neutron/xs/NucleonNucleonXsCalculator.hh

0001 //----------------------------------*-C++-*----------------------------------//
0002 // Copyright 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/neutron/xs/NucleonNucleonXsCalculator.hh
0007 //---------------------------------------------------------------------------//
0008 #pragma once
0009
0010 #include "corecel/Macros.hh"
0011 #include "corecel/Types.hh"
0012 #include "corecel/math/Quantity.hh"
0013 #include "celeritas/Quantities.hh"
0014 #include "celeritas/Types.hh"
0015 #include "celeritas/grid/GenericCalculator.hh"
0016 #include "celeritas/grid/PolyEvaluator.hh"
0017 #include "celeritas/neutron/data/NeutronInelasticData.hh"
0018
0019 namespace celeritas
0020 {
0021 //---------------------------------------------------------------------------//
0022 /*!
0023  * Calculate nucleon-nucleon (NN) cross sections from NeutronInelasticData
0024  */
0025 class NucleonNucleonXsCalculator
0026 {
0027   public:
0028     //!@{
0029     //! \name Type aliases
0030     using ParamsRef = NeutronInelasticRef;
0031     using Energy = units::MevEnergy;
0032     using BarnXs = units::BarnXs;
0033     //!@}
0034
0035   public:
0036     // Construct with shared and state data
0037     inline CELER_FUNCTION NucleonNucleonXsCalculator(ParamsRef const& shared);
0038
0039     // Compute cross section
0040     inline CELER_FUNCTION BarnXs operator()(ChannelId el_id,
0041                                             Energy energy) const;
0042
0043     static CELER_CONSTEXPR_FUNCTION Energy high_otf_energy()
0044     {
0045         return Energy{10};
0046     }
0047
0048     static CELER_CONSTEXPR_FUNCTION Energy low_otf_energy()
0049     {
0050         return Energy{1};
0051     }
0052
0053   private:
0054     // Shared constant physics properties
0055     NeutronInelasticRef const& shared_;
0056 };
0057
0058 //---------------------------------------------------------------------------//
0059 // INLINE DEFINITIONS
0060 //---------------------------------------------------------------------------//
0061 /*!
0062  * Construct with shared and state data.
0063  */
0064 CELER_FUNCTION
0065 NucleonNucleonXsCalculator::NucleonNucleonXsCalculator(ParamsRef const& shared)
0066     : shared_(shared)
0067 {
0068 }
0069
0070 //---------------------------------------------------------------------------//
0071 /*!
0072  * Compute nucleon-nucleon (NN) cross section
0073  *
0074  * The parameterization of nucleon-nucleon cross sections below 10 MeV takes
0075  * the following functional form,
0076  * \f[
0077  *  SF(E) = coeffs[0] + coeffs[1]/E + coeffs[2]/E^{2}
0078  * \f]
0079  * where the kinetic energy of the incident nucleon, \em E is in [1, 10] MeV.
0080  * Below 1 MeV, \f$ SF(E) = slope/E \f$ down to \f$ E = slope/xs_zero \f$ while
0081  * \f$ SF(E) = xs_zero \f$ if \em E is in [0, slope/xs_zero] MeV.
0082  */
0083 CELER_FUNCTION
0084 auto NucleonNucleonXsCalculator::operator()(ChannelId ch_id,
0085                                             Energy energy) const -> BarnXs
0086 {
0087     CELER_EXPECT(ch_id < shared_.nucleon_xs.size());
0088     real_type result;
0089
0090     if (energy < this->high_otf_energy())
0091     {
0092         // Calculate NN cross section according to the Stepanov's function
0093         // for the incident nucleon kinetic energy below 10 MeV
0094         StepanovParameters const& par = shared_.xs_params[ch_id];
0095
0096         if (energy <= this->low_otf_energy())
0097         {
0098             result = celeritas::min(par.slope / energy.value(), par.xs_zero);
0099         }
0100         else
0101         {
0102             using StepanovFunction = PolyEvaluator<real_type, 2>;
0103             result
0104                 = StepanovFunction(par.coeffs)(real_type{1} / energy.value());
0105         }
0106     }
0107     else
0108     {
0109         // Get tabulated NN cross section data for the given channel
0110         GenericGridRecord grid = shared_.nucleon_xs[ch_id];
0111
0112         // Calculate NN cross section at the given energy
0113         GenericCalculator calc_xs(grid, shared_.reals);
0114         result = calc_xs(energy.value());
0115     }
0116
0117     return BarnXs{result};
0118 }
0119
0120 //---------------------------------------------------------------------------//
0121 }  // namespace celeritas