Charge state models for ions(heavy ions)

Particles, Track, Event, Run and Biasing
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Upon reviewing the documentation on the charge state models for ions, I noticed that Geant4 provides only an effective charge treatment. Specifically, the G4ionIonisation class implements a model that assumes a rapid establishment of equilibrium between the ion and the medium. Under this assumption, the model dynamically computes an average (effective) charge state as a function of the ion’s velocity and the properties of the material, and uses this to determine energy loss and ionization behavior.

Given this, I would like to ask whether such an assumption could introduce significant inaccuracies for heavy ions. In practical scenarios, the equilibration of charge states between ions and matter typically requires a finite path length or interaction time. Therefore, is the use of an instantaneous equilibrium model likely to lead to non-negligible deviations from the actual charge evolution, especially for high-Z or low-velocity ions?

_Geant4 Version:_9.6
_Operating System:_ubuntu14.04
Compiler/Version:
CMake Version:

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Dear @Ziqing_Zhang,

Thank you for raising this interesting point!

There are indeed situations where the Geant4 treatment may be at the edge of its applicability, such as:

  • Entrance foils or thin detectors,
  • Gaseous detectors in low-energy heavy ion experiments,
  • Ion separators (where tools like LISE++ may be more appropriate)

To help assess the potential discrepancies, do you have a specific case in mind (e.g., ion, energy, material) or any experimental data? That would help evaluate whether Geant4’s model introduces significant deviations in your scenario, or if the approximation is reasonable for typical HEP applications.

Looking forward to your thoughts!

And thank you for your time!

Best,
Alvaro