em/xs/MottRatioCalculator.hh

0001 //----------------------------------*-C++-*----------------------------------//
0002 // Copyright 2023-2024 UT-Battelle, LLC, and other Celeritas developers.
0003 // See the top-level COPYRIGHT file for details.
0004 // SPDX-License-Identifier: (Apache-2.0 OR MIT)
0005 //---------------------------------------------------------------------------//
0006 //! \file celeritas/em/xs/MottRatioCalculator.hh
0007 //---------------------------------------------------------------------------//
0008 #pragma once
0009
0010 #include "corecel/Macros.hh"
0011 #include "corecel/Types.hh"
0012 #include "corecel/math/ArrayUtils.hh"
0013 #include "celeritas/em/data/WentzelOKVIData.hh"
0014 #include "celeritas/grid/PolyEvaluator.hh"
0015
0016 namespace celeritas
0017 {
0018
0019 //---------------------------------------------------------------------------//
0020 /*!
0021  * Calculates the ratio of Mott cross section to the Rutherford cross section.
0022  *
0023  * This ratio is an adjustment of the cross section from a purely classical
0024  * treatment of a point nucleus in an electronic cloud (Rutherford scattering)
0025  * to a quantum mechanical treatment. The implementation is an interpolated
0026  * approximation developed in [LQZ95] and described in the Geant Physics
0027  * Reference Manual [PRM] (Release 1.11) section 8.4
0028  *
0029  * [LQZ95] T. Lijian, H. Quing and L. Zhengming, Radiat. Phys. Chem. 45 (1995),
0030  *     235-245
0031  *
0032  * The parameter \c cos_theta is the cosine of the scattered angle in the
0033  * z-aligned momentum frame.
0034  */
0035 class MottRatioCalculator
0036 {
0037   public:
0038     //!@{
0039     //! \name Type aliases
0040     using MottCoeffMatrix = MottElementData::MottCoeffMatrix;
0041     //!@}
0042
0043   public:
0044     // Construct with state data
0045     inline CELER_FUNCTION
0046     MottRatioCalculator(MottCoeffMatrix const& coeffs, real_type beta);
0047
0048     // Ratio of Mott and Rutherford cross sections
0049     inline CELER_FUNCTION real_type operator()(real_type cos_t) const;
0050
0051   private:
0052     MottCoeffMatrix const& coeffs_;
0053     real_type beta_;
0054 };
0055
0056 //---------------------------------------------------------------------------//
0057 // INLINE DEFINITIONS
0058 //---------------------------------------------------------------------------//
0059 /*!
0060  * Construct with state data.
0061  */
0062 CELER_FUNCTION
0063 MottRatioCalculator::MottRatioCalculator(MottCoeffMatrix const& coeffs,
0064                                          real_type beta)
0065     : coeffs_(coeffs), beta_(beta)
0066 {
0067     CELER_EXPECT(0 <= beta_ && beta_ < 1);
0068 }
0069
0070 //---------------------------------------------------------------------------//
0071 /*!
0072  * Compute the ratio of Mott to Rutherford cross sections.
0073  */
0074 CELER_FUNCTION
0075 real_type MottRatioCalculator::operator()(real_type cos_theta) const
0076 {
0077     CELER_EXPECT(cos_theta >= -1 && cos_theta <= 1);
0078
0079     // (Exponent) Base for theta powers
0080     real_type fcos_t = std::sqrt(1 - cos_theta);
0081
0082     // Mean velocity of electrons between ~KeV and 900 MeV
0083     real_type const beta_shift = 0.7181228;
0084
0085     // (Exponent) Base for beta powers
0086     real_type beta0 = beta_ - beta_shift;
0087
0088     // Evaluate polynomial of powers of beta0 and fcos_t
0089     MottElementData::ThetaArray theta_coeffs;
0090     for (auto i : range(theta_coeffs.size()))
0091     {
0092         theta_coeffs[i] = PolyEvaluator(coeffs_[i])(beta0);
0093     }
0094     real_type result = PolyEvaluator(theta_coeffs)(fcos_t);
0095     CELER_ENSURE(result >= 0);
0096     return result;
0097 }
0098
0099 //---------------------------------------------------------------------------//
0100 }  // namespace celeritas