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Question Deposited energy larger than incoming energy in HadronElastic 

Forum: Fast Simulation, Transportation & Others
Date: 28 Sep, 2009
From: Estela Suarez <Estela Suarez>


I am simulating neutrons in the energy range 1MeV to 10MeV interacting in a plastic scintillator detector. I am quite puzzled about a phenomena that I have often observed when looking at the output of the GEANT4 simulation.

When an incoming neutron interacts with a proton of the scintillator via HadronElastic process, I have observed that in many cases the energy transmitted to the proton is larger than the one the neutron originally had.

I show you here an example of the verbose output where you can see that:

* G4Track Information:   Particle = neutron,   Track ID = 1,   Parent ID = 0
   1 12.340542 cm  13.62 cm 8.9103372 cm 4.150874 MeV     0 eV 30.735689 cm 30.735689 cm        World  Transportation
   2 12.250517 cm  13.42 cm 8.8474109 cm 4.150874 MeV     0 eV 2.2817578 mm 30.963864 cm    PMreplica  Transportation
  ... //some more transportation steps here that I remove to save space
  28 11.657142 cm 12.10175 cm 8.4326477 cm 4.150874 MeV     0 eV 11.408789 um 32.467828 cm   av_2_impr_46_scintelem_pv_0  Transportation
  29 11.598697 cm 11.971909 cm 8.3917955 cm      0 eV      0 eV 1.4813341 mm 32.615961 cm   scintillator  HadronElastic
Track (trackID 1, parentID 0) is processed with stopping code 2
### pop requested out of 1 stacked tracks.

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

   1 11.588893 cm 11.950127 cm 8.3849425 cm      0 eV 4.1565704 MeV248.77296 um 248.77296 um   scintillator       hIoni

So, as you can see, the neutron energy was 4.150874 MeV , and the proton energy is after the Elastic interaction 4.1565704 MeV, i.e. 15.6964 keV higher.

I was wondering if this is a result of some mistake in my physics list that allows for energy violation, or if this extra energy is coming from somewhere else. Could it be something related with the difference between the neutron and proton mass? The mass ratio mp/mn = 0.99756, according to literature. I have calculated for some of my outputs the ratio Ep/En, and I have obtained values which are around 0,99863. Is it just by chance or are those values related?

I would be very thankful if somebody could give a clue of what is going on here.

Cheers, Estela.

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