This is probably a very dumb question, but I'm stuck with it. The cross sections one finds on http://www.nndc.bnl.gov/sigma/ as a function of incident energy, is that energy given in the lab frame or in the cog frame ? For heavy a nuclide, this doesn't matter, but for hydrogen for instance ? If I have a (lab frame) neutron at 1MeV impinging on (thermal) hydrogen, do I read the table at 1MeV or at 250KeV ? Thanks, cheers, Patrick.