Problem 2585 - Incorrect ATIMA energy loss in compound materials
Summary: Incorrect ATIMA energy loss in compound materials
Status: ASSIGNED
Alias: None
Product: Geant4
Classification: Unclassified
Component: processes/electromagnetic/standard (show other problems)
Version: 11.1
Hardware: All All
: P4 minor
Assignee: Vladimir.Ivantchenko
URL:
Depends on:
Blocks:
 
Reported: 2024-01-15 16:27 CET by Valentin Piau
Modified: 2024-01-20 11:17 CET (History)
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Description Valentin Piau 2024-01-15 16:27:35 CET 
Hi,

I found out that the energy loss formula used in the ATIMA model may not be correct when applied to compound materials.
Specifically, in G4AtimaEnergyLossModel::ComputeDEDXPerVolume, the stopping power is calculated from the effective charge (zt) of the input material and its associated mass (at) from NIST:
"
G4double zt = material->GetIonisation()->GetZeffective();
zt = std::min(zt,93.); 
G4double at = nist->GetAtomicMassAmu(G4lrint(zt));
G4double dedx = StoppingPower(p->GetPDGMass(), p->GetPDGCharge(), kineticEnergy/(MeV), at, zt) *material->GetDensity()/(g/cm3);
"
(from source/processes/electromagnetic/standard/src/G4AtimaEnergyLossModel.cc)

While this works well with simple materials, it seems wrong when dealing with compounds. This effect can be observed by calculating some ion ranges in a compound (e.g. plastic) and comparing ATIMA with the default energy loss model.

I suppose a possible fix (if this is confirmed to be a bug) could be to use Bragg's rule, as in the C++ ATIMA library (catima).

Best regards,
Valentin