On Wed, Jun 13, 2012 at 5:57 AM, Jones Beene <[email protected]> wrote:
> > The study of neutrons at cryogenic temperature is well-known. And in fact nickel, in particular, is known to reflect cold neutrons, when it would > otherwise absorb them if they were warmer. Are ULM neutrons somehow warm? > LOL. > According to the Wikipedia article, 58Ni (the most abundant natural isotope) has the highest neutron optical potential (likelihood of reflecting a neutron). That's really funny. Thanks for the pointer. The page that Lou mentioned indicates that certain isotopes of nickel have a neutron capture cross section in the range of 10^3 - 10^4 barns for very low energies, and the graphs increase as you go from right to left. But the ones for 58Ni and 60Ni have a sharp drop at around 10,000 neV -- is this due to the neutron optical potential? http://nucleus.iaea.org/sso/NUCLEUS.html?exturl=http://www-nds.iaea.org/ngatlas2/ 58Ni (68 percent) and 60Ni (26.2 percent) are the most abundant isotopes. The remaining 5.8 percent will be the others, all with relatively high cross sections. But what this seems to mean is that in order to have neutron-generated power and avoid seeing thermalized neutrons that would be picked up by a detector, you need next to no neutrons below the neutron optical potentials for 58Ni and 60Ni or you need a change to occur in the optical potential. Assuming the latter does not happen, there appears to be an energy threshold below which you will see neutrons in a detector -- 335 neV in the case of 58Ni. That seems to eliminate a convenient asymptotic trend to arbitrarily high cross sections that would be capable of making every neutron that is generated disappear before it leaves the system. Without a decent simulation or some number crunching, it is hard to know exactly how the numbers would turn out for different starting energies. But needless to say there's a prima facie case against slow neutrons. If you want to defend W-L, which is impossible, start by trying to imagine > how “ultra low momentum” differs from “ultra cold” No desire on my part to defend W-L, in particular, although I don't have the scorn for them that some do. It's a luxury of my having no training in physics to not have the gag reflex that many more knowledgeable people do when they hear about W-L. I took physics 101 in college and did fine, but not physics 201, so most of this stuff is new to me. Can you elaborate on what you have in mind in contrasting "ultra low momentum" with "ultra cold"? and then ask yourself how > the authors and supporters of such a brain-dead theory can continue to > overlook the 800 pound gorilla in the closet? > The plausibility of neutron-based explanations aside, I think there are many 800 pound gorillas. I'm distressed that my nano-Polywell reactor will probably have to deal with the usual branching ratio gorilla and with a prompt gamma to soft x-ray/extreme ultra violet conversion gorilla. I guess it partly comes down to which fantastic set of modifications to physics that one is willing to defend. Eric
