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Question neutron capture cross section data 

Keywords: G4HPNeutronCaptureData
Forum: Physics List
Date: 24 Apr, 2008
From: Steve Farrell <sf72@phy.duke.edu>

I am looking at neutron capture in various materials, and came across
something I did not understand.  I'm currently firing 10MeV neutrons
into water.  I noticed a considerable difference in neutron track 
lengths whether or not I used the G4HPNeutronCaptureData. My usual 
neutron physics is:

...
else if (particleName == "neutron")
{
  // elastic scattering
  G4HadronElasticProcess* theNeutronElasticProcess =
    new G4HadronElasticProcess;
  G4LElastic* theElasticModel1 = new G4LElastic;
  theElasticModel1->SetMinEnergy(20.*MeV);
  theNeutronElasticProcess->RegisterMe(theElasticModel1);
  theNeutronElasticProcess->RegisterMe(new G4NeutronHPElastic());
  theNeutronElasticProcess->AddDataSet(new G4NeutronHPElasticData());
  pmanager->AddDiscreteProcess(theNeutronElasticProcess);

  // inelastic scattering
  G4NeutronInelasticProcess* theInelasticProcess =
    new G4NeutronInelasticProcess();
  G4BinaryCascade* theBinaryModel = new G4BinaryCascade();
  theBinaryModel->SetMinEnergy(20*MeV);
  theInelasticProcess->RegisterMe(theBinaryModel);
  theInelasticProcess->RegisterMe(new G4HENeutronInelastic());
  theInelasticProcess->RegisterMe(new G4NeutronHPInelastic());

  theInelasticProcess->AddDataSet(new G4NeutronHPInelasticData());
  pmanager->AddDiscreteProcess(theInelasticProcess);

  // capture
  G4HadronCaptureProcess* theCaptureProcess =
    new G4HadronCaptureProcess;
  G4LCapture* theCaptureModel = new G4LCapture;
  theCaptureModel->SetMinEnergy(20*MeV);
  theCaptureProcess->RegisterMe(theCaptureModel);
  theCaptureProcess->RegisterMe(new G4NeutronHPCapture());
  theCaptureProcess->AddDataSet(new G4NeutronHPCaptureData());

  pmanager->AddDiscreteProcess(theCaptureProcess);
}
...

Now, when I use this as written, I see a peak in track lengths around
0.55m.  However, when I comment out the line that adds the 
G4NeutronHPCaptureData dataset, the track length peak shifts to the left
to about .25m.  So the track length of the peak decreases by about 30cm.
Now, I expect the cross section to be less precise without the extra
data, but certainly not inaccurate.  By the way I am using hydrogen
from the NIST database and G4NDL3.10.
I've posted the track length histogram here:
http://phy.duke.edu/~sf72/TrkLNeutrons_Dataset.gif

Can anybody explain this, or point me in a proper direction to figure 
out where the discrepancy comes from?  Thanks

Steve Farrell

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1 None: Re: neutron capture cross section data   (Koi, Tatsumi - 24 Apr, 2008)
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