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DgsScatteredTransmissionCorrectionMD v1

../_images/DgsScatteredTransmissionCorrectionMD-v1_dlg.png

DgsScatteredTransmissionCorrectionMD dialog.

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