ReflectometryMomentumTransfer v1¶

ReflectometryMomentumTransfer dialog.

Table of Contents

Summary
Properties
Description
- Conversion to momentum transfer
- $Q_{z}$ resolution
Usage
References
Source

Summary ¶

Convert wavelength to momentum transfer and calculate the Qz resolution for reflectometers at continuous beam sources.

Properties ¶

Name	Direction	Type	Default	Description
InputWorkspace	Input	MatrixWorkspace	Mandatory	A reflectivity workspace in wavelenght.
OutputWorkspace	Output	MatrixWorkspace	Mandatory	The input workspace with DX values set to the Qz resolution.
ReflectedBeamWorkspace	Input	MatrixWorkspace	Mandatory	A reflected beam workspace in wavelength.
ReflectedForeground	Input	int list	Mandatory	A two element list [start, end] defining the reflected beam foreground region in workspace indices.
DirectBeamWorkspace	Input	MatrixWorkspace	Mandatory	A direct beam workspace in wavelength.
DirectForeground	Input	int list	Mandatory	A two element list [start, end] defining the direct beam foreground region in workspace indices.
SummationType	Input	string	SumInLambda	The type of summation performed for the input workspace. Allowed values: [‘SumInLambda’, ‘SumInQ’]
Polarized	Input	boolean	False	True if the input workspace is part of polarization analysis experiment, false otherwise.
PixelSize	Input	number	Mandatory	Detector pixel size, in meters.
DetectorResolution	Input	number	Mandatory	Detector pixel resolution, in meters.
ChopperSpeed	Input	number	Mandatory	Chopper speed, in rpm.
ChopperOpening	Input	number	Mandatory	The opening angle between the two choppers, in degrees.
ChopperRadius	Input	number	Mandatory	Chopper radius, in meters.
ChopperPairDistance	Input	number	Mandatory	The gap between two choppers, in meters.
Slit1Name	Input	string	Mandatory	Name of the first slit component.
Slit1SizeSampleLog	Input	string	Mandatory	The sample log entry for the first slit opening.
Slit2Name	Input	string	Mandatory	Name of the second slit component.
Slit2SizeSampleLog	Input	string	Mandatory	The sample log entry for the second slit opening.
TOFChannelWidth	Input	number	Mandatory	TOF bin width, in microseconds.

This algorithm converts a reflectivity workspace from wavelength to momentum transfer $Q_{z}$ and calculates the $Q_{z}$ resolution. The resolution is added as the Dx (X Errors) field in the output workspace.

The two additional input workspaces, ReflectedBeamWorkspace and DirectBeamWorkspace are the raw reflected and direct beam workspaces before foreground summation. They are needed for the resolution calculation.

The instruments of all three input workspaces are expected contain two components representing the two slits in the beam before the sample. The names of these components are given to the algorithm as the Slit1Name and Slit2Name properties. The slit openings (width or height depending on reflectometer setup) should be written in the sample logs (units ‘m’ or ‘mm’). The log enties are named by Slit1SizeSampleLog and Slit2SizeSampleLog.

The Polarized property should be used to indicate whether InputWorkspace is part of a polarization analysis dataset.

The SummationType property reflects the type of foreground summation used to obtain the reflectivity workspace.

Example - ReflectometryMomentumTransfer

# Load data.
reflectedWS = LoadILLReflectometry('ILL/D17/317370.nxs', XUnit='TimeOfFlight')
ConvertToDistribution(reflectedWS)
directWS = LoadILLReflectometry('ILL/D17/317369.nxs', XUnit='TimeOfFlight')
ConvertToDistribution(directWS)

# Extract some instrument parameters.
chopperPairDistance = 1e-2 * reflectedWS.run().getProperty('Distance.ChopperGap').value
chopperSpeed = reflectedWS.run().getProperty('VirtualChopper.chopper1_speed_average').value
chopper1Phase = reflectedWS.run().getProperty('VirtualChopper.chopper1_phase_average').value
chopper2Phase = reflectedWS.run().getProperty('VirtualChopper.chopper2_phase_average').value
openoffset = reflectedWS.run().getProperty('VirtualChopper.open_offset').value

# Normalize to time.
duration = reflectedWS.run().getProperty('duration').value
reflectedWS /= duration
duration = directWS.run().getProperty('duration').value
directWS /= duration

# Calculate reflectivity.
refForeground = SumSpectra(reflectedWS, 198, 209)
dirForeground = SumSpectra(directWS, 190, 210)
refForeground = RebinToWorkspace(WorkspaceToRebin=refForeground, WorkspaceToMatch=dirForeground)
R = refForeground / dirForeground

# Convert TOF to wavelength, crop.
R = ConvertUnits(R, 'Wavelength')
R = CropWorkspace(R, XMin=4.3, XMax=14.0, StoreInADS=False)
n = reflectedWS.getNumberHistograms()
reflectedWS = ConvertUnits(reflectedWS, 'Wavelength')
reflectedWS = CropWorkspaceRagged(reflectedWS, XMin=n*[4.3], XMax=n*[14.0], StoreInADS=False)
directWS = ConvertUnits(directWS, 'Wavelength')
directWS = CropWorkspaceRagged(directWS, XMin=n*[4.3], XMax=n*[14.0])

outws = ReflectometryMomentumTransfer(
    R,
    reflectedWS,
    directWS,
    ReflectedForeground=[198, 209],
    DirectForeground=[190, 210],
    SummationType='SumInLambda',
    Polarized=False,
    PixelSize=0.001195,
    DetectorResolution=0.0022,
    ChopperRadius=0.36,
    ChopperSpeed=chopperSpeed,
    ChopperOpening=45. - (chopper2Phase - chopper1Phase) - openoffset,
    ChopperPairDistance=chopperPairDistance,
    Slit1Name='slit2',
    Slit1SizeSampleLog='VirtualSlitAxis.s2w_actual_width',
    Slit2Name='slit3',
    Slit2SizeSampleLog='VirtualSlitAxis.s3w_actual_width',
    TOFChannelWidth=57.
)

qs = outws.readX(0)
dqs = outws.readDx(0)
print('First refectivity point Qz = {:.4f} +- {:.4f} A-1'.format(qs[0], dqs[0]))
print('and last Qz = {:.4f} +- {:.4f} A-1'.format(qs[-1], dqs[-1]))

Output:

First refectivity point Qz = 0.0118 +- 0.0001 A-1
and last Qz = 0.0381 +- 0.0005 A-1

References ¶

[1]	P. Gutfreund, T. Saerbeck, M. A. Gonzalez, E. Pellegrini, M. Laver, C. Dewhurst, R. Cubitt, arXiv:1710.04139 [physics.ins-det]

Categories: Algorithms | ILL\Reflectometry | Reflectometry

Source ¶

C++ source: ReflectometryMomentumTransfer.cpp (last modified: 2018-04-27)

C++ header: ReflectometryMomentumTransfer.h (last modified: 2018-06-21)

ReflectometryMomentumTransfer v1¶

Summary ¶

Properties ¶

Description ¶

Conversion to momentum transfer ¶

$Q_{z}$ resolution ¶

Usage ¶

References ¶

Source ¶