Low energy alpha stopping power

Hi experts

I am trying to simulate propagation of alpha particles though thin targets.
The alpha particles have energies of 200 keV - 7 MeV, and the materials are approximately 200nm Carbon.
The calculated energy loss does not agree with similar calculations from SRIM. The difference is on the order of 10-20%.
If the target material is heavier, such as Silicon or Aluminum, the two simulations agree.

I have tried using G4EmLivermorePhysics, G4EmStandardPhysics_option2 and G4EmStandardPhysics_option3, and they all give the same result.

Does anyone know a more appropriate physics package to simulate such energy losses?

/ Andreas

Hi, you get the same results because the models/processes for alpha are the same in the EM physics constructors you are using. Did you try to limit the step? Then, how is the energy loss calculated in SRIM? if it is based on the stopping power multiplied by the thickness target, you may need to increase the cut in the G4 sim in order not to produce any secondary particle.
In addition, does SRIM model statistical fluctuations in the energy loss?
So, in summary, make sure you are comparing apples with apples.


Hi Guatelli
Thank you for the reply!

I have tried increasing the cut to not produce any secondary particles, but this made no difference.
Also, limiting the step size did nothing as well.

Do you have a recommendation of what to use, if I want no other processes except for stopping power?

Hi, If you would like to model only energy loss, I think the multiple scattering should be switched off. However, I am not sure how switching off the multiple scattering will affect your results (your target is very thin).
The I suggest to compare directly the Stopping Power of Geant4 and SRIM w.r.t. the energy of the incident alpha. TestEM0, in the extended examples, may be used to calculate SPs.


We can study Stopping Power with TestEm0, TestEm5, TestEm18.
I attach macros for each example.
I have checked SP against ASTAR (NIST) at 200 keV, 1 MeV, 10 MeV.
It do agree within 1%
angadEm0.mac.txt (197 Bytes)
angadEm5.mac.txt (512 Bytes)
angadEm18.mac.txt (428 Bytes)


it is needed to compare SRIM and ASTAR also.