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Forum: Hadronic Processes
Re: None Neutron Angular Distribution with LElastic Model (B R)
Date: 19 Jun, 2007
From: Vladimir IVANTCHENKO <vnivanch@mail.cern.ch>

On Tue, 19 Jun 2007, B R wrote:

> *** Discussion title: Hadronic Processes
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/hadronprocess/717"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
> 
> 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.
> 

Hello,

Please, consult PhysicsLists of 

examples/extended/hadronic/Hadr01
examples/extended/electromagnetic/TestEm7

Binary Cascade for protons, neutrons, ions is reasonably good, also HP
precise but slow models can be applied for neutrons below 20 MeV. Note,
that Precompound model is used inside Binary cascade at 30 MeV for protons
and neutrons. Also you need one of the new elastic processes: G4QElastic
or G4UHadronElasticProcess.  In exampoles it is shown how to use bulders
from $G4INSTALL/source/physics_lists subdirectory. In principle, you can 
use directly QGSP_BIC or QGSP_BIC_HP Physics Lists, then results will be 
more reasonable.

VI

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1 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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