3.5

SANSDirectBeamTransmission v1

../_images/SANSDirectBeamTransmission-v1_dlg.png

SANSDirectBeamTransmission dialog.

Table of Contents

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: Algorithms | Workflow | SANS | UsesPropertyManager