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None Neutron Angular Distribution with LElastic Model 

Forum: Hadronic Processes
Date: 19 Jun, 2007
From: B R <B R>

I am having a problem with a neutron simulation at 30 MeV and I wondered if anyone else had had a similar problem and knew of a solution? I am doing a simulation of a detector module of liquid scintillator made from hydrogen and carbon, and I am looking at what happens to the neutron after it scatters inside the detector. I get an angular distribution for the neutrons that is peaked at forward angles and decays exponetially with increasing angle (as expected). However, there is a large peak in the distribution at theta = 16 deg., followed by a hole in the distribution immediately following the peak at around 20 deg. This peak is not there at very low energies (< 2 MeV), begins to appear around 3 MeV and then moves from 90 degs. toward 0 degs. as energy increases. As one approaches 100 MeV, however, the peak disappears. The peak does not appear if I use in the simulation a "detector" of pure hydrogen and it does not appear if I do not add the Elastic Scattering Model (LElastic) to the neutrons. If I only add the LElastic model (and do not use any other models with the neutron), the peak is there.

Attached is the Physics List I am currently using (for the neutrons):
  pManager = G4Neutron::Neutron()->GetProcessManager();

// Create Pointers for Neutron nuclear processes

   G4HadronElasticProcess* N_LE_ElasticProcess = new G4HadronElasticProcess();
   G4HadronCaptureProcess* N_LE_CaptureProcess = new G4HadronCaptureProcess();
   G4HadronFissionProcess* N_LE_FissionProcess = new G4HadronFissionProcess();
   G4NeutronInelasticProcess* Neutron_InelasticProcess = new G4NeutronInelasticProcess();

// Neutron Nuclear Scattering Models

   G4LElastic* N_LE_Elastic = new G4LElastic();
   G4LCapture* N_LE_Capture = new G4LCapture();
   G4LFission* N_LE_Fission = new G4LFission();

   // Choose Inelastic Interaction!!!
   // Pre-Compound Model - from Hadronic Physics

   G4ExcitationHandler *theHandler = new G4ExcitationHandler();
   G4PreCompoundModel *thePreCompModel = new G4PreCompoundModel(theHandler);

   // Bertini Cascade Model 
   // G4CascadeInterface *theCascade = new G4CascadeInterface();

   G4NeutronInelasticCrossSection* the_Neutron_IE_Cross_Section_Data = new G4NeutronInelasticCrossSection();

 //
 // Add neutron processes
 //
   N_LE_ElasticProcess->RegisterMe(N_LE_Elastic);

   N_LE_CaptureProcess->RegisterMe(N_LE_Capture);
   N_LE_FissionProcess->RegisterMe(N_LE_Fission);
   Neutron_InelasticProcess->RegisterMe(thePreCompModel);
   // Neutron_InelasticProcess->RegisterMe(theCascade);

   Neutron_InelasticProcess->AddDataSet(the_Neutron_IE_Cross_Section_Data);

   pManager->AddDiscreteProcess(N_LE_ElasticProcess);
   pManager->AddDiscreteProcess(N_LE_CaptureProcess);
   pManager->AddDiscreteProcess(N_LE_FissionProcess);
   pManager->AddDiscreteProcess(Neutron_InelasticProcess);
// End attached code

Has anyone else had a similar problem and can suggest a solution? Thanks for the help. B.R.

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1 None: Re: Neutron Angular Distribution with LElastic Model   (Vladimir IVANTCHENKO - 19 Jun, 2007)
(_ Agree: Re: Neutron Angular Distribution with LElastic Model   (BrianR - 20 Jun, 2007)
1 None: Re: Neutron Angular Distribution with LElastic Model   (Vladimir IVANTCHENKO - 20 Jun, 2007)
2 Feedback: Re: Neutron Angular Distribution with LElastic Model   (Gunter Folger - 20 Jun, 2007)
1 Feedback: Re: Neutron Angular Distribution comp with Models   (BrianR - 20 Jun, 2007)
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