6.3

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PaalmanPingsAbsorptionCorrection v1

../_images/PaalmanPingsAbsorptionCorrection-v1_dlg.png

PaalmanPingsAbsorptionCorrection dialog.

Summary

Calculates the attenuation due to absorption and single scattering in a generic sample shape for all Paalmin-pings terms.

Properties

Name Direction Type Default Description
InputWorkspace Input MatrixWorkspace Mandatory The X values for the input workspace must be in units of wavelength
OutputWorkspace Output WorkspaceGroup Mandatory Output workspace name
NumberOfWavelengthPoints Input number Optional The number of wavelength points for which the numerical integral is calculated (default: all points)
ElementSize Input number 1 The size of one side of an integration element cube in mm
ContainerElementSize Input number Optional The size of one side of an integration element cube in mm for container.Default to be the same as ElementSize.

Description

This algorithm was adapted from AbsorptionCorrection v1. This algorithm uses a numerical integration method to calculate Paalman-Ping attenuation factors resulting from absorption and single scattering in a sample and container with the material properties given. Factors are calculated for each spectrum (i.e. detector position) and wavelength point, as defined by the input workspace. The sample is first bounded by a cuboid, which is divided up into small cubes. The cubes whose centres lie within the sample make up the set of integration elements (so you have a kind of ‘Lego’ model of the sample) and path lengths through the sample and container are calculated for the centre-point of each element, and a numerical integration is carried out using these path lengths over the volume elements.

The output workspace will be a WorkspaceGroup containing workpsace with the attenuation factors for \(A_{s,s}\), \(A_{s,sc}\), \(A_{c,c}\) and \(A_{c,sc}\). This output can be applied as the CorrectionsWorkspace input of ApplyPaalmanPingsCorrection v1.

Note that the duration of this algorithm is strongly dependent on the element size chosen, and that too small an element size can cause the algorithm to fail because of insufficient memory.

Assumptions

This algorithm assumes that the (parallel) beam illuminates the entire sample unless a ‘gauge volume’ has been defined using the DefineGaugeVolume v1 algorithm (or by otherwise adding a valid XML string defining a shape to a Run property called “GaugeVolume”). In this latter case only scattering within this volume (and the sample) is integrated, because this is all the detector can ‘see’. The full sample is still used for the neutron paths.

It is worth pointing out that the parameter ContainerElementSize has very limited impact on the final absorption correction factor, therefore it is generally safe to use the same element size for both sample and container regardless of the actual geometry difference when running this algorithm.

Usage

Example: A cylinder sample in can

ws = CreateWorkspace(DataX=[1.7981, 1.7983], DataY=[0.0]*4, NSpec=4, UnitX="Wavelength", YUnitLabel="Counts")
EditInstrumentGeometry(ws,
    PrimaryFlightPath=5.0,
    SpectrumIDs=[1, 2, 3, 4],
    L2=[2.0, 2.0, 2.0, 2.0],
    Polar=[10.0, 90.0, 170.0, 90.0],
    Azimuthal=[0.0, 0.0, 0.0, 45.0],
    DetectorIDs=[1, 2, 3, 4],
    InstrumentName="Instrument")
SetSample(ws,
    Geometry={"Shape": "Cylinder", "Height": 5.68, "Radius": 0.295},
    Material={"ChemicalFormula": "La-(B11)5.94-(B10)0.06", "SampleNumberDensity": 0.1},
    ContainerGeometry={"Shape": 'HollowCylinder', 'Height': 5.68, 'InnerRadius': 0.295, 'OuterRadius': 0.315},
    ContainerMaterial={"ChemicalFormula": "V", "SampleNumberDensity": 0.0721})
abs = PaalmanPingsAbsorptionCorrection(ws)
for a in ["ass", "assc", "acc", "acsc"]:
    print("{:4} {:.4f}(θ=10) {:.4f}(θ=90) {:.4f}(θ=170) {:.4f}(θ=90,φ=45)".format(a, *(mtd["abs_"+a].readY(i)[0] for i in range(4))))

Output:

ass  0.1298(θ=10) 0.1708(θ=90) 0.2119(θ=170) 0.1332(θ=90,φ=45)
assc 0.1253(θ=10) 0.1650(θ=90) 0.2048(θ=170) 0.1280(θ=90,φ=45)
acc  0.9418(θ=10) 0.9416(θ=90) 0.9422(θ=170) 0.9311(θ=90,φ=45)
acsc 0.3258(θ=10) 0.4221(θ=90) 0.5782(θ=170) 0.4014(θ=90,φ=45)

Categories: AlgorithmIndex | CorrectionFunctions\AbsorptionCorrections