices.
DirectLineWorkspace	Input	MatrixWorkspace		The (not summed) direct beam workspace (units wavelength).
WavelengthRange	Input	dbl list	0	The wavelength bounds.

Description ¶

This algorithm is typically the second step in the reflectometry reduction workflow. It consumes the output of ReflectometryILLPreprocess, producing a workspace with a single spectrum.

The reflectivity output of this algorithm can be forwarded to ReflectometryILLConvertToQ or, in case of polarization analysis, ReflectometryILLPolarizationCor.

The following diagram gives an overview of the algorithm:

The algorihtm runs ReflectometryBeamStatistics when processing the reflected beam. This adds some sample log entries to OutputWorkspace and DirectLineWorkspace. See the algorithm’s documentation for more details.

Summation type ¶

The SummationType property controls how the foreground pixels are summed.

SumInLambda: extracts the centre pixel histogram using ExtractSingleSpectrum and adds the intensities of the rest of the foreground pixels.
SumInQ: sums the foreground pixels using ReflectometrySumInQ. Before summation, the data is divided by the direct beam.

The chosen SummationType will be added to the sample logs of OutputWorkspace under the foreground.summation_type entry.

Foreground pixels ¶

If InputWorkspace has been processed by ReflectometryILLPreprocess, the foreground information is available in the sample logs under the entries starting with foreground.. By default these are used automatically.

The sample logs can be overridden using the Foreground property. It is a list of three integers defining the range and centre pixels as workspace indices: [start, centre, end]. The start and end values are inclusive.

Usage ¶

Note

To run these usage examples please first download the usage data, and add these to your path. In Mantid this is done using Manage User Directories.

Example - Sum in wavelength

# Use same foreground and background settings for direct and reflected
# beams.
# Python dictionaries can be passed to algorithms as 'keyword arguments'.
settings = {
    'ForegroundHalfWidth':[5],
    'LowAngleBkgOffset': 10,
    'LowAngleBkgWidth': 20,
    'HighAngleBkgOffset': 10,
    'HighAngleBkgWidth': 50,
}

# Direct beam
direct = ReflectometryILLPreprocess(
    Run='ILL/D17/317369.nxs',
    Measurement='DirectBeam',
    **settings
)
# We need the summed direct beam for the reflectivity
directFrg = ReflectometryILLSumForeground(direct)

# Reflected beam
reflected = ReflectometryILLPreprocess(
    Run='ILL/D17/317370.nxs',
    Measurement='ReflectedBeam',
    **settings
)
reflectivity = ReflectometryILLSumForeground(
    InputWorkspace=reflected,
    DirectForegroundWorkspace=directFrg,
    DirectLineWorkspace=direct,
    SummationType='SumInLambda',
    WavelengthRange=[2, 15],
)

# Reflectivity is a single histogram
print('Histograms in reflectivity workspace: {}'.format(reflectivity.getNumberHistograms()))
# The data is still in wavelength
print('Reflectivity X unit: ' + reflectivity.getAxis(0).getUnit().unitID())

Output:

Histograms in reflectivity workspace: 1
Reflectivity X unit: Wavelength

Example - Sum in momentum transfer

# Use same foreground and background settings for direct and reflected
# beams.
# Python dictionaries can be passed to algorithms as 'keyword arguments'.
settings = {
    'ForegroundHalfWidth':[5],
    'LowAngleBkgOffset': 10,
    'LowAngleBkgWidth': 20,
    'HighAngleBkgOffset': 10,
    'HighAngleBkgWidth': 50,
}

# Direct beam
direct = ReflectometryILLPreprocess(
    Run='ILL/D17/317369.nxs',
    Measurement='DirectBeam',
    **settings
)

# We need the summed direct beam for the reflectivity
directFrg = ReflectometryILLSumForeground(direct)

# Reflected beam
reflected = ReflectometryILLPreprocess(
    Run='ILL/D17/317370.nxs',
    Measurement='ReflectedBeam',
    **settings
)
reflectivity = ReflectometryILLSumForeground(
    InputWorkspace=reflected,
    DirectForegroundWorkspace=directFrg,
    DirectLineWorkspace=direct,
    SummationType='SumInQ',
    WavelengthRange=[0., 14.]
)

# Reflectivity is a single histogram
print('Histograms in reflectivity workspace: {}'.format(reflectivity.getNumberHistograms()))
# The data is still in wavelength
print('Reflectivity X unit: ' + reflectivity.getAxis(0).getUnit().unitID())

Output:

Histograms in reflectivity workspace: 1
Reflectivity X unit: Wavelength

Categories: AlgorithmIndex | ILL\Reflectometry | Workflow\Reflectometry

Source ¶

Python: ReflectometryILLSumForeground.py