CylinderAbsorption

From MantidProject

Contents 1 Summary 2 Properties 3 Description 3.1 Restrictions on the input workspace 3.2 References 4 Source Code

Summary

Calculates bin-by-bin correction factors for attenuation due to absorption and scattering in a cylindrical sample.

Properties

Order	Name	Direction	Type	Default	Description
1	InputWorkspace	Input	Workspace	Mandatory	The name of the input workspace. The input workspace must have X units of wavelength.
2	OutputWorkspace	Output	Workspace	Mandatory	The name to use for the output workspace.
3	AttenuationXSection	Input	double	Mandatory	The attenuation cross-section for the sample material in barns.
4	ScatteringXSection	Input	double	Mandatory	The scattering cross-section for the sample material in barns.
5	SampleNumberDensity	Input	double	Mandatory	The number density of the sample in .
6	NumberOfWavelengthPoints	Input	integer	All points	The number of wavelength points for which the numerical integral is calculated
7	ExpMethod	Input	string	Normal	Method to use to calculate exponentials, normal or a fast approximation
8	EMode	Input	double	Elastic	The energy mode (Elastic, Direct or Indirect).
9	EFixed	Input	double	0.0	Value of fixed energy: EI (emode=Direct) or EF (emode=Indirect) (meV). Must be set for indirect instruments, either here or in the instrument definition.
10	CylinderSampleHeight	Input	double	Mandatory	The height of the cylindrical sample in centimetres.
11	CylinderSampleRadius	Input	double	Mandatory	The radius of the cylindrical sample in centimetres.
12	NumberOfSlices	Input	integer	1	The number of slices into which the cylinder is divided for the calculation.
13	NumberOfAnnuli	Input	integer	1	The number of annuli into which each slice is divided for the calculation.

Description

This algorithm uses a numerical integration method to calculate attenuation factors resulting from absorption and single scattering in a cylindrical sample with the dimensions and 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 divided up into a stack of slices, which are then divided into annuli (rings). These annuli are further divided (see Ref. [2], Appendix A) to give the full set of elements for which a calculation will be carried out. Thus the calculation speed depends linearly on the total number of bins in the workspace and on the number of slices. The dependence on the number of annuli is stronger, going as 3n(n + 1).

Path lengths through the sample are then calculated for the centre-point of each element and a numerical integration is carried out using these path lengths over the volume elements.

Restrictions on the input workspace

The input workspace must have units of wavelength. The instrument associated with the workspace must be fully defined because detector, source & sample position are needed.

References

The method used here is based upon work presented in the following two papers, although it does not yet fully implement all aspects discussed there (e.g. there's no multiple scattering and no concentric cylinders).

1. I.A. Blech & B.L. Averbach, Multiple Scattering of Neutrons in Vanadium and Copper, Phys. Rev. 137 4A (1965) A1113.
2. A.K. Soper & P.A. Egelstaff, Multiple Scattering and Attenuation of Neutrons in Concentric Cylinders, NIM 178 (1980) 415.

Source Code

Header CylinderAbsorption.h

Source CylinderAbsorption.cpp