Concept of Setcut value

Physics Processes, Models and Cross Sections
1

Hello Geant4 experts.

I’m sampling the bremsstrahlung spectrum using 40 keV electron and 1mm depth tungsten target.
I used the FTFP_BERT_EMZ physics list.
I saw the default cut value is 1mm in the document.
I could not see any Bremsstrahlung photon without adjusting the cut value since the electron energy was quite wrong.
But when I used the command “/run/setCut 0.001 mm” in the macro file, I could see the Bremsstrahlung photons.
I have a question on this point.
I checked that there is a lowest threshold to avoid infrared divergence.
I used 0.001mm cut value, and there is no reason.
Is a lower cut value always better? (When there is no infrared divergence and if don’t care about computing resources)
If not, how can I select or calculate the best cut value?

I appreciate your help in advance.

Best regards
Hyeonseok

2

The Z of tungsten is very high so I am not surprised you need a very low cutoff.

You need to care about computing resources when the infrared divergence gets exponentially larger. They are one and the same.

Generally the range is a tradeoff is between full accuracy and simulation time. But there can also be more logical cutoffs such as machine precision for materials.