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Question The weird recoil energy  

Forum: Hadronic Processes
Date: Jan 30, 17:27
From: <DMHunter>

Dear Geant4ers,

We recently met a weird problem with Geant 4.10.3.

Our simulation is pretty simple: we have 2.45 MeV neutrons emitted isotropically from a neutron generator, the neutrons then hit the reflector. Some of neutrons will be reflected into the water tank. For this thread, we only care about the recoil energy of the neutrons hit on the reflector. The attached schematic drawing shows such a setup. The material of the reflector is Deuterium only.

The weird thing we found is: the recoil energy spectrum of the reflector has a "cliff", (more accurately, the maximum recoil energy), at ~ 1000 keV, as another attachment shown. If everything is correct, the expected "cliff" would be around 2178 keV, with the calculation of 4.0*A/(1+A)/(1+A)*2.45, where A is the atomic number of the material of the reflector, 2.45 is energy of incident neutrons, with the unit of MeV. We have tested with other elements like Carbon and Hydrogen, the "cliff" appeared at the expected energy consistent with the above equation.

Beside, when we set the material of the reflector as composed of Carbon, Deuterium and Hydrogen with the mass fraction of 85.8%, 14.15% and 0.05%, respectively, this "cliff" also appeared at the same energy place, ~ 1000 keV.

Using the same equation and the maximum recoil of ~ 1000 keV, we figure out the appropriate A value would be 8, which is very confusing since we have set the reflector to have only one type of element : Deuterium.

The definition of Deuterium in our script is as following:

    density = 0.953*g/cm3;
    G4Isotope* H2 = new G4Isotope("H2",1,2,2.0*g/mole);
    G4Element* D  = new G4Element("Heavy Water", "D", 1);
    D->AddIsotope(H2, 100*perCent);
    G4Material* EJ315 = new G4Material(name="EJ315",density,ncomponents=1);
    EJ315->AddElement(D, fractionmass=100.0*perCent);

Can any people please comment it ?

Thanks.

Best, DMHunter.

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2019/01/30/17.11-83250-topView90-270.png
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2019/01/30/17.11-87067-Only_D_UploadedToForm.pdf

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1 Idea: Re: The weird recoil energy   (Vladimir Ivanchenko - Feb 01, 10:13)
1 None: Re: The weird recoil energy   (DMHunter - Feb 01, 15:37)
(_ Idea: Re: The weird recoil energy   (Vladimir Ivanchenko - Feb 07, 02:56)
2 None: Re: The weird recoil energy   (michel maire - Feb 10, 10:05)
1 None: Re: The weird recoil energy   (DMHunter - Mar 11, 11:22)
(_ None: Re: The weird recoil energy   (michel maire - Mar 12, 10:55)
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