TOFSANSResolutionByPixelCalculator.cpp

Go to the documentation of this file.

// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2018 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
#include "MantidAlgorithms/TOFSANSResolutionByPixelCalculator.h"
#include <cmath>
namespace Mantid::Algorithms {
 
double TOFSANSResolutionByPixelCalculator::getWavelengthIndependentFactor(double r1, double r2, double deltaR,
                                                                          double lCollim, double l2) const {
  return (4.0 * M_PI * M_PI / 12.0) * (3.0 * r1 * r1 / (lCollim * lCollim) +
                                       3.0 * r2 * r2 * (lCollim + l2) * (lCollim + l2) / (lCollim * lCollim * l2 * l2) +
                                       (deltaR * deltaR) / (l2 * l2));
}
 
/*
 * Calculates the sigmaQ value
 * @param moderatorValue: The value of the moderator for a certain wavelength
 * @param wavlengthIndependentFactor: the geometry-dependent prefactor
 * @param q: the momentum transfer
 * @param wavelength: the neutron's wavelength
 * @param deltaWavelength: the wavelength spread for that wavelength
 * @param l1: the l1 length
 * @param l2: the L2 length
 * @returns the sigma q value
 */
 
double TOFSANSResolutionByPixelCalculator::getSigmaQValue(double moderatorValue, double wavlengthIndependentFactor,
                                                          double q, double wavelength, double deltaWavelength,
                                                          double l1, double l2) const {
  // Calculate the moderator uncertainty
  const double sigModerator = moderatorValue * 3.9560 / (1000.0 * (l1 + l2));
 
  // Calculate the wavelength uncertainty
  const double sigWavelengthSquared = deltaWavelength * deltaWavelength / 12.0 + sigModerator * sigModerator;
 
  // Calculate the q uncertainty
  const double qbyWavelengthSquared = q * q / (wavelength * wavelength);
 
  return sqrt(wavlengthIndependentFactor / (wavelength * wavelength) + (sigWavelengthSquared * qbyWavelengthSquared));
}
} // namespace Mantid::Algorithms