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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. > >
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.