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ComptonPeakProfile

Description

The ComptonPeakProfile describes the Neutron Compton profile with either a Voigt or Gaussian approximation, depending on an energy cutoff value. It takes three input parameters:

• Intensity: \(I\)

• Position: \(P\)

• SigmaGauss: \(\sigma_G\)

and three attributes,

• WorkspaceIndex

• Mass

• VoigtEnergyCutOff

The VoigtEnergyCutOff is used to determine whether a Gaussian or Voigt function is used to fit the peak. If the final energy, as read from the input workspace, is greater than the VoigtEnergyCutOff a normalised Gaussian approximation is used,

\[\frac{I}{2\pi \sigma_T^2}\exp \left( -0.5*\frac{(x-P)^2}{\sigma_T^2} \right)\]

where \(\sigma_T^2\) is the total variance, defined by

\[\sigma_T^2 = \sigma_G^2 + \Gamma^2\]

where \(\Gamma\) is the half-width-half-maximum, estimated from the input data.

If instead, the energy is below the cutoff an approximation to a Voigt function is used with the following inputs:

\[\text{LorentzAmp} = I\]

\[\text{LorentzPos} = P\]

\[\text{LorentzFWHM} = 2\Gamma\]

\[\text{GaussianFWHM}= 0.5 \sigma_G \sqrt{\ln(4)}\]

Attributes (non-fitting parameters)

Name	Type	Default	Description
Mass
VoigtEnergyCutOff
WorkspaceIndex

Properties (fitting parameters)

Name	Default	Description
Intensity	1.0	Intensity parameter
Position	1.0	Peak position parameter
SigmaGauss	1.0	Width parameter

Categories: FitFunctions | General

Source

C++ header: ComptonPeakProfile.h

C++ source: ComptonPeakProfile.cpp