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collision_track.rst

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Collision Track File Format

When collision tracking is enabled with mcpl=false (the default), OpenMC writes binary data to an HDF5 file named collision_track.h5. The same data may also be written after each batch when multiple files are requested (collision_track.N.h5) or when the run is performed in parallel. The file contains the information needed to reconstruct each recorded collision.

The current revision of the collision track file format is 1.2.

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Attributes:
  • filetype (char[]) -- String indicating the type of file. For collision-track files the value is "collision_track".
Datasets:

  • collision_track_bank (Compound type) -- Collision information for each stored event. Each entry in the dataset corresponds to one collision and contains the following fields:

    • r (double[3]) -- Position of the collision in [cm].
    • u (double[3]) -- Direction unit vector immediately after the collision.
    • E (double) -- Incident particle energy before the collision in [eV].
    • dE (double) -- Energy loss over the collision (E_\text{before} - E_\text{after}) in [eV].
    • time (double) -- Time of the collision in [s].
    • wgt (double) -- Particle weight at the collision.
    • event_mt (int) -- ENDF MT number identifying the reaction.
    • delayed_group (int) -- Delayed neutron group index (non-zero for delayed events).
    • cell_id (int) -- ID of the cell in which the collision occurred.
    • nuclide_id (int) -- PDG number of the nuclide (100ZZZAAAM).
    • material_id (int) -- ID of the material containing the collision site.
    • universe_id (int) -- ID of the universe containing the collision site.
    • n_collision (int) -- Collision counter for the particle history.
    • particle (int32_t) -- Particle type (PDG number).
    • parent_id (int64_t) -- Unique ID of the parent particle.
    • progeny_id (int64_t) -- Progeny ID of the particle.

In an MPI run, OpenMC writes the combined dataset by gathering collision-track entries from all ranks before flushing them to disk, so the final file appears as though it were produced serially.