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SANSDirectBeamTransmission v1

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Summary

Compute transmission using the direct beam method

Properties

Name	Direction	Type	Default	Description
InputWorkspace	Input	MatrixWorkspace	Mandatory
SampleDataFilename	Input	string	Mandatory	Allowed values: [‘xml’, ‘nxs’, ‘nxs.h5’]
EmptyDataFilename	Input	string	Mandatory	Allowed values: [‘xml’, ‘nxs’, ‘nxs.h5’]
BeamRadius	Input	number	3	Beam radius [pixels]
ThetaDependent	Input	boolean	True	If true, a theta-dependent correction will be applied
DarkCurrentFilename	Input	string		Allowed values: [‘xml’, ‘nxs’, ‘nxs.h5’]
UseSampleDarkCurrent	Input	boolean	False	If true, the sample dark current will be used
BeamCenterX	Input	number	0	Beam center position in X
BeamCenterY	Input	number	0	Beam center position in Y
ReductionProperties	Input	string	__sans_reduction_properties	Property manager name for the reduction
OutputWorkspace	Output	MatrixWorkspace	Mandatory	Workspace containing the data corrected for the transmission.
TransmissionWorkspace	Output	MatrixWorkspace		Workspace containing the fitted transmission distribution.
RawTransmissionWorkspace	Output	MatrixWorkspace		Workspace containing the transmission distribution before fitting.
MeasuredTransmission	Output	number
MeasuredError	Output	number
OutputMessage	Output	string		Output message

Description

Worfklow algorithm used to compute and apply the sample transmission correction using the direct beam method. The transmission is calculated by the CalculateTransmission as follows:

\(T=\frac{\sum_{i;\ d(i,j)<R}\ \sum_{j} \frac{I_{sample}(i,j)}{T_{sample}}}{\sum_{i;\ d(i,j)<R}\ \sum_{j} \frac{I_{beam}(i,j)}{T_{beam}}}\)

where \(I_{sample}\) and \(I_{beam}\) are the pixel counts for the sample data set and the direct beam data set, respectively. The sums for each data set runs only over the pixels within a distance R of the beam center equal to the beam radius. \(T_{sample}\) and \(T_{beam}\) are the counting times for each of the two data sets. If the user chose to normalize the data using the beam monitor when setting up the reduction process, the beam monitor will be used to normalize the sample and direct beam data sets instead of the timer. If the user chose to use a dark current data set when starting the reduction process, that dark current data will be subtracted from both data sets before the transmission is calculated.

For each detector pixel, the transmission correction is applied by the ApplyTransmissionCorrection as follows:

\(I'(x,y)=\frac{I(x,y)}{T^{[1+\sec(2\theta)]/2}} \sigma_{I'(x,y)}=[[{\frac{\sigma_I}{{T^{[1+\sec(2\theta)]/2}}}}]^2 + [{\frac{I(x,y)\sigma_T(\frac{1+\sec(2\theta)}{2})}{{T^{[\sec(2\theta)-1]/2}}}}]^2]^{1/2}\)

This algorithm is rarely called directly. It is called by HFIRSANSReduction or EQSANSDirectBeamTransmission.

Categories: AlgorithmIndex | Workflow\SANS\UsesPropertyManager

Source

Python: SANSDirectBeamTransmission.py