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None serious problem with benchmark 

Keywords: neutron ambient dose
Forum: Hadronic Processes
Date: 25 Sep, 2006
From: Sylvia Studeny <sylvia.studeny@gsf.de>

Hi, For many month now, I try to replikate results of a quite basic benchmark. I want to calculate the ambient dose equivalent for neutrons. This is defined und the results are tabled in ICRU57. It consists of an 30cm orb and a 1mm sensitive box volume, placed in 1cm depth (coming from beam direction). You have to calculate the deposited energy from every particle and multiply it by the quality factor Q(LET) which depends on the linear energy transfer:

G4double RE02SteppingAction::Q(G4double LET)
{
  G4double let = LET/(keV/(1e-6*m));
  if(let<10.){return 1.;}
  else if(let>100.){return 300./sqrt(let);}
  return (0.32*let-2.2);
}

I got the LET out of:
  const G4MaterialCutsCouple* couple = aTrack->GetMaterialCutsCouple();
  Ekin = aStep->GetPreStepPoint()->GetKineticEnergy();
  DEDX = theLossTableManager->GetDEDX(Particle,Ekin,couple);

And got :
 H  = edep / mass * Q(DEDX);

Both the Q and the DEDX look fine (I tested them seperately).

The problem is that the value of H summed over many,many primary particles (4*10^8) and normalized to one incomming particle is quite wrong.

I tried different physics lists: LHEP_PRECO_HP, RE02-physics-list corrected for low-energy EM and low energy neutron:

  G4HadronElasticProcess* thenElasticProcess 
                         = new G4HadronElasticProcess();
(*) thenElasticProcess->AddDataSet(new G4NeutronHPElasticData);

   G4LElastic* thenElasticModel = new G4LElastic();
   thenElasticModel->SetMinEnergy(19.*MeV);
   G4NeutronHPElastic* theNeutronHPElasticModel= new G4NeutronHPElastic();
   theNeutronHPElasticModel ->SetMaxEnergy(20.*MeV);
   thenElasticProcess->RegisterMe(thenElasticModel);
   ...

(with and without the line (*), without it is quite faster but simulates the place of the next reaction with standart crossections?)

I also calculated the statistical error, which was smaller than 5%. The discrepancy are quite big: up to 66% for the LHEP_PRECO_HP-list. The geometry is quite simple, so I assume I made no mistake there. Do you have an idea where else I can look? The only thing I can imagine is that I do something quite wrong in the physics part. Unfortunately for me, this is quite difficult to comprehend, as there is no detailed desciption. There is no point for me to try further in my real task if I cannot even reproduce such a simple quantity! Please help! Sylvia

P.S.: I use SuSE linux 9.0 with geant4.8.0 and the new crosssection version G4NDL3.8. Program running stable (as far as I can see).

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1 None: Re: serious problem with benchmark   (Koi, Tatsumi - 25 Sep, 2006)
1 None: Re: serious problem with benchmark   (Sylvia Studeny - 25 Sep, 2006)
(_ None: Re: serious problem with benchmark   (Koi, Tatsumi - 25 Sep, 2006)
(_ None: Re: serious problem with benchmark   (Sylvia Studeny - 25 Sep, 2006)
(_ None: Re: serious problem with benchmark   (Sylvia Studeny - 04 Oct, 2006)
(_ None: Re: serious problem with benchmark   (Koi, Tatsumi - 04 Oct, 2006)
(_ None: Re: serious problem with benchmark   (Sylvia Studeny - 10 Oct, 2006)
(_ None: Re: serious problem with benchmark   (Sylvia Studeny - 12 Oct, 2006)
3 None: Re: serious problem with benchmark   (Sylvia Studeny - 31 Oct, 2006)
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