Created attachment 197 [details]
plot of total energy after interaction

part of energy is lost in atomic deexcitation following an IT mode of radioactive decay. This does not happen in the atomic deexcitation following an electromagnetic process (e.g. photo electric effect)

I attach 2 macros for TestEm1. In gado1.mac, gamma 80 keV is shooted in Gadolinium. Gamma interacts by photoelectric effect. Then Gadolinium does cascade deexcitation. Plot is sum of energy of secondaries : it is perfectly 80 keV.

In gado2.mac, particleGun is an excited state of Gd158, which deexcite via RadioactiveDecay. Sum of energy of secondaries is not always 80 keV. 

I hope the plot is clear. 

 # Macro file for "TestEm1.cc"
#
#  Photon 80 keV; photoelectric effect
#
/control/verbose 2
/run/verbose 2
#
/testem/det/setMat G4_Gd
/testem/det/setSize 100 m
#
/testem/phys/addPhysics local
#
/run/initialize
#
# no Compton nor conversion
/process/inactivate compt
/process/inactivate conv
#
/process/em/fluo true
/process/em/auger true
#
/testem/phys/setCuts 1 um
#
/testem/gun/setDefault 
/gun/particle gamma
/gun/energy 80 keV
/gun/position 0 0 0 mm
#
###/testem/histo/setFileName gado1
###/testem/histo/setHisto 4 100 60 90 keV	#total edep
/analysis/setFileName gado1
/analysis/h1/set 4 100 60 90 keV	#total edep
#
/testem/event/printModulo 10000
#
/run/beamOn 100000


 # Macro file for "TestEm1.cc"
#
/control/verbose 2
/run/verbose 2
#
/testem/det/setMat Aluminium
/testem/det/setSize 100 m
#
/testem/phys/addPhysics  local
#
/run/initialize
#
/process/em/fluo true
/process/em/auger true
#
/testem/phys/setCuts 1 um
#
/testem/gun/setDefault
/gun/particle ion
/gun/ion 64 158 0 80 keV
/gun/energy 1 eV
/gun/position 0 0 0 mm
#
###/testem/histo/setFileName gado2
###/testem/histo/setHisto 4 100 60 90 keV	#total edep
/analysis/setFileName gado2
/analysis/h1/set 4 100 60 90 keV	#total edep
#	 
/testem/event/printModulo 10000
#
/run/beamOn 100000
#