Is it necessary to activate single scattering for 60 keV electron beam

Dear FLUKA experts,

I am writing to ask for your help in checking if it is needed to only use single scattering for an electron beam of 60 keV as stated in page 6 in FLUKA manual.

The electron beam is being used to irradiate thin metal samples in my simulation. Here I attached the flair files for one of the samples, Ni.
Ni.flair (13.3 KB)
Ni.inp (11.4 KB)
Could you possibly check if I set the correct MULSIOPT setting if the single scattering is needed? I referred the setting as Activating single scattering stated.

Your any comments and help will be much appreciated.


Dear @xili,
Your questions are on two totally different topics. Please, split them and post them in two different threads.

Hi @amario,
Thank you for the reminder. I have done it. :slightly_smiling_face:


As a rule of thumb, you need to ensure that the particle is undergoing ~10-20 single scattering events in a medium in order for the multiple scattering approximation to be valid. This is due to the underlying truncated series development for MCS failing for a low number of events.

A good proof that single scattering is necessary can be obtained by printing the step length for 60 keV electrons in Nickel. You then compare that value to the range of the electrons or the thickness of your target, whichever is shorter. MCS can only be used if the step length you printed is much shorter than that length.

As a reminder, you can request the step length (CTRACK) through the mgdraw user routine. This is requested by inserting a USERDUMP card with WHAT(1) >= 100 and WHAT(3) = 2, see the correponding manual page for details

As for your MULSOPT card, it is correctly setup in the input you have attached.

Hello @pschoofs,

Thank you very much for your reply. This is very helpful.

Unfortunately I never used user routine method before, so I read all the discussions related to USRDUMP and mgdraw.f on this forum. However, I am still struggling with the procedures to do this simulation. Do you have possibly a guideline about how to compile and run it with Flair so that I can go through it to customize my fortran file?

Besides, I have tried the simulation with/without single scattering settings by MULSOPT card. Both results showed that no DPA was detected (i.e. DPA: 0 for this case). I am wondering, if the MCS step length is shorter than the thickness of target, are there any other ways to solve this to run a successful simulation?

Thank you for your time.