Dedx Table information

Dear All,

I have some questions about the printout of the dedx table using the G4EmCalculator.

I obtain the table printed on the terminal but I’d like to have some information about that:

  1. What material the table is referred to? (i have defined many materials in my simulation and the method to print the table doesn’t need the material)
  2. why there are two tables (0-th vector and 1-th vector)? what is their difference?
  3. What is the unit of measure of the data? because they are very different from what I aspected (not only of a factor 10…)

Thank you for your help


On which printout do you refer ? which G4 example ?

It is in my own application.
I have createad an object of the class G4EmCalculator and the i called the method PrintdedxTable() that print the computed dedx table.

1 material : I hope @civanch will answer
2 and 3 : first column is energy binning in MeV. second column is restricted dE/dx in MeV/mm

reminder : internal units of Geant4 are based on nanosecond, mm, MeV

Thank you for you help!

About the question 2, do you know something?

Thanks again!


the order of vectors of energy loss is the same as the order of materials. The same as the printout of cuts.


Ok, now it’s clear, thank you!

Another question…

If I print the dedx table of an alpha particle in water (the only material I defined), I can read that at 1 MeV the dedx is about 25.8 MeV/mm, or 258 MeV/cm.
But the stopping power of an alpha particle at 1 MeV in water from NIST database is 2193 MeV/cm

Note: If i use the function “ComputeTotalDEDX()” i obtain 219 MeV/mm, that is the right value!

Why there is this difference?

Thank you

DEDX formula for ions (deuteron, alpha, generic ions) is the same as for proton, with a scaling factor.
To save space, we build tables only for proton and apply scaling factor at last moment, when dedx value is retrieved from tables.
the function PrintDEDXTable() only dumps content of tables, while ComputeDEDX() apply the scaling factor as done at tracking time.


I would agree, that we should extended the printout to make it more clear. This will takes some time. So, for the time being you may rely on information printed for cuts and simple dump which is provided now.


An improvement of the printout would be great!

Thank you very much for your help.