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None Strange gamma's kinetic spectra in Gd(n,g) reactions 

Forum: Hadronic Processes
Date: 13 Jul, 2017
From: Vitaly Mechinsky <Vitaly Mechinsky>

Hi All!

I would like to obtaine kinectic energy of ingividual gammas in Gd(n,g) reaction. In my program the monoenergetic neutron flux pass through 2mm Gd layer. I collect kinetic energy by next code in my SensitiveDetector:

//====================================================
void WindowSD::Initialize(G4HCofThisEvent*)
  {
  	edepG = 0;
  }

G4bool WindowSD::ProcessHits(G4Step* step, G4TouchableHistory*)
 {
  G4Track* track = step->GetTrack();
  G4String particleName = track->GetDefinition()->GetParticleName();

   if (particleName == "gamma")
   {

    G4double eg = track->GetKineticEnergy();
    edepG = eg;
    track->SetTrackStatus(fStopAndKill);
    return fKill;
   }
//====================================================

and send Ekin data to histogram:

//====================================================
void WindowSD::EndOfEvent(G4HCofThisEvent*)
 {
  runAction->FillDepositedHistG(edepG);
 }
//====================================================

I use QGSP_BIC_HP physics list. For neutrons with anergy more than ~80keV-100keV the data is quite correct -- there are a lot of peaks in Ekin gammas spectra starting with ~50 keV (good match with measured spectra by Compton suppressed HPGe spectrometer from "Handbook of Prompt Gamma Activation Analysis", see sreenshot for Gd2O3 in attached Gd2O3.jpg).

But when I irradiate Gd layer by neutrons with En < 80 keV I see strange "stepped" spectra without any peaks -- only 511 keV annihilation peak (see gd_hr_spectra.png)

Does anyone have any ideas?

Vitaly.

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2017/07/13/03.09-6258-Gd2O3.jpg
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2017/07/13/03.09-63348-gd_hr_spectra.png

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