Problem 359

Hi,


We are working on Geant4 simulation of neutron detector.
We got  critical problems when simulating the inelastic interaction of neutron
with hydrogen and Carbon.
In the following table you will find the tracking results  for the Geant4
simulated  inelastic interaction  of a 400. MeV neutron with an hydrogen
target.Note that in this simulation  no electromagnetic interactions were
considered
and a StopParticle process was added to obtain only one inelastic scattering
perevent.



*********************************************************************************************************
* G4Track Information:   Particle = neutron,   Track ID = 1,   Parent ID = 0
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng
NextVolume ProcName
    0        0        0      500       400        0        0         0
WorldPV           initStep
    1        0        0      200       400        0      300       300
Target           Transportation
    2        0        0      100       400        0      100       400
Target           User Limit
    3        0        0        0       400        0      100       500
Target           User Limit
    4        0        0    -72.8         0        0     72.8       573
Target           nLEInelastic

*********************************************************************************************************
* G4Track Information:   Particle = pi-,   Track ID = 4,   Parent ID = 1
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng
NextVolume ProcName
    0        0        0    -72.8       141        0        0         0
Target           initStep
    1 -4.65e-42 -2.16e-42    -72.8       141        0 5.22e-42  5.22e-42
Target           StopParticle

*********************************************************************************************************
* G4Track Information:   Particle = proton,   Track ID = 3,   Parent ID = 1
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng
NextVolume ProcName
    0        0        0    -72.8       336        0        0         0
Target           initStep
    1 -6.99e-45 -7.43e-44    -72.8       336        0 5.31e-42  5.31e-42
Target           StopParticle

*********************************************************************************************************
* G4Track Information:   Particle = proton,   Track ID = 2,   Parent ID = 1
*********************************************************************************************************

Step#    X(mm)    Y(mm)    Z(mm) KinE(MeV)  dE(MeV) StepLeng TrackLeng
NextVolume ProcName
    0        0        0    -72.8       400        0        0         0
Target           initStep
    1    -14.6    -7.08     -171       400        0      100       100
Target           User Limit
    2    -18.8    -9.13     -200       400        0     28.9       129
WorldPV           Transportation
    3     -729     -354   -5e+03       400        0 4.86e+03  4.99e+03
OutOfWorld Transportation



As you can see  in this n+p->pi-+p+p the total energy  of reaction products is
much higher than what is expected.  Moreover in all piMeson production reaction
which we have simulated we always obtain a neutron or a proton (if charge
exchange occured) with the same energy than the energy of the incoming neutron
(See Track ID 2 in example).
For nC inelastic scattering (not shown here)  the energy is not conserved, for
all reaction channels (not only pi production).



We have noticed that such non energy conservation problem was already reported
for the HEInelastic model in bug report #171 by David Bailey at University of
Toronto.  This bug report  refers to the URL
"http://helios.physics.utoronto.ca/~dbailey/ATLAS_GEANT4_6Nov2000/sld002.htm"
 In this URL   non energy conservation  by using the  LEInelastic model for
neutron-proton and for proton-proton reaction at 1GeV are also illustrated.
From  David Bayley's URL its seems that this problem comes form  the Gheisha
model. My questions are:

-Since 2000-11-07 when the #171 bug was reported, did some corrections have
beenbrought to the LEInelastic model? May be only the HEInelastic model has been
corrected?

-We have the feeling that the only other model which could be used in
replacement of G4LEInelastic for simulating Neutron inelastic interaction in
theenergy range 20MeV-20Gev is the G4PreCompound model. As far as we know  this
model is just producing nucleons, alpha, triton, deuterium and spallation
nuclei. Is there  any other model than G4LEInelastic which could be used for
simulating pi-meson production reaction   below 20 GeV?

-If no other models exist, are there plans to implemant such a model in the
nextgeant4 release?

-Which is the actual status of the G4KineticModel? As far as we know it is not
yet available in Geant4. Will this model be implemanted? Will this model
consider pi production?

-If no replacement solutions are foreseen in the next future do you have any
other solution in mind?


Thanks for your help


Desorgher Laurent and Michael Moser