3.11

ApplyPaalmanPingsCorrection v1

../_images/ApplyPaalmanPingsCorrection-v1_dlg.png

ApplyPaalmanPingsCorrection dialog.

Summary

Applies a calculated absorption correction in the Paalman and Pings factor style.

Properties

Name Direction Type Default Description
SampleWorkspace Input MatrixWorkspace Mandatory Name for the input Sample workspace.
CorrectionsWorkspace Input WorkspaceGroup   Name for the input Corrections workspace.
CanWorkspace Input MatrixWorkspace   Name for the input Can workspace.
CanScaleFactor Input number 1 Factor to scale the can data
CanShiftFactor Input number 0 Amount by which to shift the container data
OutputWorkspace Output MatrixWorkspace Mandatory The output corrections workspace.
RebinCanToSample Input boolean True Enable or disable RebinToWorkspace on CanWorkspace.

Description

Applies absorption corrections calculated in the Paalman and Pings absorption factor format. The various partial absorption factors are denoted as A_{a,b} where the subscript a denotes the component the neutron is scattered from and b denotes the component where the neutron is absorbed. The various partial absorption factors, and what their names must contain in the CorrectionsWorkspace group are detailed in the table below. If any of the partial absorption factors are not supplied, they are assumed to be one.

Symbol Scatter From Absorbed By Workspace Name
A_{s,s} sample sample ass
A_{s,sc} sample sample and container assc
A_{c,c} container container acc
A_{c,sc} container sample and container acsc

This algorithm can be used to apply absorption corrections calculated with either the CylinderPaalmanPingsCorrection and FlatPlatePaalmanPingsCorrection algorithms as well as the legacy indirect calculate corrections routine, providing that the sample and container are first converted to wavelength and the corrections are interpolated to match the sample as demonstrated in the example below.

All workspaces are converted into wavelength using the appropriate mode of ConvertUnits. Then CanShiftFactor is added to wavelength of the CanWorkspace. Then the following equation is performed:

I_s = \frac{1}{A_{s,sc}} \left( I_{sc}^E - I_c^E K_c \frac{A_{c,sc}}{A_{c,c}} \right)

The variables that are not defined above are

Variable Parameter Name Default
I_s OutputWorkspace N/A
I_{sc}^E SampleWorkspace N/A
I_{c}^E CanWorkspace 0
K_c CanScaleFactor 1
A_{a,b} CorrectionsWorkspace 1

The workflow diagrams below are another representation of the equation above with the simplifications for when the various terms are missing or one.

Workflow

Depending on the input workspaces provided to the algorithm it may operate in one of three ways, each of which is described on a separate workflow diagram.

Container Scale Only

In the case where only a container workspace and no correction factors are provided.

../_images/ApplyPaalmanPingsCorrection-v1_canscaleonly_wkflw.png

Sample Corrections Only

In the case where only correction factors and no container workspace is provided.

../_images/ApplyPaalmanPingsCorrection-v1_samplecorrectiononly_wkflw.png

Full Corrections

In the case where both a container workspace and correction factors are provided.

../_images/ApplyPaalmanPingsCorrection-v1_fullcorrection_wkflw.png

Usage

Example: using with legacy indirect corrections data

# Load the sample and can
sample_ws = Load('irs26176_graphite002_red.nxs')
can_ws = Load('irs26173_graphite002_red.nxs')

# Convert sample and container workspaces to wavelength
sample_ws = ConvertUnits(InputWorkspace=sample_ws,
                         Target='Wavelength',
                         EMode='Indirect',
                         EFixed=1.845)
can_ws = ConvertUnits(InputWorkspace=can_ws,
                      Target='Wavelength',
                      EMode='Indirect',
                      EFixed=1.845)

# Load the corrections workspace
corrections_ws = Load('irs26176_graphite002_cyl_Abs.nxs')

# Interpolate each of the correction factor workspaces to match the
# binning of the smaple
# Required to use corrections from the old indirect calculate
# corrections routines
for factor_ws in corrections_ws:
    SplineInterpolation(WorkspaceToMatch=sample_ws,
                        WorkspaceToInterpolate=factor_ws,
                        OutputWorkspace=factor_ws,
                        OutputWorkspaceDeriv='')

corr = ApplyPaalmanPingsCorrection(SampleWorkspace=sample_ws,
                                   CorrectionsWorkspace=corrections_ws,
                                   CanWorkspace=can_ws)

print 'Corrected workspace has %d spectra over %d bins' % (
      corr.getNumberHistograms(), corr.blocksize())

print 'Type of correction applied: %s' % (
      corr.getRun()['corrections_type'].value)

Output:

Corrected workspace has 10 spectra over 1905 bins
Type of correction applied: sample_and_can_corrections

References

  1. H. H. Paalman, and C. J. Pings. Numerical Evaluation of X‐Ray Absorption Factors for Cylindrical Samples and Annular Sample Cells, Journal of Applied Physics 33.8 (1962) 2635–2639 doi: 10.1063/1.1729034

Categories: Algorithms | Workflow\MIDAS