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On Wed, 06 Jul 2011 04:39:42 GMT, Neoh wrote:
> Hi, > > I simulated prompt gamma activation from neutron capture on natural > carbon at neutron energy 2.45 MeV +- 200 keV. My hadron physics list is > QGSP_BIC_HP, electromagnetic physics list is emlivermore. > > I have three peaks of gamma energies at 1858,3854,4946 keV, but the > first two of them disagree with experimental values (I compare with > Evaluated Gamma-ray Activation File). The experimental values are > 1261,3683,4945 so the third value fits quite well. My question is, may I > know where is the gamma energy being calculated? Or more generally, how > is the secondaries energy being sampled in geant4? > > > thanks > > Neoh >
The Physics Reference Manual describes the sampling of photons from radiative capture in section 36.2.3. That particular data looks to me like it may be based on CNDL data, after looking at the NNDC website. At the least, the CENDL data,
appears to match your results better than the only other data I can find, the CapGam data from ENSDF,
There are two photon production data files for Carbon, both in $G4NEUTRONHPDATA/Capture/FS. The first is called 6_12_Carbon, and matches up perfectly with the CENDL data, and based on your results I would say that is what is getting sampled. It you look, you find that it actually has all of the peaks you were looking for, along with several others. The other file is called 6_nat_Carbon. It contains only the peaks you expected, but is obviously not the one being sampled. This means that somehow, when you are constructing your materials, Geant4 is seeing C-12 rather than natural carbon.
It seems worth noting that at first glance the C-12 data seems obviously better than the natural carbon data, wherever each originated from. Natural carbon should have all of the lines that C-12 has, plus lines for C-13, but in this data, it has far fewer lines than just C-12.
I hope this helps, Joel
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