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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