|Message: Re: Cross Sections used to determine Elastic Scattering||Not Logged In (login)|
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On Mon, 27 Jun 2011 18:31:08 GMT, Evan Askanazi wrote:
> Well I used the energy ranges 0.2 millivolt, 2 millivolt, 5 millivolt > and 10 millivolt. That is what I meant by meV, I should have specifed > that the first time, my mistake. So I am not doing any calculations of > neutron elastic scattering in the range of MeV, of Megavolts. I looked > to use the mean free path legnth model to determine the rate of elastic > scattering for neutrons in Aluminium in the range of .2 to 10 meV, > millivolts, where the resonances of the cross section arent an issue > like they are from 30 keV to 10 MeV. > > And I also find it interesting that your data agrees as well as it does > with the ENDF/B-VII data. According to this link : > > geant4.slac.stanford.edu/UPenn2011/HadPhys2.pdf > > dated May 17 of 2011, Geant4 has not yet migrated to ENDF/B-VII data > yet. Maybe it was still desinged to agree with ENDF/B-VI but still > agrees with ENDF/B-VII reasonably well because the data from version VI > to VII hasnt changed dramatically, just different results from doing the > calculations and maybe different levels of accuracy, though the results > for neutron elastic scattering in Aluminium in ENDF/B-VI are mostly > within standard experimental error of the ENDF/B-VII results. >
I am moderately confused. I come from the nuclear engineering end of the spectrum, rather than the pure physics end, so perhaps the standard terminology is different, but I have never of volts (or millivolts, etc) used as a unit of energy, only of potential difference. Are you using millivolts synonymously with millielectron volts? Assuming that you are, then yes, obviously resonance is no longer an issue.
You are correct, the ENDF data in Geant4 is VI, not VII, but for the most part they are not drastically different. Unfortunately, at low energies, the Al-27 does not agree with either ENDF/B-VI or ENDF/B-VII.
The plot I have attached shows the GNDL3.13/3.14 data (Al-27 elastic has not changed) and ENDF/B-VII data (which is basically identical to the ENDF/B-VI data, I just checked) from 1e-5 eV to 100 eV (which covers the range I think you are talking about). As you can see, the GNDL data is almost flat, whereas the ENDF data shows the curve you would expect to see. In fact, all the major databases (JEFF-3.1, JENDL-4.0, CENDL-3.1, ROSFOND, all found at nndc.bnl.gov) show that downsloping curve, so I have no idea where the GNDL data originates. If you were working in that energy range, I also have no idea how your geant4 results ended up agreeing with hand calcs based on ENDF/B-VI.
It's moments like this when I wish Geant4 could use ENDF-format data, so you could actually choose what data you were using, knowing what the data was and where it came from.