Problem 335

In Geant4.4.0 and 4.3.2 versions the calculation of neutron life time in
hydrogen-content mediums (e.g. water, liguid scintillators, etc.) at room
temperature gives the wrong results. The obtained neutron lifetime ~20%
lower than the reference values.
 In Geant4.3.01 version the calculations of neutron lifetime at room
temperature is correct.
 The discrepancy in 4.3.2 and 4.4.0 versions comes from wrong treatement of
hydrogen capture libraries. The energy of incident neutron is recalculated,
taking into account the temperature movement of Hydrogen atoms. See files
G4NeutronHPCapture.cc and G4NeutronHPCapturData.cc.
 But the hydrogen capture crossection data (GNDL libraries) for thermal
neutrons had been measured at room temperature and already take into
account the temperature Maxwell distribution of Hydrogen atoms.
See for example:"Traite de neutronique", Jean Bussac, ISBN 2 7056 6011 0,
1985, France or other book on neutron physics.
 The previous version of Geant4 - 4.3.01 gives the correct value of
neutron lifetime due to the fact that in files G4NeutronHPCapture.cc
and G4NeutronHPCaptureData.cc there were no additional recalculations
for temperature movements of medium atoms.

	Olivier Dadoune  dadoun@in2p3.fr
	Bernard Lefievre lefievre@in2p3.fr
	Igor Machulin    machulin@in2p3.fr