Geant4 and SRIM radon-222 range agreement

I’m having issues getting Geant4 and SRIM to agree on the range of 86.26 keV radon in an infinite medium of liquid argon with a density of 1.395 g/cm3. If SRIM is to be trusted, it seems that Geant underestimates the range considerably (SRIM range = ~80.9 nm and Geant range = ~62.9 nm). I’m sure that I’m missing something simple and have beat my head against my keyboard enough and am finally reaching out for help. I’m using the examples/extended/hadronic/Hadr06 example physics while replacing G4EmStandardPhysics_option3 with G4EmStandardPhysics_option4 and commenting out the gamma physics. Any assistance would be greatly appreciated. (4.5 KB)

The issue here is what you are comparing. My impression is that SRIM calculates the CSDA range. You can obtain the same quantity in Geant4 by deactivating the multiple scattering, switching off the energy loss fluctuations and increasing the cut so high not to produce secondary particles.


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Here, a macro for TestEm1, to be run in interactive mode.
In Geant4 11.0 the csda range of 86.26 keV radon in liquid Argon is 603.67 nm, not 62.9 nm (~ a factor 10 ?).
You can double check this value with TestEm0.
I also noticed that 603.67 nm correspond to 0.08391 mg/cm2. What is the unit of range in SRIM ?
hellinger.mac.txt (694 Bytes)

Thank you for this suggestion. I used this idea when I was first looking into this issue and realized that the particles were only interacting once. I proceeded to add

/process/eLoss/StepFunctionMuHad 0.001 0.01 nm
/process/eLoss/StepFunctionLightIons 0.001 0.01 nm

into the macro file. Unless I am mistaken, this decreases the stepping size which allows Geant4 tracking to obtain more information on the trajectory. Once this is implemented, the range of the radon particle decreases by a factor of 10.

Susanna, you are correct. SRIM does output the CSDA range. Even after disabling multiple scattering and straggling in Geant4 as well as increasing the cut, the values between SRIM and Geant4 still do not match.

Sorry, forgot to mention to reduce the step

Should I be worried that the values still don’t match? There’s still a difference of about 25% between the projected ranges of Geant4 and SRIM, with the values still equaling what I stated initially. To your knowledge, is there anything else I could implement?

Dear Aaron,

I suggest you calculate the Stopping Powers with Geant4 and SRIM. Let’s see if you find differences consistent with what you find for the projected range. The projected range is different from the CSDA range (NIST: Appendix for ESTAR, PSTAR, and ASTAR). Could you please make sure you compare CSDA ranges?

Attached is the output file for SRIM. SRIM outputs stopping power. From there, the CSDA range can be calculated. Extrapolating to 86.26 keV gives a stopping power of dE/dx = 846.69 keV/mg/cm2. Dividing by the energy and inverting gives a value of 0.102 mg/cm2.

Geant4 outputs the CSDA range as 0.08391 mg/cm2. There is an 18% difference in these numbers. The projected range was a 22.2% difference.

ok, please, can you retrive from Geant4 the Stopping Power tables?
so, then it is possible to see if the difference is justified by different parameterisations of the stopping power.

I apologize, I seem to be confused on what you want. Are you just wanting to see how the energy changes per step, i.e. the output in the terminal? Or is there something else I’m missing?

Hi, I would like to see the table of the stopping powers. You can retrieve the stopping power tables for the material of interest using the G4EmCal. My impression is that TestEm0 shows how to do this. Then, you compare the Geant4 and the SRIM stopping Powers. The CSDA ranges are calculated from the SP. So I think it is useful to know if the differences you see are originated from differences in the “original” SP tables used in the calculations. I hope it makes sense now. Let me know.


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I just realized something strange that I didn’t catch before I clicked reply, so I’m deleting my last post. Apologies. I have attached a snippet of TestEm0 using radon-222 in liquid argon.

SRIM nuclear stopping power is approximately 10900 keV(cm2/mg)
Geant4 nuclear stopping 383.937 keV(cm2/mg)

SRIM electron stopping power is approximately 846.69 keV(cm2/mg)
Geant4 electron stopping power is 1293.44 keV(cm2/mg)

SRIM total stopping power is approximately 17000 keV(cm2/mg)
Geant4 total stopping power is 1679.03 keV(cm2/mg)

Any ideas as to why the stopping power is calculated so differently?

Also, thank you so much for your help these last few days.


Hi, ok, so the CSDA ranges are so different because of the Stopping Powers. I know that below ~ 2 MeV/amu the parameterisations of the stopping powers can be different depending on the used model.

May I ask you to repeat the same SP calculations using Geant4 11.p01 and the G4LinhardSorensenIonModel?

Then, another thing of interest would be to plot the SPs with respect to the energy.


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@civanch, let me try to summarize the situation.

Ion radon, 80 keV, in liquid Argon

1- electronic stopping power was ~1.73 GeV/cm, now it is 18.34 MeV/cm !
curiously, stopping range remains unchanged : ~582 nm
anyway, according SRIM, dE/dx would be 1.13 GeV/cm …

2- nuclear stopping power is 537 MeV/cm.
in SRIM, it is ~13.79 GeV/cm

radon.mac.txt (289 Bytes)
radon.out.txt (1.6 KB)

I am having trouble implementing the G4LinhardSorensenIonModel. According to the manual, it is part of the G4ionIonisation class, however I have been unsuccessful at getting Geant4 to recognize that it even exists. Do you know of an example I can view to make sure I’m doing this correctly?