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SANSBeamSpreaderTransmission v1

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Summary

Compute transmission using the beam spreader method

Properties

Name	Direction	Type	Default	Description
InputWorkspace	Input	MatrixWorkspace	Mandatory
SampleSpreaderFilename	Input	string	Mandatory	Allowed values: [‘xml’, ‘nxs’, ‘nxs.h5’]
DirectSpreaderFilename	Input	string	Mandatory	Allowed values: [‘xml’, ‘nxs’, ‘nxs.h5’]
SampleScatteringFilename	Input	string	Mandatory	Allowed values: [‘xml’, ‘nxs’, ‘nxs.h5’]
DirectScatteringFilename	Input	string	Mandatory	Allowed values: [‘xml’, ‘nxs’, ‘nxs.h5’]
SpreaderTransmissionValue	Input	number	1	Transmission of the beam spreader
SpreaderTransmissionError	Input	number	0	Error on the transmission of the beam spreader
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
ReductionProperties	Input	string	__sans_reduction_properties	Property manager name for the reduction
OutputWorkspace	Output	MatrixWorkspace	Mandatory
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 beam spreader (“glassy carbon”) method. The transmission is calculated by the CalculateTransmission as follows:

\(T=\frac{N_{gc,\ sample}/T_{gc,\ sample} - T_{gc}N_{sample}/T_{sample}}{N_{gc,\ empty}/T_{gc,\ empty} - T_{gc}N_{empty}/T_{empty}}\)

where \(N_{gc}\), sample and \(N_{gc}\), empty are the sums of all pixel counts for the sample and direct beam data sets with glass carbon, and \(N_{sample}\) and \(N_{empty}\) are the sums of all the pixel counts for the sample and direct beam without glassy carbon. The T values are the corresponding counting times. 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 all 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 all 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.

Categories: AlgorithmIndex | Workflow\SANS\UsesPropertyManager

Source

Python: SANSBeamSpreaderTransmission.py