Fast neutrons vs thermal neutrons

[nuke21]

If an nuclide can be fissioned by thermal neutrons does that always mean it can be fissioned by fast neutrons. If not how can one tell this by looking at the neutron cross section?

 

[Astronuc]

Nuclides that readily fission by thermal neutron absorption are termed 'fissile' as opposed to those which can only be fissioned by fast neutrons which are termed 'fertile'. Fertile really means that the nuclide can absorb a neutron and decay to a fissile nucleus.

Fissile radionuclides (e.g., U-233, U-235, Pu-239, . . . ) to fission by fast neutrons, but the fission cross-section is lower.