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Forum: Geometry
Re: Question Element definition (Steve Quillin)
Re: None Re: Element definition (michel maire)
Date: 10 Jul, 2015
From: Steve Quillin <Steve Quillin>

On Thu, 09 Jul 2015 14:08:45 GMT, michel maire wrote:
> On Tue, 07 Jul 2015 18:57:25 GMT, Steve Quillin wrote:
> 
> > Hello
> > 
> > I'm trying to simulate some publicised data on spallation and have made
> > a simple Geant4 application that fires 1 GeV protons into a 10 cm
> > uranium sphere and counts the numbers of neutrons emitted. My problem is
> > with the material definition: results seem to be dependant on the order
> > in which I add isotopes to an element.
> > 
> > My material definitions and the results of "printing" them are attached
> > below. All 3 materials appear identical apart from the isotope order,
> > yet the neutron multiplicity is smaller by a factor of ~2 (geometry
> > dependant) when the target sphere is built from Uranium_b than the
> > others. The fraction of protons that generate neutrons is the same for
> > all materials.
> > 
> > Have I made an error in the material definitions or is there something
> > else going on?
> > 
> > I'm using geant4-10-01-patch-01 multithreaded with QGSP_BIC and other
> > physics lists.
> > 
> 
>   I ran example Hadr03 with the 2 Uranium definitions.
>   I attach macro and extract of outputs (which are big, at 1 GeV)
>   The number of generated neutrons are close, althrough not exactly the same.
>   (spectrum in attachment)
> 
>   I do not know how much is signifiant this difference of behaviour between the 2 material definitions.
> 
>          

Thanks Michel

I will look at your macro and see if I can tweak it to enhance the effect in Hadr03. The issue seems to be linked to neutron gain as secondary particles are transported through the material; a larger sphere shows a greater effect. It may be specific to U235 though I haven't investigated other materials.

Would it help if I posted my application code?

I will post a bug report when I get a chance.

Steve Quillin

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