Physics Lists for Secondary Emission Simulations

Physics Lists
1

Hi,

I am trying to simulate the secondary emission current in SEM monitors, located at CERN beamline TT20.

The primary beam is 400 GeV protons. I am interested in simulating both low energy secondary emission electrons (~20eV or slightly less) and any other high energy charged particles that could be produced due to beam losses.

Could you please advise me on which physics list to use for this purpose?

Thanks :slight_smile:

2

Ciao,

probably the the standard_opt3 EM builder is a fair compromise between precision and CPU performance. The simulation is going to be very CPU-intensive, as you start with 400 GeV primaries and you want to follow secondaries down to a few tens of eV.

Ciao, hope it helps
Luciano

3

Hi Luciano,

Thanks a lot for your suggestion. Any ideas about which hadronic models to use? I am also interested in other charged particles (not just electrons) that could contribute towards the signal.

Cheers,
Luana

4

Hi Luana,

I am not expert about hadronic list, but I would give a first try with QGSP_BERT or QGSP_BIC. If you care about neutrons, and you are willing to spend extra CPU time, you can use the corresponding _HP versions.

Ciao,
Luciano

5

Thank you! I will try that.

6

Hello,

it is possible to use the default FTFP_BERT Physics List or QGSP_BIC, as Luciano suggested.

The real problem is in production of the emission spectra at very low energy. Geant4 ionisation model have a low energy limit - mean ionisation potential for a material of the target. Secondary electrons are normally produced down to production threshold, which is the maximum of two value: one obtained from conversion of cut in range to minimal kinetic energy of secondary electrons, second - mean ionisation potential.

If your task allows to have such limit - fine. If not, there is a much complicate way to add required emission spectra using G4VSubCutProducer interface. It is a hook to the Geant4 ionisation process. You will need to develop a model for spectra of electrons below the threshold and add this on top of any Physics List in your application.

VI

7

Hi Vladimir,

Thanks a lot for your message. From what I understand it is relevant to understand the minimum ionisation potential for each Geant4 EM model. I have found it quite difficult to find this information. So far I have information for some of the low energy EM models:

But there are others for which I haven’t been able to find this information. Do you know which model has the lowest ionisation limit? And what the limit is?

My understanding is the minimum energy for electrons that I am interested is about 6eV. is there a Geant4 model reaching this energy?

Cheers,
Luana

8

Hi Vladimir,

Do you know where I can find more information on how to use the G4VSubCutProducer? I have tried to find information about it online, but have not found much documentation describing it.

Cheers,
Luana