I am running Geant4 v11.0.2, and I want to use scintillation by particle type in Liquid Argon(LAr), to distinguish different particles by their ratio of prompt vs delayed light, by setting different yields for the two decay components of LAr for different particles.
As far as Im aware and have seen in the forum, when setting ScintByParticleType = true, the only supported particles are electron,proton,deuteron,alpha,triton and generic ion. I have already used this successfully. I would like to extend this to also include muons, gammas and neutrons.
for neutrons I really mean doing this for a recoil Ar nucleus since neutrons don’t induce scintillation themselves. I have noticed that when changing Generic Ion’s parameters I seem to get correct results - is it true that Generic Ion also applies to an Ar nucleus?
Does anyone have a recommendation on how to implement this? or perhaps this is already supported in some newer version of Geant4?
Based on the comment below [1], it appears that muons are treated as electrons (default option)
// Electrons (must also account for shell-binding energy
// attributed to gamma from standard photoelectric effect)
// and, default for particles not enumerated/listed above
I believe the most significant difference in scintillation between muons and electrons of the same energy would occur around the MeV range, although such energies might be relatively rare. Could you please confirm if this is correct, and if so, whether this applies to your experimental setup?
Regarding neutral particles such as gammas and neutrons, as you mentioned, scintillation typically occurs indirectly via secondary particles (electrons or ion recoil). If the electromagnetic secondary production cuts are set high, gamma/neutron may deposit energy directly in the material, and I guess that the scintillation process treat them as electrons (default option), which may not be fully accurate.
For accurate simulation of secondary production, it is recommended to use the standard electromagnetic physics 4 (EMZ) [2] along with low production cuts.
You can observe the difference of secondary production by enabling detailed tracking with the command: /tracking/verbose 2.
I am not an expert in optical physics, so I would welcome input from others who might have more experience in this area.
I tried to test scintillation by muons and it seems to be completely controlled by the scintillation parameters set to electrons, so it could be the case that they are treated as electrons, thought I’m not 100% sure. I’m also not sure about the difference between muons and electrons scintillation, and I plan on using cosmic muons (so ~1-10 GeV) in my simulation.
Regarding gammas I guess you are right that they only produce scintillation via secondaries (in this case electrons), so the scintillation should also be controlled by the electron paramaters?
It would be great if someone who knows about this topic can verify these things, and also regarding the Generic Ion applying for recoil Ar nucleus or not
This is correct. Individual nuclear species are all handled at the process level via GenericIon. Individual nuclei can be created during running (via nuclear recoils or radioactive decays), so GenericIon carries the ProcessManager for all of them.
As Alvaro said, if you have production cuts set high, you can end up with gammas or neutrons apparently depositing energy or scintillating directly. To avoid this (and probably increase your CPU burden!), you can set production cuts low. The “proton” cut also applies to nuclei, so if you set it low, then you’ll get the nuclear recoils treated properly.
Only one question for what both of you mentioned - how do I change production cuts? I don’t think I have this issue since I don’t see gammas/neutron directly depositing energy/causing scintillation, but just to make sure I have everything setup correctly. I use QGSP_BERT_HP with EM option 4 and optical physics, so I suspect the cuts are applied appropriately automatically somewhere.
I set them globally in our physics list (see the G4VUserPhysicsList::SetCutValue() and nearby commands in G4VUserPhysicsList.hh). There are also macro commands if you want to adjust them by job.