WentzelVI model settings

Physics Processes, Models and Cross Sections
1

Dear all,
for what I understood, the WentzelVI model is a mixed scheme to simulate the single and multiple scattering, depending on a threshold scattering angle.
I have read that the threshold angle is 0.2 rad, for which collisions are considered as “single scattering” if theta>0.2 and multple scattering, if below.

Is there a way to change this default parameter to see how close I get to single scattering without increasing too much the computational time?

Thanks for helping!!

1 Like
2

Hello,

please, note that this is a maximal limit angle. The real limit is dynamic - defined by momentum of a particle. This maximal limit is effective only at low momentum. It can be changed via UI command:

/process/msc/ThetaLimit 0.1 radian

The default value 0.2 is optimized using existing Physics Lists and number of test setups. It cannot be considered as the best value, extra study is needed to make a conclusion. The optimum may be different for different particle type - this is not known so far.

VI

3

Ok thank you very much.
I also read that together wiht the G4WentzelVIModel I need to have implemented the G4eSingleCoulombScatteringModel or the G4eCoulombScatteringModel. Correct?
What happens in case this is not implemented? Everything is treated as pure MSC?

Thanks again

4

In the reference EM physics configurations G4WentzelVIModel used in multiple scattering process, G4eCoulombScatteringModel - in G4CoulombScattering process. They share that same parameters, so angular limits are the same. EM constructors Opt0 and others configured correctly.

In custom physics all kind of mistakes are possible: double counting, holes in applicability of models…

VI

6

Hi!

I would like to scan several parameters for the ThetaLimit angle. Is it possible to do a loop for this value?
I tried with the /control/loop ThetaLimit but I get this error in output:

***** Illegal application state </process/msc/ThetaLimit {ThetaLimit} rad> *****

***** Batch is interrupted!! *****

------- WWWW ------- G4Exception-START -------- WWWW -------
** G4Exception : UIMAN0201
issued by : G4UImanager::Foreach
oop aborted due to a command execution error - error code 200
** This is just a warning message. ***
------- WWWW -------- G4Exception-END --------- WWWW -------

Thanks for your help.
Tommaso

7

Hello,

there are two types of EM parameters: defined once before initialisation and parameters, which may be changed between runs within the same job or during interactive session. It is not possible to change any parameter in the middle of a run.

VI