Lowest energy deposition

Geometry, Fields and Transportation
1

Hi All,

Out of curiosity, what is the lowest energy deposition possible in GEANT4? Is there an intrinsic limit? I have energy deposition as low as 10^-4 eV ( I assume this is due to cut).

Abhinab

2

There’s no minimum for “possible energy deposition” in Geant4. It depends on the physics processes, and on how you may have configured your simulation. Here are a couple of possibilities:

  1. In your simulation, did you configure your physics list to set the production cuts to zero? if so, then electromagnetic processes may produce some individual ionization electrons, rather than rolling their energy into the TotalEnergyDeposit of a step. You could modify your sensitive detector class to report whether secondaries were produced in steps where the energy deposit is very low.

  2. Are you looking at low energy neutron interactions? If you do not have production cuts set to zero, then a neutron elastic scatter can produce a very low energy nuclear recoil. Geant4 is likely, in that case, to discard the tracking of the recoiling nucleus, and instead assign that kinetic energy as TotalEnergyDeposit for the neutron. You could modify your sensitive detector to test for this by reporting when the energy deposit is assigned to a neutron, along with the process which limited the step.

3

Thanks for the quick response and Happy Holidays!

1] I set the production to the small value of 0.001*mm. However, I also investigating exotic particles that are feebly interacting with charges of 0.001e (with a modified physics list). The ionization energy parameters were set to

param->SetMinEnergy(2e-3*eV);
 param->SetMaxEnergy(100*PeV);

The lowest energy deposition was 9*10E-4 eV (close to SetMinEnergy). This was why I was curious if it could go lower than set Min. However, I realized that production cut also depends on material properties, and for me its PVT scintillators.

2] No I am currently not looking at low-energy neutron interactions.

4

Oh, ho. If you’re looking at FCPs, especially with such a tiny charge, you’re definitely going to get very very low energy deposits. You’re talking about something like 1e-6 of minimum ionizing.

The SetMinEnergy() and SetMaxEnergy() functions specify the kinetic energy of the track, not the energy loss.

5

I see thank you a lot. I was wondering about the lowest Edep for FCPs as some of the FCPs do pass through plastic scintillators but don’t seem to deposit energy. I wrongly assumed that maybe energy deposition is so small that GEANT4 rounds down if below certain threshold but it maybe that they don’t interact if they small through very small length of plastic scintillator?

6

We have included FCP (or “LIP”) physics in our experiment’s simulation framework. It required modifications to both EM processes and models in order to get interaction rates and energy loss correct. I presume that you’ve developed similar processes and models for your work.

If you want to validate your code with FCPs with such low charge, I’d recommend creating a world and detector at least several meters long, in order to get sufficient interactions to draw meaningful conclusions. Once you’ve done that validation, then you can use a realistic detector size, and have more confidence that the results are sensible.

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