MCNP6.2 - Are results of FMESH tallies already divided by cell volume?

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SUMMARY

The FMESH tally results in MCNP6.2 are indeed divided by the mesh cell volume, not the geometry cell volume. This conclusion is supported by the comparison with F4 tallies, where results align under the assumption that FMESH results are volume-normalized. Additionally, the "out=cf" option in MCNP6.3.0 confirms that tally results are printed in relation to volume, reinforcing the understanding that FMESH calculations account for mesh cell volume. This clarification is crucial for accurate tally comparisons in MCNP simulations.

PREREQUISITES
  • Understanding of MCNP6.2 and MCNP6.3.0 software
  • Familiarity with FMESH and F4 tally concepts
  • Knowledge of mesh cell and geometry cell definitions
  • Basic principles of radiation transport and tallying in computational physics
NEXT STEPS
  • Review the MCNP® Code Version 6.3.0 Theory & User Manual for detailed tally explanations
  • Explore the implications of using the "out=cf" option in MCNP for output analysis
  • Investigate the differences between FMESH and TMESH tallies in MCNP
  • Learn about advanced tally techniques in MCNP for improved simulation accuracy
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Researchers, physicists, and engineers working with MCNP simulations, particularly those focusing on radiation transport modeling and tally accuracy in computational studies.

19matthew89
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TL;DR
It's not clear whether the results of mesh tally for FMESH are already divided by the cell volume
Hi everyone,

I am struggling to understand whether the results of FMESH tallies are already divided by the cell volume or not.

I'd actually expect so considering:
1. the comparison with an F4 tally in the same cell where results are comparable only if I assume that the mesh tallies results are already divided by the cell volume
2. the fact that the option "out=cf" is available. With this option "the volume and the tally results multiplied by the volume are also printed". And so it would make sense multiplying the standard tally results by the volume only if its standard output were already divided by the volume
3. for "similarity" with TMESH, where indeed "average fluence is particle weight times track length divided by volume in units of number/cm2"

But I could not find anywhere in MCNP manual (MCNP® Code Version 6.3.0 Theory & User Manual) a clear statement about it.

Could you confirm, please?

Thanks in advance
 
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The FMESH calculation includes a division by the mesh cell volume, not the geometry cell.

So if you had a geometry cell and a mesh cell that were totally coincident you'd expect the F4 and the FMESH cell tally to match.
 
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Alex A said:
The FMESH calculation includes a division by the mesh cell volume, not the geometry cell.

So if you had a geometry cell and a mesh cell that were totally coincident you'd expect the F4 and the FMESH cell tally to match.
Great! Thanks!
 

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