How to calculate scattering cross section from elastic, inelastic, and non-elastic cross section I'm trying to find the scattering cross section of U-235 as outlined in Weston M. Stacy's reactor physics book.
I see ENDF gives me elastic, inelastic and 'non-elastic' scattering cross sections.
First, what is meant by 'non-elastic scattering'?
Second, how do I get the scattering cross section?  Can I just sum up the elastic, inelastic, and non-elastic cross sections?
 A: ENDF (and the associated ENSDF database) is a very powerful tool for neutron scattering info. Hitting the 'Help' tab can yield lots of information. In particular, look at the Help listings on 'Reactions', paying some attention to the 'MT number'. The 'Reaction' associated with a given MT Number can be directly requested from the database, or you can request 'n,*' as the desired reaction and you will get a listing of all available neutron cross sections for the requested nucleus. 
In particular:
n,tot -> total neutron cross section.
n,el -> total elastic cross section
n,inl -> total inelastic cross section, considered to be the sum of all MT numbers from 50-91 (one neutron goes in, another comes out usually leaving the nucleus in an excited state).
n,non -> the non-elastic cross section, a sum across a variety of MT numbers, generally those with a neutron going in and a variety of things coming out (like n,gamma or n,n+a which is a different neutron plus an alpha coming out). 
There are hundreds of MT numbers and associated Reactions that you can query for. One easy place to start is with 'n,*' and look at the list of all available reactions for your desired target. Remember to scroll down if you have not specified one particular library to search, since the different libraries can contain different sets of MT numbers. 
Have fun exploring.
