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None mean excitation energy of G4_WATER 

Forum: Geometry
Date: 19 Dec, 2012
From: Fada Guan <Fada Guan>

In Geant4.9.6 user guide,
http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForApplicationDeveloper/fo/BookForAppliDev.pdf

this mean excitation energy is 75 eV on page 348.

On NIST website, this energy is also 75 eV
http://physics.nist.gov/cgi-bin/Star/compos.pl?refer=ap&matno=276

However, when we run Geant4, this energy is 78 eV:

Material: G4_WATER H_2O density: 1.000 g/cm3 RadL: 36.083 cm Nucl.Int.Length: 75.517 cm Imean: 78.000 eV
   ---> Element: H (H) Z = 1.0 N = 1.0 A = 1.01 g/mole
   ---> Isotope: H1 Z = 1 N = 1 A = 1.01 g/mole abundance: 99.99 %
   ---> Isotope: H2 Z = 1 N = 2 A = 2.01 g/mole abundance: 0.01 % ElmMassFraction: 11.19 % ElmAbundance 66.67 %
   ---> Element: O (O) Z = 8.0 N = 16.0 A = 16.00 g/mole
   ---> Isotope: O16 Z = 8 N = 16 A = 15.99 g/mole abundance: 99.76 %
   ---> Isotope: O17 Z = 8 N = 17 A = 17.00 g/mole abundance: 0.04 %
   ---> Isotope: O18 Z = 8 N = 18 A = 18.00 g/mole abundance: 0.20 % ElmMassFraction: 88.81 % ElmAbundance 33.33 %

Yes, I know if we use self-defined water material, this energy is different from the one used for G4_WATER, for example, according to my definition, it is 68.981 eV.

Material: Water density: 1.000 g/cm3 RadL: 36.086 cm Nucl.Int.Length: 75.510 cm Imean: 68.981 eV
   ---> Element: Hydrogen (H) Z = 1.0 N = 1.0 A = 1.01 g/mole ElmMassFraction: 11.20 % ElmAbundance 66.69 %
   ---> Element: Oxygen (O) Z = 8.0 N = 16.0 A = 16.00 g/mole ElmMassFraction: 88.80 % ElmAbundance 33.31 %

My understanding is we'd better use G4_WATER with 78 eV when we select water material to make simulation result better fit with the measurement.
I suggest the value should be updated in the user guide.

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1 Idea: Re: mean excitation energy of G4_WATER   (Vladimir Ivanchenko - 04 Jan, 2013)
2 Ok: Re: mean excitation energy of G4_WATER   (Michael H. Kelsey - 05 Jan, 2013)
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