Problem 631

The range of proton in water dose not reproduce the value given by ICRU,
when I use the G4hLowEnergyIonisation with the setting of ChemicalFormula of
a water to "H_2O".
(G4hIonisation also does not reproduce the ICRU value, but I don't know the
reason.)

 I adopted G4hLowEnergyIonisation for 200MeV protons, and measured a range
in water without any processes such as elastic/inelastic/multiple scattering
for protons.
 Without the setting of ChemicalFormula of water to "H_2O", the Geant4 can
reproduce the ICRU value. But, with the setting of a ChemicalFormula of water
to "H_2O", the range become shorter than the ICRU value.

 The reason of this problem is thought to be a illegal collection factor to
the dE/dX calculation in G4hLowEnergyIonisation (paramB).

 In the G4hParametrisedLossModel, the calculation method of dE/dX at the
kinetic energy below 2MeV is switched according to the setting of
ChemicalFormula. Then the collection factor (paramB in G4hLowEnergyIonisation)
is applied for the dE/dX at higher kinetic energy region which is calculated
from BetheBloch formula. The factor is used for the smooth connection of dE/dX
value at 2MeV.

 Without the setting of ChemicalFormula, the collection factor is just about a
few percent. But with the setting of ChmicalFormula, the collection factor is
about 10%. This illeagal large collection factor makes energy loss of the
protons larger. As a result the range in water becomes shorter than the
expected.

 The smooth connection with small collection factor at 2MeV has to be
considered. Otherwise, at least, we can not reproduce the proton energy loss
in water.

 One of the solution is to replace the dE/dX caluculation with non-
ChemicalFormula case at the energy range of 0.8MeV to 2MeV. This can make a
smooth connection of dE/dX at 2MeV with small correction factor.

 The result of my study is provided on the attached URL.

 Best regards,

 Toyama College of Maritime Technology.
 T.Aso