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DgsScatteredTransmissionCorrectionMD v1

Summary

Isotropic scattering transmission correction for Inelastic data

Properties

Name	Direction	Type	Default	Description
InputWorkspace	Input	MDEventWorkspace	Mandatory	Input MDEventWorkspace. Either QSample (or QLab) frame plus DeltaE, or just Qmod plus DeltaE
ExponentFactor	Input	number	Optional	Depletion rate exponent
OutputWorkspace	Output	MDEventWorkspace	Mandatory	The output MDEventWorkspace with the correction applied

Description

In instruments where there is a polarization analysis stage in the scattered beam, neutron intensity is reduced by an absorption factor [1]. This has an exponential dependence on the scattered energy. To correct for this, the detected intensity \(I\) of every event collected is corrected by:

\(E_f = E_i-\Delta E\)

\(I' = I e^{c E_f}\)

\(\delta I' = \delta I e^{c E_f}\)

[1] Andrei T. Savici et al, 2017, J. Phys.: Conf. Ser. 862 012023

Usage

Example - Run Transmission Correction

we1 = CreateSampleWorkspace(WorkspaceType='Event',
                            Function='Flat background',
                            BankPixelWidth=1,
                            XUnit='DeltaE',
                            XMin=-10,
                            XMax=19,
                            BinWidth=0.5)
AddSampleLog(Workspace=we1,LogName='deltaE-mode', LogText='Direct', LogType='String')
AddSampleLog(Workspace=we1,LogName='Ei', LogText='20.', LogType='Number')
MoveInstrumentComponent(Workspace=we1, ComponentName='bank1', X=3, Z=3, RelativePosition=False)
MoveInstrumentComponent(Workspace=we1, ComponentName='bank2', X=-3, Z=-3, RelativePosition=False)
SetGoniometer(Workspace=we1, Axis0='0,0,1,0,1')

c = 1. / 11  # the exponential factor for the correction

# old way
we1s = ScaleX(InputWorkspace=we1, Factor=-20., Operation='Add') # deltaE - Ei becomes -Ef
we1s = ScaleX(InputWorkspace=we1s, Factor=-1.0, Operation='Multiply') # the X-axis becomes Ef
# The ExponentialCorrection algorithm multiplies signal by C0*exp(-C1*x), where x is Ef
we1s = ExponentialCorrection(Operation="Multiply", InputWorkspace=we1s, C0=1., C1=-c)
we1s = ScaleX(InputWorkspace=we1s, Factor=-1.0, Operation='Multiply') # the X-axis becomes -Ef
we1s = ScaleX(InputWorkspace=we1s, Factor=20., Operation='Add') # Ei - Ef converts back to DeltaE
md1_old = ConvertToMD(InputWorkspace=we1s, QDimensions='Q3D')

# use algorithm DgsScatteredTransmissionCorrectionMD
md1 = ConvertToMD(InputWorkspace=we1, QDimensions='Q3D')
md1_new = DgsScatteredTransmissionCorrectionMD(md1, ExponentFactor=c)

r = CompareMDWorkspaces(md1_old, md1_new, CheckEvents=True, Tolerance=0.00001)
print('Number of MDEvents: {} == {}'.format(md1_old.getNEvents(), md1_new.getNEvents()))
print('md1_old and md1_new being equal is {}'.format(r.Equals))

Output:

Number of MDEvents: 1972 == 1972
md1_old and md1_new being equal is True

Categories: AlgorithmIndex | MDAlgorithms

Source

C++ header: DgsScatteredTransmissionCorrectionMD.h

C++ source: DgsScatteredTransmissionCorrectionMD.cpp