Revert change to scintillation position sampling

Author: amandalund

src/celeritas/optical/gen/GeneratorData.hh

@@ -53,15 +53,13 @@ struct GeneratorDistributionData
     real_type step_length{};
     units::ElementaryCharge charge;
     OptMatId material;
-    real_type alongstep_edep_fraction{};
     EnumArray<StepPoint, GeneratorStepData> points;
 
     //! Check whether the data are assigned
     explicit CELER_FUNCTION operator bool() const
     {
         return type != GeneratorType::size_ && num_photons > 0
-               && step_length > 0 && material && alongstep_edep_fraction >= 0
-               && alongstep_edep_fraction <= 1;
+               && step_length > 0 && material;
     }
 };
 

src/celeritas/optical/gen/OffloadData.hh

@@ -56,18 +56,11 @@ struct OffloadPreStepData
 
 //---------------------------------------------------------------------------//
 /*!
- * Energy deposition and particle speed after the continuous part of the step.
+ * Particle speed after the continuous part of the step.
  */
 struct OffloadPrePostStepData
 {
     units::LightSpeed speed;
-    units::MevEnergy energy_deposition;
-
-    //! Check whether the data are assigned
-    explicit CELER_FUNCTION operator bool() const
-    {
-        return speed > zero_quantity() || energy_deposition > zero_quantity();
-    }
 };
 
 //---------------------------------------------------------------------------//

src/celeritas/optical/gen/OffloadGatherAction.hh

@@ -33,11 +33,11 @@ class CoreParams;
  * beginning-of-step properties so that optical photons can be generated
  * between the start and end points of the step.
  *
- * The pre-post-step action stores the particle's speed and the energy
- * deposition following the continuous energy loss but before the particle
- * undergoes a discrete interaction. These must be cached for scintillation,
- * which offloads the distribution data post-step rather than pre-post-step
- * because it also requires the local energy deposition from the interaction.
+ * The pre-post-step action stores the particle's speed following the
+ * continuous energy loss but before the particle undergoes a discrete
+ * interaction. These must be cached for scintillation, which offloads the
+ * distribution data post-step rather than pre-post-step because it also
+ * requires the local energy deposition from the interaction.
  *
  * \sa OffloadGatherExecutor
  */

src/celeritas/optical/gen/ScintillationGenerator.hh

@@ -11,7 +11,6 @@
 #include "corecel/Types.hh"
 #include "corecel/math/ArrayOperators.hh"
 #include "corecel/math/ArrayUtils.hh"
-#include "corecel/random/distribution/BernoulliDistribution.hh"
 #include "corecel/random/distribution/ExponentialDistribution.hh"
 #include "corecel/random/distribution/GenerateCanonical.hh"
 #include "corecel/random/distribution/NormalDistribution.hh"
@@ -87,6 +86,7 @@ class ScintillationGenerator
     UniformRealDist sample_phi_;
     NormalDistribution<real_type> sample_lambda_;
 
+    bool is_neutral_{};
     units::LightSpeed delta_speed_{};
     Real3 delta_pos_{};
 };
@@ -105,6 +105,7 @@ ScintillationGenerator::ScintillationGenerator(
     , shared_(shared)
     , sample_cost_(-1, 1)
     , sample_phi_(0, real_type(2 * constants::pi))
+    , is_neutral_{dist_.charge == zero_quantity()}
 {
     if (shared_.scintillation_by_particle())
     {
@@ -209,21 +210,8 @@ CELER_FUNCTION TrackInitializer ScintillationGenerator::operator()(Generator& rn
     }();
     CELER_ASSERT(is_soft_orthogonal(photon.polarization, photon.direction));
 
-    // Sample the position
-    real_type u = [&rng, &p = dist_.alongstep_edep_fraction] {
-        // The number of photons generated along the step (continuous energy
-        // loss) and at the interaction site (local energy deposition) is
-        // proportional to their respective energy contributions. If both
-        // components are present, sample where to generate using the fraction
-        // of the energy deposited along the step.
-        if (p == 1 || (p != 0 && BernoulliDistribution{p}(rng)))
-        {
-            // Sample uniformly along the step
-            return UniformRealDist{}(rng);
-        }
-        // All energy deposited at the endpoint
-        return real_type(1);
-    }();
+    // Sample position: endpoint (collision site) if neutral, else uniform
+    real_type u = is_neutral_ ? 1 : UniformRealDist{}(rng);
     photon.position = dist_.points[StepPoint::pre].pos;
     axpy(u, delta_pos_, &photon.position);
 

src/celeritas/optical/gen/ScintillationOffload.hh

@@ -63,7 +63,6 @@ class ScintillationOffload
     OffloadPreStepData const& pre_step_;
     optical::GeneratorStepData post_step_;
     NativeCRef<ScintillationData> const& shared_;
-    real_type alongstep_edep_frac_;
     real_type mean_num_photons_{0};
 
     static CELER_CONSTEXPR_FUNCTION real_type poisson_threshold()
@@ -91,7 +90,6 @@ CELER_FUNCTION ScintillationOffload::ScintillationOffload(
     , pre_step_(pre_step)
     , post_step_({pre_post_step.speed, pos})
     , shared_(shared)
-    , alongstep_edep_frac_(pre_post_step.energy_deposition / energy_deposition)
 {
     CELER_EXPECT(step_length_ > 0);
     CELER_EXPECT(shared_);
@@ -151,7 +149,6 @@ ScintillationOffload::operator()(Generator& rng)
         result.step_length = step_length_;
         result.charge = charge_;
         result.material = pre_step_.material;
-        result.alongstep_edep_fraction = alongstep_edep_frac_;
         result.points[StepPoint::pre].speed = pre_step_.speed;
         result.points[StepPoint::pre].pos = pre_step_.pos;
         result.points[StepPoint::post] = post_step_;

src/celeritas/optical/gen/detail/OffloadPrePostGatherExecutor.hh

@@ -44,7 +44,6 @@ OffloadPrePostGatherExecutor::operator()(CoreTrackView const& track)
 
     OffloadPrePostStepData& step = state.step[track.track_slot_id()];
     step.speed = track.particle().speed();
-    step.energy_deposition = track.physics_step().energy_deposition();
 }
 
 //---------------------------------------------------------------------------//

src/celeritas/optical/gen/detail/ScintOffloadExecutor.hh

@@ -75,7 +75,6 @@ CELER_FUNCTION void ScintOffloadExecutor::operator()(CoreTrackView const& track)
     // Get the cached state data from after the along-step kernel
     CELER_ASSERT(tsid < pre_post_steps.step.size());
     auto const& pre_post_step = pre_post_steps.step[tsid];
-    CELER_ASSERT(pre_post_step);
 
     Real3 const& pos = track.geometry().pos();
     auto edep = track.physics_step().energy_deposition();

test/celeritas/optical/Scintillation.test.cc

@@ -58,21 +58,12 @@ class ScintillationTestBase : public ::celeritas::test::OpticalTestBase
     //! Set up mock pre-generator step data
     OffloadPreStepData build_pre_step()
     {
-        OffloadPreStepData result;
-        result.speed = LightSpeed(0.99862874144970537);  // 10 MeV
-        result.pos = {0, 0, 0};
-        result.time = 0;
-        result.material = opt_mat_;
-        return result;
-    }
-
-    //! Mock data for post-along-step
-    OffloadPrePostStepData build_pre_post_step(LightSpeed speed)
-    {
-        OffloadPrePostStepData result;
-        result.speed = speed;
-        result.energy_deposition = edep_;
-        return result;
+        OffloadPreStepData pre_step;
+        pre_step.speed = LightSpeed(0.99862874144970537);  // 10 MeV
+        pre_step.pos = {0, 0, 0};
+        pre_step.time = 0;
+        pre_step.material = opt_mat_;
+        return pre_step;
     }
 
   protected:
@@ -260,7 +251,7 @@ TEST_F(MaterialScintillationGaussianTest, pre_generator)
     auto particle
         = this->make_particle_track_view(post_energy_, pdg::electron());
     auto const pre_step = this->build_pre_step();
-    auto const pre_post_step = this->build_pre_post_step(particle.speed());
+    OffloadPrePostStepData pre_post_step{particle.speed()};
 
     ScintillationOffload generate(particle,
                                   this->make_sim_track_view(step_length_),
@@ -301,7 +292,7 @@ TEST_F(MaterialScintillationGaussianTest, basic)
     auto particle
         = this->make_particle_track_view(post_energy_, pdg::electron());
     auto const pre_step = this->build_pre_step();
-    auto const pre_post_step = this->build_pre_post_step(particle.speed());
+    OffloadPrePostStepData pre_post_step{particle.speed()};
 
     // Pre-generate optical distribution data
     ScintillationOffload generate(particle,
@@ -435,7 +426,7 @@ TEST_F(MaterialScintillationGaussianTest, stress_test)
     auto particle
         = this->make_particle_track_view(post_energy_, pdg::electron());
     auto const pre_step = this->build_pre_step();
-    auto const pre_post_step = this->build_pre_post_step(particle.speed());
+    OffloadPrePostStepData pre_post_step{particle.speed()};
 
     ScintillationOffload generate(particle,
                                   this->make_sim_track_view(step_length_),