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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 (last modified: 2021-03-31)

C++ source: ComptonPeakProfile.cpp (last modified: 2021-03-31)