Wrong mean excitation energy of materials

Dear experts:

I have a problem when I try to get mean excitation energy of materials. For materials in ICRU145, I got a bigger I value than formula calculated or Geant4 results.

For example , the brain material. The material definition is:

and I use DELTARAY card to obtain stopping power and material related information.

I found a smaller stopping power than geant4 simulated and then I examed the material mean excitation energy. The value is 100.97 eV in Fluka and 68.74 in Geant4. Also , I used the formula to calculate it and get a value of 68.7415, which is consistent with Geant4 but differs significantly from the Fluka result.

The fomula I used is:

I have simulated the elements related and got the same mean excitation energy as NIST data; I also simulated liquid water and muscle ,skeletal and got the same results compared to NIST.

So it seems like when I simulate the materials predefined, I get the reasonalbe results. But for materials user-defined, it has trouble. I use DEFAULTS=HADROTHE and proton beam energy is 230 MeV.

I also noticed that there are two warnning for this material in output file. Do they have relationship?

Hello Qinqin,

notice that in ICRU145 the brain composition is given by mass percentage, while in your card you are giving the atomic fraction. Trying with your case, using the mass fraction, I obtained:

Average excitation energy : 7.3778E+01 eV, weighted Z/A : 5.5239E-01

Also, since you are using materials from databases, I suggest you to read slides 9 and 10 from the course lecture, they can be useful: https://indico.cern.ch/event/1123370/contributions/4715951/attachments/2445260/4189933/06_Materials_2022_ULB.pdf


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