In the recent multigroup (MG) changeset (PR #29), MG emissivity is calculated by multiplying singularity-opac EmissivityPerNu by the frequency width of each group. Since source particle weights are calculated directly from the final value of the emission CDF, which is simply the prefix sum of the MG emissivity, this introduces a discretization error in the particle weights. Either the LTE analytic form or the generic total Emissivity from a singularity-opac mean opacity object (if instantiated via the MG opacity) could be used to set the particle weights instead. This issue similarly affects the evaluation of the cell-based Fleck factor.
In the recent multigroup (MG) changeset (PR #29), MG emissivity is calculated by multiplying
singularity-opacEmissivityPerNu by the frequency width of each group. Since source particle weights are calculated directly from the final value of the emission CDF, which is simply the prefix sum of the MG emissivity, this introduces a discretization error in the particle weights. Either the LTE analytic form or the generic total Emissivity from asingularity-opacmean opacity object (if instantiated via the MG opacity) could be used to set the particle weights instead. This issue similarly affects the evaluation of the cell-based Fleck factor.