gtsimulation.interaction.nuclear_interaction#

Functions

convert_to_numpy(run_result)

Convert C++ Geant4 result object to structured NumPy arrays.

sim_worker(input_queue, output_queue, seed)

Geant4 worker process loop.

Classes

NuclearInteraction([max_generations, ...])

Geant4-backed nuclear interaction simulator with optional process restarts.
class gtsimulation.interaction.nuclear_interaction.NuclearInteraction(max_generations: int = 1, grammage_threshold: float = 10.0, seed: int = None, restart_limit: int = 20)[source]#

Geant4-backed nuclear interaction simulator with optional process restarts.

This class wraps a Geant4 simulation that propagates a single charged particle through a homogeneous material layer and returns the final primary particle state and the list of produced secondary particles.

The simulation is executed in an isolated multiprocessing.Process. This makes it possible to fully reset Geant4 state by restarting the worker process when needed.

Performance note: restarting the worker is mainly useful when the medium is frequently updated (e.g., many unique material compositions/densities over time). In that scenario, Geant4 internal tables may grow and recalculations for previously used (now irrelevant) materials can slow down subsequent runs, so periodic restarts can keep performance stable.

If you keep using the same material configuration for many runs, restarts are usually unnecessary; the worker can stay alive and repeated calls are significantly faster.

The target geometry is a cylinder filled with a user-defined material mixture:

  • Cylinder length is computed as thickness = mass / density / 1e2 [m].

  • Cylinder radius equals its length.

  • The primary particle starts at (0, 0, 0) and travels along the +Z axis.

  • Tracking stops when the primary particle dies or reaches the cylinder boundary.

Internally, the C++ result object is converted to structured NumPy arrays with the dtypes PRIMARY_DTYPE and SECONDARY_DTYPE.

Parameters:

  • max_generations (int, default=1) – Maximum number of secondary particle generations to model in the simulation.

  • grammage_threshold (float, default=10.) – Grammage threshold [g/cm²] above which the Geant4 subroutine is triggered. Should be set as a fraction of the expected nuclear interaction length in the material.

  • seed (int) – Random seed used to initialize the Geant4 simulator inside the worker process.

  • restart_limit (int, default=20) – Number of runs after which the worker process is restarted automatically.

run_matter_layer(pdg: int, energy: float, mass: float, density: float, element_name: list[str], element_abundance: list[float])[source]#

Simulate interaction of a charged particle with a homogeneous material layer.

Parameters:

  • pdg (int) – PDG code of the primary particle.

  • energy (float) – Primary particle kinetic energy in MeV.

  • mass (float) – Traversed mass thickness in g/cm^2.

  • density (float) – Medium density in g/cm^3.

  • element_name (list of str) – Chemical element symbols (e.g. ["N", "O"]) forming the medium.

  • element_abundance (list of float) – Mass fractions (or the fractions expected by your Geant4 material definition); the sum should be 1.

Returns:

  • primary (numpy.ndarray) – Structured NumPy array of shape (1,) with dtype PRIMARY_DTYPE. Fields:

    • Name : str

    • PDGcode : int

    • Mass : float, MeV

    • Charge : int

    • KineticEnergy : float, MeV

    • MomentumDirection : (3,) float, unit vector

    • Position : (3,) float, m

    • LastProcess : str

  • secondary (numpy.ndarray) – Structured NumPy array with dtype SECONDARY_DTYPE and shape (N,), where N is the number of secondary particles (may be 0). Fields:

    • Name : str

    • PDGcode : int

    • Mass : float, MeV

    • Charge : int

    • KineticEnergy : float, MeV

    • MomentumDirection : (3,) float, unit vector

gtsimulation.interaction.nuclear_interaction.convert_to_numpy(run_result)[source]#

Convert C++ Geant4 result object to structured NumPy arrays.

Parameters:

run_result (matter_layer.RunResult) – C++ result object returned by the Geant4 simulator.

Returns:

  • primary (numpy.ndarray) – Structured array of shape (1,) with dtype PRIMARY_DTYPE containing the final state of the primary particle.

  • secondary (numpy.ndarray) – Structured array of shape (N,) with dtype SECONDARY_DTYPE containing secondary particles produced during the interaction (empty if N=0).

Notes

This is an internal utility function used by the multiprocessing worker to ensure efficient serialization of complex C++ objects across process boundaries.

gtsimulation.interaction.nuclear_interaction.sim_worker(input_queue, output_queue, seed)[source]#

Geant4 worker process loop.

Runs in an isolated process and owns a single matter_layer.Simulator instance. Receives simulation parameters via input_queue, executes events, and returns results via output_queue. Automatically terminates when receiving None.

Parameters:

  • input_queue (multiprocessing.Queue) – Input queue containing parameter tuples: (pdg, energy, mass, density, el_names, el_fracs).

  • output_queue (multiprocessing.Queue) – Output queue for results: (primary_array, secondary_array, material_count).

  • seed (int) – Random seed passed to the Geant4 simulator constructor.

Notes

Internal worker function for NuclearInteraction. Not intended for direct use. The worker process is restarted periodically to control Geant4 memory growth.