Refactor back to ParticleType that stores PDG number

paulromano · Feb 3, 2026 · Jan 23, 2026 · Jan 23, 2026 · Jan 27, 2026 · Jan 27, 2026
commit c942f5987a1a34c1f501c2bb151a1da97a740044
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -372,7 +372,7 @@ list(APPEND libopenmc_SOURCES
   src/particle.cpp
   src/particle_data.cpp
   src/particle_restart.cpp
-  src/pdg_number.cpp
+  src/particle_type.cpp
   src/photon.cpp
   src/physics.cpp
   src/physics_common.cpp

diff --git a/include/openmc/event.h b/include/openmc/event.h
@@ -24,7 +24,7 @@ namespace openmc {
 // to achieve consistent locality improvements.
 struct EventQueueItem {
   int64_t idx;      //!< particle index in event-based particle buffer
-  PDGNumber type;   //!< particle PDG
+  ParticleType type; //!< particle type
   int64_t material; //!< material that particle is in
   double E;         //!< particle energy
 

diff --git a/include/openmc/particle.h b/include/openmc/particle.h
@@ -49,7 +49,7 @@ class Particle : public ParticleData {
   //! \param E Energy of the secondary particle in [eV]
   //! \param type Particle type
   //! \return Whether a secondary particle was created
-  bool create_secondary(double wgt, Direction u, double E, PDGNumber type);
+  bool create_secondary(double wgt, Direction u, double E, ParticleType type);
 
   //! split a particle
   //

diff --git a/include/openmc/particle_data.h b/include/openmc/particle_data.h
@@ -3,7 +3,7 @@
 
 #include "openmc/array.h"
 #include "openmc/constants.h"
-#include "openmc/pdg_number.h"
+#include "openmc/particle_type.h"
 #include "openmc/position.h"
 #include "openmc/random_lcg.h"
 #include "openmc/tallies/filter_match.h"
@@ -46,7 +46,7 @@ struct SourceSite {
   double wgt {1.0};
   int delayed_group {0};
   int surf_id {SURFACE_NONE};
-  PDGNumber particle;
+  ParticleType particle;
 
   // Extra attributes that don't show up in source written to file
   int parent_nuclide {-1};
@@ -68,7 +68,7 @@ struct CollisionTrackSite {
   int material_id {0};
   int universe_id {0};
   int n_collision {0};
-  PDGNumber particle;
+  ParticleType particle;
   int64_t parent_id;
   int64_t progeny_id;
 };
@@ -87,7 +87,7 @@ struct TrackState {
 
 //! Full history of a single particle's track states
 struct TrackStateHistory {
-  PDGNumber particle;
+  ParticleType particle;
   std::vector<TrackState> states;
 };
 
@@ -494,7 +494,7 @@ class ParticleData : public GeometryState {
   MacroXS macro_xs_;
   CacheDataMG mg_xs_cache_;
 
-  PDGNumber type_ {PDG_NEUTRON};
+  ParticleType type_;
 
   double E_;
   double E_last_;
@@ -590,10 +590,8 @@ class ParticleData : public GeometryState {
   const CacheDataMG& mg_xs_cache() const { return mg_xs_cache_; }
 
   // Particle type (n, p, e, gamma, etc)
-  PDGNumber& type() { return type_; }
-  const PDGNumber& type() const { return type_; }
-  PDGNumber& pdg() { return type_; }
-  const PDGNumber& pdg() const { return type_; }
+  ParticleType& type() { return type_; }
+  const ParticleType& type() const { return type_; }
 
   // Current particle energy, energy before collision,
   // and corresponding multigroup group indices. Energy

diff --git a/include/openmc/particle_type.h b/include/openmc/particle_type.h
@@ -0,0 +1,142 @@
+//==============================================================================
+// ParticleType class definition
+//==============================================================================
+
+#ifndef OPENMC_PARTICLE_TYPE_H
+#define OPENMC_PARTICLE_TYPE_H
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <string_view>
+#include <type_traits>
+
+#include "openmc/constants.h"
+
+namespace openmc {
+
+//------------------------------------------------------------------------------
+// PDG constants (canonical particle identity as simple integers)
+//------------------------------------------------------------------------------
+
+inline constexpr int32_t PDG_NEUTRON = 2112;
+inline constexpr int32_t PDG_PHOTON = 22;
+inline constexpr int32_t PDG_ELECTRON = 11;
+inline constexpr int32_t PDG_POSITRON = -11;
+inline constexpr int32_t PDG_PROTON = 2212;
+inline constexpr int32_t PDG_DEUTERON = 1000010020;
+inline constexpr int32_t PDG_TRITON = 1000010030;
+inline constexpr int32_t PDG_ALPHA = 1000020040;
+
+//------------------------------------------------------------------------------
+// ParticleType class (standard-layout, trivially copyable)
+//------------------------------------------------------------------------------
+
+class ParticleType {
+public:
+  //----------------------------------------------------------------------------
+  // Constructors
+
+  // Default constructor: defaults to neutron
+  constexpr ParticleType() : pdg_number_(PDG_NEUTRON) {}
+
+  // Constructor from PDG code
+  constexpr explicit ParticleType(int32_t pdg_number) : pdg_number_(pdg_number)
+  {}
+
+  // Constructor from particle name string (e.g., "neutron", "photon", "Fe56")
+  explicit ParticleType(std::string_view str);
+
+  // Constructor from Z, A, and metastable state for nuclear particles
+  constexpr ParticleType(int Z, int A, int m = 0)
+    : pdg_number_(1000000000 + Z * 10000 + A * 10 + m)
+  {}
+
+  //----------------------------------------------------------------------------
+  // Accessors
+
+  // Accessor for the underlying PDG number
+  constexpr int32_t pdg_number() const { return pdg_number_; }
+
+  //----------------------------------------------------------------------------
+  // Methods
+
+  // Convert to string representation
+  std::string str() const;
+
+  // Check if this represents a nucleus (vs elementary particle)
+  constexpr bool is_nucleus() const
+  {
+    // PDG nuclear codes are >= 1000000000 (100ZZZAAAI format)
+    return pdg_number_ >= 1000000000;
+  }
+
+private:
+  int32_t pdg_number_;
+};
+
+//------------------------------------------------------------------------------
+// Static assertions to ensure standard-layout and trivially copyable
+//------------------------------------------------------------------------------
+
+static_assert(std::is_standard_layout_v<ParticleType>,
+  "ParticleType must be standard-layout");
+static_assert(std::is_trivially_copyable_v<ParticleType>,
+  "ParticleType must be trivially copyable");
+static_assert(sizeof(ParticleType) == sizeof(int32_t),
+  "ParticleType must be same size as int32_t");
+
+//------------------------------------------------------------------------------
+// Comparison operators (free functions for symmetry)
+//------------------------------------------------------------------------------
+
+constexpr bool operator==(ParticleType lhs, ParticleType rhs)
+{
+  return lhs.pdg_number() == rhs.pdg_number();
+}
+
+constexpr bool operator!=(ParticleType lhs, ParticleType rhs)
+{
+  return lhs.pdg_number() != rhs.pdg_number();
+}
+
+constexpr bool operator<(ParticleType lhs, ParticleType rhs)
+{
+  return lhs.pdg_number() < rhs.pdg_number();
+}
+
+//------------------------------------------------------------------------------
+// Transport indexing helpers (for dense arrays keyed by transport kind)
+//------------------------------------------------------------------------------
+
+constexpr int transport_index(ParticleType type)
+{
+  switch (type.pdg_number()) {
+  case PDG_NEUTRON:
+    return 0;
+  case PDG_PHOTON:
+    return 1;
+  case PDG_ELECTRON:
+    return 2;
+  case PDG_POSITRON:
+    return 3;
+  default:
+    return C_NONE;
+  }
+}
+
+constexpr bool is_transportable(ParticleType type)
+{
+  return transport_index(type) != C_NONE;
+}
+
+//------------------------------------------------------------------------------
+// Legacy conversion helpers
+//------------------------------------------------------------------------------
+
+// Legacy enum code (0..3) to ParticleType conversion
+ParticleType legacy_particle_index_to_type(int code);
+
+} // namespace openmc
+
+#endif // OPENMC_PARTICLE_TYPE_H
diff --git a/include/openmc/pdg_number.h b/include/openmc/pdg_number.h
diff --git a/include/openmc/reaction_product.h b/include/openmc/reaction_product.h
@@ -10,7 +10,7 @@
 #include "openmc/chain.h"
 #include "openmc/endf.h"
 #include "openmc/memory.h" // for unique_ptr
-#include "openmc/particle.h"
+#include "openmc/particle_type.h"
 #include "openmc/vector.h" // for vector
 
 namespace openmc {
@@ -49,7 +49,7 @@ class ReactionProduct {
   //! \param[inout] seed Pseudorandom seed pointer
   void sample(double E_in, double& E_out, double& mu, uint64_t* seed) const;
 
-  PDGNumber particle_;         //!< Particle PDG
+  ParticleType particle_;      //!< Particle type
   EmissionMode emission_mode_; //!< Emission mode
   double decay_rate_; //!< Decay rate (for delayed neutron precursors) in [1/s]
   unique_ptr<Function1D> yield_;      //!< Yield as a function of energy

diff --git a/include/openmc/source.h b/include/openmc/source.h
@@ -12,7 +12,7 @@
 #include "openmc/distribution_multi.h"
 #include "openmc/distribution_spatial.h"
 #include "openmc/memory.h"
-#include "openmc/particle.h"
+#include "openmc/particle_type.h"
 #include "openmc/vector.h"
 
 namespace openmc {
@@ -127,7 +127,7 @@ class IndependentSource : public Source {
   SourceSite sample(uint64_t* seed) const override;
 
   // Properties
-  PDGNumber particle_type() const { return particle_; }
+  ParticleType particle_type() const { return particle_; }
 
   // Make observing pointers available
   SpatialDistribution* space() const { return space_.get(); }
@@ -148,7 +148,7 @@ class IndependentSource : public Source {
 
 private:
   // Data members
-  PDGNumber particle_ {PDG_NEUTRON}; //!< Type of particle emitted
+  ParticleType particle_;            //!< Type of particle emitted
   UPtrSpace space_;                  //!< Spatial distribution
   UPtrAngle angle_;                  //!< Angular distribution
   UPtrDist energy_;                  //!< Energy distribution