-----Original Message-----
From: Abd ul-Rahman Lomax
> Slow neutrons have high capture cross-sections, "ultra-low-momentum
neutrons" will simply have very high capture cross-sections. They
will be efficient at producing transmutations ("neutron activation").That appears to be incorrect, as a general rule. Apparently you are thinking that the response of thermal neutrons to Uranium is typical. Fissile materials are not typical, and nickel is different. Do you have a reference for nickel being more efficient for ultracold neutrons ? If not, you simply cannot make that generalization. The target atom is more important than the momentum, and even though low momentum (temperature) often has much higher cross-section, this is not true with some elements - in fact the opposite can be true. Read the Wiki article: "For a given target and reaction, the cross section is strongly dependent on the neutron speed. In the extreme case, the cross section can be, at low energies, either null or, on the contrary, much larger than the cross section at high energies. I cannot find a reference to nickel to ultracold neutrons, but for thermal neutrons (cool, not cold) Ni is does not have a particularly high cross cross-section, so it is arguable that transmutations will NOT be more efficient in the case of WL.
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