Hey,
You know when a particle crosses a cell and openMC only checks the neighboring cells to see if the particle is within it (section 2.5 in the theory manual).
does that imply that if you have a very small cell, and the particle overshoots it, the particle is effectively lost since openMC only checks the neighboring cells and not those beyond it?
To be clear, OpenMC always stops particles at the defined surfaces of a cell, so it is difficult for the particle to become lost. When a particle hits a surface and initiates a “neighbor search”, the neighboring cell would have to be a vanishingly small (less than a nanometer) for the search to miss it. Even in this case, as long as there is another cell beyond the vanishingly small cell, it will just put the particle in that cell instead.
Best regards,
Paul