4.2

LoadILLPolarizationFactors v1

../_images/LoadILLPolarizationFactors-v1_dlg.png

LoadILLPolarizationFactors dialog.

Summary

Loads ILL formatted reflectometry polarization efficiency factors.

Properties

Name Direction Type Default Description
Filename Input string Mandatory Path to the polarization efficiency file.
OutputWorkspace Output MatrixWorkspace Mandatory An output workspace containing the efficiencies at the reference workspace’s wavelength points.
WavelengthReference Input MatrixWorkspace Mandatory A reference workspace to get the wavelength axis from.

Description

This algorithm loads reflectometry polarization efficiency data from ILL’s IDL-style text files. The output is a workspace with the efficiency factors calculated for each bin or point in the first spectrum of the WavelengthReference workspace. The output workspace is populated with five histograms carrying the following vertical axis labels:

P1
the probability of neutrons not being correctly polarized
P2
the probability of neutrons not being correctly analyzed
F1
the probability of neutron polarization being flipped at the pre-sample flipper
F2
the probability of neutron polarization being flipped at the post-sample flipper
Phi
the combined polarizer-analyzer efficiencies

Note, that the order of the histograms in the output workspace is unspecified. The histograms should be identified by the above labels instead.

The errors in the output histograms are estimated by multiplying the efficiencies by constant factors.

Usage

Note

To run these usage examples please first download the usage data, and add these to your path. In MantidPlot this is done using Manage User Directories.

Example - Loading sample data and corresponding efficiencies

# We need reference wavelengths. Lets use some real data for that.
# Load direct beam for detector angle calibration.
db = LoadILLReflectometry(Filename='ILL/D17/317369.nxs',
                          OutputBeamPosition='direct_beam_pos',
                          XUnit='TimeOfFlight')
rb = LoadILLReflectometry(Filename='ILL/D17/317370.nxs',
                          DirectBeamPosition='direct_beam_pos',
                          XUnit='TimeOfFlight')
# Sum over the reflected beam.
rb_grouped = GroupDetectors(rb, GroupingPattern='201-203')
rb_in_wavelength = ConvertUnits(rb_grouped, Target='Wavelength')
rb_cropped = CropWorkspace(rb_in_wavelength, XMin=0)
pol_factors = LoadILLPolarizationFactors(Filename='ILL/D17/PolarizationFactors.txt',
                                         WavelengthReference=rb_cropped)
# Grab the vertical axis.
axis = pol_factors.getAxis(1)
axisSize = axis.length()
factors = []
for i in range(axisSize):
    factors.append(axis.label(i))
print("The following factors were loaded from the file: {}".format(factors))

Output:

The following factors were loaded from the file: ['F1', 'F2', 'P1', 'P2', 'Phi']

Categories: AlgorithmIndex | DataHandling\Text | ILL\Reflectometry

Source

C++ source: LoadILLPolarizationFactors.cpp (last modified: 2019-06-17)

C++ header: LoadILLPolarizationFactors.h (last modified: 2018-10-05)