How to evaluate XS over E_max?

[njchoi]

Hello!
Thank you for a nice library.
It looks like the E_max values for major isotopes such as U235 are quite small compared to the maximum energy we encounter in neutronics simulation.
How do I compute the cross sections over E_max? Do I need to be augmented by point-wise XS?

[paulromano]

E_max is typically chosen the top of the resolved resonance range (or equivalently the bottom of the unresolved resonance range, if there is one), so you would need to have pointwise data above E_max. Generally speaking, in a simulation you'd also need probability tables in the unresolved resonance range, which do depend on temperature. In the fast energy region, it is typically assumed that the there is no dependence on temperature (as the target velocity is small compared to the velocity of the incident neutron).

In any event, I believe the good folks at MIT are looking into extending the multipole formalism beyond the top of the resolved resonance region, so I'll let them comment on whether there is any hope there.

[njchoi]

Thanks a lot for your help!