Jack slep Feb 21, 2016:

Depending on material, check if it's fissile or fissionable, the latter being the more common translation in my experience."Fissile" is distinct from "fissionable." A nuclide capable of undergoing fission (even with a low probability) after capturing a high energy neutron is referred to as "fissionable." A fissionable nuclide that can be induced to fission with low-energy thermal neutrons with a high probability is referred to as "fissile."[3] Although the terms were formerly synonymous, fissionable materials include also those (such as uranium-238) that can be fissioned only with high-energy neutrons. As a result, fissile materials (such as uranium-235) are a subset of fissionable materials.