Cross Sections for Neutron Scattering in Different Frames

[vanesch]

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.

 

[Astronuc]

As far as I know, one uses the lab frame, i.e. a 1 MeV neutron has incident energy of 1 MeV.

Where did the 250 keV come from? COM?

 

[vanesch]

As far as I know, one uses the lab frame, i.e. a 1 MeV neutron has incident energy of 1 MeV.

Where did the 250 keV come from? COM?

Yes: half the speed (for hydrogen), hence 1/4 the KE...

Thanks for the answer !

In fact, this is how I wrote a Monte Carlo, and then I got worried that the energy might be given in the COM frame, because the angular distribution is, as far as I understand, given in the COM frame.

 

[NewClear]

hay this site http://www.nndc.bnl.gov/sigma/ is really good :)