Separation of primary electron and photon dose components

[erjft]

Hi, I have a bremsstrahlung converter in EGSnrc, and was wondering how I might distinguish the contributions of the primary electrons (as contaminant dose) to the photons dose (that ends up as secondary electrons) in a water phantom downstream - I have a feeling ECUT and ESAVE may be involved. Any advice would be greatly appreciated :)

[rtownson]

Currently there's not an easy way to accurately separate dose from primaries or secondaries in egs++. It is available for fluence scoring though, for example:

https://nrc-cnrc.github.io/EGSnrc/doc/pirs898/classEGS__PlanarFluence.html

If you're using a phase-space with BEAMnrc, the LATCH variable does provide a way to do this. In DOSXYZnrc you can filter particles from the phase-space based on the LATCH that was set in BEAMnrc.

[erjft]

Thanks Reid, I was thinking maybe I turn on photon production, but then cut the tracking so that I would just measure electrons that are transmitted through the materials. Unfortunately I'm not using a phase space, but rather, calculating it all on the fly with a few sensitive water voxel regions.

[rtownson]

If you're using egs_chamber, there's region-by-region ECUT and PCUT setting. This would allow you to set PCUT high in the region following brems production to kill them. Then, all you would get through would be the original electrons, plus some electrons set in motion by the brems photons or by other interactions in the target. You would also miss some relaxation x-rays produced by electron impact ionization. So it's not a perfect method, but it will give you an estimate.