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SANSSensitivityCorrection v1¶

Properties ¶

Name	Direction	Type	Default	Description
InputWorkspace	Input	MatrixWorkspace
Filename	Input	string	Mandatory	Flood field or sensitivity file. Allowed extensions: [‘_event.nxs’, ‘.xml’]
UseSampleDC	Input	boolean	True	If true, the dark current subtracted from the sample data will also be subtracted from the flood field.
DarkCurrentFile	Input	string		The name of the input file to load as dark current. Allowed extensions: [‘_event.nxs’, ‘.xml’]
MinEfficiency	Input	number	Optional	Minimum efficiency for a pixel to be considered (default: no minimum).
MaxEfficiency	Input	number	Optional	Maximum efficiency for a pixel to be considered (default: no maximum).
FloodTransmissionValue	Input	number	Optional	Transmission value for the flood field material (default: no transmission).
FloodTransmissionError	Input	number	0	Transmission error for the flood field material (default: no transmission).
BeamCenterX	Input	number	Optional	Beam position in X pixel coordinates (optional: otherwise sample beam center is used)
BeamCenterY	Input	number	Optional	Beam position in Y pixel coordinates (optional: otherwise sample beam center is used)
MaskedFullComponent	Input	string		Component Name to fully mask according to the IDF file.
MaskedEdges	Input	int list		Number of pixels to mask on the edges: X-low, X-high, Y-low, Y-high
MaskedComponent	Input	string		Component Name to mask the edges according to the IDF file.
OutputWorkspace	Output	MatrixWorkspace
ReductionProperties	Input	string	__sans_reduction_properties
OutputSensitivityWorkspace	Output	MatrixWorkspace
OutputMessage	Output	string

This SANS workflow algorithm will compute the sensitivity correction from a given flood field data set. It will apply the proper corrections to the data according the the input property manager object. Those corrections may include dark current subtraction, moving the beam center, the solid angle correction, and applying a patch.

If an input workspace is given, the computed correction will be applied to that workspace.

A Nexus file containing a pre-calculated sensitivity correction can also be supplied for the case where we simply want to apply the correction to an input workspace.

The relative detector efficiency is computed using the CalculateEfficiency algorithm the following way:

\(S(x,y)=\frac{I_{flood}(x,y)}{1/N_{pixels}\sum_{i,j}I_{flood}(i,j)}\)

where \(I_{flood}(x,y)\) is the pixel count of the flood data in pixel (x,y). If a minimum and/or maximum sensitivity is given, the pixels having an efficiency outside the given limits are masked and the efficiency is recomputed without using those pixels. The sample data is then corrected by dividing the intensity in each pixels by the efficiency S:

\(I'_{sample}(x,y) = \frac{I_{sample}(x,y)}{S(x,y)}\)

The pixels found to have an efficiency outside the given limits are also masked in the sample data so that they don’t enter any subsequent calculations. If the user chose to use a dark current data set when starting the reduction process, that dark current data will be subtracted from the flood data. The subtraction is done before the sensitivity is calculated. If the user chose to use the solid angle correction for the reduction process, that correction will be applied to the flood data before the sensitivity is calculated.

This algorithm is usually called by SANSReduction or HFIRSANSReduction.

Note 1: The solid angle correction is either not applied at all, or applied to both the flood data to calculate the sensitivity correction and applied to the sample data as part of the reduction process.

Note 2: EQSANS has the option to patch masked areas of the detector using the efficiency calculated for the unmasked portion of each tube. This creates a sensitivity file that covers the entire detector. This option can be enabled by using the ComputeSensitivity workflow algorithm to create a sensitivity workspace, which can then be saved and used for EQSANS reduction as a pre-calculated sensitivity file.

Categories: AlgorithmIndex | Workflow\SANS\UsesPropertyManager