Table of Contents
Name | Direction | Type | Default | Description |
---|---|---|---|---|
InputWorkspace | Input | MatrixWorkspace | Mandatory | An input workspace in units of energy transfer. |
PolarizationAngle | Input | number | Mandatory | In plane angle between polatrization and incident beamMust be between -180 and +180 degrees |
Precision | Input | number | 0.1 | If cosine of twice the Scharpf angle is closer to 0 than the precision, the intensities and errors will be set to 0 |
OutputWorkspace | Output | MatrixWorkspace | Mandatory | An output workspace. |
This algorithm is applying a polarization correction for single crystal
inelastic experiments. If one measures scattering intensity with polarization
along the momentum transfer , perpendicular to it in the horizontal
plane, and in the vertical direction, one can write the spin incoherent
contribution as:
where the sf and nsf subscripts stand for spin flip and non-spin flip.
The x direction is parallel to , y is perpendicular in the horizontal
plane, while z is vertically up. NOTE: this is not the Mantid convention.
However, for instruments with multiple detectors and using time of flight
neutrons, one has a constantly varying angle between and polarization.
If we call this angle
(Scharpf angle), the above equation can
be written as:
This algorithm calculates the Scharpf angle for every event or energy transfer bin,
then divides the intensity by .
In places where F is less than the Precision, the intensity of the output workspace is set to 0.
For a detector at angle in the horizontal plane, the angle
between
and
is given by
The Scharpf angle is then:
Note
This algorithm assumes that all scattering is in the horizontal plane (good enough approximation for Hyspec instrument, in polarized mode).
For more information, see
Example - HyspecScharpfCorrection
# Create a workspace (NXSPE equivalent)
w = CreateSampleWorkspace(Function='Flat background', NumBanks=1,
BankPixelWidth=1, XUnit='DeltaE',
XMin=-10.25, XMax=20, BinWidth=0.5)
MoveInstrumentComponent(Workspace=w, ComponentName='bank1', X=3, Z=3, RelativePosition=False)
AddSampleLog(Workspace=w,LogName='Ei', LogText='17.1', LogType='Number')
wsOut = HyspecScharpfCorrection(InputWorkspace=w,
PolarizationAngle=-10,
Precision=0.2)
# Get the data
intensity = wsOut.readY(0)
bin_boundaries = wsOut.readX(0)
energy_transfer = 0.5*(bin_boundaries[1:]+bin_boundaries[:-1])
# at DeltaE=5meV, Q makes an angle of 55.7 degrees with incident beam
# If polarization angle is -10 degrees, the intensity should be 0
# Below this energy, the Scharpf angle correction is negative, above
# is positive. If energy transfer is greater than Ei, intensity is
# set to 0
print('Intensity at DeltaE= 0meV: {0:.2f}'.format((intensity[energy_transfer==0])[0]))
print('Intensity at DeltaE= 5meV: {0:.2f}'.format((intensity[energy_transfer==5])[0]))
print('Intensity at DeltaE=10meV: {0:.2f}'.format((intensity[energy_transfer==10])[0]))
print('Intensity at DeltaE=19meV: {0:.2f}'.format((intensity[energy_transfer==19])[0]))
Output:
Intensity at DeltaE= 0meV: -2.37
Intensity at DeltaE= 5meV: 0.00
Intensity at DeltaE=10meV: 1.99
Intensity at DeltaE=19meV: 0.00
Categories: Algorithm Index | CorrectionFunctions\SpecialCorrections | Inelastic\Corrections
C++ source: HyspecScharpfCorrection.cpp (last modified: 2019-01-07)
C++ header: HyspecScharpfCorrection.h (last modified: 2018-10-05)